We have measured the total cross sections of ${\Omega }^{-}$ and ${\overline{\Omega }}^{+}$ forward ($x_{\mathrm{F}}>~0$) inclusive production in $K_L^0$-carbon interactions in the range $E_{K^0}=80\mathrm{} \mathrm{to} 280$ GeV to be 3.5±1.4 and 2.4±1.0 μb, respectively. We observe that the $x_{\mathrm{F}}$ distributions for both of these states are increasing from $x_{\mathrm{F}}=0\mathrm{}$ to $x_{\mathrm{F}}\approx 0.6$. The $p_{\perp }^2$ distributions are described as an exponential function in $p_{\perp }$ with an average $p_{\perp }^2$ of 0.540 Ge${\mathrm{V}}^2$/${\mathit{c}}^2$.

A variant of the conventional Skyrme model is investigated. At the tree level the Wess-Zumino action is absent but elementary fermions (quarks) are present. The Wess-Zumino action is generated by integration over the fermions and it depends nontrivially on the fermion masses. Consequently large skyrmions have a baryon number and a half-integer spin, while small skyrmions have no baryon number and an integer spin.

The first systematic study of inclusive pion double charge exchange in nuclei is reported. Doubly differential cross sections for the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({\pi }^{+}, {\pi }^{-})X$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}({\pi }^{+}, {\pi }^{-})X$ have been measured at incident pion energies of 120, 150, 180, 210, 240, and 270 MeV at three to five angles in the range from 25° to 130° with complete coverage of the outgoing pion energy spectrum. Similarly, the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({\pi }^{-}, {\pi }^{+})X$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{C}({\pi }^{-}, {\pi }^{+})X$ were studied at 180, 210, and 240 MeV at three angles.

The dynamics of the first-order liquid-gas phase transition in the final expansion stage of a high-energy heavy-ion collision is studied. The high entropy values extracted from light-particle abundances measured at low bombarding energies, $E_{\mathrm{lab}}=(50-300)A$ MeV, are explained as a consequence of the liquid-gas phase coexistence at the breakup of the nuclear matter.

The collective properties of ${}_{}{}^{70,72,74,76}{}_{}{}^{}\mathrm{Ge}$ have been explored through the measurement of the transition charge densities of the first two $2^{+}$ states up to a momentum transfer of 3.0 ${\mathrm{fm}}^{-1\mathrm{}}$. Their spatial structure and their apparently anomalous behavior are readily explained in the framework of the interacting boson model.

The meson-exchange currents and nucleon-nucleon short-range correlation have been invoked in the calculation of the charge form factor of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ in the shell model with a harmonic-oscillator basis. The contribution from exchange current to the correlated form factor is not large for small momentum transfer but becomes significantly noticeable around the first minimum. A second minimum at $q^2=26.0\mathrm{}$ ${\mathrm{fm}}^{-2\mathrm{}}$ is predicted by correlation but the exchange-current contribution brings this to around $q^2=24.0\mathrm{}$ ${\mathrm{fm}}^{-2\mathrm{}}$.

We have measured the deuteron magnetic form factor $B\left(q^2\right)$ for values of the momentum transfer squared between 7 and 28 ${\mathrm{fm}}^{-2\mathrm{}}$. The data are compared with relativistic and nonrelativistic predictions including meson-exchange-current contributions. Significant disagreement is found for large momentum transfers.

Supersymmetry, recently proposed in the context of the interacting-boson model, is extended to include simultaneously odd-even, even-odd, and odd-odd partners of a given even-even nucleus. The quartet of nuclei ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Pt}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ is shown to be well described within this frame-work.

A double-resonance technique is used to make the first direct observation of collision-induced electronic energy transfer in a diatomic molecule through an energy gap much greater than $\mathrm{kT}$ (208 ${\mathrm{cm}}^{-1\mathrm{}}$ at $T=300\mathrm{}$ K). Surprisingly, $J$ specificity is observable in this transfer process which appears to follow optical-like propensity rules in spite of the large energy gap of ∼ 1760 ${\mathrm{cm}}^{-1\mathrm{}}$ between the initially populated ${\mathrm{N}}_2^{+}$ $A(v^{\prime }=4)$ state and the lower-lying $X(v^{\prime \prime }=7)$ ground-state level to which it is quenched. Room-temperature helium is the collision partner.

A new method for wave functions especially suited to studies of transition-metal systems is proposed and applied to ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{Cr}}_2$, and ${\mathrm{Mo}}_2$, where it provides accurate bond energies and bond distances. The resulting potential curve for ground state ${\mathrm{Cr}}_2$ has a double well, and experiments to detect this unusual feature are suggested. The ${\mathrm{Mo}}_2$ studies lead to an assignment for the long-lived emitter observed in matrix studies (it is the $\delta {\delta }^{*}{}_{}{}^3{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ state).

New techniques are presented for the calculation of lower bounds to energies of atoms and ions. A combination of effective-field and intermediate-problem methods is used to seek intermediate operators which rapidly approximate the lower spectrum of the full Hamiltonian. Effectiveness of the techniques is demonstrated by showing that very small-scale calculations suffice to free the ground state of Li from the continuum, and to approximate the ${\mathrm{Li}}^{+}$ ground state within 0.8%.

We present a method of accurately solving the time-dependent Dirac equation in the presence of strong electromagnetic fields. A hybrid space-time lattice is employed which permits the simultaneous description of electron- and positron-production processes in heavy-ion collisions. We apply our method to interpret the positron spectra observed in low-energy U + U and U + Cm collisions.

We present measurements of the fluid velocity in a rotating Couette-Taylor system of aspect ratio $L$ near 1. At small angular speed $\omega$ of the inner cylinder, the system contains a symmetric vortex pair. As $\omega$ increases, the vortex boundary moves off center, and a suitably defined order parameter $\psi$ becomes nonzero. This bifurcation changes from forward to backward as $L$ is increased. Results for $\psi$ agree quantitatively with the predictions of a Landau model for tricritical behavior.

Superfluorescence emitted from small regions of the output face of an initially inverted medium is found to exhibit ringing; this confirms that coherent ringing is an intrinsic property of superfluorescence. The system studied is a pure two-level Rb transition at $\lambda =2.73\mathrm{}$ μm, prepared in a cell by means of cw single-mode radiation. The Fresnel number of the sample is 1.7.

In this Letter we show that the fixed points of the Ikeda map are more unstable to perturbations with a short-scale transverse structure than to plane-wave perturbations. We correctly predict the most unstable wavelength, the critical intensity, and the growth ratés of these disturbances. Our result establishes that, for a large class of nonlinear waves, spatial structure is inevitable and drastically alters the route to chaos. In an optical cavity the consequence is that the period-doubling cascade is an unlikely scenario for transition to optical chaos.

An ultraviolet-laser-ionized channel in low-pressure benzene has been successfully used to guide and focus a 7-kA relativistic electron beam over distances up to 4 m. In addition, phase-mix damping of coherent, transverse beam motion has been demonstrated. A simple analytical model of the equilibrium beam profile is presented which is in reasonable agreement with the data.

Detailed studies of low-frequency microturbulence are presented. We utilize a unique multi-channel far-infrared ($\lambda =1.22\mathrm{}$ mm) laser scattering system capable of measuring the entire $S(k_{\perp }, \omega )$ spectrum during a single tokamak discharge. A statistical dispersion is unfolded for $k_{\theta }$ which exhibits a phase velocity $\simeq 3v_{\mathrm{De}}$ at low $k_{\theta }$ with a distinct rolloff for $k_{\theta }>~9$ ${\mathrm{cm}}^{-1\mathrm{}}$. In addition, a strong spatial asymmetry is observed in the $k_{\theta }$ density-fluctuation distribution which reverses with toroidal current direction.

A new scheme for accelerating electrons, employing a bunched relativistic electron beam in a cold plasma, is analyzed. We show that energy gradients can exceed 1 GeV/m and that the driven electrons can be accelerated from ${\gamma }_{0}m{c}^2$ to $3{\gamma }_{0}m{c}^2$ before the driving beam slows down enough to degrade the plasma wave. If the driving electrons are removed before they cause the collapse of the plasma wave, energies up to $4{\gamma }_0^{c}m{c}^2$ are possible. A noncollinear injection scheme is suggested in order that the driving electrons can be removed.

For an electron plasma which is magnetically confined in a cylindrical field geometry, radial expansion occurs only if the angular momentum of the plasma changes. We discuss nonlinear collective processes by which perturbing, static, asymmetric fields can transfer angular momentum, but not energy, to the plasma and produce radial expansion. For example, the field asymmetry can act as a pump which excites daughter modes via the decay instability. Alternatively, the pump can drive a mode by induced scattering from particles.

Fractal-like structures have been observed in sputter-deposited thin films of Nb${\mathrm{Ge}}_2$. These structures exhibit a striking resemblance to those produced by computer simulations of diffusion-limited aggregation using the Witten-Sander model. An effective fractal dimensionality of about 1.9 has been determined from digitized photomicrographs. Our results indicate a two-stage growth process in which an initial structure with a fractal dimensionality of about 1.7 is thickened by a subsequent growth process.