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We have used high‐resolution magnetic birefringence to study very dilute mixtures of the nonionic surfactant pentaethylene glycol mono‐dodecyl‐ether (C12E5) in water at fields to H=18 T. The induced refractive index anisotropy Δn shows distinct H dependencies in the Lα‐lamellar and L3‐‘‘sponge’’ phases, and demonstrates that these are separated by a two‐phase coexistence region. In the L3 phase and for surfactant concentrations γ≂0.02 (the vicinity of the Lα phase terminus), we observe a sharp change in the magnitude and H dependence of Δn. A quantitative analysis shows this to be consistent with a crossover from a highly‐connected ‘‘symmetric sponge’’ to a droplet or ‘‘asymmetric sponge’’ structure as a function of γ, a result previously suggested by neutron scattering and electrical conductivity measurements [R. Strey, R. Schomacker, D. Roux, F. Nallet, and U. Olssen, J. Chem. Soc. Faraday Trans. II 86, 2253 (1990)]. Finally, for γ≳0.02 and at large H, we present evidence of a field‐induced transformati...

From numerical solutions of two colliding electromagnetic solitary waves, it is shown that their shapes are modified, and a trailing wake of plasma oscillations is produced by the collision. They therefore cannot be classified as solitons. For sufficiently large relative velocities, however, it is shown that the modifications to the vector and scalar potentials, as well as to the wake due to the collision, are small.

The effects of a cold ion beam on an ion‐acoustic solitary wave whose potential is large enough to reflect the ion beam are studied in the regime in which the solitary‐wave response to the beam is adiabatic. It is shown that the solitary wave can be amplified by a large factor, and that it is accelerated until its velocity equals the beam velocity.

The properties of solitary waves in a plasma with an ion beam are investigated. The two conditions for the existence of solitary‐wave solutions are determined and presented graphically in parameter space. Electron inertia is shown to restrict the regime of the fast and slow beam solitary waves to beam velocities that are less than the electron thermal velocity.

The properties of arbitrary‐amplitude solitary waves in a plasma consisting of drifting ions and nondrifting electrons are investigated. The conditions for the existence of solitary‐wave solutions are determined. It is shown that electron inertia has the significant effect of restricting the regime of solitary waves to ion drift velocities that are less than the electron thermal speed. Because of this restriction relativistic effects are small.

For a weakly nonuniform medium, a solitary wave solution of the variable‐coefficient nonlinear Schrodinger equation is obtained through second order in the expansion parameter. From a generalization of the second‐order result, the form of the solution to all orders is derived from which the conditions for an exact, distortionless solitary wave in a nonuniform medium are obtained. By use of a transformation, these results are shown to apply a weakly dissipative medium.

The soliton modifications resulting from the addition of a small third derivative term, due to higher‐order dispersion, to the nonlinear Schrodinger equation are investigated. Based on direct perturbation theory, it is shown that through first order, the soliton phase and velocity are modified, but the shape, amplitude, and width are unchanged. The radiation stimulated by the third derivative term, which is not predicted by the perturbation theory, is also derived. The expression obtained confirms the result of Wai (Ph.D. thesis, University of Maryland, 1988), which was obtained by a different method. The rate of change of the soliton amplitude due to this radiation, which emerges in front of the soliton, is calculated. The nonlinear term that drives the radiation is shown to grow to a value that is much larger than the unperturbed value.

Some properties of small‐amplitude ion‐acoustic solitons in a plasma consisting of nondrifting electrons and drifting ions are investigated. Electron inertia effects are shown to be considerably more important than relativistic effects. It is also shown that ion‐acoustic soliton solutions exist only if the ion drift velocity is less than the electron thermal velocity.

We have studied the current-carrying capability of high quality epitaxial MgB2 films synthesized using the hybrid physical-chemical vapor deposition technique by both transport measurement in nanobridge constrictions and magnetization measurement. An extremely high self-field critical current density Jc(0)>108A∕cm2, approaching the theoretical depairing current of MgB2, was observed on a 150nm bridge, indicating an excellent current-carrying capability in these films. The magnetization measurement also showed very high Jc.