1,048 research outputs found
A numerical study of a method for measuring the effective in situ sound absorption coefficient
The accuracy of a method [Wijnant et al., “Development and applica-
tion of a new method for the in-situ measurement of sound absorption”, ISMA 31,
Leuven, Belgium (2010).], for measurement of the effective area-averaged in situ
sound absorption coefficient is investigated. Based on a local plane wave assump-
tion, this method can be applied to sound fields for which a model is not available.
Investigations were carried out by means of finite element simulations for a typical
case. The results show that the method is a promising method for determining the
effective area-averaged in situ sound absorption coefficient in complex sound fields
Optimization of inhomogeneous electron correlation factors in periodic solids
A method is presented for the optimization of one-body and inhomogeneous
two-body terms in correlated electronic wave functions of Jastrow-Slater type.
The most general form of inhomogeneous correlation term which is compatible
with crystal symmetry is used and the energy is minimized with respect to all
parameters using a rapidly convergent iterative approach, based on Monte Carlo
sampling of the energy and fitting energy fluctuations. The energy minimization
is performed exactly within statistical sampling error for the energy
derivatives and the resulting one- and two-body terms of the wave function are
found to be well-determined. The largest calculations performed require the
optimization of over 3000 parameters. The inhomogeneous two-electron
correlation terms are calculated for diamond and rhombohedral graphite. The
optimal terms in diamond are found to be approximately homogeneous and
isotropic over all ranges of electron separation, but exhibit some
inhomogeneity at short- and intermediate-range, whereas those in graphite are
found to be homogeneous at short-range, but inhomogeneous and anisotropic at
intermediate- and long-range electron separation.Comment: 23 pages, 15 figures, 1 table, REVTeX4, submitted to PR
Supersonic strain front driven by a dense electron-hole plasma
We study coherent strain in (001) Ge generated by an ultrafast
laser-initiated high density electron-hole plasma. The resultant coherent pulse
is probed by time-resolved x-ray diffraction through changes in the anomalous
transmission. The acoustic pulse front is driven by ambipolar diffusion of the
electron-hole plasma and propagates into the crystal at supersonic speeds.
Simulations of the strain including electron-phonon coupling, modified by
carrier diffusion and Auger recombination, are in good agreement with the
observed dynamics.Comment: 4 pages, 6 figure
Phenotype standardization for statin-induced myotoxicity
Statins are widely used lipid-lowering drugs that are effective in reducing cardiovascular disease risk. Although they are generally well tolerated, they can cause muscle toxicity, which can lead to severe rhabdomyolysis. Research in this area has been hampered to some extent by the lack of standardized nomenclature and phenotypic definitions. We have used numerical and descriptive classifications and developed an algorithm to define statin-related myotoxicity phenotypes, including myalgia, myopathy, rhabdomyolysis, and necrotizing autoimmune myopathy.</p
Correlation effects in a quantum dot at high magnetic fields
We investigate the effects of electron correlations on the ground state
energy and the chemical potential of a droplet confined by a parabolic
potential at high magnetic fields. We demonstrate the importance of
correlations in estimating the transition field at which the first edge
reconstruction of the maximum density droplet occurs in the spin polarized
regime.Comment: 11 pages (revtex) 3 postscript figures are included at the end of the
tex file. To appear in Phys. Rev.
Correlation effects in MgO and CaO: Cohesive energies and lattice constants
A recently proposed computational scheme based on local increments has been
applied to the calculation of correlation contributions to the cohesive energy
of the CaO crystal. Using ab-initio quantum chemical methods for evaluating
individual increments, we obtain 80% of the difference between the experimental
and Hartree-Fock cohesive energies. Lattice constants corrected for correlation
effects deviate by less than 1% from experimental values, in the case of MgO
and CaO.Comment: LaTeX, 4 figure
Roundoff-induced Coalescence of Chaotic Trajectories
Numerical experiments recently discussed in the literature show that
identical nonlinear chaotic systems linked by a common noise term (or signal)
may synchronize after a finite time. We study the process of synchronization as
function of precision of calculations. Two generic behaviors of the average
coalescence time are identified: exponential or linear. In both cases no
synchronization occurs if iterations are done with {\em infinite} precision.Comment: 6 pages, 3 postscript figures, to be published in Phys. Rev.
An exchange-correlation energy for a two-dimensional electron gas in a magnetic field
We present the results of a variational Monte Carlo calculation of the
exchange-correlation energy for a spin-polarized two-dimensional electron gas
in a perpendicular magnetic field. These energies are a necessary input to the
recently developed current-density functional theory. Landau-level mixing is
included in a variational manner, which gives the energy at finite density at
finite field, in contrast to previous approaches. Results are presented for the
exchange-correlation energy and excited-state gap at 1/7, 1/5, 1/3, 1,
and 2. We parameterize the results as a function of and in a form
convenient for current-density functional calculations.Comment: 36 pages, including 6 postscript figure
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