Bean-shaped configurations have been successfully formed in the PBX tokamak and $\beta$ values of over 5% have been obtained. These discharges still lie in the first stability regime for ballooning modes, and magnetohydrodynamics stability analysis implicates the external kink as responsible for the present $\beta$ limit.

Microwave generation by electron beams in virtual-cathode configurations can achieve significant power levels. However, most designs inherently have two competing mechanisms generating microwaves: the oscillating virtual cathode and the reflexing electrons. These mechanisms interfere destructively with each other. This paper reports investigation of a novel idea of using an external axial magnetic field and a thick anode with an appropriate collimating slot to extract the electron beam and to suppress the reflexing electrons. It was found that high-power, narrow-band, monochromatic microwaves could be generated with efficiency of 10% to 20%.

Novel constraints on collisionless relaxation and transport in drift-Alfvén turbulence are reported. These constraints arise as a result of the effects of mode coupling and incoherent fluctuations as manifested by the proper application of self-consistency conditions. The result that electrostatic fluctuations alone regulate transport in drift-Alfvén turbulence follows directly. Quasilinear transport predictions are discussed in light of these constraints.

We present experimental evidence of a distinct dense branching morphology as a fundamental pattern for diffusion-controlled interfacial growth. The dense branching morphology is characterized by its circular envelope modulated by leading branch tips. The development of this pattern in two dimensions is studied in a Hele-Shaw cell and in amorphous annealing. We find agreement between the Hele-Shaw experiment and a linear stability analysis including a kinetic term.

Measurements of the specific heat of quasi one-dimensional conductors, ${\left(\mathrm{T}\mathrm{a}{\mathrm{Se}}_4\right)}_2$I and ${\left(\mathrm{N}\mathrm{b}{\mathrm{Se}}_4\right)}_3$I, between 0.1 and 8 K, are reported. Whereas no deviation from the $T^3$ law occurs at low temperature for ${\left(\mathrm{N}\mathrm{b}{\mathrm{Se}}_4\right)}_3$I, we have measured two anomalies in ${\left(\mathrm{T}\mathrm{a}{\mathrm{Se}}_4\right)}_2$I: an excess heat capacity with a peak at $T=1.75\mathrm{}$ K and a specific heat which follows a $T^{0.2}$ law below 0.4 K. We ascribe this excess heat capacity to the charge-density-wave phase excitations above their pinning frequency in the insulating Peierls state ($T_{\mathrm{P}}=263\mathrm{}$ K).

Observations of apparently nonuniversal exponents at the lower consolute points of micellar solutions of $n$-dodecyl-octaoxyethylene glycol monoether in ${\mathrm{H}}_2$O, ${\mathrm{D}}_2$O, etc., are analyzed by use of crossover scaling-theory and Ising-model results. The data quantitatively sustain a picture of stable micelles of radius $R$ undergoing ordinary criticality with crossover to Ising behavior delayed by an increasing range of interaction measured by ${\xi }_0$, the observed correlation-length amplitude: The crossover points, $t_{\times }\equiv \frac{(T_c-T_{\times })}{T_c}\sim {\left(\frac{R}{{\xi }_0}\right)}^6$, vary by a factor ≳ ${10}^2$ correlating with the changes seen in ${\gamma }_{\mathrm{eff}}$ and ${\nu }_{\mathrm{eff}}$.

We report high-pressure, low-temperature x-ray scattering measurements on the organic conductor ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$Re${\mathrm{O}}_4$. The anion-ordering phase diagram has been established up to 17 kbar. In addition to the low-pressure phase characterized by the wave vector $q=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$, we have discovered a new high-pressure phase with an unexpected wave vector $q=(0,\frac{1}{2},\frac{1}{2})$. Coexistence of these two types of ordering has been observed in an intermediate pressure range.

Molecular-dynamics simulations on the structure and energy of a bicrystal model reveal an interfacial melting transition at a temperature distinctly lower than bulk melting. Below the transition, thermal disorder occurs but interfacial width remains essentially unchanged; above the transition, the interfacial region behaves like a melt while its width grows significantly with temperature.

Experiments with negative ions in rotating superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}-A$ show strong retardation and deformation of ion pulses drifting parallel to the angular velocity $\Omega$. This is caused by the interaction between the ions and the $\mathbf{l}$ texture in the soft cores of $A$-phase vortices. The interaction is mediated by the anisotropic ion mobility: $\mathbf{v}={\mu }_{\perp }\mathbf{E}-\Delta \mu \left(\mathbf{E}·\mathbf{l}\right)\mathbf{l}$. The ($\Omega ,T$) dependence of the retardation is explained by a model that assumes focusing of ions into the vortex cores, along which the mobility ${\mu }_c$ is lower than that in the bulk liquid, ${\mu }_{\perp }$. We find ${\mu }_c={\mu }_{\perp }-0.6\mathrm{}\Delta \mu$.

We study how a deformable charge-density wave in the presence of random impurities responds to driving fields with both ac and dc components. Features in the differential resistivity are found when an internal frequency proportional to the velocity is either a harmonic or subharmonic of the driving frequency. Even infinitely large systems can exhibit true mode locking to the driving frequency. The behavior cannot be described by an equation of motion for a single effective degree of freedom.

The first observation of the elusive ${\mathrm{Fe}}^{4+}$ charge state coming from the nuclear decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}_{}^{3+}{}_{}{}^{}$ has been found in the Mössbauer emission spectra of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$:${\mathrm{La}}_2$${\mathrm{Li}}_{0.5}$${\mathrm{Co}}_{0.5}$${\mathrm{O}}_4$. A Ti-doped sample was prepared in order to show that the ${\mathrm{Fe}}^{4+}$ fraction can be conveniently monitored. Both results were predicted on the basis of the electronic energy-band scheme of these oxides.

Pion creation via the Primakoff effect is normally associated with the electric fields of single atoms. However, in special cases when pions are produced by very high-energy photons aligned with a crystal axis, the crystal structure can influence the production of pions. Resonant peaks in the pion-creation rate, as a function of the incident photon energy, should occur when the momentum transfer in the alignment direction equals a reciprocal-lattice vector of the crystal. Numerical results presented for the example of a diamond crystal show that this coherent Primakoff effect could be observed with present-day accelerator technology.

A group of photoluminescence lines recently observed in thermally treated Si was studied in detail by transient spectroscopy, excitation spectroscopy, and temperature- and excitation-density-dependent measurements. An earlier interpretation in terms of free-to-bound transitions cannot explain these results. Instead, the lines are found to be due to an inhomogeneously broadened distribution of isoelectronic centers which can bind from one to four excitons.

By using compiled, updated experimental data, we have demonstrated that the correlation between the temperature coefficient of electrical resistivity $\alpha$ and the resistivity $\rho$ for disordered metals at room temperature is not universal. The origin of the nonuniversality of the Mooij correlation stems mostly from a competition between the quantum mechanical effects of incipient localization and the classical Boltzmann electron transport. Results of a numerical analysis based on localization indicate that there is a unique and monotonic correlation between $\alpha$ and $\rho$ for a specific disordered metallic system, in accord with the essential features of our new Mooij ($\alpha \mathrm{vs} \rho$) plot.

High-resolution neutron scattering from a single crystal of the randomly diluted antiferromagnet (${\mathrm{Mn}}_{0.5}$${\mathrm{Zn}}_{0.5}$)${\mathrm{F}}_2$ has been observed at $T=5\mathrm{}$ K. We find sharp spin waves near the zone center which broaden rapidly with increasing wave vector; at about $0.3q$ (zone boundary) there is a crossover to a very broad and continuous energy spectrum. Equivalently, the low-energy spin waves cross over to quasilocalized excitations at higher energies $\hslash \omega \gtrsim 1.5$ meV. These results are related to the recent conjecture of "fractons" in disordered media.

The far-infrared conductivity of Ce${\mathrm{Pd}}_3$ has been obtained from temperature-dependent reflectivity measurements between 0.4 and 400 meV. The low-temperature results are consistent with simple Fermi-liquid ideas, even though the conduction-carrier density is less than 0.3 electron per formula unit.

A simple one-component version of Fermi-liquid theory is applied to measurements of the specific heat of U${\mathrm{Pt}}_3$ and shown to suggest that U${\mathrm{Pt}}_3$ is an odd-parity superconductor of purely electronic origin. The calculated transition temperature as a function of pressure is found to be in quantitative agreement with experiment.

For quantum bound systems whose classical versions are nonintegrable, coupled dynamical equations for both energy levels and eigenfunctions with a nonintegrability parameter $t$ taken as "time" are shown to be a completely integrable Calogero-Moser system in 1 + 1 dimensions with internal complex vector space. Lax forms and their complete algebraic solutions are given which, in place of statistical mechanics procedures, determine possible energy spectrum and wave-function patterns at an arbitrary value of $t$.

It is known that anomalies can be expressed as a quantity in a short-time limit of the proper time (Schwinger parameter) in point-particle field theories. A natural extension of these expressions for the anomalies is given in the heterotic-string theory. It is shown that the gauge and gravitational anomalies in the heterotic-string theory can be expressed as a surface integral over the Schwinger parameter. The modular invariance of hexagon anomalies allows us to restrict the region of integration to the boundary of the fundamental region. This invariance also shows that the surface integral vanishes, i.e., hexagon gauge and gravitational anomalies are absent in the heterotic-string theory.

For $N$ generations of fermions, we propose $\mathrm{Sp} \mathrm{}\left(2N\right)\mathrm{}$ as the flavor gauge group. It is shown that there is a partial Glashow-Iliopoulos-Maiani mechanism which suppresses flavor-changing neutral-current processes. For four generations, we find that there can be an additional light, neutral ${\tilde{Z}}^0$ boson with mass ≳ 100-200 GeV.