Theoretical study of the HS (v',,j' = 1) + O2;(v''=0,j''=1) reaction

We report a theoretical study of the title four-atom reaction for a wide range of translational energies, considering the reactants in the ground vibrational state and also in some vibrationally excited levels of the HS radical. All calculations have employed the quasi-classical trajectory (QCT) method and a reported double many-body expansion potential energy surface for ground electronic state of HSO2. Cross sections as well as specific rate constants for HS elimination are reported and compared with literature data for such processes. To account the zero-point energy problem in QCT calculations, an internal energy quantum mechanics threshold (IEQMT) criteria is used. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 200

Application of the Ergun's Equation in Porous Ceramic Based on CaO-Stabilized ZrO2

AbstractThe study of the permeability in porous ceramics with potential application as filters is essential because this parameter includes a number of processing variables such as porosity and pore size of great importance in the development of porous media. The knowledge of the relationship between permeability and these variables, provide a better criterion to determine the process variables that result in an optimization of the permeability. The optimization of this parameter is a basic requirement for an adequate operation of the ceramic as a filter material. In this study, the permeability of porous ceramic prepared from different compositions of the mixture of ZrO2 and a high alumina cement with 30 wt% CaO and sintered at 1400 ¡ C was experimental and theoretically evaluated. Theoretical evaluation of permeablity was performed using the Ergun«s equation, which describes the permeability constant as a funtion of the porosity and mean pore size of the porous materia

VLT X-shooter spectroscopy of the nearest brown dwarf binary

The aim of the project is to characterise both components of the nearest brown dwarf sytem to the Sun, WISE J104915.57-531906.1 (=Luhman16AB) at optical and near-infrared wavelengths. We obtained high signal-to-noise intermediate-resolution (R~6000-11000) optical (600-1000 nm) and near-infrared (1000-2480nm) spectra of each component of Luhman16AB, the closest brown dwarf binary to the Sun, with the X-Shooter instrument on the Very Large Telescope. We classify the primary and secondary of the Luhman16 system as L6-L7.5 and T0+/-1, respectively, in agreement with previous measurements published in the literature. We present measurements of the lithium pseudo-equivalent widths, which appears of similar strength on both components (8.2+/-1.0 Angstroms and 8.4+/-1.5 Angstroms for the L and T components, respectively). The presence of lithium (Lithium 7) in both components imply masses below 0.06 Msun while comparison with models suggests lower limits of 0.04 Msun. The detection of lithium in the T component is the first of its kind. Similarly, we assess the strength of other alkali lines (e.g. pseudo-equivalent widths of 6-7 Angstroms for RbI and 4-7 Angstroms for CsI) present in the optical and near-infrared regions and compare with estimates for L and T dwarfs. We also derive effective temperatures and luminosities of each component of the binary: -4.66+/-0.08 dex and 1305(+180)(-135) for the L dwarf and -4.68+/-0.13 dex and 1320(+185)(-135) for the T dwarf, respectively. Using our radial velocity determinations, the binary does not appear to belong to any of the well-known moving group. Our preliminary theoretical analysis of the optical and J-band spectra indicates that the L- and T-type spectra can be reproduced with a single temperature and gravity but different relative chemical abundances which impact strongly the spectral energy distribution of L/T transition objects.Comment: 12 pages, 9 figure, 3 tables, accepted to A&

Thermodynamic relations in a driven lattice gas: numerical exprements

We explore thermodynamic relations in non-equilibrium steady states with numerical experiments on a driven lattice gas. After operationally defining the pressure and chemical potential in the driven lattice gas, we confirm numerically the validity of the integrability condition (the Maxwell relation) for the two quantities whose values differ from those for an equilibrium system. This implies that a free energy function can be constructed for the non-equilibrium steady state that we consider. We also investigate a fluctuation relation associated with this free energy function. Our result suggests that the compressibility can be expressed in terms of density fluctuations even in non-equilibrium steady states.Comment: 4 pages, 4 figure

The gravitational-wave memory from eccentric binaries

The nonlinear gravitational-wave memory causes a time-varying but nonoscillatory correction to the gravitational-wave polarizations. It arises from gravitational waves that are sourced by gravitational waves. Previous considerations of the nonlinear memory effect have focused on quasicircular binaries. Here, I consider the nonlinear memory from Newtonian orbits with arbitrary eccentricity. Expressions for the waveform polarizations and spin-weighted spherical-harmonic modes are derived for elliptic, hyperbolic, parabolic, and radial orbits. In the hyperbolic, parabolic, and radial cases the nonlinear memory provides a 2.5 post-Newtonian (PN) correction to the leading-order waveforms. This is in contrast to the elliptical and quasicircular cases, where the nonlinear memory corrects the waveform at leading (0PN) order. This difference in PN order arises from the fact that the memory builds up over a short "scattering" time scale in the hyperbolic case, as opposed to a much longer radiation-reaction time scale in the elliptical case. The nonlinear memory corrections presented here complete our knowledge of the leading-order (Peters-Mathews) waveforms for elliptical orbits. These calculations are also relevant for binaries with quasicircular orbits in the present epoch which had, in the past, large eccentricities. Because the nonlinear memory depends sensitively on the past evolution of a binary, I discuss the effect of this early-time eccentricity on the value of the late-time memory in nearly circularized binaries. I also discuss the observability of large "memory jumps" in a binary's past that could arise from its formation in a capture process. Lastly, I provide estimates of the signal-to-noise ratio of the linear and nonlinear memories from hyperbolic and parabolic binaries.Comment: 25 pages, 8 figures. v2: minor changes to match published versio

Breakup Reactions of 11Li within a Three-Body Model

We use a three-body model to investigate breakup reactions of 11Li (n+n+9Li) on a light target. The interaction parameters are constrained by known properties of the two-body subsystems, the 11Li binding energy and fragmentation data. The remaining degrees of freedom are discussed. The projectile-target interactions are described by phenomenological optical potentials. The model predicts dependence on beam energy and target, differences between longitudinal and transverse momentum distributions and provides absolute values for all computed differential cross sections. We give an almost complete series of observables and compare with corresponding measurements. Remarkably good agreement is obtained. The relative neutron-9Li p-wave content is about 40%. A p-resonance, consistent with measurements at about 0.5 MeV of width about 0.4 MeV, seems to be necessary. The widths of the momentum distributions are insensitive to target and beam energy with a tendency to increase towards lower energies. The transverse momentum distributions are broader than the longitudinal due to the diffraction process. The absolute values of the cross sections follow the neutron-target cross sections and increase strongly for beam energies decreasing below 100 MeV/u.Comment: 19 pages, 14 figures, RevTeX, psfig.st

Gravity with extra dimensions and dark matter interpretation: Phenomenological example via Miyamoto-Nagai galaxy

A configuration whose density profile coincides with the Newtonian potential for spiral galaxies is constructed from a 4D isotropic metric plus extra dimensional components. A Miyamoto-Nagai ansatz is used to solve Einstein equations. The stable rotation curves of such system are computed and, without fitting techniques, we recover with accuracy the observational data for flat or not asymptotically flat galaxy rotation curves. The density profiles are reconstructed and compared to that obtained from the Newtonian potential.Comment: 10 pages, 10 figures, submitted to Brazilian Journal of Physic