Incorporation of capacitive discharge energy in the heat equation yields results consistent with some aspects of the observed behavior of threshold switching devices not only for the case in which all points on the $V-I$ curve are accessible, but also for the case in which abrupt switching at constant current is observed. The type of switching displayed by a given device is material dependent. We present a relationship for the prediction of device behavior.

It is shown that Lee's nonunique phase-shift parameters ${\eta }_l\left(\kappa \right)$, determined from the experimental Fermi surfaces of Cu and the alkali metals, can be transformed into a unique set of parameters consisting of logarithmic derivatives $L_l$ at corresponding atomic radii $S_l$. The physical significance of these parameters is discussed and it is shown that they give direct information about the conduction electrons in the metal.

We study the motion of electron-hole drops in pure Ge at 2°K. An analysis of their luminescence by a time- and space-resolved technique yields their diffusion coefficient (150 ${\mathrm{cm}}^2$ / sec) and their lifetime (40 μsec). We also measure the formation time (0.1-0.7 μsec) of drops containing about ${10}^6$ electron-hole pairs. A discussion of these new results is given.

A photoemission study of amorphous Si for $5.5<~\hslash \omega <~11.7$ eV has been made with emphasis placed on checking an earlier report of photoemission evidence for a tailing of the density of states into the energy gap. A comparison of photoelectron energy distribution curves from amorphous Si with those of Au and crystallized Si yielded no evidence for tailing of the density of states. It is concluded that the large tailing of the density of states previously reported is not an intrinsic property of amorphous Si but probably a result of the different sample preparation. In both our amorphous and crystallized Si films the Fermi level is located 0.28 ± 0.05 eV above the valence band maximum at the surface.

The appropriate measurements and interpretation for deciding on the existence of a tail in the density of states at the top of the valence band of amorphous semiconductors are described. The data presented clearly show the existence of such a tail. The magnitude of the latter depends on method of preparation and annealing. The tail is therefore attributed to short-range defects.

We have made a detailed study of the temperature dependence of the optical absorption of the parity- and spin-forbidden transitions ${}_{}{}^1{}_{}{}^{}T_{2g}^{}{}_{}{}^{}\left(t_{2g}{e}_g\right)$ in Ni${\mathrm{Br}}_2$ and ${}_{}{}^1{}_{}{}^{}T_{2g}^{}{}_{}{}^{}$, ${}_{}{}^1{}_{}{}^{}E_g^{}{}_{}{}^{}\left({t_{2g}}^2\right)$ in Ni${\mathrm{Cl}}_2$. It is proposed that the oscillator strength magnitude, its temperature dependence, and the band shape of both transitions are due to a strong electron-magnon interaction.

We propose a Zener-like model for narrow bands, which includes the intra-atomic Hund's-rule coupling of $d$ electrons. Each of Hubbard's split bands is then shown to split again into spin-polarized sub-bands, yielding ferromagnetism when the density of Zener electrons is low but yielding antiferromegnetism when the density increases.

A coincidence study of three-body breakup of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}+p$ and the $d+d$ system has been made with the multidetector system BOL at 69-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ energy and 26-MeV deuteron energy. Strong contributions from quasi two-body reactions (final-state interaction and quasifree scattering) are found. The Watson-Migdal theory and the plane-wave impulse approximation model do not consistently explain the data. The discrepancies are particularly striking where different two-body mechanisms overlap.

Precise transition probabilities have been measured for the first $2^{+}$ states of ${}_{}{}^{230,232}{}_{}{}^{}\mathrm{Th}$, ${}_{}{}^{234,236,238}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{238,240,242,244}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{244,246,248}{}_{}{}^{}\mathrm{Cm}$, and ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ by Coulomb excitation with 17- and 18-MeV $\alpha$ particles. Comparison is made with theoretical values. An excitation energy of 44.0 ± 0.5 keV was measured for the first excited level of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$.

A single low-lying $0^{+}$state is observed with about 15% of the ground-state strength in the reactions ${}_{}{}^{160,158,156}{}_{}{}^{}\mathrm{Gd}\mathrm{}(p,t)\mathrm{}{}_{}{}^{158,156,154}{}_{}{}^{}\mathrm{Gd}$ at 18 MeV. The change in shape at $N=88\mathrm{}$ is observed in the reaction ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}\mathrm{}(p,t)\mathrm{}{}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}$, with two excited $0^{+}$ states being strongly populated. A similar change in the Sm nuclei has been observed earlier. An excited $0^{+}$ state is observed in the reaction ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}\mathrm{}(p,t)\mathrm{}{}_{}{}^{150}{}_{}{}^{}\mathrm{Gd}$ with ∼10% of the ground-state strengths.

The correspondence between the upper fragment of the split electromagnetic giant dipole resonance and the parent dipole mode excited by muon capture is investigated for nuclei with a neutron excess. Results already found for light ($N=Z$) nuclei are extended to heavier ($N>Z$) nuclei, suggesting new types of experiments to demonstrate the isospin origin of this splitting.

We have made measurements of polarization in ${\pi }^{-}p$ elastic scattering, with emphasis over the backward region, at 1.60 to 2.28 $\frac{\mathrm{GeV}}{c}$. The results indicate the absence of $u$-channel dominance in the backward region, as was observed in the case of ${\pi }^{+}p$ scattering. Comparisons have been made with predictions of various phase-shift analyses which show that the agreement is generally very poor in the backward region.

The ${\pi }^{+}$ photoproduction cross section in hydrogen has been measured at 180° for photon energies from 0.22 to 3.1 GeV by detecting the pion in the backward direction. The statistical accuracy of the measurements varies typically from 3 to 10% depending on the energy. The data are compared with other recent experimental results and predictions of phenomenological theories.

The general form of the ${\tau }_1$ distribution function for favored and disfavored fragmentation is obtained from the fragmentation picture. The ${\mathrm{}(1-x)\mathrm{}}^{\beta }$ dependence for the ${\tau }_1$ function is found to be in very good agreement with existing experimental data.

We have measured fine-structure separations in some ${}_{}{}^3{}_{}{}^{}P$ states of He I ($n=3, 4, 5$) and Li II ($n=4, 5$) by observation of modulated light-intensity decay curves using the beam-foil technique.

Many-particle antisymmetric spin eigenstates are formulated in a manner that leads to simple expressions for expectation values of spin-independent many-particle operators. Explicit matrix elements are given for one- and two-particle operators.

Unidentified metastable autoionizing states of highly stripped and excited oxygen and fluorine ions have been observed and their energies measured. Possible assignments are discussed. Appreciable populations of identifiable lithiumlike states of high electronic spin and high excitation energy have also been observed and their energies compared with the results of variational calculations. The lifetime of a level identifiable as either $1s2p3p{}_{}{}^4{}_{}{}^{}P_{}^e{}_{}{}^{}$ or $1s2s4s{}_{}{}^4{}_{}{}^{}S_{}^e{}_{}{}^{}$ has been measured to be 1.00 ± 0.04 nsec.

A variational method is constructed for the Feshbach equations for scattering. An example is carried out on the $S$-wave electron-hydrogen system. It is shown that fast convergence of the phase shift can be obtained throughout the energy range of interest including the resonance region. No anomalous singularities have been encountered.

Although mode-locked lasers may often produce $\pi$ pulses, it is shown that this is not an inevitable consequence of mode locking. It is found for a mode-locked, three-mode He-Ne laser that different locking regimes do not produce pulses of unique area. The parameter $I{\tau }^3$ is shown to be constant only in certain relatively limited situations.

We show that if Fermi-liquid effects are neglected the perturbation calculation of Rice yields the same result as the Boltzmann-equation treatment of Bekarevich and Khalatnikov. By considering their limits of applicability the equivalence of the two approaches is established. There is, however, no a priori reason for neglecting Fermi-liquid effects which, through the existence of zero sound modes, are essential for understanding direct measurements of the acoustic impedance.