The phase shift predicted by Aharonov and Casher for a magnetic dipole diffracting around a charged electrode has been observed for the case of thermal neutrons, using a neutron interferometer containing a 30-kV/mm vacuum electrode system. The judicious use of the Earth’s gravitational field introduces a spin-independent phase shift which enables unpolarized neutrons to be used. A supplementary magnetic bias field of the correct magnitude allows first-order sensitivity to be achieved; even so, the theoretically predicted phase shift is only 1.50 mrad for the geometry and conditions of the experiment. We observe a phase shift of 2.19±0.52 mrad.

Flat, cylindrical, and spherical soliton solutions to various model equations are known. Many of these exact solutions have been seen in numerical simulations. However, there are few simulations that actually show that exact flat solitons can break up into an array of exact cylindrical or spherical solitons and follow this on a step by step basis. This Letter presents the first of these two kinds of transition for the Zakharov-Kuznetsov equation governing ion acoustic solitons in strongly magnetized plasmas.

The optical diffusion coefficient D and photon absorption time ${\mathrm{\tau }}_{\mathrm{a}}$ in a sample of titania spheres in air are determined from measurements of picosecond pulse transmission over the wavelength range 514–650 nm. At 514 nm, D=1.45×${10}^4$ ${\mathrm{cm}}^2$/s. This corresponds to an anomalously small value of the effective mean free path l̃==3D/v=250 Å, where v is the velocity of light in the medium. Throughout the wavelength range measured, l̃≤0.15λ. Assuming that D is reduced by coherent backscattering and that the optical mobility edge is given by the Ioffe-Regel criterion, the renormalization factor at 514.5 nm is 2.8.

Inverted micelles are found to exhibit marked viscoelasticity with a pronounced dependence on volume fraction. The frequency dependence, measured using both ultrasonic and Brillouin techniques, reflects the dynamics of the interactions between the micelles. At low frequencies they behave as isolated spheres, while at high frequencies they behave as an instantaneous connected network. The rigidity of this network exhibits power-law scaling with volume fraction, consistent with rigidity percolation.

We report frequency locking at Farey fractions of an electrically modulated semiconductor laser within an external cavity. The winding numbers as a function of the ratio of the modulation frequency to inverse resonator round trip time show the hierarchy of a Farey tree and the structure of a devil’s staircase. The dimension of the set complementary to the stairs is determined to be 0.89. This demonstrates that the external-cavity semiconductor laser exhibits the universal properties characteristic for nonlinear systems driven by two competing frequencies.

Quasielastic light scattering from Brownian particles in the rarefied environment of a glow discharge exhibits Gaussianlike intensity correlation functions owing to the long mean free paths of the particles. The shape of the correlation function depends on the particles’ average thermal velocity and friction coefficient, which can be related to aggregate mass and structure, and indicates a crossover from kinetic to hydrodynamic behavior.

We report the first direct observation of the electromagnetic deflection of high-energy electron and positron beams as they pass each other with small impact parameters. Measurements of the deflection amplitude are found in agreement with theoretical expectations. This phenomenon, which is sensitive both to the relative position of the two beams and to their transverse sizes, has been used successfully to optimize and maintain collisions at the interaction point of the SLAC Linear Collider.

Fermat’s principle shows that a definite convex set of feasible slowness models, depending only on the traveltime data, exists for the fully nonlinear traveltime inversion problem. In a new iterative reconstruction algorithm, the minimum number of nonfeasible ray paths is used as a figure of merit to determine the optimum size of the model correction at each step. The numerical results show that the new algorithm is robust, stable, and produces very good reconstructions even for high contrast materials where standard methods tend to diverge.

In this Letter we study subcritical transitions in spatially extended systems when topological defects are present. The behavior of a single defect is discussed in the framework of Ginzburg-Landau models. We show how the transition from one stable state to the other is affected by the presence of defects. Our results, claimed to be independent of these models, are illustrated with examples coming from Couette-Taylor, liquid crystals and convective instabilities.

We have directly measured the time-dependent electromagnetic shock wave generated by an electric surface-dipole distribution propagating faster than the phase velocity in the underlying dielectric substrate. The results are in good agreement with a theory describing the moving volume-dipole distribution with the inclusion of an equal strength surface reflection.

The question of whether it is possible to have a kinematic magnetic dynamo for a conducting fluid with time-independent (steady) velocity field v(x) and vanishingly small electrical resistivity has remained an open question in the understanding of the origin of magnetic fields in nature. By considering the zero resistivity dynamics, examples of steady dynamos are found. Analysis of these examples supports the conjecture that, for sufficiently small resistivity, 2 dynamo action can occur in typical, smooth, steady, three-dimensional, chaotic fluid flows.

A spirally deformed surface due to a single-atomic shear of a screw dislocation emerging on a GaAs(110) surface has, for the first time, been observed in the precision of ∼0.01 Å by interferometrically measuring the phase of the reflected electrons. In the case of an obliquely emerging dislocation, the surface around the dislocation core was observed to be deformed rather asymmetrically than uniformly. The result can be explained by considering surface stress relaxation.

Using digital subtraction radiography, we study the basic modes of a granular material (here sand) flowing through a flat hopper. These modes take the form of density waves whose formation and propagation is controlled by several parameters, including the mass flow rate M and the hopper angle θ. We consider the effect of roughness on pattern formation in this system using mixtures of smooth and faceted sand and show the existence of a bifurcation at a mass fraction of faceted sand X≊0.2. Propagating patterns form in faceted sand but not in smooth sand of the same size.

Results from a quasioptical gyrotron experiment with a 20–28-cm mirror separation are presented showing operation from 95–130 GHz at powers up to 148 kW and output efficiencies up to 12%. The output coupling could be varied from 0.4%–3% by changing the mirror separation and operating frequency. Efficiency optimization by variation of output coupling and by tapering the magnetic field has been demonstrated and regions of single-mode operation at powers up to 125 kW have been characterized.

We report measurements of the temporal autocorrelation function g(t) of light scattered from critical binary liquid mixtures which are being continuously and turbulently stirred. The functional form of g(t) changes dramatically when the turbulent shear is changed from weak to strong. In the strong shear regime g(t) becomes a stretched exponential function, with an exponent that decreases as the temperature approaches the critical temperature. This stretched exponential behavior is associated with spatially intermittent suppression of critical fluctuations produced by the turbulence.

A novel multipole wiggler and an associated beam line have been installed in the accumulation ring for the TRISTAN project at the National Laboratory for High Energy Physics (KEK). An intense source of circularly polarized synchrotron radiation in the energy ranging 40 to 80 keV has been achieved for the first time. A degree of circular polarization, ${\mathrm{P}}_{\mathrm{c}}$≃0.7, at 60 keV of photon energy was in good agreement with a theoretical prediction in the 6-GeV operation of the accumulation ring.

We show that shallow water waves in a viscous fluid are not damped if the fluid is adequately heated from below. The critical temperature gradient needed to sustain the wave as well as its frequency are determined analytically. The nonlinear evolution of the wave is governed by the Korteweg–de Vries equation.

Collisions of electron and positron bunches at the interaction point of the linear collider at SLAC have led to the first detected emission of beamstrahlung. This radiation, caused by the collective electromagnetic fields of one beam deflecting particles of the other, is a potential tool for optimizing collisions in linear colliders.

The problem of determining a scattering potential from measurements of the far-field intensity distribution obtained in a set of scattering experiments is addressed within the Born approximation. It is shown that this problem admits a conceptually and computationally simple approximate solution if the incident and scattered radiation are mutually coherent in the far field and if the spatial resolution at which the far-field distribution of total intensity is measured is sufficiently high. The resolution of the inversion procedure is discussed and a computer simulation illustrating the proposed method is presented.

A method of describing turbulence in terms of dynamical connectivity in the wave-number space is proposed. The connectivity is quantified by the information theoretical quantities, i.e., mutual information and cross information flow rate. This method is applied to the analysis of two simple examples of turbulence in one spatial dimension. Although the examples have quite different physical origins, the information structures of the wave-number space turn out to be quite similar: The wave-number space consists of several regions generating information in different ways, and how information flows between these regions reflects the dynamical structure of turbulence.