A novel method for measuring the hyperfine interval $\Delta \nu$ of muonium in "zero" magnetic field is described. It consists in applying two successive coherent microwave pulses (lengths $\tau$, separation $T$) to muonium, and observing the change in muon polarization at $t>T+2\mathrm{}\tau$. By extrapolating two low-pressure runs in Kr we obtain $\Delta \nu \mathrm{}\left(0\right)=4463.3013\mathrm{}\left(40\right)\mathrm{}$ MHz, while a joint fit with earlier Chicago Kr data gives $\Delta \nu \mathrm{}\left(0\right)=4463.3012\mathrm{}\left(23\right)\mathrm{}$ (0.5 ppm). With $\frac{f_{\mu }}{f_p}=3.183\mathrm{}338\left(13\right)\mathrm{}$ this implies (a) ${\alpha }^{-1}-137=0.036\mathrm{}19\left(30\right)\mathrm{}$ (2.2 ppm) and (b) a proton polarizability ${{\delta }_N}^{\mathrm{}\left(2\right)\mathrm{}}=-(4\mathrm{}\pm 4)$ ppm.

The very precise, low-pressure measurements of the hfs interval $\Delta \nu \mathrm{}\left(p\right)\mathrm{}$ of muonium in Ar and Kr described in the preceding Letter are combined with the high-pressure measurements from Yale to determine the magnitude of quadratic pressure shifts. Fitting by the form $\Delta \nu =\Delta \nu \mathrm{}\left(0\right)[1+ap+b{p}^2]$, we find $b\left(\mathrm{Ar}\right)=7.1\mathrm{}\left(2.3\right)\mathrm{}$ and $b\left(\mathrm{Kr}\right)=8.7\mathrm{}\left(3.1\right)\mathrm{}$ (in units of ${10}^{-15\mathrm{}}$ ${\mathrm{Torr}}^{-2\mathrm{}}$). Older evidence for these quadratic shifts from similar fits involving earlier Chicago data is reviewed.

We report two new results concerning the propagation of electromagnetic waves with a strength parameter $\nu =\frac{\mathrm{eE}}{m\omega c}$ sufficiently large ($\nu \gg 1$) to cause relativistic electron velocities. The first is an analytic solution of the nonlinear equations for linearly polarized waves in a uniform medium. The second is that propagation in a nonuniform medium increases the nonlinear penetration effect; the maximum nonrelativistic plasma frequency ${\omega }_p$ which allows transmission of a strong wave is ${{\omega }_p}^2\approx {\left(\frac{\omega L}{c}\right)}^{\frac{1}{2}}\frac{e{E}_i\omega }{\mathrm{mc}}$, where $L$ is the density-gradient scale length and $E_i$ the electric field in the absence of a plasma.

The mobility of electrons on the surface of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been measured from 0.9 to 3.2°K. Although scattering from atoms in the vapor appears to be the dominant scattering mechanism, the mobility of the surface electrons is significantly lower than that of free electrons in the vapor. No evidence for surface-wave scattering is discernible.

It is shown that large-amplitude linearly or elliptically polarized Alfvén waves propagating parallel to ${\overrightarrow{\mathrm{B}}}_0$ can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfvén wave. The damping rate can be large even in a cold plasma ($\beta \ll 1$, but not zero), and the mechanism which we propose may be the dominant one in many plasmas of astrophysical interest.

A complete set of time-dependent Ginzburg-Landau equations are solved to find the current, charge, and field distributions when the vortices in a superconductor are forced into motion by a transport current. We find that in general the local electric field is not proportional to the local magnetic field and backflow is an essential feature.

A slight modification of the "mixing" term in Anderson's model of a magnetic impurity produces an exactly solvable model. Results of some preliminary calculations are given, and upper and lower bounds on Anderson's model are obtained by means of the exact solutions.

The ground-state energy of an exciton bound to ionized donors in III-V and II-VI compounds is calculated with the electron-phonon coupling taken into account. Results for thirteen crystals are in very good agreement with the available experimental data.

A new model is proposed in which the observed magnetoresistance curves for potassium are qualitatively analyzed as a synthesis of four superposed behaviors: (1) a phonon saturating behavior exhibiting the predicted temperature dependence for umklapp scattering, (2) a new residual saturating behavior due to impurities and defects, (3) a negative saturating behavior agreeing quantitatively with size-effect theory, and (4) a newly identified low-field quadratic behavior which becomes asymptotically linear at high fields due to macroscopic inhomogeneities.

The bound electron states associated with higher-valence impurities in alkali-metal solvents are calculated by using Hartree-Fock-Slater methods and a dielectric approximation to the electron-gas response. The core diamagnetism and the conduction-electron magnetism together provide a quantitative account of the observed giant diamagnetism.

Electron paramagnetic resonance of ${\mathrm{Eu}}^{2+}$ in various samarium chalcogenides and ${\mathrm{Mn}}^{2+}$ in SmTe have been observed. The $g$ values are shifted by as much as 10% from their usual values near $g=2\mathrm{}$. The large $g$ shifts are described in terms of the impurity-samarium exchange interactions.

The cathodoluminescence spectrum of magnetite indicates optical transitions which correspond to energy separations of 2.6 and 3.2 eV. These luminescence data, coupled to the available optical absorption and soft x-ray data, lead to the first proposed semiquantitative band model for this material.

In a heat-pulse experiment performed at liquid helium temperatures in InSb samples containing a few times ${10}^{17}$ electrons per ${\mathrm{cm}}^3$, we have observed a strong attenuation of the longitudinal phonon pulse and no attenuation of the transverse pulses. Both these observations are related to basic properties of the electron-phonon interaction.

A new technique was used for the study of the reflectivity on KI, NaI, and KBr in vacuum ultraviolet; the cleavage of the samples was done in liquid helium at 1.8°K, avoiding any pollution of the surface. With this method we observed new structures and, in particular, for the first time the pure triplet exciton state predicted a few years ago by Onodera and Toyozawa.

Multiple NMR spin echoes, up to 22, have been observed for a two-pulse excitation. Possible explanations of this effect are proposed.

We have studied the phase transitions of magnetic systems with large biquadratic interactions in the molecular-field approximation. Quadrupole and dipole phase transitions occur at different temperatures whenever the biquadratic interactions are greater than the bilinear terms for effective spin interactions with $\mathcal{S}>~\frac{3}{2}$. For isotropic or Ising-like interactions with $\mathcal{S}=1\mathrm{}$ there is only a quadrupole phase transition when the biquadratic interactions are larger.

The pnictides, a series of rare-earth group-V intermetallic compounds, have the unique property that these cubic materials distort 2-3°K above the Néel point. We are able to explain this unusual behavior by using a model in which the lattice distortions are driven by quadrupole phase transitions which occur at higher temperatures than the magnetic phase transitions.

The photoelectron spin polarization in Ni has been estimated numerically using an interpolated band structure and assuming direct optical transitions. In the experimental energy range of Bänninger et al., agreement is obtained for the sign but not the magnitude of the polarization. Detailed predictions for the polarization as a function of both electron energy and photon energy are also presented and display striking variations.

The reaction ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}({}_{}{}^6{}_{}{}^{}\mathrm{Li},\alpha d)$ ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ was studied at $E_{{}_{}{}^6{}_{}{}^{}\mathrm{Li}}=24\mathrm{} \mathrm{and} 27$ MeV by observing $d-\alpha$ coincidences for particles emitted into the same solid angle. At $E_{{}_{}{}^6{}_{}{}^{}\mathrm{Li}}=24\mathrm{}$ MeV the reaction proceeds predominantly by a sequential process of Coulomb excitation of the 2.184-MeV, $J^{\pi }=3^{+}$ state, followed by breakup into $\alpha$ and $d$. When the strong dipole polarization of the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ projectile is taken into account, a $B(E2;1^{+}\to 3^{+})=24\mathrm{}{e}^2$ ${\mathrm{fm}}^4$ is found, in good agreement with a recent ($e,e^{\prime }$) experiment.

The two-nucleon data in the energy range 290-350 MeV are found to contain an additional solution to the one recently reported by MacGregor et al. Potential models are much closer to this additional solution. Experiments are proposed for deciding between the two solutions.