Reversible and irreversible components of torque have been measured at 4.2 K on a sample of Au-doped ${\mathrm{Cu}}_{0.85}$${\mathrm{Mn}}_{0.15}$ in various cooling ($H_c$) and measuring ($H_m$) fields. The irreversible torque has an angular dependence, which, at fixed $H_m$, depends strongly upon the remanent moment, $M_r$. This behavior is explained quantitatively in terms of a simple model of the loss mechanism, utilizing parameters obtained from the reversible torque and from zero-field-cooled measurements.

Spin- and momentum-resolved bremsstrahlung isochromat spectra from Fe(110) at $\hslash \omega =9.7\mathrm{}$ eV are presented, a combination which allows for the first time the determination of experimental final-state dispersions $E\left(k_{\parallel }\right)$ for direct interband transitions into majority and minority final bands separately. Data are in good agreement with relevant theoretical $E\left(k_{\parallel }\right)$ values from bulk band-structure calculations as far as minority final states are concerned. Theoretical predictions for the majority states exhibit a stronger dispersion than observed experimentally.

Experimental evidence for the occurrence of optical bistability using the biexciton two-photon resonance in CuCl is presented. These observations agree with recent theoretical predictions that require an intensity of 10 MW/${\mathrm{cm}}^2$ and 10-μm-thick etalons with 90% reflective coatings. Earlier much less demanding predictions neglected two important physical effects: unsaturable background absorption at the biexciton from the tail of the exciton resonance and broadening of the biexciton resonance with intensity.

A real-space renormalization-group transformation for quantum systems is proposed, based on an equivalent classical representation. Classical real-space renormalization groups and in particular Monte Carlo renormalization groups can then be used to study quantum systems. This formulation is valid for zero temperature as well as finite temperature. The Ising model in a transverse field in one and two dimensions is treated by Monte Carlo renormalization group.

The possibility of the existence of ideal conductivity at finite temperatures in clean quasi two-dimensional conductors under conditions similar to the quantized Hall effect is discussed. It is found that for metallic electron densities and realistic values of the magnetic field the electronic system should break into two coexisting diamagnetic phases, for which the chemical potential is pinned in the middle of a magnetic energy gap, and the system is nondissipative. The experimental feasibility of the proposed mechanism is briefly discussed.

Susceptibility data on an amorphous GdAl spin-glass show an irreversibility onset line $t=-A{}_{-}{}^{}{}_{}{}^{}H_{}^{\frac{2}{{\phi }_{-}}}{}_{}{}^{}$ and a susceptibility crossover line $t=+A{}_{+}{}^{}{}_{}{}^{}H_{}^{\frac{2}{{\phi }_{+}}}{}_{}{}^{}$ ($t$ is reduced temperature; $H$ is field). The exponents $\phi$ are both close to 3, and the amplitudes $A$ differ only by a factor of 2. In contrast to earlier explanations of the irreversibility in terms of a de Almeida-Thouless mean-field instability, here both crossovers are explained in terms of a non-mean-field scaling theory.

It is calculated that spin-orbit coupling induces a predominant orbital magnetic moment ($-1.5\mathrm{}{\mu }_{\mathrm{B}}$) antiparallel to the spin moment ($1.0{\mu }_{\mathrm{B}}$) in the spin-polarized energy bands of UN. The shape of the magnetic form factor, pressure dependence of the moment, and presence of large magnetic anisotropy then become compatible with itinerant-electron theory.

An algorithm is suggested for the Mössbauer spectrum $I\left(\omega \right)$ of an atom undergoing one-dimensional Brownian motion in an arbitrary potential. The algorithm reproduces simultaneously the low- and high-frequency dependence of $I\left(\omega \right)$ to a desired accuracy.

The spectra of density fluctuations caused by strings in a universe dominated either by baryons, neutrinos, or axions are presented. Realistic scenarios for galaxy formation seem possible in all three cases. Examples of grand unified theories which lead to strings with the desired mass scales are given.

It is shown that electromagnetic and clock-transport synchronization procedures are not necessarily equivalent. In noninertial frames and in gravitational fields both procedures can be path dependent. Even for the same path ∼ 100 km above the Earth, the two procedures can give different errors, ∼ 89 μsec/day (clock-transport synchronization) and ∼ 60 μsec/day (electromagnetic synchronization).

It is shown that for hard-sphere systems in a constant external potential revised Enskog theory yields the correct single-particle equilibrium distribution function, whereas standard Enskog theory does not.

The motion of a quantum mechanical particle is studied in the presence of a periodic potential and frictional forces. Depending on the parameters, the behavior changes from diffusion to localization.

Recent $\gamma \gamma \to {\rho }^{+}{\rho }^{-}$ data in the 1.3-2.0-GeV region show a strong suppression as compared to $\gamma \gamma \to {\rho }^0{\rho }^0$ data in the same region which suggests an interference between an isoscalar and an exotic isotensor structure. Both the ${\rho }^0{\rho }^0$ and the ${\rho }^{+}{\rho }^{-}$ data can be accounted for quantitatively in terms of the unique flavor and color-spin structures of the $I=0\mathrm{}$ and $I=2\mathrm{}$ $Q^2{\overline{Q}}^2$ states. The possible connection to ${\rho }^0{\rho }^0$ structure in $\frac{J}{\psi }$ radiative decay is suggested. Other $2^{++}$ $Q^2{\overline{Q}}^2$ candidates in hadronic collisions are briefly discussed.

The result of a measurement of $\sigma ({\nu }_{\mu }+e^{-}\to {\nu }_{\mu }+e^{-})$ is presented. With use of neutrinos of mean energy 1.5 GeV from the Brookhaven National Laboratory alternating gradient synchrotron and a massive, active, high-resolution detector, a signal of 51±9 events with an average signal-to-background ratio greater than 2:1 is observed. $\sigma ({\nu }_{\mu }{e}^{-}\to {\nu }_{\mu }{e}^{-})=[1.60\mathrm{}\pm 0.29(\mathrm{stat})\pm 0.26(\mathrm{sys}\left)\right]E_{\nu }\left(\mathrm{GeV}\right)\times {10}^{-42\mathrm{}}$ ${\mathrm{cm}}^2$ is obtained.

When a massless, isospinor Dirac field is confined to a finite region of space by means of a chiral boundary condition parametrized by an angle $\theta$, the baryon number of the vacuum is shown to be $\left(\frac{\chi }{2\pi }\right)(\theta -sin\theta cos\theta )$ where $\chi$ is the Euler characteristic of the bounding surface. Some implications for chiral bag models are discussed.

The yrast bands in ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$ have been studied up to spin ${26}^{+}$ by Coulomb excitation using ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ beams of 5.1 and 5.3 MeV/u. In the case of ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$ a pronounced backbending has been observed for the first time in an actinide nucleus. Microscopic calculations are presented which indicate that the observed anomalies in the yrast sequences of both nuclei are due to alignment effects in the $i_{\frac{13}{2}}$ proton shell.

Cross sections, analyzing powers, and spin-flip probabilities have been measured at small angles in the reaction ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}(p,p^{\prime }){}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}_{}^{*}{}_{}{}^{}$ at 319 MeV. A rich fine structure is observed in the previously proposed $M1\mathrm{}$ giant resonance region; angular distributions of most of these structures are consistent with $M1\mathrm{}$ excitation. The spin-flip measurements reveal a large cross section for spin excitations distributed roughly uniformly over the excitation energy region from about 8 to 25 MeV.

The spectra of protons and the cross section of the ($\pi$,$\mathrm{pp}$) and ($\pi$,$\mathrm{pn}$) reactions induced by 65-MeV ${\pi }^{+}$ and ${\pi }^{-}$ on C and Al were measured. Ratios $R$, the pion absorption cross section for a $\mathrm{pn}$ nucleon pair to that for a $\mathrm{pp}$ or $\mathrm{nn}$ nucleon pair, were estimated to be 3.9±1.0 for C, and 3.8±0.9 for Al. These $R$ values are well explained by recent microscopic theories, which suggest that pion absorption on ${}_{}{}^3{}_{}{}^{}P$ nucleon pairs is important in the ($\pi$,$\mathrm{pn}$) process for these nuclei.

It is shown that the Nilsson prescription for calculating equilibrium deformation of nuclei under the constraint of constant volume is equivalent to a Hartree mean-field approximation applied to nucleons interacting via many-body forces. Such an interaction is obtained in closed form, having a Taylor expansion beginning with the familiar quadrupole-quadrupole interaction.

Clusters of He atoms formed in a supersonic free jet expansion have been studied by electron-bombardment ionization and mass spectrometry. Distinct magic-number enhancements of ion intensity are observed for clusters of 7, 10, 14, and 30 atoms for both helium isotopes, and for 23 atoms of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. Dramatic differences in the onset of cluster formation between the two isotopes may be related to the stability of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ dimers.