The analyzing power for proton-proton bremsstrahlung has been measured at TRIUMF with 280-MeV polarized protons. All three outgoing particles were detected in coincidence. After appropriate cuts were applied, over 160 000 $\mathrm{pp}\gamma$ events remained, an order of magnitude more than in previous $\mathrm{pp}\gamma$ experiments. The analyzing-power measurements are in good agreement with calculations based on modern potential models of the $\mathrm{NN}$ interaction, but disagree with the predictions of the soft-photon approximation.

The $\alpha -d$ momentum distribution in the ground state of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ has been measured in parallel kinematics with the reaction ${}_{}{}^6{}_{}{}^{}\mathrm{Li}{\mathrm{}(e,e\text{'}d)\mathrm{}}^4\mathrm{He}$ in the momentum range $0<\mathrm{}{p}_m<270\mathrm{}$ MeV/c. The reaction can be described by a direct coupling of the virtual photon to a deuteron in ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. The results agree well with the predictions of a three-body $\alpha \mathrm{NN}$ model of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$.

Spin-spin effects in neutron-nucleus interactions have been studied with a polarized ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ target and polarized neutrons of energies 5 to 17 MeV. Because of nuclear Ramsauer interference, real and imaginary spin-spin terms in the optical potential give rise to energy dependences of spin-spin effects which are out of phase. We find a central real potential $V_{\mathrm{ss}}=750\mathrm{}\pm 440$ keV, consistent with folding-model calculations, and a central volume imaginary potential $W_{\mathrm{ss}}=-780\mathrm{}\pm 320$ keV, related to compound-nuclear absorption effects.

The (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$,${}_{}{}^6{}_{}{}^{}\mathrm{He}$) reaction was studied on targets of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ at $E_{\mathrm{Li}}=210\mathrm{}$ MeV. A striking proportionality between cross sections for Gamow-Teller transitions and the corresponding $\beta$-decay strengths is observed. This should serve as a calibration of the reaction for use in studies of spin-transfer strength in nuclei. A variety of tests suggests that the reaction proceeds predominantly by a one-step mechanism.

A new method of microwave oscillator phase locking, exploiting the extended nature of the gyroklystron configuration, is accomplished by modulation of the electron beam before it reaches the cavity oscillator. The amount of power required to give phase locking in a gyrotron is decreased by more than an order of magnitude from that predicted by Adler's theory. In addition, oscillator priming is observed at drive powers far below all other systems tested to date. These new methods provide the coherence required of rf sources for linear accelerators and may enhance gyrotron performance for fusion heating.

The recent prediction of Liewer, Gould, and Bellan that a moving plasma-vacuum boundary significantly lowers the effectiveness of ac helicity injection is generalized by resolution of the apparent discrepancy between the helicity-conservation equations of Jensen and Chu and of Moffatt. It is shown that, if there are axisymmetric circular flux surfaces and a moving vacuum-plasma boundary, then the helicity injected by oscillating fields (if net injection occurs) is simply consumed by an increase in helicity dissipation due to the same oscillating fields.

We report on a series of capillary-flow experiments with spin-polarized hydrogen in which we observe a strong enhancement (> 10×) of the flow rate in comparison to ordinary Knudsen flow. This is related to a vanishing sticking probability $s$ for $T\to 0$ K as predicted by theory. With ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ surfaces we find that $s=0.33T$ for $145 \mathrm{mK}<T<\mathrm{}526\mathrm{} \mathrm{mK}$. Within experimental error $s$ did not change upon the addition of up to 50% ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at 150 mK. Results for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$/${}_{}{}^4{}_{}{}^{}\mathrm{He}$ surfaces were obtained for $73 \mathrm{mK}<T<\mathrm{}174\mathrm{} \mathrm{mK}$ and are also described by $s=0.33T$.

The intensity of the Raman light scattered from localized vibrational modes in a disordered material is expressed as a function of frequency shift and fractal and spectral dimensions. This expression which is obtained interprets the low-frequency Raman scattering from a silica gel and clearly shows the fractal structure of this material.

Contrary to the current interpretation of inelastic-neutron-scattering data on $\alpha$-AgI, molecular-dynamics calculations show that inelastic neutron scattering is dominated by coherent scattering from ${\mathrm{Ag}}^{+}$ ions. The calculations agree with the available data. ${\mathrm{Ag}}^{+}$ ions diffuse by jumps between tetrahedral sites, the consequences being in complete accord with the Chudley-Elliot model only if the full geometrical complexity of these sites is included. Phonon modes due to ${\mathrm{I}}^{-}$ motions are predicted for certain wave vectors.

Diffraction of x rays from a crystal during total external reflection imposes structure on the x-ray wave field in three dimensions. Standing-wave interference modulates the x-ray intensity parallel to the surface, while boundary effects damp the intensity with distance normal to the surface both within the crystal and in the region above the surface. Experiments on carefully prepared Ge single crystals show that the x-ray wave field can be manipulated to provide model-independent information on the structure of surfaces.

Forces acting between tunnel tip and sample during scanning tunneling microscopy were explored experimentally. Force gradients were detected as resonance shifts of cantilever beams used as sample stage. Beam deflections caused by force variations were also recorded. We present data for tungsten tips and polycrystalline silver surfaces prepared under UHV conditions. Large positive force gradients were found for the range of tunnel distances investigated. Force maps show pronounced features correlating directly with topographic images.

"Thermodynamic slowing down" effects on interdiffusion are demonstrated in binary mixtures of normal and deuterated polystyrene. The interdiffusion coefficient is shown to undergo a minimum in the vicinity of a critical blend composition ${\Phi }_c$. This effect increases with decreasing temperature.

Effective Hamiltonians for interfaces which arise, e.g., in the theory of wetting are studied by a nonlinear functional renormalization group exact in linear order and apparantly accurate for all spatial dimensionalities, $d$. Two nontrivial fixed points are found for $d<\mathrm{}3\mathrm{}$ which describe the critical manifold and the completely delocalized phase, respectively. As $d$ varies, these do not bifurcate from the Gaussian fixed point at $d_u=3\mathrm{}$ but rather mutually annihilate leaving behind a line of unusual "drifting" fixed points. Correspondingly the critical exponents exhibit singular behavior as $d\to 3-$.

The dynamics of the transformation out of a nonequilibrium metastable phase is discussed within a mean-field theory at temperatures below the transition temperature $T_c$. We show that fluctuations are important and lead to an unusual time dependence of the order parameter, in particular a sharp delay time for the onset of the stable phase. This model is applied to the dynamics of the paraelectric to ferroelectric transition in BaTi${\mathrm{O}}_3$ where the mediating forces arise from long-range strain fields.

Radiative temperatures and electrical conductivities were measured for fluid nitrogen compressed dynamically to pressures of 18-90 GPa (180-900 kbar), temperatures of 4000-14 000 K, and densities of 2-3 g/${\mathrm{cm}}^3$. The data show a continuous phase transition above 30 GPa shock pressure and confirm that ${\left(\frac{\partial P}{\partial T}\right)}_v<0\mathrm{}$, as indicated previously by Hugoniot equation-of-state experiments. The first observation of shock-induced cooling is also reported. The data are interpreted in terms of molecular dissociation and the concentration of dissociated molecules is calculated as a function of density and temperature.

It is experimentally demonstrated that a circularly polarized laser beam normally incident on a homeotropically aligned nematic film can induce a collective precession of the molecules in the film if the laser intensity is above the threshold for the Fréedericksz transition. The effect is shown to result from a transfer of angular momentum from the laser beam to the medium.

The phase diagram of silver iodide is simulated by the method of constant-stress molecular dynamics with use of the Parrinello-Rahman Langrangean. The $\beta$, $\alpha$, rocksalt, and liquid phases are reproduced and the boundaries are similar to those observed for real AgI. The supercooled $\alpha$ phase and the equilibrium rocksalt phase both have diffuse fast-ion transitions and the latter cuts the rocksalt-$\alpha$ boundary causing it to cusp into an apparent triple point with an order-disorder transition in the $\alpha$ phase. This is characterized by a heat-capacity anomaly and a rise in the cation diffusion coefficient.

Dynamic coarsening of crystal surfaces by formation of macrosteps is explained by an improved model for impurity absorption. It is related to interface propagation in random media. Some unusual recursive equations are encountered. The model is analyzed by various methods and exhibits some universal features. We find coarsening to proceed logarithmically with time in agreement with experiments.

We have analyzed the metastable defects in undoped semi-insulating GaAs from a new perspective, that of the electronic Raman scattering of holes generated on the compensated, residual shallow acceptors by cw neodymium-doped yttrium aluminum garnet laser radiation. The scattering results, when correlated with the several photoquenching phenomena, provide information on (i) the charge state of $\mathrm{EL}2\mathrm{}$ defects before they undergo the transition from a normal to a metastable state, and (ii) the relationship between ${\mathrm{As}}_{\mathrm{Ga}}$ compensating centers and metastable $\mathrm{EL}2\mathrm{}$ defects.

We report the first femtosecond spectroscopic investigation of ultrafast electronic processes in $a$-Si:H. By tuning the probe wavelength in a wide range around the optical gap, we are able to follow the time evolution of carrier trapping in band-tail states. At moderate injected carrier density, the band-tail states are populated by multiple trapping. As more carriers are injected, the shallow band-tail states saturate and deeper band-tail states capture carriers by direct trapping, which is a faster process (1-2 ps) than multiple trapping (10 ps).