The energy dependence of incomplete-fusion reactions ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$,$\alpha$) and ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$,$2\alpha$) has been studied by means of $\alpha -\gamma$ coincidences in the range of bombarding energies 7.5-16.7 MeV/A. Excitation functions are interpreted in terms of a generalized concept of critical angular momentum. An energy threshold (of about 15 MeV/A) is predicted at which projectile fragmentation processes set in rapidly at the cost of the decreasing cross section for binary massive-transfer reactions.

The theoretical prediction that polarized photoelectrons can be ejected from unpolarized atoms by unpolarized radiation has been experimentally verified for xenon atoms. The wavelength dependence of the polarization has been measured and compared with theoretical results at helium and neon resonance wavelengths between 74.4 and 46.1 nm.

It is suggested that the 12.3-Å feature in the spectra from compressed neon-filled microballoons, previously identified as the second-order silicon Lyman-$\alpha$ line, is actually a blend of neon dielectronic satellite lines. The relative intensities of these satellite lines, some of which are strong functions of electron density, agree with a numerical model of collisional mixing of the Ne ix $2l2l^{\prime }$ doubly excited levels.

We report the solution of the problem of saturation and ac Stark splitting of a resonant transition in a strong chaotic field of arbitrary bandwidth. We present results for double optical resonance and resonance fluorescence and compare them to those obtained for a phase-diffusion field.

Pure rotational transitions in doubly degenerate torsional states of ${\mathrm{C}}_2$${\mathrm{H}}_6$, with selection rules $\Delta K=0\mathrm{}$, $\Delta J=0,\pm 1$, are shown to be made allowed by Coriolis interaction between torsion and dipole-allowed vibrations. Expressions for integrated intensities are presented from which strengths of lines in the millimeter region are calculated.

The transverse beam breakup instability, for a uniform axial focusing magnetic field, has been investigated utilizing the approach of the well-known klystron instability. An expression for the gain is obtained. It is proportional to the beam current and the cavity equivalent shunt resistivity at the radius of the beam surface and inversely proportional to the cyclotron frequency and the cavity frequency, resulting in instability at high beam current, in contrast to the standard klystron instability which occurs at low currents and is self-stabilized at high beam currents.

The theory of Alfvén resonance effects on the wave modes of a tokamak is extended beyond the incompressible magnetohydrodynamic model to include finite-($\frac{\omega }{{\Omega }_i}$) effects and compressibility. The discrete spectrum of compressional Alfvén waves consists of a sequence of frequencies with finite damping decrements resulting from the Alfvén resonance. The finite-frequency effects can cause the damping to almost vanish. This permits Alfvén resonance heating via high-$Q$ eigenmodes in large tokamaks.

The total and specular reflectances of 1.06- and 0.53-μm laser pulses were measured on planar copper targets. The measurements were made with 30-ps pulses and an intensity on target of ${10}^{14}$ W/${\mathrm{cm}}^2$. The direction of polarization and angle of incidence (0°-70°) were varied. Only a weak dependence of reflectance on wavelength is found; at both wavelengths reflectance is governed by the characteristic angle and polarization dependence of resonance absorption.

For a "slowly" time-dependent Hamiltonian system exhibiting ergodic motion, the volume inside the hypersurface on which the Hamiltonian equals a constant is an adiabatic invariant. It is shown that the error in the constant is diffusive and scales as ${\left(\frac{{\tau }_C}{\tau }\right)}^{\frac{1}{2}}$, where ${\tau }_C$ is a certain correlation time of the ergodic motion, and $\tau$ is the time scale over which the Hamiltonian changes.

Results of molecular-dynamics calculations on melting in a two-dimensional (2D) Lennard-Jones system are presented. We find that this system loses its resistance to shear at a temperature $T_1(\approx 0.36)$. However, long-range "orientational" order persists up to a higher temperature $T_2(\approx 0.57)$. These observations are compatible with the existence of a liquid-crystal-like phase with sixfold anisotropy separated from both the solid and the isotropic-fluid phase by second-order phase transitions. Such two-stage melting behavior in 2D has been predicted by Halperin and Nelson.

Using molecular-beam diffraction we have observed surface corrugation effects due to charge-density waves in Ta${\mathrm{S}}_2$. Satellite peaks have about the same intensity as Bragg peaks, contrary to results obtained from electron, neutron, and x-ray diffraction.

The noncritical background thermal diffusion is extracted from experimental data and found to be relatively strong. This produces large transient corrections in the critical relaxation rates. The negative amplitude of the slow transient strongly perturbs the entropy relaxation rate. Inclusion of both slow and fast transient yields an excellent fit with Ahler's thermal conductivity data. Light scattering data are also well accounted for.

The Brillouin scattering efficiencies of exciton polaritons in CdS have been calculated with two different models. The first model, which assumes Pekar's additional boundary condition (ABC) results in qualitative disagreement with experiment. The second model employs the ABC proposed by Birman and Sein, by Agarwal et al., and by Maradudin and Mills and assumes a lossy layer on the sample surface. This model results in quantitative agreement between theory and experiment.

A model of the early universe is proposed which initially contains a zero-temperature quark phase. The entropy of the cosmic background radiation is generated by an irreversible transition to the usual radiation-dominated nucleon gas. At recombination time the model has density fluctuations with a characteristic mass of ${10}^6$ solar masses.

Numerical studies by Betts and Oitmaa have led those authors to conjecture that in the $\mathrm{XY}$ model the ground-state magnetization $M_z$ is zero. This is a model of spins on a lattice with interactions $-J({S_n}^x{S_m}^x+{S_n}^y{S_m}^y)$, that can also describe a hard-sphere boson fluid. In the present note I prove the conjecture for arbitrary spins $\mathcal{S}=\frac{1}{2}, 1, \frac{3}{2}, \dots$ for positive $J$, and treat various generalizations.

A sum rule is derived from the connection of the critical specific heat with the critical correlation function in the disordered symmetric state. The "Ornstein-Zernike hole" which appears above the critical point must, by virtue of this sum rule, be canceled exactly by the "Fisher-Langer tail." It follows that the anomalous dimension index $\eta$ is fixed by the shape of the spectral function. A spectral function satisfying certain general properties yields $\eta \approx 0.04$.

A high-statistics photon spectrum from the reaction ${\pi }^{-}d\to \gamma \mathrm{nn}$, measured with a 0.72-meV-resolution pair spectrometer is compared with different theoretical spectra folded with the measured photon line from the reaction ${\pi }^{-}p\to \gamma n$. A value of $a_{\mathrm{nn}}=-18.5\mathrm{}\pm 0.5$ fm (theoretical error included) is deduced assuming a fixed value of ${\mathcal{r}}_{\mathrm{nn}}=2.8\mathrm{}\pm 0.1$ fm. The problem of extracting ${\mathcal{r}}_{\mathrm{nn}}$ using the present theories is indicated.

We present results of an experiment to detect axions produced by bremsstrahlung of 45-MeV electrons. No signal is found. We interpret our upper limits in terms of two models.

The first experimental evidence for electron correlation in nuclear electron-capture ratios is reported. The measured $\frac{M}{L}$ capture ratio of ${}_{}{}^{37}{}_{}{}^{}\mathrm{Ar}$, 0.073±0.007, is inconsistent with Hartree-Fock calculations, but can be explained by final-state correlation, if the disputed $3s3p^6$ assignment in Cl i is adopted. The discrepancy in the experimental $\frac{K\beta }{K\alpha }$ x-ray intensity ratio of Cl is removed, and the designation of $L_{23}$ x-ray and $3s$ photoemission satellites in Cl is revised.

Alpha-transfer reactions (${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$), (${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$), and (${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$) on a ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ target were studied at 262, 153, and 149 MeV, respectively. Analysis in terms of the direction-reaction theory reproduced the observed continuum spectra and angular distributions well, except for the cross section of the reaction (${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$) at small angles, which is attributed to a projectile breakup process.