Quantum-to-classical crossover of quasibound states in open quantum systems

In the semiclassical limit of open ballistic quantum systems, we demonstrate the emergence of instantaneous decay modes guided by classical escape faster than the Ehrenfest time. The decay time of the associated quasibound states is smaller than the classical time of flight. The remaining long-lived quasibound states obey random-matrix statistics, renormalized in compliance with the recently proposed fractal Weyl law for open systems [W.T. Lu, S. Sridhar, and M. Zworski, Phys. Rev. Lett. 91, 154101 (2003)]. We validate our theory numerically for a model system, the open kicked rotator.     

Fermionic atoms in a three dimensional optical lattice: observing Fermi surfaces, dynamics, and interactions

We have studied interacting and noninteracting quantum degenerate Fermi gases in a three-dimensional optical lattice. We directly image the Fermi surface of the atoms in the lattice by turning off the optical lattice adiabatically. Because of the confining potential, gradual filling of the lattice transforms the system from a normal state into a band insulator. The dynamics of the transition from a band insulator to a normal state is studied, and the time scale is measured to be an order of magnitude larger than the tunneling time in the lattice. Using a Feshbach resonance, we increase the interaction between atoms in two different spin states and dynamically induce a coupling between the lowest energy bands. We observe a shift of this coupling with respect to the Feshbach resonance in free space which is anticipated for strongly confined atoms.     

Interface model for non-equilibrium evaporation

A microscopic interface condition for condensing/evaporating interfaces is developed by combining a velocity dependent condensation probability [T. Tsuruta, H. Tanaka, T. Masuoka, Int. J. Heat Mass Transfer 42 (1999) 4107] and Maxwell type interface conditions with accommodation. Using methods from kinetic theory, macroscopic interface conditions for mass and energy transport across the phase boundary are derived. This model only applies to simple substances, where diffusive effects in the bulk phases are not present. The results are compared to classical non-equilibrium thermodynamics. The interface conditions are considered for the limit of small deviation from equilibrium, and the corresponding Onsager coefficients are computed. These results are useful as boundary conditions for non-equilibrium evaporation and condensation problems, as done previously by our group [M. Bond, H. Struchtrup, Phys. Rev. E 70 (2004) 061605].     

Bottom-up driven involuntary attention modulates auditory signal in noise processing

Background  

Auditory evoked responses can be modulated by both the sequencing and the signal-to-noise ratio of auditory stimuli. Constant sequencing as well as intense masking sounds basically lead to N1m response amplitude reduction. However, the interaction between these two factors has not been investigated so far. Here, we presented subjects tone stimuli of different frequencies, which were either concatenated in blocks of constant frequency or in blocks of randomly changing frequencies. The tones were presented either in silence or together with broad-band noises of varying levels.     

Baryon rapidity loss in relativistic Au + Au collisions

An excitation function of proton rapidity distributions for different centralities is reported from AGS Experiment E917 for Au+Au collisions at 6, 8, and 10.8 GeV/nucleon. The rapidity distributions from peripheral collisions have a valley at midrapidity which smoothly change to distributions that display a broad peak at midrapidity for central collisions. The mean rapidity loss increases with increasing beam energy, whereas the fraction of protons consistent with isotropic emission from a stationary source at midrapidity decreases with increasing beam energy. The data suggest that the stopping is substantially less than complete at these energies.     

Ignition of dimethyl ether/air mixtures by hot particles: Impact of low temperature chemical reactions

Understanding and characterizing ignition of flammable mixtures by hot particles is important for assessing and reducing the risk of accidental ignition and explosion in industry and aviation. Recently, many studies have been conducted for ignition of gaseous mixtures by hot particles. However, the effects of low-temperature chemistry (LTC) on ignition by hot particles received little attention. LTC plays an important role in the ignition of most hydrocarbon fuels and may induce cool flames. The present study aims to numerically assess the effects of LTC on ignition by the hot particles. We consider the transient ignition processes induced by a hot spherical particle in quiescent and flowing stoichiometric dimethyl ether/air mixtures. 1D and 2D simulations, respectively, are conducted for the ignition process by hot-particles in quiescent and flowing mixtures. A detailed kinetic model including both LTC and high-temperature chemistry (HTC) is used in simulations. The results exhibit a premixed cool flame to be first initiated by the hot particle. Then a double-flame structure with both premixed cool and hot flames is observed at certain conditions. At zero or low inlet flow velocities, the hot flame catches up and merges with the leading cool flame. At high inlet flow velocities, the hot flame cannot be initiated due to the short residence time and large convective loss of heat and radicals. Comparing the results with and without considering LTC confirms that LTC accelerates substantially ignition via HTC in a certain range of hot particle temperatures. The mechanism of ignition promotion by LTC is interpreted by analyzing the radical pool produced by the LTC and HTC surrounding the hot particle. Moreover, the influence of inlet flow velocity on ignition by hot particles is assessed. Non-monotonic change of ignition delay time with flow velocity is observed and discussed.     

Physical properties of some McVittie metrics

A class of McVittie's new nonquadratic solutions is investigated in some detail with regard to its physical properties. It is found that decreasing pressure and density are not compatible with center regularity for these perfect fluid spheres. It is further seen that for gaseous spheres (i.e., the density drops to zero at the outer boundary of the sphere together with the pressurep) oscillatory motions arenot possible. For these gaseous models the pressure and the density are both positive inside the outer surface, and their respective gradients are negative. For the outer gaseous shells models are constructed where for a certain time interval the pressure is increasing for contracting models. Without any restriction with respect to time, for these shell models it found that the density is increasing for contracting models, and the adiabatic speed of sound is less than the speed of light. It is also found that the trace of the energy-momentum tensor is positive, the total mass is negative, and for collapsing shells the rate of change of circumference as measured by an observer riding on the shell is an increasing function of time. However, all these models have the strange geometric feature that the physical radius is a decreasing function of comoving radial coordinate.