The depths of shower maximum of cosmic-ray showers have been determined in the sea-level size range ${10}^5<N_e<{10}^7$ with use of atmospheric Cherenkov techniques. The mean depth has been found to increase rapidly in the middle of this range, suggesting a change in the mean primary composition from heavy to light nuclei.

A ring of tightly torsion-coupled, overdamped pendulums is subject to fluctuations and to a static applied torque. Over a wide range of forces, motion in this system occurs through the nucleation of a kink and antikink pair, their subsequent separation through the driving force, and eventual annihilation by collision with other kinks. This picture is used to calculate the mean angular pendulum velocity as a function of applied torque.

The positive-mass conjecture states that for a nontrivial isolated physical system, the total energy, which includes contributions from both matter and gravitation, is positive. This assertion has been demonstrated in the important case when the space-time admits a maximal slice. Here this assumption is removed and the general mass conjecture is demonstrated. Also the topology of all possible asymptotically flat space-times satisfying the local energy condition is determined.

A model based on the group SU(9) is proposed to relate three quark-lepton generations. There is sufficient unification to give two new relations between the nine fermion masses. The guiding principle is to minimize the number of Higgs scalars necessary to obtain mass relations.

The static quadrupole moment, $Q_{2^{+}}$, and $B(E2;0^{+}\to 2^{+})$ of the first excited state of ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ have been measured using the reorientation effect in Coulomb excitation, giving $Q_{2^{+}}=-5\mathrm{}\pm 6(+1\mathrm{}\pm 6)e·{\mathrm{fm}}^2$ and $B(E2;0^{+}\to 2^{+})=253\mathrm{}\pm 30 (261\mathrm{}\pm 30)e^2·{\mathrm{fm}}^4$ if the interference from the second excited state is constructive (destructive). The result for $Q_{2^{+}}$ indicates that Hartree- Fock calculations which ignore solutions other than those with $K=0\mathrm{}$ are inadequate, and supports shell-model calculations and band-mixed Hartree- Fock calculations.

The inclusive pion spectrum from the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}$+${}_{}{}^6{}_{}{}^{}\mathrm{Li}$→${\pi }^{-}+X$ at 910 MeV was measured at 0° with moderate resolution up to the kinematic limit of the two-body final-state reaction. A first analysis shows that the production of high-energy pions cannot be explained by the $\mathrm{NN}\to \mathrm{NN}\pi$ process using conventional nucleon momentum distributions. At the end of the spectrum a clear deviation from the general falloff slope is observed and attributed to the doubly coherent reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}$+${}_{}{}^6{}_{}{}^{}\mathrm{Li}$→${}_{}{}^9{}_{}{}^{}\mathrm{C}$+${\pi }^{-}$.

It is shown that the reduction in the strengths of analog-antianalog $\gamma$ transitions ($M1\mathrm{}$) can be understood without taking recourse to the presence of core polarized states. The results of calculations for various transitions are presented and compared with experimental data.

Total cross sections for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$($\gamma$,${\pi }^{-}$)${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$($\gamma$,${\pi }^{-}$)${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ have been measured from threshold to 360 MeV photon energy by detecting the radioactivity of the residual nuclei, thereby singling out the ground state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ and the ground and first excited states of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$. The cross sections are found to peak at about 40 MeV pion energy and then to fall gradually. In contrast to pion charge exchange and other photopion experiments, these results are well reproduced both in shape and in magnitude by distorted-wave impulse-approximation calculations.

Total cross sections for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$($\gamma$,${\pi }^{-}$)${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$($\gamma$,${\pi }^{-}$)${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ are evaluated in the impulse approximation, with use of the Blomqvist-Laget photoproduction operator and pion distorted waves. A peak at low energies and the falloff of the cross section with increasing energy are found to be consequences of the changing overlap of pion waves with nuclear transition densities.

The reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$\alpha$)${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$\alpha$)${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$ were investigated at an incident energy of 145 MeV. In the reaction with the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ target, broad peaks are observed at forward angles which correspond to the molecular resonance states of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system, while the spectra with ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ target show only a smooth continuum.

Kinematically complete experiments have been performed on the three-body exist channels in 7.5 MeV/amu ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ + ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ + ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$. No evidence was found for an instantaneous three-body breakup. Instead, a two-step nature with minimum scission-to-scission times of ${10}^{-20\mathrm{}}$ s has been derived even for intermediate nuclei $Z>\mathrm{}110\mathrm{}$. However, the observed fission-fragment angular distributions in this region are incompatible with the usual saddle-point concept.

The entropy of the fireball formed in central collisions of heavy nuclei at center-of-mass kinetic energies of a few hundred MeV per nucleon is estimated from the ratio of deuterons to protons at large transverse momentum. The observed paucity of deuterons suggests that strong attractive forces are present in hot, dense nuclear matter, or that degrees of freedom beyond the nucleon and pion may already be realized at an excitation energy of 100 MeV per baryon.

We have measured cross sections for evaporation residues, fission, and direct and evaporative ${}_{}{}^1{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in reactions of 222-340-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ with ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{164}{}_{}{}^{}\mathrm{Dy}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. Fusion cross sections are also presented for 77-167-MeV ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{182}{}_{}{}^{}\mathrm{W}$ and 187-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$. The $Z$ dependence of the evaporative H/He indicates a breakdown of phase-space models for fission-evaporation competition. The large cross sections observed for direct H/He emission force serious consideration of energy dissipation by H/He ejection during the initial impact.

A very simple procedure to extract pseudopotentials from ab initio atomic calculations is presented. The pseudopotentials yield exact eigenvalues and nodeless eigenfunctions which agree with atomic wave functions beyond a chosen radius ${\mathcal{r}}_c$. Moreover, logarithmic derivatives of real and pseudo wave functions and their first energy derivatives agree for $\mathcal{r}>{\mathcal{r}}_c$ guaranteeing excellent transferability of the pseudopotentials.

By a generalization of the Herbst-Simon dispersion relation for hydrogen in an electric field, an expansion asymptotic in $N$ for the perturbed energy coefficient ${E_{n_1{n}_{2}m}}^{\mathrm{}\left(N\right)\mathrm{}}$ is obtained from the formal asymptotic expansion (in the field strength $F$) for the ionization rate. Perturbation-theory calculations of ${E_{n_1{n}_{2}m}}^{\mathrm{}\left(N\right)\mathrm{}}$ to $N\sim 150$ confirm the formula. Via reverse use of the dispersion relation, perturbation-theory values of ${E_{n_1{n}_{2}m}}^{\mathrm{}\left(N\right)\mathrm{}}$ yield numerical values for constants in the ionization-rate expansion that are tediuous to obtain directly. Ionization rates so calculated compare favorably with values obtained by others.

Experimental evidence for filamentation of C${\mathrm{O}}_2$-laser radiation in an underdense, hydrogen plasma has been obtained from temporally resolved x-ray measurements. Transient x-ray bursts due to high-energy electrons in a filament of size $\sim 2\lambda$ are observed superimposed upon the cold thermal bremsstrahlung emission. A strong correlation between the high-energy x-ray emission and stimulated Brillouin scattering has also been observed, both in saturation characteristic and spatial dimensions.

The quasilinear theory of collisionless test particle diffusion in stochastic magnetic fields is extended to include the effects of finite gyroradius, particle drifts, and magnetic trapping. Runaway-electron confinement is substantially improved relative to earlier estimates which assumed that particles exactly followed field lines. Trapped particles are not expected to be stochastic.

The specific heat of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ from 0.8 to 20 mK at zero pressure has been measured. Above ∼ 3 mK the specific heat is linear in temperature and $\frac{C}{\mathrm{nRT}}=2.11\mathrm{}$ ${\mathrm{K}}^{-1\mathrm{}}$, which is 30% less than the currently accepted value. Below 3 mK, $C$ appears to deviate increasingly from this relationship reaching, at the superfluid transition $T_c=1.04\mathrm{}$ mK, a value 9% in excess of the extrapolated linear specific heat. This Letter discusses the anomalous behavior and its consequences with regard to the interpretation of our data.

Evidence is presented for the trapping of positive muons at monovacancies and divacancies in quenched aluminum. The annealing of vacancies as sensed by the muon-spin-rotation effect is compared to positron annihilation measurements on identically prepared samples, showing that whereas positrons are trapped primarily at small vacancy clusters, muons are trapped mainly at monovacancies and diavancancies. Furthermore, the data indicate that it may be possible to study monovacancies and divacancies separately with the muon-spin-rotation technique.

We have studied, using computer simulation techniques, the properties of edge and screw dislocations in an amorphous Lennard-Jones solid. We find the edge dislocation to be unstable and the screw to be stable. The elastic properties of the screw dislocation in the amorphous solid are like those in a crystal.