Observations are presented that are consistent with the presence of helical textures in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ close to the transition temperature. The discovery of anisotropy in the heat flow is also reported.

We show that a suitable electron paramagnetic resonance experiment can discriminate sufficiently against the predominantly harmonic fluctuations characterizing a system undergoing a displacive phase transition, that a cluster-induced order-disorder component of the local behavior is exposed. We find evidence that, at $T_c$, the oxygen octahedra in SrTi${\mathrm{O}}_3$ oscillate about quasiequilibrium positions displaced by, typically, ±0.22° from the high-symmetry site. This result provides quantitative understanding of the incomplete softening of the phonon mode.

We show the existence of localized low-energy excitations of configurational nature in a one-dimensional model of a disordered solid. The corresponding extra specific heat is computed and its relation to glasses and superionic conductors is discussed.

The anisotropic interaction between the crystal lattice and the flux-line lattice results in a misalignment between the applied magnetic field and the fluxoids in a type-II superconductor. Small-angle neutron diffraction has been used to provide the first direct observations of this phenomenon. It is shown that the misalignment angle in the intermediate mixed state is related to the relative anisotropy in the lower critical field $H_{c1\mathrm{}}$, and this relationship is tested for a spherical sample of pure niobium.

Liquid and solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been cooled by adiabatic compression to the solid ordering temperature in fields of 2.0 and 2.8 T. Chart traces of pressure versus time show a new feature which suggests a first-order transition near the $A_1-A_2$ superfluid transitions.

The surface extended x-ray-absorption fine structure (EXAFS) of a single crystal has been measured for the first time. By comparison with parameters obtained from bulk aluminum EXAFS, a decrease of the interatomic distance ($\Delta \mathcal{r}=0.15\mathrm{}\pm 0.05$ Å) at the Al(111) surface has been found. No relaxation is found of the Al-Al separation on the (100) face.

In a neutron-diffraction study of insulating ${\mathrm{Eu}}_x{\mathrm{Sr}}_{1-x}\mathrm{S}$ with $x=0.40, 0.50, 0.52, \mathrm{and} 0.54$, the critical concentration for the spin-glass-to-ferromagnetism transition is determined to be as high as $x_c=0.51\mathrm{}$. For $x$ just above $x_c$, magnetic microdomains coexist with longrange ferromagnetic order, decoupled from one another by competing antiferromagnetic bonds. For the first time the breakdown of ferromagnetic order into microdomains is directly observed by decreasing the temperature, and it is interpreted as a ferromagnetism-to-spin-glass transition.

Time-resolved measurements of optically induced changes in the near-band-gap transmission spectrum of GaAs at 80°K, following excitation with an ultrashort laser pulse, provide a means of directly monitoring the hot-carrier distribution as it cools to the lattice temperature with a time constant of 4 psec. Exciton screening and band-gap renormalization are observed to occur in less than 0.5 psec.

A self-consistent cellular multiple-scattering technique is used to calculate the density of states of uranium telluride. The $5f$ band is found to be highly polarized and energetically localized although presenting enough itinerant character to keep its position at the Fermi level. The material shows a coupling between the $5f$ and $6d$ states. This interaction explains the observed negative spin polarization from photoelectrons up to 7 eV above the photothreshold.

Measurements of time-resolved photoluminescence spectra at 2 K from amorphous ${\mathrm{As}}_2$${\mathrm{S}}_3$ on a 10-nsec time scale demonstrate that two independent luminescence processes exist simultaneously. The higher-energy luminescence process at 1.75 eV has a very short lifetime and is rapidly quenched at higher temperatures. The other process appears at lower energy (1.45 eV) and shifts to considerably lower energy with increasing time delay. A model to explain this result is proposed.

We have analyzed a simple model of a periodically modulated magnetic system. The phase diagram includes multiple phase transitions between commensurate phases, similar to those observed in CeSb. We argue that our model, and CeSb, are possible candidates for the "devil's stairs" behavior.

Spin models with random anisotropic fields and random magnetic fields are studied. It is shown that integral-index textural singularities of these fields act as disclination sources and participate in destroying long-range ferromagnetic order. Half-integral-index singularities give rise to frustration. The relation of these models to bond disordered spin-glasses is discussed.

We present preliminary measurements of the linear polarization of the cosmic microwave background (3 K blackbody) radiation. These ground-based measurements are made at 9-mm wavelength. We find no evidence for linear polarization, and set an upper limit for a polarized component of 0.8 mK with 95% confidence level. This implies that the present rate of expansion of the Universe is isotropic to 1 part in ${10}^6$, assuming no reionization of the primordial plasma after recombination.

Using the exact relativistic eigenstates of electrons and positrons, I obtain the cross sections for $e^{+}{e}^{-}\to 1\gamma$ and $e^{+}{e}^{-}\to 2\gamma$ annihilation in strong magnetic fields, which enables one to decide which of the two processes should be predominant in pulsar magnetospheres.

We have studied the energy distributions of Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, and Si emerging from high-energy proton-xenon and proton-krypton collisions in the $20<\mathrm{}{p}_{\mathrm{inc}}<400\mathrm{}$ GeV/c momentum range. Based on the fragment mass dependence of the slope characterizing these energy distributions, there is a natural division of the fragments into two groups. The production of fragments heavier than carbon can be understood in terms of a two-body disintegration of a residual nucleus possessing a single slope parameter.

Using pulsed optical excitation we have measured the $g$ factors of twelve hyperfine levels ($K=1\mathrm{} \mathrm{through} 6$) of the $A{{}_{}{}^2{}_{}{}^{}\Sigma _{\frac{1}{2}}^{}{}_{}{}^{}}^{+}$ state of OH by observation of quantum beats. The results are consistent with Hund's case (b) coupling to within the experimental uncertainty of 0.35% (principally limited by magnetic field calibration). However, the ratios of the $g$ factors of a given hyperfine doublet, which are independent of field and accurate to about 0.15%, show significant discrepancies from theory.

A newly designed, large-aperture and high-resolution bent-crystal spectrometer has been used to observe high-intensity sources of pionic x rays. The pionic x-ray source was a target of natural titanium which was placed adjacent to a copper pion-production target in the external beam of the Nevis synchrocyclotron. The energy difference between the $5g\to 4f$ and $5f\to 4d$ transitions in pionic titanium was measured to be 87.6 ± 1.8 eV. Comparison with the prediction of the Klein-Gordon equation is made.

A free-electron laser excited by traveling microwave radiation is suggested and discussed. Some desirable features of the microwave free-electron laser are given.

The radial distribution of a nonneutral electron cloud confined in a magnetic mirror was measured. The cloud is compressed by the magnetic field to a final radius of 4 mm from an initial radius of 4.5 cm with a final kinetic energy of 0.3 MeV and 2×${10}^{11}$ electrons. The radial distribution of the cloud is hollow up to 150 μsec after injection. When the cloud is neutralized by a background plasma, filling in of the center does not occur.

We report the results of experiments on the ISX-$A$ (impurity-study experiment) tokamak that demonstrate the technique of plasma fueling by solid-hydrogen-pellet injection. The results show that density increases of up to 30% or more can be realized without apparent deleterious effects on plasma stability and confinement.