We consider the elastic softening of quasi-one-dimensional materials near the Peierls transition caused by critical fluctuations in the charge-density-wave order parameter. Singularities in the elastic constants and thermal expansion are related to those in the specific heat. Our analysis suggests that a correction to scaling dominates the asymptotic critical behavior over the observed range of temperatures. Experimental data are used to estimate the width of the critical region according to the Ginzburg criterion.

We present systematic local-density-functional calculations for the interaction energies of 3d and 4sp impurities (Sc–Br) with vacancies in Cu and Ni crystals. We apply the Kohn-Korringa-Rostoker Green’s-function method and evaluate the full anisotropic charge density. The interaction energies are obtained by total-energy calculations and by a newly derived formula based on the Hellmann-Feynman theorem. Both methods agree very well and confirm the experimentally known trends.

The ${\mathit{L}}_{23}$ x-ray-emission spectra of Cu and Zn have been recorded using tunable-synchrotron-radiation-excited fluorescence spectroscopy. The satellite structure was studied in detail by varying the excitation energy from threshold to several hundred eV above. Strong satellites are observed which can unambiguously be associated with the decay of multiply excited states. This disproves recent claims of a breakdown of the sudden approximation in this regime.

The temperature dependence of the conduction- and valence-band tails has been determined by total-photoelectron-yield spectroscopy for doped and undoped a-Si:H and a-SiGe:H alloys. We find that all films possess purely exponential conduction- and valence-band-tail densities of states; however, the characteristic energy of the conduction-band tail increases much more rapidly with temperature than that of the valence-band tail. This indicates that the conduction-band tail is considerably more susceptible to thermal disorder than to structural disorder, whereas the reverse holds for the valence-band tail.

We report the first full band-structure calculation of frequency-dependent second-harmonic generation in odd-period (Si${)}_{\mathit{n}}$(Ge${)}_{\mathit{n}}$ superlattices. We use these results in conjunction with a simple model to estimate second-harmonic generation at Si/Ge interfaces.

We have generalized the multichannel Landauer formula to the case of leads with a variable cross section. Local equilibrium is achieved as a result of widening the constriction, rather than by the usual introduction of reservoirs and inelastic scattering. The generalized formula provides an explicit dependence of the conductance on the position of the voltage probes. We show that the previous Landauer formulas are obtained as limiting cases. Application of this formula to ballistic transport predicts new structure for the conductance.

It is shown that, within a Gutzwiller type of approach to correlated electrons, the effective mass of quasiparticles composing an almost-localized Fermi liquid is spin dependent and varies strongly with magnetic field. The magnetization of such a system saturates in physically accessible fields. The results are used to explain the field dependence of both the effective mass and of the specific heat in the heavy-fermion systems at low temperature.

We consider the problem of the charge distribution of holes among the various ${\mathrm{CuO}}_2$ layers in the unit cell for compounds of the type ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{2\mathit{n}+4\mathrm{}}$. In analogy with graphite intercalation compounds, the charge distribution is strongly nonhomogeneous (for n≥3) with a depletion in the central layers. This result points to a special importance of the bounding layers and it provides a way to understand the observed maximum ${\mathit{T}}_{\mathit{c}}$ as a function of n.

The long-distance decay of correlation functions in the one-dimensional Hubbard model is determined for arbitrary band filling and correlation strength, using the exact solution of Lieb and Wu. In particular, for either infinitely strong on-site repulsion U, or in the close proximity of half filling for any U, spin-spin correlations decay like cos(2${\mathit{k}}_{\mathit{F}}$x)${\mathit{x}}^{\mathrm{-}3/2}$ ${\ln }^{1/2}$(x). For infinite U the results are generalized to the case of nonzero nearest-neighbor interaction. The behavior of the frequency-dependent conductivity is also discussed, in particular in the proximity of the metal-insulator transitions occurring for half and quarter filling.

We derive an exact expression for the low-temperature correlation function in the eight-vertex-equivalent Ising model. We provide a phenomenological interpretation of the qualitative nature of the transfer-matrix spectrum in terms of bubble excitations and speculate about the behavior in nonzero magnetic field.

We extend a nonlinear generalization of quantum mechanics, recently formulated by Weinberg, to systems of composite spin, such as atoms. We have used hydrogen (H) masers to set a limit of 3.7×${10}^{20}$ eV (8.9 μ Hz) on the magnitude of a nonlinear correction to the quantum mechanics of atomic spins. This result is of comparable magnitude to the limit recently set in a single-valued (nuclear) spin system. In the absence of nonlinear effects, the experiment provides a new and stringent test of H-maser clock performance and the applicability of standard maser theory.

γ-ray-initiated shower cascades in the atmosphere were observed by a detector loaded on a cargo airplane with an angular resolution of approximately 1°. The γ-ray threshold was estimated to be 40 GeV. A peak search was carried out in the region of -40°<l<80° -30°<b<30° with a bin size of 2°×2°. We observed nine γ-ray point-source candidates. Of these, eight sources were distributed along the galactic plane. The strongest source candidate (4.4σ peak) was located at (l,b)=39°,2°). The integral intensities of these sources were typically several times ${10}^{\mathrm{-}8}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ at 40 GeV.

Primordial baryon-number fluctuations can be damped at temperatures ≊20 keV when the photon mean free path becomes larger than the high-density-region length scale. This dissipation process may result in mixing of the high- and low-density material on a time scale comparable to or shorter than that of the universal expansion. The nucleosynthesis yields in inhomogeneous cosmologies can be altered by this process for any ${\mathrm{\Omega }}_{\mathit{b}}$. ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ can be reduced to an abundance consistent with observations of Population II halo stars and the abundances of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ can be reduced by several orders of magnitude.

We show that for the effective four-dimensional N=1 supergravity governing string theory around a large class of vacua the scalar potential is the sum of non-negative terms even in the presence of supersymmetry breaking. It is therefore naturally minimized with vanishing cosmological constant. Our result relies only on generic features of these vacua that have been proven for string tree level and at all orders in σ-model perturbation theory, but appear to apply more generally, for example, holding exactly in the σ-model couplings for (0,2) ${\mathit{Z}}_{\mathit{N}}$ orbifold models of rank 16.

We determine the resonant substructure of ${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$ decays using a five-dimensional maximum-likelihood technique to extract the relative fractions and phases of the amplitudes contributing to this final state. We find that two-body decay modes account for at least 76% of all decays. We obtain branching ratios for several decay modes including B(${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathit{a}}_1^{+}$) =(9.0±0.9±1.7)%, B(${\mathit{D}}^0$→K¯ ${}_{}{}^{\mathrm{*}0}{}_{}{}^{}\mathrm{\rho }_{}^0{}_{}{}^{}$)=(1.9±0.3±0.7)%, and B(${\mathit{D}}^0$→${\mathit{K}}_1$(1270${)}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$) =(1.8±0.5 ±0.8)%. For the decay mode ${\mathit{D}}^0$→K¯ ${}_{}{}^{\mathrm{*}0}{}_{}{}^{}\mathrm{\rho }_{}^0{}_{}{}^{}$, the K¯ ${}_{}{}^{\mathrm{*}0}{}_{}{}^{}$ and ${\mathrm{\rho }}^0$ are found to be polarized with their spins oriented in the direction of their motion as seen from the ${\mathit{D}}^0$ frame.

First data are presented for the polarized-target asymmetry in the reaction ${\mathrm{\pi }}^{+}$p→${\mathrm{\pi }}^{+}$pγ at an incident pion energy of 298 MeV. The geometry was chosen to maximize the sensitivity to the radiation of the magnetic dipole moment ${\mathrm{\mu }}_{\mathrm{\Delta }}$ of the ${\mathrm{\Delta }}^{++}$(1232 MeV). A fit of the asymmetry in the cross section ${\mathit{d}}^5$σ/d${\mathrm{\Omega }}_{\mathrm{\pi }}$ d${\mathrm{\Omega }}_{\gamma }$ dk as a function of the photon energy k to predictions from a recent isobar-model calculation with ${\mathrm{\mu }}_{\mathrm{\Delta }}$ as the only free parameter yields ${\mathrm{\mu }}_{\mathrm{\Delta }}$=1.64(±0.19expΔ,±0.14 theor)${\mathrm{\mu }}_{\mathit{p}}$. Though this value agrees with bag-model corrections to the SU(6) prediction ${\mathrm{\mu }}_{\mathrm{\Delta }}$=2${\mathrm{\mu }}_{\mathit{p}}$, further clarifications on the model dependence of the result are needed, in particular since the isobar model fails to describe both the cross section and the asymmetry at the highest photon energies.

One of the superdeformed rotational bands in ${}_{}{}^{194}{}_{}{}^{}\mathrm{Hg}$ has transition energies (rotational frequencies) that are equal within about 0.1% to those of the (only known) band in ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$. This excited (two-quasiparticle) band in ${}_{}{}^{194}{}_{}{}^{}\mathrm{Hg}$ has an aligned spin of (1.00±0.04)ħ relative to the very similar band in ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$, suggesting an interpretation in terms of aligned pseudo (intrinsic) spin. The implied pseudospin symmetry may be a clue as to why the rotational frequencies are so similar.

Using dynamic nuclear polarization we obtained proton spin-polarization values of +(95±5)% and -(97±5)% in radiation-doped frozen ammonia. Moreover, the polarization reached 90% in about 25 min. These results were obtained using our new 1-K high cooling power ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ evaporation refrigerator operating in a 5-T magnetic field with 140-GHz microwaves. This unexpectedly large and rapid polarization coupled with about 1 W of cooling power should allow significant improvements in high-energy spin-physics experiments and may have some physics interest in itself.

It is pointed out that the usual oscillation condition of the H maser is only a necessary condition for steady operation. Reducing the coupled field-matter dynamics to the complex Lorenz equations we derive a second requirement which together with the first forms a set of necessary and sufficient conditions for the steady operation to be stable. The instability of the steady state predicted by the equations should be easily accessible experimentally for the cryogenic H maser. It will be characterized by a pulsed output power which, depending on the detuning, is either periodic or chaotic.

We report a measurement of multielectron capture (Δq=2,...,6) emission cross sections of ${\mathrm{Kr}}^{18+}$-Kr and ${\mathrm{Kr}}^{18+}$-Ar collisions at 360-keV energy. Rydberg transitions of Kr xvii to Kr xii with n=9,...,18 and l=8,...,17 have been identified and have allowed us to determine multicapture emission cross sections. For Kr vii, Kr vi, and Ar vii, Ar vi recoil ions have been also observed and give an additional proof of multicapture. Variation of multicapture emission cross sections with charge transferred Δq is linear.