The conversion of a proton inside a nucleus into a positron, energy-momentum being shed into the final state, is consdered. For ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ it is found that the lifetime of a proton due to this mechanism is of the same order (probably ∼ 3 times smaller) as that due to the conventional two-quark fusion. The experimental signature is different, a positron track against a star of nuclear fragments, with eventual pions.

It is shown how present measurements of ${{sin}^2\theta }_{\mathrm{W}}$ are hampered by contributions of higher-twist operators, which are even more important than recently calculated electro-weak radiative corrections. The resulting limit of accuracy for measurements of ${{sin}^2\theta }_{\mathrm{W}}$ is estimated to be of the order of 5% at presently available energies.

The spectra of levels in the hypernuclei ${}_{\Lambda }{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{\Lambda }{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{\Lambda }{}^{18}{}_{}{}^{}\mathrm{O}$, excited by 800-MeV/c kaons in the ($K^{-}$,${\pi }^{-}$) reaction, have been observed at the Brookhaven alternating-gradient synchrotron. Data were recorded for scattering angles from 0° to 25°, corresponding to momentum transfers from 50 to 330 MeV/c. The levels are interpreted in terms of a $\Lambda$ hyperon coupled to a strangeness-zero nuclear core. The results provide insights into the properties of the $\Lambda$-nucleon and $\Lambda$-nucleus interactions.

A comprehensive shell model for light hypernuclei has been developed and applied to ${}_{\Lambda }{}^{13}{}_{}{}^{}\mathrm{C}$. Absolutely normalized distorted-wave calculations yield angular distributions in excellent agreement with experiment, allowing spin assignments to be made. Coherences arising from the distinguishability of the $\Lambda$ are predicted theoretically and observed in the data. The overall comparison with experiment places constraints on residual interaction matrix elements.

Inclusive energy spectra of the H and He isotopes emitted in the reactions of 860-MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ with Ni, Ag, and Ta provide evidence that a statistically dominated projectile fragmentation mechanism entirely analogous to that observed at relativistic energies occurs when the projectile velocity becomes comparable to the Fermi velocity in the projectile. Additional particle emission not characteristic of either a fragmentation or compound nucleus source is observed.

The asymmetries $\Sigma ({\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=\frac{\pi }{2})$ for the reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}(\gamma ,n)p$ have been measured with use of a monochromatic and linearly polarized $\gamma$-ray beam, obtained by backward Compton scattering of laser light against high-energy electrons. Contributions from meson exchange currents must be included in the theoretical calculations to reproduce our data.

The existence of magic numbers for atomic microclusters has been found experimentally for the first time. The magic numbers $n^{*}$ manifest themselves in the mass spectra of free xenon clusters, nucleated in the gas phase. The observed numbers $n^{*}=13, 55, \mathrm{and} 147$ coincide with the numbers of spheres required for complete-shell icosahedra. The appearance of further magic numbers (19, 25, 71, and 87) is only partially explained by previous calculations.

The vacuum-ultraviolet absorption spectra of isolated Ba, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Ba}}^{++}$ have been measured. In Ba and ${\mathrm{Ba}}^{+}$ most of the $4d$ absorption oscillator strength is in the continuum, but in ${\mathrm{Ba}}^{++}$ several very strong discrete transitions are observed. Such behavior has never before been observed in the $4d$ photoabsorption of vapors, solids, or compounds. An interpretation is given in terms of the partial collapse of the $\mathrm{nf}$ bound states in ${\mathrm{Ba}}^{++}$.

New data are analyzed for the hard-sphere fluid at densities $\rho {\sigma }^3=0.95-1.08\mathrm{}$ in the metastable range. In this region the diffusion coeffiecient behaves as in laboratory fluids, following a Doolittle equation with normal parameters rather than a Batchinski-Hildebrand equation. The diffusing, internally equilibrated, metastable fluid can be arrested at different densities by sudden "quenching" to obtain the glassy state. A new high-density limit for random close packing, 3% greater than that of Bernal packing, is identified.

Subharmonic sequences in the shallow-water surface waves generated in a resonator with one-dimensional properties are shown to exhibit departures from period doubling for long-period subharmonics.

The symmetric implosion of pellet shells will require sideways thermal-transport smoothing of any laser intensity nonuniformities. A scaling law shows a surprisingly strong laser wavelength dependence for this smoothing mechanism; it places a large premium on the use of longer-wavelength near-infrared lasers. This smoothing requirement conflicts with the advantages of shorter laser wavelengths for controlling deleterious plasma instabilities.

Coherent and incoherent elastic scattering of He was observed from Cu(001) and adsorbed layers of CO and Xe. It is shown that specular and off-specular elastic scattering can yield insight into adsorption mechanisms at low coverages. The variation of incoherent elastic scattering with coverage shows different behavior for CO (random) and Xe (island) adsorption. A maximum appears in the incoherent elastic for CO as predicted theoretically for site adsorption.

A model for the equation of state of condensed matter in the "intermediate" pressure region (0.5-10 TPa) is proposed. The dominant pressure and thermal ionization effects are simulated through a modification of Saha's ionization theory. The pseudopotential method which includes core ionization effects is used to obtain the cold and lattice thermal contributions. The model is applied to Al and Mo.

The dominance of vacancy migration in grain boundary self-diffusion has been established by molecular-dynamics simulation of a bcc iron $\Sigma =5\mathrm{}$ tilt boundary. The data yielded a reasonable value of the activation energy for migration and showed that the jump processes are highly structure dependent. The use of a temperature-dependent transition-probability matrix to describe the diffusion of the vacancies in the grain boundary is suggested. Formation of one type of boundary interstitial was observed, and the interstitial was found to be immobile during its lifetime.

Microscopic observations of blackbody emission from high-power cw-laser-irradiated silicon films on silica reveal: (I) Radiation of 1.06 μm produces a thermal runaway phenomenon in polycrystalline Si that terminates with the melt. (II) The laser-induced melt is inhomogeneous at the melting temperature. Lamellae of solid Si, which has a high emissivity, coexist with the low-emissivity melt. These lamellae transmit near-band-gap radiation, which is blocked by the molten phase, and they appear and disappear dynamically.

The flow birefringence in the binary liquid mixture 2, 6-lutidine and water is measured near its critical point. The effect was produced by periodic variation of the shear, $S=\frac{\partial v_x}{\partial y}$, at an angular frequency, ${\omega }_0$, of 7.5 ${\sec }^{-1\mathrm{}}$, whereas typical average values of $S$ were 10 ${\sec }^{-1\mathrm{}}$. Measurements of the temperature dependence of the birefringence phase shift, $\delta$, are in fair agreement with a steady-state theory of Onuki and Kawasaki.

Methods of extending Monte Carlo renormalization-group calculations to include transformations in momentum space are proposed to investigate systems for which block spins are difficult or impossible to construct—such systems include fluids, for which particles are not confined to a lattice, three-dimensional fcc antiferromagnets, and lattice gauge models in four dimensions. The feasibility of these transformations is demonstrated by calculations in two and three dimensions.

Dilute $\mathrm{Pb}\mathrm{Mn}$ alloys have been prepared in a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$/${}_{}{}^4{}_{}{}^{}\mathrm{He}$-dilution cryostat by low-temperature implantation of ${\mathrm{Mn}}^{+}$ ions into annealed Pb films forming the counter electrode of Mg-MgO-Pb tunnel junctions. The tunnel conductance as a function of the Mn concentration was measured at 200 mK. Two pronounced impurity bands are found within the superconducting gap at $\frac{\omega }{\Delta }=0.23\mathrm{} \mathrm{and} 0.79$, respectively. The results can be described by existing theories if scattering of different partial waves is taken into account.

Inelastic electron scattering from the vibrations of ${\mathrm{N}}_2$, CO, ${\mathrm{O}}_2$, and ${\mathrm{H}}_2$ adsorbed in monolayers and multiple layers on Ag films at $T\sim 20$ K show energy-dependent cross sections characteristic of resonance scattering via temporary negative-ion states. The resonances for these adsorbed phases generally occur at lower energies than in the gas phase and have spectral features which indicate negative-ion lifetimes of less than ${10}^{-14\mathrm{}}$ sec.

Rotational state distributions for NO scattered from Ag(111) have been measured over the incident kinetic energy range of 0.1 to 1.7 eV with use of rotationally cold molecular beam and laser-induced-fluorescence detection. The measured distributions divide into two parts: a low rotational state portion ($J\lesssim 20.5$) which is described by a Boltzmann distribution and a high-$J$ portion which shows a broad structure tentatively interpreted as resulting from a rotational rainbow.