The fourth-order radiative correction to the slope at $q^2=0\mathrm{}$ of the Dirac form factor of the free-electron vertex is calculated using computer techniques. The result, $m^2\frac{\partial {F_1}^{\mathrm{}\left(4\right)\mathrm{}}\mathrm{}\left(0\right)\mathrm{}}{\partial q^2}={\left(\frac{\alpha }{\pi }\right)}^2[0.48\mathrm{}\pm 0.07],$ disagrees with previous calculations, and implies a new theoretical value for the order ${\alpha }^2{\left(Z\alpha \right)}^{4}m{c}^2$ contribution to the Lamb shift. The new values for the $2S_{\frac{1}{2}}-2\mathrm{}{P}_{\frac{1}{2}}$ separation in H and D are increased by (0.35 ± 0.07) MHz and are in good agreement with the results of recent experiments.

Mössbauer spectra obtained with carefully annealed sources consisting of ${\mathrm{Ga}}^{67}$ in ${\mathrm{Zn}}^{66}$O and with ${\mathrm{Zn}}^{67}$O absorbers show a well-resolved hyperfine structure that can be attributed to equal quadrupole splittings in source and absorber, with coupling constants $e^{2}qQ=2.47\mathrm{}\pm 0.03$ MHz. The resonant absorption for the strongest line of the spectrum ranges from about 0.15 to 0.55% and its linewidth from 2.7 to 5 times the natural width $2{\Gamma }_0$. A pressure of about 40 kbar applied to the source gives rise to about an 8% reduction in its quadrupole coupling constant.

We have used a three-terminal capacitor incorporated in a flow vessel to search for the theoretically predicted difference in the thickness $\Delta d$ between the moving and the static saturated He II film. The observations indicate that $\Delta d=0\mathrm{}$ to within a few Å.

Various experiments, especially recent experiments by Keller, clearly demonstrate that the thickness of a helium film is independent of the flow rate $Q$. This is consistent with our current picture of the hydrodynamics of a helium film if there are temperature gradients in the film which produce a thermodynamic potential ${\varphi }_T=\int \mathrm{SdT}$ that cancels the $\frac{{\rho }_S{v_S}^2}{2\rho }$ term in the hydrodynamic potential $\mu$. If such temperature gradients exist, they would produce unacceptably large evaporation rates unless the saturated vapor pressure $p_{\mathrm{vap}}$ is a function of $\mu$ rather than $T$. If $p_{\mathrm{vap}}=p_{\mathrm{vap}}\left(\mu \right)$, then there should be no thinning of the film with changes in $Q$, and the theory is in complete agreement with Keller's results.

The influence of ac fields on liquid-crystal mixtures of the nematic anisylidene-$p-n$- butylaniline (ABUTA) and the cholesteric oleyl cholesteryl carbonate was investigated. It was established that the cholesteric Grandjean plane texture could be induced with fields of the order of 2.5×${10}^5$ ${\mathrm{V}}_{\mathrm{rms}}$/cm at frequencies above 0.1 kHz for samples containing 40% ABUTA. With larger ABUTA contents the frequency required to produce the Grandjean texture increased.

Rapid electron heating by two counterstreaming ion beams has been observed in computer experiments. The results are compared with the predictions of quasilinear theory and found to be in substantial agreement.

The energy distribution $N_i\left(E_i\right)d{E}_i$ of the recoil atoms within polycrystalline targets of Al, Ti, Ni, Cu, and Ag under bombardment with ${\mathrm{Ar}}^{+}$ ions of 900 eV are deduced from the measured energy distributions of neutral sputtered particles in the energy range below 20 eV. It is found that $N_i\left(E_i\right)\sim {\left(\frac{E_i}{S}\right)}^{-2\mathrm{}}$, where $S$ describes the binding energy within the bombarded solid.

Four-photon stimulated scattering has been observed in borosilicate glass under high-power 5300-Å picosecond-pulse excitation. Parametric emission is generated from 4000 to 7000 Å from filaments formed in the glass, the wavelength depending on the emission angle.

A peak has been reported in the thermal conductivity (and hence the Lorenz function) of Cr at the Néel temperature. The investigators reporting this effect have ignored a considerable body of previous results on several chromium specimens. None of the previous results indicate a peak in the thermal conductivity. We feel that the effect is suspect and may be associated with defects in experimental technique.

A photostimulated channel for tunneling in GaAs tunnel diodes is described and identified with the presence of Au impurities on the $n$ side of the space-charge region. The mechanism for the impurity-assisted tunneling is identified with an inelastic excitation of the electronic states associated with the Au impurities.

Frequency broadening and small-scale filaments were observed in calcite, quartz, sodium chloride, and several glasses under picosecond pulse excitation. The physical mechanism responsible for these processes is the change in refractive index resulting from electronic distortion.

The electronic spectrum of amorphous Ge is examined in view of the recent Letter of Brust. Using Brust's calculations, it is shown that even a partial retention of $\overrightarrow{\mathrm{k}}$ as a quantum number results in prediction of a strong modulation in photoemission energy-distribution curves. Such moducation is not found experimentally. It is concluded that there is no evidence that $\overrightarrow{\mathrm{k}}$ is a meaningful quantum number in this amorphous material and that the density of states of the amorphous and the crystalline materials differ quite significantly. It is pointed out that Brust's model should be particularly useful in examining the amorphous-to-crystalline transformation.

Bulk magnetic measurements indicate that polarization clouds with giant moments ($\sim 10{\mu }_{\mathrm{B}}$) persist well into the paramagnetic composition range of Ni-Cu alloys.

A two-center shell model with oscillator potentials, $\overrightarrow{\mathrm{l}}·\overrightarrow{\mathrm{s}}$ forces, and ${\overrightarrow{\mathrm{l}}}^2$ terms is developed. The shell structures of the original spherical nucleus and those of the final fragments are reproduced. For small separation of the two centers the level structure resembles the Nilsson scheme. This two-center shell model might be of importance in problems of nuclear fission.

We have measured the energy distributions of fission fragments following formation of muonic and pionic ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. We have confirmed earlier results on the mean lives for muon capture by ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and extended the study to ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$. Additional data have also been obtained on the process whereby a muon induces fission by transferring its excitation energy to the nucleus in a radiationless transition to the $1s$ level.

For nuclei with $N>Z$, isospin invariance is explicitly broken in the Hartree-Fock (HF) approximation. It is shown that isospin polarization correlations in the HF ground state restore this symmetry and lead to a natural framework for a microscopic description of analog states. We discuss the approximations under which the Lane potential model is obtained.

The evolution of an elongated rotating configuration by gravitational radiation and the possibility of a secular instability being induced by it are considered in the context of the classical homogeneous figures of Maclaurin and Jacobi. The triaxial Jacobian ellipsoid evolves in the direction of increasing angular velocity and approaches (exponentially) the point of bifurcation where it ceases to radiate. Further, radiation reaction does not make the Maclaurin spheroid secularly unstable past the point of bifurcation.

Results of a phase-shift analysis with and without the use of a Regge-pole model in $K^{+}p$ elastic scattering from 0.86 to 1.95 GeV/c are described. We have obtained four possible solutions, all of which indicate resonantlike behavior in one partial-wave amplitude. Three of our solutions yield a $P_{\frac{3}{2}}$ partial wave with a behavior consistent with the Breit-Wigner resonance formula. The properties of such a $Z^{*}$ resonance are described.

Evidence for structure near the ${\omega }^0$ mass in the (${\pi }^{+}{\pi }^{-}$) mass spectrum from the reaction $\overline{p}p\to 2{\pi }^{+}2{\pi }^{-}$, at incident momenta from 1.26 to 1.65 GeV/c, is presented. We interpret this structure as arising from $\rho -\omega$ interference in the $2\pi$ decay mode, with a statistical significance of about 3.5 standard deviations. The effect can be well fitted by a partial width $\Gamma (\omega \to 2\pi )$ in the range 0.18 to 5.3 MeV (95% confidence level). Alternatively, if $\Gamma (\omega \to 2\pi )$ is taken from $e^{+}{e}^{-}$ colliding-beam results, our data can be used to study both the relative phase and coherence of $\rho$ and $\omega$ production in $\overline{p}p$ annihilation.

The effects of the cuts correction to Regge-pole amplitudes is investigated at intermediate energies. It is shown that, as a consequence of this correction, "resonance" bumps appear in total cross sections.