Experiments utilizing electron quantum interferences manifested in the magnetoresistance of pure strain-free single crystals of magnesium have produced a new regime of magnetotransport characterized by quantum mechanical rather than semiclassical properties.

Starting from an established correlation between the $\sigma$ shape resonance position in nearedge x-ray-absorption fine-structure spectra and the intramolecular C-C bond length for gas-phase hydrocarbons, we derive a similar relation for chemisorbed molecules. The linear relation obtained allows us to determine the C-C bond length for chemisorbed molecules from near-edge x-ray-absorption fine-structure spectra with a ruler to an accuracy of <0.04 Å. Examples are given for bonding and bond-length changes of ${\mathrm{C}}_2$${\mathrm{H}}_2$ and ${\mathrm{C}}_2$${\mathrm{H}}_4$ on Pt(111).

Differential equations for the electric fields and polarizations inside a nonlocal dielectric, including a continuous surface potential, are numerically integrated outwards right up to the surface and the reflectivities are calculated for both $s$- and $p$-polarization geometries. We find that for strongly repulsive potentials the choice of boundary conditions additional to those of Maxwell makes no difference to the results.

The static susceptibility of a single-crystal copper specimen has been measured at nanokelvin temperatures, parallel and perpendicular to the external magnetic field $B$. Below $B_c=0.27\mathrm{}$ mT, three different antiferromagnetically ordered regions are described at small values of entropy $S$. The $B-S$ phase diagram is presented. Metastabilities and the observed nonadiabaticity during the final stages of demagnetization are discussed.

We discuss coherent excitation of ions incident on crystal surfaces at grazing angles and show that substantial gains for soft x rays can be achieved for reasonable beam currents.

Accretion onto closed loops of vacuum string results in the formation of compact objects of subgalactic mass which are comparable in number to the frequency of active galactic nuclei and quasars. Such structure develops in baryon- and neutrino-dominated, as well as in axion-dominated, cosmological models. Planar wakes also develop behind relativistically moving open strings and generate fluctuations of order unity in the galaxy density on scales comparable to those of galaxy superclusters.

Certain unstable periodic orbits are shown to permanently scar some quantum eigenfunctions as $\hslash \to 0$, in the sense that extra density surrounds the region of the periodic orbit.

Certain nonlinear sigma models with fermions suffer from an anomaly similar to the one in non-Abelian gauge theory. We exhibit this anomaly using both perturbative and global methods. The affected theories are ill defined and hence unsuitable for describing low-energy dynamics. They include certain supersymmetric models in four-space dimensions.

The breaking of isospin symmetry in the electroweak theory with a dynamical Higgs sector is analyzed. The natural size of the breaking in various amplitudes is estimated, given that the breaking is very large in the fermion mass matrix. Special attention is paid to the parameter $\rho \equiv \frac{M_W^2}{M_Z^2{cos}^2{\theta }_W}$. Hypercolor models are then investigated. There it is noted that $\rho -1\mathrm{}$ will naturally exhibit a sensitive, linear dependence on the fermion-doublet mass splittings.

We use two-body Dirac equations (derived from Dirac's constraint mechanics and super-symmetry) to make the naive quark model fully relativistic. Our covariant equations incorporate not only relativistic kinematics but also dynamical recoil effects that generalize Breit corrections to forms that have well-defined quantum short-distance behavior. In these equations, a crude but covariant generalization of Richardson's static quark potential produces a surprisingly good one-parameter relativistic fit to the meson spectrum.

In the two-valence-neutron nucleus ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$, in-beam ${}_{}{}^{148}{}_{}{}^{}\mathrm{Sm}(\alpha ,4n)$ and (${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$3n$) measurements have identified nine ${\nu }^2\times \mathrm{octupole}$ levels with $3<I<\mathrm{}14\mathrm{}$. The measured half-life of the ${(\nu f_{\frac{7}{2}}^2\times 3^{-})}_{9^{-}}$ state gives $B(E3,9^{-}\to 6^{+})=55\mathrm{}\mathrm{}\left(6\right)\mathrm{}{B}_{\mathrm{W}}$. A high-lying ${12}^{+}$ level, which decays by $E3\mathrm{}$ to the $9^{-}$ state, as well as a ${14}^{+}$ level are shown to be two-phonon octupole excitations of stretched ${\nu }^2\times 3^{-}\times 3^{-}$ character. All these results can be quantitatively derived from the experimental data for the coupling of one neutron to the core octupole observed in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$.

Strong indirect evidence exists for the existence of attractive forces between nuclei making surface contact. Experimentally, the recent observations of spontaneous positron production in heavy-ion collisions can only be understood if nuclei stick together for times long compared to the collision time. We show that any such tendency for nuclei to attract implies the existence of nuclear molecules with entirely new kinds of collective modes. We present a simple model for these modes and apply it to ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$-${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$.

The direct breakup of 70-MeV ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ scattered from a ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ target is investigated at forward angles. Inside the grazing angle, it is found that the breakup is dominated by the Coulomb interaction between projectile and target.

The reaction of ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$+Ta at 680 MeV has been studied with a system able to detect coincidences between projectilelike particles of charge $Z>~3$. We have observed coincidences between all possible pairs of $Z=3\mathrm{}$ to $Z=8\mathrm{}$ fragments and have measured the energy correlations of the coincident fragments. These correlations show the production mechanism to be sequential projectile breakup.

We show both experimentally and by a semiempirical multichannel quantum-defect-theory analysis that the profile of the $\mathrm{Ne}(n{s}^{\prime },J=1)$ autoionizing resonances varies with the character of the $\mathrm{Ne}(2\mathrm{}{p}^{5}3p,J=1,2)$ state, from which the resonance is excited, whereas the resonance width is constant.

The capture of an electron from an inner atomic shell, namely, from the argon $L$ shell, into projectile continuum states [electron capture to the continuum, (ECC)] has been observed for proton impact around 300-keV collision energy. The energy distribution of ejected electrons detected in forward direction in coincidence with $\mathrm{LMM}$ Auger electrons shows the pronounced cusp-shaped peak characteristic for the ECC process. This also provides the first ECC measurement in the low-impact-velocity regime.

The propagation of femtosecond-duration optical pulses in electro-optic materials is observed to produce a Cherenkov cone of pulsed far-infrared radiation in the terahertz spectral range. Coherent detection of the electric field of this far-infrared pulse by electro-optic sampling shows it to have a duration of approximately one cycle and an amplitude of 10 V/cm making it a potentially attractive source for transient far-infrared spectroscopy.

Experiments in Tokapole II demonstrate the shear Alfvén resonance in a tokamak by direct probe measurement of the wave magnetic field within the plasma. The resonance is driven by external antennas and is identified as radially localized enhancements of the poloidal wave magnetic field. The radial location agrees with calculations which include toroidicity and noncircularity of the plasma cross section. Other properties such as polarization, radial width, rise time, and wave enhancement also agree with magnetohydrodynamical theory.

The thermal ion-acoustic fluctuation spectrum of a high-density, low-temperature (2 eV, ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$), collisional plasma was measured in a C${\mathrm{O}}_2$-laser scattering experiment. The measured spectra differed substantially from spectra observed in collisionless plasmas. Fluctuations at the ion-acoustic frequency were strongly enhanced and the width of the resonance was significantly narrowed in comparison to the collisionless case. The Bhatnagar-Gross-Krook theory proved most successful in describing the data.

The oscillatory temperature amplitude of a low-Prandtl-number fluid in Rayleigh-Bénard convection is shown to exhibit critical slowing down near the onset of oscillatory convection. The data are analyzed in the context of a mean-field Landau-Hopf equation. We find the magnitude of the power-law exponent for the dynamic relaxation to be 1.01±0.02 and 1.00±0.02 above and below onset, respectively, in agreement with the theoretical predictions.