Fizik
http://digitalarchive.boun.edu.tr/handle/123456789/11607
2024-06-15T19:17:00ZElectrical detection of spin-orbit torque in antiferromagnets
http://digitalarchive.boun.edu.tr/handle/123456789/21455
Electrical detection of spin-orbit torque in antiferromagnets
Göksal, Cemal İlkin.
Ferromagnetic spintronics has been a game changer for memory technologies, until it has been understood that at some point ferromagnetic properties of these devices won’t be able to compensate for the demand on volume and performance. At this point, antiferromagnetic (AFM) spintronics emerged as the most promising alternative and this accelerated the research and investment on AFM spintronics. AFM materials are known with their magnetic toughness due to zero net magnetization in bulk and promising bit per volume ratio thanks to their two spin lattices pointing in opposite directions. In this study, our aim is to achieve current induced manipulation of antiferromagnetic moments. Though there are multiple suggested ways for AFM magnetization manipulation, we study DC electrical transport experiments where by we utilize spin-orbit torque (SOT) effect on metallic AFM materials (IrMn4,IrMn3FeMn). The underlying mechanism for spin manipulation is a mixture of Spin Hall Effect (SHE) and interfacial Rashba effect (IRE). We start our investigation with bi-layers of high SOC heavy metals (Pt, Ta) and AFM metal(IrMn4,FeMn) hetero structures of [HM/AFM]. Following these experiments, we also investigate the cumulative properties of SOT effect by demonstrating DC electrical transport experiments on HM/AFM/HM trilayer hetero structures and stacks of [HM/AFM/HM] × n, (where n=2,3,4 etc.). These results will help to improve understanding of the nature of electrical manipulation of AFM spin and determine the conditions to use them as spintronic devices.
2022-01-01T00:00:00ZAnalytic solutions of scalar field cosmology with minimal and nonminimal coupling and deformed discrete and finite quantum systems
http://digitalarchive.boun.edu.tr/handle/123456789/19828
Analytic solutions of scalar field cosmology with minimal and nonminimal coupling and deformed discrete and finite quantum systems
İldeş, Medine.
In this thesis first, we study analytic solutions of cosmology. We investigate the most general cosmological model with real scalar field which is minimally coupled to gravity and Brans- Dicke cosmology. Field equations consist of three differential equations. We switch independent variable from time to scale factor by change of variable ˙a/a = H(a). Thus a new set of differential equations are analytically solvable with known methods. a(t) can be explicitly found as long as methods of integration techniques are available. We investigate the dynamics of the universe at early times as well as at late times in light of these formulas. We find mathematical machinery which turns on and turns off early accelerated expansion. On the other hand late time accelerated expansion is explained by cosmic domain walls. φ 4 potential is studied in Brans-Dicke Cosmology. In this thesis we also study discrete and finite quantum systems. We define a deformed kinetic energy operator for a discrete position space with a finite number of points. The structure may be either periodic or nonperiodic with well-defined end points. It is shown that for the nonperiodic case the translation operator becomes nonunitary due to the end points. This uniquely defines an algebra which has the desired unique representation. Energy eigenvalues and energy wave functions for both cases are found. In addition, we uncover the mathematical structure of the Schwinger algebra and introduce almost unitary Schwinger operators which are derived by considering translation operators on a finite lattice.
2022-01-01T00:00:00ZPerturbative and non-perturbative physics from singularities
http://digitalarchive.boun.edu.tr/handle/123456789/19827
Perturbative and non-perturbative physics from singularities
Pazarbaşı, Cihan.
A function that representing a physical quantity has singularities which con tain perturbative or non-perturbative information about the physical system under investigation. Moreover, the theory of resurgence tells us that these perturbative and non-perturbative parts are intimately connected and it is possible to use one of them to obtain the other one. In this thesis, we combine these two ideas with a focus on the functions formulated in integral representations. Specifically, first consider ing two different examples on the semi-classical expansion in quantum mechanics and the pair production problem in electromagnetic backgrounds, we will concentrate on the quantum action which we express in the Schwinger’s integral representation. We will show that the perturbative and non-perturbative information about the physical system is hidden in singularities of the propagator TrU(t). The way we obtain the non-perturbative one is very similar to the Borel method which is used to handle the divergent perturbation series. Contrary to the Borel method, by probing the singular ities of TrU(t) directly and using the iε prescription, we will be able to prevent the Borel ambiguity problem in the physical cases that it leads to the violation of the uni tarity. Later, we will turn our attention to the renormalon problem in non-relativistic quantum mechanics. After presenting the existence of the renormalon divergence in a scattering problem with a background potential consisting of 2D δ-potential perturbed with a tilted 1D δ-potential, we will argue that the Borel ambiguity in the summation of the divergent series can be prevented again by a careful application of the iε pre scription and the resulting non- perturbative contribution due to the renormalon obeys the causality condition.
2022-01-01T00:00:00ZThe role of trigger waves in cancer angiogenesis
http://digitalarchive.boun.edu.tr/handle/123456789/19826
The role of trigger waves in cancer angiogenesis
Debir, Birses.
This study includes mathematical modeling of biological observations and numer ical solutions of these models. Our study focused on different phenomenons, including; vessel formation, intracellular calcium ion concentration, traveling wave solutions, and cytosol elasticity. Understanding signaling in diseases is essential for a proper response. For this reason, understanding the secondary messenger signaling that mechanisms of ten prefer to use and their interaction with the mechanisms enables the system’s re sponse to be better understood. This study examined the interaction of angiogenesis, a mechanism that contributes to tumor growth, and cytosolic calcium ion, an intracel lular secondary messenger. Therefore, we simulated a mathematical model involving essential angiogenesis and calcium homeostasis elements using previously used models. In our simulations, we developed two and multiple cell scenarios and examined the results of our system in distributions of different angiogenic stimulus uptake. Since angiogenesis requires the cell to move in a specific direction, we simulated the cytosolic gelation- solution mechanism, inspired by another model used in the literature. We examined the condition under which the wave direction persists in the traveling wave configuration.
2022-01-01T00:00:00Z