Browsing by Subject "Scattering theory"
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Item Open Access Numerical solution of time-dependent three-particle Faddeev equations: calculation of rearrangement S matrices(American Physical Society, 2020) Kuruoğlu, Zeki C.The time-dependent Faddeev equations (TDFEs) are employed for the first time as a computational tool for three-particle scattering problems. Rearrangement transition amplitudes over a wide range of collision energies are extracted from a single numerical wave-packet solution of the TDFE. To numerically solve the TDFE in momentum space for a given initial wave packet, finite-element-type discretizations of Jacobi momenta in terms of local basis functions is employed to convert the TDFE into a set of first-order differential equations in time. Central difference formula for the time derivative is used for the time propagation step. Two forms of TDFE are considered and incorporation of permutational symmetry for three identical particles into these equations is carried out. The proposed method is tested on a three-body model that is often used as a benchmark to compare different computational approaches to three-particle problem. Rearrangement S-matrix elements obtained from the analysis of the wave-packet solution of TDFE at asymptotic times are compared with the results of well-established time-independent methods. These results establish that the TDFE approach is a viable and competitive addition to the existing arsenal of computational methods for the three-body scattering problem.Item Open Access Resonances in the electromagnetic scattering by very large finite-periodic grids of circular dielectric wires(IEEE, 2010-06) Natarov, D. M.; Benson, T. M.; Altıntaş, Ayhan; Sauleau, R.; Nosich, I.Diffraction of plane waves by infinite gratings is a classical research topic in the scattering theory. Using the Floquet theorem, one can reduce the infinite grating problem to the one-period problem. A characteristic feature of infinite-grating scattering is the drastic transformation of the scattering pattern and reflectance intensity if, in the process of changing the frequency or the angle of incidence, one of the Floquet harmonics is "passing over horizon." This phenomenon was first explained by Rayleigh [1] who studied theoretically the "anomalies" discovered experimentally by Wood [2]. In the simplest case of the normal incidence, these Rayleigh-Wood anomalies are observed if the period of the grating is multiple to the wavelength. © 2010 IEEE.Item Open Access Thermoelectric efficiency in model nanowires(Bilkent University, 2013) Badalov, SabuhiNowadays, the use of thermoelectric semiconductor devices are limited by their low efficiencies. Therefore, there is a huge amount of research effort to get high thermoelectric efficient materials with a fair production value. To this end, one important possibility for optimizing a material’s thermoelectric properties is reshaping their geometry. The main purpose of this thesis is to present a detailed analysis of thermoelectric efficiency of 2 lead systems with various geometries in terms of linear response theory, as well as 3 lead nanowire system in terms of the linear response and nonlinear response theories. The thermoelectric efficiency both in the linear response and nonlinear response regime of a model nanowire was calculated based on Landauer-B¨uttiker formalism. In this thesis, first of all, the electron transmission probability of the system at the hand, i.e. 2 lead or 3 lead systems are investigated by using R-matrix theory. Next, we make use of these electron transmission probability of model systems to find thermoelectric transport coefficients in 2 lead and 3 lead nanowires. Consequently, the effect of inelastic scattering is incorporated with a fictitious third lead in the 3 lead system. The efficiency at maximum power is especially useful to define the optimum working conditions of nanowire as a heat engine. Contrary to general expectation, increasing the strength of inelastic scattering is shown to be a means of making improved thermoelectric materials. A controlled coupling of the nanowire to a phonon reservoir for instance could be a way to increase the efficiency of nanowires for better heat engines.