The process of wetting of a monodisperse foam by the continuous addition of liquid from the top has been investigated for a cylindrical column. The velocity of the interface between dry and wet foam was found to vary as the square root of the rate of addition of liquid. Evidence of a structural transformation was found around gas fraction Φ=0.87. It was interpreted as arising from the collapse of the four-sided faces of the (Kelvin) polyhedra which constitute the foam cells, and this was directly observed when large bubbles were used. There is a second transition at around Φ=0.6, with the onset of bubble motion.

We derive the form and properties of the generalization error for a self-similar feedforward network (constructed through an iterative procedure of test set partitioning combined with majority voting). We discuss the universality of these results and conjecture that the generalization error rate ε(α) as a function of the amount of training α never decreases faster than ε(α)-1/2∼ √α in the limit α→0. We show how the self-similar architecture can be used to improve the generalization performance.

A scheme to realize an optical switch with quantum coherence between its ‘‘open’’ and ‘‘closed’’ states is presented. It involves a single atom in a superposition of circular Rydberg states crossing a high Q cavity. A combination of switches could be used to prepare a quantum superposition of coherent microwave field states located simultaneously in two cavities. Such nonclassical states and their decoherence due to cavity dissipation could be studied by performing atom correlation experiments.

A new experimental limit to the possible time variation of the proton gyromagnetic ratio times the electron-to-proton mass ratio has been obtained from the frequency comparison data between Cs and Mg atomic beam standards. The measurements, made over a period of one year, lead to an upper limit for the rate of change of ${\mathit{g}}_{\mathit{p}}$(${\mathit{m}}_{\mathit{e}}$/${\mathit{m}}_{\mathit{p}}$) of 5.4×${10}^{\mathrm{-}3}$/yr. This result, based only on the validity of the quantum mechanical theory of the atomic spectra, together with astrophysical data regarding analogous products of atomic fundamental constants, leads also to a new limit for the time stability of the fine structure constant α (2.7×${10}^{\mathrm{-}13}$/yr).

String theory provides an example of the kind of apparent inconsistency that the principle of black hole complementarity deals with. To a freely infalling observer a string falling through a black hole horizon appears to be a Planck size object. To an outside observer the string and all the information it carries begin to spread as the string approache the horizon. In a time of order the ‘‘information retention time’’ it fills the entire area of the horizon.

A precise test of the theory of stellar evolution can be performed by measuring the difference in average energy between the neutrino line produced by ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ electron capture in the solar interior and the corresponding neutron line produced in a terrestrial laboratory. The high temperatures in the center of the Sun broaden the line asymmetrically, FWHM =1.6 keV, and cause an average energy shift of 1.3 keV. The width of the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ neutrino line should be taken into account in calculations of vacuum neutrino oscillations.

We show that a cosmological baryon asymmetry generated at the grand unified theory scale, which would be destroyed at lower temperatures by sphalerons and possible new B- or L-violating effects, can naturally be preserved by an asymmetry in the number of right-handed electrons. This results in a significant softening of previously derived baryogenesis-based constraints on the strength of exotic B- or L-violating interactions.

We show that for a large range of parameters in a SU(2${)}_{\mathit{L}}$×U(1) electroweak theory with two Higgs doublets there may exist classically stable flux tubes of Z boson magnetic field. In a limit of an extra global Ũ(1) symmetry, these flux tubes become topologically stable. These results are automatically valid even if Ũ(1) is gauged.

Nonrenormalizable couplings in supergravity-coupled supersymmetric theories can give rise to power-law divergences that destabilize the weak-scale hierarchy. For the case of the standard-model gauge group, the problem can arise in theories with SU(3)×SU(2)×U(1) gauge-singlet chiral superfluids. The minimal supersymmetric standard model is free from such destabilizing divergences.

Though screened at large distances, a pointlike electric charge can still participate in a long-range electromagnetic interaction in the Higgs phase, namely, that with the Aharonov-Bohm field produced by a localized magnetic flux. We show that this follows from the fact that the screening charge, induced in the presence of a Higgs condensate, does not interact with the Aharonov-Bohm field. The same phenomenon occurs, if a Chern-Simons term is incorporated in the action. This observation provides a physical basis for the recently proposed classification of the superselection sectors of this model in terms of a quasi-Hopf algebra.

Full pion four-point functions at zero momentum are calculated with Kogut-Susskind quarks on a ${12}^3$×20 lattice at β=5.7 and ${\mathit{m}}_{\mathit{q}}$=0.01 in quenched lattice QCD, employing the wall source method without gauge fixing. For both I=0 and 2 channels, results for the s-wave scattering lengths are in agreement with the prediction of current algebra and PCAC (partial conservation of atral-vector current).

We report the measurement of new modes of the charmed baryon ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$ using data recorded by the CLEO II detector at the Cornell Electron Storage Ring. We find branching ratios, relative to ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→${\mathit{pK}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$, of 0.070±0.011±0.011 for ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→${\mathrm{\Sigma }}^{+}$${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{-}}$, 0.069±0.023±0.016 for ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→Σφ, 0.078±0.013±0.013 for ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→${\mathrm{\Xi }}^0$${\mathit{K}}^{+}$, and 0.053±0.016±0.010 for ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→${\mathrm{\Xi }}^{\mathrm{*}0}$${\mathit{K}}^{+}$. These measurements indicate that W-exchange diagrams contribute to ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$ decay. We have also made a new measurement of the previously found mode ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→${\mathrm{\Xi }}^{\mathrm{-}}$${\mathit{K}}^{+}$${\mathrm{\pi }}^{+}$.

We present a measurement of the b-quark cross section in 1.8 TeV p-p¯ collisions recorded with the Collider Detector at Fermilab using muonic b-quark decays. In the central rapidity region (‖${\mathit{y}}^{\mathit{b}}$‖<1.0), the cross section is 295±21±75 nb (59±14±15 nb) for ${\mathit{p}}_{\mathit{T}}^{\mathit{b}}$>21 GeV/c (29 GeV/c). Comparisons are made to previous measurements and next-to-leading order QCD calculations.

We propose a new definition of natural invariant measure for trajectory segments of finite duration for a many-particle system. On this basis we give an expression for the probability of fluctuations in the shear stress of a fluid in a nonequilibrium steady state far from equilibrium. In particular we obtain a formula for the ratio that, for a finite time, the shear stress reverse sign, violating the second law of thermodynamics. Computer simulations support this formula.

We formed the first ‘‘atomic-optics’’ beam of electron-spin-polarized hydrogen atoms using a quasiparabolic polished copper mirror coated with a hydrogen-atom-reflecting film of superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The mirror was located in the gradient of an 8-T solenoidal magnetic field and mounted on an ultracold cell at 350 mK. After the focusing by the mirror surface, the beam was again focused with a sextupole magnet. The mirror, which was especially designed for operation in the magnetic field gradient of our solenoid, increased the focused beam intensity by a factor of about 7.5.

Optical guiding of intense laser pulses over a distance of more than 20 Rayleigh lengths in a plasma is demonstrated using a two-pulse technique. The first pulse prepares a shock-driven, axially extended radial electron density profile which guides a second pulse, injected after an optimum delay which increases with mass of the plasma ions. In the intensity range considered here (${10}^3$–${10}^{14}$ W/${\mathrm{cm}}^2$), the channel is observed to support mode structure reminiscent of an optical waveguide.

Measurements of the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR spectrum, spin-lattice, and spin-spin relaxation rates in ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ reveal the existence of two distinct molecular motions of the same ${\mathrm{C}}_{60}$ molecule above 200 K, with respective activation energies of 2600±300 and 6800±500 K. We propose a simple model to explain these data implying fast axial jump rotation of the ${\mathrm{C}}_{60}$ molecules combined with slow jumps around perpendicular axes. The analysis of the spectra indicates an abrupt change in the molecular motion below 200 K suggestive of a phase transition also evidenced by calorimetric measurements.

The steady states of a crack moving in a triangular lattice are calculated and shown to become unstable at a certain velocity.

We investigate models which have more than one coupling constant and which have no (codimension one) fixed point in the renormalization group flow in an ε=4-d expansion. We show that the pseudocritical behavior of these systems is dominated by a minimum in the flow. By using the local potential approximation of the renormalization group, the properties of such minima are described. If a minimum is ‘‘good enough,’’ it can fake a fixed point, but there are corrections to the relation between the exponents. Finally, we show that similar results hold in an ε expansion.

We report on numerical evidence for a statistical mechanics description of the probability distribution of clusters grown on a square lattice with the η model. The morphology selection mechanism in Laplacian growth phenomena is formulated in terms of two functions α(η) and β(η), which play the role of a free energy and an inverse temperature, respectively. Invariants of the growth process such as the fractal dimension of a typical cluster and the singularity spectrum of its harmonic measure are computed from these thermodynamic quantities.