The spin-dependent potentials in the formalism of Eichten and Feinberg and of Gromes are generalized. Consistency of the observed spin splittings in the $\frac{J}{\psi }$ and $\Upsilon$ systems with QCD imposes stringent constraints on the type of nonperturbative spin-dependent forces allowed.

We use the SU(3) ⊗ SU(2) ⊗ U(1) renormalization-group equations to constrain fermion masses and charged-scalar couplings in supersymmetric grand unified theories.

We have observed ${\Lambda }_c$ baryons in nonresonant $e^{+}{e}^{-}$ annihilation at energies around $\sqrt{s}=10.5\mathrm{}$ GeV through their decay to $\Lambda {\pi }^{+}{\pi }^{+}{\pi }^{-}$. We measure the branching fraction to be (2.8 ± 0.7 ± 1.1)%. The momentum spectrum of the ${\Lambda }_c$ is similar to that of charmed mesons, providing a constraint on models of charmed-quark hadronization.

The chiral gauge anomaly is studied by use of the U(1) holonomy on the space of all gauge fields. On this space an Abelian gauge structure is identified and the anomaly is related to the pertinent field-strength tensor and computed by use of the $\eta$ invariant of a five-dimensional Dirac operator.

We present a new and fundamental approach for generating rapidly convergent lower and upper bounds to the ground-state energy of a bosonic system, $E_g$. The bosonic ground-state wave function defines a moments problem because it both is nonnegative and exhibits rapid asymptotic decrease. Through the use of the Hankel-Hadamard determinant inequalities associated with this moments problem one can constrain $E_g$ through exponentially convergent bounds. Extensions to excited bosonic states and fermionic systems are briefly outlined.

Simulations of relativistic electron beams propagating in air show axisymmetric hollowing instabilities of the beam, caused by avalanche ionization of the air near the beam axis. This produces an induced return current peaked on axis, which weakens the pinch force there and triggers the instability for $\frac{E}{p}>130\mathrm{}$ kV ${\mathrm{cm}}^{-1\mathrm{}}$ ${\mathrm{atm}}^{-1\mathrm{}}$ and current neutralization >50%. We performed experiments verifying the existence of this instability on a 6-kA/ns, 70-kA, 4-MeV beam for air pressures less than ∼80 Torr, the predicted threshold.

In the axisymmetrized tandem mirror GAMMA 10, thermal-barrier and plug potentials have been formed in the axisymmetric mirror cells at both ends and directly measured with Au neutral-beam probes and end-loss analyzers. Strong end-loss reduction associated with the potential formation results in enhancement of the axial particle confinement time 100 times over the mirror confinement time without plugging, in reasonable agreement with Pastukhov formula. An empirical scaling on nonambipolar radial ion confinement time in the axisymmetrized field configuration is presented.

Cross-magnetic-field transport due to like-particle collisions is discussed for the parameter regime ${\lambda }_{\mathrm{D}}\gg r_{\mathrm{L}}$, where ${\lambda }_{\mathrm{D}}$ is the Debye length and $r_{\mathrm{L}}$ is the characteristic Larmor radius of the colliding particles. A new theory based on collisionally produced E×B drifts predicts a particle flux which exceeds the flux predicted previously, by the factor ${\left(\frac{{\lambda }_{\mathrm{D}}}{r_{\mathrm{L}}}\right)}^2\gg 1$.

It is found that ion cyclotron resonance frequency can create an ion-plugging plasma potential equal to several times $\frac{T_e}{e}\left(\simeq \frac{T_i}{e}\right)$ in the Phaedrus tandem mirror end cells or at the end of the central cell. A model based on a local balance of electron expulsion by the rf field ${\tilde{E}}_z$ and trapping by Coulomb scattering predicts the magnitude and scaling of the potential with density and rf antenna current. This model is in reasonable agreement with experimental observations. This ion-cyclotron resonance-frequency enhanced potential increases as the plasma density decreases and as the antenna current increases.

Scanning tunneling microscopy shows that warm-condensed Ag films consist of a gently rolling surface topography with compact boundary regions. In contrast, cold-condensed films retain structure on the nanometer scale after annealing to room temperature: These intercrystallite channels or trenches show a strong similarity in width (<1-3 nm), separation (5-15 nm), and possibly depth [3-(>4.5) nm] to the surface topographic models for surface-enhanced-Raman-scattering activated films. This suggests that postannealing does not imply the annihilation of channels, also termed "pores" or "cavities," postulated by some current models.

Precise measurements of the velocity of 5-MHz longitudinal sound in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been made over a broad range of temperatures (0.3 to 30 mK) and pressure (0.3 to 34 bars). The zero-temperature asymptotic velocity in the $B$-phase superfluid is measured and found to be the same as the hydrodynamic value in the normal Fermi liquid. The pressure dependence of $F_2^s$, the second symmetric Landau parameter for the Fermi liquid, is deduced.

The crystallography of In adsorbed at room temperature on cleaved GaAs (110) has been studied with reflection high-energy-electron diffraction. In adsorbs as three-dimensional prism-shaped islands that align in two orientations relative to the substrate. The average island size remains constant for coverages from 0.2 to ∼5 monolayers. At 5 monolayers, the approximate coverage at which the Fermi level has been found to pin, the islands are still physically separated. These results are evidence for a Debye-length relationship for Fermi-level pinning in this system.

The contribution to the low-temperature magnetic susceptibility of a small number of vacancies in bcc ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is analyzed with recent NMR data used to estimate the vacancy contribution. It is shown that the susceptibility anomaly at very high molar volumes near the melting curve can be attributed to the polaron effect of a very small concentration of vacancies.

The spectral properties of a $d$-dimensional bond-percolating network have been examined by real-space rescaling methods. Both the triangular and face-centered-cubic lattices have been studied with the $d$-dimensional Sierpinski gasket used to model the backbone. The vibrational density of states has been calculated as a function of $p-p_c$ and we find that two excitation regimes exist which are characterized by two separate dimensionalities. There is a low-frequency phonon regime and a higher-frequency fracton regime. The specific heat exhibits a smooth crossover from phonon to fracton behavior as a function of $p-p_c$.

We have utilized a novel technique to measure both the magnetization and magnetoresistance of a single crystal of ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$Cl${\mathrm{O}}_4$ in the regime where the magnetic field induces a series of metal-to-semimetal transitions. We find anisotropic magnetization with extremely sharp oscillatory structure similar to that expected for a quantized two-dimensional electron gas. However, the temperature and field dependences of the anomalies suggest a series of first-order phase transitions as opposed to the conventional de Haas-van Alphen effect. The entropy loss is comparable to the entropy of the electron gas.

I report on the first complete experimental characterization of elastic and inelastic two-electron scattering processes in a ferromagnet. By explicit measurement of the spin polarization of primary and scattered electrons the contributions of all four partial scattering rates are determined. The Stoner continuum in Fe at finite $q$ is observed for the first time.

X-ray diffraction studies to 73 GPa show that CsI becomes orthorhombic at about 56 GPa. Infrared absorption studies show the band gap dropping from 6.4 to 0.36 eV at 62 GPa. At 65 ±5 GPa, CsI becomes metallic and reflects in the red, which we attribute to the plasma edge being in the visible. The interatomic distances of the nearest like neighbors are reduced from the zeropressure value by 28% at metallization where CsI has a pseudo tenfold coordination.

A microscopic model is proposed which explains recent observations that acceptor shallow levels in crystalline silicon can be inactivated by atomic hydrogen. We are assuming that substitutionalboron-interstitial-hydrogen complex pairs are being formed which passivate the shallow acceptor action of the boron impurity. Rigorous self-consistent calculations show that the acceptor level is removed from the gap and the boron electrical activity is clearly neutralized.

Cyclotron-resonance experiments on conduction electrons in InSb are performed in crossed magnetic and electric fields with use of a metal-oxide-semiconductor structure. The data are successfully described on the basis of a three-level k·p band model. The electron behavior in crossed fields is interpreted as a spectacular example of an analogy between electrons in narrow-gap semiconductors and relativistic electrons in vacuum.

Electron standing waves formed in the vacuum gap between the probe and the sample of the tunneling microscope are observed. The sensitivity of the standing-wave positions and frequencies to the surface potential are demonstrated. Further effects possibly due to Bragg backscattering from the surface atomic planes of the sample are discussed.