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Search Results: 1 - 10 of 111928 matches for " Durdu O. Guney "
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Negative Refraction Gives Rise to the Klein Paradox
Durdu O. Guney,David A. Meyer
Physics , 2009, DOI: 10.1103/PhysRevA.79.063834
Abstract: Electromagnetic negative refraction in metamaterials has attracted increasingly great interest, since its first experimental verification in 2001. It potentially leads to the applications superior to conventional devices including compact antennas for mobile stations, imaging beyond the diffraction limit, and high-resolution radars, not to mention the anamolous wave propagation in fundamental optics. Here, we report how metamaterials could be used to simulate the "negative refraction of spin-zero particles interacting with a strong potential barrier", which gives rise to the Klein paradox--a counterintuitive relativistic process. We address the underlying physics of analogous wave propagation behaviours in those two entirely different domains of quantum and classical.
Intra-connected three-dimensionally isotropic bulk negative index photonic metamaterial
Durdu O. Guney,Thomas Koschny,Costas M. Soukoulis
Physics , 2010, DOI: 10.1364/OE.18.012348
Abstract: Isotropic negative index metamaterials (NIMs) are highly desired, particularly for the realization of ultra-high resolution lenses. However, existing isotropic NIMs function only two-dimensionally and cannot be miniaturized beyond microwaves. Direct laser writing processes can be a paradigm shift toward the fabrication of three-dimensionally (3D) isotropic bulk optical metamaterials, but only at the expense of an additional design constraint, namely connectivity. Here, we demonstrate with a proof of-principle design that the requirement connectivity does not preclude fully isotropic left-handed behavior. This is an important step towards the realization of bulk 3D isotropic NIMs at optical wavelengths.
Reducing Ohmic Losses in Metamaterials by Geometric Tailoring
Durdu O. Guney,Thomas Koschny,Costas M. Soukoulis
Physics , 2010, DOI: 10.1103/PhysRevB.80.125129
Abstract: Losses in metamaterials render the applications of such exotic materials less practical unless an efficient way of reducing them is found. We present two different techniques to reduce ohmic losses at both lower and higher frequencies, based on geometric tailoring of the individual magnetic constituents. We show that an increased radius of curvature, in general, leads to the least losses in metamaterials. Particularly at higher THz frequencies, bulky structures outperform the planar structures.
Surface Plasmon Driven Electric and Magnetic Resonators for Metamaterials
Durdu O. Guney,Thomas Koschny,Costas M. Soukoulis
Physics , 2011, DOI: 10.1103/PhysRevB.83.045107
Abstract: Using interplay between surface plasmons and metamaterials, we propose a new technique for novel metamaterial designs. We show that surface plasmons existing on thin metal surfaces can be used to "drive" non-resonant structures in their vicinity to provide new types of electric and magnetic resonators. These resonators strictly adhere to surface plasmon dispersion of the host metal film. The operating frequency of the resultant metamaterials can be scaled to extremely high frequencies, otherwise not possible with conventional split-ring-resonator-based designs. Our approach opens new possibilities for theory and experiment in the interface of plasmonics and metamaterials to harvest many potential applications of both fields combined.
Magneto-optical metamaterial
Mehdi Sadatgol,Mahfuzur Rahman,Ebrahim Forati,Miguel Levy,Durdu O. Guney
Physics , 2015,
Abstract: We propose a new class of metamaterials called magneto-optical metamaterials that offer enhanced angle of rotation in polarization compared to bulk magneto-optical materials. In the proposed approach, the permittivity tensor of a magneto-optical material is tailored by embedded wire meshes behaving as artificial plasma. We have shown that the angle of rotation in the magneto-optical metamaterial can be enhanced up to 9 times compared to bulk magneto-optical material alone while the polarization extinction ratio remains below -20dB and insertion loss is less than 1.5dB.
Optical Absorption in Nano-Structures: Classical and Quantum Models
Anand Kulkarni,Durdu Guney,Ankit Vora
ISRN Nanomaterials , 2013, DOI: 10.1155/2013/504341
Abstract: In the last decade, nano-structured materials have gained a significant interest for applications in solar cells and other optical and opto-electronic devices. Due to carrier confinement, the absorption characteristics in these structures are quite different from the absorption in bulk materials and thin films. Optical absorption coefficients of a silicon nano-wire are obtained based on a semi-classical model where the photon-electron interaction is described by the interaction of an electromagnetic wave with the electrons in the valence band of a semiconductor. The absorption characteristics showed enhanced optical absorption but no resonant peaks. In our modified model, we have identified optically active inter band transitions by performing electronic structure calculations on unit cells of nano-dimensions. The absorption spectrum obtained here shows explicit excitonic processes. This absorption is tunable from the visible region to near UV portion of the solar spectrum. In our previous work on thin films (100?nm) of ITO, we have used classical Drude model to describe free electron absorption. Using the imaginary part of the calculated complex dielectric function, we have plotted the absorption coefficient versus wavelength of the photon and compared with the experimental data showing good agreement between theory and experiment. 1. Introduction The efficiency of a solar cell is dependent on the optical absorption of the material used to fabricate the solar cell. In bulk crystalline materials and even in thin films, the bulk absorption coefficient is the most important parameter that determines the optical absorption. Classical models such as Drude model or Drude-Lorentz model describe the optical absorption based on the complex dielectric function [1, 2]. This approach works very well for the absorption of photons by the electrons inside a band, for example, conduction band. However, from band to band excitation of electrons, a detailed understanding of the band structure of the material is essential. To calculate band structure in semiconductors, one has to invoke quantum mechanical models using Schrodinger's wave equation [3, 4]. In this paper, we illustrate the applications of classical and quantum models with examples from our past research on indium tin oxide (ITO) thin films [5, 6], silicon quantum dots [7], and silicon nanowires [8]. In nanostructures, excitons play a dominant role [9, 10]. 2. Classical Models 2.1. Drude Model When the energy of incident radiation is less than the band gap energy of a semiconductor (typically 1?eV), free
A Review Study on the Marriage and Relationship Research in Turkey  [PDF]
Sevgi Guney
Psychology (PSYCH) , 2011, DOI: 10.4236/psych.2011.25077
Abstract: The aim of this study is to examine the studies on marriage and relationship in Turkey.127 studies (82 research studies and 45 scale studies) published and unpublished between 1997-2008 were examined toprovide an overview for professionals about the marriage and relationship research done in Turkey. The studies were reviewed in terms of their general characteristics, conceptual frameworks and methods of investigation. The results were discussed and suggestions were given in terms of future directions.
Relationship Between Some Polymorphic Parameters and Performances in Damascus Goats
O. Guney,O. Ozuyanik,O. Torun,M. Gorgulu
Pakistan Journal of Biological Sciences , 2003,
Abstract: The objective of this study was to determine the types of haemoglobin and transferrin found in Damascus goats and demonstrate their relationship with different performance traits. The Hb B allele was observed in the Damascus goats studied. No significant deviation from Hardy-Weinberg equilibrium was observed. We observed nine genotypes, namely Tf AA, AC, AD, BB, BC, BD, CC, CD, DD; C and D were the two most commonly occuring alleles at the locus and A was the rare -globin variant. The frequencies of Tf C and D were higher than those of the other transferrin genotypes. There was no significant effect of transferrin genotype on performance (p>0.05).
Tzanck Cytology in Diagnosis of Autoimmune Bullous Diseases
Murat Durdu
Turkderm , 2011,
Abstract: Tzanck smear test is a simple, rapid, repeatable, and inexpensive diagnostic method based on the investigation of characteristics of individual cells. For diagnosis of cutaneous diseases, cytology was first used by Arnault Tzanck in 1947. After this date, Tzanck cytology has been used in the diagnosis of various erosive-vesiculobullous, nodular, and tumoral skin lesions. In daily dermatology practice, the most common use areas of cytology are diagnosis of herpetic infections, cutaneous leishmaniasis, leprosy, and autoimmune bullous diseases. The purpose of cytology in autoimmune bullous diseases is to rapidly distinguish pemphigus from subepidermal bullous disease. In this review article, taking and staining methods of cytologic specimen for the diagnosis of autoimmune bullous diseases, and the cytologic findings have been reviewed.
Tzanck Cytology in Diagnosis of Autoimmune Bullous Diseases Sürekli E itim
Murat Durdu
Turkderm , 2011,
Abstract: Tzanck smear test is a simple, rapid, repeatable, and inexpensive diagnostic method based on the investigation of characteristics of individual cells. For diagnosis of cutaneous diseases, cytology was first used by Arnault Tzanck in 1947. After this date, Tzanck cytology has been used in the diagnosis of various erosive-vesiculobullous, nodular, and tumoral skin lesions. In daily dermatology practice, the most common use areas of cytology are diagnosis of herpetic infections, cutaneous leishmaniasis, leprosy, and autoimmune bullous diseases. The purpose of cytology in autoimmune bullous diseases is to rapidly distinguish pemphigus from subepidermal bullous disease. In this review article, taking and staining methods of cytologic specimen for the diagnosis of autoimmune bullous diseases, and the cytologic findings have been reviewed. (Turkderm 2011; 45 Suppl 1: 39-43)
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