Ising and Heisenberg ferromagnets and spin-glasses are studied at the percolation threshold for power-law bond distributions, P(J)∼‖J${\Vert }^{\alpha \mathrm{-}1}$ for J→0. Nonuniversal, α-dependent, critical behavior is found. A hierarchical model for the ‘‘backbone’’ yields, via finite-size scaling, expressions for the exponent t in the relation Υ∝(p-$p_c$${)}^t$ for the generalized stiffness coefficient, and for the percolation-to-thermal crossover exponent φ.

Neutron scattering demonstrates the coexistence of antiferromagnetic order and superconductivity below 1 K in the heavy-electron system ${\mathrm{URu}}_2$${\mathrm{Si}}_2$. It is found that the upper (17.5 K) transition is to an antiferromagnetic phase with a (100) modulation wave vector and spins along the tetragonal c-axis. The ordered moment is unusually small, (0.03±0.01)${\mathrm{\mu }}_{\mathrm{B}}$. However, spin waves develop from damped, finite-gap excitations above ${\mathrm{T}}_{\mathrm{N}}$, and they are intense, propagating, and longitudinal with a zone centre gap of 1.8 meV.

A quantitative test of the theory of large polarons has been achieved by precise measurement of the cyclotron resonance of polarons in silver halides in magnetic fields up to 16 T. We find that a good agreement between the measurements and their theoretical interpretation is achieved by variational polaron theory, but the best quantitative agreement is achieved by a recent theory of the magnetoabsorption of polarons, based on a generalization of the Feynman polaron model.

The low-intensity luminescence of ${\mathrm{ZnSe}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Te}}_{\mathrm{x}}$ with x=1% exhibits several unusual features which are attributed to the occurrence of efficient exciton self-trapping induced by Te atoms. This type of exciton localization is strikingly different from that observed in other II-VI or III-V mixed crystals.

We report the results of magnetoresistance measurements on amorphous hydrogen-doped ${\mathrm{Zr}}_2$Ni samples and compare them with the current theoretical concepts based on weak localisation in three-dimensional systems in the presence of strong spin-orbit interaction. We find that the hydrogen dopant strongly suppresses the spin-orbit and the Maki-Thompson contributions to magnetoresistance.

We show that in a donor-doped multivalley semiconductor or multivalley semimetals, at very high magnetic fields, there exists a critical temperature below which a new triplet superconducting phase must arise. This phase is a mirror image of the spin-up, spin-down Cooper-pair condensation where the spins are replaced by the indices of the valleys. Because the magnetic field does not couple to the indices this transition is strongly enhanced in the presence of a magnetic field.

Optical detection of magnetic resonance is reported for isolated interstitial ${\mathrm{Zr}}_1^{+}$ in ZnSe produced by 2.5-MeV electron irradiation at 4.2 K. It is detected as a reduction of the distant-donor–to–Frenkel-pair recombination luminescence at 625 nm. Resolved hyperfine interaction with the central zinc ion and two shells of Se neighbors reveals a highly localized ‘‘deep’’ state for the paramagnetic electron. It is stable only to ∼220 K.

A burst of eight neutrino events preceding the optical detection of the supernova in the Large Magellanic cloud has been observed in a large underground water Cherenkov detector. The events span an interval of six seconds and have visible energies in the range 20–40 MeV.

The time evolution of an initially localized state of a quantum particle coupled to a dissipative environment with spectral density I(ω)∝${\mathrm{\omega }}^{\mathrm{\alpha }}$ for low frequencies is discussed. At finite temperatures, the width of the state can grow subdiffusively or superdiffusively, depending on α. For α>2 damping becomes ineffective for long times and the state spreads kinematically. At zero temperature the spreading is slower and for α<1 an initially localized state remains localized for all times.

To study properties of self-avoiding surfaces, we consider D-dimensional elastic manifolds embedded in d-dimensional space. In the (d,D) plane there is a line separating ideal (Gaussian), and self-avoiding (interacting) behaviors. We develop the techniques for systematic perturbation expansions, and renormalization-group analysis, about any point on this line. The usual ε expansion for polymers about d=4 is a special case. The exponents ν and γ are calculated to lowest order, providing very good values for polymers (D=1), and reasonable indications for surfaces (D=2).

The Rydberg constant $R_{\infty }$ was determined to 3 parts in ${10}^{10}$ by direct comparison of the four H,D Balmer-β transitions with a National Bureau of Standards standard laser. This is the most precise value: $R_{\infty }$=109 737.315 73(3) ${\mathrm{cm}}^{\mathrm{-}1}$; it approaches the limits of accuracy for optical measurements. The fine-structure splittings and isotope shift are in excellent agreement with theory. The result agrees with less precise experiments by Zhao et al. and Biraben and Julien but disagrees with the result of Hildum et al.

Random superpositions of plane waves, designed to mimic the local behavior of completely random eigenfunctions of classically chaotic Hamiltonian systems, are shown to have surprising properties, including structures which may be precursors of periodic orbit scar localization.

Polyakov’s theory of surfaces embedded in Euclidean space-time with an extrinsic curvature term is stable under small fluctuations only if the number of dimensions is positive and less than 26.

We show how Witten’s noncommutative geometry may be extended to describe the closed bosonic string. An explicit representation of the ∮ and * product for closed strings is provided.

The proton and neutron magnetic form factors, the axial-vector form factor, and the leading N-Δ transition form factor are connected by the nucleon distribution amplitude. If the distribution-amplitude moments obey the QCD sum-rule results, a correlation exists between the neutron magnetic form factor $G_{\mathrm{Mn}}$ and the leading N-Δ transition form factor. For existing proposed distribution amplitudes, one or the other of them will be small and the other not. We comment on what available data say.

We have measured the single and correlated magnetic-substate population parameters for the $2^{+}$ and $2^{+}$-$2^{+}$ excitations in ${}_{}{}^{24}{}_{}{}^{}$Mg${+\mathrm{}}^{24}$Mg in the region of two strong resonances seen in inelastic scattering. We interpret our data in terms of an isolated resonance decaying through one preferred l value in both the $2^{+}$ and $2^{+}$-$2^{+}$ channels. Our data suggest a spin assignment of $J^{\pi }$${=36\mathrm{}}^{+}$ for the resonance at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=45.70\mathrm{}}$ MeV, and a value of l=34 for the grazing angular momentum for both the single and mutual inelastic-scattering channels.

The first optically enhanced electron attachment involving electronically excited molecules is reported. The metastable (triplet) states responsible for the photoenhanced electron attachment were produced indirectly via internal conversion from higher excited singlet states which are strongly optically allowed and are reached by excimer-laser excitation.

We report the alteration of visible spontaneous emission by atoms coupled to the degenerate modes of a confocal resonator. The partial emission rate into the resonator modes is enhanced by a factor of 19 when the resonator is tuned to the atomic transition frequency and inhibited by a factor of 42 when it is detuned. This results in a fractional increase of 1.6% and decrease of 0.5%, respectively, in the total spontaneous emission rate, which we verify by monitoring changes in the intensity of light emitted out the sides of the resonator as it is tuned.

Resonant collisional energy transfer between atoms with small relative velocity is shown to have such long collision times, ∼0.17 μs, or equivalently such narrow linewidths, 6 MHz, that it may be used to make spectroscopic measurements. Specifically, we report the use of the sharply resonant collisional energy transfer ns+(n-2)d→np +(n-1)p, between velocity-selected K atoms to determine an improved value, 1.711?5(5), and the K np-state quantum defect.