On-line resonance-ionization mass spectrometry has been applied to determine the isotope shift and hyperfine structure of ${}_{}{}^{185\mathrm{-}189}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{189\mathrm{m}}{}_{}{}^{}\mathrm{Au}$ in the 6s ${}^2$$S_{1/2}$→6p ${}^{2p}$${}_{1/2}$ (λ=268 nm) transition. The Au atoms were obtained as daughters of mass-separated Hg isotopes produced at the ISOLDE facility at CERN ionized by a three-color, two-step resonant photoionization process, detected and mass-selected by time of flight. A drastic change of the nuclear charge radius was observed between ${}_{}{}^{187}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$, which is interpreted as an onset of strong deformation of β≊0.25 in ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{185}{}_{}{}^{}\mathrm{Au}$.

The proton-induced fission cross section for ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ targets has been measured for ${\mathrm{E}}_{\mathrm{p}}$=1–4 MeV for the first time. Compared with the measurements at higher energies, the present results indicate a pronounced change in the slope of the excitation function below 4 MeV such that standard optical-model estimates fall far short of the observed cross sections. No plausible explanation in terms of fission of either the target or the compound nucleus can be found.

Ionic fragmentation following Pb 5d core-level ionization in tetramethyl lead (${\mathrm{PbMe}}_4$) has been studied with synchrotron radiation. In the wavelength range between 45 and 75 nm, photoionization of the Pb 5d core levels is observed in the threshold electron spectrum of ${\mathrm{PbMe}}_4$. The efficiency for the production of ${\mathrm{Pb}}^{+}$ ions increases dramatically in this region, while those of other fragment ions decrease. It is shown that the ${\mathrm{Pb}}^{+}$ ion is predominantly produced following 5d photoionization, by use of the threshold electron—photoion coincidence technique.

First-principles, total-energy electronic structure calculations have been used to study the effects of charge transfer in graphite intercalation compounds. Together with an in situ diffraction study on graphite undergoing intercalation with sulphuric acid, the results strongly support the idea of a universal relationship between charge transfer and the C—C bond length.

The chain trajectory in physical gels prepared from isotactic polystyrene has been investigated by neutron scattering. It is found that the chain possesses a wormlike conformation with a persistence length of about 80 Å, a value most unusual for this polymer (b≃20 Å in the vitreous state). Accordingly, the gel state may be the third state for this type of polymer.

Well-ordered atomic structures of silicon surfaces have been obtained with the field-ion microscope for the first time. Two distinctive atomic structures coexist for the {130} surface. These two structures can be formed by slightly different lateral displacements of atoms in the (1×1) layer. The {123} surface shows a rhombic structure with an angle of 79±3°. Two-dimensional defects can also be seen in all these surfaces. An atom-probe analysis shows that no impurity atoms are present in these surfaces.

A linear electro-optic effect in a cholesteric liquid crystal is described and attributed to the flexoelectric effect. An electric field applied perpendicular to the helix axis rotates the director about an axis parallel to the field. This produces a periodic splay-bend pattern in the helix, which couples flexoelectrically to the field.

Dendritic growth of crystals in two dimensions is analyzed by a Green’s-function method. A one-sided diffusional model is treated in quasistationary approximation. Anisotropy is found necessary for dendritic growth. We find scaling with anisotropy to be in agreement with recent results for needle crystals in the symmetric model. For fixed anisotropy the growth rate is proportional to the square of the Peclet number. The side-branch pattern is in qualitative agreement with experiments in three dimensions for different anisotropies.

The critical fluctuations of a polymer blend (PVME/d-PS) were investigated by neutron small angle scattering. A mean-field behavior was observed, except in a region very close to the critical temperature where a transition to an Ising-like behavior occurs. The width of this region is T-${\mathrm{T}}_{\mathrm{c}}$≃2.4 K for a mixture with average molecular weights of 89 000 (PVME) and 232 000 (d-PS).

We present qualitative theoretical evidence that interstitial bond-centered hydrogen or muonium in diamond is stable as a result of unusually large lattice relaxation. The two geometrical configurations of neutral interstitial muonium explain the structures and properties of anomalous muonium (bond centered) and normal muonium (tetrahedral interstitial site), including the thermal conversion of normal to anomalous muonium and represent a well-defined example of interstitial metastability.

A first-principles theory of the quasiparticle surface-state energies is given. The electron self-energy operaor is evaluated with inclusion of both local fields and dynamical screening effects in a surface calculation using a repeated slab geometry. The results for the prototypical Ge(111):As surface are in excellent agreement with recent angle-resolved photoemission data and show a substantially larger gap between the empty and occupied surface states in comparison to local-density–functional calculations. Implications for local-density–functional calculations of surface-state energies in semiconductors are discussed.

Si 2p and Ag 4d photoelectron spectra have been measured for the Si(111)√3 × √3 -Ag surface at both surface- and bulk-sensitive photon energies. A dramatic shift of the bulk Si 2p component for the √3 × √3 surface has been observed and is attributed to the presence of an inherently charged √3 × √3 layer. A single component of surface Si 2p levels is found for the √3 × √3 surface. Discussion of structural and growth models of the √3 -Ag surface is made.

The localization and solvation of excess electrons in pure water have been resolved at the femtosecond time scale. Before it becomes solvated, the electron thermalizes and reaches in 110 fs a localized state absorbing in the infrared. This transient species with lifetime 240 fs has been postulated to exist but has not been observed previously in liquid water.

A nonlinear transport behavior was observed in the magnetic-field–induced spin-density–wave state above B=7.5 T at T=1.5 K in (TMTSF${)}_2$${\mathrm{ClO}}_4$. The nonlinearity appeared in the transverse conductivity, but not in the Hall conductivity. The threshold electric field was very small and undetectable in some samples. The sliding spin-density wave is one of the plausible mechanism of this nonlinear transport. Small-period oscillations with the period Δ(1/B)=0.004 ${\mathrm{T}}^{\mathrm{-}1}$, similar to the Shubnikov–de Haas effect, showed a decrease in amplitude with increasing electric field.

A new kind of point-contact spectroscopy is described: The magnitude of the transverse electron focusing signal in a Ag single crystal is measured as a function of the energy of the injected electrons. For low energies, this is a direct measurement of the energy dependence of the electron-phonon interaction strength of electrons in a specific orbit on the Fermi surface. Also for higher energies effects of the anisotropy of the electron-phonon interaction are observed.

Two features have been observed in the infrared absorption spectrum of the new superconductors ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_4$. The higher-frequency feature at 677 ${\mathrm{cm}}^{\mathrm{-}1}$ in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ dominates the spectrum for x=0. However, small Sr replacements (x≳0.03) cause the 677-${\mathrm{cm}}^{\mathrm{-}1}$ band to be reduced dramatically in intensity and to disappear entirely by x=0.15. We propose that this is a zone-boundary phonon that is folded to the center of the zone and that the frozen-in charge-density–wave distortion proposed by Mattheiss gives rise to the strong transition moment we observe. Sr doping suppresses this distortion.

The new high-$T_c$ superconductor YBaCuO was prepared and characterized. Measurements were performed to determine the superconducting and magnetic properties of the samples. Onset of superconductivity was found above 90 K. Antiferromagnetism was also observed, probably associated with the nonsuperconducting pairs of the samples. Modest critical current density as well as large upper critical fields were inferred from the data.

An analytic approach to the phase space for a network of cosmic strings is presented, based on earlier work of Frautschi and Carlitz. It correctly predicts the main features of the network at formation, and is in good agreement with the picture emerging from string simulations. Our results also have important implications for superstrings or heterotic strings in the early Universe.

Nonstandard electroweak models permitting relatively rapid neutrino decay, with emission of ultraviolet photons, stimulate new interest in astronomical methods of detection of the emitted photons. We do not support the detection of a step in the cosmic background spectrum that has been reported recently. New and more sensitive measurements are urgently needed.

A procedure is described whereby the result of the measurement of any of the three Cartesian components of the spin of a single spin-(1/2) particle at a single time can be inferred with certainty from the result of two other measurements, one of which is carried out before, and the other after, the time in question.