A new approach to the problem of the transition of an $A=3\mathrm{}$ ground state to scattering states via a weakly acting Hamiltonian is presented; calculations are made feasible with realistic nucleon-nucleon potentials. Muon capture by ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ leading to three neutrons is taken as a test case and is carried through till numerical results are obtained.

A search has been made for the the decay ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}\to {}_{}{}^{87}{}_{}{}^{}\mathrm{Sr}_{}^m{}_{}{}^{}+\mathrm{neutrals}$. No evidence of such decays was observed. However, from this experiment an improved lower limit of ≥1.9 × ${10}^{18}$ yr has been established for the lifetime against the charge-nonconserving decay $n\to p+\mathrm{neutrals}$.

This Letter reports the first measurement of tensor polarization ($t_{20}$) in $\pi -d$ elastic scattering and also measurements of the $\pi -d$ elastic-scattering cross section at 180°. The measurements were performed using the low-energy pion channel at Clinton P. Anderson Meson Physics Facility and a novel high-efficiency deuteron polarimeter. The result of the polarization measurement, $t_{20}=-0.23\mathrm{}\pm 0.15$ at $T_{{\pi }^{+}}=140\mathrm{}$ MeV, is in disagreement with all theoretical predictions.

In the heavy-ion excitation of nuclei near closed shells, an amplitude involving singleparticle degrees of freedom interferes with a collective, core-polarization amplitude which has a large Coulomb component. Thus details of the nuclear structure and of the microscopic reaction mechanism may have significant effects on the observed Coulombnuclear interference pattern. Calculations are given which demonstrate such effects and resolve the outstanding problem in the heavy-ion excitation of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$.

Shape-resonant enhancements in the kinetic-energy range 10 to 40 eV are predicted to be a common feature in electron-molecule scattering. These features are usually difficult to detect in elastic and total cross sections, but can emerge clearly in vibrational excitation. A calculation of the $e^{-}$-C${\mathrm{O}}_2$ symmetric-stretch spectrum, just confirmed experimentally by Tronc et al., is given as an example. Such resonances can be predicted by analysis of the corresponding inner-shell photoionization spectra.

Asymmetric satellites corresponding to interferences between $6p_{\frac{1}{2}}15d_{\frac{5}{2}}$ and $6p_{\frac{1}{2}}n{d}_{\frac{5}{2}}$ states ($n\ne 15$) in the autoionization spectrum of Ba for the transition $6s15d{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\to 6p_{\frac{1}{2}}-15\mathrm{}{d}_{\frac{5}{2}}$ are observed. A simple line-shape theory based on first principles allows us to measure "two-electron" transition-matrix elements in terms of one-electron dipole-transition matrix elements. These values are compared to those calculated using a quantum-defect model which also explains the sign of the observed asymmetries.

The absorption of three to eight photons from a 10-GW laser by electrons emitted from a heated oxide cathode has been separately measured. Each of the photon absorption processes has been identified. This is the first measurement of absorption of photons of such high order by the electrons.

A study by experiment, simulation, and theory has found that a plasma responds paramagnetically to the external rf magnetic field applied perpendicular to the static magnetic field with frequency $\omega <{\omega }_m$, ${\omega }_m$ being the Alfvén ion cyclotron frequency. This effect can be exploited in the rf plugging and heating of plasmas; it explains the earlier rf plugging experiment (type-3 coil) of Watari et al. at Nagoya and possibly the rf heating experiment of Dikii et al. on the Uragan stellarator.

High-resolution x-ray-scattering studies of the Martensitic phase transition in ${\mathrm{V}}_3$Si show significant pretransition $d$-spacing fluctuations at temperatures as high as 40 K above $T_{\mathrm{M}}\left(21\mathrm{} \mathrm{K}\right)$. Neutron scattering measurements, with similar resolution, show no broadening of the same Bragg peak. These striking results are compared with existing theoretical and experimental evidence for precursive effects in ${\mathrm{V}}_3$Si.

We report the first light-scattering study of a critical mixture (aniline-cyclohexane) under shear flow $S$ which affects critical fluctuations with relaxation time $\tau$ only in the region $S\tau >1\mathrm{}$. All anomalies can be expressed as a function of $S\tau$ only and can be interpreted by a lowering of the critical temperature $\Delta T_0\mathrm{}\left(S\right)=T_1{S}^{\frac{1}{3\nu }}$, where $T_1$ is a constant. In addition the scattered light is found to exhibit a noticeable anisotropy with respect to the flow direction.

This paper reports investigation of the role of spin fluctuations (paramagnons) in the superconductors Nb and V. For this purpose, experimental data on specific heat and magnetic susceptibility are reanalyzed. Furthermore, the Eliashberg equations including the particle-hole $t$ matrix are solved numerically. It is found that in Nb and V, spin fluctuations substantially reduce $T_c$, while their contribution to the mass enhancement $\frac{m^{*}}{m}$ is typically of order 0.2.

This Letter presents for the first time a detailed two-photon spectrum of the even-parity excitons of the yellow series in ${\mathrm{Cu}}_2$O. Contrary to one-photon data, it is possible to measure directly $S$ and $D$ exciton contributions without applying external perturbations. The two-photon spectrum gives evidence for a strong mixing between the yellow and the green series which is explained by exchange interaction and nondiagonal parts in the effective-mass Hamiltonian.

The universal depression of the superconducting transition temperature $T_c$ in disordered $A-15\mathrm{}$ compounds is examined. Existing energy-band calculations are used to calculate the density of electron states, which is possibly enhanced by disorder in some cases such as ${\mathrm{Nb}}_3$Ge. The dramatic drop in $T_c$ in ${\mathrm{Nb}}_3$Ge at a critical value of the resistivity is attributed to overdamping of acoustic plasmons which decreases the electron pairing interaction despite small changes in the density of states.

Bifurcation theory is used to study the transition from a low-density nondegenerate electron gas to an "electron solid," in a superstrong magnetic field. The dynamics of the gas are described by a set of nonlinear equations, and the transition is seen as the bifurcation of spatially periodic solutions from the trivial constant solution. Electron solids are a good approximation for condensed matter in the outer crust of magnetic neutron stars.

A superconducting contribution $\delta \sigma \mathrm{}\left(T\right)\mathrm{}$ to the electrical conductivity $\sigma \mathrm{}\left(T\right)\mathrm{}$ has been observed at temperatures up to about twice the transition temperature $T_c\simeq 1.17$ K for bulk aluminum. The form of $\delta \sigma \mathrm{}\left(T\right)\mathrm{}$ is found to be $\alpha {\left[\frac{T_c}{(T-T_c)}\right]}^n$, with $\alpha$ independent of $\sigma \mathrm{}\left(T\right)\mathrm{}$, in agreement with the theory of superconducting fluctuations. However, significant differences from the theory are found, with $\alpha$ more than two orders of magnitude too large and $n\simeq \frac{3}{4}$ rather than ½.

The possibility of observing previously postulated neutron-proton correlations in the nuclear ground state via relativistic heavy-ion reactions is examined. The isotope-production cross sections from the reaction of 213-MeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ are calculated with a correlated abrasion-ablation model and with an uncorrelated intranuclear cascade model, and the results compared to recent experimental data. The neutron-proton correlations may only be visible in products near the mass of the fragmenting nucleus.

Data on inclusive electron scattering from ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ over a large range of momentum transfer (2-7 ${\mathrm{fm}}^{-1\mathrm{}}$) are presented and compared with a one-nucleon knockout calculation based on a Faddeev spectral function.

A Coulomb polarization potential is obtained by solving the inverse problem for the elastic component of the Coulomb-excitation $S$ matrix. It takes account of multiple excitation and, for heavier systems, exhibits significantly less absorption than existing single-excitation potentials.

All features of a $\Delta I=1\mathrm{}$ band displaying Coriolis-like distortions based on a $4^{+}$ isomeric state, recently discovered in ${}_{}{}^{76}{}_{}{}^{}\mathrm{Br}$, are successfully described within the framework of a two-noninteracting-quasiparticle-plus-rotor calculation. Assuming the intrinsic state to be of $\tilde{\pi }{g}_{\frac{9}{2}}\otimes \tilde{\nu }{g}_{\frac{9}{2}}$ parentage it is possible to account in a natural way for the apparent relationship noted between this $4^{+}$ state and the ${\frac{5}{2}}^{+}$ ground-state band of the neighboring isotone ${}_{}{}^{77}{}_{}{}^{}\mathrm{Kr}$.

It is shown that optical second-harmonic generation is possible in dispersive atomic vapors since a static electric field is spontaneously created by the fundamental laser beam. When multiphoton ionization of atoms occurs simultaneously in the interaction, the spontaneous field and second-harmonic generation are significantly enhanced. Our experimental results for atomic sodium vapor irradiated by picosecond Nd-doped yttrium-aluminum-garnet laser pulses agree well with the theoretical predictions.