311,216 research outputs found

    Nuclear Flow in Consistent Boltzmann Algorithm Models

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    We investigate the stochastic Direct Simulation Monte Carlo method (DSMC) for numerically solving the collision-term in heavy-ion transport theories of the Boltzmann-Uehling-Uhlenbeck (BUU) type. The first major modification we consider is changes in the collision rates due to excluded volume and shadowing/screening effects (Enskog theory). The second effect studied by us is the inclusion of an additional advection term. These modifications ensure a non-vanishing second virial and change the equation of state for the scattering process from that of an ideal gas to that of a hard-sphere gas. We analyse the effect of these modifications on the calculated value of directed nuclear collective flow in heavy ion collisions, and find that the flow slightly increases.Comment: 12 pages, REVTeX, figures available in PostScript from the authors upon reques

    Quantum corrections to thermodynamics of quasitopological black holes

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    Based on the modification to area-law due to thermal fluctuation at small horizon radius, we investigate the thermodynamics of charged quasitopological and charged rotating quasitopological black holes. In particular, we derive the leading-order corrections to the Gibbs free energy, charge and total mass densities. In order to analyse the behavior of the thermal fluctuations on the thermodynamics of small black holes, we draw a comparative analysis between the first-order corrected and original thermodynamical quantities. We also examine the stability and bound points of such black holes under effect of leading-order corrections.Comment: 15 pages, 20 captioned figures, to appear in Phys. Lett.

    Locality, Causality and Noncommutative Geometry

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    We analyse the causality condition in noncommutative field theory and show that the nonlocality of noncommutative interaction leads to a modification of the light cone to the light wedge. This effect is generic for noncommutative geometry. We also check that the usual form of energy condition is violated and propose that a new form is needed in noncommutative spacetime. On reduction from light cone to light wedge, it looks like the noncommutative dimensions are effectively washed out and suggests a reformulation of noncommutative field theory in terms of lower dimensional degree of freedom. This reduction of dimensions due to noncommutative geometry could play a key role in explaining the holographic property of quantum gravity.Comment: 16 pages, LaTeX, 4 figure

    Inflationary Predictions and Moduli Masses

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    A generic feature of inflationary models in supergravity/string constructions is vacuum misalignment for the moduli fields. The associated production of moduli particles leads to an epoch in the post-inflationary history in which the energy density is dominated by cold moduli particles. This modification of the post-inflationary history implies that the preferred range for the number of e-foldings between horizon exit of the modes relevant for CMB observations and the end of inflation (Nk)(N_k) depends on moduli masses. This in turn implies that the precision CMB observables nsn_s and rr are sensitive to moduli masses. We analyse this sensitivity for some representative models of inflation and find the effect to be highly relevant for confronting inflationary models with observations.Comment: 17 pages, 3 figures; v2 minor additions in tex

    Regional Tourism Competition in the Baltic States: a Spatial Stochastic Frontier Approach

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    This paper aimed at a statistical analysis of competition for tourists between regions within Baltic states (Estonia, Latvia, Lithuania) and estimation relative efficiency levels of regions. We apply a modern approach called Spatial Stochastic Frontier and corresponded to spatial modification of a stochastic frontier model. We specify two alternative spatial stochastic frontier models – distance and travel-time based to identify an influence of existing transport network on research results. Using the model we analyse region-specific factors (tourism infrastructure, employment, geographical position and natural attractors) having an effect on a number of visitors and estimate regions' efficiency values. We discover a significant level of inefficiency of Baltic states regions and propose some ways to improve the situation.spatial stochastic frontier, efficiency, competition, regional tourism, transport network

    Effect of Cr spacer on structural and magnetic properties of Fe/Gd multilayers

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    In this work we analyse the role of a thin Cr spacer between Fe and Gd layers on structure and magnetic properties of a [Fe(35A)/Cr(tCr)/Gd(50A)/Cr(tCr)]x12 superlattice. Samples without the Cr spacer (tCr=0) and with a thin tCr=4A are investigated using X-ray diffraction, polarized neutron and resonance X-ray magnetic reflectometry, SQUID magnetometery, magneto-optical Kerr effect and ferromagnetic resonance techniques. Magnetic properties are studied experimentally in a wide temperature range 4-300K and analysed theoretically using numerical simulation on the basis of the mean-field model. We show that a reasonable agreement with the experimental data can be obtained considering temperature dependence of the effective field parameter in gadolinium layers. The analysis of the experimental data shows that besides a strong reduction of the antiferromagnetic coupling between Fe and Gd, the introduction of Cr spacers into Fe/Gd superlattice leads to modification of both structural and magnetic characteristics of the ferromagnetic layers

    Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations

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    We analyse the performance of twelve different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and disc stability. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in the Hernquist and Katz (1989) algorithm. For all tests we find that the artificial viscosity is the most important factor distinguishing the results from the various implementations. The second most important factor is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included has comparatively little effect on the results. Combining the equation of motion presented in Thomas and Couchman (1992) with a modification of the Monaghan and Gingold (1983) artificial viscosity leads to an SPH scheme that is both fast and reliable.Comment: 30 pages, 26 figures and 9 tables included. Submitted to MNRAS. Postscript version available at ftp://phobos.astro.uwo.ca/pub/etittley/papers/sphtest.ps.g
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