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Istanbul, Turkey

Koç University is a non-profit private university in Istanbul, Turkey. It started education in temporary buildings in İstinye in 1993, and moved to its current Rumeli Feneri campus near Sarıyer in 2000. University currently consists of Colleges of Social science and Humanities, Administrative science and Economics, Science, Engineering, Law, Nursing and Medicine. Koç University offers 22 undergraduate, 31 graduate and 16 PhD programs. Wikipedia.


Mostafazadeh A.,Koc University
Physical Review Letters | Year: 2013

We introduce a notion of spectral singularity that applies for a general class of nonlinear Schrödinger operators involving a confined nonlinearity. The presence of the nonlinearity does not break the parity-reflection symmetry of spectral singularities but makes them amplitude dependent. Nonlinear spectral singularities are, therefore, associated with a resonance effect that produces amplified waves with a specific amplitude-wavelength profile. We explore the consequences of this phenomenon for a complex δ-function potential that is subject to a general confined nonlinearity. © 2013 American Physical Society. Source


Mostafazadeh A.,Koc University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

For a general complex scattering potential defined on a real line, we show that the equations governing invisibility of the potential are invariant under the combined action of parity and time-reversal (PT) transformation. We determine the PT-symmetric as well as non-PT-symmetric invisible configurations of an easily realizable exactly solvable model that consists of a two-layer planar slab consisting of optically active material. Our analysis shows that although PT symmetry is neither necessary nor sufficient for the invisibility of a scattering potential, it plays an important role in the characterization of the invisible configurations. A byproduct of our investigation is the discovery of certain configurations of our model that are effectively reflectionless in a spectral range as wide as several hundred nanometers. © 2013 American Physical Society. Source


Mostafazadeh A.,Koc University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We show that in one dimension the transfer matrix M of any scattering potential v coincides with the S matrix of an associated time-dependent non-Hermitian 2×2 matrix Hamiltonian H(τ). If v is real valued, H(τ) is pseudo-Hermitian and its exceptional points correspond to the classical turning points of v. Applying time-dependent perturbation theory to H(τ) we obtain a perturbative series expansion for M and use it to study the phenomenon of unidirectional invisibility. In particular, we establish the possibility of having multimode unidirectional invisibility with wavelength-dependent direction of invisibility and construct various physically realizable optical potentials possessing this property. We also offer a simple demonstration of the fact that the off-diagonal entries of the first-order Born approximation for M determine the form of the potential. This gives rise to a perturbative inverse scattering scheme that is particularly suitable for optical design. As a simple application of this scheme, we construct an infinite-range unidirectionally invisible potential. © 2014 American Physical Society. Source


Ozsomer A.,Koc University
Journal of International Marketing | Year: 2012

By studying consumer samples in an emerging market, Turkey, and two mature markets, Singapore and Denmark, the author tests the chain of relationships that drive consumers' likelihood of purchasing the global brand in the presence of a local brand in a linear structural relations framework. The results indicate that perceived brand globalness is positively related to local iconness in an emerging market, but the relationship is negative in advanced markets. Developing local iconness helps build the perception of prestige in all three markets. Furthermore, local iconness is positively related to local brand quality perceptions in the culturally grounded categories of food in an emerging market, whereas in nonfood categories, local iconness has no connection to quality. In terms of cross-effects, as expected, the perceived quality of the local brand is negatively associated with global brand purchase likelihood in all markets and categories studied. In contrast, local brand prestige dampens global brand purchase likelihood for older consumers in an emerging market. The article concludes with implications for global and local brand managers. ©2012, American Marketing Association. Source


Atomically detailed simulations were used to assess the performance of zeolite imidazolate frameworks (ZIFs) for separation of CH4/H 2, CO2/CH4, and CO2/H2 mixtures to provide information for material selection in adsorbent and membrane designs. Adsorption isotherms and self-diffusivities of gas mixtures in ZIFs were computed using grand canonical Monte Carlo and equilibrium molecular dynamics simulations, respectively. Adsorption selectivity, diffusion selectivity, and permeation selectivity of ZIF membranes were calculated on the basis of the results of atomistic simulations. Selectivity and permeability of gases through ZIF membranes were compared to well-known zeolite membranes and metal organic framework (MOF) membranes. Results showed that ZIF-3 and ZIF-10 exhibit significantly higher adsorption and permeation selectivities for separation of all gas mixtures as compared to widely studied MOF membranes. © 2010 American Chemical Society. Source

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