The first relativistic self-consistent-field calculation of two-photon transition rates in atomic inner shells is described. Results agree very well with recent measurements of Xe $\mathrm{ns}\to 1s$ and $\mathrm{nd}\to 1s$ ($n=2,3,4\mathrm{}$) transitions, except for $2s\to 1s$ where an unexplained discrepancy by a factor of ∼3 occurs.

Conclusive evidence is presented for resonant transfer and excitation to specific intermediate states in collisions of Li-like ${\mathrm{O}}^{5+}$ with He. Using the technique of high-resolution 0° Auger-electron spectroscopy, we observed a maximum in the cross section for production of Be-like $1s2s2p^2{}_{}{}^3{}_{}{}^{}D$ and $1s2s2p^2{}_{}{}^1{}_{}{}^{}D$ states as a function of incident ion energy. The peak appears at ∼13 MeV with a width of ∼7 MeV and is in good agreement with the impulse-approximation model for resonant transfer and excitation.

Novel flows between rotating concentric cylinders have been found in which domains of dynamically distinct behavior occur in spatially separate regions along the cylinders. Such flow states consist of Taylor vortices with a variety of secondary flows. The distinct secondary flows are correlated with variations in the axial wavelength of the vortex structure occurring over distances small compared with the system length. The results are compared with model systems that exhibit spatially nonuniform behavior and domain formation.

Laboratory results are presented to show the existence of a new type of double layer which has monotonic potential variations but can be triggered with an electron drift velocity less than the electron thermal velocity. These double layers are always found to evolve from virtual-cathode potential wells at the electron injection boundary, independent of the electron drift velocity. However, the amplitudes of these double layers are determined by the initial drift velocity of the injected electrons. Double layers with potential drops less than the ambient electron temperature are found to be unstable to ion-ion streaming instabilities and decay into ion acoustic double layers.

The surprising tendency of clean (001) Si surfaces to become primitive upon annealing is explained by a $\pi$-bonded step reconstruction that lowers the relative enthalpy of reconstructed biatomic ($\frac{a_0}{2}$) steps on one particular fcc sublattice by 0.04 eV per step atom, and by correlation, which freezes out the step configurational entropy thereby suppressing the formation of other types of steps.

The structure of the germanium-silicon interface has been analyzed by x-ray standing waves in an ultrahigh-vacuum environment. Structural models of the Si(111) (7×7) surface have been tested through the structure and energetics of the Si(111)(7×7)-Ge interface. Our results agree with the dimer-adatom stacking-fault model of Takayanagi et al. for the bare surface. At the interface, Ge atoms occupy the atop sites on the surface atoms that offer dangling bonds as well as on the adatoms of the dimer-adatom stacking-fault model of the Si(111) (7×7) surface.

The static structure factor and pair distribution function of high-density amorphous ${\mathrm{D}}_2$O ice, which is made by apparently melting ice I at 10.5 kbar and 77 K, have been determined by neutron diffraction at 17 K and zero pressure. The pair distribution function, scaled to 10 kbar, is compared with the same function for ${\mathrm{D}}_2$O liquid at 9.8 kbar and 321 K. The functions are very similar, which suggests that the structure of the high-density amorph is very similar to that of the, as yet hypothetical, glass that would be obtained by the quenching of water of 10 kbar.

Using an evanescent-wave ellipsometric technique, we have studied the wall-induced orientational order in the isotropic phase of $4^{\prime }-n-\mathrm{pentyl}-4-\mathrm{cyanobiphenyl}$ (5CB) at a silane-treated glass surface. Near the isotropic-nematic transition temperature $T_{\mathrm{NI}}$, a weak nematic layer appears at the interface with its thickness exhibiting a critical divergence as $T\to T_{\mathrm{NI}}$ according to ${(T-T_{\mathrm{NI}})}^{-0.5\mathrm{}}$. This observed pretransitional behavior is qualitatively at variance with the existing theories.

We present an integrodifferential-operator formulation of the problem of linear stability around the selected needle crystal pattern in dendritic crystal growth. We show by explicit computation that (a) all members of the discrete set of allowed steady states aside from the fastest are unstable and (b) the fastest such shape is linearly stable at least for large enough anisotropy. We comment on the implications of our work for the issue of side-branch wavelength determination.

We describe a technique capable of directly resolving and identifying the sublattices occupied by the different constituents of compound semiconductors, under conditions which allow simple interpretation of the images. We present experimental lattice images of InP, GaP, and GaAs, which are direct representations of the sample structure and allow the simultaneous resolution and identification of the sublattices for the first time. We thus establish that the technique is applicable to all zinc-blende semiconductor compounds

The average relaxation of the top layers of a germanium-atom-tagged Si(111) surface has been measured by x-ray interferometric and fluorescence methods. The results indicate a slight outward displacement (∼2%) of the outer layers on a (5 × 5) reconstructed surface relative to a perfectly terminated silicon crystal surface. The results are in good quantitative agreement with atom positions predicted from a tight-binding-based energy-minimization calculation of the dimer-adatom stacking-fault model of the Si(111) (7 × 7) or (5 × 5) surface.

We report the results of a study of picosecond-laser-annealed ${\mathrm{Pd}}_{77}$${\mathrm{Si}}_{23}$ glassy metals by means of x-ray diffractometry, metallography, laser-pulse crystallization, and differential scanning calorimetry. We observe that the laser annealing completely removes the nucleation sites for crystallization from the surface of the material and also reduces the nucleation-site density in the bulk by about 5 orders of magnitude. As a result the samples display two-dimensional, bulk, growth-dominated crystallization and superior stability against devitrification in comparison with the as-quenched ribbons.

Stable crystalline compound analogs of ternary quasicrystals are successfully isolated by quantum structural diagrams, which also predict many possible new quasicrystals. Physical mechanisms responsible for the formation and certain features of quasicrystals are suggested, including the six-dimensionality of the hypercubic protolattices.

Neutrons propagating in a crystal under diffraction conditions exhibit an effective inertial mass which is lower by 5-6 orders of magnitude than their vacuum rest mass and of both positive and negative sign. This is verified experimentally by measurement of the enormously enhanced deflection of neutrons subjected to a magnetic force while passing through a silicon crystal.

We show a universality in the quantum Hall effect in that the flux-averaged Hall conductivity in any two- or three-dimensional system with or without disorder is given by a topological invariant quantized in units of $\frac{e^2}{h}$ at $T=0\mathrm{}$ for every energy level in a finite system. Relevance to the observable Hall conductivity over the whole energy spectrum is presented together with numerical results for lattice systems.

Measurements on discontinuous thin gold films near the percolation threshold show that the current at which nonlinear response takes place, $I_{\mathrm{ex}}^c$, scales with the conductance ${\Sigma }_0$, as $I_{\mathrm{ex}}^c\sim \Sigma _0^{}{}_{}{}^x$, $x=1.47\mathrm{}\pm 0.10$. Two possible theoretical models have been considered and studied analytically and numerically. The first is based on local nonlinear contributions from the metallic constituents. The second models nonlinear hopping or tunneling across narrow insulating bridges. Only the second model is compatible with the experiment.

A spherical model of Ising spins, placed on sites that are arranged in a cluster hierarchy, is studied. For the ferromagnetic transition, the critical exponents are found to have nonuniversal values in a certain range of system parameters, while they assume classical values in another range. Correlation functions show a behavior which is very different from the uniform systems. For antiferromagnetic interactions, the system has no transition, which is related to the fact that condensation cannot occur in localized modes.

The behavior of the magnetoresistance of single and arrays of disordered metal rings is investigated. The average localization length, $L_c$, which is related to the conductance, is found to oscillate with a strong half-flux-quantum harmonic at low magnetic field. The ratio of the amplitude of the full-flux oscillations versus the half-flux oscillations is shown to decrease with the number of rings. All numerical results follow a universal law where the amplitude of oscillations of $L_c$ is found to be proportional to the square of the ratio of $L_c$ to the perimeter of the ring. At high magnetic fields, full-flux oscillations are observed.

When amorphous ${\mathrm{Co}}_{1-x}{\mathrm{Ti}}_x$ soft ferromagnetic thin films are deposited by rf sputtering in the presence of a dc magnetic field one observes a somewhat bell-shaped variation of the induced in-plane uniaxial anisotropy energy $K_u$ as a function of the pressure of the sputtering gas $P_{\mathrm{Ar}}$. The maximum value of $K_u\mathrm{}\left(x\right)\mathrm{}$, ${\left[K_u\mathrm{}\right(x\left)\right]}_{max}$, is obtained for the same $P_{\mathrm{Ar}}$ for the whole concentration range studied $0.14\le x\le 0.22$. The origin and the overall variations of $K_u$ are interpreted for the first time in terms of the atomic local anisotropies. The continuous decrease of ${\left(K_u\right)}_{max}$ with increasing Ti concentration is explained by the progressive change of the local structure.

We employ a supersymmetric functional-integral formalism based on the method of Bohr and Efetov to study the influence of both "site" and "bond" disorder on the nature of the ground state of the continuum model of polyaceteylene. We find exact results for the electronic density of states and the amplitude of the Peierls dimerization as functions of the strength of the disorder. As the disorder is increased, the dimerization amplitude decreases to zero continuously for bond disorder and discontinuously for site disorder.