Submonolayer ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on Grafoil at density $n$ just below the density of the registered phase, $n_c$, corresponds to a low-density solid with vacancy concentration $\frac{(n_c-n)}{n_c}$. Under suitable circumstances, these vacancies cause the solid to undergo a ferromagnetic transition.

We present a new formulation of lattice dynamics especially suitable for transition metals and their compounds. Calculations of the phonon dispersion in $4d$ bcc metals and alloys based on it reproduce all the observed anomalous structure and elucidate the physical origin of the anomalies.

A recent suggestion by Farrell and Chandrasekhar that a major part of the critical-temperature ($T_c$) reduction in $A15\mathrm{}$ superconductors, caused by radiation-induced defects, is a manifestation of a large gap anisotropy is examined for ${\mathrm{Nb}}_3$Sn. Electron-irradiation data show that the $T_c$ changes with damage are inconsistent with a large gap anisotropy. However, if one assumes that the initial changes in $T_c$ with fluence are indeed due to gap anisotropy, then it is shown that the anisotropy parameter $〈a^2〉$ for ${\mathrm{Nb}}_3$Sn is ≲ 0.03.

The positrons produced in fusion processes in matter stars will have predominantly a "right" helicity due to the nonconversation of parity in weak interactions. This helicity is transferred to bremsstahlung and forward in-flight annilation radiation, which will be right-circularly polarized. In antimatter stars, $\mathrm{CP}$ symmetry will make the equivalent radiation left-circularly polarized. The helicity of such radiation can be used to distinguish between astronomical objects composed of matter and antimatter.

A quantitative model for vibrational relaxation of impurity molecules in host crystals is presented, and applied to the vibrational relaxation of NH and ND in solid Ar. Realistic impurity-host interaction and impurity-cage geometry are employed. It is shown that impurity rotation is the dominant receiving mode in the relaxation, and only a small fraction of the energy released goes directly into phonon modes. The results explain the faster relaxation of NH compared with ND and the temperature independence of the measured decay rates.

We present theoretical calculations and experimental measurements of the phonon linewidth for Nb. The calculations employ the rigid muffin-tin approximation and a realistic band structure. The measurements were done at low temperature to minimize the contributions to the linewidth from phonon-phonon interactions. The calculations predict and experiments confirm strong electron-phonon coupling for the longitudinal phonon modes in the [110] direction.

Nonlinear cw NMR behavior, similar to that observed on ferromagnets at high rf powers, has been observed in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ using a superconducting quantum interference device (SQUID) magnetometer in fields of 31, 102, 180, and 308 Oe and at a pressure of 21 bar. It is observed that beyond some threshold value of the transverse $H_1$ field the $z$ component of magnetization anomalously decreases and is followed by a rapid increase back to the normal resonance curve as the frequency of the $H_1$ field is swept through resonance.

We show rigorously that for dilute classical systems with finite-range interactions the pair-correlation function has the form predicted by Ornstein and Zernike.

We have performed optical measurements on a hydrodynamic instability occurring in a dilute polymer solution characterized by a negative value of the thermal diffusion ratio and heated from above. We determine the threshold condition and the behavior of the convected mass flow above threshold. Qualitative evidence of critical slowing down is also reported together with a discussion on the convective-mode wavelength.

The temperature dependence of the $cos\varphi$ conductance in Sn-O-Sn Josephson tunnel junctions has been measured just below the critical temperature, $T_c$. From the resonant microwave response at the junction plasma frequency as the temperature is decreased from $T_c$ it is deduced that the amplitude of the $cos\varphi$ term first increases from near zero to positive values and only at $\frac{T}{T_c}\lesssim 0.96$ attains values of order-1.

A neutron diffraction study of the field-dependent magnetic ordering in TmSe is reported. The magnetic strucutre in zero field is antiferromagnetic fcc type I with $T_{\mathrm{N}}=3.2\mathrm{}$ K. The magnetic phase diagram may be understood as a successive domain reorientation and metamagnetic transitions for $T<\mathrm{}3\mathrm{}$ K with increasing field. We can explain this quantitatively using a simple classical spin Hamiltonian. The mixed-valent character manifests itself mainly in a reduced moment and in a markedly altered crystal field.

The energy gap in one-dimensional Fermi systems with weak attractive interaction is expressed in terms of the parameters of the Hamiltonian and the electron density. The models of Hubbard and phonon-mediated interactions are studied in detail. The result for the Hubbard model is compared with numerical calculations.

Inelastic-neutron-scattering studies show triple degeneracy of the ${\Gamma }_1-{\Gamma }_4$ exciton along [111] and double degeneracy along [100] with a band-structure-related softening of the longitudinal branch at $X$. The ${\Gamma }_1-{\Gamma }_4$ and ${\Gamma }_4-{\Gamma }_5$ transitions decrease with increasing pressure suggesting the occurrence of a pressure-induced soft-mode magnetic transition.

Results of ab initio self-consistent energy-band calculations on the full 18-atom/unit-cell ternary alloys $M{\mathrm{Rh}}_4{\mathrm{B}}_4$ ($M=\mathrm{Y},\mathrm{E}\mathrm{r}\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{H}\mathrm{o}$) are reported and used to discuss their superconducting and magnetic properties—including the observation of reentrant magnetism in the normal state at $T<\mathrm{}0.9\mathrm{}$ K in Er${\mathrm{Rh}}_4$${\mathrm{B}}_4$.

Oxygen adsorbed on porous Vycor glass, a heterogeneous substrate, displays properties of an amorphous antiferromagnet. However, no antiferromagnetic ordering transition is seen for submonolayer coverages in the temperature range studied (1.9-95 K) although these coverages have paramagnetic Curie temperatures as large as -50 K.

Ultrathin granular niobium nitride films have been found to behave like an array of zerodimensional superconducting grains coupled through grain boundaries by a Josephsontype interaction. The temperature dependence of the current at which a voltage first appears fits the Josephson-junction-like critical-current predictions remarkably well. The films exhibit a paraconductivity which extends to 24 K, more than twice the critical temperature, $T_{\mathrm{cG}}$, of the grains and varying as ${(T-T_{\mathrm{cG}})}^{-2\mathrm{}}$.

The existence of both empty and filled surface states derived from the rehybridization of dangling Sb bonds is demonstrated for the first time in GaSb. The empty states are nearly degenerate with those derived from dangling cation bonds and are located near the bottom of the conduction band. The filled states lie ∼0.8 eV below the valence-band edge. Similar sets of states were observed for Sb adsorbed on GaAs and InAs.

Proton-proton elastic scattering has been measured in the region $4.9<\mathrm{}\left|t\right|<12.1\mathrm{}$ ${\mathrm{GeV}}^2$ at a beam momentum of 201 GeV/c. If the form $\exp \mathrm{}\left(\mathrm{At}\right)\mathrm{}$ is fitted to the data, the exponent $A$ gradually changes from 1.5 to 0.9 ${\mathrm{GeV}}^{-2\mathrm{}}$ over our $t$ range. The data are consistent with the form $\exp (-6.6\mathrm{}{p}_{\perp })$. A comparison with intersecting storage ring results shows that in this kinematical region the slopes are about the same, but $\frac{d\sigma }{\mathrm{dt}}$ at fixed $t$ is still dropping with energy.

On the assumption that the new resonance $\Upsilon \mathrm{}\left(9.5\right)\mathrm{}$ is a vector meson, its leptonic- and hadronic-decay widths are calculated in analogy to those of $\psi \mathrm{}\left(3.1\right)\mathrm{}$. Then, using the Breit-Wigner formula, the production cross section in $e^{+}{e}^{-}$ annihilation is predicted. The tensor dominance of the Pomeron, together with the vector-dominance model, is invoked to estimate the photoproduction cross section.