Temperature hysteresis is theoretically studied for the volume phase transition of chemically cross-linked gels. The condition of the appearance of a ‘‘surface skin layer’’ of new phase is formulated and calculated. The result predicts that the surface skin layer is destabilized near the critical point of the transition due to volume fluctuations. We discuss the relevance of this result to inaccessibility to the Ising critical point [L. Golubović and T. C. Lubensky, Phys. Rev. Lett. 63, 1082 (1989)].

The possible use of loosely bound Rydberg atoms for remote gravimetric measurements is explored. The first-order corrections to the nonrelativistic nS and nP states for n>2 are obtained for the first time. A procedure to evaluate corrections of any order is outlined and applied to the 1S state in a spherical symmetry. It is shown that observations of the effects described in this Letter near objects of neutron-star-like densities are possible in principle only in the absence of significant magnetic fields.

Random-lattice fermions have been shown to be free of the doubling problem if there are no interactions or interactions of a nongauge nature. On the other hand, gauge interactions impose stringent constraints as expressed by the Ward-Takahashi identities which could revive the free-field suppressed doubler modes in loop diagrams. Comparing random-lattice, naive, and Wilson fermions in two-dimensional Abelian background gauge theory, we show that indeed the doublers are revived for random lattices in the continuum limit. Some implications of the persistent doubling phenomenon on random lattices are also discussed.

We examine the possibility of fermion mass generation in (2+1)-dimensional gauge theory from the current algebra point of view. In our approach the critical behavior is governed by the fluctuations of pions which are the Goldstone bosons for chiral symmetry breaking. Our analysis supports the existence of an upper critical ${\mathit{N}}_{\mathit{F}}$ and exhibits the explicit form of the gap equation as well as the form of the critical exponent for the inverse correlation length of the order parameter.

We investigate the spectral properties of a random matrix model which in the large N limit embodies the essentials of the QCD partition function at low energy. The exact spectral density and its pair correlation function are derived for an arbitrary number of flavors and zero topological charge. Their microscopic limits provide the master formulae for sum rules for the inverse powers of the eigenvalues of the QCD Dirac operator, as recently discussed by Leutwyler and Smilga.

For simple models of the nuclear charge operator, measurements of the Coulomb sum and the charge form factor of a nucleus directly determine the proton-proton correlations. We examine experimental results obtained for few-body nuclei at Bates and Saclay using models of the charge operator that include both one- and two-body terms. Previous analyses using one-body terms only have failed to reproduce the experimental results. However, we find that the same operators which have been used to successfully describe the charge form factors also produce substantial agreement with measurements of the Coulomb sum.

A technique based on the injection of highly charged ions from new low-energy ion sources into a Kingdon ion trap has been used to measure millisecond or longer lifetimes τ of metastable levels in ground terms of the ions. The technique has been initially applied to ions of argon, with the results τ(${\mathrm{Ar}}^{10+}$,2${\mathit{p}}^4$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$)=14.8(1.1) ms, τ(${\mathrm{Ar}}^{9+}$,2${\mathit{p}}^5$ ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$)=8.53(0.24) ms, and τ(${\mathrm{Ar}}^{2+}$,3${\mathit{p}}^4$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$)=159.7(9.7) ms.

A neutral beam of oriented ${\mathrm{CH}}_3$Cl molecules in the ‖111〉 rotational eigenstate is crossed with a 700-eV beam of electrons inside a uniform electrostatic field of about 20 V/cm. Ions formed directly upon impact are collected by the uniform field electrodes, but some ${\mathrm{CH}}_3$${\mathrm{Cl}}^{+}$ ions are observed in a mass spectrometer with its ionizer turned off. These ‘‘indirect’’ ${\mathrm{CH}}_3$${\mathrm{Cl}}^{+}$ ions are forward scattered, undeflected by the uniform field, and must therefore be neutral during the flight out of the uniform field. This strongly suggests that the precursor of these ions is a highly excited long-lived molecule, ${\mathrm{CH}}_3$${\mathrm{Cl}}^{\mathrm{*}\mathrm{*}}$. The ‘‘indirect’’ ${\mathrm{CH}}_3$${\mathrm{Cl}}^{+}$ ion signal is greater when the electron attacks at the Cl end of the molecule.

We analyze the quantum properties of the signal near field emitted by a degenerate parametric oscillator below threshold, including diffraction and its effects on the threshold for signal generation. The field is probed by a local oscillator field of arbitrary spatial configuration. The results are expressed in terms of an appropriate spectrum which describes how the level of squeezing varies with the angle from the direction of propagation. The results hold for cavities both with plane and with spherical mirrors.

Chaotic experimental systems are often investigated using delay coordinates. Estimated values of the correlation dimension in delay coordinate space typically increase with the number of delays and eventually reach a plateau (on which the dimension estimate is relatively constant) whose value is commonly taken as an estimate of the correlation dimension ${\mathit{D}}_2$ of the underlying chaotic attractor. We report a rigorous result which implies that, for long enough data sets, the plateau begins when the number of delay coordinates first exceeds ${\mathit{D}}_2$. Numerical experiments are presented. We also discuss how lack of sufficient data can produce results that seem to be inconsistent with the theoretical prediction.

We demonstrate the existence of an interference contribution to the average magnetoconductance, G¯(B), of ballistic cavities and use it to test the semiclassical theory of quantum billiards. G¯(B) is qualitatively different for chaotic and regular cavities (saturation versus linear increase) which is explained semiclassically by the differing classical distribution of areas. The magnitude of G¯(B) is poorly explained by the semiclassical theory of coherent backscattering (elastic enhancement factor); interference between trajectories which are not exactly time reversed must be included.

The cubic complex Ginzburg-Landau equation is often used to model oscillatory media. In 1D it has a one-parameter family of moving ‘‘hole’’ solutions acting as sources for traveling waves (Nozaki and Bekki). We find that this family is destroyed by arbitrarily small generic perturbations leaving only the stationary phase-slip solutions. Its stability as well as the border of spatiotemporal chaos depend crucially on the sign of the perturbation. For ‘‘stabilizing’’ perturbations one also finds oscillations of the holes. The scenario can be modeled by the Van der Pol oscillator.

We report the first direct measurement of coherent backscattering of scalar acoustic waves by disordered scattering medium. In two and three dimensions an excellent agreement between experimental data and the predictions of simple diffusion theory is found. These measurements have been done for the time dependent and independent cases.

We present experimental results on Rayleigh-Bénard convection in ${\mathrm{SF}}_6$ near the gas-liquid critical point. We measured the critical temperature difference for the onset of convection, Δ${\mathit{T}}_0$, as a function of the reduced average temperature τ=(T¯-${\mathit{T}}_{\mathit{c}}$)/${\mathit{T}}_{\mathit{c}}$ and found Δ${\mathit{T}}_0$=525×${\mathrm{\tau }}^{1.89}$, which is close to the expected power law behavior. The strong temperature dependence of the physical properties is used to scan the Prandtl number in a wide range. A new, many ‘‘target’’ pattern state, initiated by a defect instability, was observed.

In Bénard-Marangoni convection in a square vessel, of small aspect ratio, a sequence of bifurcations is observed as control parameters are slightly changed. Some of the emerging patterns are stationary and others are oscillatory in nature. The stationary patterns break the symmetry and the oscillatory ones can be classified in three kinds. We show that this dynamics can be explained assuming that the system is close to a Takens Bogdanov bifurcation.

Vortical flows in shallow water interact with long surface waves by virtue of the nonlinear terms of the fluid equations. Analytical formulas are derived that quantify the spontaneous generation of such waves by unsteady vorticity as well as the scattering of surface waves by vorticity. In the first Born approximation the radiated surface elevation is linearly related to the Fourier transform of the vorticity. The ‘‘dislocated’’ wave fronts that are analogous to the Aharonov-Bohm effect are obtained as a special case.

When a cylindrical pure electron plasma is displaced from the center of the trap, it performs a bulk circular orbital motion known as the l=1 diocotron mode. The slow application of a perturbing potential to a patch on the trap wall distorts the orbit into a noncircular closed path. Experiments and a simple theoretical model indicate that the area by the loop is an adiabatic invariant. Detailed studies are made of the breaking of the invariant when perturbations are rapidly applied. When the perturbation is applied with discontinuous time derivatives, the invariant breaking greatly exceeds the predictions of the standard theory for smooth perturbations.

X-ray diffraction illustrates that a two-dimensional smectic liquid crystal is formed in a melting process of an anisotropic, incommensurate monolayer of n-propanol physisorbed on graphite. In this phase a hydrogen-bonded head-to-head association of molecules is arranged in rows with their long axes on average normal to the row. Parallel to the rows there is only short-range translational order of the molecules.

With a scanning tunneling microscope the Pb (110) surface was studied from room temperature to temperatures where surface melting occurs. At room temperature scanning tunneling microscopy images of Pb(110) can be recorded with atomic resolution. At higher temperatures we observe a jump to contact by the surface, resulting in the formation of a connecting neck of Pb between the surface and the tip. As the tip is retracted, the neck elongates and finally breaks. The dependence of the average neck height just before rupture on temperature and retraction speed suggests that mobile adatoms are responsible for the growth of the neck.

We present a quantitative method which systematically finds tunneling systems in glasses and hence allows a microscopic check of the standard tunneling model. We apply this method to a two-component model amorphous alloy. The major assumptions of the standard tunneling model are qualitatively verified. Small quantitative differences in the distribution of the tunneling matrix elements explain why the experimental temperature dependence of the specific heat is superlinear and the thermal conductivity is subquadratic. Connections to the soft-potential model and recent strong-coupling models are discussed.