We present the outline of a new and efficient technique for the calculation of loop amplitudes in a gauge theory. The technique is based on the technology of four-dimensional heterotic strings. We display here the application to the calculation of the one-loop corrections to gluon-gluon scattering, in ordinary dimensional regularization. We find complete agreement with the previous Feynman-diagram calculation of Ellis and Sexton.

The longitudinal structure function ${\mathit{F}}_{\mathit{L}}$ at small x is a very direct probe of the gluon distribution. Studies have shown that measurements at the DESY ep collider HERA can distinguish various possible theoretical small-x behaviors. Phenomenological analyses to date have used leading-order expressions for the structure function. We use the recent O(${\mathrm{\alpha }}_{\mathit{s}}^2$) calculation of Kazakov et al. to extend the analysis to next-to-leading order. We also investigate the effect of the b-quark threshold on the longitudinal structure function. We show that both these effects are numerically under control, and therefore do not change the conclusion that there is indeed a very direct connection between ${\mathit{F}}_{\mathit{L}}$ and the gluon.

A superdeformed band of twenty transitions has been found in ${}_{}{}^{142}{}_{}{}^{}\mathrm{Eu}$ following the reaction ${}_{}{}^{110}{}_{}{}^{}\mathrm{Pd}$${(}^{37}$Cl,5n${)}^{142}$Eu at 160 MeV. This is the first case to be found intermediate to the A∼135 and A∼150 regions. The ${\mathit{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$ dynamic moment of inertia remains remarkably constant, suggesting that the configuration is π$6^1$ν$6^3$, blocking both proton and neutron band crossings. The band has been estimated to have ∼3.6% of the channel intensity. This is remarkably intense, and is possibily due to a lowering of the odd-odd configuration by a strong residual n-p correlation.

Using laser-induced nuclear-orientation and optical-saturation techniques, we have produced sub-Doppler changes in the anisotropy of the angular distribution of the 514-keV γ rays from the 1-μs isomer ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}_{}^{\mathit{m}}{}_{}{}^{}$. This permits high-resolution measurements of D1 and D2 hyperfine transitions of atoms of the isomer, which give the isomer’s nuclear electric quadrupole moment, -0.73±0.17 b, and its nuclear magnetic dipole moment, (6.043±0.005)${\mathrm{\mu }}_{\mathit{N}}$. The isomer shift, -113±8 MHz relative to the ground state of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$, corresponds to a change in the mean-square charge radius of +0.174±0.008 ${\mathrm{fm}}^2$.

Using a merged-beam apparatus, we have measured the absolute cross section for the associative ionization process H(1s)+H(2s)→${\mathrm{H}}_2^{+}$+${\mathit{e}}^{\mathrm{-}}$ between 0.5 and 10 eV. The total cross section rises until a maximum of 2.4×${10}^{\mathrm{-}17}$ ${\mathrm{cm}}^2$ at the ${\mathrm{H}}_2^{+}$ dissociation threshold (3.4 eV) and exhibits a minimum around 2 eV. We attribute this feature to interferences between two reaction paths. Calculations combining a quantum-defect treatment of the multichannel ionization with a close-coupling treatment of the atom-atom half collision yield results in good agreement with experiment.

We develop a space-time renormalization-group method to study diffusion in a disordered medium. We prove rigorously that a random walk with transition probabilities given by a random matrix diffuses in a Brownian way for weak disorder if d>2. We also show that the disorder induces polynomial decay of velocity-velocity correlations.

Using a simple wake function, it is shown that the equilibrium bunch length in electron storage rings with localized wake can have a cusp-catastrophe behavior. Contrary to the results of the conventional theory for a distributed wake force, the system becomes bistable (period 1 and period 2) and exhibits hysteresis in some region of the parameter space. These features are predicted by a Gaussian approximation and confirmed by multiparticle tracking.

The equilibrium polarization of the electron spin has been measured at the TRISTAN electron-positron storage ring. The measurement was carried out by using a laser polarimeter detecting an asymmetry in the Compton scattering of a circularly polarized laser beam on polarized electrons. The laser polarimeter allows for simultaneous measurements of the transverse and longitudinal polarization with sufficient accuracy. The polarization level was relatively high, 40% at an electron-beam energy of 29 GeV, and the polarization vector was inclined at an angle of about 30°.

We present a physical model to describe the equilibrium probability distribution function (PDF) of velocity differences across an inertial-range distance in 3D isotropic turbulence. The form of the non-Gaussian PDF agrees well with data from direct numerical simulations. It is shown that these PDF’s obey a self-similar property, and the resulting inertial-range exponents of high-order velocity structure functions are in agreement with both experimental and numerical data. The model suggests a physical explanation for the phenomenon of intermittency and the nature of multifractality in fully developed turbulence, namely, local self-distortion of turbulent structures.

For the first time a heavy-ion beam was focused using a z-pinch plasma lens. The diameter of an incident, parallel, 460-MeV argon-ion beam was reduced from ∼8 mm (FWHM) to ∼2 mm within 230 mm downstream of the plasma. Inside a cylindrically symmetric plasma column a high-gradient, azimuthal magnetic field is produced during a z-pinch discharge. For axially moving, high-energy charged particles this field configuration provides strong, first-order focusing simultaneously in both transversal planes. The measured spot size agrees with numerical calculations taking into account the finite beam emittance, and charge exchange as well as energy-loss processes contributing to aberrations.

Static light-scattering experiments on pseudoternary systems of salted water, pentanol, and salium dodecyl sulfate are presented. The results show evidence for a second-order phase transition between two isotropic phases which is not a classical liquid-liquid phase separation. We discuss these results in the frame of the sponge-asymmetric phase transition which has been described for systems of self-avoiding connected membranes. Both the correlation function and the critical behavior of the scattered intensity are analyzed and are shown to be in agreement with theory.

We apply the theory of Dzyaloshinskii, Lifshitz, and Pitaevskii to ice, water, and vapor at the triple point and find that electromagnetic interactions do not permit a liquid film of macroscopic thickness at the ice-vapor interface. Hence the surface melting of ice is at most incomplete. However, the thickness of the film which is permitted is surprisingly large, with retardation effects setting the scale. Our estimate is about 30 Å. Further liquid appears as droplets with a contact angle of about 0.2°. The film thickness decreases rapidly with temperature.

New modes of operation of a scanning tunneling microscope (STM) with laser radiation coupled into the tip of the tunneling junction are demonstrated. The dc current generated by rectifying the laser light and the difference-frequency signal produced in the STM by two laser beams are used to obtain atomic-resolution surface images of graphite, as well as to control the tip-sample distance. Such a laser-driven STM can generate surface images without external bias voltage and, when the difference-frequency signal is used for the distance control, even without any dc current between the tip and the sample. This mode of operation may also allow insulators to be studied.

Scanning tunneling microscopy of Ni deposited on Au(111) at room temperature reveals strikingly ordered island nucleation. Ni islands grow with spacing 73 Å along [12¯1] in rows 140 Å apart at surface-lattice dislocations induced by the Au(111) ‘‘herringbone’’ reconstruction. The island arrays are explained by a model in which Ni atoms diffuse on the surface and aggregate at these dislocations. Island size varies by more than the shot-noise limit, suggesting that the initial sticking probability is low when a diffusing atom encounters a dislocation.

Scanning tunneling microscopy and LEED reveal that on regularly stepped Ni(771) the oxygen-driven missing-row reconstruction of the (110) terraces proceeds in a very transparent manner: Substrate atoms can move to adjacent terraces without crossing steps, where they line up with remaining atom rows to form linear O-Ni chains. On the resulting double-width terraces perfect missing-row structures all over the surface are formed in contrast to flat Ni(110); to surmount the double-step barrier, elevated temperatures (≥250 °C) are required.

The binding sites for adsorption of a single Si atom on the reconstructed Si(100) surface are identified using first-principles total-energy calculations. We establish several saddle points for the migration of the adatom by mapping out the total energy as a function of its position on the surface. For the diffusion parallel to the dimer rows on the surface, we find an activation energy of 0.6 eV; for diffusion perpendicular to the rows, the activation energy is 1.0 eV. One-dimensional hopping motion of individual adatoms should be observable by scanning tunneling microscopy at moderately low temperatures.

The Si(113) surface is very stable despite its high index but until now its atomic structure has been uncertain. Using a scanning tunneling microscope, we have obtained images of both empty and filled states which provide strong evidence for a particular structural model with a 3×2 unit cell. We explain our results in terms of a general rehybridization principle which accounts for the low surface energy and the spatial distribution of empty and filled states. Our images reveal a high density of domain boundaries which introduce energy states that pin the Fermi level and explain earlier reports of a 3×1 reconstruction.

We present experimental data for the thermally activated capture of electrons on Si-induced impurity states in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As in the strong-lattice-relaxation regime (DX centers). Experiments have been performed after photoionization in the region of transition from the normal to the metastable state of the defect, using hydrostatic pressure up to 8 kbars. An analysis of the isothermal as well as the thermostimulated capture kinetics strongly supports the hypothesis of the negative charge state of the DX Center.

Synchrotron-radiation and x-ray photoemission studies of the valence states of condensed phase-pure ${\mathrm{C}}_{60}$ showed seventeen distinct molecular fetaures extending ∼23 eV below the highest occupied molecular states with intensity variations due to matrix-element effects involving both cluster and free-electron-like final states. Pseudopotential calculations established the orign of these features, and comparison with experiment was excellent. The sharp C 1s main line indicated a single species, and the nine satellite structures were due to shakeup and plasmon features. The 1.9-eV feature reflected transitions to the lowest unoccupied molecular level of the excited state.

Anisotropic-conductiity (σ), thermopower, and dielectric-constant studies show that oriented polyaniline salt is representative of a class of quasi-one-dimensional disordered conductors where coupled parallel chains form ‘‘metallic’’ bundles in which electron wave functions are extended three dimensionally. This is in contrast to isolated conducting chains in conventional 1D conductors. The bundles correspond to crystalline regions of the polymer. The results are important for understanding the stabilization of metallic states and achievement of high σ in conducting polymers.