The energy in the baryon-number-2 sector of the Skyrme model is shown to be minimized by a localized static soliton solution. If this solution has a particular discrete symmetry, the lowestenergy state of the soliton can have the spin, isospin, and parity quantum numbers of the deuteron. This identification is supported by approximate calculations of its charge radius and its magnetic and quadrupole moments.

A systematic on-line nuclear-orientation study of heavy isotopes by use of anisotropic $\alpha$ emission is reported for the first time. The anisotropies recorded for ${}_{}{}^{199}{}_{}{}^{}\mathrm{At}$, ${}_{}{}^{201}{}_{}{}^{}\mathrm{At}$, and ${}_{}{}^{203}{}_{}{}^{}\mathrm{At}$ are remarkably pronounced and strongly varying. At lower neutron number the $\alpha$ particles are more preferentially emitted perpendicularly to the nuclear-spin direction. This may be interpreted in terms of the high sensitivity of the $\alpha$-emission probability to changes in the nuclear shape.

Iterative maps on SO (3) with two stable fixed points are described. These generate bistable spectroscopic excitation sequences for isolated two-level systems. From such sequences, tailored population inversion over specific ranges of parameters such as the resonance frequency or radiation amplitude can be obtained. The ideas developed here suggest ways of designing tailored excitation sequences useful in spatially selective NMR, spin decoupling, $\mathrm{nk}$-quantum selective multiple-quantum NMR, and isotope-selective zero-field NMR.

It is pointed out that the charge-state distribution produced by intense ultraviolet laser radiation is a Poissonian, rather than the binomial which prevails under infrared radiation, and hence that ionization occurs stepwise during the pulse. This result is shown to be consistent with experimental data as well as with recent theoretical advances.

Photoelectron spectroscopy excited by monochromatic synchrotron radiation (68-80 eV range) is used to study the Br $3d$ excitation in HBr. The transition to an antibonding orbital is shown to produce a resonant state whose repulsive nature has been observed directly. A two-step relaxation process involving a fast neutral dissociation followed by the autoionization of the excited fragment has been shown for the first time.

By reduction of the electromagnetic field fluctations in one quadrature phase, squeezed light can inhibit the phase decay of an atom. This gives three relaxation times: the usual longitudinal relaxation time and two different transverse relaxation times, which are inversely proportional to the variances of the two quadrature phases of the incident light. With sufficient reduction of one variance, the corresponding relaxation time can be made arbitrarily long. The two transverse decay times are observable in the spectrum of the fluorescent light, thus providing measure of the squeezing in the incident light.

A phase transition has been observed in the system pyridine adsorbed on Ag(111) at 100 K by near-edge x-ray-absorption fine-structure measurements in real time. At low pyridine coverages an angle between the ring plane and the surface plane of 45° ±5° was observed. This phase converts sharply at a submonolayer coverage to a phase with an angle between the ring plane and the surface plane of 70° ±5°. Continued exposure gradually leads to a randomly oriented multilayer.

A second-order twin boundary in Si, of the $\Sigma 9$ type, is investigated with first-principles density-functional theory and with an empirical tight-binding model. Of two proposed reconstructions studied, the one supported by recent experiment is energetically favored, with less bond stretching than the other. A conduction-band-edge interface electronic state associated with bond-angle strains is found. A phonon resonance, the interfacial analog of a Rayleigh mode, is predicted; Raman spectroscopy should be able to detect it.

A new method, involving the solution of a nonlinear eigenvalue equation, is proposed for finding the ground-state configurations and energies of the Frenkel-Kontorova and similar onedimensional models which can show complicated transitions between commensurate and incommensurate phases. It is used to show that a distinctive phase diagram can arise if a cosine potential is perturbed by the addition of suitable harmonics.

We report experimental studies of the statics and dynamics of diffusion-limited polymerization. The fractals obtained were produced electrochemically from neutral precursors, and have a Hausdorff dimension of 1.74±0.03. The width of the active growth zone increases at the same rate as the fractal radius. The chemical dimensionality determined by scale-dependent conductivity measurement is 0.96±0.04. This implies a value for the spectral dimensionality of 1.26±0.04.

Phases with ($2\times n$) structure ($6<n<\mathrm{}10\mathrm{}$) can be formed on Si(100) by rapid quenching from high temperatures. The nominal (2×7) phase has been investigated by high-resolution low-energy electron diffraction. The structure involves two atomic levels, is metastable, and decays with first-order kinetics. The structure can be explained by ordering of excess missing-dimer defects, which apparently are present on the surface with any of the standard surface preparation techniques for Si(100).

We propose that alkali-metal migration in oxide glasses at low temperature occurs through Si${\mathrm{O}}_2$ units structurally relaxed by irradiation. With a combination of percolation and diffusion equations, we are able to explain all experimental data obtained by Pantano et al.

New phase transitions in Ge were observed by energy-dispersive x-ray diffraction techniques for pressures up to 125 GPa (1.25 Mbar) as follows: the $\beta$-Sn structure to the simple hexagonal (sh) phase at 75 ± 3 GPa and to the double hexagonal close-packed structure (dhcp) at 102 ± 5 GPa. These are the highest pressures for which a crystalline structure change has been directly observed by x-ray diffraction. Total-energy pseudopotential calculations predict 84 ± 10 GPa for the $\beta$-Sn to sh phase transition and 105 ± 2 GPa for sh to hcp (not dhcp) transition. The role of 3 $d$ core electrons in increasing the transformation pressures in Ge, as compared to Si, is emphasized.

We suggest that dendritic sidebranches may, under some circumstances, be generated by selective amplification of noisy fluctuations near the tip. Our proposal is based on numerical and analytic studies of the dynamics of the two-dimensional boundary-layer model with kinetic crystalline anisotropy. Certain features of this stochastic process should make it experimentally distinguishable from a deterministic, dynamical sidebranching mechanism.

We have measured Young's modulus $Y$ and internal friction $\delta$ of the charge-density-wave (CDW) conductors Ta${\mathrm{S}}_3$ and Nb${\mathrm{Se}}_3$, in the presence of combined ac and dc electric fields. In the pinned CDW state, the elastic properties are sensitive to even small ac-field amplitudes. In the sliding-CDW state, sharp harmonic and subharmonic anomalies are observed in $Y$ and $\delta$; these coincide with Shapiro-type interference in the electronic response. Our experiments demonstrate that internal degrees of freedom (incoherence) of the CDW condensate are intimately tied to the dc- and ac-field-induced elastic anomalies.

The inelastic-neutron-scattering technique was used to measure the magnetic excitation spectrum of ${\mathrm{Mn}}^{2+}$ triads in Cs${\mathrm{Mn}}_{0.28}$${\mathrm{Mg}}_{0.72}$${\mathrm{Br}}_3$. It is shown that biquadratic two-spin and particularly three-spin interaction terms distinctly contribute to the spin coupling of the ${\mathrm{Mn}}^{2+}$ ions. The present work thus provides direct experimental evidence of the existence of three-body forces in an interacting system.

We show that the conductance of metals is sensitive to the motion of a single scattering center. At zero temperature and in two dimensions, the motion of one strong scattering center induces changes of the conductance of order $\frac{e^2}{h}$, independent of sample size. We discuss the implications of this result for room-temperature $\frac{1}{f}$ noise in disordered metals and we predict an anomalous low-temperature $\frac{1}{f}$ noise in metallic glasses, due to two-level systems.

A functional renormalization-group $5-\epsilon$ expansion is used to calculate the exponent $\zeta$ which measures the roughness of an interface in a disorded Ising system as a function of length scale. Formal dimensional reduction is explicitly shown to break down at leading order in $\epsilon$ and field-theoretic methods fail. For random-field disorder $\zeta =\frac{\epsilon }{3}$ is obtained which resolves the discrepancy between various previous calculations; for random-bond disorder, $\zeta \approx 0.2083\epsilon$ to leading order.

The band-gap problem is studied for an exactly solvable semiconductor model. The exact exchange-correlation potential is constructed and its discontinuity is studied. Depending on the parameter range, a large or a small discontinuity is obtained. The "scissor-operator" method is compared with the local-density approximation for an impurity calculation. In general, the local-density approximation is closer to the exact solution. Some general features of the density-functional formalism are illustrated.

We have obtained the first energy-resolved real-space images of the filled and empty surface states of the Si(111)-(7×7) surface, with 3-′A lateral resolution. This ability to resolve spatially these surface states with a scanning tunneling microscope depends upon a new method to acquire and separate geometric and electronic information. Our results not only are in good agreement with previous spectroscopic studies but also directly reveal the atomic location and geometric origin of the Si(111)-(7×7) surface states.