By monitoring the change in the interference figure for an oriented nematic (optic axis perpendicular to the incident light cone) as twist deformation is induced by a magnetic field (Freedericksz transition), one is led to a simple and direct method for measuring $\frac{K_{22}}{{\chi }_a}$ and $\frac{{\gamma }_1}{{\chi }_a}$. An analytic expression is obtained for the effect of twist on the interference figure and is verified experimentally.

The radiation resulting from decaying surface plasmons in small metallic particles has been observed for the first time. The surface plasmons were excited in colloidal silver by x rays. The spectrum of the observed radiation is presented and compared with theoretical predictions.

We show that an electron-impurity interaction with a screening radius longer than the cyclotron radius gives rise to a cyclotron-resonance linewidth for a nondegenerate semiconductor in the quantum limit, which increases and approaches a constant value with increasing magnetic field. This is in contradiction to earlier theoretical work of Kawamura et al. and to the interpretation of the recent experimental work of Apel et al., both of which are discussed in the light of this calculation.

Apparent $1s$-to-$2p$ transitions, observed with far-infrared spectrometers at 5.9 and 7.2 meV, exhibit linear Zeeman splitting but are not otherwise consistent with the effective-mass hydrogenic model because the activation energy is an order of magnitude too small and the quadratic Zeeman shift is absent. Cyclotron resonance was observed at 5 K but not at 1.3 K, which confirms the existence of shallow bound states.

Photoemission spectra are used to identify unusually narrow chemisorbed levels of ${\mathrm{O}}^{2-}$ on Ba and Sr at 4.6 and 4.8 eV below the Fermi level $E_{\mathrm{F}}$, respectively. Nitrogen on Ba forms narrow states 1.3 and 5.3 eV below $E_{\mathrm{F}}$. Measurements of sticking probability and of electron emission in the dark show that the oxygen-metal chemical activity is initially small, increases to a maximum, and then abruptly decreases as the mass of oxide increases.

We provide a new spectroscopic criterion for the observation of the insulator-metal transition in a two-component system, which is based on the disappearance of Wannier exciton states in the metallic region. This effect has been observed in the vacuum-ultraviolet spectra of mercury/xenon mixtures deposited at 10-30°K, where the Xe Wannier states are abruptly washed out at (55±5)% of Hg.

Measurements of the proton relaxation time $T_1$ in ${\left(\mathrm{C}{\mathrm{H}}_3\right)}_4$NMn${\mathrm{Cl}}_3$ are reported as a function of temperature between 4.0 and 1.2 K. Results are interpreted in terms of a direct relaxation process with spin waves in a one-dimensional antiferromagnet. They represent the first observation of direct-process NMR relaxation by magnons in any system and show that any gap in the spectrum at $q=\frac{\pi }{a}$ has to be less than 0.07 meV.

The fundamental relaxation mechanisms by which the uniform and magnetostatic modes decay in an antiferromagnet are identified by antiferromagnetic-resonance linewidth observations in Mn${\mathrm{F}}_2$ at 4.2°K in fields of 85 kOe. The dependence of the linewidth—0.2 Oe in the narrowest instance—on sample geometry, surface preparation, and impurity concentrations makes quantitative comparison with the Loudon-Pincus theory possible. The predominant relaxation process is surface pit scattering into the degenerate spin-wave manifold in all but the most impure crystals.

Magnetic-susceptibility and specific-heat measurements in Van Vleck paramagnetic Pr${\mathrm{Cu}}_2$ down to 30 mK reveal that the Pr nuclei enter an antiferromagnetically ordered state below 54 mK. This high nuclear ordering temperature results from magnetic exchange interactions between the Pr ions, which must be close to the critical value necessary for spontaneous electronic magnetic order in this compound.

In a complete experiment on the reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}(n, 2n)\mathrm{H}$ we have observed neutron-neutron and neutron-proton final-state interactions. The analysis by a three-body calculation with separable potentials gives $a_{\mathrm{nn}}=-14.5\mathrm{}\pm 0.8$ fm for the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ neutron-neutron scattering length and ${\mathcal{r}}_m=2.7\mathrm{}\pm 0.5$ fm for the effective range.

A study is reported of one-, two-, and three-nucleon transfer reactions induced by 114-MeV ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ions on targets of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. A prominent feature is the extreme selectivity of the reaction mechanism in exciting simple one-, two-, and three-particle stretched configurations in the residual nuclei.

A systematic investigation of the one-proton transfer reaction (${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$) on $\mathrm{fp}$-shell target nuclei has been performed at bombarding energies near and above the Coulomb barrier. Angular distributions are qualitatively explained in terms of semiclassical theories. Peak cross sections show a marked $Q$ dependence due to the importance of angular-momentum matching. The main features of the studied reactions are well reproduced both qualitatively and quantitatively by finite-range distorted-wave Born-approximation calculations.

We re-examine the theory and data of the Kreuzer experiment to measure the relative difference $\frac{\Delta \kappa }{\kappa }$ in the gravitational constant $\kappa$ between two elements. Significant errors appear in the statistical analysis of Kreuzer which vitiate his conclusions. The upper bound for F and Br from his experimental data correctly becomes ${\left(\frac{\Delta \kappa }{\kappa }\right)}_{max}=2\mathrm{}\times {10}^{-2\mathrm{}}$, about 10 times the limit already set on the general vairation of $\kappa$ over the elements by direct use of a Cavendish balance.

If the early universe possessed the maximum degree of irregularity compatible with its present large-scale uniformity and isotropy, dissipation of energy at redshifts $z\gtrsim {10}^4$ would have generated a thermal microwave background with present temperature ∼3°K.

The angular distributions of $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratios in photoproduction from deuterium were measured for fourteen photon energies between 260 and 800 MeV. The energy dependence of ${\sigma }^{-}-{\sigma }^{+}$ near the ${\Delta }_{33}\mathrm{}\left(1236\right)\mathrm{}$ resonance region shows no dip structure, consistent with an absence of the isotensor term. The differential cross sections of $\gamma n\to {\pi }^{-}p$ at $k=350\mathrm{}$ MeV are considerably larger than the ones obtained from the inverse reaction ${\pi }^{-}p\to \gamma n$, but the two are in fair agreement at $k=500\mathrm{}$ MeV.

A possible explanation is given for the dipole behavior of the neutron and proton electromagnetic form factors.

Mössbauer studies with ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ atoms following the decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ in solid Xe find these atoms in two states: the stable Fe $3d^{6}4s^2$ state and an unstable ${\mathrm{Fe}}^{+}$ $3d^7$ state. The isomer-shift analysis yields $\frac{\Delta R}{R}=-(8.7\mathrm{}\pm 0.3)\times {10}^{-4\mathrm{}}$ for the 14.4-keV $\gamma$ transition in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$. We obtain information about the charge-transfer mechanism and recombination time of Fe ions in solid xenon.

We report a study of the oscillations of two superfluid helium baths coupled through a small hole. At low temperature they are associated with gravitational potential energy and kinetic energy through the hole. At high temperature, an entropy term must be added and the oscillations are dispersive. From an amplitude study we show that two critical velocities appear, depending on the presence or absence of a superleak. This experiment is an analog of Josephson plasma oscillations in that the phase of the wave function oscillates with time.

The temperature dependence of the flow alignment angle has been measured in two nematic liquid crystals, $p^{\prime }$-methoxybenzylidene-$p-n$-butylaniline and $p-n$-hexyloxybenzylidene-$p^{\prime }$-aminobenzonitrile. For both compounds this angle reaches a peak value at the nematic-isotropic transition point. Experimental evidence is reported for the first time that flow alignment does not occur over the entire mesophase of certain nematics.

de Gennes's equations for the Bogoliubov amplitudes in an inhomogeneous superconductor are solved in a simple geometry with the use of a one-parameter Ansatz for the pair potential. The solutions are used to determine the parameter self-consistently. In the limit $T\to T_c$, the results agree with the Ginzburg-Landau theory, but the present method is applicable at all temperatures $T<\mathrm{}{T}_c$.