The theory of exciton-enhanced Raman scattering is formulated in terms of the scattering of polaritons by optical phonons via the exciton part of the coupled modes. The expression for the exciton contribution to the scattering tensor is given, within a constant factor, in terms of the same parameters that determine the exciton contribution to the frequency-dependent dielectric constant. The theory also provides a new mechanism for the exciton contribution to the electro-optic effect.

We have measured branching ratios for the isospin-nonconserving particle decays of the 15.1-MeV $T=\frac{3}{2}$ states in ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ to the (0.0, $0^{+}$) and (4.44, $2^{+}$) states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. By comparing ratios of reduced widths with the $0^{+}$ and $2^{+}$ states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ for the mirror decays, we show that the form of the isospin impurity in the 15.1-MeV states depends on $T_z$.

Neutron particle-hole states have been observed in the decay of isobaric analog resonances formed in the reaction ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ plus proton. Analysis of the on-resonance inelastic data has given inelastic proton partial widths, spectroscopic factors, spins, and parities of several of the observed particle-hole states.

The static quadrupole moment of the first excited $J^{\pi }=2^{+}$ state in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ was measured to be $Q=-0.243\mathrm{}\pm 0.035$ b. The experimental technique developed for this measurement uses the reorientation effect in heavy ion Coulomb excitation and allows accurate determinations of static quadrupole moments to be made, particularly in light nuclei.

It is shown that exchange degeneracy leads to dips in differential cross sections when trajectories pass through nonsense, wrong-signature values. The proof does not assume the absence of Gribov-Pomeranchuk fixed poles.

It is conjectured that, although no model is capable of explaining its motivating small parameters, an assortment of complementary models collectively may span the entire hadronic $S$ matrix, with all parameters determined.

It is pointed out that high-energy, backward pion photoproduction is the best place to look for right-signature fixed poles. We also summarize a new argument, based on a potential-theory model, that such fixed poles are absent when the external particles lie on Regge trajectories.

It is argued that the usual value of the $f-f^{\prime }$ mixing angle ($tan\theta =\frac{1}{\sqrt{2}}$) is the extremum value consistent with the flat Pomeranchuk trajectory. This statement is valid in the approximation of neglecting the $t<~m_f^{}{}_{}{}^2$ portion of the double spectral function ${\rho }_{\mathrm{st}}$ with $T=0\mathrm{}$ in the $t$ channel at $s\to \infty$.

The high-energy elastic scattering cross sections of the deuteron are shown, because of the $d$-state admixture, to be strongly dependent on the polarization of the deuteron spin. The polarization dependence is shown to explain the absence of a pronounced minimum in the differential cross section for unpolarized deuterons. For polarized deuteron targets, on the other hand, the minimum should assume a clearly observable form.

We have measured the photoproduction of ${\rho }^0$ mesons from hydrogen and deuterium as a function of the photon energy, $k_{\gamma }$, and the square of the momentum transfer, $t$. The assumption that the $\rho$ is produced by a purely diffractive mechanism is midly contradicted by the data.

We have measured the photoproduction of ${\rho }^0$ mesons from several complex nuclei. Good agreement with a diffraction model is obtained, and comparison is made with the vector-dominance model. If we write the $\rho$-photon coupling constant as $\frac{em_{\rho }^{}{}_{}{}^2}{2{\gamma }_{\rho }}$ we find $\frac{\gamma _{\rho }^{}{}_{}{}^2}{4_{\pi }}=1.10\mathrm{}\pm 0.15$.

A level-crossing effect in stimulated emission is used to determine precisely the hfs in an excited electronic state of ${\mathrm{Xe}}^{129}$. The effect arises from a resonant change in nonlinear polarization induced by a monochromatic field as appropriate tunable level pairs are made to cross.

The method of optical pumping of diamagnetic atoms with zero orbital angular momentum (${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$) has been extended to an atom with nonzero orbital angular momentum (${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$), yielding ${\left|{\mu }_I\right|}_{\mathrm{uncorrected}}=0.5726\mathrm{}\left(6\right)\mathrm{}{\mu }_N$ for the nuclear moment of ${\mathrm{Pb}}^{207}$. The cross sections for disorientation by collisions with the inert gases, hydrogen, and nitrogen are all less than ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$.

Observation of the nonsecular frequency shift in the NMR line of solid ${\mathrm{He}}^3$ associated with the off-diagonal elements in the dipolar Hamiltonian is reported. The method used is to look for the shift directly following a change in sample pressure. The result is in good agreement with the theory of Kubo and Tomita using published data for the spin-exchange rate.

Experimental results obtained with a $Q$ machine demonstrate the effect of a nonlinear mechanism called periodic pulling that has been proposed to explain the transition to turbulence in a bounded plasma characterized by weakly unstable modes. The effect is characteristic of any distributed-parameter system that can be described by the van der Pol equation and is related to phenomena observed in solid-state oscillators and the gas laser.

We present a microscopic calculation of the effective mass and interactions of ${\mathrm{He}}^3$ quasiparticles in dilute ${\mathrm{He}}^3$-${\mathrm{He}}^4$ solutions. The theory is first-principles in the sense that it requires no other information than the bare masses of the helium atoms and a realistic two-particle potential. In this note we report our findings in the limiting case of zero concentration.

The effects of electron plasma and magnetic field on the polaritons in GaAs are studied by Raman scattering at small angles.

Substitutional impurities in undeformed covalent crystals theoretically generate localized states with binding energies of order 1 eV even when the valence of the impurity is equal to that of the atom it has replaced. The weakness of observed binding energies is ascribed to lattice deformations. The observed binding energies are therefore identified as remnants of the original large binding energy.

The extrinsic photoconductivity of $n$-type silicon has revealed dips in its spectral response due to transfer of electrons among the equivalent conduction-band valleys by intervalley phonon emission. Intervalley LA phonons of energy 26.9 and 47.4 meV (±0.5 meV) are observed to contribute approximately equally to the total scattering of electrons.

The inelastic magnetic scattering of neutrons has been studied in Cr and ${\mathrm{Cr}}_{0.95}$-${\mathrm{Mn}}_{0.05}$ both below and above the Néel temperature. The temperature dependence of the spin-wave velocity in the alloy has been measured below $T_{\mathrm{N}}$. The scattering above $T_{\mathrm{N}}$ may also be interpreted in terms of spin-wavelike excitations, which persist far into the paramagnetic phase.