5,363 research outputs found
Long-time and unitary properties of semiclassical initial value representations
We numerically compare the semiclassical ``frozen Gaussian'' Herman-Kluk
propagator [Chem. Phys. 91, 27 (1984)] and the ``thawed Gaussian'' propagator
put forward recently by Baranger et al. [J. Phys. A 34, 7227 (2001)] by
studying the quantum dynamics in some nonlinear one-dimensional potentials. The
reasons for the lack of long time accuracy and norm conservation in the latter
method are uncovered. We amend the thawed Gaussian propagator with a global
harmonic approximation for the stability of the trajectories and demonstrate
that this revised propagator is a true alternative to the Herman-Kluk
propagator with similar accuracy.Comment: 14 pages, 4 figures, corrected typos and figure 1 (d
Investigations on finite ideal quantum gases
Recursion formulae of the N-particle partition function, the occupation
numbers and its fluctuations are given using the single-particle partition
function. Exact results are presented for fermions and bosons in a common
one-dimensional harmonic oscillator potential, for the three-dimensional
harmonic oscillator approximations are tested. Applications to excited nuclei
and Bose-Einstein condensation are discussed.Comment: 13 pages, 7 postscript figures, uses 'epsfig.sty'. Submitted to
Physica A. More information available at
http://obelix.physik.uni-osnabrueck.de/~schnack
The confined-deconfined interface tension, wetting, and the spectrum of the transfer matrix
The reduced tension of the interface between the confined and
the deconfined phase of pure gauge theory is determined from numerical
simulations of the first transfer matrix eigenvalues. At we find
for . The interfaces show universal
behavior because the deconfined-deconfined interfaces are completely wet by the
confined phase. The critical exponents of complete wetting follow from the
analytic interface solutions of a -symmetric model in three
dimensions. We find numerical evidence that the confined-deconfined interface
is rough.Comment: Talk presented at the International Conference on Lattice Field
Theory, Lattice 92, to be published in the proceedings, 4 pages, 4 figures,
figures 2,3,4 appended as postscript files, figure 1 not available as a
postscript file but identical with figure 2 of Nucl. Phys. B372 (1992) 703,
special style file espcrc2.sty required (available from hep-lat), BUTP-92/4
Epigenetic modification of the oxytocin receptor gene is associated with emotion processing in the infant brain
The neural capacity to discriminate between emotions emerges early in development, though little is known about specific factors that contribute to variability in this vital skill during infancy. In adults, DNA methylation of the oxytocin receptor gene (OXTRm) is an epigenetic modification that is variable, predictive of gene expression, and has been linked to autism spectrum disorder and the neural response to social cues. It is unknown whether OXTRm is variable in infants, and whether it is predictive of early social function. Implementing a developmental neuroimaging epigenetics approach in a large sample of infants (N = 98), we examined whether OXTRm is associated with neural responses to emotional expressions. OXTRm was assessed at 5 months of age. At 7 months of age, infants viewed happy, angry, and fearful faces while functional near-infrared spectroscopy was recorded. We observed that OXTRm shows considerable variability among infants. Critically, infants with higher OXTRm show enhanced responses to anger and fear and attenuated responses to happiness in right inferior frontal cortex, a region implicated in emotion processing through action-perception coupling. Findings support models emphasizing oxytocin's role in modulating neural response to emotion and identify OXTRm as an epigenetic mark contributing to early brain function
Why Do Some People Want to Legalize Cannabis Use?
Preferences and attitudes to illicit drug policy held by individuals are likely to be an important in uence in the development of illicit drug policy. Amongst the key factors impacting on an individuals preferences over substance use policy are their beliefs about the costs and benefits of drug use, their own drug use history, and the extent of drug use amongst their peers. We use data from the Australian National Drug Strategy's Household Surveys to study these preferences. We find that current use and past use of cannabis are a major determinants of being in favor of legalization. We also find that cannabis users are more in favor of legalization the longer they have used cannabis and, among past users, the more recent their own drug using experience. This may be re ecting the fact that experience with cannabis provides information about the costs and benefits of using this substance. We also find some evidence that peers use of cannabis impacts on preferences towards legalization.cannabis use;drugs policy
Non-Oberbeck-Boussinesq effects in two-dimensional Rayleigh-Benard convection in glycerol
We numerically analyze Non-Oberbeck-Boussinesq (NOB) effects in
two-dimensional Rayleigh-Benard flow in glycerol, which shows a dramatic change
in the viscosity with temperature. The results are presented both as functions
of the Rayleigh number (Ra) up to (for fixed temperature difference
between the top and bottom plates) and as functions of
"non-Oberbeck-Boussinesqness'' or "NOBness'' () up to 50 K (for fixed
Ra). For this large NOBness the center temperature is more than 5 K
larger than the arithmetic mean temperature between top and bottom plate
and only weakly depends on Ra. To physically account for the NOB deviations of
the Nusselt numbers from its Oberbeck-Boussinesq values, we apply the
decomposition of into the product of two effects, namely
first the change in the sum of the top and bottom thermal BL thicknesses, and
second the shift of the center temperature as compared to . While
for water the origin of the deviation is totally dominated by the second
effect (cf. Ahlers et al., J. Fluid Mech. 569, pp. 409 (2006)) for glycerol the
first effect is dominating, in spite of the large increase of as compared
to .Comment: 6 pages, 7 figure
Wind reversals in turbulent Rayleigh-Benard convection
The phenomenon of irregular cessation and subsequent reversal of the
large-scale circulation in turbulent Rayleigh-B\'enard convection is
theoretically analysed. The force and thermal balance on a single plume
detached from the thermal boundary layer yields a set of coupled nonlinear
equations, whose dynamics is related to the Lorenz equations. For Prandtl and
Rayleigh numbers in the range and 10^{7} \leq
\Ra \leq 10^{12}, the model has the following features: (i) chaotic reversals
may be exhibited at Ra ; (ii) the Reynolds number based on the
root mean square velocity scales as \Re_{rms} \sim \Ra^{[0.41 ...
0.47]} (depending on Pr), and as
(depending on Ra); and (iii) the mean reversal frequency follows an effective
scaling law \omega / (\nu L^{-2}) \sim \Pr^{-(0.64 \pm 0.01)} \Ra^{0.44 \pm
0.01}. The phase diagram of the model is sketched, and the observed
transitions are discussed.Comment: 4 pages, 5 figure
Classification of phase transitions of finite Bose-Einstein condensates in power law traps by Fisher zeros
We present a detailed description of a classification scheme for phase
transitions in finite systems based on the distribution of Fisher zeros of the
canonical partition function in the complex temperature plane. We apply this
scheme to finite Bose-systems in power law traps within a semi-analytic
approach with a continuous one-particle density of states for different values of and to a three dimensional harmonically
confined ideal Bose-gas with discrete energy levels. Our results indicate that
the order of the Bose-Einstein condensation phase transition sensitively
depends on the confining potential.Comment: 7 pages, 9 eps-figures, For recent information on physics of small
systems see "http://www.smallsystems.de
Prandtl-Blasius temperature and velocity boundary layer profiles in turbulent Rayleigh-B\'{e}nard convection
The shape of velocity and temperature profiles near the horizontal conducting
plates in turbulent Rayleigh-B\'{e}nard convection are studied numerically and
experimentally over the Rayleigh number range and the Prandtl number range . The results show that both the temperature and velocity
profiles well agree with the classical Prandtl-Blasius laminar boundary-layer
profiles, if they are re-sampled in the respective dynamical reference frames
that fluctuate with the instantaneous thermal and velocity boundary-layer
thicknesses.Comment: 10 pages, 6 figure
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