The complex electrical conductivity σ(ω) is determined from the linear ac susceptibility between 3 Hz and 3 MHz measured in fields between 0.4 and 12 T paralle and perpendicular to the c axis of a twinned crystal. Dynamical scaling of ‖σ‖ and σ’’/σ’ reveals ordering temperatures ${\mathit{T}}_{\mathit{g}}$(B) and field-independent scaling functions by using the variable (${\mathit{T}}_{\mathit{c}2}$-${\mathit{T}}_{\mathit{g}}$)/‖T-${\mathit{T}}_{\mathit{g}}$‖. For B⊥c, the critical exponents ν and z agree with values obtained on films indicating isotropic vortex-glass fluctuations, whereas those for B∥c indicate elongated fluctuations in the c direction mediated by correlated pinning via the edges of twin boundaries.

The helicity modulus for a fluctuating type-II superconductor is computed within the elastic medium approximation, as a probe of superconducting phase coherence and the Meissner effect in the mixed state. We argue that at the vortex line lattice melting transition, there remains superconducting coherence parallel to the applied magnetic field, provided the vortex line liquid retains a finite shear modulus at finite wave vector.

We present a theory of frustrated, two-dimensional, quantum antiferromagnets in the vicinity of a quantum transition from a noncollinear, magnetically ordered ground state to a quantum-disordered phase. Using a sigma model for bosonic, spin-1/2, spinon fields, we obtain universal scaling forms for a variety of observables. Our results are compared with numerical data on the spin-1/2 triangular antiferromagnet.

The first evidence for a wide distribution in the critical mode wave vectors above the spin wave instability threshold for subsidiary absorption is reported. The Brillouin light scattering BLS measurements were done on 4.15 μm thick yttrium iron garnet films with the static field and the 8.47 GHz linearly polarized microwave field in plane. The distribution in the critical mode wave number is broad, with widths of about 0.5×${10}^4$–2×${10}^4$ ${\mathrm{cm}}^{\mathrm{-}1}$ and shapes which change with field and power. These results cast doubts on the validity of simple two mode models for the analysis of self-oscillation, chaos, and related effects above threshold.

Anisotropy of the energy dependent polar magneto-optical Kerr effect as a function of the angle between the magnetization and crystallographic axes is reported. The results are obtained on epitaxially oriented opaque films of hcp Co grown in two different crystallographic orientations by molecular beam epitaxy. Respective Kerr spectra of fcc Co films are found to be insensitive to the magnetization direction. This Kerr anisotropy is correlated with the presence of strong magnetocrystalline anisotropy in the hcp phase of Co. A perturbation theory treatment of the spin orbit coupline correctly predicts the order of magnitude of this new effect.

We present the first observation of 4.4 eV photoluminescence (PL) decay in an oxygen-deficient-type silica excited with ultraviolet and vacuum ultraviolet photons from synchrotron radiation. The lifetime of the 4.4 eV PL is 4.2, 4.3, and 2.1 ns for the 5.0, 6.9, and 7.6 eV excitations, respectively, indicating the presence of multiple decay channels. This can be explained by an energy diagram involving the interconversion between two states of the oxygen-deficient-type defect.

An exact solution for the one-dimensional kinetics of the diffusion-controlled reaction A+B→B is obtained by means of the three-particle correlation functions. Because of a lattice discreteness each site could be occupied by a single particle only which leads to the so-called ‘‘bus effect’’: Recombination of any particle A is defined by a spatial configuration of two nearest particles B only surrounding A from its left and right. This results in the unusual algebraic decay law, n(t)∝${\mathit{t}}^{\mathrm{-}1}$, which asymptotically (as t→∞) does not depend on the trap B concentration.

We show that, contrary to what is commonly believed, the isotropic phase of side-chain liquid-crystal polymers has viscoelastic properties which are totally different from those of ordinary flexible melt polymers. The results can be explained by the existence of a transient network created by the dynamic association of mesogenic groups belonging to different chains. The extremely high sensitivity of the compound to the state of the surfaces with which it is in contact offers us an unexpected method of studying surface states.

Bounds for the generalization ability of neural networks based on Vapnik-Chervonenkis (VC) theory are compared with statistical mechanics results for the case of the parity machine. For fixed phase space dimension, the VC dimension can grows arbitrarily by increasing the number K of hidden units. Generalization is impossible up to a critical number of training examples that grows with the VC dimension. The asymptotic decrease of the generalization error ${\mathrm{\varepsilon }}_{\mathit{G}}$ comes out independent of K and the VC bounds strongly overestimate ${\mathrm{\varepsilon }}_{\mathit{G}}$. This shows that phase space dimension and VC dimension can play independent and different roles for the generalization process.

We consider some of the fundamental statistical mechanics of the electrodiffusion of a long polyelectrolyte, DNA, in a microlithographically constructed 2D rectangular array of cylindrical posts. The DNA polymer is shown to be free draining when not hooked on a post, and the mean time to unhook is explicitly calculated and compared to our measurements.

We analyze the effect of internal degrees of freedom on the movability properties of localized excitations on nonlinear Hamiltonian lattices by means of properties of a local phase space which is at least of dimension six. We formulate generic properties of a movability separatrix in this local phase space. We prove that due to the presence of internal degrees of freedom of the localized excitation it is generically impossible to define a Peierls-Nabarro potential in order to describe the motion of the excitation through the lattice. The results are verified analytically and numerically for Fermi-Pasta-Ulam chains.

We observe critical phenomena in spherical collapse of radiation fluid. A sequence of spacetimes S[η] is numerically computed, containing models (η≪1) that adiabatically disperse and models (η≫1) that form a black hole. Near the critical point (${\mathrm{\eta }}_{\mathit{c}}$), evolutions develop a self-similar region within which collapse is balanced by a strong, inward-moving rarefaction wave that holds m(r)/r constant as a function of a self-similar coordinate ξ. The self-similar solution is known and we show near-critical evolutions asymptotically approaching it. A critical exponent β≃0.36 is found for supercritical (η>${\mathrm{\eta }}_{\mathit{c}}$) models.

The evidence for electroweak radiative corrections not contained in α(${\mathit{m}}_{\mathit{Z}}$) is examined. At low energies there is very strong evidence in the analysis of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. At ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ and pp¯ collider experiments the current direct signals are not strong, but there is substantial indirect evidence, which will likely become sharper when ${\mathit{m}}_{\mathit{t}}$ is determined. The advantage of using (Δr${)}_{\mathrm{res}}$ as a measure of these effects is emphasized. In order to improve the direct evidence, more accurate measurements of ${\mathit{m}}_{\mathit{W}}$ and the on-resonance asymmetries are indicated.

Using the Euclidean path-integral formulation for the hadronic tensor, we show that the large difference between u¯ and d¯ does not come from the disconnected quark-loop insertion. Rather, it can come from the connected (quark line) insertion involving quarks propagating backwards in time. We study the influence of the backward time propagator in the axial-vector and scalar matrix elements in lattice gauge calculations and give an estimate of the violation of the Gottfried sum rule.

We find a significant excess of ultrahigh-energy cosmic-ray events at large transverse momenta with respect to the prediction by standard perturbative QCD at ${\mathit{E}}_{\mathrm{lab}}$∼${10}^4$–${10}^5$ TeV, an energy regime beyond the reach of existing colliders but within the range of future hadron colliders. Such a large deviation cannot be accounted for by a compositeness model of quarks with a characteristic energy scale ${\mathrm{\Lambda }}_{\mathit{c}}$>1.4 TeV allowed by current collider experiments, pointing towards new physics.

The discovery of the new proton emitter ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cs}$ with an energy of 807±7 keV and a half-life of 500±100 μs is reported. WKB half-life calculations indicate ${\mathit{d}}_{5/2}$ proton emission with a low spectroscopic factor comparable to values for ${}_{}{}^{109}{}_{}{}^{}\mathrm{I}$ and ${}_{}{}^{113}{}_{}{}^{}\mathrm{Cs}$. This behavior is consistent with the onset of deformation in this region. The odd-odd nuclides ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cs}$ and ${}_{}{}^{108}{}_{}{}^{}\mathrm{I}$ have significantly lower ${\mathit{Q}}_{\mathit{p}}$ values than the corresponding isotopes lying closer to stability, which is attributed to strong pairing forces between the odd nucleons. The half-life of ${}_{}{}^{113}{}_{}{}^{}\mathrm{Cs}$ has been measured with improved precision as 17±2 μs.

The Lamb shift and fine structure of the $2^3$S-$2^3$P transition in helium has been precisely measured using laser excitation of an atomic beam. The Lamb shift is 5311.27(7) MHz, agreeing with the best previous measurement but a factor of 40 more precise. The 13 parts per ${10}^6$ precision makes this Lamb shift one of the most precisely known in atomic physics. The results for the fine structure intervals have precisions equal to or exceeding the best previous rf measurements but are not in good agreement with them. Our results provide timely benchmarks for the testing of atomic theory and QED in helium.

For paramagnetic molecules subjected to a uniform magnetic field, the Zeeman interaction produces widely tunable, aligned pendular states in which the molecular magnetic dipole librates about the field direction. We demonstrate such alignment by observing spectroscopic transitions at ≊1 T involving the ${\mathit{A}}^3$${\mathit{II}}_1$ excited state of ICl, and extract characteristic pendular eigenproperties that arise from the hybridization of field-free rotor states. Unlike the electric analog, magnetic pendular states can be created for nonpolar molecules and molecular ions.

Experiments demonstrating the role of cluster formation on multiphoton-induced x-ray emission and the scaling of this phenomenon into the kilovolt range have been performed on Kr. For the Kr M shell, augmentation of ${\mathrm{Kr}}_{\mathit{n}}$ formation leads to a large increase in ${\mathrm{Kr}}^{9+}$ (4p→3d) emission (∼100 Å) and the appearance of a strong band at ∼90 Å. The observation of L-shell transitions (∼5–7.5 Å) demonstrates the scaling of this phenomenon into the kilovolt region and leads to the conclusion that the interaction produces direct inner-shell excitation with the emission of prompt x rays.

Cross sections for inelastic collisions of aligned, excited atoms are calculated using ab initio molecular potential curves and couplings and a fully quantum mechanical scattering treatment. Agreement with currently available data is reasonable. The cross sections for specific transitions exhibit strong, energy-dependent oscillations, which are attributed to an interference effect.