Operator-product expansions near the light cone are used to study the convergence and saturation properties of some mass dispersion relations. We develop a general formalism and apply it to justify partial conservation of axial-vector current and to correct vector-meson dominance. We specifically treat the $K_{l3\mathrm{}}$ form factors and the decays ${\pi }^0\to \gamma \gamma$, $\omega \to \pi \gamma$, and $\omega \to 3\pi$.

The relationship between the dimensionality of the cosmic-ray propagation function and the statistical distribution of anisotropies is demonstrated and an argument is presented in favor of "essentially" one-dimensional propagation. This implies that a fluctuation explanation of low observed anisotropy cannot be ruled out as has been stated by previous authors.

High-resolution sweep spectroscopy has been extended to submillimeter wavelengths as short as 0.37 mm. The sensitivity of microwave spectroscopy in the submillimeter region (0.37 to 1 mm) has been improved by more than an order of magnitude. The highest-frequency spectral lines measured are the $J=6\mathrm{}\to 7$ transition of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 806 651.719 MHz and the $J=66\mathrm{}\to 67$ transition of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ at 813 353.706 MHz. The rotational constant $B_0$ for DF is observed to be 325 584.96 MHz.

The transition probabilities for induced emission and absorption of electromagnetic radiation by an excited atom interacting, in addition to the radiation field, with a system of "perturbers" (in single, binary, and completed encounters) are evaluated. It is found that Dirac's result $\frac{W_{\mathrm{ind}}}{W_{\mathrm{abs}}}=\frac{({\overline{n}}_{l\sigma }+1)}{{\overline{n}}_{l\sigma }}$ must be modified by a factor $\frac{{(1-\alpha n)}^2}{{(1+\alpha n)}^2}$, where $\alpha$ is related to the interaction potential of the emitter-perturber system as well as to the level structure of the "colliding" atoms, and $n$ is the perturber number density.

Two fixed, spatially separated detectors are used to measure the decay in flight of a cooled, thermal beam of pulsed metastable helium atoms. The preliminary value obtained for the radiative lifetime of the metastable $2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state of helium is 20 ± 2 msec.

Electric quadrupole ($4f\to 2p$ and $3d\to 1s$) atomic transitions have been observed in muonic ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. An identification based upon energy and relative intensity determination provides good agreement with theoretical predictions.

Time-resolved measurements of plasma temperatures, current, and density have been made in a turbulent heating experiment. Rapid ion heating ceases at the instant when the mean electron velocity falls below the critical value for generation of ionacoustic waves.

The results reported here, obtained by the heterodyne technique, show unambiguously that the relaxation of concentration fluctuations is exponential even very close to $T_c$. This experimental work thus confirms Kawasaki's assumption on the shape of this relaxation.

Propagation of a quasi transverse extraordinary wave through an inhomogeneous magnetized plasma is studied. Modulation of the reflection coefficient of the plasma is predicted due to density fluctuations in the region of evanescence of the wave. A measurement of the modulation is proposed as a diagnostic of certain plasma instabilities.

Light scattering measurements were made in the ternary system bromobenzene-water-acetone, with the acetone playing the role of an impurity. Because of the long range of the concentration fluctuations exhibited by this system, it was possible to explore with relative ease the nonhydrodynamic as well as the hydrodynamic regimes. Measurements of both the intensity and spectral width of the scattered light yielded a number of parameters which could be compared with several forms of theory.

Associated with the stability limit of the liquid phase, we find a soft mode with purely imaginary frequency at a wave vector corresponding to the first peak of the structure factor. The corresponding critical fluctuations show up in neutron-scattering experiments as the de Gennes narrowing of the quasielastic peak.

Aligned $U$-center pairs (containing ${\mathrm{H}}^{-}$ and ${\mathrm{D}}^{-}$ ions) were produced by a reaction of interstitial ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and HD molecules with optically aligned $M$ centers. The study of their local-mode spectra revealed several new bands in the infrared. From the polarization of these local modes in aligned systems, the observed bands can be clearly assigned to the different optically active vibrations of the $〈110〉$-oriented pair centers.

Resistivity and lattice-constant measurements under high pressure on SmS show that a $4f\to 5d$ electronic transition in SmS occurs discontinuously at 6.5 kbar at room temperature, whereas such a transition takes place continuously over a broad pressure range in SmTe and SmSe. The pressure-induced semiconductor-to-metal transition in the Sm chalcogenides and their pressure-volume relationship are consistent with the conversion of ${\mathrm{Sm}}^{2+}$ to ${\mathrm{Sm}}^{3+}$. Optical-absorption measurements in these materials correlate well with the resistivity data under pressure. The semiconductor-to-metal transition in Sm chalcogenides appears to fit the model recently proposed by Falicov and Kimball for a system with a localized state and a conduction band.

It is shown that a quantum-mechanical calculation of the surface resistance of a free-electron metal can provide a natural explanation of the broad anomaly found by Baraff, Grimes, and Platzman in their perpendicular-field cyclotron resonance experiments on potassium.

The electron-excited emission spectrum of solid neon is found to be unique among the condensed rare gases in exhibiting a narrow atomiclike exciton line (located at 743 ÅA) In addition, the spectra of both solid and liquid neon show broad lines, probably attributable to radiation from ${\mathrm{Ne}}_2$ molecules

The thermal expansivity and ultrasonic response of SrTi${\mathrm{O}}_3$ have been studied in the vicinity of its structural transition. The nature of the expansivity discontinuity indicates that the transition is second order and that the temperature region in which critical fluctuations are appreciable is less than the strain-broadened transition width. The ultrasonic behavior near $T_a$ is complex and appears to be dominated by structural inhomogeneities.

It is shown that, if the Gomer-Schrieffer induced-covalent-bond mechanism is responsible for the chemisorption of hydrogen on strongly paramagnetic metals, then the rates of chemical reactions involving the adsorped hydrogen may be dominated by energy transfers between the bond and spin fluctuations in the metal.

Anderson's theory of localization in disordered systems is extended. It is shown that mobility edges exist, in agreement with the Mott-Cohen-Fritzsche-Ovshinsky model. As the randomness increases, the mobility edges move inwards into the band, and their coincidence is termed Anderson's transition. A criterion is developed restricting the energy regions where mobility edges can be found; explicit results are obtained for a Lorentzian distribution of single-site energies.

We carry out an exact study of the relaxation of a single magnetic impurity embedded in a linear quantum chain. We obtain a rigorous result for the expectation value of any spin in the chain, and find that it relaxes to its equilibrium value as $t^{-1\mathrm{}}$.

The magnetic field dependence of the energy of long-wavelength mangons in Tb-10% Ho has been studied by inelastic neutron scattering. The results agree with the "frozen-lattice" model, provided that the second-order magnetoelastic effect is taken into account. The planar anisotropy is almost entirely the result of magnetoelastic effects. The temperature dependences of the anisotropy parameters have been deduced from the results.