Using optical detection, we have observed rf nutation, free-induction decay, and echoes, on the 16.70-MHz nuclear hyperfine transition of dilute ${\mathrm{Pr}}^{3+}$ in La${\mathrm{F}}_3$ at 2 K. From a comparison of free-induction decay and echo decay we find that the previously observed linewidth of 200 kHz is inhomogeneous and that the homogeneous width is 19 kHz. On the basis of these measurements it is suggested that optical dephasing times for the ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\leftrightarrow {}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}\leftrightarrow {}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ transitions are as long as ∼20 μ sec.

The spin-lattice relaxation time ($T_1$) of the interstitial ${\mu }^{+}$ spin in the paramagnetic phase of a weak itinerant-electron helimagnet MnSi has been measured near the magnetic-ordering temperature in a 700-Oe longitudinal magnetic field. The observed temperature dependence of $\frac{1}{T_1}$ is represented very well by $\frac{T}{(T-T_c)}$ which was predicted on the basis of the self-consistent renormalization theory of spin fluctuations in itinerant-electron ferromagnets.

A resonancelike structure has been reported in the frequency spectrum of light emitted from small-particle tunnel junctions. Here we present a calculation of the frequency-dependent dipole moment and the radiation emission spectrum for a small particle located above a metal film. The dipole moment exhibits a resonance structure associated with a localized surface plasma mode at a frequency corresponding to the peak in the structure observed in the emission spectra.

We present for the first time two-photon measurements on rutile Sn${\mathrm{O}}_2$. The detailed polarization analysis yields ${{\Gamma }_3}^{+}$ symmetry for the direct forbidden $1S$ exciton and the upper valence band. Our results clear up the long-standing controversy concerning the symmetry of the upper valence band.

We report Raman scattering measurements on the $E_{\mathrm{g}}$ (${{\Gamma }_{12}}^{+}$) optical phonon measured from 50-340 K on a single crystal of ${\mathrm{V}}_3$Si. This phonon line has an anomalous width, shape, and temperature dependence, suggesting direct coupling between the phonon and electronic excitations.

The lowest-energy defects in tetrahedrally bonded amorphous semiconductors, in particular silane-decomposed films, are analyzed semiquantitatively. The creation energy and effective correlation energy of each defect center are estimated. It is concluded that twofold-coordinated atoms play an important role in these films. The lowest-energy center yielding an EPR signal is not a dangling bond but a positively charged twofold-coordinated atom. The results explain the observed peaks in the density of localized states and the mechanism for the doping of these materials by P and As.

Two independent quark-model predictions of the $\Lambda$ magnetic moments, in agreement with one another and with experiment to 1%, are obtained by using two different inputs for SU(3) breaking in quark masses: (1) $\left(\frac{m_s}{m_u}\right)=\frac{(M_{{\Sigma }^{*}}-M_{\Sigma })}{(M_{\Delta }-M_N)}$; and (2) $m_s-m_u=M_{\Lambda }-M_N$. I discuss the implications of the surprising sucess of a description of quark magnetic moments as Dirac moments with quark masses related so simply to hadron masses.

We present measurements of the proton-proton elastic differential cross section for $1.0<\mathrm{}\left|t\right|<2.0\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ and incident proton momenta between 30 and 250 GeV/c. The minimum in the cross section near $t\simeq -1.5\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ develops monotonically with increasing incident proton momentum and the cross section remains nonzero up to our highest incident momentum of 250 GeV/c. The cross section at the second maximum near $t\simeq -1.8\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ falls with increasing incident momentum up to 210 GeV/c after which it starts to rise.

The action of conformal transformations on gauge potentials can be defined in a gauge-covariant fashion. This unconventional procedure is used in several branches of theoretical physics, with the consequence that gauge potentials do not transform according to a representation of the conformal group; rather, they provide a representation for the "group of paths" of the conformal group. The nonintegrable phase factor is central to the construction.

The cross section of ${}_{}{}^4{}_{}{}^{}\mathrm{He}(p, d){}_{}{}^3{}_{}{}^{}\mathrm{He}$ at $\theta =22.5\mathrm{}°$ has been measured between $T_p=200\mathrm{} \mathrm{and} 500$ MeV, which together with previous data provides the first excitation function for the ($p, d$) reaction up to $T_p=700\mathrm{} \mathrm{MeV} \mathrm{and} 0.7 \mathrm{GeV}/c$ momentum transfer. The energy variation is found mainly to reflect a strong dependence upon momentum transfer. Using known nuclear wave functions we examine the contributions from ordinary neutron pickup and certain multinucleon reaction mechanisms.

The transverse electromagnetic form factors squared of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ $2^{+}$ levels at 4.439 MeV ($T=0\mathrm{}$) and at 16.107 MeV ($T=1\mathrm{}$) have been measured by means of 180° electron scattering over a momentum-transfer range from $q=0.51\mathrm{} \mathrm{to} 2.05$ ${\mathrm{fm}}^{-1\mathrm{}}$. Evidence is presented for appreciable contributions of nuclear convection currents to the transverse 4.439-MeV form factor at low $q$, and spin magnetization contributions to the transverse 16.107-MeV form factor at higher $q$.

A systematic study of the deep-inelastic electron-scattering response function of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been carried out at scattering angles of 60° and 130° and electron energies between 160 and 520 MeV. A pronounced transverse strength, the origin of which is not understood, is found in the region between the quasielastic and the $N$ peak.

Using a three-step laser-excitation process we have selectively excited each of the four autoionizing ${(6\mathrm{}{p}_j, 20s_{\frac{1}{2}})}_J$ states of barium although the ${(6\mathrm{}{p}_j, 20s_{\frac{1}{2}})}_{j\pm \frac{1}{2}}$ pairs are separated by less than their autoionization linewidth. The energy and linewidth of each of the states have been measured. The ${(6\mathrm{}{p}_{\frac{1}{2}}, 20s_{\frac{1}{2}})}_1$ state has an anomalous width which implies that it autoionizes primarily into excited ${\mathrm{Ba}}^{+}$ ${\mathrm{Ba}}^{+}\left(6\mathrm{}{p}_{\frac{1}{2}}\right)$ ions.

We have measured the wavelengths of the $2s{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-2p{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ and $2s{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-2p{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ transitions in Cl xvi to be 613.825±0.013 Å and 705.854±0.076 Å. Our precision is sufficient to provide measurements of the $2s_{\frac{1}{2}}-2\mathrm{}{p}_{\frac{1}{2}}$ and $2s_{\frac{1}{2}}-2\mathrm{}{p}_{\frac{3}{2}}$ Lamb shifts to an accuracy of ±0.3% and to test quantum electrodynamics (QED) theory in the strong-field region. We compare our results with the one-electron QED theories of Mohr and Erickson and discuss the accuracy of calculations of electron correlation in two-electron atoms.

In the presence of the baroclinic vector, $\nabla n\times \nabla p$, vortices may be generated in a plasma. Formation of a stationary vortex is essential to the creation of a magnetic field. Examples of exact stationary vortex solutions and the conditions of existence of such solutions are presented. The vortex has a linear scale of $\frac{c}{{\omega }_{\mathrm{pi}}}$ which is modified nonlinearly by the Mach number of the vortex flow.

Stage-III recovery in copper after electron and proton irradiation and after quenching is investigated by observation of perturbed $\gamma \gamma$ angular correlations. Two different types of intrinsic defects can be trapped at the radioactive impurities. The identity of the defects trapped after different damaging conditions proves that the recovery in stage III is mainly caused by two types of mobile defects, a monovacancy and a small vacancy complex, the latter being more mobile than the monovacancy.

Rules governing intensity features of selective adsorption data are derived. Minima or mixed maxima-minima in the specular intensity are predicted for resonant channels that strongly couple to the specular, and maxima for resonance states that couple only indirectly to the specular. These rules, which facilitate the identification of resonance positions and intensity features, are corroborated by available experimental data. Resonance shifts are also calculated. The characteristic asymmetric splitting of overlapping resonances is accounted for.

We show by application to Si that polarimetric measurements on radiation reflected nonspecularly from rough surfaces can distinguish between geometric-optics (facet or tangent-plane) and Rayleigh-Fano (random diffraction grating) scattering models, thus providing new details about surface roughness. A class of macroscopically rough but microscopically smooth surfaces is found that gives accurate specular ellipsometric data while being unsuitable for reflectance measurements.

I report implementation of the coherent-potential approximation for obtaining the electronic density of states and component charge densities in disordered muffin-tin alloys. Illustrative results for ${\mathrm{Cu}}_x{\mathrm{Ni}}_{1-x}$ are presented. The extent to which the self-consistency in treating disorder influences the electronic spectrum is considered.

Angle-resolved spectra for emission in a mirror plane as a function of emission angle and photon energy $h\nu$ show critical-point behavior in interband intensities for transitions on zone boundaries. For such transitions, the absolute energies $E$ and crystal momentum $\overrightarrow{\mathrm{k}}$ for both the initial and final states are given by $h\nu$ and the emission angle. $E\left(\overrightarrow{\mathrm{k}}\right)$ dispersions have been determined for several $d$ bands and conduction bands along the $\Delta$, $\Lambda$, and $\Sigma$ axes of copper.