The photoemission intensity of alkali-metal valence electrons from Na-covered Cu(100) depends on coverage and photon energy in a manner which can be explained in terms of the surface barrier emission from a thin jellium layer with an electron density proportional to the Na coverage.

An exact analytic solution for the random-phase-approximation dielectric response including the surface correction is derived for a semi-infinite layered electron gas with different dielectric media on either side of the surface. The Raman intensity is calculated. The bulk plasmon line shape agrees with experiment; conditions for experimental observation of surface plasmons are described.

The time scale for solvent ‘‘caging’’ in the classic ${\mathrm{I}}_2$ photodissociation reaction appears to be ≤15 ps, on the basis of examination of new picosecond absorption spectra. The previously observed slow recovery (>100 ps) of molecular absorption is shown to be due to both ground-state vibrational relaxation and excited-state trapping in the recombined molecule. In addition, newly observed absorptions in the 350–400-nm region provide direct information on solvent-induced predissociation and excited-state vibrational relaxation.

A thermodynamic theory of phase separation in self-associating micellar solutions is presented which incorporates (1) a distribution of micellar aggregates controlled by multiple chemical equilibrium, and (2) interactions between the aggregates. Low-order moments of the micellar distribution provide the link between the phenomena of phase separation and self-association. The theoretical predictions are in excellent agreement with experimental findings in micellar solutions of dioctanoyl-phosphatidylcholine and water.

The temporal evolution of binary mixtures of hard rods in a ring is simulated in a computer with random initial velocities ±v. The time the system takes to reach a Maxwellian distribution dramatically diverges as the mass ratio ε→1 and it also increases, although rather slowly, when ε→∞. A negative ‘‘long-time tail,’’ i.e., a slow, power-law decay in the velocity autocorrelation function at large values of the time t, is observed whose behavior changes from ${\mathrm{t}}^{\mathrm{-}3}$ to ${\mathrm{t}}^{\mathrm{-}\mathrm{\delta }}$, δ≲1, as ε is increased from ε=1. .AE

Physical Processes are reviewed as computations, and the difficulty of answering questions about them is characterized in terms of the difficulty of performing the corresponding computations. Cellular automata are used to provide explicit examples of various formally undecidable and computationally intractable problems. It is suggested that such problems are common in physical models, and some other potential examples are discussed.

Formal scattering theory is recast in a Lie-algebraic form. The central result is an algebraic Lippmann-Schwinger equation for the wave operator from which an algebraic form of the Born series (containing only linked terms) is obtained. When a finite Lie algebra is sufficient, The Mo/ller wave operator, on the energy shell, can be solved for explicitly as an element of the corresponding group. The method is illustrated for the separable potential whose relevant algebra is found to be U(1,1).

The configuration of the electromagnetic field between two conducting plates in the presence of a point source is studied. It is shown that the discretization of the field modes effectively decreases the radiative mass of the source as well as its anomalous magnetic moment. Both effects are finite, cutoff independent, and separable from continuum results and can be measured by precision experiments.

A quark model for baryons, in which the valence quarks are moving in a deformable mean field, is considered. A q-q interaction, consisting of one-gluon-exchange and one-pion-exchange potentials, is diagonalized exactly in the model space of deformed orbitals. With four model parameters, the masses of both the even- and odd-parity states and the radiative transition amplitudes for the L=0 excited states are obtained in fair agreement with experiment.

Using the expression for the topological charge proposed by Lüscher, we calculate the topological susceptibility in SU(2) lattice gauge theory. This problem has become tractable numerically because we were able to integrate one variable analytically. We verify the validity of this definition at present values of β and compare our results to previous work.

The charmonium χ states are observed in both ${\pi }^{\mathrm{-}}$ and p Be interactions near 200 GeV/c via their radiative decay into J/ψ. The χ(3510) and χ(3555) are produced with roughly equal cross sections in ${\pi }^{\mathrm{-}}$ collisions while the χ(3555) dominates in p collisions. Simple gluon fusion can account for χ production with incident protons but additional mechanisms are needed for incident ${\pi }^{\mathrm{-}}$.

The recent data at √s =0.546 TeV from the CERN pp¯ collider confirm once more the predictions of the impact picture, which is based on quantum field theory. These predictions on pp and pp¯ total and elastic differential cross sections are extended to higher energies up to √s =40 TeV. They are of direct interest for future experiments at CERN, Fermilab, and the superconducting super collider.

We propose a simple mechanism to generate a sizable analyzing power in high-energy pp elastic scattering at large angles. Our predictions are of direct interest for the experimental program in progress at Brookhaven National Laboratory for near-future experiments which will be undertaken elsewhere.

The total hadronic cross section for virtual photon-photon interactions is reported for center-of-mass energy, W, between 2 and 20 GeV. The data were obtained via the process $e^{+}$$e^{\mathrm{-}}$→$e^{+}$$e^{\mathrm{-}}$${\gamma }^{\mathrm{*}}$${\gamma }^{\mathrm{*}}$→e ${}_{}{}^{+}{}_{}{}^{}e_{}^{\mathrm{-}}{}_{}{}^{}$+hadrons with both scattered $e^{+}$ and $e^{\mathrm{-}}$ detected. Each photon’s four-momentum squared, $q^2$, ranges from -0.1 to -1.6 ${\mathrm{GeV}}^2$. Dependence upon $q^2$ agrees with a generalized vector-meson-dominance model. The total cross section shows little W dependence, averaging 125 nb at $q_1^2$=$q_2^2$=-0.3. Photon helicity interference terms are determined.

Combining the skyrmion picture of the nucleon and the axial Ward identities in nuclear medium, we show that in a baryon-rich environment, the coupling constants ${\mathrm{g}}_{\mathrm{A}}$ and ${\mathrm{f}}_{\mathrm{\pi }}$ are fundamentally quenched and the rms size of the nucleon consequently enhanced..AE

Results are presented from an investigation of the mean free path in nuclear emulsion of multiply charged fragments, produced by 1.8A-GeV argon nuclei. Charge identification of 6965 fragments with charges Z≥2, producing 2192 secondary interactions, has been made. No dependence of the mean free path on the distance from the preceding collision is observed and thus our result is consistent with the nonexistence of anomalons.

Pion double charge exchange has been used to populate the double isobaric analog state (DIAS) in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Po}$ with use of the doubly magic target ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. The DIAS was found at an excitation energy of 32.46±0.17 MeV with a width of 0.85±0.40 MeV. The excitation energy of the DIAS can be used along with the energy of the isobaric analog state to determine separately the linear and the quadratic terms of the isobaric multiplet mass equation. The resulting linear and quadratic terms are b=-31.6±3.7 MeV and c=0.33±0.09 MeV, respectively.

Isovector low-lying collective $2^{+}$ states are studied in the Samarium isotopes in terms of the interacting-boson model. On the basis of E2 transition data, it is pointed out that the $2_3^{+}$ states of ${}_{}{}^{148}{}_{}{}^{}$,150Sm are isovector. The first calculation including different proton and neutron boson charges is reported for the E2 transitions $0_1^{+}$→$2_1^{+}$. $2_2^{+}$, and $2_3^{+}$ of ${}_{}{}^{148154}{}_{}{}^{}\mathrm{Sm}$, giving rise to the first comprehensive agreement with experiment. Some predictions of B(M1) values are presented for further confirmation of the isovector properties.

This letter gives a newly considered mechanism for positron production which consists of filling of long-lived, supercritical, multiple-vacancy states via higher-order perturbations, with interference terms of the same order of magnitude as in the case of the previously considered single vacancies. This mechanism could be relevant to the structure in positron energy spectra observed at Gesell- schaft für Schwerionenforschung in heavy-ion collisions. A possible directional anisotropy of positron emission is discussed.

The attractive interaction between atoms is described as a self-energy in which the effects of recoil and finite relative velocity are treated exactly. For systems involving positronium significant deviations from the van der Waals potential are found due to both recoil and relative motion.