It is shown that the resistive behavior of Pr${\mathrm{Sn}}_3$, namely a local maximum followed by a rather abrupt drop at low temperatures, is not solely due to the presence of magnetic ordering. This result is established by the resistive behavior of ${\mathrm{La}}_{1-x}{\mathrm{Pr}}_x{\mathrm{Sn}}_3$ where the salient resistive features persist even to values of $x$ for which $T_{\mathrm{N}}$ has been depressed to zero. An explanation in terms of inelastic scattering from crystalline-electric-field-split ion levels is presented.

The electrical resistivity of ${\mathrm{La}}_{1-x}{\mathrm{Pr}}_x{\mathrm{Sn}}_3$ compounds ($x=0.0, 0.1, 0.2, 0.4, \mathrm{and} 1.0$) has been measured between 1 and 300 K. A resistivity minimum is observed, which arises from a Kondo effect due to excited crystal-field levels of the praseodymium ion, the ground state being nonmagnetic. The plot of $\rho \left({\mathrm{La}}_{1-x}{\mathrm{Pr}}_x{\mathrm{Sn}}_3\right)-\rho \left(\mathrm{La}{\mathrm{Sn}}_3\right)$ versus $\ln T$ is approximately linear above 25 K.

The intrinsic lifetime width in x-ray photoemission spectroscopy, due to mixing decays, is shown to decrease rapidly as a function of the number of $4f$ electrons. In a system near configuration crossover, mixing decays may also strongly broaden (or render unobservable) ionic resonances at frequencies as low as the far infrared; this is illustrated by model calculations for Sm and Eu salts.

In a run with a predominantly $\overline{\nu }$ beam we have observed seven dimuon events which show clearly that dimuons are produced by $\overline{\nu }$ as well as by $\nu$. Using the signature of those events we tentatively identify twelve dimuon events from earlier runs as $\overline{\nu }$-induced. The characteristics of the total sample support the explanation that dimuons arise from new hadron production.

We have analyzed dimuon distributions due to the diffractive production of a new hadronic vector boson in neutrino scattering. Characteristic features that distinguish this mechanism from heavy-lepton-mediated dimuon distributions are presented.

We have for the first time located and identified a four-quasiparticle isomer in a deformed nucleus. Its energy may be used as a test for the effective interaction between quasiparticles. We can account for the energy quite well with a simple $\delta$-function interaction, but not with an interaction derived from Brueckner theory.

The 3.8% decrease in half-life of the 2.38-keV ${}_{}{}^{90m}{}_{}{}^{}\mathrm{Nb}$ isomer when Nb is converted from metal to a fluoride complex is one of the largest reported chemical effecs on the internal conversion process. We present experimental and theoretical evidence that this effect is not due, as had been conjectured, to the "switching off" of $L_3$ conversion through increased $L_3$ binding energy.

We measured the isotope shift of the $1S-2S$ transition in atomic hydrogen and deuterium to be 670.933±0.056 GHz, using Doppler-free two-photon spectroscopy with a frequency-doubled, pulsed, dye laser. The Balmer-$\beta$ line is simultaneously observed in saturated absorption with the fundamental dye-laser output. A comparison of the intervals $1S-2S$ and $2P_{\frac{3}{2}}-4\mathrm{}{D}_{\frac{5}{2}}$ determines the Lamb shift of the $1S$ ground state to be 8.20±0.10 GHz (H) and 8.25±0.11 GHz (D), in agreement with the theoretical values.

We present results of one-, two-, and three-dimensional calculations for the H + ${\mathrm{H}}_2$ exchange reaction which provide the first evidence for dynamical internal excitation (Feshbach) resonances in chemical reactions using noncollinear calculations. The change of the resonance energy and width with collision dimensionally and with total angular momentum is analyzed and indicates the existence of observable effects on certain reactive cross sections.

The $J=0\mathrm{}\to 1$ rotational transition of the HC${\mathrm{O}}^{+}$ ion has been observed with the same apparatus used earlier for detection of C${\mathrm{O}}^{+}$. A discharge in various mixtures of hydrogen and carbon monoxide cooled to near liquid-nitrogen temperature was employed in a slow-flow system. The frequency we have obtained is 89 188.545±0.020 MHz, but because of the ion drift velocity in the dc discharge this exceeds, by an unknown but small amount, the true rest frequency. This observation confirms the long-standing contention that the radio astronomical $X$-ogen line is in fact due to HC${\mathrm{O}}^{+}$.

I present a theory of the orientation and alignment of atoms observed upon emergence from tilted foils. The interaction with the foil surface is taken into account in the production process of particular states. Once they are produced, the evolution of these states, under the influence of the residual field near the surface, is calculated in the fashion introduced by Eck. The most general effect of this evolution is presented.

Saturation effects, occurring when a laser beam tuned close to a resonance propagates through an absorbing gaseous medium, were observed by means of a second beam sent in a nearly opposite direction. In addition to the well-known signal of saturated absorption, a signal directly related to the variation of the refractive index of the medium was observed. An experiment was performed to obtain simultaneously the signals of saturated absorption and saturated dispersion of iodine vapor.

We study experimentally the interaction of an electron beam modulated near the lower-hybrid frequency with a longitudinally magnetized inhomogeneous plasma. At high levels of beam modulation above a certain threshold, the beam pumps the parametric decay instability into the lower-hybrid wave and ion-acoustic wave, and correspondingly plasma heating takes place rapidly. The instability threshold is determined in a parameter space. These results are compared with theory, and reasonable agreement is obtained.

We have studied the behavior of several nematics in Couette flow with homeotropic boundary conditions. When Leslie's viscosity ${\alpha }_3>0\mathrm{}$, the director tumbles at a critical shear rate, $S_c$. When $S>\mathrm{}{S}_c$ a stable, stationary state is observed. When $S>\mathrm{}{S}_E>S_c$, the flow becomes cellular. We calculate $S_c$ and $S_E$. Knowing $S_c$, $S_E$, the shear viscosity ${\gamma }_1$, and the Frank elastic constants, it is possible to deduce separately the Leslie viscosities ${\alpha }_3$ and ${\alpha }_2$ when $\left|{\alpha }_2\right|>\mathrm{}{\alpha }_3>0\mathrm{}$.

The superfluid density of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ confined to porous Vycor glass has been determined from fourth-sound measurements over a temperature range from below 0.1 K to within 10 mK of the transition. For temperatures below 1.4 K the normal-fluid fraction can be described in terms of a roton contribution with gap $\frac{\Delta }{k_{\mathrm{B}}}=5.85\mathrm{}$ K and a "one-dimensional," $T^2$, phonon contribution. Near the transition temperature, $T_c=1.955\mathrm{}$ K, the superfluid density is found to vary as ${(T_c-T)}^{\zeta }$ with $\zeta =0.65\mathrm{}\pm 0.03$.

Defects introduced into superconducting Nb-Ge films by 2-MeV ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ particles produce a $T_c$-resistance-ratio correlation similar to that for as-grown films and a $T_c$-lattice-parameter correlation resembling both film and bulk behavior. It is suggested that simple antistructure defects in a perfect lattice are not primarily responsible for lowering $T_c$ for the case of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ damage in the sputtered films.

A model is discussed which for the first time provides a unified description of many electrical and optical properties of chalcogenide glasses. It is proposed that localized gap states are at dangling bonds, and that lattice-distortion effects are sufficiently strong that these states exhibit an effective negative electron-electron correlation energy.

We have observed a $\lambda$ anomaly in the nuclear heat capacity of a single crystal of praseodymium known not to order down to 1.8 K. The anomaly is associated with a cooperative magnetic ordering of the hexagonal-site nuclei at 25-30 mK of the type discussed by Murao. This result is in contrast to earlier calorimetric measurements where ionic order has precluded cooperative nuclear processes. The cooperative anomaly is suppressed by a field of 1.5 T.

Under fast optical excitation and with a fast detector we were able to resolve in time the onset and growth of the electron-hole liquid phase Ge. We found that the onset of luminescence was delayed by 35 nsec. Thereafter the luminescence increased to a quasisteady state with a time constant of 550 nsec and subsequently decayed with a 35-μsec time constant.

A method is developed which generates a class of nonlinear evolution equations in two and three spatial dimensions from an associated eigenvalue problem and its time dependence. Special cases include the equations describing nonlinear, resonantly interacting, wave envelopes in two and three dimensions; a "nonlinear Schrödinger" equation in two dimensions; and a two-dimensional analog of the Korteweg- de Vries equation.