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 $\sigma_{cd}$ of the interface between the confined and the deconfined phase of $SU(3)$ pure gauge theory is determined from numerical simulations of the first transfer matrix eigenvalues. At $T_c = 1/L_t$ we find $\sigma_{cd} = 0.139(4) T_c^2$ for $L_t = 2$. 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 $\Z(3)$-symmetric $\Phi^4$ 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 $10^8$ (for fixed temperature difference between the top and bottom plates) and as functions of "non-Oberbeck-Boussinesqness'' or "NOBness'' ($\Delta$) up to 50 K (for fixed Ra). For this large NOBness the center temperature $T_c$ is more than 5 K larger than the arithmetic mean temperature $T_m$ 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 $Nu_{NOB}/Nu_{OB}$ 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 $T_c$ as compared to $T_m$. While for water the origin of the $Nu$ 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 $T_c$ as compared to $T_m$.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 $10^{-2} \leq \Pr \leq 10^{3}$ and 10^{7} \leq \Ra \leq 10^{12}, the model has the following features: (i) chaotic reversals may be exhibited at Ra $\geq 10^{7}$; (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 $\Re_{rms} \sim \Pr^{-[0.66 ... 0.76]}$ (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 $\Omega(E)\sim E^{d-1}$ for different values of $d$ 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 $10^8\lesssim Ra\lesssim3\times10^{11}$ and the Prandtl number range $0.7\lesssim Pr\lesssim5.4$. 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