Neutron-diffraction studies have been carried out of the various two-dimensional phases of C${\mathrm{D}}_4$ physisorbed on graphite and a phase diagram has been constructed. Registered, expanded, and compressed solid phases and a disordered fluidlike phase have been identified. The lattice constant, intensity, and cluster size have been measured as functions of temperature and coverage and the nature of the transitions between the phases has been investigated.

It is shown that minority-carrier injection into trap-free semiconductors at low current densities can lead to a local field maximum and resistance increase. These features disappear at high current densities, and only then is the more familiar expectation of a resistance decrease fulfilled.

We report the first observation of standing spin-wave modes by means of Brillouin light scattering in thin sputtered films of amorphous metallic ${\mathrm{Fe}}_{80}$${\mathrm{B}}_{20}$. Results agree with a classical theory and permit determination of spin-wave stiffness $D=(1.4\mathrm{}\pm 0.2)\times {10}^{-9\mathrm{}}$ Oe ${\mathrm{cm}}^2$. The value of $D$ is twice as large as that obtained from low-temperature magnetization measurements.

Picosecond relaxation of optically induced absorption in $a$-Si, $a$-Si:H, and ${\mathrm{As}}_2{\mathrm{S}}_{3-x}{\mathrm{Se}}_x$ ($0.25<~x<~0.75$) was studied with a passively mode-locked cw dye laser. In silicon, the results can be described in terms of trapping by defects. The fast recovery of absorption in chalcogenides indicates that recombination of highly localized excitons is the dominant mechanism in the decay of carriers excited at the Urbach edge.

We introduce the idea of an incoherence length $L_2$ at which inelastic collision broadening equals electronic energy-level separation. The two-dimensional conductance crosses over at $L_2$ from a $\ln L$ dependence suggested recently by Abrahams et al. to Ohmic behavior. These ideas and plausible relaxation and heating models are used to explain the nonlinear conductivity observations of Dolan and Osheroff.

Resistance measurements were made on high-resistivity thin-film metal strips at temperatures as low as 10 mK. Unexpected logarithmic variations of the resistance with temperature and applied electric field were observed for strips with sheet resistance below $R_{\square }\sim 10$ kΩ/□ and widths ≳ 1 μm. Exponential increases in resistance were observed for similar films when the film width was decreased to about 0.1 μm or when $R_{\square }$ was increased to ∼ 10 kΩ/□.

The electrical properties of wires with cross-sectional areas ($A$) in the range 1×${10}^{-11\mathrm{}}$ to 3×${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^2$ have been studied. At temperatures below about 10 K the resistance of the wires increases with decreasing temperature. The size of the increase varies as $A^{-1\mathrm{}}$ and becomes larger as the impurity resistance is made larger, in qualitative agreement with recent theoretical predictions by Thouless. The size of the increase is in order-of-magnitude agreement with the theory but the temperature dependence is not.

The magnetic field dependence (hysteresis curve) and the temperature dependence of the magnetization at a Ni(110) surface was measured by polarized low-energy electron diffraction. The diffracted intensities are spin dependent by a few percent. The temperature dependence of the surface magnetization measured in the range $0.5<\mathrm{}\frac{T}{T_c}<0.8\mathrm{}$, is significantly different from that of the bulk.

It is shown that the solution of Einstein's equations recently found by Kundu can be written in the same form of the Van Stockum solution with the use of an appropriate transformation.

The possibility that jets fragment with limited momentum transverse not to the jet momentum but to a color-anticolor axis is considered. This broadens jets somewhat in multijet events and leads to secondary maxima in the laboratory distributions of jet fragments.

Fast, forward-peaked protons, deuterons, and tritons observed in the reactions of 135-and 165-MeV ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ions with ${}_{}{}^{152,154}{}_{}{}^{}\mathrm{Sm}$ and 166-MeV ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ ions with ${}_{}{}^{148}{}_{}{}^{}\mathrm{Nd}$ are shown to originate in massive-transfer reactions. These reactions are also demonstrated to have merit as probes of angular momentum space in nuclei at very high spin.

The capture of fast polarized neutrons incident on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ has been measured at an incident neutron energy of 10.0 MeV. The results indicate a significant non-$E1\mathrm{}$ contribution in the giant-dipole-energy region of ${}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$. When the data at $E_n=10\mathrm{}$ MeV are analyzed with the use of a model, they are found to be consistent with an $E2\mathrm{}$ strength which is (3.2±2.7)% of the total capture cross section. Some of the implications of this result are discussed.

The inelastic scattering of 162-MeV ${\pi }^{+}$ and ${\pi }^{-}$ by ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ was studied at larger momentum transfer. Several high-spin particle-hole states are observed to be preferentially excited in this reaction. These include the 9.70-MeV ($5^{-}$,$T=0\mathrm{}$), 11.58-MeV ($6^{-}$,$T=0\mathrm{}$) and 14.36-MeV ($6^{-}$,$T=1\mathrm{}$) states. The ratios of the cross sections of the $6^{-}$, $T=0\mathrm{}$ state to the $6^{-}$, $T=1\mathrm{}$ state are ${1.5}_{-0.2\mathrm{}}^{+0.4\mathrm{}}$ for ${\pi }^{+}$ and 1.7±0.4 for ${\pi }^{-}$, in contrast to ratios of about 4 predicted by simple distorted-wave impulse-approximation calculations.

Data for two-neutron transfer reactions on even tungsten nuclei are presented and shown to possess some simple systematic features. These data are discussed in terms of the underlying single-particle structure as well as pairing and interacting-boson models.

In-plane angular and energy correlations between $\alpha$ particles and heavy ejectiles have been measured for the reaction ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at 148 MeV. The coincidence cross sections may be parametrized as a product of singles cross sections for the detection of $\alpha$ particles and heavy ejectiles. The observed correlations indicate that the $\alpha$ particles are emitted at an early stage, prior to the formation of the deep-inelastic fragments.

The intensities and angular correlations of yrast transitions measured in coincidence with light fragments from 96-MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$ reactions are used to determine amount and alignment of the angular momentum transferred to the heavy fragment as a function of the reaction $Q$ value. It is found that fluctuations of the spin axis about the scattering normal are small at the most probable $Q$ value of - 32 MeV but increase strongly with increasing inelasticity.

Neutral hydrogen beams of 13 and 14 keV at equivalent proton currents of 5 and 3 A, respectively, were injected into a target plasma in a tandem mirror. The space potential at plugs increased more than 10 V relative to the space potential at the central cell and was sustained for more than 0.3 ms. The potential increase is due to the heating of electrons with trapped hot ions and is explained by the relation $\varphi =T_e\ln \left(\frac{n_p}{n_c}\right)$.

The phase behavior and structures of several liquid crystals of the $n\mathrm{O}.\mathrm{}m$ (${\mathrm{C}}_n{\mathrm{H}}_{2n+1}-\mathrm{OPhCHNPh}{\mathrm{C}}_m{\mathrm{H}}_{2m+1\mathrm{}}$) series of compounds have been established by a variety of experiments. The hexagonal close-packed layers of the $S_B$ phases have a bilayer stacking sequence. The structure is increasingly modulated with decreasing temperature by periodic displacements of the molecules along their long axes. An additional displacement of this type occurs at the $S_B-S_H$ transition.

A first measurement of the intrinsic thermal expansion coefficient of Frenkel defects produced by a low-temperature neutron irradiation in aluminum leads us to a value 12 times larger than the coefficient of thermal expansion for the pure metal.

The purpose of the Letter is to point out the possibility of a new interference technique in x-ray and $\gamma$-ray optics—the simple idea of impedance-matched grazing-incidence films—and to discuss applications to pure nuclear coherent reflections, resonant filtering of synchrotron radiation, and x-ray interferometry.