The Equation of State for Cool Relativistic Two-Constituent Superfluid Dynamics

The natural relativistic generalisation of Landau's two constituent superfluid theory can be formulated in terms of a Lagrangian $L$ that is given as a function of the entropy current 4-vector $s^\rho$ and the gradient $\nabla\varphi$ of the superfluid phase scalar. It is shown that in the ``cool" regime, for which the entropy is attributable just to phonons (not rotons), the Lagrangian function $L(\vec s, \nabla\varphi)$ is given by an expression of the form $L=P-3\psi$ where $P$ represents the pressure as a function just of $\nabla\varphi$ in the (isotropic) cold limit. The entropy current dependent contribution $\psi$ represents the generalised pressure of the (non-isotropic) phonon gas, which is obtained as the negative of the corresponding grand potential energy per unit volume, whose explicit form has a simple algebraic dependence on the sound or ``phonon" speed $c_P$ that is determined by the cold pressure function $P$.Comment: 26 pages, RevTeX, no figures, published in Phys. Rev. D. 15 May 199

Persistent currents in a Bose-Einstein condensate in the presence of disorder

We examine bosonic atoms that are confined in a toroidal, quasi-one-dimensional trap, subjected to a random potential. The resulting inhomogeneous atomic density is smoothened for sufficiently strong, repulsive interatomic interactions. Statistical analysis of our simulations show that the gas supports persistent currents, which become more fragile due to the disorder.Comment: 5 pages, RevTex, 3 figures, revised version, to appear in JLT

An Alternative Method to Deduce Bubble Dynamics in Single Bubble Sonoluminescence Experiments

In this paper we present an experimental approach that allows to deduce the important dynamical parameters of single sonoluminescing bubbles (pressure amplitude, ambient radius, radius-time curve) The technique is based on a few previously confirmed theoretical assumptions and requires the knowledge of quantities such as the amplitude of the electric excitation and the phase of the flashes in the acoustic period. These quantities are easily measurable by a digital oscilloscope, avoiding the cost of expensive lasers, or ultrafast cameras of previous methods. We show the technique on a particular example and compare the results with conventional Mie scattering. We find that within the experimental uncertainties these two techniques provide similar results.Comment: 8 pages, 5 figures, submitted to Phys. Rev.

On low temperature kinetic theory; spin diffusion, Bose Einstein condensates, anyons

The paper considers some typical problems for kinetic models evolving through pair-collisions at temperatures not far from absolute zero, which illustrate specific quantum behaviours. Based on these examples, a number of differences between quantum and classical Boltzmann theory is then discussed in more general terms.Comment: 25 pages, minor updates of previous versio

Possible experiment for determination of the role of microscopic vortex rings in the \lambda-transition in He-II

It is suggested that microscopic vortex rings (MVR) play an important role in the \lambda-transition in helium-II and substantially determine the value of T_{\lambda}. For very thin films of He-II, with thickness d less than the size of the smallest MVR, the rings do not fit in and, therefore, do not exist in such films. Consequently, for superfluid films of He-II, a peculiarity in the form of a smoothed-out jump should be observed in the curve T_{m}(d) at the values of thickness approximately equal to the size of the smallest MVR, d= 3 - 9 A (T_{m} is the temperature of the maximum of the broad peak on the curve of the dependence of the specific heat on temperature). The absence of a similar peculiarity will be an evidence that MVR do not influence the values of T_{\lambda} and T_{m}, and do not play any key role in the \lambda-transition. The currently available experimental data are insufficient for revealing the predicted peculiarity.Comment: 6 pages, 2 figure

Synchronous picosecond sonoluminescence: Developing and characterizing a new light source. Final report, December 1991--December 1994

Sonoluminescence is the remarkable physical process whereby sound energy is transduced into light by the motion of a trapped bubble of gas in a liquid. Interest in sonoluminescence (or SL as we like to call it) is based upon our insight that sound energy must focus by over twelve orders of magnitude to make light. Thus SL is Nature`s most nonlinear oscillator

PRESSURE RELEASE SOUND MODES IN He II

Les modes acoustiques de l'He II dans un guide d'onde partiellement rempli de poudre tassée sont étudiés dans le cas où la pression à la surface supérieure du guide d'onde est maintenue constante. Expérimentalement, ceci est obtenu en utilisant la surface libre de l'He II comme limite du guide d'onde. Deux modes de propagation sont observés : le premier est une onde de température analogue aux oscillations adiabatiques d'un tube en U, et le second est une onde de gravité modifiée par la presence de la poudre tassée.The acoustic modes of He II in a waveguide partially filled with superleak are investigated for the case of a pressure release boundary condition at the upper surface of the waveguide. Experimentally this is obtained by using the free surface of the He II to form the top of the waveguide. Two propagating modes are found ; one is a temperature wave analogous to adiabatic U-tube oscillations, and the other is a gravity wave modified by the presence of the superleak

Turbulence of Second Sound Waves in Superfluid 4He: Effect of Low-Frequency Resonant Perturbations.

We report the results of investigations of acoustic turbulence in a system of nonlinear second sound waves in a high-quality resonator filled with superfluid 4He. It was observed that subharmonics of a periodic driving force applied to the system may be generated via a parametric instability. We find that application of an additional low-frequency pumping to the turbulent system results in the generation of waves at combination frequencies of the driving forces and also leads to substantial changes in the energy spectrum of the acoustic oscillations