It has been predicted that an intense light beam in a plasma will break up into a number of self-focused filaments. We show that as a result of filamentation, strong plasma heating can occur in a wider range of densities than has been expected. The laser light decays into lower frequency modes which then heat the electrons and assist in the further development of a narrow filament.

The lower hybrid mode excited in a plasma with cross-field current and density gradient induces an attractive potential between the negative- and positive-energy modes of the plasma. The growth rate is thereby reduced and becomes comparable with the damping rates due to wave-particle interaction. This leads to the saturation of the turbulent field. Some applications have been made to the turbulent heating experiments in plasmas where cross-field current is present.

Recent observations of propagating order-parameter collective modes in a dirty superconductor are explained on the basis of a microscopic theory developed previously by the authors. It is shown how approximate charge neutrality of the metal is maintained in these modes.

The heat capacity of niobium at constant magnetic induction has been measured in the immediate neighborhood of $T_c\mathrm{}\left(B\right)\mathrm{}$ with millikelvin temperature resolution. An enhanced heat capacity attributable to fluctuations is observed both above and below $T_c\mathrm{}\left(B\right)\mathrm{}$. The temperature dependence throughout the transition region can be described over a wide temperature range by a universal curve with a temperature scale uniquely determined by measured thermodynamic parameters.

Ginzburg's theory of critical fluctuations is used to calculate the specific heat of a type-II superconductor in a magnetic field near the upper critical field. A scaling law for the specific heat is found, and the scaling temperature is given in terms of measurable quantities. Some distance from $T_c$ the fluctuation contribution is proportional to ${|T-T_c|}^{-\frac{3}{2}}$, with known coefficients. The dependence on $\kappa$ is explored. The diamagnetic susceptibility should have the same temperature dependence as the specific heat.

It is shown that the recently observed interesting but somewhat unexpected features of the dynamic structure factor of an electron liquid can be understood on the basis of a simple modification of the theory of the dielectric response function of Vashishta and Singwi.

It is pointed out that a model which agrees well with the observed properties of semiconducting glasses is an attractive Hubbard model of localized states. Such a model has no gap for two-electron excitations but an energy gap for one-electron ones. The suggested physical model for a two-electron excitation is a new covalent bond in the structure, which is severely localized. It is also proposed that the one-electron excitation spectrum is wholly, or almost wholly, extended, and all observed gaps are identical with the mobility gap.

We formulate an expression for the single-electron photoexcitation cross section, $\sigma \left(\omega \right)$, exploiting the orthogonality of the final electron eigenstate to the occupied states of the excited solid. We find that $\sigma$ depends significantly on the final-state angular momentum. The predictions of a simple model calculation correspond closely with experimental photoabsorption in several metals, as shown explicitly for the $K$ shell in Li and the $K$ and $L$ shells in Al.

The electronic exchange energy $J$ of a radical pair trapped in crystals of 1-methyl uracil has been measured precisely by observing the effect on the ESR spectra of mixing the singlet and triplet states. The interradical distance and exchange energy were varied by thermal expansion of the crystal. Values of 0.3105 ± 0.001 ${\mathrm{cm}}^{-1\mathrm{}}$ were obtained for $\frac{J}{\mathrm{hc}}$ at 95 K and - (3.29 ± 0.16) × ${10}^{-3\mathrm{}}$ ${\mathrm{K}}^{-1\mathrm{}}$ for its thermal variability between 95 and 111 K.

Mössbauer studies of the 86-keV transition of ${\mathrm{Gd}}^{155}$ in ${\mathrm{Gd}}_{1-x}{R}_x$ compounds yield the hyperfine interaction parameters as a function of lattice dimensions and the angle $\theta$ between the magnetization and the $c$ axis. The magnetic hyperfine field is anisotropic, $\frac{H_{\mathrm{eff}}(\theta =28\mathrm{}°)}{H_{\mathrm{eff}}(\theta =47\mathrm{}°)}=1.13\mathrm{}$. The ratios between the electric field gradients in various metallic crystals are in agreement with the point-charge model. The absolute values of the gradients are about twice the theoretical values.

Ratios of cross sections for 200-MeV ${\pi }^{\pm }$ reactions on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ leading to mirror levels in ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, observed by their $\gamma$ decays, were measured and compared. For the first ${\frac{3}{2}}^{-}$ levels, the ratios are ${\left(\frac{{}_{}{}^{15}{}_{}{}^{}\mathrm{O}}{{}_{}{}^{15}{}_{}{}^{}\mathrm{N}}\right)}_{{\pi }^{-}}=1.7\mathrm{}\pm 0.4$ and ${\left(\frac{{}_{}{}^{15}{}_{}{}^{}\mathrm{O}}{{}_{}{}^{15}{}_{}{}^{}\mathrm{N}}\right)}_{{\pi }^{+}}=\frac{1}{(1.8\mathrm{}\pm 0.4)}$, indicating charge symmetry.

Strongly structured (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, $d$) angular distributions exhibiting systematic variations with $A$ for $A=40\mathrm{}$ to $A=90\mathrm{}$ target nuclei are well reproduced by $\alpha$-stripping calculations using a single set of potential parameters. Zero-range and finite-range distorted-wave Born-approximation results are found very similar both in the shapes of the angular distributions and in the relative magnitudes. The question of nuclear-structure dependence in the angular distributions is discussed.

In proton-nucleus interactions at 200 GeV in nuclear emulsion we have found that in the projectile region the multiplicity is independent of the target nucleus, while in the target region it is approximately proportional to the nuclear thickness. After carefully excluding the elastic and the coherent events, we find that the secondary particles produced in $p$-nucleus collisions obey the same Koba-Nielsen-Olesen scaling as found previously in $p-p$ collisions.

We have measured the polarization parameter and differential cross sections in $K^{+}p$ elastic scattering from a polarized target from small $\mathrm{}\left|t\right|\mathrm{}$ and small $\mathrm{}\left|u\right|\mathrm{}$ at five momentum points: 1.7, 2.1, 2.4, 2.7, and 3.0 GeV/c. The polarized-proton target was butanol cooled at 0.5° by a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ refrigerator; a combination of multiwire proportional chambers and scintillation counters detected the scattered particles. The results for small $\mathrm{}\left|u\right|\mathrm{}$ are discussed in the context of pure Regge-pole models with exchange-degenerate $\Lambda$ trajectories.

We present transverse-momentum distributions of ${\pi }^{-}\text{'}\mathrm{s}$ produced in the reaction $p_1{p}_2\to p_{3}X$ at 28.5 GeV/c observed by the Multiparticle Argo Spectrometer System. As the transverse momentum of the trigger proton $p_3$ is raised from 0.4 to 1.6 GeV/c we find that the shape of the ${\pi }^{-}$ momentum distribution normal to the ($p_1, p_3$) plane remains unchanged. The shape of the distribution in the plane is also relatively constant but the distribution shifts to balance transverse momentum.

We have searched for heavy penetrating particles produced in nucleon-nucleon interactions with incident energies between 30 and 300 GeV. From a study of the transverse-momentum range between 1.0 and 2.25 GeV/c at a laboratory angle of 91 mrad, we conclude that the Lorentz-invariant production cross section is less than 6.4×${10}^{-35\mathrm{}}$ ${\mathrm{cm}}^2$ GeV/${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^3$ for stable particles in the mass range 1 to 5 GeV/${\mathit{c}}^2$. For unstable particles this limit must be reduced, but because of the compact detector significant limits can still be achieved for lifetimes in the nanosecond region.

We suggest that the recently discovered long-lived particles $\psi \mathrm{}\left(3105\right)\mathrm{}$ and $\psi \mathrm{}\left(3695\right)\mathrm{}$ are members of a family of "colored" vector mesons. Our scheme is a natural generalization of SU(6) ⊗ SU(3)′. The narrow widths of these states are understood because of color conservation and the difficulty of radiating colored photons. The spectroscopy of these new colored states, which is very rich, is discussed along with predictions for photoproduction.

The $l^{+}{l}^{-}$ decays of the new narrow resonances are discussed as a good test of the hypothesis of asymptotic SU(4) and of the assignment of $\psi \mathrm{}\left(3105\right)\mathrm{}$ to an uncharmed member of the set of $1^{--}$ mesons belonging to the 15 ⊕ 1 dimensional representation of SU(4).

The space-time propagator for multichannel scattering is cast in the form of a Feynman path integral where the action is a matrix and the interactions are nonlocal in time. The $S$ matrix is evaluated in the semiclassical limit, leading to trajectories which naturally follow individual channel potentials in noninteracting regions and adiabatic-like ones in strongly interacting ones. A numerical example is provided for the curve-crossing problem, and the agreement with exact quantum results is good even when the interaction region is large and/or encompasses classical turning points.

Positrons in metals and positronium in quartz have been observed to thermalize down to nearly liquid-helium temperatures before annihilation. The achievement of such low temperatures by both positrons and positronium in approximately ${10}^{-10\mathrm{}}$ sec indicates that phonon scattering plays a major role in thermalization. These results have important implications for the ability to achieve high precision in Fermi-surface studies by the positron-annihilation technique.