95,671 research outputs found
Isomorphs in model molecular liquids
Isomorphs are curves in the phase diagram along which a number of static and
dynamic quantities are invariant in reduced units. A liquid has good isomorphs
if and only if it is strongly correlating, i.e., the equilibrium
virial/potential energy fluctuations are more than 90% correlated in the NVT
ensemble. This paper generalizes isomorphs to liquids composed of rigid
molecules and study the isomorphs of two systems of small rigid molecules, the
asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for
both systems we find that the isochoric heat capacity, the excess entropy, the
reduced molecular center-of-mass self part of the intermediate scattering
function, the reduced molecular center-of-mass radial distribution function to
a good approximation are invariant along an isomorph. In agreement with theory,
we also find that an instantaneous change of temperature and density from an
equilibrated state point to another isomorphic state point leads to no
relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be
more approximative than those of the asymmetric dumbbell model, which is
consistent with the OTP model being less strongly correlating. For both models
we find "master isomorphs", i.e., isomorphs have identical shape in the
virial/potential energy phase diagram.Comment: 20 page
Information in Black Hole Radiation
If black hole formation and evaporation can be described by an matrix,
information would be expected to come out in black hole radiation. An estimate
shows that it may come out initially so slowly, or else be so spread out, that
it would never show up in an analysis perturbative in , or in 1/N
for two-dimensional dilatonic black holes with a large number of minimally
coupled scalar fields.Comment: 12 pages, 1 PostScript figure, LaTeX, Alberta-Thy-24-93 (In response
to Phys. Rev. Lett. referees' comments, the connection between expansions in
inverse mass and in 1/N are spelled out, and a figure is added. An argument
against perturbatively predicting even late-time information is also
provided, as well as various minor changes.
Distinguishing Solar Flare Types by Differences in Reconnection Regions
Observations show that magnetic reconnection and its slow shocks occur in
solar flares. The basic magnetic structures are similar for long duration event
(LDE) flares and faster compact impulsive (CI) flares, but the former require
less non-thermal electrons than the latter. Slow shocks can produce the
required non-thermal electron spectrum for CI flares by Fermi acceleration if
electrons are injected with large enough energies to resonate with scattering
waves. The dissipation region may provide the injection electrons, so the
overall number of non-thermal electrons reaching the footpoints would depend on
the size of the dissipation region and its distance from the chromosphere. In
this picture, the LDE flares have converging inflows toward a dissipation
region that spans a smaller overall length fraction than for CI flares. Bright
loop-top X-ray spots in some CI flares can be attributed to particle trapping
at fast shocks in the downstream flow, the presence of which is determined by
the angle of the inflow field and velocity to the slow shocks.Comment: 15 pages TeX and 2 .eps figures, accepted to Ap.J.Let
Condensate growth in trapped Bose gases
We study the dynamics of condensate formation in an inhomogeneous trapped
Bose gas with a positive interatomic scattering length. We take into account
both the nonequilibrium kinetics of the thermal cloud and the Hartree-Fock
mean-field effects in the condensed and the noncondensed parts of the gas. Our
growth equations are solved numerically by assuming that the thermal component
behaves ergodically and that the condensate, treated within the Thomas-Fermi
approximation, grows adiabatically. Our simulations are in good qualitative
agreement with experiment, however important discrepancies concerning details
of the growth behaviour remain.Comment: 28 pages, 11 figures. Changes made to the introduction, Sec. VI, Sec.
VII, and included additional growth curves in Fig. 1
Volume-energy correlations in the slow degrees of freedom of computer-simulated phospholipid membranes
Constant-pressure molecular-dynamics simulations of phospholipid membranes in
the fluid phase reveal strong correlations between equilibrium fluctuations of
volume and energy on the nanosecond time-scale. The existence of strong
volume-energy correlations was previously deduced indirectly by Heimburg from
experiments focusing on the phase transition between the fluid and the ordered
gel phases. The correlations, which are reported here for three different
membranes (DMPC, DMPS-Na, and DMPSH), have volume-energy correlation
coefficients ranging from 0.81 to 0.89. The DMPC membrane was studied at two
temperatures showing that the correlation coefficient increases as the phase
transition is approached
Astrophysical factors:Zero energy vs. Most effective energy
Effective astrophysical factors for non-resonant astrophysical nuclear
reaction are invariably calculated with respect to a zero energy limit. In the
present work that limit is shown to be very disadvantageous compared to the
more natural effective energy limit. The latter is used in order to modify the
thermonuclear reaction rate formula so that it takes into account both plasma
and laboratory screening effects.Comment: 7 RevTex pages. Accepted for publication in Phys.Rev.
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
The x-ray photoelectron valence band spectrum and x-ray emission valence-band
spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented
(analyzed in the common energy scale) and interpreted on the basis of a
band-structure calculation for an idealized I4/mmm structure of this material.Comment: 6 pages + 7 PostScript figures, RevTex3.0, to be published in
Phys.Rev.B52 (Oct.95). Figures also available via anonymous ftp at
ftp://ftp.physik.uni-osnabrueck.de/pub/apostnik/BiTiO
Transfer of K-types on local theta lifts of characters and unitary lowest weight modules
In this paper we study representations of the indefinite orthogonal group
O(n,m) which are local theta lifts of one dimensional characters or unitary
lowest weight modules of the double covers of the symplectic groups. We apply
the transfer of K-types on these representations of O(n,m), and we study their
effects on the dual pair correspondences. These results provide examples that
the theta lifting is compatible with the transfer of K-types. Finally we will
use these results to study subquotients of some cohomologically induced
modules
Infrared Excess in the Be Star Delta Scorpii
We present infrared photometric observations of the Be binary system delta
Scorpii obtained in 2006. The J,H and K magnitudes are the same within the
errors compared to observations taken 10 months earlier. We derive the infrared
excess from the observation and compare this to the color excess predicted by a
radiative equilibrium model of the primary star and its circumstellar disk. We
use a non-LTE computational code to model the gaseous envelope concentrated in
the star's equatorial plane and calculate the expected spectral energy
distribution and Halpha emission profile of the star with its circumstellar
disk. Using the observed infrared excess of delta Sco, as well as Halpha
spectroscopy bracketing the IR observations in time, we place constraints on
the radial density distribution in the circumstellar disk. Because the disk
exhibits variability in its density distribution, this work will be helpful in
understanding its dynamics.Comment: 12 pages, 14 figures, to be published in PASP May 200
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