We present a phenomenological analysis of an experiment to observe the condensate fraction of helium-4 by firing low-energy pulses of helium atoms at suspended droplets of the superfluid and observing the resulting emission of helium atoms from the fluid. Emission occurs through a conventional process in which rotons are produced and propagate to the other side of the droplet, and through a second process depending on the existence of the condensate. If A is the area of the incoming beam, the cross section scales with ${\mathit{A}}^2$ (first process) and ${\mathit{A}}^4$ (second process), respectively, for small A. Aspects of a fully many body calculation and the performance of such an experiment are briefly discussed.

We examine the motion of the contact line as it is depinned from a single defect. The main features of the time evolution are in agreement with the ‘‘pinched cord’’ model of de Gennes. In particular, the contact line shape is well described by a logarithmic form with width increasing linearly and maximum distortion decreasing logarithmically in time. The velocity characteristic of the width increase, however, is larger than expected. Evidence is presented that this is a consequence of the role played by the dynamic contact angle in real situations, which is not accounted for in the present theory.

We present first-principles studies of the adsorption of Sb and Ag on clean and Sb-covered Ag(111). For Sb, the substitutional adsorption site is found to be greatly favored with respect to onsurface fcc sites and to subsurface sites, so that a segregating surface alloy layer is formed. Adsorbed silver adatoms are more strongly bound on clean Ag(111) than on Sb-covered Ag. We propose that the experimentally reported surfactant effect of Sb is due to Sb adsorbates reducing the Ag adatom mobility. This gives rise to a high density of Ag islands which coalesce into regular layers.

A well-defined silicon oxide/silicon interface way synthesized by the reaction of the precursor cluster ${\mathrm{H}}_8$${\mathrm{Si}}_8$${\mathrm{O}}_{12}$ with Si(100) surface and characterized using Si 2p core level photoemission spectroscopy. Information gained regarding the assignments of silicon oxide group shifts and peak widths is used to evaluate assumptions and assignments of photoemission spectra of silicon oxide interfaces.

We present results obtained from a molecular dynamics study of the behavior of isolated copper atoms placed on a copper substrate. The atomic interactions are modeled by the embedded atom method. At 900 K we find that diffusion frequently proceeds by a two-step exchange-mediated process. In the first step of the process an isolated surface atom enters the Cu(100) substrate creating a strain along a close-packed row. In the second step the strain is relieved by an atom in the strained row returning to the surface of the Cu(100) substrate. The atom which returns to the surface may be several atoms removed from the atom which entered the substrate.

We have calculated the surface core-level energy shifts of the 4d and 5d transition metals by means of local-density theory and a Green’s-function technique based on the linear muffin-tin orbitals method. Final-state effects are included by treating the core-ionized atom as an impurity located in the bulk and at the surface, respectively. It is shown that the study of surface core-level shifts provides an ideal tool for an accurate determination of the surface segregation energy of a substitutional (Z+1) impurity in a Z metal host (Z denotes atomic number).

The results of a high resolution photoemission study of the Be(0001) surface carried out at temperatures between 100 and 450 K are reported. At 100 K, three distinctly shifted Be 1s levels, exhibiting shifts of -825, -570, and -265 meV, are revealed and interpreted to originate from the three outermost atomic layers. Identification of two subsurface core level shifts and a first layer surface shift of -825 meV is unique among close-packed metal surfaces. Temperature dependent broadening effects observed in the bulk and surface BE 1s peaks are also reported.

Core-level energy shifts for the beryllium surface region are calculated by means of a Green’s function technique within the tight-binding linear muffin-tin orbitals method. Both initial- and final-state effects in the core-ionization process are fully accounted for. Anomalously large energy shifts are found for the three topmost surface layers in agreement with recent experimental data. The reason for this extraordinary behavior is explained.

Electron diffraction of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NiO}}_{4+\mathit{x}}$ (0≤x≤1) reveal at low temperatures the presence of sharp, quasi-2D superlattice peaks around the (π,π) point. We show that the modulation wave vector δ measured from the (π,π) point decreases with increasing hole concentration. However, a plateau with δ∼1/3 was observed for 0.075≤x≤0.2 and the superlattice peaks were found to collapse into a single spot at the (π,π) point with a truly 2D ordering for x=0.5 where anomalous change of physical properties has been previously reported. Our results can be understood in terms of the ordering of polarons.

We demonstrate that electrons in a ballistic field effect transistor behave as a fluid similar to shallow water. Phenomena similar to wave and soliton propagation, hydraulic jump, and others should take place in this electron fluid. We show that a relatively slow electron flow should be unstable because of plasma wave amplification due to the reflection from the device boundaries. This provides a new mechanism for the generation of tunable far infrared electromagnetic radiation.

The charge transfer per molecule in a ${\mathrm{C}}_{60}$ monolayer on Au(110), on K/Au(110)c(2×2), and on a K multilayer has been determined by studying the electronic excitations from the valence bands and from the C 1s core level and the vibrational modes of the systems by electron energy loss spectroscopy. The electrons transferred are 1±1, 3±1, and 6±1, respectively. These results indicate strong chemical bonding of ${\mathrm{C}}_{60}$ on such metal surfaces.

We develop a phenomenological hydrodynamic description of the transport properties of a viscous vortex liquid in realistic geometries with nonuniform currents, including the effects of the boundaries of the sample. This approach should be useful for modeling multiterminal transport measurements in the vortex liquid regime of, for example, YBCO.

The density of states of the lowest unoccupied molecular orbital band as a function of K doping was investigated by yield spectroscopy excited with visible and near-uv photons. The Fermi level position was determined at each composition with high precision. The superconducting phase ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ exhibits a clear metallic edge, although the Fermi level is positioned at low state density [N(${\mathit{E}}_{\mathit{f}}$)=0.8±0.2 states/eV molecule] past the band maximum. The ${\mathrm{K}}_4$${\mathrm{C}}_{60}$ phase is insulating. Correlation effects are necessary to explain the data as a function of doping.

The specific heat of ${\mathrm{Nd}}_{2\mathrm{-}\mathit{y}}$${\mathrm{Ce}}_{\mathit{y}}$${\mathrm{CuO}}_4$, 0≤y≤0.2, was measured between 35 mK and 10 K. A Schottky anomaly in ${\mathrm{Nd}}_2$${\mathrm{CuO}}_4$, due to exchange interactions between Nd and Cu moments, shifts upon Ce doping to lower temperatures. In the metallic state (y≥0.15), a linear term with coefficient γ≃4J/${\mathrm{K}}^2$ per mole Nd is found below 300 mK. For y=0.2, a constant value of the magnetic susceptibility in the same temperature range and changes of ${\mathit{C}}_{\mathit{p}}$ in applied magnetic fields suggest an interpretation in analogy to a heavy-fermion system resulting from the coupling between Nd moments and conduction electrons.

We find the exact quasiparticle spectrum, elastic S matrix, and free energy for the continuum Kondo problem of k species of electrons coupled to an impurity of spin S. Here, the impurity becomes an immobile quasiparticle sitting on the boundary. The particles are ‘‘kinks,’’ which can be thought of as field configurations interpolating between adjacent wells of a potential with k+1 degenerate minima. For the overscreened case k>2S, the impurity in the continuum is a kink as well, which explains the noninteger number of boundary states.

We report the observation of nuclear resonant diffraction of synchrotron radiation by a synthetic multilayer. The nuclear period of the ${[}^{57}$Fe(22 Å)/Sc(11 Å)/Fe(22 Å)/Sc(11 Å)×25 multilayer was chosen to be twice the electronic period to obtain a pure nuclear Bragg reflection. Strong enhancement of the radiative scattering channel provided a fast time response for the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ resonant scattering at the Bragg peak, with a decay time of 4 ns. The nuclear multilayer will be useful as a narrow bandpass monochromator for synchrotron radiation.

The sensitivity of magneto-optical spectra to alloy chemical ordering is established. This is demonstrated for a new ordered ${\mathrm{Co}}_3$Pt phase, which was synthesized in thin film form using molecular beam epitaxial growth. This compound consists of alternating planes of Co and CoPt atoms with a hexagonal ABAB. . . layer sequence. The chemical ordering is accompanied by a substantial electronic structure change as reflected in a new peak in magneto-optical spectra at ∼3.2 eV photon energy.

It is found that acrylamide gel shows combined collapse-swelling behavior in dilute aqueous solution of poly(vinyl methyl ether) when transferred from the equilibrium swelling state in pure water. Namely, it starts to collapse quickly and then it is swollen again with its volume approaching the original value in water. The phenomenon can be explained by thermodynamic analysis of osmotic pressure. The re-swelling is caused by the penetration of linear polymer into the network. The analysis can also explain differences of the collapsing and re-swelling behavior between samples with different shapes.

We investigate the dynamics of a model of electrically coupled pacemaking cardiac sino-artial node cells. Cell models are biophysically detailed, and include voltage-dependent membrane currents, pump-exchanger currents, and time-varying internal ion concentration changes similar to those seen in real sino-atrial node cells. It is found that at low, yet physiologically realistic coupling conductance values, complex dynamics including chaos can arise. Occurrence of these complex dynamics in coupled pacemaker cells may provide an explanation for the origin of certain cardiac arrhythmias.

We enumerate the number of minimum energy compact structures (MECS) for a two dimensional heteropolymer model consisting of hydrophobic (H) and hydrophilic beads averaged over all possible sequences as a function of the total number of beads N and the number of H beads ${\mathit{N}}_{\mathit{H}}$. The analysis of the average number of compact structures, which grows exponentially with N, gives no indication of logarithmic corrections to the free energy. For intermediate values of the ratio ${\mathit{N}}_{\mathit{H}}$/N, we estimate that the average number of MECS—which has a minimum at ${\mathit{N}}_{\mathit{H}}^{\min }$/N=0.6±0.1—does not grow with N. Our results suggest that the late stages of protein folding should be restricted to the sampling of MECS only.