Standing wave acoustic fields can segregate partially ionized gas by temperature via a generalized acoustic radiation pressure that we have called the pycnoclinic acoustic force. Thus far, these sound fields have been excited and sustained with a microwave source pulsed near the resonance frequency of a cavity. Consideration of the temperature and luminosity oscillations due to the adiabatic compression of a sound wave suggests an alternative method of driving the sound field necessary for confinement. Acoustic temperature oscillations in the presence of continuous (i.e., not pulsed) microwave fields may cause variable microwave absorption in phase with the acoustic oscillation so as to add energy to the sound field. If the energy added by microwave absorption exceeds that lost to acoustic damping, amplification, and possibly self-oscillation will occur. We give theoretical criteria for amplification and present the apparatus and measurements intended to find signatures of plasma thermoacoustics.

Acoustics is used to probe the temperature profile within a sulfur plasma lamp. A spherically symmetric temperature profile is assumed that drops with the square of the radius, consistent with a constant volumetric heating model. Acoustic resonance frequencies are calculated exactly in the case of an ideal gas. Experimental measurement of a few resonant frequencies allows determination of the temperature profile curvature. This technique can be viewed as an extension of ultrasonic resonant spectroscopy to systems that are highly non-uniform due to off-equilibrium energy flow.

Simulations of sparks in 10 atmosphere Xenon gas by Levko and Raja [Phys. Plasmas 23, 073513 (2016)] are unable to reproduce the experimental fact of their opacity to visible light [Bataller et al., Appl. Phys. Lett. 105, 223501 (2014)]. Levko and Raja have argued the discrepancy is due to enhanced ionization from the probing laser radiation and/or cathode field emission. Having observed comparable opacity in similar systems without probing lasers and without electrodes, we instead argue that the enhanced ionization is a thermodynamic result of dense plasma screening effects that lower the effective ionization potential. Levko and Raja do not adequately address these density effects in their spark discharge simulations.

We establish the existence of a special class of unitary transformations that act on the parameter space of a broad class of physical Hamiltonians (including externally imposed electromagnetic fields). For this class, we calculate the quantum amplitudes for adiabatically induced transitions. Processes described include transitions between bound states and transitions from a bound state to the continuum. The leading terms of the adiabatic limit are evaluated in closed form.

The adiabatic dynamics of a two level atom with spontaneous decay is studied. The existence of a complex adiabatic phase shift is established: The real part being the usual Berry’s phase. A closed-form expression for this phase and the adiabatic transition amplitudes is obtained. Incorporation of a finite preparation time for the initial state yields a new asymptotic form for the adiabatic transition amplitudes which is significantly different from the standard Landau–Zener–Dykhne formula.

The leading-order contributions to the transition amplitudes in adiabatically driven quantum systems are presented in closed form for a physical class of Hamiltonians that have a specified scaling property. For smooth parametric variations the transition amplitudes are beyond all orders of perturbation in the parameter of slowness. The quantum and classical cases are contrasted. Specific applications include the particle in a box and the harmonic oscillator.

A great number of physical systems display power spectra that diverge in the limit of low frequency. This divergence that is approximately proportional to the inverse of the frequency f is referred to as 1/f noise. According to the second law of thermodynamics the power spectrum of a closed equilibrium system is determined by the fluctuation-dissipation relation. Except for the unusual case where the coefficient of diffusion is linear in f, the equilibrium power spectrum does not possess a region of 1/f noise. Therefore, 1/f noise is a manifestation of off-equilibrium dynamics. It is due to the dominance of high-order reversible nonlinear processes over the irreversible linear transport response.

The fluorescence radiation of a steadily illuminated atom can display intermittent intervals of darkness which are very long compared to all of its natural lifetimes as well as all of its Rabi flopping periods. During these dark intervals the atomic wave function is a coherent superposition of states which develops continuously with time. The average duration τL of these ultralong radiationless intervals is proportional to the inverse of the intensity of illumination. Thus the intensity can be adjusted so as to change τL by many orders of magnitude.

In the realsitic approximation that the expansion coefficient of a fluid vanishes, the hydrodynamic fluctuations around a steady state characterized by a small temperature gradient are determined entirely by the variations of the strength of the random forces from point to point. The assumption of local hydrodynamic equilibrium for the random forces leads to a long-range static density momentum correlation, as well as to a significant odd-in-frequency correction to the Brillouin light scattering, whose integrated intensity agrees with other work of Ronis et al. and Kirkpatrik et al. Consequences of the long-range correlations for $\frac{1}{f}$ noise $^{4}\mathrm{He}$ and local equilibrium postulates are discussed.

The results of an experiment to observe the nonlinear conversion of second sound to first sound within a waveguide show that this resonant process occurs at precisely the predicted frequency. Unique procedures are used to calibrate the first-sound transducers and we find the amplitude of the mode-converted first sound has its predicted value value which is determined principally by $\frac{\ensuremath{\partial}\ensuremath{\rho}}{\ensuremath{\partial}({w}^{2})}$ where $w$ is the difference between the normal-fluid and superfluid velocities and $\ensuremath{\rho}$ is the density.

The low-frequency fluctuations resulting from the nonlinear coupling of high-frequency fluctuations is shown to possess a 1f noise spectrum.Received 14 June 1977DOI:https://doi.org/10.1103/PhysRevLett.39.585©1977 American Physical Society

When nonlinear effects are included, first and second sound are coupled, and the possible resonant mode conversion is calculated. The meniscus of the free surface due to second sound is also investigated and depends upon whether the propagation is isothermal or isentropic. Other second-order effects investigated are first- and second-sound streaming and the mass density, momentum density, and mass flow in a sound wave.