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Archived Theses
Farklı çinko ve azot uygulamaları altında yetişen buğday ve mısırda çinkonun alımı, taşınması ve tanede birikimi
Chronic zinc (Zn) deficiency is a major health issue affecting over two billion people, caused by heavy reliance on staple crops (i.e. wheat, rice and maize) which are inherently low in Zn. This project was devoted to reveal the individual and combined effects of genetic and agronomic Zn biofortification in wheat and maize. The first part focused on understanding the mechanisms involved in differences in uptake and translocation of foliar-applied Zn among wheat and maize species. It was shown that wheat has a greater capacity of leaf uptake and translocation of foliar-applied Zn compared to maize. The second part investigated the effect of nitrogen (N) supply on uptake and accumulation of Zn in maize and wheat. Improving N supply significantly enhanced the shoot accumulation as well as leaf uptake of Zn from foliar Zn sprays in wheat and maize. The third part studied the effectiveness of Zn fertilizers in the form of soil, foliar and soil + foliar for improving growth, grain yield and nutrients uptake by genetically biofortified HarvestPlus wheat genotypes. It was demonstrated that the genetically biofortified genotypes have higher capacity to uptake, utilize and translocate Zn from soil and/or foliar applications as compared to conventional cultivars. These results conclude that the most sustainable way of tackling human Zn deficiency would be to improve grain Zn concentration of cereal crops by unifying genetic and agronomic biofortification strategies.
Gövde alan ağlarının güvenliği için fizyolojik sinyaller kullanılarak sözde rasgele anahtarlar oluşturulması
With the help of recent technological advancements especially in the last decade, it has become much easier to extensively and remotely observe medical conditions of the patients. This observation is done through wearable devices named "biosensors" that act as connected nodes on the Body Area Network (BAN). The main goal of these biosensors is to collect and provide critical and sensitive health data concerning the host individual, communicate with each other in order to make decisions based on what has been captured and relay the collected data to remote healthcare professionals. The sensitive nature of this critical data makes it extremely important to process it as securely as possible. Biosensors communicate with each other through wireless medium that is vulnerable to potential security attacks. Therefore, secure mechanisms for both data protection and intra-BAN communication are needed. Moreover, these mechanisms should be lightweight in order to overcome the hardware resource restrictions of biosensors. Random and secure cryptographic key generation and agreement among the biosensors take place at the core of these security mechanisms. In this thesis, we propose SKA-PSAR (Secure Key Agreement Using Physiological Signals with Augmented Randomness) system. The main goal of this system is to produce highly random cryptographic keys for the biosensors for secure communication in a BAN. Similar to its predecessor SKA-PS protocol by Karaoğlan Altop et al., SKA-PSAR also employs physiological signals, such as heart rate and blood pressure, as inputs for the keys and utilizes the set reconciliation mechanism as basic building block. Novel quantization and binarization methods of the Secure Key Agreement Protocol of the proposed SKA-PSAR system distinguish it from SKA-PS in a way that the former has increased the randomness of the generated keys. In addition, the generated cryptographic keys in our proposed SKA-PSAR system have distinctive and time variant characteristics as well as long enough bit sizes that can be considered resistant against a cryptographic attack. Moreover, correct key generation rate of 100% and false key generation rate of 0% have been obtained. Last but not least, results of the computational complexity, communication complexity and memory requirements of our proposed system are quite higher as compared to SKA-PS, but this is a cost that needs to be paid for achieving high randomness level.
Demir oksit nanoparçacıkların ilaç/gen taşınımı ve tedavi amaçları için ısısal ve mekanik manipülasyonu
Superparamagnetic iron oxide nanoparticles provide a platform to deliver therapeutic agents to any desired group of cells in a safe fashion. These particles can be manipulated by externally applied magnetic fields, targeted to specific tissues and heated in focused fields for cancer treatment. Hyperthermia performance of SPIONs depends on the magnetic field strength as well as the field frequency. A part of this dissertation displays the therapeutic effect of Poly(acrylic acid)-coated, anti-HER2-tagged SPIONs on breast cancer cells using a low magnetic field strength of 0.8 kAm-1, which is significantly lower compared to the literature, with a frequency of 400 kHz. HER2-positive SKBR3 and MDA-MB-453 cell lines successfully internalized the nanoparticles. The particles, which were not toxic to these cell lines, led to a prominent decrease in cell proliferation and survival in MDA-MB-453 cells when subjected to hyperthermia. Gene therapy is another developing method for the treatment of various diseases. A strong alternative is magnetofection, which involves the use of SPIONs and external magnetic field to enhance the localization of SPIONs at the target site. A new magnetic actuation system consisting of four rare earth magnets on a rotary table was designed and manufactured to have improved magnetofection. The actuation effect was revealed with green fluorescent protein DNA bearing-nanoparticle transfection to MCF7 cells. The applied magnetic field in this system increased the transfection efficiency and viability relative to traditional transfection methods. At the same time, it also reduced the transfection time (down to 1 hour) of the standard polyethylenimine transfection protocol. Keywords: Hyperthermia, induction heating, breast cancer, superparamagnetic iron oxide nanoparticles, magnetic actuation, magnetofection
Nanokompozit yakıt hücreleri
The interactions between the components of the nanocomposite fuel cell electrolyte were investigated. Surface charges were thought to be responsible for the differences in the ionic conductivity. The literature claims that ionic transport in hybrid electrolytes does not happen primarily in the solid oxide or the matrix phase but at the interface between them. The surface charges of oxide particles are dissociating the matrix salt molecules into positive and negative ion complexes. The complex with the opposite charge sticks to the surface of the particles. The counter-ion moves freely under the influence of the electrical field, thus causing fast ionic current. Therefore, it is postulated that by modifying the surface charges one can affect the ionic conductivity. The strength of surface acidity was manipulated by reduction without significantly changing the chemistry of the oxide material. TiO2 (Rutile) was selected as the material whose surface charge was altered by reduction. Ionic conductivities were measured by impedance spectrometry. Surface charges were obtained by isoelectric point measurements. The amounts of reduction were measured by thermogravimetric analysis. Oxides with different surface charges resulted in different ionic conductivities. Sub-stoichiometric oxides had different strength of surface charges that resulted in correlated ionic conductivities. These interactions of surface charges and the ionic conductivities are explained with the help of a developed model for the composite electrolyte.
Metal-organik kafes/grafen oksit türevli gözenekli karbonların platin bazlı oksijen indirgenme reaksiyonu elektrokatalizörlerinde kullanımı
Fossil fuel-based energy economy is bound to change at some point within the 21st century as fossil fuels are inherently limited sources. Energy conversion and storage devices such as batteries, fuel cells, solar cells and supercapacitors need to advance in terms of efficiency for the fruition of a renewable energy ecosystem. Hierarchically porous materials are utilized as catalyst supports in polymer electrolyte membrane fuel cells (PEMFCs) and batteries to increase mass transfer and active site density in the catalyst. Metal-organic frameworks (MOFs) are tailorable crystalline solids where organic linker units are connected to metal centers. They may form molecular gates, channels and pores within the framework in angstrom to nanometer scale. Porous carbons derived from metal-organic frameworks are promising catalyst supports owing to their high surface area and 3-D network structure. In this thesis, a porous carbon has been produced from pyrolysis of a hybrid material based on Zn based MOF called zeolitic imidazolate framework-8 (ZIF-8) and graphene oxide (GO). As observed by physical and chemical characterization, ZIF-8 were coordinated to GO during the synthesis conditions of ZIF-8 and formed a hybrid structure in contrast with simple mixing. Evolution of macro/mesoporosity have been observed when the hybrid was exposed to pyrolyzing temperatures owing to the exfoliating effect of GO on ZIF-8. Pt nanoparticle (Pt NP) deposition on this porous carbon has resulted in catalyst Cat-1, which has been tested via voltammetric experiments against two reference materials; Pt decorated on pyrolyzed ZIF-8 (Cat-0) and Pt decorated on reduced GO (Pt/rGO). Cat-1 exhibits increased mass and specific activity against Pt/rGO at 0.8 V for oxygen reduction reaction (ORR). The nature of increased activity is proposed to be increased mass transport properties of Cat-1 sample that originates from its hierarchical porosity.
Sarmal kenar elekronlarının nükleer spinlerden eşevreli saçılımı
Topological insulators (TIs) are symmetry-protected states of matter characterized by a topological index, featuring gapless edge or surface states that are topologically protected, hence robust to weak disorder as long as the relevant anti-unitary symmetry is preserved. In this thesis, we focus on a particular TI, namely the quantum spin Hall insulator, where the relevant symmetry is the time-reversal (TR) symmetry. However, most topological insulators contain nuclear spins, which interact with the helical edge states via hyperfine coupling, breaking the TR symmetry and thus destroying the topological protection of the edge states. We perform numerical simulations to calculate the hyperfine-enabled backscattering probabilities of the helical edge electrons for edges containing up to 10 nuclear spins. We presented the plots of total reflection probabilities for a range of single-nucleus reflection amplitudes and discuss how our results apply to dynamic nuclear polarization. We also propose a universal extremum of the total reflection probability curves, independent of the system size, and expose which particular arrangements of nuclear spins cause the universal extremum.
Topolojik meta-materyallerde topolojik geçişlerin teşviki ve kuvantum taşınımı
In this Thesis, we propose a novel method that changes the topological order in superconductor wires. We first consider the case of disorder in one dimensional topological superconductors and show how disorder can destroy or create topological order leading to reentrant topological phases. We then consider the effects of a superlattice potential, a zero-average piecewise continuous weak electrostatic potential, on p-wave and s-wave topological superconductor wires. We call such stacked wires leading to weak periodic potential modulation, meta-topological superconductor wires. Topological superconducting wires in their non-trivial phases exhibit Majorana modes as their edge states. We show that by stacking topologically trivial pieces of superconductors, it is possible to induce a topological phase which feature Majorana states at the edges of the superlattice: the meta-topological superconductor. The presence of an electrostatic superlattice allows us to control the topological phase space via the geometry of the electrostatic superlattice. We consider strictly one dimensional meta-topological superconductor wires as well as their quasi-one dimensional multichannel counterparts and show that reentrant topological phases in multichannel meta-topological superconductors occur. Finally, we consider the analogous case of a meta-topological insulator, a quantum anomalous Hall insulator featuring a weak superlattice of magnetic modulation, and show that the transmission can be topologically controlled as a function of energy. The topological protection leads to binary transmission (either transmit or reflect) through the metatopological quantum anomalous Hall insulator, details of which can be controlled by tuning the properties of the weak superlattice.
Robot yapım problemlerine hibrit planlama yaklaşımı
We study robot construction problems where multiple autonomous robots rearrange prefabricated components to build stable structures. Robot construction problems can play a vital role in construction industries where the tasks such as designing a desired structure, planning for the necessary actions, and constructing structures from available components can be performed by the robots. Robotic construction may especially be useful in places, such as disaster zones or the space, where it is not safe or feasible for humans to visit. In these unsafe or hard-to-reach places, robots can build necessary buildings, bridges or shelters using the surrounding materials. We view robot construction problems as planning problems: find a plan (i.e., a sequence of actions) to obtain a final stable configuration of prefabricated objects satisfying some goal conditions, from a given initial configuration. These problems are challenging from the perspective of task planning since they may need incorporation of preexisting structure into the final design, pre-assembly of movable substructures, and use of extra blocks as temporary supports or counterweights during construction. These problems are challenging from the perspective of geometric reasoning as well, since they need feasibility checks to ensure reachability of a block, to avoid collisions of blocks, and to ensure stability of complex structures. We propose a formal hybrid planning framework to address these challenges using Answer Set Programming, and state-of-the-art feasibility checkers. This framework not only decides for a stable final configuration of the structure, but also computes the order of manipulation tasks for multiple autonomous robots to build the structure from an initial configuration, while simultaneously ensuring the stability, supportedness and other desired properties of the partial construction at each step of the plan. We show the usefulness of our approach on a wide variety of robot construction tasks, including bridge building and overhang construction scenarios, and using different types of objects, including cylindrical ones. We demonstrate the applicability of our approach through dynamic simulations and physical implementations with a bi-manual Baxter robot.
Genetik algoritması kullanarak serbestleşmiş elektrik piyasalarında gizli anlaşmaları tespit etme
Deregulated electricity markets allow competition over the electricity price among the power companies. However, in an oligopolistic environment, the strategic behavior of the power companies in the electricity market may lead to collusive opportunities. The independent system operator (ISO) is an authorized entity which is responsible for administrating the electricity market. Therefore, ISO shall be able to detect and avoid collusive opportunities among generators. In this study, we propose a metaheuristics approach to assist ISO in the decision-making process to prevent collusions. We develop a method, based on principles of genetic algorithm to detect the collusive opportunities in deregulated electricity markets. We test our algorithm on three problems of varying size. Our results are promising in terms of both speed and accuracy. For the large-scale problem, our algorithm works much faster than the existing alternatives in the literature.
Grafen büyütmede bakırdaki içsel karbonun ve hidrojen yardımıyla tüketilmesinin rolü
Growth of graphene on Cu by chemical vapor deposition (CVD) method is a multidimensional process. Therefore, a comprehensive understanding of the parameters involved in this process is essential to achieve a reproducible and optimized growth recipe. In this work, the role of intrinsic carbon in the bulk of Cu on nucleation of graphene is revealed and it is disclosed that CVD growth of graphene on Cu foil is not a pure surface process. We uncovered that hydrogen-assisted carbon depletion (HACD) effect causes carbon content within Cu bulk to diffuse out during annealing under hydrogen atmosphere and is a critical mechanism in the nucleation of graphene crystals. Additionally, we investigated the role of hydrogen on the diffusion of carbon toward the Cu surface during annealing. We showed that this interplay is not a linear mechanism, but depending on its concentration hydrogen either can boost or diminish the surface density of segregated carbon atoms from bulk. From that, we managed not only to grow a graphitic film on Cu foil but also and more importantly, illustrate spontaneous nucleation of graphene crystals during hydrogen annealing in the absence of external carbon precursor. To our knowledge, this is the first time such a growth has been realized. This finding can clarify the role of intrinsic carbon on the nucleation mechanism of graphene in the CVD process. We also showed that intrinsic carbon in Cu can effect the formation of ad-layers under as-grown graphene layer.