It is shown that the presence of a Dirac magnetic pole in topologically massive (Abelian) p-form electrodynamics implies the quantization of the topological mass. The analysis is carried out in detail for a one-form in (2+1)-dimensional space-time. The generalization to a p-form in 2p+1 dimensions is also indicated.

The boundary conditions of the first-quantized compactified closed bosonic string constrain the eigenvalues of the zero-mode operators. Requiring that internal symmetries result from compactification, we show that the simplest boundary conditions imply that the ‘‘left’’ and ‘‘right’’ lattices must be self-dual at the first-quantized level. The one-loop corrections to such models satisfy modular invariance.

The problem of thermalization of quarks and gluons in relativistic nuclear collisions is considered in a way that minimizes the explicit dependence on the details of the soft QCD interaction. With nuclear transparency and distributed contraction as essential inputs, it is found that, when the collision energy is asymptotically high, the average initial temperature is in the range 300–500 MeV and the thermalization time has a lower bound of order 0.15 fm/c.

On the basis of very general dynamical properties of antinucleon-nucleon coupling it is shown that the (p¯,n¯) reaction should be a highly selective probe of longitudinal spin excitations.

We describe the first experiments in which negative ions formed in interactions involving highly excited (laser-selected) atoms are identified by mass. We therefore report the first observations of negative ions produced by Rydberg–ground-state interactions (at low n) and by Rydberg-Rydberg interactions (at high n).

A measurement of the azimuthal dependence of the angular distribution of photoelectrons from ${13}^3$${\mathrm{D}}_{3/2}$-state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(φ)=1+0.026(6)cosφ where φ=0 is the direction of the laser beam. This departure from the symmetry I(φ)=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.

We report the first measurement of a fully state selected (${\mathrm{v}}_{\mathrm{i}}$,${\mathrm{j}}_{\mathrm{i}}$,‖${\mathrm{m}}_{\mathrm{i}}$‖)→(${\mathrm{v}}_{\mathrm{f}}$, j ${}_{\mathrm{f}}{}^{}{}_{}{}^{}$,‖${\mathrm{m}}_{\mathrm{f}}$‖) differential cross section in atom-molecule collisions. We have studied ${\mathrm{Na}}_2$-Ne, (0,6,‖${\mathrm{m}}_{\mathrm{i}}$‖)→(0,0,0) rotationally inelastic scattering at a collision energy of 190 meV. The data verify a pronounced ‖Δm‖≪j propensity with respect to the direction of linear momentum transfer. A realistic estimate for the relative contribution of collision processes with ‖Δm‖>0 gives an upper limit of 10%.

Calculations are presented that show the response of an atom to a picosecond laser pulse which resonantly excites a manifold of Rydberg states. The coherent atomic state that is produced is of the form of a spatially localized wave packet. The motion, decay, and reformation of the wave packet are described and related to the complicated quantum beat pattern that appears in the subsequent spontaneous decay.

An analysis shows that atomic inner-shell states can be strongly excited by coherently driven outer-shell electrons. A time-dependent Hartree-Fock treatment illustrates the nature of this nonlinear intershell coupling. A substantial fraction of the absorbed energy can be channeled into inner-shell excitation.

We consider the effect of a spatially periodic forcing at the onset of one-dimensional periodic patterns in nonequilibrium systems. It is shown that the competition between periodicities can lead to a commensurate-incommensurate transition mediated by solitons as in equilibrium systems. This result is in agreement with a recent experiment.

Adiabatic expansion is proposed as a method of increasing the degree of correlation of a magnetically confined pure electron plasma. Quantum mechanical effects and correlation effects make the physics of the expansion quite different from that for a classical ideal gas. The proposed expansion may be useful in a current experimental effort to cool a pure electron plasma to the liquid and solid (crystalline) states.

When the Van der Waals equation of state is valid for a real gas bubble in a liquid, the bubble radius will decrease by diffusion until the Van der Waals forces are in stable equilibrium with the surface tension.

The pulsed heating of Si (100) and (111) surfaces has been simulated by molecular dynamics. The (111) crystal-melt interface propagates by layer-by-layer growth whereas the (100) interface grows in a continuous fashion. The equilibrium crystal-melt interface is sharp for the (111) orientation and broad for the (100) orientation. These simulations are the first use of nonpairwise potentials to study interfaces between condensed phases, and the results support models of interfaces which heretofore had to be deduced from indirect experimental information.

We present experimental results showing that colloidal silica spheres can be induced to aggregate either slowly or very rapidly. The slow process always yields clusters with a fractal dimensionality ${\mathrm{d}}_{\mathrm{f}}$=2.08±0.05, but the rapid process can produce clusters with either ${\mathrm{d}}_{\mathrm{f}}$=1.75±0.05 or ${\mathrm{d}}_{\mathrm{f}}$=2.08±0.05. However, clusters with ${\mathrm{d}}_{\mathrm{f}}$=1.75 are always observed to restructure so as to yield ${\mathrm{d}}_{\mathrm{f}}$=2.08±0.05.

We show that for conformally invariant two-dimensional systems, the amplitude of the finite-size corrections to the free energy of an infinitely long strip of width L at criticality is linearly related to the conformal anomaly number c, for various boundary conditions. The result is confirmed by renormalization-group arguments and numerical calculations. It is also related to the magnitude of the Casimir effect in an interacting one-dimensional field theory, and to the low-temperature specific heat in quantum chains.

We show that the leading finite-size correction to lnZ for a two-dimensional system at a conformally invariant critical point on a strip of length L width β(β≪L) is (π/6)c(L/β), where c is the conformal anomaly. Equivalently, the leading low-temperature correction to the free energy of a one-dimensional quantum system is -(π/6)cL(kT${)}^2$ħv, where v is the effective ‘‘velocity of light.’’ The latter formula is used to check recently derived critical theories of spin-s quantum chains against Bethe-Ansatz solutions.

We report here new LEED data for the H/W(110) surface, showing that W(110) undergoes a reconstruction induced by adsorption of hydrogen above a critical coverage. The structural change consists of a lateral shift of the top layer of W atoms relative to the bulk. We also propose a driving mechanism for the transition which may be important in other chemisorption systems as well. The surfaces most likely to undergo this type of reconstruction are those with adsorption sites consisting of flat potential wells.

One-phonon cross sections calculated from sagittally polarized vibrational normal modes account for most salient inelastic-scattering intensities seen in He-LiF(001) 〈100〉 and 〈110〉 measurements published by Brusdeylins, Doak, and Toennies. We have found that most inelastic intensities which cannot be attributed to potential resonances can be explained as kinematically enhanced scattering from both surface and pseudosurface bulk modes.

The modulation in the magnetic moment and in the interplanar spacing (strain) in the superlattice [${\mathrm{Gd}}_{21}$${\mathrm{Y}}_{21}$]×40 has been determined by use of synchrotron and rotating-anode x-ray sources. The average moment appears to decrease in the interfacial regions, and the width of the strain interface increases with decreasing temperature.

We monitor the refractive index n+ik of an optically thin silicon layer following femtosecond photoexcitation below the threshold fluence ${\mathrm{E}}_{\mathrm{th}}$ for melting, in order to measure the rate of lattice temperature rise. We find that most of the heating is delayed with respect to the photoexcitation, but becomes faster as ${\mathrm{E}}_{\mathrm{th}}$ is approached. A model based on delayed Auger heating is presented.