A Lagrangian is obtained by deriving the path-integral representation of the diffusion process. It can be applied, e.g., to nonequilibrium thermodynamics and to quantized motion in general relativity. In second quantization it is shown to lead to a particularly well-behaved energy-momentum tensor as a source of gravity.

The reaction ${\pi }^{-}p\to \omega n$ in the beam-momentum range from 20 to 200 GeV/c has been studied using data acquired at Fermilab. In this Letter, the integral and differential cross sections for this reaction are presented. The integral cross sections are considerably larger than those previously reported. The differential cross sections can be reproduced quite easily by Regge models. As predicted by such models, natural-parity exchange dominates production throughout this energy region.

A flight-time-difference method was used to measure the energy distribution of H-H fragment pairs arising from dissociative charge-exchange collisions of ${\mathrm{H}}_2^{+}$ ions. The spectrum exhibits sharp peaks which coincide with the energies of vibrational levels of the $c{}_{}{}^3{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}$ state of ${\mathrm{H}}_2$ above the dissociation limit of the ground state. Predissociation into the $b{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}$ state is the main decay channel of the $c{}_{}{}^3{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}$ state. The lifetime is estimated to be ≤ ${10}^{-8\mathrm{}}$ sec.

Coherent radiation at the 1.28-μm electric-dipole-forbidden $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ transition in thallium vapor has been produced by the simultaneous application of a magnetic field and two collinear, overlapping laser beams nearly resonant with the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ and $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ transitions, respectively. The effect of the magnetic field is to mix hyperfine levels—atomic polarization effects are negligible. The optical difference-frequency power generated at low magnetic field varies as the square of the magnetic-field component normal to the laser-beam propagation direction.

The $N_5-O_{2,3}{O}_{2,3}$ ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ Auger peak of xenon following ionization in the $N_5$ shell by photons of different energy has been investigated. When the photon energy is lowered close to threshold a shift of the position of the peak maximum to higher energies and a characteristic asymmetric intensity distribution of the Auger line are observed. The observed shifts agree well with values calculated with the classical Berker-Berry model modified because of the velocity change of the slow photoelectron in the Coulomb field of the inner-shell ionized atom.

The transmission characteristics of molecules subjected to an intense standing-wave laser radiation are monitored by a probe laser. In addition to the usual Bennett holes, we observe several saturated absorption and emission features caused by velocity-tuned multiphoton processes. These direct experimental observations confirm the theoretical predictions of Haroche and Hartmann.

An analytic theory is developed to calculate poloidal beta ${\beta }_I$ and the diamagnetic parameter ${\mu }_I$ for axisymmetric toroidal magnetohydrodynamic equilibria confining high-pressure plasmas [$\beta \sim O\left(\frac{a}{R}\right)$] under the constraint of flux conservation. To satisfy the equilibrium equations, the plasma current increases with pressure as $p^{\frac{1}{3}}$. Previously calculated equilibrium limits on poloidal $\beta$ are avoided.

A microscopic model is presented for the ferroelectric phase transition in the tetragonal tungsten-bronze-structure ferroelectrics (e.g., ${\mathrm{Sr}}_{1-x}{\mathrm{Ba}}_x{\mathrm{Nb}}_2{\mathrm{O}}_6$) which, for the first time, provides a description of its essential features, including the fact that it is a displacive transition but has no "soft"-phonon mode. The model employs an interaction between the ferroelectric phonon displacement and local structural changes, which are important in these materials; and it describes well important features of the Raman spectra, dielectric constant, and refractive index.

We propose a new mechanism for a current instability in single-valley semiconductors based on the momentum loss of hot carriers by Bragg reflection. We construct a simple model which gives rise to bulk negative differential conductivity of the uniform current state above a critical field $E_c$ associated with a soft dielectric relaxation mode, and to traveling dipole-domain solutions. The possibility for this mechanism to occur in realistic situations is discussed.

We describe nuclear orientation experiments performed on dilute alloys of $\mathrm{Pd}\mathrm{Co}$. Assuming the proportionality between the hyperfine field and the magnetization, we show that the Co impurity is in a Kondo-like state at low temperatures ($T<\mathrm{}100\mathrm{}$ mK). We discuss the link between the Co positive hyperfine field and its weak Kondo coupling.

We analyze the ideal resistivity, $\rho$, of a one-dimensional metal at high temperatures. We have adapted a diagrammatic technique introduced by Berezinskii in the context of static disorder. Retaining the dominant vertices in the limit of vanishing electron-phonon coupling constant, $g$, and phonon frequency, ${\Omega }_0$, with $\frac{g^2}{{\Omega }_0}$ finite, we obtain a dc resistivity $\rho \propto T^2$ instead of $T$. The result may be interpreted in terms of diffusion of electrons.

Amorphous films of composition ${\mathrm{Gd}}_{0.37}$${\mathrm{Al}}_{0.63}$ are found to exhibit a transition to a spin-glass state below 16 K. The magnetic properties show thermal hysteresis and relaxation below the spin-glass transition. The susceptibility maximum at 16 K, when measured in dc fields ≤10 Oe, sharpens into an asymmetric cusp, consistent with the Edwards-Anderson picture of the transition as one into a random, but rigid, state. Using the theory of Sherrington and Kirkpatrick, we extract the spin-glass order parameter from the observed cusp, and find deviations from simple mean-field behavior.

The ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ chemical-shift tensors $\overleftrightarrow{\sigma }$ have been determined as a function of temperature on going through the ferroelectric phase transition in a single crystal of K${\mathrm{D}}_2$P${\mathrm{O}}_4$, and an abrupt change in $\overleftrightarrow{\sigma }$ was found at $T_c$. The results show that the transition is not driven by an electronic instability but is a pure lattice transition of the order-disorder type, and demonstrate the usefulness of chemical-shift studies of structural phase transitions in solids.

We have measured the infrared and visible thermoreflectance of $2H$-Ta${\mathrm{Se}}_2$ in the charge-density-wave onset temperature range. New features that appear in the spectrum are compared with a model two-dimensional 3×3 charge-density-wave calculation. We stress connection between the infrared result and the multiplet of transitions inside the $d_{z^2}$ manifold.

The ${\mu }^{+}$ spin-rotation method was used to probe conduction-electron polarization in ferromagnetic $\mathrm{Pd}\mathrm{Fe}$ (0.28 at.%) and spin-glass $\mathrm{Pd}\mathrm{Fe}$ (0.015 at.%) from 0.11 to 300 K with reference to pure Pd. The result was explained in terms of the Ruderman-Kittel-Kasuya-Yosida spin oscillation in the region outside the giant moment.

The transverse-momentum distribution of charged pions produced in 28.5-GeV/c $\mathrm{pp}$ interactions was studied. Scaling of the transverse-momentum distribution versus the "mean" variable $\frac{p_T}{〈p_T〉}$ was observed, independent of charge multiplicity, missing mass, and energy, in the central region. From the scaling behavior of the pions, the limiting temperature was determined to be $T_0=117\mathrm{}\pm 4$ MeV.

A microscopic model is presented which provides a practical means for selecting the states necessary for the development of nuclear collective rotational and quadrupole vibrational motions in a shell-model calculation. The model is based on the noncompact $\mathrm{Sp}(3, R)$ algebra and is a natural generalization of Elliott's SU(3) model to include many major shells.

A new method for measuring cross sections for the scattering of electrons by laser-excited atoms is described. It is a generalization of the atomic-beam recoil technique, taking advantage of the recoil of atoms during resonant photon interactions to spatially separate excited from nonexcited atoms. A preliminary value for the total cross section for the scattering of electrons by the $3{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}(m_F=3)$ state of sodium at 4.4 eV is presented.

Crossed molecular and C${\mathrm{O}}_2$ laser beams were used to study collisionless multiphoton dissociation of S${\mathrm{F}}_6$. Dissociation products were found to be S${\mathrm{F}}_5$ and F. Angular and velocity distributions of the S${\mathrm{F}}_5$ fragment were measured. The results indicate that the average excess energy absorbed by an S${\mathrm{F}}_6$ molecule beyond the dissociation limit was definitely less than 8000 ${\mathrm{cm}}^{-1\mathrm{}}$ and the activation energy for dissociation was less than 70 ${\mathrm{cm}}^{-1\mathrm{}}$.

Crossed molecular and C${\mathrm{O}}_2$ laser beams were used to study collisionless multiphoton dissociation of S${\mathrm{F}}_6$. Dissociation products were found to be S${\mathrm{F}}_5$ and F. Angular and velocity distributions of the S${\mathrm{F}}_5$ fragment were measured. The results indicate that the average excess energy absorbed by an S${\mathrm{F}}_6$ molecule beyond the dissociation limit was definitely less than 8000 ${\mathrm{cm}}^{-1\mathrm{}}$ and the activation energy for dissociation was less than 70 ${\mathrm{cm}}^{-1\mathrm{}}$.