The critical current $J_c$ of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ through 0.8-μm-diam channels has been measured. For small currents the pressure difference $\Delta P=0\mathrm{}$ along the flow channels within the resolution, implying small or zero dissipation. $\Delta P$ grows rapidly with increasing current above $J_c$; a clear transition to dissipative flow is thus observed. The temperature dependence of $J_c$ indicates that the superfluid density and the critical temperature are reduced inside the narrow flow channels.

New data are reported for liquid xenon shock compressed to a pressure of 130 GPa (1.3 Mbar), a molar volume of 13.7 ${\mathrm{cm}}^3$/mole, and a calculated temperature of 29 000 K. The data are consistent with the theory of Ross and McMahan, which indicates that xenon undergoes an insulator-to-metal transition at 9 ${\mathrm{cm}}^3$/mole at about 130 GPa or greater at 0 K. The minimum molar volume achieved in these experiments corresponds to a pressure of 60 GPa on the 0-K isotherm.

dc magnetization measurements at millikelvin temperatures on dilute ZnMn, CdMn, and MgMn single crystals show that in accordance with the sign of the single-site anisotropy $D$, ZnMn is "Ising-like," i.e., the Mn moments lie parallel to the $c$ axis. CdMn is "$X-Y$-like" with the easy axis in the basal plane. MgMn is isotropic, "Heisenberg-like." Dominance of spin-orbit scattering leads to a qualitative understanding of the anisotropy.

A lattice model of a $d$-dimensional disordered system is considered. The model is studied by a Migdal-Kadanoff renormalization-group transformation. In particular, localization in a macroscopically inhomogeneous medium is considered, and it is demonstrated that macroscopic disorder (above the percolation threshold) does not affect the critical exponents of the Anderson transition.

$4f^7\rightleftarrows 4f^6+e$ charge fluctuations (inferered from ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ Mössbauer spectroscopy) in Eu${\mathrm{Pd}}_2$${\mathrm{Si}}_2$ show a strong nonlinear thermal dependence when compared to those observed in dilute Eu in La${\mathrm{Pd}}_2$${\mathrm{Si}}_2$. This nonlinear behavior is well described by extending the interconfigurational fluctuation model to include a cooperative intersite coupling of the interconfigurational fluctuation excitation energy to the $4f$ occupation number. Eu nuclear vibrational damping occurs in the region of greatest charge instability.

Periodic oscillations in the luminescence spectra of amorphous hydrogenated carbon are reported. The period of these oscillations is 0.185 ± 0.010 eV, which is equal to the C-H wagging-mode energy. These oscillations are a function of the photoexcitation energy $E_{\mathrm{ex}}$; they appear when $E_{\mathrm{ex}}<~2.16$ eV and are absent when $E_{\mathrm{ex}}>~2.60$ eV, suggesting that localized electron-hole pairs are created by the former and extended states by the latter.

A new equilibrium characterization of the spin-glass-paramagnet transition is presented. It is based on the size dependence of the sensitivity of the free energy to the boundary conditions. Results of numerical studies of a three-dimensional Heisenberg spin-glass at $T=0\mathrm{}$ are consistent with an algebraic decay of this sensitivity and suggest a zero-temperature phase transition.

It is proved that under any time-periodic Hamiltonian, a nonresonant, bounded quantum system will reassemble itself infinitely often in the course of time. To illustrate these results computer experiments are performed on both a pulsed quantum rotor and an electron in the field of periodic electromagnetic pulses.

A bifurcation diagram for a driven nonlinear semiconductor oscillator is measured directly, showing successive subharmonic bifurcations to $\frac{f}{32}$, onset of chaos, noise band merging, and extensive noise-free windows. The overall diagram closely resembles that computed for the logistic model. Measured values of universal numbers are reported, including effects of added noise.

Some of the most sensitive tests of time-reversal invariance in particle and nuclear physics involve the measurement of certain polarization quantities in elastic scattering which are thought to be exactly zero when time-reversal invariance holds. It is shown that a nonzero result for such quantities need not indicate a violation of time-reversal invariance, but can be the consequence of a dynamics which is time-reversal invariant but which violates rotation or Lorentz invariance. These two alternatives can be told apart by subsidiary measurements.

A direct test is presented of higher-order QED (${\alpha }^4$) at large momentum transfers (up to ∼100 Ge${\mathrm{V}}^2$). These tests were carried out with the MARK-J detector at PETRA by comparing the measured cross section for the process $e^{+}{e}^{-}\to e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$ with the prediction of QED for $12 \mathrm{GeV}<~\sqrt{s}<~36.7 \mathrm{GeV}$. The cross sections and the various kinematic distributions agree with QED.

Parity nonconservation in $p\alpha$ scattering has been studied by comparing the cross sections ${\sigma }^{+}$ and ${\sigma }^{-}$ for longitudinally polarized 46-MeV protons of positive and negative helicity. The longitudinal analyzing power is found to be $A_z=(0.3\mathrm{}\pm 1.3)\times {10}^{-7\mathrm{}}$. This result, together with earlier measurements on parity nonconservation in $\mathrm{pp}$ scattering, gives new limits for the weak pion-nucleon coupling constant.

The differential cross section for $\gamma d\to \mathrm{pn}$ has been measured in the energy range between 180 and 600 MeV at c.m. angles 15°, 30°, 42°, and 72°, by using tagged photons. The results, in particular at smaller angles, are in disagreement with theoretical calculations which take into account the effect of dibaryon resonances.

The ${\pi }^{+}$ production in $85A$-MeV C+C and C+Au reactions has been studied for $20 \mathrm{MeV}<~E_{\pi }<~80 \mathrm{MeV}$ and ${\theta }_{\mathrm{lab}}>55\mathrm{}°$. The cross sections, $\frac{d^2\sigma }{d\Omega \mathrm{dE}}$, fall exponentially with $E_{\pi }$ and are 9 times larger for C+Au than for C+C. The angular distribution is backward peaked for C+Au in the nucleon-nucleon c.m. system, while it is weakly forward peaked in the nucleus-nucleus c.m. system. An independent nucleon-nucleon scattering model can explain the data only if diffuse internal momentum distributions are introduced.

Measurements have been made of spectra of electrons resulting from autoionization of a doubly excited quasimolecular state in a ${\mathrm{Li}}^{+}$-He collision. An isolated peak is observed beyond the classically accessible energy region of the backward electron emission. The occurrence of this peak is interpreted as due to a new type of interference among the probability amplitudes of the ejected electrons.

The pulse velocity in the linear regime in samples of GaP: N with a laser tuned to the bound $A$-exciton line is measured with use of a picosecond time-of-flight technique. The pulse is seen to propagate through the material with little pulse-shape distortion, and with an envelope velocity given by the group velocity even when the group velocity exceeds 3×${10}^{10}$ cm/sec, $\mathrm{equals}\pm \infty$, or becomes negative. The results verify the predictions of Garrett and McCumber.

A limit to the ratio of central-cell to plug $\beta$ of 1.8±1.0 is measured in the Phaedrus tandem mirror for central-cell $\beta \text{'}\mathrm{s}$ of 2% to 5%. This is consistent with the limiting ratio of 2.0 predicted for interchange stability, and is the first experimental test of the effect on the interchange limit from varying the plasma pressure along a magnetic field line in a tandem-mirror configuration.

Confinement of a plasma initiated and heated by electron cyclotron-resonance-frequency waves has been studied in the Heliotron-E. The observed plasma parameters were $T_e=500-100\mathrm{}$ eV, $T_i\simeq 100$ eV, ${\overline{n}}_e=4\mathrm{}\times {10}^{12}$ ${\mathrm{cm}}^{-3\mathrm{}}$ at $B=10\mathrm{}$ kG. The electron energy decay time was 40±8 msec and the particle confinement time was estimated to be more than 70 msec. These results offer a considerable improvement in energy confinement over Ohmically heated plasmas.

An experimental study of the injection of a intense relativistic electron beam into a plasma confined in a toroidal magnetic field is described. An increase in toroidal current after beam injection was observed and is argued to be the result of both beam-induced and additional Ohmic-heating-driven plasma currents. Typical current-drive efficiencies (beam net current to injected-beam current) of (10-30)% were observed.

Periodic spinodal decomposition can be realized by changing the reduced temperature periodically. Experimental predictions are made for solid and fluid binary mixtures. The scattered light (or neutron) intensity is shown to be much enhanced as a result of periodic formation of domains. A phase transition is also discussed, which occurs as the average temperature is lowered with a fixed size of the temperature vibration.