Recently Added Theses
View AllProton iletken polimer/metal organik kafes yapılar içeren kompozit membranlar
Proton exchange membrane fuel cells (PEMFCs) are one of the most innovative research areas in search of novel power sources, especially because of their no to low greenhouse gas emissions, high efficiency, diverse fuel options and low maintenance costs. Hence, PEMFCs are regarded as one of the potential alternatives for the conventional power generators. Proton exchange membrane (PEM) is the core component of the PEMFC. Still, Nafion® and PBI are the commonly used membrane materials in fuel cell technology. The development of novel PEMs with high proton conductivity, good mechanical and chemical stability and cost-effective manufacturing remain as obstacles for the commercialization of PEMFCs. In this thesis for the first time, we present preparation and characterization of two types of novel composite proton exchange membranes which consist of zeolitic imidazolat framework-8 (ZIF-8). In the first part of this study, consisting of poly(vinyl alcohol) (PVA), poly(2- acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and zeolitic imidazolat framework-8 (ZIF-8) ternary Nafion-like composite membranes were prepared with different composition to use in the PEMFCs which of their operation temperatures below 100 0C. All of the membranes were structurally characterized and their proton conductivities were measured by electrochemical impedance spectroscopy. The fully hydrated membrane with 55 PVA/40 PAMPS/5 ZIF-8 composition shows the highest proton conductivity with about 0.13 S cm-1 at 80 0C and the result thus obtained is comparable to the proton conductivity value of the Nafion in the literature. The aim of second part of this study is the preparing of membranes for high temperature proton exchange fuel cells (HTPEMFCs), which operate between 1 00-200 0C, the binary mixed membrane were manufactured incorporation of PBI and ZIF-8. In the membrane PBI was used as host polymer whereas ZIF-8 is used as filler material. Among the structurally well-characterized membranes, the membrane with 12.5 ZIF-8/PBI membrane has the highest proton conductivity with about 0.0045 S cm-1 at 160 0C under anhydrous condition. Keywords: Proton exchange membrane fuel cells, PAMPS, PVA, PBI, ZIF-8,
Manyetik levitasyon sisteminin kayan kip ve PID temelli referans takip kontrolü ve donanım içeren benzetim testleri
Magnetic levitation systems are convenient to provide frictionless, reliable, fast and economical operations in wide-range applications. The effectiveness and applicability of these systems require precise feedback control designs. The position control problem of the magnetic levitation plant can be solved with a cascade control method. In this thesis, sliding mode and PID based cascade controllers are designed to render high position control performance and robustness to the magnetic levitation. Sliding mode control (SMC) based cascade controller is proposed for controlling magnetic levitation. The SMC based controllers for the inner current loop are designed to eliminate the effects of the inductance related uncertainties of the electromagnetic coil of the plant. For the outer position loop, the integral SMC is designed to eliminate disturbances around operating point resulting from the linearization of the mechanical part. Finally, numerical simulation and experimental results for various cascaded controllers are provided and compared in order to validate the efficacy of the approaches.
Ekran ve kataliz uygulamaları için yeni nanomalzemelerin geliştirilmesi
Nanomaterials established a research presence due to their large variety and unique properties for many areas such as biotechnology, energy, fabrics, construction, food etc. Transparent conductors and catalysis applications are also two other important areas in which nanomaterial studies are carried out. For display applications, metal nanowires, especially silver and copper, draw too much attention as transparent conductors as an alternative to indium tin oxide (ITO), which is the most used material in this market, due to their high conductivity, low cost and availability for flexible device applications which are limitations for ITO. In catalysis applications, using nanomaterials are also important to provide two essential parameters: increasing the efficiency of reactions and lowering the cost. In this thesis, on the whole, we present the synthesis of silver and copper nanowires by optimizing some parameters for controlling the length and diameter of nanowires. For the surface passivation of nanowires, we offered some coating methods with noble metals such as gold, platinum and palladium. Also we investigated the catalytic activity of copper nanowires on dye wastewater treatment. In the first part of this study, effects of polyvinylpyrrolidone (PVP) polymer length and PVP:AgNO3 molar ratio on the efficiency of silver nanowire synthesis and nanowire size were investigated for polyol synthesis method. The results showed that reaction yield is highly depended on these parameters. Also, by using different coating methods such as direct addition or biphasic titration, and by using different noble metal precursors, galvanic exchange reactions on silver nanowire surfaces were studied. The results for coating showed that it is possible to replace silver and noble metal atoms through these methods. The next part of the thesis reports the copper nanowire synthesis by two different methods: hydrothermal and solution based synthesis. The copper nanowires showed different size properties for these two methods. In addition, the same coating processes were also performed for copper nanowires and the results are promising as silver nanowires. In the last part, catalytic performance of copper nanowires was studied on degradation reactions of three different organic dyes. Great differences between catalyzed and uncatalyzed reaction periods were observed for all dyes.
Mikro/nano manyetik parçacıkları kullanarak biyosensörlerin hassasiyetini iyileştirme
Currently micro/nanoparticles such as magnetic beads are not only used as labels to acquire signals from biosensors but they are also used to enhance the signals obtained from various biosensors. Magnetic beads or target are linked to other molecular labels such as fluorescence and chemiluminescence labels by biomolecules such as antibody to reach higher sensitivity and provide signal amplification for the measurement. This dependency on biomolecular binding has several disadvantages such as molecular binding is sensitive to environmental conditions such as pH and temperature, labels are costly and molecular binding may require extra time. In this thesis a time and cost efficient signal amplification method that does not need any biomolecular coating but based on magnetic interaction of magnetic micro/nanoparticles is developed. Magnetic particles subjected to external magnetic field are magnetized and form a local field around them, attract each other and accumulate along the magnetic field lines. These controlled accumulations can be used to amplify the pixel area or the contrast of magnetic particles. Accumulation dynamics of magnetic particles under magnetic field are studied and the application of this method to the Escherichia coli 0157:H7 sample is demonstrated. Lastly the integration of this signal amplification method to a flow chamber and a complete biosensing procedure is pursued. Magnetic micro/ nano particles that are immobilized on gold-coated surface under external magnetic field inside a flow chamber attract the iron nanoparticles in a running fluid to form chains of accumulations around them. The accumulations formed under magnetic field are used to improve the Contrast to Noise Ratio (CNR) of the images thus the sensitivity.
Bozulmuş görsel alan ve fotonik fener tabanlı eş fazlı algılama için tek modlu optik alıcı performans değerlendirmesi
Imaging at degraded visual environments is one of the biggest challenges in today's imaging technologies. Especially military and commercial rotary wing aviation is suffering from impaired visual field in sandy, dusty, marine and snowy environments. For example, during landing the rotor churns up the particles and creates dense clouds of highly scattering medium, which limits the vision of the pilot and may result in an uncontrolled landing. The vision in such environments is limited because of the high ratio of scattered photons over the ballistic photons that have the image information. In this thesis, we propose to use optical spatial filtering (OSF) method in order to eliminate the scattered photons and mainly collect the ballistic photons at the receiver. OSF is widely used in microscopy; to the best of our knowledge this thesis will be the first application of OSF for macroscopic imaging. Our experimental results show that most of the scattered photons are eliminated using the spatial filtering in a highly scattering degraded visual field. The results are compared with a standard broad area photo detector which shows the effectiveness of spatial filtering. Free space optical systems have applications in different areas such as laser ranging, three-dimensional imaging, weather predictions and optical wireless communication. Some applications require very high performance free space optical systems that are not available today. The need of systems with higher performance and lower size, weight and power (SWaP) is the biggest research motivation of free space optical systems. Between various detection techniques,coherent optical detection comes forward for applications that require high sensitivity and bandwidth. Coherent detection based LIDAR systems have the potential to provide quantum noise limited performance. However coherent systems suffer from poor free space to fiber collection efficiency due to the single mode detection characteristics and small size of the optical fiber. In order to overcome this problem, photonic lantern is introduced to effectively collect the multimode beam coming from free space and convert it to a number of single mode fibers. The photonic lantern consists of a multimode fiber to a number of single-mode fibers. The collection efficiency enhancement of photonic lanterns have been investigated, however there is no study on the signal to noise ratio –performance- improvement on the photonic lantern based free space coherent systems. In this thesis; the effect of random distribution of the optical power in the 19-port photonic lantern will be investigated mathematically. The photonic lantern based coherent detection system performance will also be simulated by using the MATLAB software. The output of this thesis may open the path to experimental demonstration and maybe even to a prototype.
Verimli aydınlatma ve ekran teknolojileri için fotometrik modellemelerin gerçekleştirilmesi
Using light emitting diodes (LEDs) as lighting devices has come to the sight as a compulsory step in terms of the energy efficiency. Almost a quarter of total consumed energy that generated whole around the world is used for lighting. Using incandescent bulbs as lighting devices is forbidden in most of Europe and light emitting devices are one of the most important choices in order to compensate that need. Their high performance in terms of both luminance levels and energy efficiency has opened a new research area to increase their performance. White light has different requirements based on an application area. Providing that necessities by engineering on light parameters is one of the main aims of this thesis. In display technology, the development from cathode ray tubes to organic light emitting devices has increased the performance of both display quality and energy efficiency. Enhancement of the color scale that can be perceived by the human eye is the main purpose so that the reference color area increases systematically. The last announced reference, Rec.2020, has two thirds of the colors perceived by human eye. In this thesis, considering the current references such as National Television System Committee (NTSC) color gamut, the broadening of Rec.2020 is also presented as a new important figure of merit. In this thesis, we have studied on the investigation of the parameters of the emitters, i.e., peak emission wavelength, full width at half maximum and peak intensity to achieve the desired quality white light. Although it is possible to get white light in each step, the high quality requirements have been implemented by four colors within the simulation range of thesis which possess color rendering index value >90, correlated color temperature <4000K and luminous efficacy of optical radiation 380 lm/Wopt. In addition, in terms of display technology, we have shown that using ultra narrow emitters is an optimal choice for achieving Rec.2020 color triangle. Using ultra-narrow emitters, it is possible to obtain 99,89% of the Rec.2020 that also almost covers the NTSC. As expected, using a fourth color component cyan has increased the reached area to 169,55% of NTSC on color space dramatically.