A quasi two-dimensional open Fermi surface with perfect nesting in the third direction is unstable in a magnetic field, versus the formation of density wave phases with quantized wave vectors. We prove that, within the same theoretical model, the Hall conductivity is exactly quantized at zero temperature in each field-induced phase. Application to quasi one-dimensional metals, such as the Bechgaard salts, is discussed.

Reaction-limited cluster aggregation is modeled with the kinetic rate (Smoluchowski) equations, using a kernel determined intrinsically by the clusters fractal geometry. The kernel scales with cluster mass as ${\mathrm{M}}_1$${\mathrm{M}}_2^{\lambda \mathrm{-}1}$ (${\mathrm{M}}_1$≫${\mathrm{M}}_2$), and ${\mathrm{M}}_1^{\lambda }$ (${\mathrm{M}}_1$≊${\mathrm{M}}_2$), with λ=1 in three dimensions, resulting in exponential kinetics and a cluster mass distribution ${\mathrm{C}}_{\mathrm{M}}$∼${\mathrm{M}}^{\mathrm{-}\mathrm{\tau }}$, with τ=(3/2), in excellent accord with experiments. The singular nature of this solution forces the adjustment of the cluster fractal dimension, ${\mathrm{d}}_{\mathrm{f}}$, thereby determining its value.

The first self-consistent, three-dimensional analysis of plasma cloud evolution in the ionosphere is presented. It is demonstrated that there is a preferred perpendicular scale size associated with 3D plasma clouds given by ${\mathrm{r}}_{\mathrm{c}}$∼c(${\mathrm{T}}_{\mathrm{e}}$+${\mathrm{T}}_{\mathrm{i}}$)/${\mathrm{eB}}_{\mathrm{z}}$${\mathrm{V}}_{\mathrm{n}}$${\mathrm{\Gamma }}_{\mathrm{c}}$, where ${\mathrm{r}}_{\mathrm{c}}$ is the cloud radius, ${\mathrm{T}}_{\mathrm{\alpha }}$ is the temperature of the α species, ${\mathrm{B}}_{\mathrm{z}}$ is the ambient magnetic field, and ${\mathrm{V}}_{\mathrm{n}}$ is the neutral wind speed, and ${\mathrm{\Gamma }}_{\mathrm{c}}$<1/ √2 .

It is demonstrated that the ${\mathrm{\pi }}^0$/γ ratio can never be a definite signal of the quark-gluon plasma but may be a rather useful diagnostic of the plasma only if measured in combination with dileptons in the kinematic regime ${\mathrm{p}}_{\mathrm{T}}$≊2–4 GeV/c.

The analyzing-power behavior and the isospin dependence of the cross sections for near-threshold reactions ${}_{}{}^{13}{}_{}{}^{}$C(p,${\pi }^{\pm }$) and ${}_{}{}^{12}{}_{}{}^{}$C(p,${\pi }^{+}$) are compared with expectations from pion production measurements in free two-nucleon collisions. The general agreement for ($p_{\mathrm{pol}}$,${\pi }^{+}$) suggests that the stable analyzing-power pattern observed for ($p_{\mathrm{pol}}$,${\pi }^{\mathrm{-}}$) continuum transitions may reflect the as yet unmeasured free $p_{\mathrm{pol}\mathrm{n}\to \mathrm{pp}{\pi }^{\mathrm{-}}}$ behavior. We also discuss constraints imposed by quasifree ${\mathrm{NN}}_{\mathrm{pol}\to \mathrm{NN}\mathrm{\pi }}$ expectations on the interpretation of anomalous ($p_{\mathrm{pol}}$,${\pi }^{+}$) results for two strongly populated states at high excitation in ${}_{}{}^{13}{}_{}{}^{}$,14C.

We present a theory and calculations for double ionization of atomic carbon by a pulsed strong laser of intensity up to ${10}^{14}$ W/${\mathrm{cm}}^2$. Up to five-photon ionization is included in a formalism that accounts for the modification of doubly excited states by the laser field. Sequential and direct double ionization are calculated, as are excited ionic states and their role in the possibility of creation of inverted ionic populations.

The transition to turbulence via spatiotemporal intermittency observed in a partial differential equation displays statistical features typical of critical phenomena. Analogy with directed percolation is drawn.

Charge-dependent convective impurity transport is observed in the central core of PBX H-mode discharges by measurement of radial profiles for both low- and high-Z intrinsic impurities in the presence of strong sawtooth activity. The time-evolving $Z_{\mathrm{eff}}$ profile and central metallic densities are modeled to yield a diffuison coefficient and a Z-dependent inward convective pinch which are in general agreement with estimates of neoclassical transport in the central plasma region.

A clear correlation between incoherent magnetic fluctuations and transport in the outer region of the plasma was observed in a set of Doublet III beam-heated discharges which experienced repetitive transitions between a poor-confinement phase and an improved-confinement phase. The fluctuations and associated transport are consistent with a model based on an assembly of saturated microtearing modes.

The H mode in ion cyclotron-resonance-heated plasmas has been investigated with and without additional neutral beam injection. Ion cyclotron-resonance heating can cause the transition into a high-confinement regime (H mode) in combination with beam heating. The H mode, however, has also been realized—for the first time—with ion cyclotron-resonance heating alone in the D (H)-hydrogen minority scheme at an absorbed rf power of 1.1 MW.

Brillouin scattering on porous silica aerogels reveals the onset of the phonon-to-fracton crossover in both the wave-vector and density dependence of the spectra. The results are consistent with a fractal description, giving both the fractal dimension D and the spectral dimension d̃. In the hypothesis that the samples form single infinite clusters, the numerical values suggest that scalar elasticity is significant in these materials.

The relaxation time for scattering of vibrational modes by structural irregularities in d-dimensional random systems is shown to cross over from 1/τ∼${\mathrm{\omega }}^{\mathrm{d}+1\mathrm{}}$${\mathrm{\omega }}_{\mathrm{c}}^{\mathrm{-}\mathrm{d}}$ for phonons (ω<${\mathrm{\omega }}_{\mathrm{c}}$, the crossover frequency between phonon and fracton vibrational excitations) to 1/τ∼${\mathrm{\omega }}^{5\mathrm{-}3\mathrm{d}\mathrm{̃}}$ for fractons (d̃ is the fracton dimensionality). The Ioffe-Regel criterion for localization, ωτ∼1, and a scaling Ansatz, then lead to the Alexander-Orbach value, d̃=(4/3), and 1/τ∼ω for all ω>${\mathrm{\omega }}_{\mathrm{c}}$. .AE

We study the onset of the Taylor instability for colloidal crystals in a narrow-gap Couette Cell. There is a natural competition between the radial flow required for Taylor rolls and the resistance to such motion caused by the anisotropy of the flowing solid. A new, combined Taylor–shear-melting instability is found at rotation rates above those expected for the formation of rolls, but below the shear rate required for shear melting in the absence of the Taylor instability. The control parameter for the shear melting transition appears to be a critical shear stress rather than the shear rate.

A variety of mechanisms give rise to interfacial profiles which approach their bulk values asymptotically like ${\mathrm{az}}^{\mathrm{-}\mathrm{\mu }}$; for most of them 0<μ≤2. In these cases the exponent as well as the amplitude can be determined uniquely by reflectivity measurements slightly above the angle of total external reflection.

We show by Monte Carlo simulation that the fluctuations in a stack of membranes with spacing d produce a pressure p=(0.148±0.006)${\mathrm{T}}^1$/κ${\mathrm{d}}^3$, where T is the temperature (in units of ${\mathrm{k}}_{\mathrm{B}}$) and κ is the curvature elastic modulus.

The reconstructed (1×2) structure formed by saturation of a Ni(110) surface with adsorbed H atoms at T<180 K was investigated by LEED. Excellent agreement between experimental and calculated I-V spectra for eleven nonequivalent beams was obtained for a model in which parallel rows of Ni atoms in the topmost layer are laterally shifted by 0.3 Å (‘‘row pairing’’) and which exhibits periodic vertical displacements (‘‘buckling’’) of the atoms in the second layer.

Transient photoconductivity measurements of holes in polyvinylcarbazole are reported. It is found that good agreement, with the dispersive transport theory of Scher and Montroll is obtained only for light intensities two orders of magnitude below values conventionally used. In contrast to earlier results we find a single temperature-independent value of α equal to 0.66(±0.05).

The effects of diffusion-enhanced Coulomb interactions in highly disordered superconductors are studied by use of coupled Eliashberg-type equations in the exact eigenstate representation. Solution of these equations shows how Coulomb induced inelastic scattering leads to gaplessness and other low-frequency structure in the superconducting state which can be qualitatively correlated with that in the normal density of states. Recent superconducting tunneling experiments compare favorably with this theory.

We study theoretically the transmission of radiation through superlattices of finite length, where the dielectric constant of one film in each unit cell contains a term linear in the local field intensity. When such a system is illuminated with radiation with frequency in a stop gap, increasing power can switch it from a state with low transmissivity to a state with transmissivity of unity. Gap solitons play a key role in the phenomenon.

The mean-field theory of dilute spin-glasses is studied in the limit where the average coordination number is finite. The zero-temperature phase diagram is calculated and the relationship between the spin-glass phase and the percolation transition is discussed. The present formalism is applicable also to graph optimization problems.