Aging to Equilibrium Dynamics of SiO2

Molecular dynamics computer simulations are used to study the aging dynamics of SiO2 (modeled by the BKS model). Starting from fully equilibrated configurations at high temperatures T_i =5000K/3760K the system is quenched to lower temperatures T_f=2500K, 2750K, 3000K, 3250K and observed after a waiting time t_w. Since the simulation runs are long enough to reach equilibrium at T_f, we are able to study the transition from out-of-equilibrium to equilibrium dynamics. We present results for the partial structure factors, for the generalized incoherent intermediate scattering function C_q(t_w, t_w+t), and for the mean square displacement msd(t_w,t_w+t). We conclude that there are three different t_w regions: (I) At very short waiting times, C_q(t_w, t_w+t) decays very fast without forming a plateau. Similarly msd(t_w,t_w+t) increases without forming a plateau. (II) With increasing t_w a plateau develops in C_q(t_w, t_w+t) and msd(t_w,t_w+t). For intermediate waiting times the plateau height is independent of t_w and T_i. Time superposition applies, i.e. C_q=C_q(t/t_r) where t_r=t_r(t_w) is a waiting time dependent decay time. Furthermore C_q=C(q,t_w,t_w+t) scales as C_q=C(q,z(t_w,t) where z is a function of t_w and t only, i.e. independent of q. (III) At large t_w the system reaches equilibrium, i.e. C_q(t_w,t_w+t) and msd(t_w,t_w+t) are independent of t_w and T_i. For C_q(t_w,t_w+t) we find that the time superposition of intermediate waiting times (II) includes the equilibrium curve (III).Comment: 9 pages, 11 figures, submission to PR

Filling of the Mott-Hubbard gap in the high temperature photoemission spectrum of (V_0.972Cr_0.028)_2O_3

Photoemission spectra of the paramagnetic insulating (PI) phase of (V_0.972Cr_0.028)_2O_3, taken in ultra high vacuum up to the unusually high temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH) insulator and not observed previously. With increasing T the MH gap is filled by spectral weight transfer, in qualitative agreement with high-T theoretical calculations combining dynamical mean field theory and band theory in the local density approximation.Comment: 4 pages, 4 figure

Origin of Strong Coupling in Lithium under Pressure

In an attempt to provide a clearer understanding of the impressive increase in T_c under pressure in elemental Li, linear response calculation of the phonon dispersion curves, electron-phonon matrix elements, phonon linewidths and mode lambda's have been carried out on a finer mesh (24^3 in the Brillouin zone) than done previously, for the volume corresponding to 20 GPa pressure. The result illustrates the great need for a fine mesh (even finer than this) for converged results of lambda and the spectral function alpha^2 F. Although the initial pressure-induced transverse T_1 phonon instability (in harmonic approximation) near the symmetry point K has dominated attention, the current results show that the high value of T_c gets strong contributions from elsewhere in the zone, particularly from the longitudinal mode along (100).Comment: Proceedings for M2

Comments on ‘‘The non-wavelike response of a continental shelf to wind’’ by G. T. Csanady

Csanady (1998) presents solutions for time-dependent wind-driven flow in a barotropic coastal ocean. We disagree with two of his three boundary condition options and wish to clarify the origin of the non-wavelike aspect of the flow

Adiabatic Elimination in a Lambda System

This paper deals with different ways to extract the effective two-dimensional lower level dynamics of a lambda system excited by off-resonant laser beams. We present a commonly used procedure for elimination of the upper level, and we show that it may lead to ambiguous results. To overcome this problem and better understand the applicability conditions of this scheme, we review two rigorous methods which allow us both to derive an unambiguous effective two-level Hamiltonian of the system and to quantify the accuracy of the approximation achieved: the first one relies on the exact solution of the Schrodinger equation, while the second one resorts to the Green's function formalism and the Feshbach projection operator technique.Comment: 14 pages, 3 figure

Luttinger liquid ARPES spectra from samples of Li0.9_{0.9}Mo6_6O17_{17} grown by the temperature gradient flux technique

Angle resolved photoemission spectroscopy line shapes measured for quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$ samples grown by a temperature gradient flux technique are found to show Luttinger liquid behavior, consistent with all previous data by us and other workers obtained from samples grown by the electrolyte reduction technique. This result eliminates the sample growth method as a possible origin of considerable differences in photoemission data reported in previous studies of Li$_{0.9}$Mo$_6$O$_{17}$.Comment: Some text adde

The effects of peer influence on adolescent pedestrian road-crossing decisions

Objective: Adolescence is a high-risk period for pedestrian injury. It is also a time of heightened susceptibility to peer influence. The aim of this research was to examine the effects of peer influence on the pedestrian road-crossing decisions of adolescents. Methods: Using 10 videos of road-crossing sites, 80 16- to 18-year-olds were asked to make pedestrian road-crossing decisions. Participants were assigned to one of 4 experimental conditions: negative peer (influencing unsafe decisions), positive peer (influencing cautious decisions), silent peer (who observed but did not comment), and no peer (the participant completed the task alone). Peers from the adolescent’s own friendship group were recruited to influence either an unsafe or a cautious decision. Results: Statistically significant differences were found between peer conditions. Participants least often identified safe road-crossing sites when accompanied by a negative peer and more frequently identified dangerous road-crossing sites when accompanied by a positive peer. Both cautious and unsafe comments from a peer influenced adolescent pedestrians’ decisions. Conclusions: These findings showed that road-crossing decisions of adolescents were influenced by both unsafe and cautious comments from their peers. The discussion highlighted the role that peers can play in both increasing and reducing adolescent risk-taking

Optimizing Replica Exchange Moves For Molecular Dynamics

In this short note we sketch the statistical physics framework of the replica exchange technique when applied to molecular dynamics simulations. In particular, we draw attention to generalized move sets that allow a variety of optimizations as well as new applications of the method.Comment: 4 pages, 3 figures; revised version (1 figure added), PRE in pres

Cryogenic-coolant He-4-superconductor interaction

The thermodynamic and thermal interaction between a type 2 composite alloy and cryo-coolant He4 was studied with emphasis on post quench phenomena of formvar coated conductors. The latter were investigated using a heater simulation technique. Overall heat transfer coefficients were evaluated for the quench onset point. Heat flux densities were determined for phenomena of thermal switching between a peak and a recovery value. The study covered near saturated liquid, pressurized He4, both above and below the lambda transition, and above and below the thermodynamic critical pressure. In addition, friction coefficients for relative motion between formvar insulated conductors were determined

Absence of martian radiation belts and implications thereof

Absence of electrons in Mars atmosphere and implications thereo