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Search Results: 1 - 10 of 123 matches for " Yurtsever Soysal "
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Mathematical Modeling and Evaluation of Microwave Drying Kinetics of Mint (Mentha spicata L.)
Yurtsever Soysal
Journal of Applied Sciences , 2005,
Abstract: The overall objective of this research was to improve the basic knowledge about the important parameters of the microwave drying of leafy herbs. Specific objectives were to determine the effects of microwave power density on drying time and drying rate, improve the product quality in terms of colour, compare the fitting ability of several drying equations to express the drying kinetics of mint leaves with the most suitable drying model and to describe the whole process in a general drying model by embedding the effects of microwave power density on the coefficients of the best fitting model for the purpose of simulation and scaling up of the process. The microwave drying of mint (Mentha spicata L.) leaves have been studied at different operating parameters of drying using mathematical models. Experiments were conducted using seven levels of microwave power density, 4, 5, 6, 7, 8, 9 and 10 W g -1. Eleven mathematical models describing drying kinetics have been investigated.
Anatomy of Taxpayers' Rights: Case Study of Turkey
Hatice Yurtsever
Pakistan Journal of Social Sciences , 2012, DOI: 10.3923/pjssci.2010.334.346
Abstract: Today it is observed that upon globalization, social structure has changed and that human rights have stood out. Regarding taxpayers rights which are considered within the scope of human rights, informative brochures on what these legal rights are have been prepared and consultancy units have been established in many countries for a long period of time. While a literature search about the concept of taxpayers rights and the practices in various countries are outlined, the current views of the European Court of Human Rights on this matter are also discussed in the study. It is observed that more recent legal regulations have been made in Turkey than in other countries which are under examination regarding the rights of taxpayers during taxation. Although, it is intended to form a legal ground for this matter with the regulations made within this framework, it is also observed that there are several problems and shortcomings in practice. While the issue of taxpayers rights in Turkey is comprehensively addressed in the study, the settlement of existing problems is discussed.
Modeling lossy propagation of non-classical light
Ulvi Yurtsever
Physics , 2009,
Abstract: The lossy propagation law (generalization of Lambert-Beer's law for classical radiation loss) for non-classical, dual-mode entangled states is derived from first principles, using an infinite-series of beam splitters to model continuous photon loss. This model is general enough to accommodate stray-photon noise along the propagation, as well as amplitude attenuation. An explicit analytical expression for the density matrix as a function of propagation distance is obtained for completely general input states with bounded photon number in each mode. The result is analyzed numerically for various examples of input states. For N00N state input, the loss of coherence and entanglement is super exponential as predicted by a number of previous studies. However, for generic input states, where the coefficients are generated randomly, the decay of coherence is very different; in fact no worse than the classical Beer-Lambert law. More surprisingly, there is a plateu at a mid-range interval in propagation distance where the loss is in fact sub-classical, following which it resumes the classical rate. The qualitative behavior of the decay of entanglement for two-mode propagation is also analyzed numerically for ensembles of random states using the behavior of negativity as a function of propagation distance.
Fundamental Limits on the Speed of Evolution of Quantum States
Ulvi Yurtsever
Physics , 2009, DOI: 10.1088/0031-8949/82/03/035008
Abstract: This paper reports on some new inequalities of Margolus-Levitin-Mandelstam-Tamm-type involving the speed of quantum evolution between two orthogonal pure states. The clear determinant of the qualitative behavior of this time scale is the statistics of the energy spectrum. An often-overlooked correspondence between the real-time behavior of a quantum system and the statistical mechanics of a transformed (imaginary-time) thermodynamic system appears promising as a source of qualitative insights into the quantum dynamics.
A note on the averaged null energy condition in quantum field theory
Ulvi Yurtsever
Physics , 1995, DOI: 10.1103/PhysRevD.52.R564
Abstract: The averaged null energy condition has been recently shown to hold for linear quantum fields in a large class of spacetimes. Nevertheless, it is easy to show by using a simple scaling argument that ANEC as stated cannot hold generically in curved four-dimensional spacetime, and this scaling argument has been widely interpreted as a death-blow for averaged energy conditions in quantum field theory. In this note I propose a simple generalization of ANEC, in which the right-hand-side of the ANEC inequality is replaced by a finite (but in general negative) state-independent lower bound. As long as attention is focused on asymptotically well-behaved spacetimes, this generalized version of ANEC is safe from the threat of the scaling argument, and thus stands a chance of being generally valid in four-dimensional curved spacetime. I argue that when generalized ANEC holds, it has implications for the non-negativity of total energy and for singularity theorems similar to the implications of ANEC. In particular, I show that if generalized ANEC is satisfied in static traversable wormhole spacetimes (which is likely but remains to be shown), then macroscopic wormholes (but not necessarily microscopic, Planck-size wormholes) are ruled out by quantum field theory.
Geometry of chaos in the two-center problem in General Relativity
Ulvi Yurtsever
Physics , 1994, DOI: 10.1103/PhysRevD.52.3176
Abstract: The now-famous Majumdar-Papapetrou exact solution of the Einstein-Maxwell equations describes, in general, $N$ static, maximally charged black holes balanced under mutual gravitational and electrostatic interaction. When $N=2$, this solution defines the two-black-hole spacetime, and the relativistic two-center problem is the problem of geodesic motion on this static background. Contopoulos and a number of other workers have recently discovered through numerical experiments that in contrast with the Newtonian two-center problem, where the dynamics is completely integrable, relativistic null-geodesic motion on the two black-hole spacetime exhibits chaotic behavior. Here I identify the geometric sources of this chaotic dynamics by first reducing the problem to that of geodesic motion on a negatively curved (Riemannian) surface.
A remark on kinks and time machines
Ulvi Yurtsever
Physics , 1994, DOI: 10.1007/BF02108071
Abstract: We describe an elementary proof that a manifold with the topology of the Politzer time machine does not admit a nonsingular, asymptotically flat Lorentz metric.
The averaged null energy condition and difference inequalities in quantum field theory
Ulvi Yurtsever
Physics , 1994, DOI: 10.1103/PhysRevD.51.5797
Abstract: Recently, Larry Ford and Tom Roman have discovered that in a flat cylindrical space, although the stress-energy tensor itself fails to satisfy the averaged null energy condition (ANEC) along the (non-achronal) null geodesics, when the ``Casimir-vacuum" contribution is subtracted from the stress-energy the resulting tensor does satisfy the ANEC inequality. Ford and Roman name this class of constraints on the quantum stress-energy tensor ``difference inequalities." Here I give a proof of the difference inequality for a minimally coupled massless scalar field in an arbitrary two-dimensional spacetime, using the same techniques as those we relied on to prove ANEC in an earlier paper with Robert Wald. I begin with an overview of averaged energy conditions in quantum field theory.
The origin of spacetime topology and generalizations of quantum field theory
Ulvi Yurtsever
Physics , 1993, DOI: 10.1088/0264-9381/11/4/017
Abstract: The research effort reported in this paper is directed, in a broad sense, towards understanding the small-scale structure of spacetime. The fundamental question that guides our discussion is ``what is the physical content of spacetime topology?" In classical physics, if spacetime, $(X, \tau )$, has sufficiently regular topology, and if sufficiently many fields exist to allow us to observe all continuous functions on $X$, then this collection of continuous functions uniquely determines both the set of points $X$ and the topology $\tau$ on it. To explore the small-scale structure of spacetime, we are led to consider the physical fields (the observables) not as classical (continuous functions) but as quantum operators, and the fundamental observable as not the collection of all continuous functions but the local algebra of quantum field operators. In pursuing our approach further, we develop a number of generalizations of quantum field theory through which it becomes possible to talk about quantum fields defined on arbitrary topological spaces. Our ultimate generalization dispenses with the fixed background topological space altogether and proposes that the fundamental observable should be taken as a lattice (or more specifically a ``frame," in the sense of set theory) of closed subalgebras of an abstract $C^{\ast}$ algebra. Our discussion concludes with the definition and some elementary
Algebraic approach to quantum field theory on non-globally-hyperbolic spacetimes
Ulvi Yurtsever
Physics , 1993, DOI: 10.1088/0264-9381/11/4/016
Abstract: The mathematical formalism for linear quantum field theory on curved spacetime depends in an essential way on the assumption of global hyperbolicity. Physically, what lie at the foundation of any formalism for quantization in curved spacetime are the canonical commutation relations, imposed on the field operators evaluated at a global Cauchy surface. In the algebraic formulation of linear quantum field theory, the canonical commutation relations are restated in terms of a well-defined symplectic structure on the space of smooth solutions, and the local field algebra is constructed as the Weyl algebra associated to this symplectic vector space. When spacetime is not globally hyperbolic, e.g. when it contains naked singularities or closed timelike curves, a global Cauchy surface does not exist, and there is no obvious way to formulate the canonical commutation relations, hence no obvious way to construct the field algebra. In a paper submitted elsewhere, we report on a generalization of the algebraic framework for quantum field theory to arbitrary topological spaces which do not necessarily have a spacetime metric defined on them at the outset. Taking this generalization as a starting point, in this paper we give a prescription for constructing the field algebra of a (massless or massive) Klein-Gordon field on an arbitrary background spacetime. When spacetime is globally hyperbolic, the theory defined by our construction coincides with the ordinary Klein-Gordon field theory on a
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