Sum rules and causality are used to obtain a general relation connecting the dynamic and static properties of any dielectric system which supports polarization waves. The Lyddane-Sachs-Teller relation appears as a special limiting case. Inhomogeneous media provide illustrative examples.

We report measurements of microwave intensity statistics in random configurations of polystyrene spheres contained in a cylinder with reflecting walls. As the sample thickness increases measurements of the intensity distribution and the intensity correlation function with frequency shift reveal a crossover from uncorrelated to correlated photon diffusion.

The spiking behavior of free-electron lasers, or sideband instability, has been observed for the first time in the time domain using an autocorrelator on the MKIII free-electron laser at Stanford University. The measurement is compared with simulations and qualitative theory.

Wetting immiscible displacement of one fluid by another in a porous medium yields self-affine (anisotropic) fractal interfaces between the two fluids. Water-air interfaces are characterized experimentally by a scale-dependent roughness w(L)=${\mathrm{AL}}^{\beta }$, with β=0.73±0.03, independent of the capillary number Ca, and A∝${\mathrm{Ca}}^{\mathrm{-}0.47\pm 0.06}$. The exponent β is related to the ‘‘box’’ and ‘‘divider’’ dimensions by $D_b$=2-β and $D_d$=1/β, respectively.

The nonlinear bistable effect presented by a mechanical string resonator is set in evidence as a hysteresis of the output intensity upon the input one. Interpretation is given through approximating the nonlinear equation of motion of a fixed boundary string.

Significant forces between dielectric objects can be induced by intense optical fields. We discuss the origin of these forces which are very long range and oscillate in sign at the optical wavelength. A consequence is that light waves can serve to bind matter in new organized forms. We experimentally demonstrate the simplest case by observing a series of bound states between two 1.43-μm-diam plastic spheres in water, and discuss the extension to more complex cases.

The dynamics of a single topological defect and the interaction between pairs, including the process of annihilation of defects of opposite topological charge, are studied experimentally and theoretically near the onset of weak turbulence in Williams domains of electroconvecting nematics. The existence of topological defects requires a gauge field theoretical treatment, enriching the commonly used ‘‘amplitude equations.’’ The gauge field carries the interaction which is found to be of finite range in agreement with detailed observations.

We present a vorrex paradigm for interpreting the evolution of shock-accelerated density-stratified interfaces beyond early times. The paradigm is investigated and illustrated through a series of numerical experiments that compare favorably with recent shock tube experiments. Color images of space-time diagrams of the one-space integrated vorticity function highlight primary and secondary features of the emerging vortex structures.

Coherent effects in synchrotron radiation (SR) have been observed for the first time from 180-MeV short electron bunches of 2.4 mm using the Tohoku 300-MeV Linac. The intensity of the coherent SR was about ${10}^5$ times as strong as that of incoherent SR in the wavelengths of 0.4–2.2 mm. This enhancement factor corresponds to the number of electrons in a bunch. The SR intensity showed a quadratic dependence on the electron beam current. The radiation was mainly polarized in the orbital plane. The possibility of induced rf in a vacuum chamber was excluded experimentally.

We studied the Gγ=2 imperfection depolarizing resonance at 108 MeV, both with and without a Siberian snake, by varying the resonance strength while storing beams of 104- and 120-MeV polarized protons at the Indiana University Cooler Ring. We used a cylindrically symmetric polarimeter to simultaneously study the effect of a depolarizing resonance on both the vertical and radial components of the polarization. AT 104 MeV we found that the Siberian snake eliminated the effect of the nearby Gγ=2 depolarizing resonance.

With the use of a standard model, beam breakup growths in all types of linacs are shown to be classified by only two dimensionless parameters which depend on the beam current, beam energy, pulse length, machine length, breakup mode frequency, focal strength, and transverse shunt impedance. This classification suggests that rf cure plays a more important role in the control of beam breakup than focusing in a long pulse beam. The converse holds for a short pulse beam.

Harmonic absolute instability in the ${\mathrm{TE}}_{21}$ mode is found to cause mode competition in a new millimeter-wave gyrotron traveling-wave experiment designed for high stability in the ${\mathrm{TE}}_{11}$ mode. Complete suppression of this instability by the application of the ${\mathrm{TE}}_{11}$ drive has been observed with beam current up to at least 6 times the instability threshold, which results in high amplified power (∼25 kW) at high efficiency (∼23%). The study is significant in that it demonstrates that cyclotron-maser amplifiers may operate at a current well above oscillation threshold without degradation in saturated performance.

A new nonclassical model is proposed for the radiation from electrons skimming over and colliding at grazing incidence with a conducting diffraction grating. Radiation originating from induced surface currents and bremsstrahlung is amplified as it passes through spatially modulated wave functions above the grating. The predicted magnitude and dependence on electron beam thickness agree with experiments at visible wavelengths and suggest the possibility of a compact x-ray laser.

We show that a semiconductor photodiode, or photoconductor, will exhibit a strong reactive response to optical radiation tuned to the transparent region just below the band gap. This response is due to the excitation of virtual electron-hole gas readily polarized by the dc electric field which can contribute a major change (>1) in the low-frequency dielectric constant. For ultrahigh speed signals, this nondissipative photoresponse can become similar to conventional dissipative photoresponse by real carriers excited above the band gap. The influence of this reactive response on zero-point electromagnetic fluctuations may aid the laboratory detection of Unruh-Davies-Fulling-DeWitt radiation.

Molecular-dynamics simulations of two immiscible fluids confined between solid walls and sheared in a Couette geometry were performed as a function of shear rate for a range of wall and fluid properties. Changes with capillary number in the interface shape and dynamic contact angle were consistent with previous analytic results. Computed velocity fields showed that the usual no-slip boundary condition broke down within ∼2 atomic spacings from the contact line. The slip appears to be associated with the breakdown of local hydrodynamic theory at atomic scales.

Two pulse photon echoes were observed in organic dye molecules in solution using 6-fs optical pulses. The results show an initial rapid dephasing of the echo due to level multiplicity followed by quantum beaks. The temporal decay of the quantum beats is characterized by a ${\mathrm{T}}_2$ of about 60 fs.

We discuss the possibility of the coexistence of two states with different wavelengths in the framework of phase dynamics. We investigate in detail this phenomenon which is intrinsically nonlinear and we give a Lyapunov functional for the case of a phase associated with a stationary pattern. The relationship of the confined states discussed here with recent experimental observations of localized states posessing a wavelength different from that in the bulk of the container for the case of slot convection and for the Taylor instability between co-rotating cylinders is critically examined.

Theoretical analysis of vorticity disturbances in axisymmetric elongational flow of dilute polymer solutions shows that polymers decrease the vorticity near the symmetry axis and increase it away from this axis, at distances larger than the square root of the ratio betwen the kinematic viscosity and the strain rate of the fluid. Enhancement of large-scale vorticity is a consequence of elastic energy storage by macromolecules that inhibits the energy cascade towards the dissipative scales. A similar mechanism may be expected to play an important role in turbulence modification by polymers.

Stability of a klystron-type free-electron laser as a new microwave source in the two-beam concept is analyzed by means of a macroparticle approach. A universal gain equation for initially bunched beams is derived and proved to have a limit cycle. Motion of the macroparticle which represents the bunch center is straightforwardly reconstructed from the solution for the gain equation and the stability analysis shows that the macroparticle’s motion is very stable over many periods.

Structural and dynamical properties of nonlinear traveling-wave states in binary fluid layers heated from below are determined by numerical integration of the proper hydrodynamic field equations with experimental horizontal boundary conditions. The fluid separates into traveling rolls of alternating high and low concentration. Phase differences drive lateral currents and Reynolds stresses generate lateral mean flow.