A very general Ansatz is made for the form of the dielectric response matrix $\epsilon (\overrightarrow{\mathrm{Q}},{\overrightarrow{\mathrm{Q}}}^{\prime })$ for a solid in terms of which it is possible to explicitly find the inverse matrix ${\epsilon }^{-1\mathrm{}}(\overrightarrow{\mathrm{Q}},{\overrightarrow{\mathrm{Q}}}^{\prime })$. The various existing models of lattice dynamics may be obtained as special cases of this Ansatz. The phonon dispersion curves for Si are calculated from a simple generalized shell model based on this theory and agree with experiment to within 20%.

We present a free-energy description of a smooth semiconductor-metal transition based on a two-band model and including electron-electron Coulomb energy and lattice-displacement energy. The assumption that the lattice-displacement energy plays a weak, secondary role appears to be needed to obtain good qualitative agreement with a number of experimental observations in ${\mathrm{Ti}}_2$${\mathrm{O}}_3$.

The Raman and Brillouin spectra of tetragonal ferroelectric BaTi${\mathrm{O}}_3$ have been studied between 7 and 133°C. In addition to providing the temperature dependences of the sound velocity and absorption, these spectra exhibit several anomalies which are quantitatively attributable to the interaction between acoustic phonons and the soft optic mode responsible for the ferroelectric phase transition in BaTi${\mathrm{O}}_3$.

An anomalously large magnetostriction has been found in ${\mathrm{Fe}}_2$Ti${\mathrm{O}}_4$. The magnetostriction constants ${\lambda }_{100}$ and ${\lambda }_{111}$ are (4.7 ± 0.4) × ${10}^{-3\mathrm{}}$ and (1.3 ± 0.4) × ${10}^{-3\mathrm{}}$, respectively, at 77°K. The origin of the giant magnetostriction has been found to be due to the reduction of the elastic constant $c_{11}-c_{12}$ as the result of the presence of Jahn-Teller ${\mathrm{Fe}}^{2+}$ ions in the tetrahedral site.

A systematic angular shift is noted between distorted-wave calculations and measured angular distributions for (${\mathrm{He}}^3$, $t$) reactions on even-even targets. The shift is apparent for final states whose isospin is one unit lower than that of the target state.

A particular $J={\frac{1}{2}}^{+}$ analog resonance in ${}_{}{}^{71}{}_{}{}^{}\mathrm{As}$, observed in elastic and inelastic scattering of protons on ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$, and corresponding to a single $l=0\mathrm{}$ state at 2.22-MeV excitation in ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$, is found to contain significant substructure encompassing many ultimate finestructure levels.

It is shown that there is an upper bound to the energy of the gravitational radiation emitted when one collapsed object captures another. In the case of two objects with equal masses $m$ and zero intrinsic angular momenta, this upper bound is $(2-\sqrt{2})m$.

It is suggested that the eighth and ninth axial-vector currents are dominated by the $J^P=0^{-}$ mesons $\eta \mathrm{}\left(549\right)\mathrm{}$, ${\eta }^{\prime }\mathrm{}\left(958\right)\mathrm{}$, and the (presumed) $J^P=1^{+}$ mesons $D\left(1285\right)\mathrm{}$ and $E\left(1422\right)\mathrm{}$. Predictions are made concerning the decay modes of $D$ and $E$ as well as for the $\mathrm{DNN}$ and $\mathrm{ENN}$ couplings.

The production of particles carrying a conserved quantum number is investigated in the multiperipheral model. The Chew-Pignotti bootstrap condition is appropriately modified. The available data for strange-particle production at laboratory energies are shown to have a natural explanation, within the model, if the effective $K^{*}$ intercept is equal to that of the $\rho$. An unexpected result is that, for precisely this value of the $K^{*}$ intercept, the ratio of $K$'s to $\pi$'s produced rises with energy, in accordance with experimental indications.

A calculation of the sixth-order anomalous magnetic moment of the electron is presented. We obtain $a_e=\frac{1}{2}\frac{\alpha }{\pi }-0.328\mathrm{}47{\left(\frac{\alpha }{\pi }\right)}^2+1.49\mathrm{}{\left(\frac{\alpha }{\pi }\right)}^3$ which is in good agreement with the present experimental answer.

Zero-field quantum beats were observed in $\mathrm{L}\mathrm{y}-\beta$ emission (1026 Å) from hydrogen atoms formed by beam-foil excitation, and the energy dependence of the magnetic-substate cross sections for $n=3\mathrm{}$, $l=1\mathrm{}$ states was determined for beam energies in the range from 230 to 500 keV/atom.

Infrared absorption spectra of electron-bombarded superfluid liquid helium have established that (a) $a{}_{}{}^3{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ helium molecules and probably $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ atoms are present in the liquid in concentrations of the order of ${10}^{13}$/${\mathrm{cm}}^3$ in an excitation volume ∼0.05 ${\mathrm{cm}}^3$, for a 1-μA bombarding beam of 160-keV electrons; (b) these states are metastable with life-times of the order of a millisecond at 1.7°K; (c) the $a{}_{}{}^3{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ molecules are de-excited by $a{}_{}{}^3{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}-a{}_{}{}^3{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ collisions in the liquid; and (d) the local configuration of the surrounding liquid helium is different for different excited states of the helium atomic and molecular systems, and the configurational interaction with the host fluid has an appreciable effect upon the electronic energies associated with these excited states.

Excited atom-like states of helium are shown to exist in stable cavities in liquid helium. A variational model, similar to that used to describe electrons in liquid helium, is employed. It is found that the cavities surrounding these excited atoms are much smaller than in the "free"-electron case. Calculated positions of several atomic lines are found to be in good agreement with measured values.

The enhancement of the scattered signal due to the mixing of two optical beams in a plasma is observed. The two beams are produced in a dual-cavity organic-dye laser pumped by a $Q$-switched ruby laser. The presence of enhanced oscillations is demonstrated by a 50% increase in the intensity of the satellite in the scattered light spectrum of a third beam.

A theory is presented for the nonlinear evolution of the beam-cyclotron instability, together with the results of a series of computer experiments confirming the main points of the theory. We conclude that at a turbulent level which is proportional to ${\left(\frac{{\Omega }_{\mathrm{ce}}}{{\omega }_{\mathrm{pe}}}\right)}^2$, a transition is made to the nonmagnetic ion acoustic instability. For small $\frac{T_i}{T_e}$, the system then evolves until the fluctuating fields become strong enough to stabilize by ion trapping.

The decay of short-range ordering of N$\mathrm{H}_4^{}{}_{}{}^{+}$ ions below $T_{\lambda }$ (235°K) in N${\mathrm{H}}_4$Br is shown to be responsible for both the specific-heat anomaly and the Raman scattering of a polarized low-frequency mode at 56 ${\mathrm{cm}}^{-1\mathrm{}}$. The temperature-weighted integrated Raman intensity is quantitatively compared with the residual specific heat below $T_{\lambda }$.

A novel application of the Born-Oppenheimer approximation is made which predicts the strength and nature of the singular threshold structure associated with plasmon satellites for a wide class of experiments involving the interactions of photons or fast electrons with solids.

Experimental data on the nonlinear excess conductivity of Al films due to the fluctuation of the order parameter have been analyzed by taking account of the Aslamazov-Larkin term and the anomalous term proposed by Maki and Thompson. The analysis shows clearly the existence of a large contribution from the Maki-Thompson term to the nonlinear excess conductivity.

We have observed plasma-resonance scattering of light from sodium particles of less than 100 Å diam produced in a flowing inert gas. The scattered light near resonance was at least 90% linearly polarized and had a nearly Lorentzian peak near 320 nm with a full width at half-maximum of 60 nm. Depending on experimental conditions, the observed plasma-resonance peak varied from 310 to 330 nm, with slightly varying widths. The wavelengths of the experimentally observed resonance were about 15% less than theoretically expected. A second maximum in scattered intensity was observed at 220 nm.

The Born model of ionic solids was used to determine theoretical solution enthalpies of divalent impurities in the alkali halides, in the limit of infinite dilution. These calculations are based upon a generalized Mott-Littleton theory for reasonable values of the host-impurity parameters. Results are reported for ${\mathrm{Sr}}^{++}$ and ${\mathrm{Ba}}^{++}$ in NaCl, KCl, and RbCl.