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Design of a prototype apparatus for on-line elemental analysis using nuclear techniques
Coal has a significant role as an energy source of the future in electricity generation worldwide. In Turkey, coal is essential as an energy source, since coal-fired power plants currently fuel about 31% of global electricity. For our country, the processes of improving the quality and preparation of the coal is important to produce the energy efficiently from the coal power plant. For that purpose, an instrument using some nuclear techniques was developed to be able to determine the content of the ash, moisture and calorific value of the coal moving on the conveyor belt as on-line. Due to the fact that being non-destructive and sensitive for some elements, neutron activation analysis (NAA) is an important technique for identifying the specific elements in materials. The technique of most devices is based on using a radioisotope such as 252Cf. The irradiation of samples depend on neutron interactions which are neutron inelastic scattering (n,n`g), and the neutron radiative capture (n,g). Because of the average neutron energy of 252Cf is about 2.5 MeV, this neutron source is convenient to analyze the samples including only the process of thermal neutron capture (n,g). The carbon content of coal which is important parameter to determine the quality of the coal, can not be detected by using 252Cf source. Therefore, a neutron generator is used to produce fast neutrons of 14 MeV releasing from deuterium – tritium (D-T) fusion reactions for the prototype device. The prototype device is composed of a neutron generator, a scintillation detector, an iron block for shadow shielding and lead shield of BGO detector. The neutron generator is a device which can be operated with pulsed mode. Therefore, the obtained gamma rays can be classified according to their interactions induced with thermal neutrons or fast neutrons. The choice of a detector is pretty significant issue for designing the prototype device. The scintillation type of detector is preferred for the reason that has high efficiency and more endurance to neutron radiation damage. As a scintillation detector, Bismuth Germinate Oxide (BGO) is chosen. The characteristic features of the BGO is studied in detailed. The energy resolution, efficiency, shape calibration are calculated by using radioactive point sources such as 60Co, 137Cs, 152Eu. Additionally, The response functions of BGO detector are experimentally found to apply on the spectrum obtained from simulation programs. A prototype apparatus can be modelled to provide nuclear techniques by using Monte Carlo simulation programs. Monte Carlo N-Particle 5 (MCNP5) and Geometry And Tracking 4 (GEANT4) simulation programs are used to design the geometry and physical interactions of the prototype apparatus. The synthetic coal samples including different element contents are simulated and analyzed.There are plenty of ways to analyze a bulk system including gamma spectrum. Some of them are peak area determination, neural network algorithm and Monte Carlo Library Least Square (MCLLS) fitting. Analyzing the obtained spectra from Pulsed Fast and Thermal Neutron Analysis (PFTNA) experiment is very difficult due to its non-linear nature. Library Least Square is a common mathematical approach for treating non-linear radiation effects in cases such as PFTNA. In this study, MCLLS technique is applied by using MCNP5 and GEANT4 simulation programs. With the aid of fixed spherical geometry, the elements inside of the coal sample are simulated individually. The obtained spectrum from MCNP5 and GEANT4 are used to build up an element library of coal sample. The method is applied on experimental spectrum which have analysis reports including element contents. So the experimental spectrum are provided to calibrate according to element library. Then, the calibrated element library is used to calculate the contents of unknown spectrum obtained experimentally. By using this mathematical approach, the element contents of experimental coal spectrum are aimed to calculate in the range of measurement precision defined commercially before.
Modeling and design of a buried explosive detector based on neutron scattering
Main goal of this thesis was to design a buried explosive detector based on the neutron scattering method. Detection of land mines and massive ammonium nitrate based explosives were targeted. In this work, the trace element is the hydrogen present in buried explosives. Detection method aims to detect the scattered thermal neutrons from the explosive. Design of the detector includes an array of Si-PIN photodiodes, a 14 MeV neutron generator and a shielding material to protect detector electronics. Monte Carlo simulations have been made to determine the optimal design parameters and the detection limits. Geant4 physics simulation package has been used for this purpose. Si-PIN photodiode is the detection element of the detector. On its own, Si-PIN photodiodes are not sensitive to neutrons. They are rather sensitive to charged particles. To be able to detect neutrons, a neutron to charged particle converter should be applied to Si-PIN photodiode surface. Possible converters were investigated and 6 LiF, 10 B and polyethylene were selected as the potential candidates. Simulations have been made to determine optimal coating thicknesses for these materials. Neutrons path through the soil is recorded via tracking implementation in Geant4. Neutron thermalization in the explosive and scattered neutron spectrum have been analysed. A significant difference has been found in the thermal neutron spectrum between the case with only soil and the case where an explosive was buried in soil. Further simulations have been prepared on this basis for landmines and ammonium nitrate based explosives. Simulations were made for different converters, explosive masses, bury depths, explosives and soil types. Signals detected at Si-PIN detector have been compared to each other. Detection efficiency were calculated in terms of separation quality z, which describes the difference between explosive and soil signal in terms of number of standard deviations. Additional studies have been made to investigate the performance of the detector when it is mounted on a vehicle. To understand the effect of humidity in the soil and the effect of asphalt, additional simulations were performed and detection efficiencies in each case were determined. Between the three candidate converter materials, 6 LiF outperformed other converters. Sensitivity of 6 LiF coated Si-PIN photodiode was high enough to detect a 500 kg ammonium nitrate based explosive down to 30 cm depth and a 15 kg anti tank mine down to 20 cm bury depth. For the same explosives, 10 B coating managed to detect ammonium nitrate based explosives down to 10 cm and anti tank mines to 15 cm. Polyethylene converter did not manage to offer a reliable detection. Possible upgrades like large area silicon pad detectors or gamma detectors have been discussed.
Physical applications of the heun equations with polynomial reduction cases
The scientific community started to encounter the Heun-type solutions more often by the end of the 20th century. Thus, the hypergeometric-type equations that were generaly studied in the mathematical formulation of the limiting cases of the physical phenomena changed by the analysis of the full problem via Heun equations. The mathematical theory of the hypergeometric equation which has a two-term recursion relation and three regular singularities is fully understood. However, the theory of the general Heun equation which has has four regular singularities and a three-term recursion relation is not well-studied. The physical applications of the Heun equations are diverse. Various quantum mechanical problems can be solved in terms of the general and confluent forms of the Heun functions. General relativity applications also play an important role in understanding the various exact solutions of the Einstein equations. Analysis of the Heun-type equations can reduce to finding polynomial solutions if the parameters satisfy some certain conditions. These conditions can put constraints on the physical parameters or yield the energy condition for quantum mechanical systems. Three problems from quantum mechanics and a problem from black hole physics are studied using the polynomial reduction method. Energy spectrum is obtained for the quantum mechanical problems. Some parameter constraints are found for the black hole system. Maple and SageMath codes are given for studying the theorem that yields the energy spectrum easily.
Greybody factor for rotating linear dilaton black holes
After the general relativity was come to light, black holes have been thought both as the answer and the comprising of the many questions about physics of the universe. It was immediately followed by spherical symmetric static solution of Einstein Field Equations known as Schwarzschild solution which describes the space-time out of a star. Schwarzschild solution was examined in detail later and it was found that the solution has two kinds of singularities; one is coordinate singularity that can be removed by a coordinate transformation and an essential curvature singularity which can not be removed by coordinate transformation at the center. These objects are called black hole,then. Say the least of it, black holes are the physical objects that contains huge amount of mass in the very tiny area. Therefore, the gravitational field of black holes are so strong and even the light cannot be able to revolt this force. Charged and rotating black hole solutions are found and presented in the literature, later. Classically, black holes are stable objects and they do not radiate. After the study of Hawking about quantum field theory in a black hole background, he revealed that black holes are thermal systems and they may emit particles so-called Hawking radiation, until they run off their energy. Since, in the frame of this theory, a black hole is not actually black and according to its emission process it may not live forever. Hawking radiation behaves like a black body at the event horizon of the black hole. However, due to the space-time geometry of the black hole background, the initial radiation is distorted passing through the potential of the black hole and goes to observer at infinity. Therefore, the observer at the infinity, cannot measure the black body spectrum of the black hole, instead one measures filtered Hawking radiation in a sense. This quantity that determines how the black body radiation altered is called greybody factor. Greybody factor is basically the transmission probabilities of the Hawking radiation through the corresponding space-time. Scattering process takes place for movement of the radiation. Due to calculate the transmission coefficients and greybody factor, different types of approaches are examined such as simple matching technique, monodromy technique. Since greybody factor is a frequency dependent quantity, or these techniques are applied for different frequency regimes. In the first chapter of this study, after the black holes and Hawking radiation are briefly explained, greybody factor are defined according to this concept. Then the previous works related with calculation the greybody factor of black hole background are reviewed. With this revision, it is realized that there are several approaches to derive the greybody factor depend on the frequency regime. In this thesis, since the greybody factor is examined for low frequency regime for Schwarzschild- like and rotating linear dilaton black hole backgrounds, semiclassical matching technique is investigated through the study. In the second part, after giving a brief introduction to thermodynamic behavior of black holes, Klein-Gordon equation for massless scalar field is constructed for four and five dimensional uncharged, static Schwarzschild-like black hole and Schrödinger-like form of the equations are found with respective effective potentials. Therefore, Klein-Gordon equation with massless scalar field for d- dimensional Schwarzschild- like black hole is generalized and transformed to the Schrödinger-like equation to express the black hole background as a potential barrier for the radiation and giving a deviation from the black body radiation spectrum as seen by an asymptotic observer. Then scattering theory of this type of black holes are reviewed to infer that greybody factor can be calculated not only by examine the scattering of a conjectural outgoing wave from horizon but the scattering of an incoming wave from infinity. This inference is the crucial part of the calculation of greybody factor. Also this choice reveal that the black hole are taken as classical black holes not semiclassical. The third chapter comprises the properties of the rotating linear dilaton black hole background for non asymptotically flat spacetime and the derivation of the greybody factor for this background according to Sakallı' s study. The matching of the solution of near horizon region with asymptotic region gives the relation between the flux of these regions. For the last chapter, phenomenon of superradiance is studied. Firstly, superradiance amplification of massive scalar fields in the Kerr black hole is reviewed according to Betri's study and superradiance condition for this black hole is found as $\omega
Quantum effects on conformally coupled scalars during inflation
The effects arising from the small (quantum) scale in the early universe help us to understand large (cosmological) scale structure formation in today's universe. Throughout this thesis, we are interested in these small scale effects in the early universe. First of all, we search to find the answer to the fundamental question "What is the source of these quantum effects?" in this thesis. The answer to this question is given by the particular example, the interactions between the "massless conformally coupled scalars (φ ̃)" and "gravitons (hμν)" in the early universe which lead to quantum effects. The reason for the particularly choice of these two particles can be summarized as: The quantum effects stem from the particles created in vacuum. In flat space, virtual particles affect on these particles created in vacuum. These effects of virtual particles diminish and finally disappear at the Planck time. But the expansion of curved space-time alters 'Heisenberg's energy-time uncertainty principle' (∆E ∆t > h ̄/2), allowing virtual particles to survive longer than in flat space. The reaction rate of interacted virtual particles increase in the expanding space-time if these particles are massless and conformally non invariant. In inflation scenarios, the expansion of curved space-time can lead to particle creation by increasing the existence time of virtual particle pairs in vacuum. If the expansion is accelerated, the effect is strongest and the virtual particles are massless and do not possess conformal symmetry. Therefore, the well known examples of the kind of these particles are massless, minimally coupled (MMC) scalars and gravitons in the literature. They can mediate large quantum effects during inflation. Also, the named as cosmological perturbations as firstly quantum gravitational observables that were predicted by Mukhanov and Chibisov at 1981 for the scalar part and by Starobinsky at 1979 for the tensor part. The MMC scalars and gravitons are the source of scalar (WMAP9, Planck) and tensor perturbations (B-mode polarization), respectively, predicted by inflationary theories. The observables from these cosmological perturbation came into prominence via Cosmic Microwave Background (CMB) power spectrum. In this thesis, the interaction between particularly "massless conformally coupled scalars" and "graviton" is taken as the source of the quantum effects during inflation and these effects are calculated as the corrections coming from the first order level. In order to analyze these effects, the effective field equation are solved. In Chapters 2. and 3., the calculations of leading order quantum gravity corrections from these interactions are detaily given in de Sitter inflation time. Firstly, the corresponding only the lowest order Feynman diagrams, i.e., one-loop order Feynman diagrams, are calculated applying the perturbation method in terms of the loop-counting parameter (κ2 ≡ 16πG). Second, fully renormalized self-mass-squared (SMS) (iM2(x;x′)) for conformally coupled scalars (CCS) is obtained by using special calculation technique, dimensional regularization. In this technique, the counterterms help to extract the finite terms from the divergences. The fully renormalized self-mass-squared is obtained for every interaction (conformal-conformal interaction, kinetic-kinetic interaction, cross interaction), separately. Then, the total of them is given as −iM2(x;x′) = −iM2(x;x′) + −iM2(x;x′) + −iM2 (x;x′), C K cross here C and K denote conformal and kinetic interactions, respectively. The total of them −iM2(x;x′) is needed for the next step of the calculations, as μν ̃ 1 ̃ ̃ 4′2 ′ ̃′ ∂μ −g ̃g ̃ ∂ν φ(x)−6φ(x)R − d xM (x;x)φ(x) =0. These difficult calculations and their outcomes are published as two works. In Chapter 4., the Schwinger-Keldysh linearized effective field equation 2 ̃⃗ 0′ 3′2′ ̃′⃗ ∂ Φ1(x;k)− dη d xM1(x;x)Φ0(x;k) =0. ηi is solved by applying the perturbation method in terms of loop-counting parameter to the obtained self-mass-squared outcomes and conformally coupling scalar as ∞ M2(x;x′) = ∑κ2lMl2(x;x′), l=1 ∞∞⃗ Φ ̃(x;⃗k) = ∑κ2lΦ ̃l(x;⃗k)= ∑κ2lu ̃l(η,k)×eik·⃗x , l=0 l=0 and using some special integral techniques. It is seen that the found quantum corrected scalar mode functions (u ̃l(η,k)) have a secular growth effect behaviour, proportional to a logarithm of the scale factor at late times with physical time. The all calculations' details and their outcomes are published in the third work. In Chapter 5., the effect of loop corrections to primordial non-Gaussianity of Cosmic Microwave Background is investigated and the findings from it can be sorted as: A huge value for the non-Gaussianity which would exceed the observed value by at least 30 orders of magnitude may be obtained for single scalar inflaton. It is shown that the non-Gaussianity is a better place for quantum gravitational corrections: While power spectrum is related to the magnitude of mode function, non-Gaussianity is related to the time derivative of the mode function. All details are included in the published last work. All outcomes are summed and the recommended future works are presented in Chapter 6.. In this way, the expected outcomes coming from quantum gravity effects for particular example from the interaction between a "massless conformally coupled scalars" and a "graviton" during inflation time are investigated in this thesis.
Prototip bir X-ray görüntüleme sisteminin daha iyi bir dedeksiyon verimi için modellenmesi
Main goal of this thesis was to use Geant4 to model and design an x-ray imaging system based on Si-PIN photodiodes. After validation of the model with other methods and experiments, the model was used for determining several parameters' influence on image quality in an x-ray imaging system. The model has two sections of Geant4 codes which can be run independently. The first section includes the code for x-ray production and the second section includes the one for image construction. Production code produces the x-ray beam from x-ray tube with a stationary anode and imaging code retrieves this energy spectrum from the simulation results and use it as an input to simulate an x-ray imaging system. X-ray imaging system consists of an x-ray beam gun, targets to be imaged, two different anti-scatter grid options to reduce the number of scattering photons that degrades the contrast in the image and a detector to obtain the signal. All of the parameters related to these components were set to be adjustable. X-ray production validation was accomplished by comparing the simulation results with experimental and other methods. In general, spectral comparison was in good agreement except the amplitudes of the characteristic peaks. This is expected since all the comparisons in literature have shown the same behavior when comparing simulation with experimental result. The simulation was used for calculating the inherent filter thickness of an x-ray tube with a simple interpolation. Different types of anodes, effects of additional filters, detection area and source-to-detector distance were studied. Detector response of Amptek XR-100CR was simulated and compared with the experimental results to validate the success of determination of efficiency by the simulations. Simulations of x-ray imaging system were conducted to investigate the effects of parameters changing the image quality such as contrast and spatial resolution. For validation, a simulation was performed and the image obtained was compared with experimental study. A line test was included into the simulation to obtain the spatial frequency of designed x-ray imaging system. Optimization of grid/collimator studies were conducted to improve the contrast of the image. An anti-scatter grid with cylindrical holes and parallel plates were added as the simulation parameters with adjustable grid size. X-ray tube high voltage and pixel size on the detector were studied to investigate their effects on the image quality. Two separate graphical user interfaces XRTS (X-Ray Tube Simulations) and XRIS (X-Ray Imaging Simulations) were also prepared to modify some basic parameters in the Geant4 codes practically. Both of the applications are aimed to be open source codes for educational and research purposes.
Surface morphology of randomly disordered liquid crystal
I have studied the quenched random disorder effects created by aerosil dispersion in an octylcyanobiphenyl liquid crystal using atomic force microscopy technique. Liquid crystals have a rich phase variety. The nematic to the smectic-A phase transition in which smectic layers are formed in one dimension while the material is still in a liquid-like condition in two dimensions within the layers is one of the common examples of LC phase transitions. Gelation process in the 8CB+aerosil gels yields a quenched random disorder network which also changes the surface topography. By increasing the aerosil concentration, the original smooth pattern of liquid crystals sample surfaces is suppressed by creating fractal aerosil surface effects; these surfaces become more porous, rougher with more rounded crevices. The dispersed aerosil also serves as pinning centers for the liquid crystal molecules. It has been observed that via the diffusion-limited-aggregation process, aerosil nano-particles yield a fractal-like surface pattern for the less disordered samples. As the aerosil dispersion increases, the surface can be described by more aggregated regions which also introduce more roughness. The results of these analyses, we showed a net correlation between the short-ranged X-Ray peak widths and the calculated surface roughness of the samples. In other words, here we have shown that these quenched random effect gels can also be characterized by their surface roughness.
Synthesis of TiO2 nanorods by hydrothermal method and their opto-electronic device applications
Titanium dioxide (TiO2) is one of the most significant semiconductor materials due to its excellent physical, chemical properties which allows to be employed for many applications. Its superior features and suitability for various applications stems from its wide band gap, crystalline phase structure, dimension, surface feature, chemical stability, morphology and low manufacturing cost. Recently, therefore, TiO2 nanorods (NRs) have attracted wide range of attention as one-dimensional material for a wide range of device applications including supercapacitors, dye sensitized solar cells, superhydrophobic/superhydrophilic surfaces, data storage devices, medical engineering, lithium batteries, and gas sensors. Although there are various synthesis techniques, hydrothermal method come into prominence for the synthesis of TiO2 NRs since it is a relatively simple, cost effective and controllable technique. In this thesis, thus, it has been mainly focused on the synthesis of TiO2 NRs via hydrothermal method under various growth parameters. It is a well-known fact that to employ hydrothermally grown TiO2 NRs in many opto-electronic device applications, the understanding of synthesis mechanism and the control over their morphological features would play a significant role. In this regard, each growth parameter such as acidity, precursor concentration, growth temperature and growth time were systematically studied in detail. For fabricated TiO2 nanorods, the scanning electron microscopy (SEM) images have clearly revealed that the length, diameter, density and distribution of TiO2 NRs on the substrate can be tuned by changing growth parameters. X-ray diffraction (XRD) analysis has shown the presence of a rutile crystal phase of fabricated TiO2 NRs which is deduced by comparing the observed reflection peaks with the ICDD (international center of diffraction data) cards in database. For the investigation of optical characteristic of synthesized TiO2 NRs, transmittance and reflectance measurements have been conducted in the 300-1000 nm wavelength range. The parameters of samples having less transmittance and less reflectance have determined, which is essential features for opto-electronic devices converted of light energy to electrical energy. Taken together the results, the optimum parameters for synthesis TiO2 NRs were determined, which can be employed for the fabrication of high performance opto-electronic devices in a cost effective way. Moreover, the hydrothermal growth parameters have efects on formation of very special structures such as nanotube and urchin-like structure as well as morphological properties of nanostructures. In this study, it was also shown that nanotubes and the spherical hollow TiO2 structure based on urchin-like structure could be produced by using hydrothermal method. Nanotubes were fabricated at two different steps including growth and etching of nanorods. The spherical hollow TiO2 structures were constructed by coalescence of urchin-like nanorods via hydrolysis reactions at high temperature. The morphological features of these different fabricated structures was also investigated by SEM images. The fabrication of such different nanostructures offer promising potential to construct high-performance opto-electronic devices. Following the synthesis process, a few device structures based on the optimized TiO2 NRs were constructed to test their performance for different opto-electronic applications. It is a well-known fact that TiO2 NRs are especially suitable for the construction of high performance visible/infrared blind ultra violet (UV) photodetectors (PDs) due to their unique properties such as large surface to volume ratio, high electron-hole separation efficiency, hole trapping by O2 adsorption and having a large band gap. As an application of the optimized TiO2 NRs, a Schottky-type UV PD was fabricated by thermally evaporating silver (Ag) metallic top contact onto TiO2 NRs. The current density- voltage (J-V) characteristics of Ag/TiO2 NRs based Schottky type PD were investigated under illuminated and dark conditions. Under dark condition, the J-V characteristic has confirmed the formation of a Schottky barrier between Ag and TiO2, deduced from the rectifying behavior of the device measured under different voltage polarities. In addition, the spectral photoresponse and the photoresponse vs. time characteristics of the constructed Schottky type- UV PD have been studied in detail, exhibited a high gain under a illumination beam consisted of photons matching the band gap of the TiO2. The synthesized TiO2 NRs were also employed for the fabrication of a core-shell FTO/TiO2-NRs/p-CdTe structured heterojunction solar cell. The results have shown that the constructed solar cell exhibits photovoltaic behavior with a power conversion efficiency of 0.42% (under AM 1.5G), which is the record efficiency reported so far for the same materails combination and device architecture.
The compact muon solenoid hadronic forward calorimeter photomultiplier tube tests during the first long shutdown
CERN, the European Organization for Nuclear Research, is an international scientific collaboration founded at 1954 near Geneva. The machines at CERN are particle accelerators and detectors. CERN complex accelerator includes many experiments apart from the LHC experiment. The LHC experiment analyses the particles at the collisions by using its detectors. They are namely ALICE, ATLAS, CMS and LHCb. ATLAS and CMS are general-purpose detectors. ALICE searchs for the structure of quark-gluon plasma which is a phase of matter just after the Big Bang. LHCb investigates the difference between matter and antimatter by using b quarks. The CMS detector is as a cylindrical shape detector and consists of ECAL, HCAL, Muon Stations and Tracking subdetectors. The CMS detector has many physical research programme from Standart Model to extra dimensions and dark matter. The HCAL analyses hadrons and also indirectly uncharged particles, neutrinos. In addition to these goals of the HCAL with ECAL, it searchs for electron/photon, muon and tau identities. The HCAL consists of four sections, barrels ones, HO and HB, endcap HE, and forward HF. The HCAL has two hadronic forward calorimeters, namely HF+ and HF-, the either side of the CMS detector. The HF was made of iron absorber as a passive medium and quartz fiber optics cable as an active medium. Totally, it consists of 36 wedges. Each wedge has two readout boxes and each readout box has 24 PMTs. Totaly, the HF calorimeter has 1728 PMTs. Before the phase 1 of LS1, photomultiplier tubes constructed on the HF are Hamamatsu R7525 PMTs. The purpose of these new Hamamatsu R7600U-M4-200 PMTs with four anodes changing with the old PMTs is to reduce the rate of the anomalous signals from background events. In order to bear this faulty, these new PMTs with higher gain, quantum efficiency and thinner window were chosen to replace with the old PMTs assembled on the HF calorimeter. Also, PMT's baseboard were tested at this station. During phase 1 of LS1, these new PMTs were tested in the PMT and baseboard test station at B904 building at CERN. There are two darkboxes instead of roboxes constructed on the HF calorimeter. Each darkbox has 24 PMTs. At the station, the primary goal is to sort the new PMTs as low, middle and high gain to be assembled on the HF calorimeter. These tests were perfomed by using the blue light emitting diode. This light was used in two types as LED and SPE having different intensities from each other. Some characteristic properties of these new PMTs were analyzed with statistical calculations with respect to PMT test data taken at LED and SPE intensity at the station.
Simultaneous scanning tunneling/atomic force microscopy investigation of diamond surfaces in ultra high vacuum
Diamond has always been one of the most outstanding naturally existing materials due to its distinguishing thermal and mechanical properties. As it is known as the hardest material, diamond has been a field of interest in plenty of mechanical studies and has taken its place in industry for different uses, as well. In the last few decades, with the pursuit of adaptation of semiconductors to the technology, the search for more durable novel materials with manipulative electronic characteristics has ascended. Thus, diamond has been one of the most popular research areas, such as the synthesis processes and surface studies, including scanning probe microscopy. Atomic Force Microscopy (AFM) studies of both natural and CVD grown diamond surfaces revealed the topography of diamond surfaces with different surface orientations and reconstructions. Besides, Scanning Tunneling Microscopy (STM) studies of diamond have shown that the electronic structure of diamond is highly related to the type of dopants and surface termination. In this study, the diamond surface has been investigated using simultaneous Scanning Tunneling/Atomic Force Microscopy in ultra-high vacuum (UHV). The investigation of diamond using simultaneous STM/AFM in UHV has been focused on polycrystalline and single crystalline diamond surfaces. The cleaning techniques including the sputtering, annealing and acid etch have also been practiced, in order to obtain atomically clean and flat diamond surfaces. The simultaneous STM/AFM system used in this study operates as using the tunnel current as the feedback parameter. By oscillating the cantilever at a specific frequency well below its resonance frequency, oscillations with sub-Ångström amplitudes were obtained. The detection of such small cantilever oscillation amplitudes was enabled by using a fiber-optic interferometry setup. Scanning the surfaces using such small cantilever oscillation amplitudes enables the true simultaneous STM/AFM operation on the diamond surfaces, by the means of being at certain operating regimes while scanning the surface. With the simultaneous STM/AFM system used in this study, surface topography, force, interaction stiffness, tunnel current modulation (measure of barrier height), phase shift (energy dissipation) and tunneling current were obtained. In this study, the diamond surfaces were scanned using two different cantilevers, a Tungsten (k=53 N/m) and a highly boron doped diamond cantilever (k=70 N/m), which were calibrated using thermal noise method. Atomic resolution imaging of different regions on diamond surfaces was achieved. Moreover, force-distance spectroscopies were conducted on different regions on the diamond surfaces, leading to obtain the interaction stiffness between the diamond and the tip. The maximum negative interaction stiffness between the polycrystalline diamond surface and the W tip is measured around -2-2.5 N/m, where the interaction stiffness between the polycrystalline diamond surface and the highly boron doped diamond tip is measured as -1.2 N/m. For the single crystalline diamond, the maximum negative interaction stiffness between the sample surface and the W tip is measured as -2.5 N/m and -1.2 N/m, with an applied bias voltage of -1 V and 1 V respectively. The maximum negative interaction stiffness between the single crystalline surface and the highly boron doped diamond tip is measured as -1.5 N/m.
Quantum aspects of molecular correlations in biological catalysis
Hydrogen bonds are of central importance in many natural phenomena in physical, chemical, and biological systems. In particular, several critical cellular processes require structural and electronic complementarity between molecules mimicking a lock and a key, and the degree of this complementarity is mainly achieved through the number and strength of intermolecular hydrogen bonds. From an information-theoretic point of view, the biomolecular complementarity described in this way is nothing but a type of correlation generated through hydrogen bonds. There are various experimental and theoretical findings suggesting the occurrence of proton tunneling through the hydrogen bonds formed during some of the critical cellular processes, including nucleic acid base pairing and enzyme catalysis. This raises the question for a relation between the quantum correlations generated by proton tunneling events and the biological functions of the hydrogen-bonded biomolecules performed inside the cell. In this respect, the object of this thesis is not only to discover how an intermolecular interaction can generate quantum correlations via proton tunnelings through hydrogen bonds, but also to investigate how an enzyme can use them to catalyze a biochemical reaction. In order to test the hypothesis that the tunneling of protons through hydrogen bonds generates intermolecular quantum correlations, we use the following plan. First, we construct a fermionic Hamiltonian for the motion of a single proton in a hydrogen-bonded system and then convert it into a two-qubit pseudo-spin Hamiltonian using the Jordan-Wigner transformation. This pseudo-spin formalism enables us to quantify the amount of correlations generated by the proton mobility using the tools of quantum information theory. It also enables us to develop a Markovian master equation approach for the open system dynamics of the proton under the influence of the stretch vibrations of single covalent bonds involving the hydrogen when memory effects are neglected. Second, we extend our pseudo-spin formalism to a twelve-qubit model of a single hexameric H2O ring. After constructing a map from the actual 3-d structures of water ice to the present 2-d model of a single hexamer based on the single-hexamer proton relocation events occurring in them, we find that the violation of the ice rules in the model corresponds to the proton-disordering phase transition in hexagonal water ice. We then consider the steady-state solution of the master equation which reveals the role of vibrations in the emergence of ice rules and depends only on two parameters. We fix these parameters using i) the unit probability of pseudo-spins to be found inside the ice-rule preserving subspace as an indicator of proton-ordered phase and ii) the entropy of pseudo-spins as a measure of proton-disorder. Using these model parameters, we show that l1 form of coherence of the pseudo-spin steady state captures the behaviour of coherent proton mobility observed in low-temperature experiments that suspect a concerted tunneling of six protons. We investigate the nature and the amount of pairwise pseudo-spin correlations by means of the entanglement of formation, the concurrence, the quantum discord, the geometric discord, and the quantum mutual information of the reduced states. We conclude that individual quantum tunneling events in the bonds of water ice are classically rather than quantum correlated at low temperatures, a point that can't be addressed by the previous studies. We also show that although the quantum correlations in hydrogen bonds seem to be insignificant when compared to their classical counterparts, temperature dependence of quantum coherent proton mobility still originates from them. Thirdly, we move on to our main hypothesis in this thesis which states that an enzyme, at least in principle, can derive its catalytic potency from the quantum correlations generated through intermolecular hydrogen bonds. To test this hypothesis, we take into account a prototypical enzyme-catalyzed nucleotide tautomerization reaction starting by the formation of two weak hydrogen bonds between an enzyme and its substrate. We describe the substrate recognition process by an induced-fit mechanism in which the initial hydrogen bonds are assumed to trigger a slow and continuous conformational change in the binding site of the enzyme. The two biomolecules are assumed to decouple from each other at the end of the binding stage after which the enzyme rapidly undergoes a subsequent conformational change to return back to its initial state. In this respect, we use our pseudo-spin formalism to construct a time-independent three-qubit Hamiltonian for the tautomeric transitions of the nucleotide. We extend our master equation approach to include the effects of conformational dynamics of the nucleotide on the intramolecular proton dynamics. We describe the enzyme-nucleotide hydrogen bonds by the two-qubit pseudo-spin model assuming that the protons stay in the ground state of the time-dependent total pseudo-spin interaction Hamiltonian during the slow conformational change of the enzyme which is induced upon substrate binding. On the other hand, the effect of the subsequent rapid conformational change of the enzyme on the proton dynamics is modeled by a post-selection measurement on the pseudo-spins of the enzyme. The quantum correlations generated through the intermolecular hydrogen bonds at the end of binding state are found to be transferred to the nucleotide when the enzyme suddenly returns back to its initial state in this way. The resulting intramolecular correlations inside the nucleotide constitute a transition state which actually corresponds to a quantum coherent superposition of the substrate and product forms. We analyze the open system dynamics of the nucleotide using our master equation approach starting after this transition state. The stationary solution is found to depend on only two parameters, which are estimated from the literature. In particular, we show that the nucleotide reaches an equilibrium such that both probabilities corresponding to substrate and product forms are equal to 1/2 when the overall entanglement generated through hydrogen bonds is chosen to be maximal at the end of binding stage. The transition state has a free energy that equals to the average of the free energies of the substrate and the product forms, a value much lower than expected in biochemical reactions. According to our results, the equilibrium probabilities are found to be unaffected when the quantum correlations generated through hydrogen bonds at the end of binding stage rapidly decay to classical correlations before the subsequent conformational change. The calculations show that the average energy is also independent from such a decoherence. On the other hand, it does make a difference to the free energies. Although this is not a significant difference at all, the direction of the change is opposite to that which one expects. The free energy of the transition state drops further as a result of the increase in the entropy that is produced by the decoherence. The rate enhancement the enzyme brings about in this way is found to be in the range of 22 to 27 orders of magnitudes for different amounts of intermolecular entanglement generation at the end of the binding stage. We compare this enzyme-catalyzed reaction with the water-mediated tautomerization of the nucleotide in which intermolecular quantum correlations are also generated through water-nucleotide hydrogen bonds. A maximal entanglement generation through intermolecular hydrogen bonds produces the product with an equilibrium probability of 1/4 in this case. Moreover, it produces cationic and ionic transition states with the same equilibrium probability. Besides this, the water-mediated tautomerization requires the right orientations of the molecule which is very unlikely inside the cellular environment. Hence we conclude that the cyclic and classical conformational change of the enzyme increases the likelihood of the formation of quantum hydrogen bonds with the nucleotide and makes them a more efficient resource for the tautomerization process.
Yüksek-rölativistik enerjilerde müon çifti üretimi
The main purpose of high energy physics is to help us to understand and explain the elementary particles that constitutes matter. For this aim the various particle accelerators have been constructed. At the RHIC(Relativistic Heavy-Ion Collider) and LHC(Large Hadron Collider) which are the largest particle accelerators, the particles produced as a result of the heavy-ion collisions performed at the center of mass frame with relativistic velocities are investigated. In heavy ion collisions, the collided particles undergo a Lorentz contraction due to their high relativistic velocities, and very strong electromagnetic fields occur at their ends. The vertical distance between the colliding particles is called the impact-parameter. If the impact-parameter is greater than the sum of the radii of the two nuclei, the peripheral collision is concerned, otherwise the central collision occurs. Central collisions occur as the form of nucleus-nucleus(or head-to-head) collision, and are thought to cause the creation of quark-gluon plasma(QGP), which is known to exist at the first formation of the universe. In the case of peripheral collisions, the interaction of strong electromagnetic fields at the ends of heavy-ions is involved. In both collisions, many particles are produced. Investigation of lepton pairs produced in these collisions has an important place in high energy physics, since it is thought to contribute to the understanding of the QGP phase state of matter. In this thesis, the process of lepton-pairs production with electromagnetic interactions in heavy ion collisions at high relativistic velocities is discussed. Firstly, it was shown how to calculate cross-sections for muon-antimuon and electron-positron pairs. For this, low-order quantum electrodynamics(QED), Gauge theory and Feynmann diagrams were used. The obtained cross-section expression were numerically solved by the Monte-Carlo method using the FORTRAN program since it contains 9-fold integrals that are difficult to solve analytically. Form factors that provide information about the charge densities of atomic nuclei were also taken into account. There are different approaches for charge distributions such as Gaussian, Uniform and Woods-Saxon (Fermi). Form factors are obtained by taking Fourier transforms of these spatial charge distributions. In this study, the cases with form factor of Woods-Saxon and Gausyen and without any form factor were examined, and the effect of these different form factors on the cross-sections of the electron-positron and muon-antimuon pairs were shown. However, the electron is hardly interacting with the atomic nucleus, because its reduced Compton wavelength (386 fm) is too large for the size of the nucleus. Therefore, the form factor effect for the electron is negligible. For the muon with a reduced Compton wavelength of 1.86 fm, the effect of form factors is of great importance. The effect of the form factor on the differential cross-sections was also clearly seen on the obtained graphs. In this study, two methods, which are method of perturbative QED including second xxi order Feynman diagrams and EPA (Equivalent Photon Approach), were emphasized to calculate the cross-section. Calculations using perturbative QED were used to obtain differential cross-section graphs based on the impact-parameter. In the graphs, it was seen that the production amount of muon-antimuon pair was lower since it is 207 times heavier than the electron. Then, the contribution of the cross-section from the electromagnetic interactions to the central collisions of heavy ions was calculated by limiting the impact-parameter in the range of 014 fm. This calculation means that all of the measured cross-section for the central collisions do not come from the Drell-Yan process. After that, the total eperipheral cross-section value was obtained for the production of muon-antimuon pairs at RHIC, and compared with the results calculated by EPA method. In the next part, the change of the cross-section according to quantities such as rapidity, transverse momentum, longitudinal momentum, energy and invariant mass which give information about the nature of the lepton-pairs produced in collisions were investigated. It was observed that the maximum lepton-pair production happened for the cases which the scattering angle is in the range of 45 < q < 90 in the plots obtained for rapidity. In the graphs obtained for lepton-pairs, it was observed that the differential cross-section of electron-positron pair was more than muon-antimuon pair. For the energy, momentum and invariant mass, the values of the electron are smaller. On the other hand, it is very difficult to examine the results of the heavy-ion collision experiments at LHC and RHIC without any limitation on parameters such as energy, momentum, invariant mass of the produce lepton-pairs. In the last part of this thesis, by applying the conditions used for the Pb+Pb heavy ions collision performed at LHC with 5:02TeV energy, the total cross-section value and the graphs for rapidity and invariant mass were obtained. Then, the calculated total cross-section value was compared with the experiment result.
Optimization of optical and electrochemical properties of PANI, PEDOT conducting polymers to design electrochromic device
Advances in natural sciences and technology dominate creative ideas by giving new pathways for the future aspects of developments in electrochromism. Diving deeper in the materials' molecular structures conceives new problems and opportunities to create valuable information about innovative technologies. Organic materials have promising applications because of their specific properties such as durability, lifetime, low costs, low energy consumption, high ion diffusion, and easy and fast production methods. Therefore, organic materials are used in electrochromic applications to manufacturing functional devices as smart materials. In this project, polymer materials were characterized by CV, CA and impedance spectroscopy methods to use electrochromic applications. PANI and PEDOT materials are mostly used organic substances to develop interesting device prototypes like electrochromic devices, storage devices, and sensors. They were characterized using different methods and experimental results to improve their electrochromic and structural properties. In addition to the improvement process, heat-treatment effect and impedance properties were investigated and equivalent circuit models of developed materials and devices were created using IVIUMSOFT software. Polyaniline comes into prominence by electrochromic properties than other materials. It has three different oxidation states and each state has own color, which is why we used it for electrochromic applications. PANI was synthesized by using different parameters such as an acidic solution, concentration and annealing temperature, voltage ranges, and the scan rate of the voltage. Polyaniline is a unique polymer. It has three oxidation states showing different colors that are yellow, green, blue and their shades that is why polyaniline was chosen for electrochromic applications. It was characterized by electrodeposition and chemical oxidation methods. Electrodeposition method has the capability to polymerize aniline but the strength and lifetime are too low because of adsorption and fast degradation under the room conditions. From this point on, heat treatment was applied to improve electrochemical properties and lifetime of polyaniline films. Advancing in parallel with this process, the chemical oxidation method was carried on to develop polyaniline films. Polyaniline films, which are heat-treated at 90oC, that were coated using the electrodeposition method. They were reached to the better parameters as polyaniline films, which are deposited by chemical oxidation method. Heat-treatment was not applied to polyaniline films developed using chemical oxidation methods because of a quite high lifetime and high adsorption properties. The unique property of chemical oxidation method is that coated films do not require conducting surface in the coating process. Chemical oxidation method was carried on stable room conditions and bath has 15oC using APS as an oxidizing agent. PEDOT films were developed by electrodeposition method onto the ITO surface. 3, 4-ethylenedioxythiophene was used as monomer prepared in acetonitrile/LiClO4 mixing solution. Compensating required ion transportation in the solid electrochromic device is the reason why PEDOT films, the counter electrode, are required to develop. For this respect, optimum parameters found in the experimental processes to polymerize EDOT onto the ITO surface. PEDOT films were found more conducting than PANI films when calculating total charge transportation in chronoamperometry measurement. If these results are taken into consideration, PEDOT films have more conductivity and have more capability for electrochromic application than PANI films. Electrolytes are important materials for electrochromic devices. Characterization of electrochromic films was carried out in solution based 3-probe cell system. PANI film was characterized in acidic media and PEDOT films were characterized in alkaline media. This is the key difference between the two films. Acid includes H+ ions but base that was used for characterization of PEDOT includes Li+ ions. These ions diffuse through the films in electrochemical processes and they show electrochromic properties after diffusion, which causes redox reactions and protonation/deprotonation processes. Gel or solid electrolytes that include ionic structures are used in solid electrochromic devices and they are the basic requirements in a diffusion process to observe electrochromic properties. In PANI/PEDOT solid device application process, durability is controlled in chronoamperometry measurement. It has a very long lifetime, which is higher than ten thousand cycles, but contrast change is quite low due to the transition of color change. The color of the PANI films toggles bleach to green/blue when voltage sweeping negative to positive but PEDOT works inversely. Positive to negative transition could not be observed easily in color change. Nevertheless, it is not the only reason to disparage PANI/PEDOT solid device also electrolyte gel layer is an important parameter for ion transportation between electrodes. It was made of LiClO4 and PMMA mixing structure in PC solution that is well-known electrolyte in such electrochromic applications. Finally, after the investigation of electrolyte for both cell and solid electrochromic devices, optical and electrochemical properties of the optimized organic films were experienced using spectroscopic, cyclic voltammetry and chronoamperometry methods. Then, coloration efficiency, diffusion constants, optical and electrical properties were determined using the required mathematical and physical tools depend on the measurement parameters and results. In the last step, the equivalent circuit model was studied using electrochemical impedance spectroscopy method using obtained data in the measurements. Under the guidance of these results, future applications of studied materials were considered to open a new path for both electrochromism and other potential applications.
Katkısız ve ZnO nanoparçacık katkılı NIPAM nanojellerininsentezlenmesi ve karakterizasyonu
Polimer tabanlı malzemelerin üzerine 20.yüzyılda odaklanılmaya ba¸slaması ile hayatın her alanına girmeleri çok hızlı bir biçimde olmuştur. Doğadaki polimerlerin çeşitliliği sayesinde gözlemler ile kullanılabilecekleri alanlar tespit edilmiş ve sanayi kullanımından, günlük ev içi kullanım alanlarına kadar geniş bir spektrumda polimerler vazgeçilmez bir yer edinmiştir. Polimerlerin fonksiyonelleştirilebilir olması ve katkılandırılarak farklı özellikler kazandırılabilmeleri sebebiyle, ilerleryen teknolojide aktif rol almalarını sağlamaktadır. Bu yüzden eczacılık, biyomedikal, moleküler biyoloji, biyofizik gibi alanlarda önem kazanmı¸slardır, sentetik ve doğal polimerler üzerindeki disiplinler arası araştırmalar hızlanarak artmaktadır. Özellikle jel yapılı malzmeler canlı yapılarında da sıklıkla karşılaşılan özellikleri sergileyebildikleri için popüler hale gelmiştir. Üzerinde durulan önemli bir polimer yapısı da çapraz bağlardan oluşan nanojellerdir. Üzerlerinde durulmasının en önemli sebeplerinden bazıları kolay sentezlenebilir olmaları, dış etkenler ile kontrol edilebilmeleri ve insan vücudu ile uyumlu biçimde çalışabilmeleridir. Bulundukları ortama göre şişip büzülme özelliği de bulunan nanojeller, bu özelliklerinden ötürü ilaç taşıyıcı olarak ve molekül algılayıcı olarak kullanılabilmektedirler. Nanojellere çeşitli katkılar yapılarak farklı özellikler kazandırılabilmektedir. Nanojel içine yerleştirilen nanoparçacıklar ilaç taşıyıcı özellikleri ile ek bir katkı sağlayabilmektedirler. Nanoparçacıklara tutunan proteinlerin yapısal bütünlüklerini koruması sayesinde iki yapının eş zamanlı kullanılması ile daha verimli bir şekilde çalışan ilaç taşıyıcı sistemler yapılabilir. Bu çalışmada N-isopropylacrylamide (NIPAM) ile hazırlanan nanojellerin sentezlenmesi ve polimerleşme sırasında ve sonrasındaki karakterizasyonu üzerinde durulmuştur. Polimerleşme ve jel oluşumu sırasındaki yapısal değişikliğin takibi amacıyla nanojellerin sentezlenmesi sırasında yapıya floresans bir molekül olan piranin katılmıştır. Katkılanan bu molekül sayesinde jelleşme boyunca oluşan değişiklikler spektroskopik olarak izlenmiştir. Elde edilen sonuçlar ile jelleşme sırasındaki sol-jel faz geçişindeki kritik nokta ve fraktal yapılar hakkında bilgi elde edilmiştir. Ayrıca tezin ikinci kısımında ZnO nanoparçacıkların nanojellerle eş zamanlı olarak sentezlenmesi ve karakterizasyonu üzerine çalışmalar yapılmıştır. ZnO nanoparçacıkların ve nanojellerin ilaç taşıyıcı etkisi bilinmektedir. Bu yüzden nanojel ile kaplanmış bir yapı üretilmesi üzerinde durulmuştur. Sentezlenen yapılardaki ZnO oluşumu spektroskopik yöntemler ile gözlemlenmiştir.
Skaler bozon aracılığıyla üst kuarkın çeşni değiştiren yüksüz akım etkileşmelerinin araştırılması
Günümüzde yüksek enerji fiziği, Standart Model (SM) çerçevesinde Higgs bozonunun da keşfedilmesiyle birlikte yeni bir evreye girmiştir. Bu evrede bilim insanları günümüze kadar ortaya konmuş olan modelin çözümlenmemiş problemlerine odaklanmıştır. Buradaki sorunların kesin çözümleri ise tartışmasız deneysel doğrulamaya muhtaçtır. Öte yandan Büyük Hadron Çarpıştırıcısı (LHC)'ndan elde edilen sonuçlar, SM'in sorunlarının çözümüne yönelik olarak öne sürülen hiçbir SM ötesi modeli doğrulayamamaktadır. Bu durum araştırmacıları daha yüksek enerjili hızlandırıcılarda yapılacak deneylerden elde edilecek verilerde yeni fizik arayışına itmektedir. Teze konu olan bu çalışmada SM'in cevapsız bıraktığı sorulara cevap bulmak amacıyla, çeşni değiştiren yüksüz akım (FCNC) türündeki etkileşimlerin yeni çarpıştırıcılardaki gözlemlenme potansiyeli, etkin alan teorisi çerçevesinde ve benzetim yöntemi kullanılarak araştırıldı. Bu doğrultuda şu anda sıklıkla çalışılan üst kuarkın anormal etkileşimleri incelendi. Bu çalışmalardan elde edilen öngörülerin deneylerle sınanması hiç kuşkusuz işin en can alıcı kısmını teşkil etmektedir. Bu tip etkileşmelerin deneysel ölçümleri çok hassastır ve öngörüler kolaylıkla test edilebilir niteliktedir. Dolayısıyla deneylere de yön gösterecek bu tipte çalışmalarla, olası yeni fizik keşiflerine ya da etkileşme sabitleri üzerine yapılabilecek dışarlamalara kapı açılması mümkündür. Bu bağlamda tezde, üst kuark ve Higgs bozonunun FCNC etkileşimi önce Yüksek Işınlıklı Büyük Hadron Çarpıştırıcısı (HL-LHC)'de aynı işaretli lepton kanalında incelenmiş ve kanalın dışarlama için uygun olduğu kanaatine varılmıştır. Dışarlama senaryosu için etkileşim sabiti \eta_{q}=0,04 ve karşılık gelen dallanma oranı HL-LHC beklentilerine uygun olarak 3,048\times10^{-4} olarak elde edilmiştir. Daha sonrasında FCC-hh için yapılan araştırmada ise keşif senaryosu için \eta_{q}=0,0059 ve karşılık gelen dallanma oranı 1,32\times10^{-5} ve dışarlama senaryosu için \eta_{q}=0,0027 ve karşılık gelen dallanma oranı 2,78\times10^{-6} olarak bulunmuştur.
Enerji hasatı ve biyomedikal uygulamalar için manyetik polimer kompozitler
Piezoelektrik polimerler ailesinden polyvinylidene fluoride (PVDF) piezoelektrik ve ferroelektrik özelliğe sahip olmasının yanı sıra esnek, hafif ve biyouyumlu olduğu için enerji hasatı ve sensör gibi teknolojik uygulamalarda öne çıkan bir malzemedir. PVDF, , , , ve olmak üzere beş farklı yarı kristal faza sahiptir. En kararlı dolayısıyla kolay üretilebilen fazının kutupluluk özelliği yoktur, teknolojik uygulamaları sınırlıdır. Oysa ve fazları kutupludur ve fazı sahip olduğu en yüksek piezoelektrik özelliği nedeniyle enerji hasatı için ideal yapıdır. PVDF'nin kristal yapısı, üretim tekniğine bağlı olarak kontrol edilebilmektedir. İki kısımdan oluşan bu çalışmanın ilk kısmında, PVDF'nin kutuplu fazların oluşumuna (Elektro Aktif faz; EA faz) elektrodöndürme yöntemindeki pompalanma hızı, mesafe, çözücü ve dönme hızı gibi parametrelerin etkileri araştırılmıştır. Üretilen PVDF fiberlerin yapısal özellikleri X-ışını kırınımı (XRD), EA faz oranındaki değişimler Fourier Dönüşüm Kızılötesi Spektroskopisi (FTIR), Diferansiyel Taramalı Kalorimetre (DSC) ve morfolojileri ise Taramalı Elektron Mikroskobu (SEM) görüntüleri ile belirlendi. Elektrodöndürmede kontrol edilen fiziksel parametreler optimize edilerek üretilen PVDF fiberlerde EA fazın oranının %80'den %97'ye kadar arttırılabildiği belirlendi. Farklı oranlarda EA faz içeren örneklerin piezoelektrik özelliklerinin belirlenmesi amacıyla d(1,2) pioezoelektrik yük katsayısının değişimi, çalışma kapsamında tasarlanan piezoelektrik katsayısı ölçüm düzeneği ile 2,7±0,2 - 7,2±0,4 [pC/N] olarak ölçüldü. Çalışmanın ikinci kısmında ise, üretilen PVDF fiberlerine 10±2 nm büyüklüğünde süperparamanyetik Fe3O4 nanoparçacıklar eklenerek oluşturulan kompozit yapıların manyetik hipertemi tedavisindeki etkinliği, manyeto-ısıl özellikler ölçülerek belirlendi. Bunun için ağırlıkça %7,57±0,01, %12,51±0,01 ve %15,40±0,01 (w/w) oranlarda (Fe3O4/(PVDF+ Fe3O4)) üç farklı nanokompozit oluşturuldu. Örneklerin RF manyetik alan altında zamana bağlı sıcaklık değişimleri ölçümlerinden Özgül Soğurma Oranları (SAR) sırasıyla 8,5±0,1; 8,4±0,1 ve 8,2 ±0,1 W/g olarak hesaplandı.
Imaging chain simulation program for earth observation satellite imagers
In the scope of this thesis study, it is aimed to characterize the imagers used in earth observation satellites by the imaging chain model method. Imager image quality performances were evaluated by using GIQE equation and NIIRS scale by imaging chain modeling. IQA (Image Quality Analysis) program was developed for imaging chain simulation. IQA program generates MTF, SNR, RER and GIQE budgets for the predefined imagers. Besides, IQA performs image simulations panchromatic and multispectral band images. Preliminary design of a multispectral TDI imager operating in panchromatic, blue, green and red bands has been made. Imaging chain links an example imager design is characterized by using IQA program. In this context, MTF, SNR, RER and GIQE performance budgets are generated under optic, electronic, platform stability ant atmosphere degradations. Operational requirement budget ranges of the imager were determined by using IQA simulations. GIQE breakdown budgets with ± 0.3. are simulated for varying platform smear errors, platform jitter errors, wavefront errors, defocusing errors, number of TDI steps and solar zenith angles. Also the panchromatic image simulations related to the degradation factors are generated.
RF magnetron kopartma tekniği ile büyütülen LiCoO2 ince filmlerin optik, elektrokromik ve yapısal özelliklerinin incelenmesi
Dünya nüfusunun hızlı bir şekilde büyümesiyle, dünya çapında fosil enerji kaynaklarına ihtiyaç artmıştır. Fosil temelli enerji kaynaklarının kullanımı sonucunda dünya, küresel ısınma, sera etkisi, ozon tabakasının delinmesi gibi problemlerle karşı karşıyadır. Teknolojinin ilerlemesi ile birlikte alternatif ve yenilenebilir enerji kaynaklarına yönelim başlamıştır. Elektrokromik malzemeler, bir elektriksel gerilim altında optik özellerini tersinir olarak değiştiren malzemelerdir. Elektrokromik malzemelerde görülen bu tersinir mekanizma elektrokromizm olarak adlandırılır. LiCoO2, hali hazırda yeniden sarj edilebilen pillerde kullanılan bir malzemedir. Yüksek verimli kapasitör özelliği taşıyan LiCoO2 malzemesinin, ince film formunun kullanım alanlarının araştırılması gereklidir. LiCoO2 ince filmlerin katıhal elektrokromik cihazlarda kullanılmabilmesi için, büyütme parametrelerinin elektrokromik özelliklerine ve renklenme mekanizmalarına nasıl etki ettiği tam olarak anlaşılmalıdır. Bu çalışmada, LiCoO2 ince filmler RF magnetron kopartma tekniği ile cam alttaşlar üzerinde büyütülmüştür. Büyütülen LiCoO2 ince filmlerin elektrokromik ve optik özelliklerine film kalınlığının, kısmi oksijen basıncının, plazma gücünün, alttaş sıcaklığının etkileri incelenmiştir. Bu tez çalışmasında optik renklenme gözlenen örneklerin optik modülasyon ve renklenme verimlilikleri hesaplanmıştır. Yapısal özellikleri X-ışınları kırınımı ve atomik kuvvet mikroskobu ile tayin edilmiştir. Yüzey görüntüleri taramalı elektron mikroskobu ile alınmıştır. Örneklerin elektrokromik analizleri yapılırken, gerilim ve zamana bağlı akım çevrimsel voltametri ve kronoamperometri ölçümleri alınmıştır. Elde edilen kronoamperometri eğrilerinin altında kalan alanlar hesaplanarak elektrokimyasal çevrimler boyunca film yüzeyine giren ve çıkan yük miktarları hesaplanmıştır. Tez kapsamında büyütülen LiCoO2 ince filmlerin elektrokromik olarak zayıf renklenme göstermekle birlikte, elektrokimyasal prosesler boyunca gözlemlenen iyon giriş ve çıkış kapasitelerinden dolayı katıhal elektrokromik cihazlarda iyon iletken tabaka olarak kullanılabileceği ön görülmüştür. Anahtar Kelimeler: LiCoO2 ince filmler, RF magnetron kopartma, elektrokromizm, renklenme verimliliği, optik modülasyon
Amorf silisyumun alüminyum ve altın etkileşimli kristalleştirilmesi, elektriksel ve soğurma özelliklerinin incelenmesi
Isıl buharlaştırma sistemi ile 65 nm alüminyum ve 20 nm altın kaplanmış alttaş üzerine plazma destekli kimyasal buhar biriktirme (PECVD) sisteminde 100 nm hidrojenlendirilmiş amorf silisyum (a-Si:H) büyütülerek cam / Al / a-Si:H ve cam / Au / a-Si:H yapısında örnekler üretildi. Örnekler 250 ile 430 oC sıcaklıklar arasında ve 1 ile 12 saat süreleri arasında tavlanarak metal etkileşimli kristalleşme (MIC) yöntemi ile amorf silisyum kristalleştirildi. Örneklerin yapısal analizi için Raman Spektroskopisi, optik özelliklerinin analizi için optik geçirgenlik ve optik yansıtıcılık ölçümleri ve elektriksel özellikleri için dört nokta yöntemi ile özdirenç ve Hall etkisi ölçümleri yapıldı. Yapısal analiz ile nanokristal silisyum yapılarının olduğu, optik geçirgenlik ve yansıtıcılık ölçümleri ile hesaplanan optik soğurma spektrumunda iki fazlı soğurmanın olduğu, elektriksel ölçümler ile mobilite değerlerinin 1 – 800 cm2/V∙s arasında olduğu gözlendi.
Protein-ligand etkileşimlerinin kuantum mekaniksel/moleküler mekaniksel simülasyon teknikleriyle incelenmesi
Bu çalışmanın temel amacı, metal iyonu bağımlı biyomoleküler sistemlerin in silico kuantum ve moleküler mekaniksel hibrit yaklaşımlarla (QM/MM) araştırılmasıdır. İnhibitör bağlı enzim yapısı üzerinde yapılan deneysel çalışmalarla tahmini yapılan doğal substratların izlediği reaksiyon konformasyonlarının hesaplamalı olarak belirlenmesi hedeflenmiştir. Moleküler dinamik (MD) ve Metadinamik (MTD) simülasyon yöntemleri kullanılarak yürütülen bu araştırmada, bir insan bağırsak ortakyaşarında bulunan Kalsiyum (Ca2+)-bağımlı alfa-mannosidaz enziminin iki inhibitör ve bir doğal substrat alfa-1,2-Mannobiyoz'u içeren üç yapısı incelenmiştir. Doğal substratı içeren yapıda şeker halkasının Cremer-Pople büzüşme koordinatları kullanılarak QM/MM MTD çalışmalarla elde edilen serbest enerji yüzeyleri, hesaplamalı çalışmalarımız ile deneysel bulguların reaktant ve geçiş hali konformasyonları etrafında uyumlu olduğunu göstermektedir. Reaktant ve geçiş hali konformasyonları tespit edilen doğal substrat bağlı yapının aktivasyon enerjisini, reaksiyon enerjisini, metal iyonunun rolünü ve substratın reaksiyon sırasında izlediği konformasyonel yolu belirleyebilmek için farklı parametrelere sahip bir dizi QM/MM MTD hesaplamalar yapılmıştır. Çalışmada kullanılan yöntem ve yaklaşımlarla elde edilen bilgiler, glikozidazların katalitik mekanizmaları üzerindeki bilgimizi genişletecek ve bir lizozomal depolama hastalığı olan alfa-mannosidoz hastalığının teşhis ve tedavisi için analogların tasarlanabilmesine katkıda bulunma potansiyeline sahip olacaktır.
MXOY(M=Ti, Si, Zn, Al) kaplanmış VO2 nanoçubukların sentezi ve karakterizasyonu
Dünyadaki mevcut enerji kaynakları 21.Yüzyıl'ın başından bu yana hızla azalmaktadır. Enerji tasarrufu, bu enerji kıtlığını çözmenin etkili yollarından biridir. Vanadyum Dioksit (VO2) Tc = 68 °C'de yarıiletken monoklinik bir fazdan metalik rutil faza geri dönüşümlü şekilde geçen ve bu özelliği sayesinde ilgi çeken ve yaygın bir şekilde kullanılan inorganik bir malzemedir. Metalik fazdaki kızılötesi geçirgenliğin ani düşüşü, VO2'i binalardaki enerji tüketimini azaltmak için yapılan termokromik akıllı camların yapımında kullanılabilir adaylardan biri yapmaktadır. Ancak uygulamada, bazı kısıtlamalardan dolayı problemlere karşılaşılmaktadır. Bunların arasında yüksek geçiş sıcaklığı, düşük optik geçirgenlik, çevresel etkenlere karşı kararsızlık ve istenmeyen güneş enerjisi modülasyonu sayılabilir. Bu problemleri çözebilmek için elementel katkılama, yüzey kaplama gibi birçok yöntem önerilmiştir. Bunların arasında önerilen kaplanmış nanoparçacık yapısı, bu problemlerin birçoğuna çözüm önerdiği için en etkili yöntemlerden biridir. Bu çalışmanın ilk aşamasında VO2 nanoçubuklar en yaygın sentezleme yöntemlerinden biri olan hidrotermal yöntem kullanılarak sentezlenip, uygun tavlama şartlarında sentezlenen malzemenin monoklinik faza geçmesi sağlanmıştır. Ardından VO2 nanoçubuklar çeşitli metal oksitlerle kaplanarak önerilen çekirdek@kabuk yapılar (VO2@SiO2, VO2@TiO2, VO2@Al2O3, VO2@ZnO) hazırlanmıştır. Metal oksitlerle kaplanan VO2 nanoçubuklar DMF içerisinde çözünerek hazırlanan çözelti, PVB içerisine belirli oranlarda yayılarak cam alttaşlar üzerinde filmler hazırlanmış, yapısal, morfolojik ve optik özellikleri karakterize edilmiştir. Bu çekirdek@kabuk yapılarının faz geçiş sıcaklığı M-VO2'in faz geçiş sıcaklığına göre bir miktar düşmekle birlikte M-VO2'in zayıf olan çevresel kararlılığı da iyileştirilmiştir. Bu yapıların termokromik uygulamalar için umut vaat ettiği düşünülmektedir.
Hassas güdümlü sistemler için iki bant kızılötesi arayıcı başlık optik tasarımı
Kızılötesi güdümlü sistemler, hedeften yayılan enerjiyi algılayarak, hedefleri tespit etmek ve etkisiz hale getirmek için kullanılır. Bu sistemlerde kullanılan optik elemanlar, kubbe, mercekler (ve/veya ayna) ve dedektördür. Çalışma kapsamında, arayıcı başlığın optik tasarımı kızılötesi spektrumun iki bandında (MWIR–LWIR) çalışacak şekilde gerçekleştirilmiştir. Bu amaçla, optik tasarım ve analiz yeteneğine sahip Zemax OpticStudio adlı program kullanılmıştır. Çalışmaya, iki bantta çalışabilen ticari dedektörler araştırılarak başlanmış ve performansları karşılaştırılarak uygun dedektör belirlenmiştir. Belirlenen dedektörün özellikleri ile optik tasarım parametreleri hesaplanarak 3 – 10 µm aralığında çalışabilen kızılötesi arayıcı başlık optik tasarımı yapılmıştır. Tasarımın –40 ile +80 °C sıcaklık aralığındaki optik performansları, farklı dört gövde malzemesi eklenerek incelenmiştir. Her bir malzemenin kullanımındaki odak bozulmaları optik pasif atermalizasyon tekniği ile düzeltilmiştir. Gövde malzemelerinin maliyet ve tedarik imkanları değerlendirilerek tasarım sonlandırılmıştır. Tasarımı yapılan arayıcı başlığın görüş açısı 16° ve modülasyon transfer fonksiyonunun (MTF) %50 olduğunda uzaysal frekansı 23 çç/mm bulunmuştur. Yapılan çalışmanın sonunda arayıcı başlık optik tasarımı, spot diyagramı, MTF, Seidel diyagramı, enerji dağılımı ile analiz edilmiş ve elde edilen sonuçlar tartışılmıştır.
Düşük yayıcı kaplama tasarımı, hazırlanması ve karakterizasyonu
Birçok ülkede üretilen enerjinin % 40'ından fazlası binaların ısıtılması ve soğutulması için harcanmaktadır. Binalarda enerji tüketiminin azaltılması pencere camlarının kızılötesi radyasyon geçirgenliğinin ve yansıtmasının kontrol edilmesiyle mümkündür. Enerji-verimli cam kaplamalarından biri olan düşük yayıcı kaplamaların kullanım amacı, yaşam alanının içi ile dış ortam arasındaki ısı transferini azaltmaktır. Bu tez çalışmasında, dielektrik/metal/dielektrik (D/M/D) şekillenimine sahip düşük yayıcı kaplamalar tasarlandı ve hazırlandı. Düşük yayıcı kaplamaların metalik/metal katmanı olarak, farklı büyütme koşullarında hazırlanan, titanyum nitrür (TiNx) veya gümüş (Ag) ince fimler, dielektrik katmanı olarak ise elmas-benzeri karbon (DLC) veya alüminyum-katkılı çinko oksit (AZO) ince filmler kullanıldı. TiNx ve DLC ince filmler DC magnetron kopartma yöntemiyle, Ag ve AZO ince fimler ise RF magnetron kopartma yöntemiyle, cam alttaşlar üzerinde büyütüldü. Hazırlanan ince filmlerin optik ve yapısal karakterizasyonu yapıldı. Film büyütme koşullarının filmlerin optik özellikleri, bağlanma özellikleri, mikroyapısı, faz bileşenleri ve kızılötesi yayma oranları üzerindeki etkileri UV-VIS-NIR spektrofotometre, XPS, Raman spektroskopisi, SEM, AFM, XRD ve FTIR ölçümleriyle incelendi. TiNx, Ag, DLC ve AZO ince filmlerin (s ve p kutuplu ışık için) ölçülen optik geçirgenlik ve optik yansıtma spektrumlarına, eş zamanlı olarak, uygun kuramsal optik modellere benzetişim (eğri çakıştırma işlemi) yapılarak, filmlerin optik sabitlerinin dalgaboyu ile değişimi, kalınlıkları ve tabaka dirençleri elde edildi. Bu yöntemle bulunan film kalınlıkları ve tabaka dirençleri, sırasıyla, profilometre ve standart dört nokta kontak yöntemleri ile doğrulandı. Ayrıca, film büyütme koşullarının AZO filmlerin kızılötesi dalgaboyu aralığında optik yansıtmasına etkisi ayrıntılı olarak araştırıldı. Düşük yayıcı kaplamalarda metal katman ve dielektrik katman olarak kullanan filmler için optimum büyütme koşulları belirlendi. Bu filmler cam alttaş üzerinde D/M/D şekilleniminde büyütülerek, farklı metal (TiNx veya Ag) ve dielektrik katmana (DLC veya AZO) sahip düşük yayıcı kaplamalar üretildi. Bu kaplamaların düşük yayıcı performansları (görünür bölgede yüksek optik geçirgenlik ve kızılötesi bölgede düşük yayma oranı) birbiriyle ve literatürde yer alan düşük yayıcı kaplamaların performansları ile karşılaştırıldı. Bu çalışmada, kızılötesi bölgede en küçük yayma oranı (ϵ=0,027) AZO/Ag/AZO düşük yayıcı kaplama için elde edildi. Bu kaplamanın uzun-dalgaboylu ısıl radyasyon dalgaboyu aralığında optik yansıtması yaklaşık % 97 ve görünür bölgedeki ortalama optik geçirgenliği yaklaşık % 75'dir. Sahip olduğu bu özellikler nedeniyle, AZO/Ag/AZO kaplama enerji-verimli binaların camlarında kullanılabilir.
CERN large hadron collider compact muon solenoid hadronic calorimeter upgrade works
The Large Hadron Collider (LHC) and its detectors have become the most discussed scientific device around the world with its discoveries. Starting from 2000s, LHC project became real in March 2010, the first successful collision. Just in 2 years, LHC discovered Higgs boson on July 4, 2012. LHC houses 4 big experiments, Compact Muon Solenoid (CMS), A Toroidal Large Hadron Collider ApparatuS (ATLAS), A Large Ion Collider Experiment (ALICE) and Large Hadron Collider beauty (LHCb). CMS is the heaviest and one of general purpose detector of LHC. CMS has hadronic calorimeter (HCAL) to measure and identify hadrons. HCAL consists of hadronic barrel (HB), hadronic outer (HO), hadronic endcap (HE) and hadronic forward (HF) calorimeters. Material of these detectors will be damaged due to increasing integrated radiation for high luminosity of LHC. For that reason, material of subsystems needs to be replaced by stronger ones. For example, hadronic endcap scintillators will be highly damaged by luminosity of High Luminosity Large Hadron Collider (HL-LHC), new phase of LHC starting from 2023. For replacement, 4 different institutes have proposed new scintillators. Irradiation test of these scintillators were done with a dark box, silicon photomultiplier (SiPM) and a readout system in 2015. Measurements were taken in March, June, September and December 2015. In order to understand how much these scintillators will be damaged by radiation, installation box of scintillators were irradiated by installing few cm close to the beam pipe inside the CMS detector –to Centauro And Strange Object Research (CASTOR) table. After taking derivatives of measurement data under different conditions, breakdown voltage (BDV) of SiPMs were calculated in ROOT software package. Adding a specific voltage to BDV, currents were compared to observe radiation damage in scintillators. Due to systematical and statistical errors in previous measurements setup new measurements will be taken via HCAL data acquisition (DAQ) system for reliable results. Work are still continue as of April 2016. In long shutdown 1 (LS1) photomultiplier tubes (PMT) of HF calorimeters were replaced by new ones. To calibrate new PMTs, sourcing data were taken with Co-60 radioactive source, and analysis were done in CMSSW. Applying several corrections and conversions, calibration coefficients of individual PMTs were calculated. New source data were taken in 2016 and analysis of new data were scheduled later this year. Alongside these tasks, there are several ongoing tasks such as HF radiation damage monitoring and online software development. HF-fiber radiation damage monitoring involves local radiation damage data in CMMSW and monitor radiation damage in time. Online software includes developing and upgrading new generation readout box manager (ngRBXManager). This software will operate to take data from readout boxes via new generation clock control module (ngCCM).
Electromagnetic form factors of Ξc and Ξ′c in lattice QCD
The Standard Model (SM) is the theory to explain the strong, electromagnetic and weak forces and the interactions among all fundamental particles in nature. In order to understand the dynamics of these fundamental forces, there are a number of methods. One of the most successful theories is the Lattice Quantum Chromodynamics (LQCD). The method uses the Lattice Gauge Theory in the theoretical background. Furthermore, the Lattice Quantum Chromodynamics is not based on any approximate or effective model and it uses computational techniques effectively to make calculations. Lattice Gauge Theory is utilized with improvements in computational techniques and high-technology provides golden opportunities to compute the action of Quantum Chromodynamics (QCD) precisely. Electromagnetic form factors provide significant knowledge for understanding composite structure of baryons. Additionally, charmed baryons are an attractive field to investigate fundamental mechanism behind hadron structure. The charmed baryons are compact particles as compared to the proton. In this work, our aim is to compute the electromagnetic form factors of singly charmed Ξc and Ξ′c baryons from 2+1-flavor simulations of QCD. The bound states of two light (up and strange) and one heavy (charm) quark regime is very significant to obtain baryon structure and properties. We define a ratio to calculate the electromagnetic form factor and magnetic moment. We express our results of the mass spectrum of Ξc and Ξ′c as simulated on 163 × 32 lattices. We make the statistical analysis of data. We calculate magnetic moments of charmed baryons and discuss individual contribution of quarks to baryon structure. The magnetic moments of singly charmed baryons are found to be dominantly determined by the light quark contribution in aligned spin state of the light quarks. The role of the charm quark effects are mainly explicit when spins of the light quarks are anti-aligned. Our results also indicate that the singly charmed baryons have compact structure as compared to proton which consists of only light quarks.
Design and production of benchtop x-ray imaging system
A low cost X-ray imaging device based on BPW-34 Si-PIN photodiode was designed and produced. X-rays were generated from a CEI OX/70-P dental X-ray tube using a custom made ±20 kV power supply. A charge sensitive preamplifier and a shaping amplifier were built for the amplification of small signals produced by photons in the BPW-34 Si-PIN photodiode. A two dimensional position control unit was used for moving the detector in small steps to measure the intensity of X-rays absorbed in the object to be imaged. An Arduino Mega 2560 micro controller and Aessent AES220B FPGA module was used for transferring the image data to a computer via USB. Images of various samples were obtained with acceptable image quality despite of the low cost of the device. Designing a device for fast imaging time was not the main motivation in this thesis. However, having an acceptable image quality together with reduced cost and simple design were the main considerations. Total cost of the imaging device presented in this thesis is under 1000 USD. Filtering applications based on known energy spectrum are helpful tools to obtain images with better quality. For that reason, energy spectra of the CEI OX/70-P tube for different tube voltages were determined. Additionaly, energy spectra of CEI OX/70-P dental tube were determined experimentally and were compared with Geant 4 simulation results. Beside the experimental and simulation comparison studies, energy spectra were taken with BPW-34 Si-PIN photodiode and a commercial spectrometer Amptek X123 to ensure the consistency within the experimental spectra. In these studies, the geometries of BPW-34 Si-PIN photodiode, CEI OX/70-P tube and Amptek X123 detector, provided by the manufacturers, were embedded in Geant 4 simulations. A power supply was necessary to provide high tension between anode and cathode of the tube. It was produced as three stages. The first stage was a Pulse Width Modulator (PWM) circuit with adjustable frequency and duty. PWM was used for generating high frequency signal for feeding up two identical step-up transformers. Two identical step-up transformers were driven by a MOSFET circuitry after the PWM in the second stage. Instead of using a high voltage transformer, driving simple transformers with an optimum frequency PWM signal has provided the high voltage we need. Finally, a well-known Villard-Cascade voltage multiplication topology was used to multiply the initial stepped-up potential to the desired value. The multiplier units are simple circuits made from diodes and capacitors. In this method, an n-stage voltage multiplier unit produce 2n folded output voltage. The multiplier unit was designed to give 10-fold increase in the output voltage. We have also designed a negative 10-stage voltage multiplier unit by simply reversing the polarities of all the multiplier diodes. Instead of running the tube for our measurements with a single supply (+40 kV), it was preferred to generate a symmetrical high voltage (±20 kV) with two independent cascade units. This helps to overcome unwanted discharges and to ease electrical isolation problems. A custom made filament transformer was wounded as an isolation transformer and it was embedded in epoxy-resin to provide electrical. The isolation transformer was used between the mains and the filament power supply running at 2 VAC and 1.5 A current in regular operating conditions. Drifts in the filament current or tube voltage cause X-ray intensity to change and this can degrade the image quality. Most industrial type power supplies used for X-ray tubes are designed with feedback circuitry to stabilize the voltage/current output. However, our design does not include such a feedback control for simplicity. Instead of this, drifts problem was solved by correcting the image when necessary by using the data obtained from an X-ray intensity monitor. Since there were no feedback controls for precise regulation of the filament current and the high voltage of the tube, X-ray intensity was continuously monitored with another BPW-34 based detector designed. In order to investigate the magnitude of X-ray intensity fluctuations which may deteriorate the image quality, we have recorded the intensity of incident X-rays during imaging time. To minimize the image reconstruction artifacts, the object-detector distance was chosen to be smallest possible and single hole aluminum collimator was used to minimize the scattered X-rays from large angles. The image data containing the position information and the count rate were constructed as gray-scale images. Scintillator crystals have an important role in nuclear imaging to convert ionizing radiation to visible or ultraviolet photons. They permit to increase speed of response, the accuracy and the sensitivity of the radiation sensors. The CsI crystals are widely used scintillators in the nuclear detection systems due to its relatively low hygroscopicity, cost and high atomic number. Vertical Bridgman crystal growth technique was studied to produce single CsI scintillator using three temperature zone Crystalox vertical Bridgman Single Crystal Growth System equipment. The system designed includes single Si-PIN photodiode as a detector. When this is the case, it is required to move either the object or the detector through the region of interest. In order to ensure the possibility of working with liquid containing samples, moving the detector within the defined limits was preferred. For that reason, a 2D scanning bench consisting of two linear trays positioned perpendicular was used. The one on top has a load-bearing panel and the detector box was fixed on it. Linear axis trays were moved by two step motors placed on each side of the trays. Since parallel port is the easiest way to communicate with the peripherals, the motor drivers were connected to the parallel port of the computer using a communication board. Mach3 CNC Software package program was used for controlling the software of the X-Y scanning bench. Coding language for Mach3 is special and called as G-code programming language. Loop properties of the G programming language was used in the automatized movements of the motors. Writing the G-code using loop structure reduced the time spent for coding and removed the motor fails. One can adjust the speed of acceleration, step size, start-stop positions with a graphical user interface (GUI). Synchronization between transferring of the data and motor motions should be established for error free data taking. A pilot signal was produced in the motor driver unit when motors were active. This pilot signal was processed to be able to transfer the image data to the computer properly. A delay circuitry was built using NE555 integrated circuit to have an interrupt during the motion of the detector between the scan steps. Thereby, we could track the position of the motors when they were moving. Image data was transferred to computer via an Arduino unit when a single Si-PIN photodiode used as a detector. Combination of hardware units enabled us to obtain X-ray images of various samples with accepted image quality. Depending on the desired resolution, images may take up to several hours even for small sized objects. However, when time is not number one priority, this device can provide a good quality X-ray images at low cost. The time requirement for imaging with only one pixel detector is relatively long. Thus, a multidetector array, which compromises 24 BPW-34 detectors was designed and produced. Imaging with this detector array required using an FPGA to transfer the data from detectors to the computer simultaneously. For test purposes, an FPGA code for four detectors was written and it was tested during real data taking. There are some improvements can be made in the future with the cost of extra labor. One of them is using a detector array to reduce the scanning time. Additionally using scintillators in front of photodiodes will dramatically increase the efficiency. Collimator studies are also worth obtaining scatter free images. These additions in hardware will not change the overall cost dramatically. However, they will shorten the scanning time.
Polimer yapı içerisinde sentezlenen ZnO nanoparçacıklarının spektroskopik ve fiziksel özelliklerinin incelenmesi
Malzemeler nanometre boyutlarına indiğinde, kuantum sınırlama etkisi nedeniyle bulk malzemelerden farklı özellikler göstermektedir. Nano boyutta elde edilen yarı iletken parçacıkların optik ve elektronik davranışlarında da çok önemli değişiklikler meydana gelmektedir. Bu ilginç kuantum doğaları nedeniyle, yarıiletken nanoparçacıklar uzun süredir bilimsel ilgiye sahip olmaktadırlar. Çinko oksit (ZnO), şeffaf elektrotlar, ince film transistörleri, ışık yayan diyotlar (ledler), ince film gaz sensörleri, güneş hücreleri, lüminesans malzeme ve biyolojik floresans etiketleme gibi bir çok alanda umut verici uygulamaları olması nedeniyle, nano ölçekte en çok çalışılan yarıiletken oksitlerden biridir. ZnO nanoyapıların düşük maliyetli olmaları, yarıiletken karaktere sahip olmaları ve diğer yarıiletkenlere göre zehirli olmamaları, antibakteriyel etkinlikleri, kolay hazırlanmaları, floresans özellik göstermeleri ve geniş enerji bant aralıkları gibi özellikleri bulunmaktadır. ZnO nanoparçacığın yaydığı ışığın dalgaboyu, parçacığın boyutu ile ayarlanabilmektedir. Bundan dolayı, sentez sırasında nanoparçacıkların boyutunun kontrolü, farklı floresans özelliklere sahip parçacık elde edebilmek için önemli bir parametre haline gelmektedir. ZnO nanoparçacıklarınının kümeleşme eğiliminini azaltmak, çeşitli özelliklerini iyileştirmek ve kullanım alanını genişletmek için polimer yapılar ile birlikte nanokompozitler üretilmektedir. Genellikle polimer çalışmalarında, nanoparçacıklar polimerden ayrı sentezlenip polimer matrisine gömülmekte ya da polimerler nanoparçacık çözeltisine eklenmektedir. Literatürde yapılan çalışmalardan farklı olarak bu çalışmamızda, ZnO nanoparçacıkları polimerik jel içerisinde sentezlenmiştir. Bu yol ile hem sentezlenen ZnO boyutu istenilen aralıkta tutulabilmekte hem de nanokompozitlere bazı yeni özellikler kazandırılmaktadır. Çalışmamızın temel amacı ZnO nanoparçacıklarının polimerik jel içerisinde sentezlenmesi ve jelin morfolojisini değiştirerek boyut kontrolünün ve dağılımının ayarlanabilmesidir. Çalışmamızda, insan vücut sıcaklığına yakın sıcaklıkta faz geçişi ile bilinen ve kullanılan sıcaklığa duyarlı polimerik yapı olan Poli(N-izopropilakrilamid) (PNIPAm) polimer malzeme olarak kullanılmıştır. İlk olarak ZnO nanoparçacıkları çözelti içerisinde sentezlenmiş ve optik özellikleri incelenmiştir. ZnO'ya ait emisyon piklerinin hangilerinin derin-tuzaklanmış (yüzeylerdeki kusurlarda olan uyarılmalar) geçişlerden hangilerinin bantlar arası geçişlerden (valans ve iletkenlik bandları arasındaki geçişler) kaynaklandığı belirlenmiştir. Ayrıca parçacıkların kaplanmasının ve sentez sıcaklığı değişiminin boyuta ve optik özelliklere etkisi TEM, SEM, XRD analizi ve floresans, absorbans ölçümleri yapılarak incelenmiştir. Jel içerisinde sentez deneylerine ön bilgi vermesi için ZnO nanoparçacıkları lineer (çapraz bağlayıcı içermeyen ağ yapısına sahip olmayan) polimer içerisinde sentezlenmiştir ve optik özellikleri incelenmiştir. Elde edilen spektrumlarda monomer (NIPA) molaritesi arttıkça ZnO'nun yeşil emisyon pikinin maksimumunun kısa dalga boyuna doğru kaydığı görülmüştür. (NIPA molaritesi arttıkça yeşil emisyon maksimumu 521 nm'den 510 nm'ye değişmiştir.) Yapılan deneyler jel içerisinde sentez yapılabileceği ve jelin iç morfolojisine bağlı olarak parçacıkların spektrumlarının değiştirilebileceği konusunda bize bilgi vermiştir. Çalışmanın sonraki bölümlerinde ZnO nanoparçacıkları silindirik PNIPAm jel matrisi içerisinde başarıyla sentezlenmiştir. Silindirik jel boyunca konumun fonksiyonu olarak parçacık boyut değişimi elde edilmiştir ve jelin şişip büzülmesi ile spektroskopik davranışların ayarlanabileceği gösterilmiştir. Bu yolla, ZnO'nun görünür ışık emisyonunun tamamen sönümlendirilebilir ya da şişirme derecesi ve çözücü tipi değiştirilerek güçlendirilebilebir olduğu görülmüştür. Bu sentez yönteminin avantajı, aynı sentezde farklı dağılımlar elde edilmesidir. Ayrıca kuru halde sadece UV, şişmiş halde ise yeşil emisyona da sahip olması farklı kullanım alanlarına göre ayarlanabilmesi açısından önemlidir. Literatürde yapılan bazı çalışmalarda ZnO'nun UV emisyonu kullanılırken diğerlerinde ise yeşil emisyon ön plana çıkmaktadır. Ayrıca jeldeki gözenekli yapıya bağlı olarak ZnO nanoparçacıklarının boyutu değiştirilebilmektedir. Farklı morfolojideki PNIPAm jellerinin iç yapısı incelendiğinde çapraz bağlayıcı konsantrasyonu arttıkça jelin gözeneklerinin daha dar ve daha homojen olduğu görülmüştür. Çapraz bağlayıcı konsantrasyonu değiştirilerek jelin morfolojisi (iç yapıdaki gözenek yapısı) değiştirilmiş ve ZnO nanoparçacıkları bu gözeneklerde sentezlenmiştir. Çapraz bağlayıcı miktarı arttıkça nanoparçacıkların boyutunun azaldığı ve buna bağlı olarak da floresans spektrumlarının değiştiği görülmüştür. Çalışmamızda önerdiğimiz sentez yöntemlerinin nanoparçacıkların boyut kontrolü yöntemi olarak umut verici olduğunu düşünmekteyiz. Son olarak, ZnO nanoparçacıklarının PNIPAm jelinin özelliklerine etkisini görmek için elde edilen farklı morfolojideki ZnO/PNIPAm nanokompozit yapılarının optik, mekanik ve termal özellikleri ayrıntılı olarak incelenmiştir. Saf ve kompozit örneklerin termal özellikleri incelendiğinde, TGA eğrilerinden kompozit örneklerin bozunmaya başlama sıcaklıklarının saf örneklere göre daha düşük olduğu görülmüştür. Mekanik ölçüm değerlerini incelediğimizde ise çapraz bağlayıcı konsantrasyonu her iki örnek grubunda da (saf ve kompozit jel örnekleri) basınç dayanımını önemli derecede etkilemiştir. Çapraz bağlayıcı konsantrasyonu azaldıkça saf jellerde basınç dayanımı 78 kPa'dan 354 kPa'ya, kompozit jellerde ise 343 kPa'dan 517 kPa'ya artmıştır. Kompozit jellerin saf jellere göre daha yüksek basınç dayanımına sahip oldukları görülmüştür. Çapraz bağlayıcı konsantrasyonu arttıkça saf jellerde elastik modülü değeri 36.5 kPa'dan 212 kPa'ya, kompozit jellerde ise 97.5 kPa'dan 314 kPa'ya artmıştır. Jel içerisinde sentezlenen ZnO nanoparçacıklarının PNIPAm jellerinin mekanik özelliklerini iyileştirdiği sonucuna varılmıştır.
Electric and magneto-transport properties of magnetic and superconductive iron pnictide and skutterudite compounds
Superconductivity has gained its popularity after the high Tc materials have been explored. Cuprates (copper-oxide systems) and Hg based 1223 systems still have research interest allowing to examine new chemical compounds for high Tc superconductors (HTS). Unconventional materials such as Fe-based pnictides (group V-B elements in 122 systems) are frontier compounds in which magnetism and superconductivity can be observed together in these materials, presenting them as an option for high Tc superconductors. Iron-arsenide (Fe-As) and copper-oxide (Cu-O) layers in the structure of a crystal are responsible for the superconductivity phenomenon observed in these systems. Fe-As system has similar properties with Cu-O like having d electrons, layered structures and antiferromagnetic (AFM) spin ordering and they are still earning interest. In addition to this, iron has a magnetic moment which plays a key role in superconductivity-magnetism colleration. Up to now, two physical problem in our study are the superconducting phase transition temperature Tc and magnetic behavior of superconducting materials. Lattice changes, symmetry breaking in the unit cell, applying pressure are some of reasons that shift Tc up or down. For the magnetic behavior of superconductive samples, establishment of a new magnetic ordering is key parameter under the Tc. Magnetic changes are said to be affect superconductivity. The exclusion of magnetic field lines by Meissner effect is a clear evidence for superconductive mechanism. Our study here is focused on iron pnictide compounds on the basis of these two physical problem. The most popular iron pnictide systems are Fe-As based ones. The material BaFe2As2 has a tetragonal structure and it goes a structural phase transition from tetragonal I4/mmm to orthorhombic Fmmm lattice. Same behaviors are found in AFe2As2 (A:Ba, Sr, Ca, etc.) systems at low temperatures like in cuprates. This kind of phase transition is named as spin density wave (SDW) transition and it is valid for both cuprates and iron-pnictides. A chemical change in composition with a dopant or applying pressure results magnetic transition in Fe-As compounds and thereby superconductivity emerges. By doping electron or hole to a AFe2As2 system like BaFe2-xPtxAs2 , superconductivity can be observed. Since the change in chemical composition may effect the Tc, Lanthanum is doped to the BaFe2-xPtxAs2 system. And a new serie of Ba1-xLaxFe1.9Pt0.1As2 polycrystalline samples are successfully synthesized by a solid-state reaction method. The synthesis of Pt and La doped compounds was physically remarkable since some of them are synthesized for the first time. Data obtained from those samples are investigated in detail by Rietveld refinement. Our target to produce "single phase" polycrystalline samples is achieved successfully. Unit cell parameters and symmetry group of samples are determined in agreement with the literature. Structural analyses of samples are made by X-Ray diffraction after the chemical synthesis part. Results are analyzed by FullProf software. Profile matching are done for whole samples and structural parameters are determined. Some samples are found single phase in which we published in the articles during our study. Resistivity measurements are performed with the liquid nitrogen followed by liquid helium by the help of a hand made glass cryostat. It is seen that the temperature dependence of the resistivity for the parent sample, BaFe2As2 exhibits the same behavior including a very close match to reported values given in the literature. The structural phase transitions from tetragonal I4/mmm to orthorhombic Fmmm lattice in BaFe2As2 and BaFe1.9Pt0.1As2 samples are observed. Temperature dependent transition is compatible with the corresponding phase changes observed at XRD measurement, which is known to be tetragonal at room temperature. Superconductive phase transition temperature, Tc for the samples in different Pt doping levels is investigated in the literature. It is found that Pt doping is effective on the change of Tc at lower doping rates like x = 0.2. x=0 sample is the parent sample (BaFe2As2) in which it is not superconductive but the BaFe1.9Pt0.1As2 sample has the highest value in Pt doped group for phase transition temperature, Tc. In addition to the literature, we revealed that superconductivity can be observed even in x=0.3 doping rates in such materials. Lanthanum doped samples are successfully synthesized in addition to the Pt doped ones. And resistivity measurements are showed that superconductivity still can be observed in such tetragonal I4/mmm systems. Resistivity of these samples are showed a clear evidence for superconductivity that our results approve. The magnetic measurements of materials are done by measuring zero field cooling (ZFC) and field cooling (FC) curves. Critical temperature, critical current density, coherence length (also known as Ginzburg-Landau parameter), volume magnetization and magnetic susceptibility values are obtained from the analysis. Magnetization behavior of samples are observed as a function of temperature and phase transition temperatures are determined. The critical current density, which is remarkable sign for how much charge a superconductor can carry, is estimated by models given in the literature. Coherence length is calculated from the M-H curves (from the Meissner effect observed in these samples). Results show that samples based on a tetragonal structure are convenient to be a host material for the superconductive behavior. This means the doping of rare-earth ions to those samples provide materials that have characteristic properties like showing zero resistivity and the exclusion of magnetic field lines. In our study, platinum and lanthanum are doped to our host material, BaFe2As2; and new sample sets are prepared. It is seen that ZFC-FC curves are separated in the phase transition temperature, Tc, showing superconductive behavior compatible with the resistivity measurements. Meissner effect is observed in both platinum and lanthanum doped samples. Critical current densities are calculated from the magnetic measurements and phase transition temperatures are determined. The samples are in superconducting regime where their temperatures are lower than the Tc. M versus H curves are measured in several temperatures in this regime below the phase transition temperature. Analysis of the results helped us to calculate coherence length z for the samples by obtaining Hc readings at different measurement temperatures. From the M-H curves of samples measured below the Tc, lines are extrapolated to T=0 K and coherence lengths are found in nm range. By transforming magnetization from emu/g to volume magnetization, susceptibility for the samples are obtained in terms of magnetization data. The termination of ZFC and FC curves in to close values to -1 in y axis, shows that samples are mostly diamagnetic with a high volume fraction. Samples are mostly presented superconductivity in general. Phase transition temperatures found from ZFC-FC curves are compatible with the resistivity data. La doped samples are showed a clear evidence for superconductivity that both resistivity and magnetic results approve. Thin films of BaFe2As2 sample is prepared and the amorphous structure is proved by the XRD measurement. Resistivity of sample is measured between 4.2-300K at liquid He. A phase transition at Tc = 6.7K is seen clearly with reproducible experiments which is very similar to a superconductive phase transition. We observe superconductivity for the first time in an amorphous thin film. This result is interesting because current macroscopic theory of superconductivity is based on Cooper pairing mechanism. The drop of resistivity down to zero obeys filamentary superconductivity that is seen in literature in principle. The difference in our study is that we create a disorder in material and it is amorphous. This process is realized in a simple flash evaporation system under vacuum. This is important because same kind of samples are produced in molecular beam epitaxy (MBE) or similar systems that we are not able to. Some studies are reported that both in bulk and thin film samples, showing that it is possible to apply pressure to the system and create disorder. This method is a way in order to trigger the superconductivity in such systems. For the first time, we observe the superconductivity in an amorphous thin film above the liquid He temperature, at ambient conditions. Magnetic characterization of this sample still continues and results will be presented in an appropriate publisher. In case of any failure in preparing superconducting samples, antimony doped compounds are prepared. BaFe4Sb12 sample is prepared first. This sample is known as skutterudite compound in literature and it is thermoelectrically efficient. Since the synthesis was successful, the thermoelectric and magnetic properties of Pt substituted BaFe4 xPtxSb12 (x = 0, 0.1, 0.2) compounds were investigated in this part of study. Thermoelectric (TE) materials are available to capture a part of wasted energy that is rejected to atmosphere and convert it into the useful electrical power. The efficiency of a TE generator is strongly depending on the dimensionless figure of merit ZT, defined as ZT = S2sT/k where S, s and k are the Seebeck coefficient, electrical conductivity, total thermal conductivity (k = ke + kL where ke is the electronic contribution and kL the lattice contribution) and T stands for the absolute temperature. Efficient thermoelectric materials are required to have high electrical conductivity, high Seebeck coefficient and lower thermal conductivity. Filled skutterudites fulfill these requirements. In the past decade years, experimental and theoretical tremendous effort have been conducted on skutterudites compounds in order to optimize their TE and magnetic properties for enhancing ZT value further and characterize low temperature behavior. The filled skutterudites with chemical formula RT4M12 where R = alkaline earth and rare earth metal, T = Fe, Ru, and Os and M = P, As, and Sb have been studied extensively due to their both high TE performance and exotic magnetic properties. Even though, there are many reports in literature on thermoelectric and magnetic properties of RT4M12 family skutterudite compounds. There is still lack of understanding about correlation between magnetic and thermoelectric phenomena for these compounds. In this work, we aim for contribute to understanding of relation between two phenomenon by characterization low temperature magnetic and thermoelectric properties BaFe4-xPtxSb12 (x = 0, 0.1, 0.2) compounds. X-Ray diffraction, resistivity, magnetic measurements, Seebeck coefficient and thermal conductivity of samples are measured. Temperature depending resistivity shows that all samples show semi metallic behavior in the temperature range of 4.2 K to 300 K. Increases in resistivity with Pt content is interpreted as existing of different scattering mechanisms such as spin fluctuation and Kondo impurity in these compounds or decreasing hole concentration. Kondo minimum are confirmed by temperature dependence of logarithmic resistivity analysis at 2-50 K which might be due to local deformation in crystal structure as a result of spin fluctuation mechanism. Local minimum and maximum in Seebeck coefficient observed might be due to paramagnon drag or spin fluctuation effect in materials. Magnetic susceptibility for the compounds x = 0.1 and x = 0.2 show that there are two successive transition, paramagnetic to magnetic state at Tc = 48 K and short range magnetic to long range magnetic ordering at lower temperatures, however there is only one transition from paramagnetic to long range ordering transition in Pt free compound. The lattice part of thermal conductivity versus temperature plot shows that the major part of total thermal conductivity is dominated by lattice contribution. Local maximum & minimum in Seebeck coefficient versus temperature plot, Kondo minimum observed in logarithmic resistivity show that there is a close relation between magnetic and thermoelectric properties due to spin fluctuation effect in Pt substituted BaFe4-xPtxSb12 (x = 0, 0.1, 0.2) compounds.
Hidrojellerde şişme işleminin floresans spektrometre ile incelenmesi ve bilgisayar modellemesi
İlk olarak amacımız, hidrojellerdeki şişme işlemi ilk kez Zaman Ayrımlı Floresans Teknik (FTRF) kullanarak incelemektir. Bir diğer hedefimiz, pireni hidrofobik yapısından çıkarıp hidrofilik forma döndürerek, saf suda hidrojel şişme sürecini FTRF ile gözlemlemektir. Bu teknikte piren ajan molekül (aromatik molekül) olarak kullanıldı. Bir diğer amaç, kolektif difüzyon sabiti Dc'nin, hem gravimetrik hem de floresans deneylerle elde edilmesidir. Son olarak bu verilere dayanarak, Dc 'nin hesabını, sadece kullandığımız 5 farklı değer için değil, aralığındaki tüm değerler için hesaplayacak bir program geliştirmektir. Ayrıca bu programın içeriğinde, hazırladığımız jelin konsantrasyonları baz alınacak şekilde çalışan bir malzeme miktarı hesaplayıcı olmasıydı. Floresans ölçümlerimizde Photon Technology International marka TM-2000 model cihazı kullandık. Şişme deneylerinde, piren molekülleri 345nm'de uyarıldı ve 395nm'de bozunum eğrileri elde edildi. Sentezlemiş olduğumuz hidrojellerde beş farklı çapraz bağlayıcı (BIS) miktarı kullanarak, şişmenin farklı BIS değerlerde nasıl gerçekleştiğini izledik ve beklentimizin olduğu yönde gerçekleşerek, BIS miktarının artmasıyla kolektif difüzyon katsayısının Dc 'nin azaldığı sonucuna ulaştık. Çapraz bağlayıcı miktarının artması ortamda oluşan çapraz bağlanmaların daha sıkı ve sık olmasına yol açtığından, çözücünün bu bağlar ortamına nüfuz edişini zorlaştırmaktadır. Ayrıca gravimetrik olarak da şişmeyi incelediğimizde gördük ki aynı şekilde artan BIS miktarlarda Dc değerleri azalma gösteriyor. Son olarak da bu incelemenin yanı sıra deneyler sonunda elde ettiğimiz sayısal bulgular ışığında, kullanıcıdan alınan BIS ve çözücü miktarını (PBS) kullanarak Dc 'yi hesaplayan bir program geliştirdik. Dc hesabına ek olarak kendi hazırlamış olduğumuz jel için kullandığımız kimyasal malzeme konstrasyonlarını baz alarak, yine kullanıcı tarafından girilen BIS ve PBS değerleri ışığında, hidrojeli sentezlemek için gerekli olan diğer üç malzeme olan başlatıcı (APS), hızlandırıcı (TEMED) ve aromatik molekül olan piren (Pyr) 'in gerekli olan miktarları program tarafından hesaplanmaktadır.
Kesikli wigner fonksiyonu
In the final chapter, through Weyl ordering, continuous Wigner function is derived. Then, using proper assignments, discrete counterpart in discrete phase space is introduced. First computing for single qubit and a pair of qubits, smallest contextual bit qutrit's discrete Wigner function is calculated both for a specific and a general initial condition. For a specific state, it has been shown thatWigner function can indeed have negative values as a quasi-probability distribution. Negative probabilities and their link to contextuality is discussed. As a result, if a qutrit's 6 tables can have at least one negative value for the general initial condition, it will mean that contextuality and negative probabilities are directly linked.
Sorting of biological cells in a microfluidic channel using holographic optical tweezers combined with raman spectroscopy
Investigation of single cells is crucial, since the measurement from population gives an average value that does not necessarily represent every individual in the population. Besides, sorting and sometimes counting the desired kind of cell is a measure of how the concentration of that cell. These types of micro-scale measurements are sometimes necessary, for example, to monitor the cell cycle, cell-signaling processes. Serving to these purposes, first a holographic optical tweezers (HOT) setup was constructed. This setup was built by improving the current optical tweezers setup in the Laser Spectroscopy Laboratory in Istanbul Technical University. A brand new Holoeye Spatial Light Modulator (SLM) was installed in the system after it was calibrated using an interferometric setup. The holograms were calculated using a Gratings and Lenses algorithm written in MATLAB and implemented by the homemade GUI that manages all the tasks needed for trapping and spectroscopy. The test particles to characterize the HOT setup were polystyrene (PS) particles. An array of four trapped PS particles was manipulated to the Raman spectrum measurement region by the software. The software communicates with the spectrometer and obtains multi-track spectra from the array that gives individual Raman spectra of each particle. These spectra identified by the software using the correlation coefficient of this measurement with the dataset that has already been prepared using PS particles and yeast cells. The test Raman measurements of biological cells using yeast cells and E.coli cells were made to investigate the signal level in low exposure times. The measurement showed that, our system would not respond enough signal to classify particles when the sample is E.coli and the exposure time is one second. However, the yeast cells responded better in short exposure time. Considering these, the sorting test experiments were made using yeast cells and PS particles. In a mixed solution of PS particles and yeast cells, an array of four particles whose members are randomly chosen was moved to the measurement region. According to the measurement and the following classification, the particles are targeted to the previously defined positions in the measurement cell. In these experiments, classifications were made with success. A study to determine the embryo quality by Raman spectroscopy was made in collaboration with Istanbul University Medical School. In this study, it was aimed to find an objective method to assess embryo viability. The preliminary results showed that the sensitivity and specificity of these measurements are %93 and %77, respectively. A Mann-Whitney U test was applied on the band areas and all band area ratios obtained by band component analysis. The most significant one was found to be the band area ratio of 903/942 cm-1. Comparing the measurements of amino acids samples, it was determined that glutamine, glycine, proline, and valine has the most intense bands in the region that includes these significant bands. Among these, glutamine and glycine are the amino acids that contribute to embryo development most, according to the literature.
Yüksek enerjili, şekillendirilmiş lazer hüzmeleri ile saydam malzeme işleme ve karakterizasyonu
Femtosaniye (fs) darbeli lazerler etkin oldukları son derece kısa zaman süreçleri sayesinde benzersiz fiziksel özellik ve uygulama potansiyellerine sahiptir. Özellikle lazer-madde etkileşimi ve malzeme işleme alanında fs darbeli lazerler yeni bir çığır açmışlardır. Bu tez kapsamında fs lazer hüzmelerinin uzamsal ve zamansal olarak şekillendirilmesi, karakteristikleri ve saydam malzemeler ile olan etkileşimlerinin yanısıra mikroakışkan uygulamalarındaki kullanımları yer almaktadır. Tez kapsamında gerçekleştirdiğimiz çalışmalarda öncelikle Bessel ve Airy hüzmelerinin kuramsal incelemesini gerçekleştirdik. Ardından bu hüzmeleri deneysel olarak ürettik ve şiddet profillerini, ilerleme özelliklerini inceledik. Daha sonra fs lazer kullanarak bu hüzmelerin saydam malzemeler ile olan etkileşimlerini ortaya koyduk. Fs lazerlerin en çok kullanıldığı bir diğer uygulama alanı mikroakışkanlardır. Çalışmalarımızda fs lazer ile süperhidrofobik yüzey üzerinde ve aerojel kitle içerisinde mikroakışkan sistem üretimini, PDMS çip içerisinde damla temelli mikroakışkan sistem üretimini gerçekleştirdik. İlk olarak süperhidrofobik yüzey üzerinde hidrofilik mikrokanallar oluşturduk. Bu mikrokanallar üzerinde sıvı filament oluşturduk ve dalga kılavuzu özelliklerini inceledik. Ardından eşsiz özelliklere sahip hidrofobik silika aerojel içerisinde üç boyutlu mikrokanalı malzemeye zarar vermeden oluşturmayı başardık. Bu kanalın optoakışkan özelliklerini inceledik. Buna ek olarak PDMS çip içerisinde damla temelli sistemlerin fs lazer ile üretilebileceğini gösterdik. Zamansal olarak şekillendirilmiş lazer hüzmelerinin malzeme ışık etkileşiminde yüksek polarizasyon bağımlılığı gibi oldukça ilginç özellikleri mevcuttur. Bu özellikler uzay zaman bağlantıları (UZB) olarak adlandırılan etkiler kapsamında açıklanabilir. Bu çalışmada UZB etkilerini kontrollü olarak değiştirerek saydam malzeme işleme üzerindeki etkilerini ayrıntılı olarak inceledik ve fiziksel detaylarını ortaya koyduk. Sonuç olarak bu tez kapsamında gerçekleştirilen çalışmalarda ultrahızlı lazer- saydam malzeme etkileşiminin anlaşılmasının bilimsel değeri oldukça yüksektir.
Tunnelling induced photon emission from surface/interface systems of graphene on copper
Imaging with the smallest order of magnitude has always been an essential topic for researchers working in various areas. Especially with the invent of Nobel Prize winner scanning probe microscopy (SPM), investigations in nanoscopic scales have been performed in terms of topographic, electronic, magnetic and optical properties. In this thesis, we have focused on electronic and optical properties of surfaces using photon scanning tunnelling microscopy (pSTM). Light emission from a planar junctions such as Metal-Insulator-Metal systems attracted noticeable attention. These studies have indicated that surface plasmons are the dominant mechanism of this light emission. Surface plasmons has been defined as collective oscillations delocalised electrons which propagate electromagnetic waves along the conducting surfaces. There might occur different modes of surface plasmons e.g. surface plasmon polariton (SPP) and localised surface plasmon (LSP). SPP defines surface plasmons which are propagating electromagnetic waves along the surface. LSPs are the charge oscillations in the gap plasmons. However, it was also reported that SPPs might be arise by LSPs as well. With the invent of scanning tunnelling microscopy (STM), photon emission from tunnel junction was applied in nanoscopic scales as well. Photon emission investigations have been performed on surfaces such as noble metals, molecule adsorbed metals, thin film combinations etc.with pSTM systems. Although some allotropes of carbon have been investigated in pSTM studies, graphene has not been stated yet in these investigations. In our work, we have focused on photon emission characteristics of chemical vapour deposition (CVD) grown graphene/copper structure. Graphene is a promising two dimensional material having honeycomb lattice. Several studies have revealed its extraordinary electronic, mechanical and optical properties. On the other hand, graphene can protect where it covers like a shield against exposing to corrosion. In our study performed under ambient conditions, graphene protects copper substrate from oxidation. Certainly the electronic properties of copper has be considered in this investigation. In this work, photon emission from metal-tunnel junction-graphene/metal system under ambient conditions was first reported. It was clearly seen that crystal orientation of copper facets has a dominant role on this tunnelling induced luminescence from Graphene/Cu sample. Based on measurements, it was determined that the occurrence of free electron surface state of Cu(111) surfaces are decisive in photon emission.
Gamma ray spectra analysis for pulsed fast thermal neutron activation (PFTNA) of bulk coal samples
In this study it is aimed to make a real time analysis of coal samples. The coal analysis is conducted in terms of its calorific value, sulphur content, ash and amount of moisture. Coal materials are classified for better combustion and minimum detrimental effects to environment. These beneficial features of coal samples are determined by burning the material before they are classified. Nuclear techniques conduct such determinations in non-destructive ways. Therefore, these methods are important in coal industry. The main principle of this array of experiments is based on the interaction of neutrons with coal material. Coal materials exposed to neutrons are radio actively excited and disintegrate by emitting gamma rays. These gamma rays have energy values which are the fingerprint of the elements presenting in coal. The elements are identified thanks to their certain gamma ray energy values. For the coal analyzing, Pulsed Fast Thermal Neutron Activation Analysis (PFTNAA) is utilized. This technique gives precise result even in a short period of time. Coal material interacts with neutrons and there are neutron inelastic scattering and thermal neutron capture processes. One of these kind of interaction branches are dominated for some of the elements. PFTNAA method also gives more precise results and information for some critical elements such as carbon and oxygen. There are other kinds of neutron sources used for neutron activation process, however these neutron sources such as Cf252 are not sufficient for identifying some certain elements. Carbon has specific energy value at 4.44MeV and this certain energy value is identified via fast neutron interaction mechanism. Neutron generator emits fast neutrons with 14 MeV energy and therefore it is detected carbon elements in material if they exist. In PFTNAA technique it is obtained two separate spectra. In these spectra some elements belong to fast and some of them belong to thermal neutron induced gamma spectra. They are identified via thermal and fast neutron interaction mechanisms. Therefore, it is nedded to separate thermal and fast neutron induced gamma ray spectra. For this purpose, collected gamma ray data is in the raw form. List mode data acquisition system allows for the data collection when the neutron generator in ON and OFF state. When the neutron generator is ON, resulted gamma rays belong to the fast neutron induced spectrum, when the neutron generator in OFF the neutrons are thermalized through the material and obtained spectrum is thermal neutron induced gamma ray. In the experiment, BGO detector gate port is directly connected to the neutron generator. In this way, BGO detector is triggered according to the ON/OFF mode of neutron generator. In order to allow fast neutrons to be thermalized, it is needed a certain duration to be waited without neutron emission. In this period of time neutrons are thermalized and they lose their energy. Operation time and duty cycle are adjusted via neutron generator interface. Voltage and current values are also set with the aid of interface control of neutron generator. PFTNAA technique is also useful in terms of radiation concern. The radiation only produced when the neutron generator is ON. Additionally, during experiment it is used WiFi router so as to study far away from the experimental setup therefore detrimental effects of the radiation. By the aid of remote desktop connection, both BGO detector and neutron generator are controlled confidentally. After obtaining the data colledcted by BGO detector, they are classified as two separate spectra. In order to obtain these spectra, it is written a C++ decoding code reading 32-word data coming from each of gamma ray entering detector. Raw data is analysed according to bitwise operators and decoding instruction of digiBASE-E module. Each bit carries its information about peak data or time of gamma ray photon striking the detector. The instruction manuel says that digiBASE-E module is active when 32-bit word first bit is 1 and it is at its OFF state when the first bit is 0. After decoding the list mode file the gamma ray photons are converted from histogram to a spectrum data. Each event corresponds to the same amplitude value are collected and stored in a channel where they belong to. In this way spectrum data is obtained. After obtaining the separate spectra, elements in coal material are identified clearly. The peaks appear individually without overlapping as in the total gamma ray spectra. The most dominant cross section values for the energy of elements are recognized in the apperant peaks in the spectra. By separating fast and thermal neutron induced gamma ray spectra element libraries are created. This database gives the information about the behavior of elements in the energy versus amplitude domain. This data store is used for a calibration process and determination of elemental content in the coal sample. This element library can be used for different coal samples but similar weights. By using library least square method element concentration of coal sample can be found easily. After data acquisition system is completed, offline analyzing methods are used for identifying the elements in coal and calculating their concentrations. There are various kinds of methods used in determination of element content. In this work it is conducted some experimental studies including both synthetic and real coal materials. There are two types of techniques are adopted for creating element library. They are; experimental studies and semi – experimental studies. These hybrid works are done with some mathematical formulation sets as well. Experimental studies can be grouped as synthetic coal sample experiments and real coal sample experiment arrays as stated. The synthetic coal sample concentration is known and therefore the system can be calibrated according to known values. Afterwards, a linear set of equations are created by using calibration coefficients in order to obtain unknown coal sample contents. The element library is found for the purpose of element concentration. This data base is found by different kinds of methods. Firstly, it is used least square method by taking inverse of a matrix obtained from a coal sample that has a known concentration. Obtained matrix includes the information for element library for coal samples with similar weights and type. In order to use this element library for another coal sample, working conditions and neutron emission durations should be the same as the experiment conducted for finding element library. Real coal samples are used for the identification and determination of some critical elements appearing in the bulk coal sample. It is tested that obtained element library works well or not by using real coal sampels. Element library data set can be found by using both experimental data and some mathematical algorithms as well. Obtained gamma ray spectra includes background information and element energy peaks are located just over this background data. These energy peaks are specific for each element and it is known their peak distribution shapes. By using these information, special Gaussian peaks are created correspond to certain energy values for the elements in coal sample. These peaks are summed with background data calculated by the aid of ROOT Background algorithm. Calculated background data gets the source data as gamma ray spectrum for real coal sample. After obtaining library set for each element, they are fitted to a real coal sample gamma ray spectrum in order to check their consistency to the real data. Both matrix inversion operation and background calculation algorithm used as fundamental techniques for elemental responses are fitted well with experimental gamma ray spectrum. Deconvolution process is other part of the offline analysis of this study. BGO detector cannot resolve accurately the energy peaks of elements. There are some multiplets appearing in the spectrum. Gamma ray – material interaction mechanisms coming from the environment interfere with fundamental nuclear reactions and then certain energy peaks cannot be identified easily. At this stage ROOT Deconvolution algorithm is used so as to separate multiplets. This mathematical formulation takes gamma ray spectrum as a source data for input and a response function for the relevant element as a second input. The result gives a spectrum for individual elements in energy – amplitude scale. They can be treated also as responses for elements. In this experimental study, it is conducted a non – destructive testing of coal material. Some critical element contents are determined in the aim of reaching calorific value, moisture, ash and sulphur concentration. These parameters have crucial importance in coal industry in terms of classification of coal. This procedure is performed by burning of coal. Our study helps to find contents of coal non – destructively and in a more accurate way. All of these experimental and numerical efforts are spent for this purpose.
Sıvı kristal ikili karışımlarında Halperin-Lubensky-Ma ölçeklenme fonksiyonunun çift kırıcılık ölçümleri ile test edilmesi
Sıvı kristal hali maddenin ara hallerinden biridir. Sıvılar izotropiktir yani her yönde aynı özellikleri gösterir. Kristal katılarsa anizotropiktir, birçok fiziksel özelliği yöne göre farklıdır. Sıvı kristal fazında ise birçok fiziksel görünüm olarak sıvıya benzeseler de, molekülleri aniztropik özellikler gösterecek şekilde düzenlidir. Sıvı kristaller iki çeşittir, birincisi liyotropik sıvı kristaller, diğeri ise termotropik sıvı kristallerdir. Liyotropik sıvı kristaller ara fazlarını çözücü konsantrasyonuna bağlı olarak gösterirler. Termotropik sıvı kristaller ise adından da anlaşılacağı üzere sıcaklığa bağlı olarak ara fazlar gösterirler. Bilimsel çalışmalarda termotropik sıvı kristaller en çok kullanılanlardır. Termotropik sıvı kristal moleküllerin konumsal yönelimsel düzenine göre farklı gruplara ayrılırlar. Temel olarak üç ana ara fazı bulunmaktadır; nematik, smektik ve kolesterik. Nematik sıvı kristaller uzun erimli yönelimsel düzene sahiptirler ve tercihli bir n ̂ (direktör) vektörü yönünde yönelirler. Smektik sıvı kristaller ise hem konumsal hem yönelimsel düzene sahiptirler ve katmanlı yapılarıyla karakterize edilirler. Tabaklar arası ve tabakanın içindeki korelasyona bağlı olarak smektiklerin farklı türleri vardır, keşfedildikleriyle sırayla alfabetik olarak (Smektik A, B, C…) kodlanmışlardır. Smektik A (SmA) fazındaki moleküller katmanlarda birbirine paralel olarak yönelmişlerdir, bu yönelim direktör yönündedir. Kolesterik sıvı kristaller kiral nematik sıvı kristallerdir, yani nematiklerden tek farklı moleküller sarmal şeklinde katmanlar halinde yönelmiştir. Faz geçişi maddenin dışarıdan bir etkiyle (sıcaklık ve basınç) bulunduğu fazdan başka bir faza geçmesidir. Faz geçişinde iki fazın birbirinden ayırt edilemediği noktaya "kritik nokta" buradaki sıcaklık ise "kritik sıcaklık" olarak adlandırılır ve T_C ile gösterilir. Eğer bir faz geçişinde gizli ısı ortaya çıkıyor ve entropinin süreksiz olarak değişiyorsa, bu birinci dereceden faz geçişi, entropi sürekli ve gizli ısı gerekmiyorsa ikinci dereceden faz geçişi olarak adlandırılır. Sıvı kristaller birçok ara faza sahiptir. Bu nedenle faz geçişleri konusunda birçok model ve teorilerin geçerliliği sıvı kristaller kullanılarak gösterilebilir. Bu çalışmada sıvı kristallerin bir anizotropik özelliği olan çift kırıcılık kullanılarak Nematik – Smektik A (N-SmA) faz geçişi civarında Halperin-Lubensky-Ma (HLM) teorisiyle uyumu incelenmiştir. Çift kırıcılık anizotropik malzemeden giren ışığın iki farklı ışığın kutuplanmasıdır, ∆n ile ifade edilir. Bu çalışmada çift kırıcılık ölçümleri yüksek hassasiyet özellikli döner analizör metotu yapılmıştır. Çift kırıcılık verileri kullanılarak nematik düzen parametresi daha önce Özbek ve ekibi tarafından gösterilen S(T)=Δn(T)/〖Δn〗_0 bağıntısıyla bulunmştur. Anisimov ve ekibi tarafından N – SmA geçişindeki düzen parametresi ψ ve direktör dalgalanmasının serbest enerjiye eklenmesiyle bu ifadeye kübik bir ifade eklendiğini göstermiştir. Bu kübik terim geçişin birinci derece olmasını gerektirir. HLM teorisinde de N – Sm A geçişi birinci derece olması gerekir. Daha sonra evrensel ölçeklenme fonksiyonunu konsantrasyon x ve S ̅ indirgenmiş entropi değişimi bağlı olarak S ̅/S ̅^* -(S ̅/S ̅^* )^(-1/2)=a ̂/S ̅^* (x-x^* )≡y-y^* ifadesiyle verilmiştir. Çetinkaya ve ekibi bu evrensel ölçeklenme fonksiyonundaki entropi değişimiyle N- SmA geçişinde nematik düzen parametresi S ilişkilendirmiştir. Bu çalışmada 8CB – 10CB ikili karışımlarında çift kırıcılık ölçümlerinden nematik düzen parametresi S, türetilmiştir. Bu S verileri T_NA N –SmA geçiş sıcaklığı civarında olası entropi süreksizliklerine ulaşmak için kullanılmıştır. Elde edilen mol kesri x'e bağlı entropi süreksizlikleri evrensel ölçeklenme fonksiyonuna iyi bir şekilde fit edilmiştir. Bu da HLM teorisindeki smektik A ve yönelimsel düzenin çiftlenimden dolayı kübik terim eklenen ortalama alan ifadesiyle tutarlıdır. Ayrıca daha önce yapılan kalorimetrik ölçümlerle bulunan sonuçlarla oldukça uyumludur. Daha sonra T_NA civarındaki S(T)'nin sıcaklık türevinin aynı kuvvet yasası ıraksaklığı (özgül ısı kapasitesi) olduğunu kullanılarak etkin kritik üstel değerleri bulunmuştur.
Atomic and island scale diffusion events on Bi2Te3 (0001) surfaces & ultra-thin Bi2Te3 films on SiO2 substrates
Topological insulators (TI) are new phase of materials. They were reported as they have conducting surface states at their edges whereas they have insulating band in bulk. While Bismuth Telluride (Bi2Te3) is well-known thermoelectric material for several decades, it attracted attention again in recent years after declared as a TI. TI are promising materials in novel fields such as spintronics, quantum computation and topological superconductivity. Before any application in these fields, further investigations on their incompleted both morphological and electronic structure require. Bi2Te3 has rhomboherdral primitive cell which contains five atoms. It consists of five atomic planes of (Te1-Bi-Te2-Bi-Te1) along c-axis named as quintuple layer (QL). QLs are bind each other with weak van der Waals bonds, yields most cleavable interface. After cleaving, resulting Te1 terminated (0001) surface has trigonal lattice, and its both morphological and electronic structure can be determined at atomic scale by means of scanning tunneling microscopy (STM). In addition, Bi2Te3 has four type of defects. Depending on the doping type, types of the observable defects may change. In this thesis, we studied general morphology of (0001) surfaces of Bi2Te3 under ambient conditions with STM, including the defects and their electronic structure. In addition to investigations on morphological structure, we focused on diffusion events of the Te1 vacancies. To the best our knowledge, we report for the first time diffusion of individual atomic scale defects as well as Ostwald ripening of vacancy islands on a TI surface. Also, we investigated the nature of mass flow on Bi2Te3 surface according to previous studies that express the thermodynamic and kinetics behind growing islands. On the other hand, the knowledge on the electronic structure of this material at ultra-thin limit is still incomplete. We modified chemical vapor deposition (CVD) technique to grow ultra-thin Bi2Te3 films on SiO2/Si wafers. In this process, we obtained ultra-thin films and micro-particles of Bi2Te3. The heights of obtained Bi2Te3 films are measured to be a few QLs. The radius of Bi2Te3 micro-particles are few micrometers. Structural and spectroscopic characteristics of these ultra-thin films are also discussed.
Hierarchical relationship of quantum teleportation protocols
Entangled states are the resources of quantum teleportation. In this thesis first, the teleportation protocols of two, three and four level systems are studied. Then, the identification of their relations by teleporting a low level system with high level system protocol is examined. We explained protocols basically with two different methods. One of the methods is to perform projective measurement in the basis of generalized Bell states of particular level, and the other method is to operate a gate array. In both methods, we call the states which can be obtained after a measurement, as recovery needed states. These are the states before recovery operation. In the teleportation of an arbitrary qubit, there are 4 recovery needed states and recovery gates. In the teleportation of an arbitrary qutrit, there are 9 recovery needed states and recovery gates. To identify the relation between the protocols of three-level and two-level system, we teleported an effective qubit by using qutrit teleportation protocol. As a result, we saw that it has 9 recovery needed states and has nothing in common with the qubit protocol. Thus, there is no hierarchical relation in between. Teleportation protocol of the ququart of two-qubit has 16 recovery needed states and recovery gates. To identify the relation between four-level and three-level, we teleported an effective qutrit by using ququart teleportation protocol. We saw that it has 16 recovery needed states and recovery gates and there is nothing in common with the real qutrit protocol. Thus, there is no hierarchical relation in between. When we teleport an effective qubit by using ququart teleportation protocol, it has 8 different recovery needed states and recovery gates, and 4 of 8 is isomorphic to the qubit teleportation protocol. Ququart protocol is not reduced to qubit protocol but involve qubit protocol as a subgroup. Generally, hierarchical relationship may not be seen in the transition between relatively prime levels. However, to reach a general result about hierarchical relation, higher-level transitions should be analyzed, in my opinion. In addition to identify the relations, we also studied on effective teleportation. To teleport effectively, living in the subspace must be guaranteed. State to be teleported must live in the subspace where it belongs to, throughout the teleportation. Finally, it is important to write a specific protocol to each case for an efficient transmission.
Thin accretion disks around black holes modeling the secondary outburst
Accretion disks are efficient engines which convert gravitational energy into heat and radiation. Since it is not possible to observe a black hole directly, it is difficult to understand and probe the physics of such environments. Accretion disks may provide essential clues about the physics near such dense objects. If the secondary star in a low–mass black hole binary fills its Roche–lobe, matter will enter the gravitational influence of the black hole. Since the transfered matter will possess some initial angular momentum, it will start to orbit the black hole instead of directly fall onto it, hence, forming an accretion disk. Due to magnetorotational instabilities, eddies will form hence leading to enhanced viscosity. Due to the viscous torques, angular momentum will be transfered outwards, allowing matter transfer towards the black hole. The viscous dissipation in the disk will produce heat and also black body radiation in soft X–rays. Such a disk can be modeled as a viscous flow towards the black hole. It is possible to make relatively accurate models using the famous a–prescription for the viscosity. By taking advantage of the conservation of mass and angular momentum, a non–linear diffusion equation is obtained which describes the temporal evolution of accretion disks. In this work, this diffusion equation is solved numerically by implementing a finite differences scheme with Crank–Nicholson discretization. The disk instability model, which determines the stability regimes of various regions of the disk, is also implemented. Also, irradiation of the disk from a central source and irradiation by a lamppost–like source is included to the numerical model. The values of the opacities in the disk is determined by realistic opacity tables. In many observations of low–mass soft X–ray transients, it is seen that a secondary maximum occurs in the light curve during the decay phase. It is argued that the reason behind such a secondary outburst may be the formation of a radiating corona. It is proposed that the geometry of the corona, allows the previously shadowed parts of the disk to be irradiated, hence leading to an increase in mass flow towards the black hole. This, in turn, leads to a secondary outburst. The preliminary numerical results have been compared to Pringle's approximate analytical solutions to the disk equation. The results with different corona sizes, corona luminosities, and corona formation times have been obtained by using the HPC at Sabancı University. It may be possible to obtain clues about the geometry of the corona, which is still an unknown, by relating it with the observed secondary outbursts.
Investigation of swift heavy ion irradiated graphitic surfaces and novel graphene based devices
Tailoring materials with atomic scale defects have been studied over decades. In recent years, It had been understood that making a functional electronic device with extremely small size (several tens of nanometers) by use of novel materials such as graphene requires introducing defects. One way of achieving this goal is swift heavy ion (SHI) irradiation. In the first part of the study, we investigated defect formation on swift heavy ion (uranium and lead) irradiated graphitic surfaces by means of Scanning Tunneling Microscopy with a focus on HOPG and dislocated graphene layers on HOPG (moiré zones). Our results showed that structures that form on HOPG surfaces due to SHI irradiation in perpendicular geometry have a variety of shapes and sizes rather than just being hillock like. Moreover, comet-like structures were observed on HOPG surfaces due to SHI irradiation under 80o incidence angle with respect to surface normal. Obtaining atomic resolution on the tail section of the comet-like structures proved that SHI does not damage the surface layers while it is traversing in the bulk of the crystal. On the other hand SHI Irradiation of moiré zones under 80o incidence angle and SHI irradiation of moiré zones under grazing incidence (87.5o) did neither show destruction of the graphene layer generating the moiré pattern, nor any unzipping of the graphene as shown to happen on SHI irradiation of graphene crystals on dielectric substrates. Rather, the defects forming as a result of these lead and uranium irradiations were comet-like both on pristine HOPG samples as well as on moiré domains. Furthermore, irradiation of moiré zones with perpendicular geometry has been studied. It was observed that moiré zones may remain unharmed or they may locally destroyed upon SHI irradiation due to electronic changes in the bulk or moiré zone itself. We also studied tribological properties of SHI irradiated HOPG surfaces by means of Friction Force Microscopy (FFM). Our FFM measurements showed complementary results to our STM measurements. We observed that the head sections of the comet like structures appeared on simultaneously measured topography and friction maps. Intriguingly, tail sections of the comet-like structures appeared on friction maps, although they could not have been observed on topography maps. In some cases tails sections showed less friction compared to pristine HOPG surface. Our results showed that friction between two surfaces can also be a function of the bulk material. In the second part of the thesis, we demonstrated transparent heating element made out from Chemical Vapor Deposition (CVD) grown graphene on copper substrates. We used wet transfer method to transfer graphene on glass and quartz substrates for producing transparent heating element and modified transfer process for our purposes. Excitingly, our transparent heating elements can go up to high temperatures (310o C) with very low power consumption (27.2 Watt). We also studied heating properties of graphene samples grown by various growth paremeters. We observed that our graphene samples have monolayer background with multilayer zones. Also we observed silicon-oxide impurities may form on the CVD grown graphene and they can be transferred on any substrate. Changing growth parameters causes differences in the impurity concentration as well as monolayer and multilayer zone concentration which results in differences in heating properties of the graphene based heating elements.
Investigating the emission properties and the geometry of black hole X-ray binaries in the outburst cycle
Depending on their initial mass, stars can live from millions up to billions of years. This mass also determines the next step in their stellar evolution when they ran out of their fuel. The cores of stars with a mass greater than 20 M collapse into a black hole (BH). This object does not produce any radiation by itself, however, if it is in a binary system, the companion star may supply matter that accretes onto the BH. The angular momentum of the accreted material prevents a direct fall and matter forms a disk around the BH. The radiation from this accretion disk is observable. Under certain circumstances, a portion of this disk thought to evaporate by the effect of heat conduction and turns into a radiatively inefficient hot-flow. The relativistic electrons in the flow Compton-up scatter the disk photons and produce hard X-rays. The material in the disk may also be ejected away on some region close the BH with the help of strong magnetic field which produces the jets observed in radio and near-infrared wavelengths. These phenomena have a tendency to repeat themselves in a hysteresis-like loop. Constant monitoring of BH X-ray binaries provided a classification based on the abrupt changes in spectral and temporal properties of the sources. According to this classification, BHXBs spend most of their time in a low flux state known as quiescence. At the very beginning of the outburst, the system goes into a hard state in which the spectrum is dominated by high energy photons and variability increases. The compact jets are also observed in this state. As the material starts to move radially inward, the luminosity increases and variability drops. This state is known as the soft state. A disk wind may be observed in this state for high inclination sources. At the end of the outburst where mass accretion rate ( Ṁ) is sufficiently low, evaporation may remove majority of the disk which cause the source returns back into its initial state. There are also intermediate states which show properties of both hard and soft states with unique features. Unfortunately, there is no universal model that explains all the dynamic properties of BHXBs in different spectral states. Some models take into account GR effects and others include dynamo process as well as change in accretion rate. Interpretation of these models allows us to understand the motivation behind the observed phenomena. For instance, jets are events which usually are observed in hard and hard-intermediate states in a timescale of hours to months. Although the mechanism behind this phenomena is still debated multi-wavelength observations put forward a strong correlation between radio and X-ray luminosity indicating a disk-jet coupling. This nonlinear relation between inner flow and outflow (X-ray-radio luminosity) is thought to be simple and unique at first. Yet, along with the increase in the amount of data, it became clear that numerous BH systems are "outliers" follow a steeper path in radio X-ray correlation. Several models have been proposed to explain this strange behavior. One of the most promising hypothesis is the condensation disk model where it is assumed that a cooler weak disk is reformed at the end of the outburst which provides the additional X-ray flux. As Ṁ decreases the disk can no longer re-condense and disperse. The outliers which joins the main track below a certain flux value are considered to experience such a process. This hypothesis can be tested by determining the geometry of the system since the corona (hot-flow) must retrieve at some point in order to allow the inner disk to reform. The first part of this thesis is devoted to testing this hypothesis by modeling the power spectrum of both regular and outlier sources with a new developed model PROPFLUC. This is a physical model based on the mass accretion rate fluctuations in the precessing corona. Temporal analyses of sources with such a model allowed us to extract the inner and outer radius of the corona. By observing the evolution of these parameters we aim to understand how disk and corona behave relative to each other during outburst decay and rise. In this part, data from 4 different BH transients (GX339-4, 4U1543-47, GRO J1655-40, XTEJ1550-564) have been analyzed in hard and hard-intermediate states for multiple outbursts between 2000-2011. Raw data were obtained from the Rossi X-ray Timing Explorer (RXTE) and processed according to the procedure stated in the Guest Observer Facility of NASA-HEASARC. Analyses are generally done in both XSPEC and IDL programs and additional bash and TCL scripts were used to automate the processes. In the outburst cycle, the transition from hard to soft state occurs at higher luminosity compared to transition from soft to the hard state. The second part of this thesis covers the spectral and timing analyses of BHXBs in outburst decay in order to obtain the luminosity distribution of these sources. By exploring the key parameters of state transition, we aim to investigate the origin of hysteresis in the hardness-intensity diagram as well as investigating the variability of state transition luminosities for multiple sources in the outburst decay. The transition luminosities were found for 2 separate classifications in the literature namely Belloni and Kalemci classifications. The analyses were done for 12 BH transients in 20 outburst decays. The spectral fits were mainly done via tbabs*smedge*(powerlaw+diskbb) model. In addition, Gauss and hecut models also tested in order to include the effect of the iron line (emission around 6.4 keV) and the exponential cut-off in the power-law predicted by thermal Componization models. The timing part was mainly modeled with multi Lorentzians where broad-band noise and QPO corresponds to broad and narrow Lorentzians respectively.
Ağır iyon çarpışmalarında lepton çiftlerinin üretilme olasılıkları
Ağır iyonların rölativistik hızlarda çevresel çarpışması birçok fiziksel olayın keşfedilmesine katkı sunduğundan dolayı, günümüze kadar birçok çalışma yapılmıştır. Rölativistik hızlarda hareket eden çekirdekler hareket yönünde Lorentz boyca kısalmasına uğrarlar ve uç noktalarda kuvvetli elektromanyetik alanlar oluşur. Bu alanlar çok sayıda sanal foton içerir. Bu alanlar vektör bozonları, zayıf bozonlar ve Higgs bozonları gibi çok sayıda parçacık üretir. Bu tezde ağır iyonlar rölativistik hızlarda çarpışırken elektromanyetik alanlardaki sanal fotonların etkileşmesinin sonucunda üretilen elektron, müon, tau çiftleri üzerinde durulacak. Tamamen iyonize olmuş ağır iyonlar LHC ve RHIC de kütle merkezi sisteminde nükleon başına sırasıyla 100 GeV ve 3400 GeV enerjilerinde çarpıştırılmaktadır. Bu tezde 3400 ve 100 GeV enerjileri için altın iyonlarının çevresel çarpışması incelene-cek ve bu çarpışmadan dolayı üretilen leptonların diferansiyel tesir kesitleri ve olası-lıkları incelenecek.
Polimetilmetakrilat/grafen nanoplatelet nanokompozitin fiziksel özellikleri
Poly (methyl methacrylate) (PMMA) is a clear, transparent thermoplastic material with good mechanical properties, high resistance to weathering and excellent heat resistance. Mechanical, thermal, electrical and radiation shielding properties of PMMA can be improved by adding several nanomaterials with excellent properties. The enhanced PMMA materials are the ideal candidates for several application areas such as medical, sensor, solar cell, electronic and aerospace areas.In this study, Graphene Nanoplatelets (GNPs) was selected as nanofiller to enhance the mechanical, thermal, electrical and radiation shielding properties of PMMA. PMMA was produced via ATRP technique. GNPs nanofiller was dispersed by in situ polymerization method because it was the most efficient method to disperse the layered GNPs nanomaterial. SEM, XRD, FTIR, TGA, hardness and compression test, ultrasonic test and gamma transmission techniques are performed to examine the changes in the characteristic properties of PMMA. SEM characterization combined with elemental mapping technique showed that GNPs nanofiller homogeneously dispersed in the PMMA polymer matrix via in situ polymerization method. Besides, the results of the ultrasound tests were supported a homogeneous structure of PMMA/GNPs nanocomposites. XRD pattern of PMMA/GNPs nanocomposites presented a pick at ~26.5° , which is corresponding to the stacking of the graphene layers at a distance of 0.34 nm. The intensity of the pick increased with the rise of the GNPs concentration. The FITR spectra of PMMA/ nanocomposite presented similar spectra with pure PMMA, indicating that interaction occurred between GNPs nanofiller and PMMA polymer matrix. TGA results showed that with the addition of 2% GNPs, the 5% weight loss temperatures shifted from 196.73°C to 243.00°C, improved by 46.27 °C. The thermal stability of PMMA enhanced significantly. With the addition of 2% GNPs the electric conductivity of PMMA improved dramatically from ~ 10-14 S/m to 0.72 S/m. In the ultrasonic test, the Shear modulus, Young's modulus and Microhardness values of pure PMMA were increased by 19.5%,16.8 %, and 14.2% respectively with the addition of 2 wt.% GNPs. Compare to the pure PMMA, with the addition of 2 wt.% GNPs the Rockwell hardness and compressive strength increased by 19.9% and 42.7% respectively. For Cs-137 and Co-60 radioisotopes, with the rise of GNPs concentration, the linear attenuation coefficients increased slightly, however, the mass attenuation coefficients decreased slowly.
Molecular dynamics study of the thermal conductivity in nanofluids
Nanofluids are a new kind of fluid which contain well-dispersed nano-sized solid particles. They tend to have higher thermal conductivity than the bulk fluid in which they are mixed. In this work, the thermal conductivity of the bulk Lennard-Jones fluid and nanofluids at various volume fractions of nanoparticles is computed thanks to equilibrium molecular dynamics (EMD) and non-equilibrium molecular dynamics (NEMD) simulations. The Green-Kubo formalism is used for the EMD simulations while a net heat flux is imposed on the system with a change of the boundary conditions for the NEMD simulations. The interactions inside the nanoparticles, between the fluid atoms, and between nanoparticles and fluid atoms are all taken as a Lennard-Jones potential. An empirical parameter, ζ , is added to the attractive part of the potential to control the hydrophilicity of the nanoparticles. Additionally, bonded atoms of nanoparticles interact with the Finitely Extensible Non-Linear Elastic (FENE) potential. The NVE ensemble is used in the simulations, for which the total number of atoms, the total volume and the total energy are constant. In order to improve the computational efficiency, we construct neighbor lists with the cell list algorithm. The equations of motion are then integrated with the Velocity Verlet algorithm with a time step of 0.001. The total energy E and the total momentum P are computed to check the validity of the code since they are both conserved quantities. Using the Lennard-Jones phase diagram from literature, we choose a phase point corresponding to a liquid state. The temperature and density are taken respectively as 1.1 and 0.7798 in dimensionless units throughout all the simulations. The initial condition of the bulk fluid has a total number of 5000 fluid atoms arranged in a regular FCC lattice. On the other hand, a spherical nanoparticle consisting of 58 atoms is generated and equilibrated in a separate molecular dynamics simulation. The bulk fluid and nanoparticles are mixed to obtain 4 simulation boxes with varying nanoparticle volume fractions of 2%, 3%, 6% and 10%. The hydrophobic parameter of the interaction potential between nanoparticles is fixed to ζ nn = 0.3 for all the simulations in order to prevent flocculation, and thus to have a well dispersed nanofluid. On the other hand, in order to study the effect of hydrophilicity on the thermal conductivity we use three different values of the hydrophilicity parameter of the fluid-nanoparticle interaction, namely ζ n f = 0.5, ζ n f = 1 and ζ n f = 1.5. In total 12 sets of simulations are initially run for 10 7 time steps of equilibration. The resulting coordinates are then used for the calculation of the average kinetic and potential energies of each atom of each species for a further 10 6 time steps. Finally, molecular dynamics simulations for collecting the heat current data are computed during 10 7 time steps. The time auto-correlation function of the heat current and its time integral are calculated in a post-processing program. The results show that the hydrophilicity of the nanoparticles did not have a measurable effect on the thermal conductivity of the nanofluid. Nanofluids with volume fractions of 2% and 3% showed an enhanced thermal conductivity with respect to the bulk fluid. The increase in the thermal conductivity is of approximately 10%. Surprisingly, nanofluids with higher volume fractions did not show any enhancement of the thermal conductivity. The numerical results obtained from EMD are then validated with NEMD simulations.
Biyolojik moleküllerin arsenik fosforen tek katmanlı hegzagonal yüzey üzerine adsorpsiyonunun incelenmesi
Nanoteknolojinin en önemli alanlarından birisi de iki boyutlu malzemelerdir. Grafenin keşfi ve yığın halinden nano boyuta geçerken göstermiş olduğu eşsiz optik, mekanik, elektronik ve manyetik özelliklerinin anlaşılması geleceğe dair umutları artırmıştır. Özellikle Grafenin keşfiyle ortay çıkan iki boyutlu malzeme sınıfının organik moleküller ile kombinasyonu sayesinde bu malzemelerin özelliklerinin ayarlanabilir olması biyomedikal alandaki kullanımını öne çıkarmaktadır. Mavi arsenik fosforen iki boyutlu aile sınıfında bulunan ve potansiyel uygulamaları konusunda teorik çalışmaları süren bir malzemedir. Bu çalışmada mavi arsenik fosforenin Glisin ve Serin organik molekülleri ile olan etkileşimini anlayabilmek için Yoğunluk Fonksiyonel Teorisi (YFT) kullanılmıştır. Çalışmanın ilk kısmında alttaş olarak kullanılan mavi arsenik fosforenin yapısal ve elektronik özellikleri ortaya konmuştur. İkinci kısımda ise yüzeyde kusurlar oluşturularak yapısal ve elektronik özelliklerin değişimi belirlenmiştir. Son bölümde de kusursuz ve kusurlu yüzeylerin biyomoleküller ile olan etkileşimi için yapısal optimizasyonları gerçekleştirilmiştir. Yüzeyin biyoalgılama kabiliyetini belirleyebilmek için yapısal ve elektronik özellikleri analiz edilmiştir. Tüm bu incelemeler sonucunda kusurlu mavi arsenik fosforen yüzeylerinin Glisin ve Serin etkileşimi için iyi bir aday olduğu görülmüştür.
Yeniden tam güçlendirme yöntemi ile doğal gaz kombine çevrim santraline dönüştürülen bir termik santralin modellenmesi ve performans değerlendirmesi
Endüstriyel gelişmenin bir sonucu olarak sürekli artan elektrik talebi, daha büyük kurulu güç ve üretim kapasitesine duyulan ihtiyacı da beraberinde getirmektedir. Bununla birlikte, mevcut yasal düzenlemeler, yeni ekipmanların sermaye maliyetleri, zamana bağlı kısıtlamalar ve enerji santrallerinin inşa edilmesine karşı toplumsal tepkiler, yeni enerji üretim projeleri için zorluklar oluşturmaktadır. Bu zorlayıcı faktörler son yıllarda "yeniden tam güçlendirme" kavramının tekrar önem kazanmasına neden olmuştur. "Ambarlı Yeniden Güçlendirme Projesi" Türkiye'de ilk defa yürütülen, dünyada ise boyutu, kapsamı ve niteliği açısından sınırlı sayıda örneği olan bir "Doğal Gaz Kombine Çevrim Santraline Dönüştürerek Yeniden Tam Güçlendirme" projesidir. Söz konusu projede mevcut fuel-oil yakıtlı buhar santrali, doğal gaz yakıtlı kombine çevrim santraline dönüştürülerek yeniden tam güçlendirilmiştir. Bu tez kapsamında, mevcut buhar türbininin ilk performans hesaplamaları ve rehabilitasyon sonrası elde edilebilir güç çıkışı detaylı olarak değerlendirilmiştir. Türbin giriş sıcaklığı, basınç ve buhar debisi gibi parametreler, kombine çevrim santralin performansının kapsamlı bir şekilde değerlendirilmesine olanak tanıyan simülasyon modeli için sınır koşulları olarak tanımlanmıştır. Geliştirilen modelin çıktılarının resmi performans test sonuçları ile karşılaştırılarak doğrulanması amacıyla detaylı bir validasyon çalışması yürütülmüştür. Sonuçlar, kondenserden ısı deşarjında sadece %25 bir artış ile santralin toplam kapasitesinin %203 oranında artırılabileceğini göstermektedir. Ayrıca yeniden güçlendirmenin, ekonomik faydalara ek olarak, NOx, SOx ve CO2 emisyonlarının azaltılması gibi önemli olumlu çevresel etkilere sahip olduğu da bulunmuştur. Resmi performans testleri ile doğrulanan bu özgün çalışmanın, gelecekte yapılacak benzer projelere ışık tutması beklenmektedir.
Yapay sinir ağları yardımıyla kendinden karışımlı (self mixing) interferometrik sistemlerde gürültü azaltma
Bir lazer diyottan çıkan ışığın bir hedeften geri yansıdıktan sonra kendi oyuğuna girerek girişim deseni oluşturması kendinden karışımlı interferometre olarak bilinir. Bu tür interferometreler az sayıda optik bileşen içerdiğinden kompakt ve düşük maliyetlidir. Yer değiştirme, hız ve mesafe ölçümü gibi çeşitli parametrelerin tespiti için kullanımının yanı sıra kırılma indisi ve yüzey pürüzlülüğü gibi malzeme karakterizasyonunda da kullanılabilmektedir. Optik geri besleme etkisine dayanarak oyuk içinde oluşan girişim sinyali, ölçümlerin doğruluğunu etkileyecek çeşitli gürültüler içermektedir. Birçok potansiyel uygulama alanı için elde edilen sinyallerin kalitesi son derece önemlidir. Yapay sinir ağlarının karmaşık kalıpları kolaylıkla öğrenebilme ve tahmin yapabilme yeteneğinin bu tür interferometrelere uygulanarak sinyal hassasiyetini arttırması umut verici bir yaklaşım sunmaktadır. Bu tez çalışmasının temelini oluşturan interferometreler için derin otokodlayıcı yapay sinir ağı modeli geliştirilerek, bu tür girişim sinyallerinin analizini kolaylaştırılacak bir ön işleme adımı önerilmiştir. Bu amaç doğrultusunda; önce temiz sentetik veri sinyalleri oluşturulmuş, daha sonra bu sinyaller üzerine beyaz gauss ve benek gürültüsü eklenmiştir. Daha sonra oluşturulan model, bu veriler ile eğitilmiştir. Bu esnada eğitim verileri, kendinden tamamen farklı değerlerle oluşturulmuş doğrulama verilerinin hata sonuçları ile kıyaslanmış ve tatminkâr bir sonuca ulaşıldığında eğitim tamamlanmıştır. Daha sonra kontrollü bir test verisi üzerinde model performansı değerlendirilmiş, çeşitli yer değişim sinyalleri için bu başarı ayrıntılı olarak incelenmiştir. Çalışmada ayrıca geliştirilen bu model, geleneksel sinyal filtreleri ile kıyaslanmıştır.
Kuantum mekaniğinin matematiksel ve kavramsal temelleri üzerine
Kuantum mekaniğinin matematiksel ve kavramsal temelleri, çeşitli Mach-Zender tipi hibrit deney düzeneklerinde, girişimölçerlerin iki ayrı kolu tarafından saçılan dolanık durumdaki bir çift parçacığın spin ölçümleriyle ilişkili korelasyon bağıntıları üzerinden incelenmiştir. Kuantum durumlarının uyumu, oluşum dolanıklığı, kuantum öze uygunluk ve Bures mesafesi, geometrik fazın dolanık parçacık çiftlerinin ilk durumlarını nasıl etkilediğini anlamak için kullanılmıştır. Elektromanyetik potansiyeller, elektromanyetik alanların bulunmadığı bölgelerde parçacıkların hareketinden dolayı bir kuantum girişimine neden olmaktadır. Bazı durumlarda, geometrik faz bilgisinin dolanık parçacık çiftlerinin son durumlarında mündemiç olduğu gösterilmiştir.
Mamografi çekimi yapılan hastalarda cranio caudal çekim protokolüne göre konvansiyonel ve dijital mamografide yüzey dozunun karşılaştırılması
Dijital mamografi cihazında 230 ve konvansiyonel mamografi cihazında 180 hastada meme üst ve iç yüzeyinden çekim alınmıştır. Konvansiyonel mamografide 50 hastadaki çekimde bunlara ilaveten meme dış ve alt yüzeyinden çekimleri eklenerek dört farklı noktadan ölçüm alınmıştır. Bunun için TLD-100 dozimetre kullanılarak dozimetrik yöntemle ölçümler yapılmıştır. Toplam 460 hastada elde edilen sonuçlar karşılaştırıldığında dijital mamografi ile yapılan çekimlerde konvansiyonel mamografiye göre meme üst ve iç yüzeyinden alınan dozların bu çalışmada daha fazla olduğu belirlenmiştir. Çalışmada aynı zamanda meme ultrasonu sırasında tespit edilen meme dansitesi değerleri, hastanın meme ölçüleri, ölçüm sırasında kullanılan kVp, mAs değerleri de çalışmaya eklenmiştir. Anahtar Kelimeler: Konvansiyonel Mamografi, Dijital Mamografi, yüzey dozu, TLD- 100 dozimetre
Noise mapping on Gaziantep University campus area
Noise is an element that needs to be taken seriously, such as all other environmental pollution, and to be controlled. There are many sources that generate noise both internally and externally. If the noise is not controlled, we will encounter in every area of our daily life and become a factor which will cause constant discomfort. This brings a lot of health problems in a long or short time, constant or instant. Noise pollution is one of important parameters for irregular urbanization. The aim is researching about the noise pollution in Gaziantep University Campus, which is caused by vehicle traffic on highway, and taking precautions. In this study, eight points of Gaziantep University Campus were examined in terms of environmental noise. Based on the vehicle loads on these points, noise map was prepared by using Grid Noise Map technique.
Conversion of radioactive and chemical energy to electrical energy
In this thesis, two types of batteries have been studied. The first is aluminum (Al) air battery and the other is nuclear battery. We have demonstrated that graphite and exfoliated graphite sheets coated with activated carbon (AC), manganese dioxide (MnO2) and other additives are a promising cathode for metal air batteries. Several low-cost, environmentally-friendly air cathodes are fabricated and their performances are tested by constructing Al air batteries whose electrolyte 6M NaOH, including ZnO inhibitor, is gelled by adding a cost-effective water retainer. The experimental results show that this new Al air battery has a good discharge performance. In the other study, we present construction and analysis of nuclear micro battery driven by Strontium 90 (Sr90). Our design is based on charge deposition on the plates of a capacitor and polarization of dielectric materials between the plates. In the construction, we have used liquid Sr90 with activity 100 mCi in cylindrical ampoule coiled up by thin film graphene as one plate and Manganese dioxide (MnO2) as other plate of the capacitor. The high energetic beta particles from the Sr90 penetrate to graphene to produce ionization and then electrons are removed from graphene to dielectric material. Electrons inside the dielectric material cause polarization of dipoles. Consequently, the radiation from the isotope produces an external current.