The intensities of $\gamma$ rays from ${\pi }^{-}$ absorption at rest on O, F, Mg, P, Ca, and Nb have been measured. The results are compared with those at 220 MeV, previously published. The $\alpha$ removal processes which have been reported to dominate at higher energies are not as pronounced in the present work.

It is pointed out that, in contrast to the case of $S$-wave two-body bound states, the size of a many-body bound state remains finite (irrespective of its angular momentum) even if its binding energy vanishes. Physical implications for barely bound many-body systems are outlined.

The bound $\left|{S_{\epsilon }}^{\mathrm{}\left(2\right)\mathrm{}}\right(f\otimes g\left)\right|<~\mathrm{const}{\mathrm{}\left|f\right|\mathrm{}}_{\mathcal{S}}{\mathrm{}\left|g\right|\mathrm{}}_{\mathcal{S}}$, uniform as the lattice spacing $\epsilon \to 0$, is sufficient to yield construction of a ${\varphi }^4$ field theory. In perturbation theory, this bound holds in spacetime dimensions $d<~4$. The bounds on the $n$-point Schwinger functions follow from the given bound by the use of Lebowitz's inequalities. They yield the growth $\left|S^{\mathrm{}\left(n\right)\mathrm{}}\right|<~O(n!)\mathrm{}$, consistent with the Osterwalder-Schrader axioms, which allow reconstruction of a real-time theory.

A white hole (a compact, long-delayed region of the big bang) cannot exist, because it suffers an exponentially growing instability that converts it into a black hole. Such instabilities might have homogenized the early universe.

A new integral formalism for gauge fields is described. Further developments are presented, including gravitation equations related to, but not identical with, Einstein's equations.

In exposures of the Argonne National Laboratory 12-ft bubble chamber filled with hydrogen and deuterium to a neutrino beam, we have observed events consisting of (1) a single ${\pi }^{+}$ meson originating in the liquid, and (2) a proton with an $e^{+}{e}^{-}$ pair pointing to it. Only a small fraction of these events can be ascribed to known reactions such as $\mathrm{np}\to \mathrm{nn}{\pi }^{+}$ and $\mathrm{np}\to \mathrm{np}{\pi }^0$. The remaining events, which correspond to a signal of about 4.5 standard deviations, we ascribe to the reactions $\nu p\to \nu n{\pi }^{+}$ and $\nu p{\pi }^0$.

We present a general formalism for calculating the renormalization effects which make strong interactions strong in simple gauge theories of strong, electromagnetic, and weak interactions. In an SU(5) model the superheavy gauge bosons arising in the spontaneous breakdown to observed interactions have mass perhaps as large as ${10}^{17}$ GeV, almost the Planck mass. Mixing-angle predictions are substantially modified.

In a large class of theories, including asymptotically free theories, and theories with an eigenvalue for the coupling constant, it is shown that under an important uniformity assumption, the electroproduction and inclusive annihilation structure functions should, for large $Q^2$, be Gaussian in the variable $y=\ln \omega$. The average and width of the distribution are increasing functions of $Q^2$. This result is compared with preliminary data from SPEAR on the one-particle inclusive distributions.

We report a direct measurement of the hyperfine splitting of the $5{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ state in sodium using a two-step excitation of an atomic beam with two cw tunable dye lasers. The linewidth obtained is 24 MHz and we measure a hyperfine splitting $\Delta \nu \left(5\mathrm{}{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\right)=159\mathrm{}\pm 6$ MHz, in good agreement with the theoretical value.

Exchange scattering has been directly observed in the excitation of the $6{}_{}{}^3{}_{}{}^{}P$ state of mercury by measuring the spin flip of polarized electrons. Between threshold and 8 eV exchange scattering dominates, resulting in a reversal of the direction of polarization of the scattered electrons. Above 8 eV the influence of exchange decreases rapidly for scattering in the forward direction.

We study the interaction of high-power microwaves with a magnetized plasma. Delayed emissions at cyclotron harmonics are observed after the termination of the pumping wave when the frequency of the pumping wave is equal to one of the harmonics of the cyclotron frequency and is near the plasma frequency.

A magnetized plasma column ($n_p<~6\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$) is heated by the injection of an intense relativistic electron beam along the magnetic field. The energy per electron-ion pair transferred to the plasma increases linearly with the beam-to-plasma density ratio $\frac{n_b}{n_p}$. The electron heating is attributed to the electron-electron beam-plasma interaction while the energetic ions are produced by an electrostatic acceleration. After heating, the plasma column oscillates radially at a frequency proportional to $\frac{B}{{n_p}^{\frac{1}{2}}}$.

The O'Neil trapping regime is known to take place only after a finite damping of the main wave. As a consequence of that finite damping, one obtains a beam-type distribution function for the detrapped particles. By including in the stability analysis this detailed distribution function, we give a new interpretation of the sideband generation.

We observe a low-frequency instability with $\omega \ll {\omega }_{\mathrm{ci}}$ in a steady high-density plasma ($n_0\simeq {10}^{13-14}$ ${\mathrm{cm}}^{-3\mathrm{}}$). This instability has components of magnetic field fluctuations as well as density fluctuations. By introducing the dispersion relation, the instability is interpreted as the coupled mode of the collisional drift wave and the Alfvén wave.

It is shown how Lawson criterion for controlled fusion might be achieved by magnetic compression of intense ion rings to field reversal.

This Letter reports the first direct observation of electron-hole drops (EHD) in germanium. An intense, focused laser beam creates a single, large EHD, whose shape and size are determined by the spatial distribution of its luminescence. The observed drops are spherical in shape with radii that increase from 0.25 mm to over 1 mm with increasing laser power. These results confirm size measurements of the EHD by recent decaykinetics and dimensional-resonance studies.

A model to explain dc electroluminescence in GaN diodes is presented. The voltage applied to the diode is partially localized at sharp points and ridges at the cathode. Electrons, tunnel-injected into the active material at the points and ridges, gain sufficient kinetic energy in the high field to cause impact excitation of the luminescent center either directly or indirectly (electron-hole-pair impact excitation across the GaN gap with subsequent hole capture by the luminescent center).

The first measurements of phonon frequencies in a metal as a function of temperature, at constant values of the atomic volume, are reported. The $\left[\zeta 00\right]\mathrm{T}$, $\zeta =0.2\mathrm{}$ mode exhibits considerable temperature dependence at constant volume, whereas modes in the $\left[\zeta 00\right]\mathrm{L}$, $\left[\zeta \zeta 0\right]\mathrm{L}$, and $\left[\zeta \zeta 0\right]\mathrm{T}1$ branches show little such dependence. The mode Grüneisen parameters are also determined.

By using a simple hydrogenic model, we are able to account for the magnitude, sign, and tensor character of the exciton contribution to the nonlinear optical susceptibility in CuCl and ZnO.

A new bond-charge model for phonons in semiconductors of diamond structure is presented. I show that the flattening of the transverse acoustic phonon branches in these materials can be understood by interactions involving the bond charges, when these move adiabatically. The phonon spectrum of Ge is calculated using only four parameters, all of which are physically meaningful, and very good agreement with experimental values is obtained.