It is found that the embedding of hypercolor in grand unification schemes requires an extended unified model of the form $G\otimes G\otimes G$ where $G\supseteq \mathrm{SU}\mathrm{}\left(3\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(2\right)\mathrm{}\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ is an ordinary grand unified simple group. For $G=\mathrm{SU}\mathrm{}\left(7\right)\mathrm{}$ properties of such a unified theory with naturally three ordinary families are explored.

Significant differences between the polarization, $P$, and analyzing power, $A$, have been measured in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(p, p^{\prime }){}_{}{}^{12}{}_{}{}^{}\mathrm{C}\left(1^{+} \mathrm{states}\right)$ at $E_p=150\mathrm{}$ MeV. It is shown that $P-A$ is different from zero primarily because of that part of the tensor exchange amplitude associated with the transferred quanta, $lsj=111\mathrm{}$, to the nucleus. This amplitude determines a combination of transition density matrix elements for the 15.11-MeV state that is largely undetermined from other experiments.

Resonant light diffraction by an atomic beam of sodium has been uncovered by careful measurements of the spatial dependence of the absorption. Recently developed modulation techniques made such measurements possible. Both on-resonance and off-resonance excitations as well as the influence of intense fields have been studied. The observed spatial behavior is in good agreement with a preliminary calculation based on the interference between the field scattered by the atoms and the excitation field.

The complete set of observables which describe elastic electron scattering from a xenon atom has been studied at energies between 30 and 360 eV. The polarization measurements presented here in conjunction with absolute measurements of the differential cross section yield the maximum possible information on the scattering process and allow complete evaluation of the complex scattering amplitudes. The results show that a correct overall description of the scattering process by theory is still missing.

A procedure is given for eliminating resonances and stochasticity in a nonaxisymmetric vacuum toroidal magnetic field. The results of this procedure are tested by the surface-of-section method. It is found that one can obtain magnetic fields with increased rotational transform and decreased island structure while retaining basically the same winding law.

The momentum distribution function, $n\left(\overrightarrow{\mathrm{p}}\right)$, is determined for liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at 1.00, 2.12, 2.27, and 4.27 K from new neutron inelastic-scattering measurements at large momentum transfers. An improved method for extracting the condensate fraction, $n_0$, from $n\left(\overrightarrow{\mathrm{p}}\right)$ is presented and used to obtain new values for $n_0$ at 1.00 and 2.12 K and a revised value at 1.1 K.

It is postulated that a quantized-vortex tangle obeys classical vortex dynamics, and that internal line-line crossings can result in topology-changing reconnections. Implementation of these rules leads to a quantitatively successful description of homogeneous superfluid turbulence.

A simple, phenomenological theory is presented for the scaling function of a phase-separating binary system. The model describes a gas of spherical droplets of the minority phase, surrounded by depletion zones, and involves a simple approximation for the two-point distribution function. Reasonable agreement is found with the structure factors for the kinetic Ising model, binary alloys, and binary liquids.

The energy dispersion curve $E\left(k_{\parallel }\right)$ has been measured for an unoccupied $\mathrm{sp}$-like surface state on Pd(111) with $k$-resolved inverse photoemission spectroscopy. At the zone center, $\overline{\Gamma }$, the energy of the surface state is 1.7 eV above the Fermi level, in good agreement with theoretical pseudopotential calculations of Louie, although the energy dispersion away from $\overline{\Gamma }$ is appreciably more rapid than in theory. The work opens up the possibility of probing unoccupied surface states in the same way that angle-resolved photoemission probes occupied surface states.

A classical model of charge-density wave motion at large velocities is used to describe the nonlinear response of the charge-density wave in fields well above the threshold. The charge-density wave is regarded as a charged, deformable medium and its interaction with pinning centers is treated in perturbation theory. The results fit the available high-field data on ${\mathrm{NbSe}}_3$ well. The observed interference effects between a large dc field and an ac field are also explained.

The exact solution is presented for the "susceptibility," $\chi$ (the number of sites covered by the maximally extended eigenfunction), for the zero-energy solutions of a hopping model on a randomly dilute Cayley tree. If $p$ is the concentration, then $\chi \sim {(p^{*}-p)}^{-1\mathrm{}}$ with $p^{*}\sim p_c{e}^{\frac{1}{{\xi }_1}}$, where $p_c$ is the critical percolation concentration and ${\xi }_1$ the one-dimensional localization length. This result is argued to hold for the dilute quantum Heisenberg antiferromagnet at zero temperature.

A simple inequality relating the root mean square deviations of position and osmotic velocity for a diffusion process is presented and, in the framework of Nelson's stochastic mechanics, is related to the Heisenberg position-momentum uncertainty relations.

A new stochastic method for the numerical study of lattice fermions is presented. Its efficiency is demonstrated on a field-theoretic model in four dimensions with coupled boson and fermion degrees of freedom. The exact fermion propagator is calculated and agrees very accurately with the numerical results of the stochastic procedure on finite lattices of ${10}^4$ and $8^3$×16 sites, respectively. The contribution of fermionic vacuum polarization to mass renormalization is evaluated with precision. The method is directly applicable to quantum chromodynamics.

Differential cross sections for ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\gamma , d)p$ have been measured at ${\theta }_p(\mathrm{c}.\mathrm{m}.\mathrm{})\sim 60° \mathrm{and} \sim 90°$ for photon energies between 150 and 350 MeV. The data have an absolute normalization uncertainty of 6% and provide absolute differential cross sections suitable for a test of time-reversal invariance when used in conjunction with comparable data on the inverse reaction.

Microwave-assisted resonant collisional energy transfer process $\mathrm{Na}\mathrm{}\left(\mathrm{ns}\right)+\mathrm{Na}\mathrm{}\left(\mathrm{ns}\right)+h\nu \to \mathrm{Na}\mathrm{}\left(\mathrm{np}\right)+\mathrm{Na}\mathrm{}\left(\right(n-1\mathrm{}\left)p\right)$ is observed between two colliding $\mathrm{Na}\mathrm{}\left(\mathrm{ns}\right)\mathrm{}$ atoms. The collisional resonance occurs when the microwave frequency $\nu$ equals the collisional energy defect $\frac{\Delta W}{h}$. The observed cross sections are very large (∼${10}^8$ ${\mathrm{\AA }}^2$) and require very low microwave power, ∼10 W/${\mathrm{cm}}^2$. These observations are in good agreement with an intuitive two-photon absorption model for these collisions.

In recent experiments on doubly charged microclusters of Xe, no ${{\mathrm{Xe}}_n}^{++}$ clusters were observed for $n$ less than 53 atoms. Computer simulations of microclusters have been carried out in which the Xe atoms interact via Lennard-Jones pair potentials and a point polarizability-dipole electrostatic model. From these simulations, it is inferred that ${\mathrm{Xe}}_{51}^{++}$ clusters have lifetimes ∼ 100 ps while ${\mathrm{Xe}}_{55}^{++}$ clusters have lifetimes ∼ 10 μs in agreement with the experimental result that 55-atom clusters are much more stable.

High-temporal-resolution measurements of electron velocity distributions, $f\left(\overrightarrow{\mathrm{v}}\right)$, have been obtained for many transits through the Earth's bow shock. Within all oblique shocks studied, the maximum of $f\left(\overrightarrow{\mathrm{v}}\right)$ is offset with respect to the ion rest frame parallel to $\overrightarrow{\mathrm{B}}$ and directed downstream. These observations indicate that electron thermalization within the bow shock consists first of a downstream acceleration parallel to $\overrightarrow{\mathrm{B}}$ by the macroscopic shock electric field, followed by beam-driven plasma instabilities.

A theoretical explanation is presented of some observations from recent C${\mathrm{O}}_2$-laser experiments by introducing a novel mechanism for harmonic light emission. The theoretical model provides new insight into the properties of large-amplitude waves in the extremely inhomogeneous environment caused by strong profile modification of the critical-density plasma.

Mode-conversion processes play an important role in the radio-frequency heating of tokamak plasmas. This paper reports the first direct observation of externally driven ion Bernstein waves in a tokamak plasma. The waves are only observed in mixed-species plasmas near the ion-ion hybrid resonance layer and are interpreted as being the result of linear mode conversion of the fast magnetosonic wave.

Experimental observation of quasidiffusive propagation of a nonequilibrium phonon distribution in ${\mathrm{Al}}_2$${\mathrm{O}}_3$: V is reported. Among the features of this propagation mode is the fact that the arrival time of the phonon pulse front varies almost linearly with propagation distance as expected for ballistic transport, even though the time-of-flight spectrum has an extended tail characteristic of diffusive transport.