The process by which a tokamak plasma evolves from an equilibrium state containing a saturated magnetic island to one which is disruptively unstable is discussed and illustrated by numerical simulation of a resistive magnetoplasma. Those elements which are required to initiate a disruption are delineated.

We report the growth and structure of fractally rough silicate particles in solution. Using small-angle x-ray scattering, we find fractal surfaces both in solution and in a porous solid made from the solution precursor. Finally, we develop a simple model which both is consistent with silicate chemistry and generates fractally rough structures.

We describe experiments that we have performed with droplets of supercooled liquid ${\mathrm{H}}_2$ in the temperature range down to 10.6 K. We have measured the nucleation rate for the production of the solid phase. Using this result, we discuss the prospects for the experimental production of superfluid ${\mathrm{H}}_2$.

We present experimental evidence for $f$-wave pair interactions in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}-A$. These interactions cause the frequency of the clapping mode to be significantly reduced relative to the value expected in a pure axial state, at temperatures arbitrarily close to $\mathrm{Tc}$. We find that the predicted $f$-wave transition temperature in the absence of $p$-wave pairing is 0.2-0.3 times the observed $\mathrm{Tc}$.

The temperature and impurity-concentration dependence of the phason gap in mixed incommensurate $\left({\mathrm{Rb}}_{1-x}{\mathrm{K}}_x\right){}_2{}^{}{}_{}{}^{}\mathrm{Zn}{\mathrm{Cl}}_4$ has been studied via the phason-induced ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ spin-lattice-relaxation contribution. The results yield novel information on the nature of the coupling of the impurities to the incommensurate modulation wave and allow for a discrimination between random-field and random-interaction effects.

While MnTe has the stable NiAs structure with a direct band gap of 1.30 eV and a Mn-Te bond length of 2.92 Å, extrapolation of the data for the zinc-blende alloy ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ to $x=1\mathrm{}$ suggests an alloy-stabilized MnTe phase with very different properties: a band gap of ∼3 eV and a Mn-Te bond length of 2.73 Å. We model the structural, magnetic, and electronic properties of such a hitherto unknown zinc-blende-like MnTe phase through spin-polarized total-energy calculations, and report its unusual properties in both ferromagnetic and antiferromagnetic spin ordering.

The fractional quantized Hall effect in channel geometries with a narrow width is discussed. Analytic arguments as well as finite-cluster calculations are presented that suggest that a gap exists in the excitation spectrum for even- as well as for odd-denominator filling factors. Possible ways that one might sort this from localization effects in experimental measurements are discussed.

We demonstrate that switching in the charge-density-wave (CDW) conductors ${\mathrm{Fe}}_x\mathrm{Nb}{\mathrm{Se}}_3$ and Nb${\mathrm{Se}}_3$ is associated with a division of the CDW condensate into distinct macroscopic regions with independent CDW depinning fields and independent CDW drift velocities. These well-defined regions are separated by localized phase-slip centers. We explicitly determine the location within the crystalline bulk, and the spatial extent, of the phase-slip interface. Switching results from initial phase breaking at either side of the phase-slip center.

We have observed the effect of magnetic field orientation on reproducible aperiodic structure in the low-field magnetoconductance ($H<\mathrm{}1.5\mathrm{}$ T) of weakly localized, pinched, Si accumulation layers. We demonstrate for the first time that the structure depends on the perpendicular component of applied magnetic field. This implies that the structure arises from interference between electronic wave functions which represent conduction paths enclosing different amounts of flux. The observed magnitude of the structure is in good agreement with theory.

We present detailed calculations of isomer shifts for a large number of dilute Fe alloys. We consider all substitutional impurities with nuclear charges $Z$ between 1 and 56 and calculate the isomer shifts on the nearest-neighbor Fe atoms. The calculated shifts agree well with the experimental data and show an astonishingly simple chemical trend. They are directly proportional to the change of number of $s$ electrons of the nearest-neighbor Fe atom and are practically independent of the local $d$ charge.

The temperature dependence of the optical absorption associated with surface states on the Si(111)2 × 1 surface is presented. The results indicate a behavior characteristic of localized excitations with a strong electron-lattice interaction, that is, a nearly Gaussian absorption that broadens roughly as the square root of the absolute temperature and shifts to lower energies upon increasing temperature. The frequency of the surface phonons that couple to the transition is smaller than hitherto assumed for the 2 × 1 surface.

We obtain an accurate density-functional exchange-correlation potential, $V_{\mathrm{xc}}\left(\mathrm{r}\right)$, for silicon, from calculations of the self-energy $\Sigma (\mathrm{r},{\mathrm{r}}^{\prime },\omega )$. No local-density approximation (LDA) is used for $V_{\mathrm{xc}}$. The band structure with this $V_{\mathrm{xc}}$ is in remarkably close agreement with that obtained with the LDA, while both differ significantly from the quasiparticle spectrum of $\Sigma$. The 50% band-gap error found in LDA calculations is therefore not caused by the LDA but by the discontinuity, $\Delta$, in the exact $V_{\mathrm{xc}}$ on addition of an electron.

A rare insulator-to-metal transition on increasing magnetic field has been observed in $n-{\mathrm{Cd}}_{0.95}{\mathrm{Mn}}_{0.05}\mathrm{Se}$ and $p-{\mathrm{Hg}}_{0.915}{\mathrm{Mn}}_{0.085}\mathrm{Te}$. The two systems belong to a new universality class due to a giant spin-splitting effect. The transition is shown to be driven by the electron-electron interactions and the newly predicted critical behavior of the conductivity is confirmed.

A one-dimensional kinetic Ising model, with hierarchical couplings, is solved. We find algebraic relaxation of the magnetization, with a temperature-dependent exponent, and breakdown of dynamic scaling. The nonlinear relaxation time diverges with the system size below a dynamic transition temperature. Possible relevance to dilute Ising systems at percolation is discussed.

We give two fundamental methods for evaluation of classical free energies of all the integrable models admitting soliton solutions; the sine-Gordon equation is one example. Periodic boundary conditions impose integral equations for allowed phonon and soliton momenta. From these, generalized Bethe-Ansatz and functional-integration methods using action-angle variables follow. Results for free energies coincide, and coincide with those that we find by transfer-integral methods. Extension to the quantum case, and quantum Bethe Ansatz, on the lines to be reported elsewhere for the sinh-Gordon equation, is indicated.

We present a solution for the dynamics of an anharmonic oscillator coupled to a zero-temperature heat bath. Comparison of observable properties in a classical and quantum description uses true joint phase-space probability densities. The time evolution of the density in the quantum case is rapidly "reduced" to that given in the classical description. The rate of reduction is proportional to the product of the damping rate and the oscillator's initial energy. Quite rapidly, typical quantum recurrence effects are destroyed and the classical "whorl" structure restored. We point out the close similarity with rapid destruction of quantum coherence through dissipation.

A search has been carried out for the production of neutrinos in the mass range 60 to 130 MeV coupling to the electron in the decay ${\pi }^{+}\to e^{+}\nu$. The dominant background from the $\pi -\mu -e$ decay chain has been suppressed by use of a new technique leading to more than an order of magnitude greater sensitivity than achieved previously.

We have measured the polarization of $\Lambda \text{'}s$ in inclusive $\mathrm{pp}$ and $K^{-}p$ reactions and of $\overline{\Lambda }\text{'}s$ in $\overline{p}p$ interactions at a beam momentum of 176 GeV/c. Data were taken in the beam-fragmentation region with hyperon transverse momenta from 0.2 to 1.5 GeV/c. The $\overline{P}$ produced $\overline{\Lambda }\text{'}s$ have the same magnitude and sign of polarization as the $p$-produced $\Lambda \text{'}s$, whereas the $\Lambda \text{'}s$ from $K^{-}p$ interactions are more highly polarized and in the opposite direction.

The metastable decomposition of sputtered, mass-selected, cluster ions is investigated under ultrahigh-vacuum conditions. Highly excited $\mathrm{Al}_n^{}{}_{}{}^{+}$ and $\mathrm{Cu}_n^{}{}_{}{}^{+}$ cluster ions are found to decompose mainly by evaporation of single neutral atoms, whereas for $\mathrm{Si}_n^{}{}_{}{}^{+}$ clusters, fission is also observed. The decay rates of $\mathrm{Cu}_n^{}{}_{}{}^{+}$ clusters are in agreement with calculations presented by Klots. Some consequences of our results for the interpretation of cluster-ion mass spectra produced by other experimental methods are discussed.

It is suggested that the megagauss magnetic fields generated in laser-produced plasmas be applied for (a) the construction of a wiggler for an x-ray free-electron laser and (b) charged-particle acceleration to high energies using the inverse free-electron laser and the autoresonance laser acceleration schemes. Coherent amplification of 10-Å radiation with a 150-MeV electron beam seems feasible and gigaelectronvolt electron beams may induce a $\gamma$-ray laser. An acceleration gradient of about [100 MV/cm] ${\left[\frac{z}{\mathrm{}\left(10cm\right)\mathrm{}}\right]}^{\frac{-1\mathrm{}}{3}}$ can be achieved at a distance $z$ along a 1-MG axial magnetic field in the autoresonance laser acceleration scheme, using a Nd:glass laser of ${10}^{18}$ W/${\mathrm{cm}}^2$.