Integrable systems related to the Korteweg–de Vries (KdV) equation are shown to be associated with the dynamics of vortex patches in ideal two-dimensional fluids. This connection is based on a truncation of the exact contour dynamics analogous to the ‘‘localized induction approximation’’ which relates the nonlinear Schrödinger equation to the motion of a vortex filament. Single soliton solutions of the periodic modified KdV problem correspond to uniformly rotating shapes which approximate the Kirchoff ellipse and known generalizations. A simple geometrical interpretation of the dual Poisson bracket structure of the modified KdV hierarchies is given.

A class of generically nonmetric couplings between nongravitational fields and the gravitational field is introduced. It is shown that these couplings violate the weak equivalence principle at a level (a priori) smaller than the current Eötvös-type experimental limits.

We argue that, classically, s-wave electrons incident on a magnetically charged black hole are swallowed with probability one: The reflection coefficient vanishes. However, quantum effects can lead to both electromagnetic and gravitational backscattering. We show that, for the case of extremal, magnetically charged, dilatonic black holes and a single flavor of low-energy charged particles, this backscattering is described by a perturbatively computable and unitary S matrix, and that the Hawking radiation in these modes is suppressed near extremality. The interesting and much more diffiult case of several flavors is also discussed.

The ultrahigh-energy (UHE) proton and neutrino spectra resulting from collapse or annihilation of topological defects surviving from the grand unification (GUT) era are calculated. Irrespective of the specific process under consideration, the UHE proton spectrum ‘‘recovers’’ at ∼1.8×${10}^{11}$ GeV after a partial Greisen-Zatsepin-Kuz’min ‘‘cutoff’’ at ∼5×${10}^{10}$ GeV and continues to a GUT-scale energy with a universal shape determined by the physics of hadronic jet fragmentation. The shape of the UHE neutrino spectrum is, however, sensitive also to the cosmological evolution of the defects involved.

Early-Universe decay of 17 keV neutrinos is likely to happen in equilibrium for lifetime ${\mathit{t}}_{\mathrm{free}}$<${10}^5$ sec. For 3×${10}^{\mathrm{-}4}$<${\mathit{t}}_{\mathrm{free}}$<1×${10}^{\mathrm{-}2}$ sec the primordial ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mass fraction ${\mathit{Y}}_{\mathit{p}}$ may be reduced by up to 0.028 relative to the standard model. Bosons from the decay can form a Bose condensate, with interesting consequences for galaxy formation and the dark-matter problem. The effects are generic to early-Universe decay of fermions, not just of relevance for 17 keV neutrinos.

Extended technicolor theories generate potentially large corrections to the Zbb¯ vertex which can be observed in current experiments at the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collider LEP.

Tests of the electric charges carried by the positron and antiproton are derived from recent measurements of the cyclotron frequencies of these particles, and from the spectroscopy of exotic atoms in which they are constituents.

Results from a complete set of polarization-transfer observables for quasifree (p→,n→) scattering at 495 MeV are reported. Measurements were carried out on ${\mathrm{CD}}_2$, carbon, and calcium targets at a laboratory scattering angle of 18° using the new neutron time-of-flight facility at LAMPF. The ratio of spin-longitudinal to spin-transverse responses at a momentum transfer of approximately 1.72 ${\mathrm{fm}}^{\mathrm{-}1}$ is extracted from the data and compared to distorted-wave calculations incorporating a random-phase approximation description of the nuclear response. No enhancement is observed in the experimental ratio.

We report exact quantum calculations for the hydrogen atom in crossed magnetic and electric fields. Employing the complex-coordinate-rotation method we are able to extend the calculations of eigenstates far into the continuum region. Calculated photoionization cross sections are found to exhibit strong Ericson fluctuations, a characteristic feature of chaotic scattering. This interpretation is supported by classical trajectory calculations which reveal a fractal dependence of the classical ionization time on the initial conditions.

We show that optical image-bearing beams manifest a generalized version of Berry’s phase. This topological phase results in a rotation, equal to Berry’s phase (with an opposite sign), of an arbitrary input optical image. Our method of measuring this phase applies to coherent as well as incoherent illumination, and thus is demonstrated experimentally using an incandescent light bulb. Furthermore, this is one of a few cases where a phase property of an ensemble of ‘‘particles’’ is unique, regardless of their energies, momenta, and spins.

We show experimentally that the output light of a single-mode semiconductor laser is changed into chaotic light after passage through a narrow spectral filter. Simple linear filtering allows us to distinguish between different statistical models of laser phase noise. The experimental results agree with the phase-diffusion model.

An investigation of the nonlinear dispersive equations of continuum mechanics reveals localized standing-wave solutions that are domain walls between regions of different wave number. These states can appear even when the dispersion law is a single-valued function of the wave number. In addition, we calculate solutions for kinks in cutoff and noncutoff modes, as well as cutoff breather solitons.

We present an experimental study of thermal plumes growing in Hele-Shaw cells which shows the existence of new objects, analogous to Saffman-Taylor fingers, for which the thermal boundary layer plays the role of the interface. The theoretical analysis reveals the underlying selection mechanism, which is provided by heat diffusion.

The energy cascade in both hydrodynamic and hydromagnetic Boussinesq convection is investigated at large Rayleigh numbers, using a scalar model for turbulence. Depending on the relative importance of direct and inverse transfer, either we observe classical Kolmogorov ${\mathit{k}}^{\mathrm{-}5/3}$ spectra or, if there is a strong inverse transfer of kinetic energy, we find a ${\mathit{k}}^{\mathrm{-}7/5}$ spectrum for the temperature fluctuation and a ${\mathit{k}}^{\mathrm{-}11/5}$ spectrum for the kinetic energy (Bolgiano-Obukhov scaling). We derive dissipative cutoff wave numbers that are consistent with these spectra.

New types of nonlinear evolution equations are derived that describe finite-amplitude surface gravity waves on a two-dimensional incompressible and inviscid fluid of finite depth. The novelty is as follows: (a) The equation can be expressed as a single equation with respect to the surface elevation, and (b) the expansion is in a steepness parameter and does not involve other approximations such as long waves or shallow water. Both the shallow- and deep-water limits of the equations are discussed.

Lower hybrid waves are a demonstrated, continuous means of driving toroidal current in a tokamak. When these waves propagate in a tokamak fusion reactor, in which there are energetic α particles, there are conditions under which the α particles do not appreciably damp, and may even amplify, the wave, thereby enhancing the current-drive effect. Waves traveling in one poloidal direction, in addition to being directed in one toroidal direction, are shown to be the most efficient drivers of current in the presence of the energetic α particles.

The simple Ohm’s law η${\mathit{j}}_{\mathrm{\parallel }}$=${\mathit{E}}_{\mathrm{\parallel }}$ is not satisfied in the a/2≲r≤a region of the REPUTE-1 reversed-field-pinch plasma. Fluctuation-induced electric fields, such as 〈ṽ×B̃〉, are not sufficient to account for η${\mathit{j}}_{\mathrm{\parallel }}$-${\mathit{E}}_{\mathrm{\parallel }}$ at the edge. Current diffusion due to magnetic fluctuations, carried by fast electrons rather than bulk cold electrons, sustains the edge parallel equilibrium current.

Molecular-dynamics simulations of the Σ3〈110〉(211) twin boundary in Ag predict a thin (1 nm) boundary phase of the 9R (α-Sm) structure. High-resolution electron microscopy shows the presence of the predicted structure. We also calculate the energy ab initio for several hypothetical structures of Cu and Ag. Low energies of the 9R structure and other polytypes, low experimental stacking-fault energies, and the hcp-fcc energy difference are correlated and explained in terms of an effective nearest-neighbor Ising interaction.

Spinodal decomposition in thin films of a blend of deuterated polystyrene and poly(styrene-co-4-bromostyrene) was studied with time-of-flight–elastic-recoil detection and light microscopy. We found different demixing behavior, depending on whether the films were prepared on the oxide layer of a silicon wafer or on a chromium-plated one. On the latter surface a bilayer of the two bulk phases is formed, whereas on the oxide layer a domain structure remains. The formation of the bilayer is ascribed to the complete wetting of each surface by the corresponding, preferentially adsorbed component.

The angle, energy, and fluence dependence of electron emission following the interaction of normally incident 100-MeV ${\mathrm{Ne}}^{9+}$ ions with thin polypropylene foils and 170-MeV ${\mathrm{Ne}}^{7+}$ projectiles with Mylar foils has been investigated experimentally. Spectra were taken for electron ejection angles of 0°, 45°, and 120° at fluences in the range of 2×${10}^{13}$ to 4×${10}^{15}$ ions/${\mathrm{cm}}^2$. A fluence-dependent carbon KLL Auger energy shift of up to 68 eV was observed. Model calculations for the nuclear track potential are consistent with the experimental findings.