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Search Results: 1 - 10 of 928 matches for " Gregor Veble "
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Dispersion interactions in stratified anisotropic and optically active media at all separations
Gregor Veble,Rudolf Podgornik
Physics , 2009, DOI: 10.1103/PhysRevB.80.075422
Abstract: We propose a method to calculate dispersion interactions in a system composed of a one dimensional layering of finite thickness anisotropic and optically active slabs. The result is expressed within the algebra of 4x4 matrices and is demonstrated to be equivalent to the known limits of isotropic, nonretarded and uniaxial dispersion interactions. The method is also capable of handling dielectric media with smoothly varying anisotropy axes.
A hybrid method for calculation of Ruelle-Pollicott resonances
Martin Horvat,Gregor Veble
Physics , 2009, DOI: 10.1088/1751-8113/42/46/465101
Abstract: We present a numerical method for calculation of Ruelle-Pollicott resonances of dynamical systems. It constructs an effective coarse-grained propagator by considering the correlations of multiple observables over multiple timesteps. The method is compared to the usual approaches on the example of the perturbed cat map and is shown to be numerically efficient and robust.
The boundary element approach to Van der Waals interactions
Gregor Veble,Rudolf Podgornik
Physics , 2007, DOI: 10.1140/epje/i2007-10211-7
Abstract: We develop a boundary element method to calculate Van der Waals interactions for systems composed of domains of spatially constant dielectric response. We achieve this by rewriting the interaction energy expression exclusively in terms of surface integrals of surface operators. We validate this approach in the Lifshitz case and give numerical results for the interaction of two spheres as well as the van der Waals self-interaction of a uniaxial ellipsoid. Our method is simple to implement and is particularly suitable for a full, non-perturbative numerical evaluation of non-retarded van der Waals interactions between objects of a completely general shape.
Comparison of the DFT and field approaches to Van der Waals interactions in planparallel geometry
Gregor Veble,Rudolf Podgornik
Physics , 2006, DOI: 10.1103/PhysRevB.75.155102
Abstract: We establish a general equivalence between van der Waals interaction energies within the formalism of the non-local van der Waals functional of the density functional theory and within the formalism of the field approach based on the secular determinants of the electromagnetic field modes. We then compare the two methods explicitly in the case of a planparallel geometry with a continuously varying dielectric response function and show that their respective numerical implementations are not equivalent. This allows us to discuss the merits of the two approaches and possible advantages of either method in a simple model calculation.
Study of Spectral Statistics of Classically Integrable Systems
Marko Robnik,Gregor Veble
Physics , 2000, DOI: 10.1143/PTPS.139.544
Abstract: In this work we present the results of a study of spectral statistics for a classically integrable system, namely the rectangle billiard. We show that the spectral statistics are indeed Poissonian in the semiclassical limit for almost all such systems, the exceptions being the atypical rectangles with rational squared ratio of its sides, and of course the energy ranges larger than L_{\rm max}=\hbar / T_0$, where $T_0$ is the period of the shortest periodic orbit of the system, however $L_{\rm max} \to \infty$ when $E \to \infty$.
Faster than Lyapunov decays of classical Loshcmidt echo
Gregor Veble,Tomaz Prosen
Physics , 2003, DOI: 10.1103/PhysRevLett.92.034101
Abstract: We show that in the classical interaction picture the echo-dynamics, namely the composition of perturbed forward and unperturbed backward hamiltonian evolution, can be treated as a time-dependent hamiltonian system. For strongly chaotic (Anosov) systems we derive a cascade of exponential decays for the classical Loschmidt echo, starting with the leading Lyapunov exponent, followed by a sum of two largest exponents, etc. In the loxodromic case a decay starts with the rate given as twice the largest Lyapunov exponent. For a class of perturbations of symplectic maps the echo-dynamics exhibits a drift resulting in a super-exponential decay of the Loschmidt echo.
Classical Loschmidt echo in chaotic many-body systems
Gregor Veble,Tomaz Prosen
Physics , 2005, DOI: 10.1103/PhysRevE.72.025202
Abstract: General theoretic approach to classical Loschmidt echoes in chaotic systems with many degrees of freedom is developed. For perturbations which affect essentially all degrees of freedom we find a doubly exponential decay with the rate determined by the largest Lyapunov exponent. The scaling of the decay rate on the perturbation strength depends on whether the initial phase-space density is continuous or not.
Decay of the classical Loschmidt echo in integrable systems
Giuliano Benenti,Giulio Casati,Gregor Veble
Physics , 2003, DOI: 10.1103/PhysRevE.68.036212
Abstract: We study both analytically and numerically the decay of fidelity of classical motion for integrable systems. We find that the decay can exhibit two qualitatively different behaviors, namely an algebraic decay, that is due to the perturbation of the shape of the tori, or a ballistic decay, that is associated with perturbing the frequencies of the tori. The type of decay depends on initial conditions and on the shape of the perturbation but, for small enough perturbations, not on its size. We demonstrate numerically this general behavior for the cases of the twist map, the rectangular billiard, and the kicked rotor in the almost integrable regime.
Confined polymer nematics: order and packing in a nematic drop
Daniel Sven?ek,Gregor Veble,Rudolf Podgornik
Physics , 2010,
Abstract: We investigate the tight packing of nematic polymers inside a confining hard sphere. We model the polymer {\sl via} the continuum Frank elastic free energy augmented by a simple density dependent part as well as by taking proper care of the connectivity of the polymer chains when compared with simple nematics. The free energy {\sl ansatz} is capable of describing an orientational ordering transition within the sample between an isotropic polymer solution and a polymer nematic phase. We solve the Euler-Lagrange equations numerically with the appropriate boundary conditions for the director and density field and investigate the orientation and density profile within a sphere. Two important parameters of the solution are the exact locations of the beginning and the end of the polymer chain. Pending on their spatial distribution and the actual size of the hard sphere enclosure we can get a plethora of various configurations of the chain exhibiting different defect geometry.
Expanded boundary integral method and chaotic time-reversal doublets in quantum billiards
Gregor Veble,Tomaz Prosen,Marko Robnik
Physics , 2006, DOI: 10.1088/1367-2630/9/1/015
Abstract: We present the expanded boundary integral method for solving the planar Helmholtz problem, which combines the ideas of the boundary integral method and the scaling method and is applicable to arbitrary shapes. We apply the method to a chaotic billiard with unidirectional transport, where we demonstrate existence of doublets of chaotic eigenstates, which are quasi-degenerate due to time-reversal symmetry, and a very particular level spacing distribution that attains a chaotic Shnirelman peak at short energy ranges and exhibits GUE-like statistics for large energy ranges. We show that, as a consequence of such particular level statistics or algebraic tunneling between disjoint chaotic components connected by time-reversal operation, the system exhibits quantum current reversals.
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