We use the time-projection chamber detector to study mechanisms of baryon production in the central rapidity region of jets from $e^{+}{e}^{-}$ annihilation. On the basis of angular correlations between protons and antiprotons, we exclude the isotropic decay of heavy mesonic clusters as a dominant source of baryons at 95% confidence level. The diquark mechanisms used in string fragmentation models reproduce the data, provided that diquarks are formed in a two-step process which allows mesons to be produced in between the baryon and antibaryon.

The Gamow-Teller strength function in ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$ has been measured by use of the reaction ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}(p, n)$ at $E_p=120\mathrm{} \mathrm{and} 200$ MeV. While a significant fraction of the total strength is associated with excited states located below particle-emission threshold, the first excited state exhibits little strength. Excited-state contributions to the total solar-neutrino capture rate for a ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ detector are about 14 solar neutrino units for the neutrino spectrum of the standard solar model and about 3-4 solar neutrino units for representative nonstandard solar models.

A measurement is reported of the mean lifetime, $\tau$, for the weak decay of ${}_{\Lambda }{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{\Lambda }{}^{11}{}_{}{}^{}\mathrm{B}$ hypernuclei. The experiment detected energetic protons from the hypernuclear nonmesonic decay $\Lambda +p\to n+p$, in coincidence with hypernuclear production by the strangeness-changing reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(K^{-}, {\pi }^{-}){}_{\Lambda }{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(K^{-}, {\pi }^{-})p, {}_{\Lambda }{}^{11}{}_{}{}^{}\mathrm{B}$. The measured ground-state decay lifetimes $\tau \left({}_{\Lambda }{}^{12}{}_{}{}^{}\mathrm{C}\right)=(2.11\mathrm{}\pm 0.31)\times {10}^{-10\mathrm{}}$ sec and $\tau \left({}_{\Lambda }{}^{11}{}_{}{}^{}\mathrm{B}\right)=(1.92\mathrm{}\pm 0.22)\times {10}^{-10\mathrm{}}$ sec are compared with $\Lambda N$ weak-interaction calculations.

Glauber theory can describe elastic scattering of $\alpha$ particles by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, and 1H at 7 GeV/c if the phase of the nucleon-nucleon elastic-scattering amplitude varies with momentum transfer. The phase variation leads to diffraction patterns differing markedly from those typical of constant-phase calculations and greatly affects the magnitudes of the intensities. These changes are mainly due to changes in the interference between amplitudes for different orders of multiple scattering and to a decrease in their moduli.

Fissionlike decay was observed for fragments resulting from reactions of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$+${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at 15.3-MeV/u incident energy. The measured probabilities for fission decay, as well as previous measurements are consistent with equilibrium fission calculations.

The frame-transformation theory of electron interaction with a vibrating diatomic core is extended to allow for energy dependence of its parameters. The Born-Oppenheimer separation of electron and nuclear motion is preserved when the electron penetrates the molecular core. The extended theory reproduces the boomerang-model treatment of vibrational excitation in resonant $e$-${\mathrm{N}}_2$ collisions.

Phase-dependent resonance transitions induced in two-level atoms by a bichromatic field are reported. Strong phase effects are observed in the interaction of a fast atomic beam with a standing-wave rf field. In the atomic rest frame, this field consists of two components with different frequencies and a controlled initial phase difference. Numerical calculations including well-defined phase factors are performed in the time-dependent density matrix formalism. The observed effects are in excellent agreement with this theory.

We report investigations of spin exchange between ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$ nuclei and optically pumped Rb vapor. Polarization of 30% ($〈K_z〉=0.46\mathrm{}$) of 2×${10}^{19}$ atoms-${\mathrm{cm}}^{-3\mathrm{}}$ has been achieved with a vapor pressure of 3×${10}^{14}$ atoms-${\mathrm{cm}}^{-3\mathrm{}}$ of Rb. This high density of alkali metal can be efficiently optically pumped only when light trapping is suppressed by inclusion of at least 100 Torr of ${\mathrm{N}}_2$. In addition, we have made the first accurate measurement of the binary-collision spin-exchange rate: $〈{\sigma }_{\mathrm{ex}}v〉=(4.66\mathrm{}\pm 0.28)\times {10}^{-19\mathrm{}}$ ${\mathrm{cm}}^3$-${\mathrm{s}}^{-1\mathrm{}}$. Extension of these techniques to ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has yielded 5% polarization of 2×${10}^{19}$ atoms-${\mathrm{cm}}^{-3\mathrm{}}$ in a preliminary experiment.

The tracer-diffusion coefficient $D_t$ of polystyrene chains in semidilute, good-solvent solutions has been measured by forced Rayleigh light scattering for different polymerization indices of both labeled and unlabeled chains ($N$ and $P$, respectively). For $\frac{P}{N}\gg 5$, $D_t$ is found to be independent of $P$, and a pure reptative behavior is observed in the entire semidilute concentration range. For $\frac{P}{N}<5\mathrm{}$, the increase of $D_t$ when $P$ is decreased demonstrates the existence of tube-renewal effects whose magnitude, for a given $P$, only depends on the number of entanglements along the test chains.

The exponential divergence or convergence of nearby trajectories (Lyapunov exponents) is conceptually the most basic indicator of deterministic chaos. We propose a new method to determine the spectrum of several Lyapunov exponents (including positive, zero, and even negative ones) from the observed time series of a single variable. We have applied the method to various known model systems and also to the Rayleigh-Bénard experiment, and have elucidated the dependence of the Lyapunov exponents on the Rayleigh number.

Two-photon-resonant excitation of the sodium $3d$ level can lead to the generation of new frequencies either by amplified spontaneous emission at the $3d\to 3p$ transition frequency or by a resonantly enhanced four-wave mixing process. Competition between these two processes has been observed. The four-wave mixing process can suppress amplified spontaneous emission by preventing the excitation of the $3d$ level due to an interference between two different pathways connecting the ground ($3s$) and $3d$ states.

We have theoretically derived and experimentally demonstrated "narrow reject" pulses which give a uniform $\frac{\pi }{2}$ excitation off resonance, and zero excitation in a sharp hole directly on resonance. They are also insensitive to relaxation effects. This shape is symmetric and has only amplitude modulation, and so it can be implemented on most commercial NMR spectrometers or with laser modulators. It can replace conventional broadband $\frac{\pi }{2}$ pulses in most NMR or laser pulse sequences, in order to give solvent suppression or measure spectral diffusion.

We present measurements and pattern visualization of convection in a cylindrical container at low Prandtl number. We demonstrate that the weak turbulence previously detected in this situation is clearly an erratic wandering of rolls. We show that the transition from a stationary to a time-dependent pattern involves spontaneous nucleation of dislocations. We analyze this phenomenon in relation to the skewed varicose instability.

Numerical simulations of a simple model for ideal magnetohydrodynamic modes have shown stationary turbulence and transport at $\beta$ values substantially below the critical $\beta$ required for linear instability. The phenomena appears to be similar to subcritical turbulence in plane-parallel pipe flow.

There is a possibility that the phase separation process is coupled with other ordering processes such as crystallization. New types of phase separation behavior during the crystallization process in polymer blends with phase diagram are presented probably for the first time. Two different types of nonequilibrium phenomena take place simultaneously and new structures and new dynamics of pattern formation are observed as the result of the competition between these two phenomena.

We have discovered a correlation between lateral compressive strain in an elemental material and the reconstructed state of its surface. We studied continuous films of pure Ge epitaxially grown on Si(111) substrates. The in-plane lattice parameter varies continuously with film thickness while the surface symmetry changes from $c2\mathrm{}\times 8 \mathrm{to} 7\times 7$. The results indicate an important role of lateral compressive stress in the 7×7 reconstruction.

Polystyrene chains in solution have been crosslinked by $\gamma$ irradiation. The gelation reaction has been stopped at various stages before the gel point and the size distribution function has been measured. We show that the distribution functions obey a simple scaling law.

When two semiconductor superlattices are separated by a moderately thick tunneling barrier, one might expect novel features in the electronic transport associated with tunneling between the different superlattice minibands. We report on the highly anomalous electronic conduction in such a structure, and interpret the data in terms of energy filtering by the superlattice minibands.

It is demonstrated, both theoretically and experimentally, that a classically opaque metallic film can appear highly transparent when the conditions are established for the incident electromagnetic wave to excite coupled surface modes on both sides of the film.

The spin polarization of the electrons emitted from iron by irradiation with a laser pulse has been measured as a function of the intensity of the radiation. For a certain range of pulse energies the spin polarization reaches 100%, i.e., all electrons are emitted with their magnetic moment parallel to the direction of magnetization.