A two-parameter model based on three-spin exchange and planar four-spin exchange gives at low field a first-order transition to the ordered phase suggested by Osheroff, Cross, and Fisher and at high field gives a second-order phase agreeing with the experiments of Godfrin et' al. and Adams et al. It also fits well the high-temperature expansion coefficients and the susceptibility of the low-field phase.

The alkali hyperoxides $A{\mathrm{O}}_2$ exhibit elastic and magnetic interactions due to the nature of the diatomic molecule ion ${\mathrm{O}}_2^{-}$. These anion sublattices represent simple magnetic spin-½ systems. In contrast to $3d$- or $4f$-electron systems, where magnetoelastic interactions induce magnetostriction, the $\mathrm{}\left(2p\right)\mathrm{}\pi$-electron system K${\mathrm{O}}_2$ exhibits magnetogyration. A crystallographic phase transition involving a considerable change in the molecular orientation can be induced by an applied magnetic field. A theoretical model based on the exchange modulation produced by this reorientation describes the salient features.

The solar-wind magnetohydrodynamic turbulence is observed to be mainly made of Alfvénic fluctuations propagating away from the sun. It is shown that such an asymmetric state is a general consequence of the evolution of developed magnetohydrodynamic turbulence, which, starting from an initial asymmetry between modes with cross helicity + 1 and - 1, tends, as a consequence of nonlinear interactions, towards a state where the only modes left are those initially prevailing (with either cross helicity + 1 or - 1).

The interferometers now being developed to detect gravitational vaves work by measuring small changes in the positions of free masses. There has been a controversy whether quantum-mechanical radiation-pressure fluctuations disturb this measurement. This Letter resolves the controversy: They do.

In this Letter, a simple model of disordered systems—the random-energy model—is introduced and solved. This model is the limit of a family of disordered models, when the correlations between the energy levels become negligible. The properties are qualitatively the same as those of the Sherrington-Kirkpatrick model. Moreover, this random-energy model looks like a simple approximation to any spin-glass model.

The decay modes $F\left(c\overline{s}\right)$,$B(b\overline{u},b\overline{c})\to \tau \nu$ are proposed as triggers for $e^{+}{e}^{-}\to F\overline{F}$,$B\overline{B}$ production. Decay branching fractions of order $B\left(F\right)\mathrm{}\simeq 15\%$ and $B\left(B\right)\mathrm{}\simeq \left(1\mathrm{} \mathrm{to} 2\right)\%$ are estimated. The sequential $\tau \to e\nu \overline{\nu }$,$\mu \nu \overline{\nu }$ decays provide clear signatures, with the hadronic decay of the associated $F$, $B$ carrying exactly half the energy. These triggers can be extended to study $F^{*}$ and $B^{*}$ resonance production and also to exploit the $\tau \to \pi \nu$,$\rho \nu$,$A_1\nu$ decays.

Using parton-model concepts together with data on resonance production in proton-proton interaction, we present a model for $p-p$ elastic scattering and total cross sections. The energy dependence is the result of gluon-gluon annihilation. The comparison with experiment shows remarkable agreement.

The ${\pi }^0$ inclusive cross section for c.m. production angles $\theta =90\mathrm{}°$ and $22°>~\theta >~5°$ at c.m. energies of $\sqrt{s}=23\mathrm{} \mathrm{and} 53$ GeV has been measured. This cross section is strongly dependent on both $\theta$ and $\sqrt{s}$ at small angles. The hypothesis of radial scaling is shown to be incapable of incorporating both $\theta$ and $\sqrt{s}$ dependence of the cross section. A recent quantum-chromodynamics calculation is in qualitative agreement with our results.

The neutron-antineutron transition which changes baryon number by two units is considered under some general assumptions. The resultant neutron oscillation time scale is found to vary as $M^4$, with $M$ the unification mass scale, if there exists a neutral, massive, Majorana lepton. In this case, the oscillation time scale is comparable to the proton lifetime. However, in the presence of matter or external magnetic fields, the detection of such oscillations, at the present time, seems improbable.

The possibility that the ${\Delta }_{D35\mathrm{}}\mathrm{}\left(1925\right)\mathrm{}$ resonance is evidence for a [56, $1^{-}$] multiplet corresponding to excitation of new gluonic degrees of freedom within baryons is examined in detail. A new group-theoretical analysis of a successful mass formula for the $N=2\mathrm{}$ multiplets of the nonrelativistic harmonic-oscillator quark model is also presented. Some results for the $N=3\mathrm{}$ level are also given together with an outline of the method for generalization to any degree of excitation of the system.

It is suggested that the magnetic monopoles predicted by grand unified theories would not be produced in significant numbers if electromagnetic gauge invariance is spontaneously broken when the temperature $T$ is greater than $T_c\gtrsim 1$ TeV. A model possessing this behavior is displayed and the cosmological implications are discussed.

Cross sections for the ${}_{}{}^{24,25,26}{}_{}{}^{}\mathrm{Mg}$($p$,$n$)${}_{}{}^{24,25,26}{}_{}{}^{}\mathrm{Al}$ reaction have been measured at 35 MeV. The strengths of the larger spin-isospin-flip transitions correspond surprisingly well with the matrix elements of the analogous giant $M1\mathrm{}$ transitions.

It is shown that the mixing of vibration-rotation states by nuclear hyperfine interactions causes crossover resonances to appear in infrared saturation spectra. Examples are displayed in the ${\nu }_3$ band of S${\mathrm{F}}_6$ and obtain the tensor centrifugal-distortion constant $t_{044}$ and the tensor spin-rotation constant $c_d$. The value of $t_{044}$ (5.7 Hz) obtained is in excellent agreement with the theoretical value. A splitting is also demonstrated between vibration-rotation states which differ only in their parity.

The new excited ${}_{}{}^1{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ states and five new excited ${}_{}{}^1{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ states of ${\mathrm{Na}}_2$ have been identified with the use of the two-step polarization labeling technique. The electronic energies of these states form a molecular Rydberg series. By extrapolating the dissociation energies, vibrational constants, and rotational constants of these Rydberg states it is possible to obtain good estimates of the same quantities for the $X{}_{}{}^2{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}$ ground state of ${\mathrm{Na}}_2^{+}$.

The linear effect of an electrostatic field on the intensity of scattering of light by gas is reported. The change in the depolarized intensity scattered by gaseous methyl chloride in the $y$ direction from a beam of right circularly polarized light propagating in the $z$ direction due to electrostatic field $F_x=7\mathrm{}\times {10}^6$ V ${\mathrm{m}}^{-1\mathrm{}}$ is -7±1 ppm. It changes sign on reversing $F_x$, the direction of scattering, and the circularity of the light. The effect should be exhibited by all materials.

The stability of a high-$\beta$ flux-conserving-tokamak equilibrium during resistive magnetic flux diffusion has been studied with use of a fully toroidal transport-equilibrium model coupled to ideal magnetahydrodynamic stability codes. With broad temperature profiles, the stability of $\overline{\beta }=10\%$ equilibria to all ideal magnetohydrodynamic modes can be maintained for as long as the external transformer can supply volt seconds. With narrower temperature profiles, instability may result during the diffusion, but even for these, stability can be reestablished in resistive steady state.

A theoretical model is presented describing the spatial structure and scaling laws of laser-driven ablative implosions. The effect of inhibited electron thermal transport is explicitly included. Simple expressions describe the ablation rate and pressure as a function of laser intensity and wavelength. The analytic results are supported by extensive comparisons with numerical hydrodynamic simulations.

With an optical technique it is found that the equilibrium interface between superfluid and hcp ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is partially faceted, showing that at least some of it is atomically smooth. This conclusion is also consistent with the behavior of the crystal during melting and growth. The surface tension ${\alpha }_{\mathrm{LS}}$ on the rounded part of the interface is found to be independent of temperature.

High-resolution ac calorimetry measurements on two different samples of 8OCB whose transition temperatures differ by less than 0.1 K show different critical behavior at the nematic-smectic-$A$ transition. ${\alpha }^{+}={\alpha }^{-}$ is near zero on one sample, agreeing with Johnson's measurements, while ${\alpha }^{+}={\alpha }^{-}$ equals 0.25 on the second sample which agrees with Garland's measurements on 8OCB. These results suggest the possibility that the nematic-smectic-$A$ transition on 8OCB is near a tricritical point or crossover between two types of critical behavior.

Scattering amplitudes for quasiparticles in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are constructed from the previously determined polarization potentials of Aldrich and Pines. The calculated results for the thermal conductivity, viscosity, spin diffusion, and normal-state quasiparticle lifetime of normal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at all pressures up to 34 atm are in good agreement with experiment.