A comparison is made of recent data on $\eta$-meson photoproduction with photoexcitation amplitudes calculated in the nonrelativistic quark model. This leads to definite multiplet assignments for all low-mass $I=\frac{1}{2}$ nucleon isobars. In particular, we find no evidence for a radial sequence beyond $n=2\mathrm{}$. The assignment of $P_{11}\mathrm{}\left(1750\right)\mathrm{}$ to an $n=3\mathrm{}$ second radially excited [56, $0^{+}$] appears ruled out; instead, we argue that consistency of results from photoproduction and diffraction scattering makes the configuration [70, $0^{+}$] the best choice for this state.

Detailed calculations show that the theoretical total cross section for the production of the intermediate vector boson $W$ by incident neutrinos is much larger than that for $W$ production by incident muons in the relevant range of National Accelerator Laboratory energies and corresponding $W$ masses.

The observation of singly stimulated two-photon emission from metastable deuterium atoms is reported. A collimated beam of metastables is produced by charge exchange between cesium vapor and 5-keV deuterons. A pulsed Nd-glass laser is used for the stimulation. The generated 1373-Å photons are detected at the exit slit of a spectrometer. Single-photon counting techniques are employed. The results obtained are in good agreement with theoretical calculations.

The temperature dependence of the torque on a Rayleigh disk immersed in rotating helium is explained qualitatively on the basis of superfluid dynamics. A heat-exchange torque peculiar to two-fluid mechanics arises due to the disk being bathed in ambient room-temperature radiation.

A strong absorption of extreme uv radiation by a laser-generated ionized metallic plasma has been observed. A discussion is made about the mechanisms likely to be responsible for this absorption. Attention is paid to photoionization and, overall, to the inverse bremsstrahlung process.

We have made precision measurements of the turbidity of S${\mathrm{F}}_6$ near its critical point using an optical analog of the Wheatstone bridge. From the measurements we obtain values for the compressibility of ${\kappa }_T=(1.39\mathrm{}\pm 0.19){(T-T_C)}^{-1.225\mathrm{}\pm 0.02}=(1.18\mathrm{}\pm 0.16)\times {10}^{-3\mathrm{}}\times \frac{{\epsilon }^{-1.225\mathrm{}\pm 0.02}}{\mathrm{atm}}$, and for the correlation length of $\xi =(72\mathrm{}\pm 11){(T-T_c)}^{-0.67\mathrm{}\pm 0.07}=(1.5\mathrm{}\pm 0.23){\epsilon }^{-0.67\mathrm{}\pm 0.07}$ Å.

The phonon spectrum of bcc ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been calculated including the leading anharmonic corrections to the self-consistent harmonic approximation. For small wave vectors an anomalous dispersion is found causing a maximum in ${\Theta }_{\mathrm{D}}\mathrm{}\left(T\right)\mathrm{}$ in agreement with experiments.

It is shown that the repulsive (not merely the positive) portion of the Lennard-Jones potential quantitatively dominates the equilibrium structure of the Lennard-Jones liquid. A simple and accurate approximation for the radial distribution function at high densities is presented.

It is shown rigorously that, for systems with non-negative interactions and integrable Mayer $f$ bonds (e.g., hard spheres), distribution functions and the thermodynamic ratio $\frac{\rho }{z}$ exist in the limit $V\to \infty$, and are analytic functions of the activity $z$, for $z<\mathrm{}\frac{1}{f}$ in the right-hand half-plane, with $f$ the absolute value of the integral of the $f$ bond. Heuristic arguments then indicate that these functions are continuous in $z$ for all $z<\mathrm{}\infty$. This would mean that no Ehrenfest phase transitions are possible for such systems.

Measurements of the absorptivity of Al and dilute Al-Mg alloys were made at 4.2 K in the 0.2- to 5-eV energy region by a calorimetric technique. In addition to the well-known conductivity peak around 1.6 eV, another peak has been found near 0.5 eV. These peaks are present in the alloys, broadened, but unshifted, as well as in Al. The peaks are at about $2\left|V_{200}\right|$ and $2\left|V_{111}\right|$, respectively, where the $V$'s are Fourier coefficients of the pseudopotential.

Capacitance-voltage measurements on graded junction diodes of PbTe which suggest that the static dielectric constant obeys a Curie-law temperature dependence with $T_C\simeq (-79\mathrm{}\pm 4)$ °K are reported. Evidence for nonlinear dependence of dielectric polarization on electric field is also given.

Exciton effects on electric field modulation line shapes at general critical points are treated using a Slater-Koster contact interaction to approximate the Coulomb potential. This interaction produces a mixing of one-electron line shapes similar to that calculated for an unperturbed solid. By comparison with experiment, we show that exciton effects are present in the $E_1$ structure of low-temperature electroreflectance data of Ge.

We give a calculation of the electron—effective-mass dependence of the energy gap $E_g=|E_{{\Gamma }_6}-E_{{\Gamma }_8}|$ which includes the higher band interactions. We show that in high-concentration HgSe and HgTe, the effective mass increases with decreasing $E_g$.

Unlike other ferroelectric perovskites, PbTi${\mathrm{O}}_3$ displays temperature-dependent Raman spectra consisting of underdamped modes, including the "soft" transverse-optical (TO) modes. Moreover, the softest TO mode shows linewidth divergence at the ferroelectric-to-paraelectric transition. Also in contrast to previously studied perovskites, Raman selection rules are rigorously obeyed in both the ferroelectric and paraelectric states.

An anisotropy has been observed in the $\beta -\alpha$ directional correlation for an allowed ${\beta }^{+}$ decay in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$. The effect is much larger than expected from interference from the second-order "weak magnetism" alone. The possibility of an enhanced $E2\mathrm{}$ interference is discussed.

Peaks in the zero-degree yield curve of the reaction ${\mathrm{C}}^{12}({\mathrm{Li}}^7,\alpha ){\mathrm{N}}^{15}$ are interpreted as due to resonances in the ${\mathrm{C}}^{12}t\alpha$ system.

It is suggested that the experimentally observed intermediate structure in the cross section of elastic ${\mathrm{O}}^{16}$ + ${\mathrm{O}}^{16}$ scattering is due to quasibound molecular states of the ion-ion system while the gross structure originates from virtually bound molecular states.

The reaction $\mathrm{pn}\to {\Delta }^{-}{\Delta }^{++}$, where ${\Delta }^{-}$ is emitted in the forward direction in the c.m. system, is observed at $6.98 \frac{\mathrm{GeV}}{c}$ with a cross section of 0.09 ± 0.03 mb. The ratio between this reaction and the reaction $\mathrm{pn}\to {\Delta }^{++}{\Delta }^{-}$ with ${\Delta }^{++}$ in the forward direction in the c.m. system is found to be $\frac{\sigma \left({\Delta }^{++}{\Delta }^{-}\right)}{\sigma \left({\Delta }^{-}{\Delta }^{++}\right)}=12.2\mathrm{}\pm 4.5$. The ${\Delta }^{-}{\Delta }^{++}$ production is discussed in terms of exotic meson exchange and double meson exchange.

The $N^{*}\mathrm{}\left(1730\right)\mathrm{}$ with a mass of 1730 ± 15 MeV and a width of 130± 30 MeV is produced in the reaction ${\pi }^{-}p\to {\pi }^{-}{N}^{*}{\mathrm{}\left(1730\right)\mathrm{}}^{+}$ at $6 \frac{\mathrm{GeV}}{c}$. The principal decay mode of this $N^{*}$ is $N\pi \pi$ and not $\Delta \pi$. The $N\pi$ decay rate is found to be much smaller, and the $\Lambda K$ decay rate is found to be much larger than the accepted rates for the well-known $N_{\frac{1}{2}}^{}{}_{}{}^{*}\mathrm{}\left(1680\right)\mathrm{}$ states ($D_{\frac{5}{2}}$ and $F_{\frac{5}{2}}$), thus establishing that the object that we observe is not the $N_{\frac{1}{2}}^{}{}_{}{}^{*}\mathrm{}\left(1680\right)\mathrm{}$.