A self-induced transparency (DIT) soliton can coexist with a nonlinear Schrödinger (NLS) soliton. This mixed state is called an SIT-NLS soliton. The phase change of the new soliton is governed solely by the NLS component and the pulse delay is determined solely by the SIT component when a detuning from the resonance is zero. It is shown for the first time that a stable 2π-(N=1) SIT-NLS soliton exists and that high-order SIT/NLS solitons always split into multiple 2π-(N=1) SIT-NLS solitons.

Stimulated Raman and Brillouin scattering in the quasi-steady-state (QSS) regime are analyzed by the inverse-scattering transform (IST) with nonoverlapping square wave packets and second-order Zakharov-Shabat scattering problem. It is shown that the important QSS characteristics, namely, the number of pulses required for establishing the QSS condition, the Stokes growth, and the development of polarization are readily calculated using IST. These results are usually obtained by extensive numerical computations which, however, do not lead to their fundamental determinations. The IST results are found to be in excellent agreement with experimental observations and numerical computations.

It is shown that stimulated synchrotron emission and absorption can act simultaneously on a relativistic electron beam with a narrow energy spread to reduce the spread significantly. This beam ‘‘cooling’’ mechanism acts most effectively for beam energies belonging to a sequence of discrete values, one for each synchrotron harmonic. The discrete energy values are absolute, and are not influenced by external parameters such as magnetic field strength. Application of this mechanism to cool beams for free-electron lasers, synchrotron-radiation lasers, and slow-wave cyclotron amplifiers is suggested.

We preent numerically obtained bounded solutions of the one-dimensional complex Ginzburg-Landau equation with a destabilizing cubic term and no stabilizing higher-order contributions. The boundedness results from competition between dispersion and nonlinear frequency renormalization. We find chaotic and also stationary and time-periodic states with spatial structure corresponding to a periodic array of pulses. An analytical description is presented. Possibly experimental results connected with the dispersive chaos found in binary-fluid mixtures can be explained.

A numerical simulation of a complex turbulent shear flow using large-eddy simulation techniques is carried out. The filtered Navier-Stokes equations are solved with a finite-volume method. The subgrid model is a local adaptation to the physical space of isotropic spectral eddy-viscosity models. The statistics of the mean field are in good agreement with the experimental data available, corresponding to low step. Calculations in a high-step case show that the eddy structure of the flow presents striking analogies with the plane shear layers, with large billows shed behind the step, and longitudinal hairpin vortices strained between these billows.

We present a geometric estimate from below on the growth rate of a small perturbation of a three-dimensional steady flow of an ideal fluid and thus we obtain effective criteria for local instability for Euler’s equations. We use these criteria to demonstrate the instability of several simple flows and to show that any flow with a hyperbolic stagnation point is unstable.

We present a new, rigorous treatment of Poisson’s equation in solids with no shape approximation to the potential. In contrast to existing techniques, this method allows the unified treatment of periodic solids, as well as materials containing imperfections such as substitutional or interstitial impurities and disordered alloys. Explicit expressions for the potential and the Coulomb part of the energy are given. The validity and utility of this approach is demonstrated by numerical calculations.

The diffusion and absorption coefficients of microwave radiation in random mixtures of metallic and dielectric spheres are determined from measurements of the intensity correlation function with frequency shift and of the scale dependence of transmission. We find a narrow window of localization in frequency and metallic concentration. The transition is rounded by the presence of absorption.

Observations of periodic intensity bursts during the start-up phase of a free-electron-laser oscillator operating in the microwave regime are reported. The bursts are composed of radiation micropulses several nanoseconds wide and separated by the resonant-cavity round-trip time (∼35 ns). The occurrence of the bursts is correlated to random current spikes superposed on the continuous electron-beam current density. The observations are compared with theoretical results from an impulse response model of a free-electron laser.

A single-particle computation, simple analysis, and a particle simulation show that energy gain of an electron in a vacuum is possible using a laser and with a weak perpendicular static electric field (${\mathit{E}}_{\mathrm{app}}$). This simple system does not need any structure to accelerate the electron. If ${\mathit{E}}_{\mathrm{app}}$=0 an electron will just oscillate, with no net acceleration because of the symmetry of the laser’s electromagnetic wave in space and time. The static electric field breaks the symmetry of the wave so that the a electron is accelerated in both half wavelengths of the wave.

High-intensity Cherenkov radiation (CR), emitted in air from a high-current 30-MeV electron bunch (2×${10}^{11}$ electrons/bunch) of the linear accelerator at the Institute of Scientific and Industrial Research was observed at wavelengths from 0.4 to 3 mm. The radiation was emitted at an angle of 38 mrad, with some spread, from the beam axis. The radiation measured was about ${10}^{11}$ times as intense as that calculated for ordinary CR. Such enhancement is attributed to the coherence which appears in CR emitted from electron bunches of relatively short length.

We report the first observation of the photorefractive effect in a polymeric material, the electro-optic polymer bisphenol-A-diglycidylether 4-nitro-1,2-phenylenediamine made photoconductive by doping with the hole-transport agent diethylamino-benzaldehyde diphenylhydrazone. The gratings formed exhibit dynamic writing and erasure, strong electric-field dependence, polarization anisotropy, and estimated space-charge fields up to 26 kV/cm at an applied field of 126 kV/cm. Application of similar concepts should provide a broad new class of easily fabricated photorefractive materials.

Microwave transmission through a random mixture of aluminum and Teflon spheres at a metal filling fraction of 0.30 is found to fall initially as 1/${\mathit{L}}^2$ in agreement with predictions of the scaling theory of localization. The renormalized diffusion coefficient is determined from measurements of transmission and of the spectral intensity correlation function. This function is found to be an expansion in ${\mathrm{\delta }}^{\mathrm{-}1}$, where δ is the product of the width and density of states in the medium. From these results we find the Ioffe-Regel criterion for photons to be ${\mathit{kl}}_{\mathit{c}}$=1.6±0.4.

A new type of electron linear accelerator realized in a vacuum system, based on the ${\mathbf{V}}_{\mathit{p}}$×B acceleration scheme observed originally in plasma, has been demonstrated. The present system has a static magnetic field applied vertically to the wave propagation direction, and the particles are accelerated along the wave front at constant phase with respect to the wave. In this scheme, a greater acceleration rate than that of conventional linear accelerators has been observed. The acceleration rate is also larger than that expected from the simple theoretical model presented so far.

We develop a space-time renormalization-group method to study diffusion in a disordered medium. We prove rigorously that a random walk with transition probabilities given by a random matrix diffuses in a Brownian way for weak disorder if d>2. We also show that the disorder induces polynomial decay of velocity-velocity correlations.

Using a simple wake function, it is shown that the equilibrium bunch length in electron storage rings with localized wake can have a cusp-catastrophe behavior. Contrary to the results of the conventional theory for a distributed wake force, the system becomes bistable (period 1 and period 2) and exhibits hysteresis in some region of the parameter space. These features are predicted by a Gaussian approximation and confirmed by multiparticle tracking.

The equilibrium polarization of the electron spin has been measured at the TRISTAN electron-positron storage ring. The measurement was carried out by using a laser polarimeter detecting an asymmetry in the Compton scattering of a circularly polarized laser beam on polarized electrons. The laser polarimeter allows for simultaneous measurements of the transverse and longitudinal polarization with sufficient accuracy. The polarization level was relatively high, 40% at an electron-beam energy of 29 GeV, and the polarization vector was inclined at an angle of about 30°.

We present a physical model to describe the equilibrium probability distribution function (PDF) of velocity differences across an inertial-range distance in 3D isotropic turbulence. The form of the non-Gaussian PDF agrees well with data from direct numerical simulations. It is shown that these PDF’s obey a self-similar property, and the resulting inertial-range exponents of high-order velocity structure functions are in agreement with both experimental and numerical data. The model suggests a physical explanation for the phenomenon of intermittency and the nature of multifractality in fully developed turbulence, namely, local self-distortion of turbulent structures.

We present experimental and theoretical results for Taylor-vortex flow subjected to a Coriolis force. The measurements were done in an apparatus consisting of two concentric horizontal cylinders with the inner one rotating, and mounted on a table rotating about a vertical axis with dimensionless angular velocity Ω. For Ω≲8.5, the first bifurcation upon increasing the inner-cylinder rotation rate was to tilted vortices. For larger Ω, there was a Hopf bifurcation to traveling tilted vortices. Measurements of the critical Reynolds number, wave number, and tilt angle are in quantitative agreement with the theory.

Laboratory experiments and numerical simulations have been conducted for plane channel flow with a streamwise-periodic array of cylinders. The primary transition in this open flow occurs as a convective rather than absolute instability and leads to traveling-wave packets, which advect out of the system. The ordered secondary state is characteristic of closed flows, in contrast with other open flows where the primary transition often leads directly to turbulence.