If electrons in a metal are heated to a temperature ${\mathrm{T}}_{\mathrm{e}}$ greater than the lattice temperature ${\mathrm{T}}_{\mathrm{L}}$, the electron-phonon interaction causes temperature relaxation ${\mathrm{dT}}_{\mathrm{e}}$/dt=${\gamma }_{\mathrm{T}}$(${\mathrm{T}}_{\mathrm{L}}$-${\mathrm{T}}_{\mathrm{e}}$) which is rapid for ${\mathrm{T}}_{\mathrm{L}}$>${\mathrm{\theta }}_{\mathrm{D}}$. A formula ${\gamma }_{\mathrm{T}}$=3ħλ〈${\mathrm{\omega }}^2$〉/π${\mathrm{k}}_{\mathrm{B}{\mathrm{T}}_{\mathrm{e}}}$ is derived, where λ〈${\mathrm{\omega }}^2$〉=η/M is an important parameter in the theory of superconductivity. Quantitative agreement with recent experiments is good.

We present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed optical transitions. These results are in marked contrast with the electronic structure of other doped conducting polymers, in that only one single broad polaron band appears deep in the gap together with a very narrow band nearly degenerate with the conduction-band edge.

We report an experimental observation of an increased ${\mathrm{T}}_{\mathrm{c}}$ up to 159 K with temperature cycling in YBaCuO and YBaCuO:F samples. This increase in ${\mathrm{T}}_{\mathrm{c}}$ is tentatively associated with a structural phase transition or ordering occurring at a well defined temperature close to 239 K. We have used the presence of this phase ordering to achieve improved-${\mathrm{T}}_{\mathrm{c}}$ material and tentatively attribute it to a two-dimensional to one-dimensional structural change.

We report the analytic, approximation-free evaluation of four different correlation functions for interacting fermions on a one-dimensional lattice in terms of the Gutzwiller wave function.

The electronic structure of a quasiperiodic superlattice with slabs of A- and B-type layers is studied within a tight-binding model by use of the transfer matrix and a perturbative approach. It is found that the band gaps vary strongly within the two-dimensional Brillouin zone and, in the case of more than one layer in a slab, there are a few eigenvalues for each ${\mathrm{k}}_{?}$ for which the eigenstates appear to be extended in the quasiperiodic direction. The latter is true even for the Fibonacci chain with more than one atom per cell.

By using highly asymmetric glass cells we have increased the wall-induced quadrupole splitting of the nuclear-spin sublevels of noble gas atoms by some 2 orders of magnitude over previously reported values. We have used these large surface interactions to make quantitative studies of the electric field gradients experienced by the nuclei of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ atoms adsorbed on glass walls.

${\mathrm{CH}}_2$${\mathrm{I}}_2$ molecules adsorbed on ${\mathrm{Al}}_2$${\mathrm{O}}_3$ and Ag surfaces are excited by a uv laser and the desorption behavior associated with photofragmentation is studied by time-of-flight mass spectrometry and x-ray photoemission and thermal desorption spectroscopies. The desorption yields as well as the mass and kinetic energy distributions are determined as functions of surface coverage and laser fluence. The results clearly reveal the characteristic electronic, thermal, and ‘‘explosive’’ desorption effects.

We report the first observation of a catalytic nitridation of a semiconductor with molecular nitrogen. The Si(100)2×1 surface modified by a sodium monolayer was studied by core-level and valence-band photoemission spectroscopy and work-function measurements using synchrotron radiation. At room temperature, the exposure to molecular nitrogen resulted in Si—N bond formation. The sodium is removed from the surface by thermal desorption at moderate temperature leading to the formation of a clean ${\mathrm{Si}}_3$${\mathrm{N}}_4$-Si interface at a much lower temperature than without the alkali metal.

We extend Einstein’s field equations and Hilbert’s action for gravity to the hyperspace of dimension ${\mathrm{N}}^2$ that is built out of N-component spinors in the way that four-dimensional time-space is built out of two-component ones. The hypergravitational field equation is of differential order N in a chronometric tensor with N indices. The natural spin structures of the unitary groups U(N) define Einstein-type cosmologies, static, U(N)-invariant, and closed, that satisfy the extended equations with neither dust nor cosmological constant, except for N=2 which requires both.

We examine the effects of relativistic dynamics and medium-modified electromagnetic form factors on the ratio of transverse to longitudinal response in (e,e’p). Calculations performed in the distorted-wave impulse approximation show that the effects of Dirac dynamics and medium-modified form factors are small. We also show that current data seem consistent with our distorted-wave impulse approximation calculations.

The very neutron-deficient isotope ${}_{}{}^{80}{}_{}{}^{}\mathrm{Zr}$ was produced in the reaction ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${(}^{58}$Ni, 2n${)}^{80}$Zr at 190 MeV with a cross section of σ=10±5 μb and was identified with the Daresbury Recoil Separator. The observation reflects a fiftyfold increase in sensitivity for in-beam spectroscopy of exotic nuclei. Coincidence measurements between the isolated isotope and prompt gamma radiation allowed the identification of decays from low-lying states at E=290 and 828 keV which indicate that ${}_{}{}^{80}{}_{}{}^{}\mathrm{Zr}$ has an extremely large quadrupole deformation of ${\beta }_2$≊0.4.

We investigated for the first time the high-lying Rydberg levels in the rare radioactive element francium (Fr). The investigations were conducted by the highly sensitive laser resonance atomic photoionization technique with Fr atoms produced at a rate of about ${10}^3$ atoms/s in a hot cavity. We measured the wave numbers of the 7$p^2$$P_{3/2}$→${\mathrm{nd}}^2$D (n=22–33) and 7$p^2$$P_{3/2}$→${\mathrm{ns}}^2$S (n=23, 25–27,29–31) transitions and found the binding energy of the 7$p^2$$P_{3/2}$ state to be T=-18 924.8(3) ${\mathrm{cm}}^{\mathrm{-}1}$, which made it possible to establish accurately the ionization potential of Fr.

By using a new photoelectron-photoelectron coincidence technique, we demonstrate that the absorption of vacuum-ultraviolet photons (20<ħω<60 eV) by rare-gas solids leads to the ejection of pairs of electrons in addition to the well-known single-electron photoemission process. We show that at least two separate processes produce pairs of electrons with a surprisingly high efficiency.

A vapor of paramagnetic atoms, under conditions in which electronic spin exchange takes place faster than collisional spin relaxation, should acquire a spontaneous spin polarization when illuminated by unpolarized light tuned to excite only certain ground-state atomic hyperfine levels. In magnetic fields above a certain size, the atomic polarization has two stable states, either parallel or antiparallel to the field. Experiments to demonstrate this effect and explore possible applications may be feasible by the use of alkali-metal vapors.

Calculations using nonlocal density-functional theory show that the total energies of atoms in states characterized by partially filled degenerate subshells are substantially lower when the charge density is not spherically averaged. This is in contrast to the case with local density theory in which spherical and nonspherical treatments of atoms give essentially identical energies. A cooperative effect of nonlocality in the exchange-correlation functional and nonsphericity in the charge density lowers the atomic total energies and greatly improves the calculated binding energies of ${\mathrm{B}}_2$, ${\mathrm{C}}_2$, ${\mathrm{O}}_2$, and ${\mathrm{F}}_2$.

Quantum jumps in the fluorescence from two three-level atoms may display cooperative effects, such as unusual intensity levels and transitions from a state with both atoms radiating directly to darkness. However, to see these experimentally, the atoms have to be well within a wavelength of light.

Rotational cooling by supersonic expansion and laser labeling spectroscopy were used to obtain high-resolution fundamental and first- and second-overtone spectra of C-H stretches of benzene in a molecular beam. Rich fine structure in the spectra has been observed. Transformation from the ‘‘normal-mode’’ picture to the ‘‘local-mode’’ picture seems to occur between v=2 and v=3. Vibrational lifetimes in local-mode bands exceed ≃0.5 psec.

Scattering theory is used to calculate the vibronic energy levels of the interacting double-minimum states in ${\mathrm{H}}_2$. The calculation is based on the accurate ab initio fixed-nuclei energies of Wolniewicz and Dressler. From these a nondiagonal reaction matrix is extracted whose elements are nuclear-coordinate dependent and involve singly and doubly excited channels. The treatment bypasses the state-by-state evaluation of vibronic coupling, and yields in principle the entire vibronic Rydberg spectrum associated with the ${\mathrm{H}}_2$${\mathrm{}}^{+}$ 1${\mathrm{\sigma }}_{\mathrm{g}}$ and 1${\mathrm{\sigma }}_{\mathrm{u}}$ cores. The first forty experimental levels are reproduced quite accurately.

The fluctuating plasma potential and electron density has been measured in Ohmic and neutral-beam–heated tokamak discharges. Radial profiles are presented in the outer two-thirds of the plasma, and the E×B transport calculated. The transport is found to be an order of magnitude larger for beam driven plasmas. Measurements indicate the linearized Boltzman equation is satisfied in the interior, but not at the plasma edge.

A simple model based on interparticle tunneling conduction and a percolative network is shown to imply a diverging distribution of high resistors in the system. This distribution is expected to yield a nonuniversal behavior of the electrical conductivity. An experimental study of carbon black–polymer composites seems to confirm this expectation, as well as explaining why a nonuniversal behavior has not been observed in previous experimental studies on such composites.