We report the first measurements of ${\sigma }_{\mathrm{AB}}$, the surface energy associated with the interface between the $A$ and $B$ phases of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ as they coexist at $T_{\mathrm{AB}}$. At melting pressure we find ${\sigma }_{\mathrm{AB}}=6\mathrm{}\times {10}^{-6\mathrm{}}$ erg ${\mathrm{cm}}^{-2\mathrm{}}$ in no magnetic field ($\frac{T_{\mathrm{AB}}}{T_C}=0.79\mathrm{}$) rising to ${\sigma }_{\mathrm{AB}}=1.6\mathrm{}\times {10}^{-5\mathrm{}}$ erg ${\mathrm{cm}}^{-2\mathrm{}}$ in a magnetic field of 4 kOe ($\frac{T_{\mathrm{AB}}}{T_C}=0.5\mathrm{}$). Theoretical calculations that we present give an estimate about 50% larger.

We have experimentally investigated the phase diagram of antiferromagnetic GdAl${\mathrm{O}}_3$ near its spin-flop multicritical point ($T_M, H_M$) in the three-dimensional space spanned by the uniform fields $H_{\parallel }$ and $H_{\perp }$ and the temperature $T$. In the $H_{\parallel }-T$ plane, ($T_M, H_M$) appears as a bicritical point, but as a tetracritical point in the $H_{\perp }-T$ plane. The approach of all six boundaries to ($T_M, H_M$) is described by a single exponent $\psi =1.17\mathrm{}\pm 0.02$. This implies crossover exponents $\varphi =1.17\mathrm{}\pm 0.02$ and ${\varphi }_v=\pm 0.03$ in excellent agreement with renormalization group theory.

Based on a Green's function formalism, a high-temperature series expansion technique applicable to systems with complicated energy levels is developed. The application of the method to magnetic systems with crystal fields is discussed. As an example, we have obtained the high-temperature series expansion of the susceptibility for a spin-1 ferromagnet with anisotropic exchange interactions and with a uniaxial crystal-field potential.

A superconducting microbridge has been used as a probe to detect quasiparticle diffusion currents and "heating", produced by a phase-slip center (PSC) in a second microbridge. The critical current of the detector is modulated by the voltage $V_{\mathrm{PSC}}$ across the PSC. This modulation provides a measure of quasiparticle current $I_Q$ thru the PSC and gives $I_Q=\frac{V_{\mathrm{PSC}}}{R_D}$ for low voltages, $R_D$ being the high-current differential resistance of the PSC.

In Sn-$I$-Sn-$I$-Pb tunneling structures the energy gap ${\Delta }_{\mathrm{Sn}}$ of Sn is reduced by quasiparticle injection via single-particle tunneling between the Sn films. ${\Delta }_{\mathrm{Sn}}$ as function of the quasiparticle density is probed by the Pb contact and found in agreement with the theory of Owen and Scalapino. An instability of the energy gap of Sn is observed at the critical gap reduction ratio predicted by this theory for a first-order phase transition.

Recent observations of radiation-stimulated superconductivity above the thermodynamic transition temperature reveal the existence of a first-order phase transition between a normal and a superconducting state. In this Letter, a Langevin equation for the order parameter is derived, which is appropriate for the nonequilibrium steady-state process under consideration, and which explains the observed discontinuous phase transition.

For both $T>\mathrm{}{T}_c$ and $T<\mathrm{}{T}_c$, we report exact expressions for the $n$-spin correlation function of the two-dimensional Ising model suitable for studying large separations between spins. In particular, the scaling limit of these correlation functions can be shown to exist and yields $n$-point Schwinger functions of some relativistic quantum field theories.

We present numerical data and scaling theories for the critical behavior of random resistor networks near the percolation threshold. We determine the critical exponents of a suitably defined resistance correlation function by a Padé analysis of low-concentration expansions as a function of dimensionality. We verify that $d=6\mathrm{}$ is the critical dimensionality for the onset of mean-field behavior. We use the coherent-potential approximation to construct a mean-field scaling function for the critical region.

We have measured $\frac{(e^{+}p\to e^{+}\gamma X)}{(e^{-}p\to e^{-}\gamma X)}=1.080\mathrm{}\pm 0.036$ in the scaling region, despite our finding $e^{+}$ and $e^{-}$ total inelastic scattering to be the same to the $\frac{1}{3}\%$ level. The magnitude and sign of the difference signal are consistent with the parton model, from which we extract a mean sum of cubes of parton charges in the proton, $〈\Sigma i^{}{Q_i}^3〉=0.89\mathrm{}\pm 0.34$. Statistics are insufficient to distinguish between fractional ($〈\Sigma i^{}{Q_i}^3〉=0.56\mathrm{}$) and integral charge ($〈\Sigma i^{}{Q_i}^3〉=1, or 0.78$ for colored quarks).

The isobar doorway model of Kisslinger and Wang is extended to include the pion single-charge-exchange channel in addition to the elastic one. By use of this model, the integrated charge-exchange cross section to the isospin analog state is calculated and compared with the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}({\pi }^{+}, {\pi }^0){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ measurements. Good agreement with experiment is achieved. The connection between elastic scattering and charge exchange is discussed.

The $B(E3; 0^{+}\to 3^{-})$ and quadrupole moment, $Q_{3^{-}}$, of the first excited state of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been measured by the reorientation effect in Coulomb excitation, giving $B(E3; 0^{+}\to 3^{-})=0.665\mathrm{}\pm 0.035e^2$ ${\mathrm{b}}^3$ and $Q_{3^{-}}=-0.42\mathrm{}\pm 0.32e\mathrm{b}$. This value for $Q_{3^{-}}$ is much smaller in magnitude than those obtained by Barnett et al., and is consistent with most theoretical predictions.

Multiplicities as a function of $\gamma$-ray energy have been measured for continuum $\gamma$ray spectra produced in argon reactions at several bombarding energies on various targets. With the heavier systems there exist regions in the spectra that have particularly high multiplicites which can be associated with the yrast (collective) cascade. The results suggest that the angular momentum in the $\gamma$-ray cascade is limited by $\alpha$ emission for $Z\lesssim 60$ and by fission for $Z\gtrsim 60$.

Very-high-energy-resolution photoneutron time-of-flight measurements in combination with high-resolution measurements of photoneutron polarizations from the reaction ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\gamma , n_0\uparrow ){}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ have enabled us to identify seven probable $1^{+}$ resonances at excitations between 8.2 and 9.5 MeV. These resonances have a total strength $B{\mathrm{}\left(M1\mathrm{}\right)\mathrm{}}_{\uparrow }\gtrsim (8.5\mathrm{}\pm 0.5){{\mu }_0}^2$. This strength plus that previously reported at 7 and at 8 MeV can account for the $M1\mathrm{}$ sum rule in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.

The shapes of the observed angular distributions for the reactions ${}_{}{}^{28,30}{}_{}{}^{}\mathrm{Si}$(${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$)${}_{}{}^{31,33}{}_{}{}^{}\mathrm{P}$ to ${\frac{3}{2}}^{+}$ and ${\frac{5}{2}}^{+}$ states differ strongly. A consistent description of this $j$ dependence and of the ground-state ${\mathrm{½}}^{+}$ angular distributions is given by distorted-wave Born-approximation calculations which assume triton cluster transfer and include spin-orbit potentials in both entrance and exit channels. We find from coupled-channel Born-approximation calculations that inelastic excitation of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ does not affect the shapes significantly.

Shape resonances cannot explain the strong vibrational excitation observed in the impact of electrons on polar molecules at threshold, because an important $s$-wave component in the wave function inhibits trapping. We explain the main features observed in HCl by invoking the concept of a virtual state to account for an enhancement of the wave function of a slow departing electron.

The hyperfine structure of the vibration-rotation transitions of H${\mathrm{D}}^{+}$ is calculated to an accuracy of ± 0.5 MHz. The theoretical spectra confirm the experimental observation that only lines near the center of each transition are intense enough to be detected by the present experiments. The complete spectrum is some 1500 MHz wide and contains structure which has not yet been resolved.

Magnetohydrodynamic instabilities limit the material that can be contained in a tokamak. The nature of the dangerous kink and ballooning modes is investigated for a typical configuration. In high-beta systems the most dangerous instabilities are ballooning modes that form large convective cells concentrated in regions of unfavorable magnetic field-line curvature.

Large-scale magnetohydrodynamic instabilities of flux-conserving tokamak equilibria are studied computationally. Stable equilibria are found with up to 5% average $\beta$. As $\beta$ is increased, the observed instabilities take on a strong ballooning character, concentrating near the outer edge of the torus with a mix of poloidal harmonics.

Pressure and temperature dependences of the Brillouin spectra for KCN are shown for pressures of 0 to 7 kbar and temperatures of 178 to 295 K. It is shown that multiphonon interactions are the dominant anharmonic effect, and it is suggested that the phase transition at 168 K comes from a ferroelastic ordering of C${\mathrm{N}}^{-}$ dipoles strongly coupled anharmonically to the phonons.

We demonstrate that the reflection of electrons from the image potential barrier outside the surface of a metal crystal induces a surface-resonance fine structure in the low-energy electron diffraction intensity profiles just below the energy of emergence of a new beam. The resonance levels are arranged in a Rydberg series with the constant $\frac{1}{16}$ Ry. The beam emergence from aluminum (001) near 18 eV is calculated and comparison with measured resonances is sought.