The pionic x-ray energies of the $4f-3d$ transition in $\pi$-P and the $5f-4d$ transition in $\pi$-Ti were measured with a bent-crystal spectrometer at the Nevis synchrocyclotron; and a new value of the pionic mass is deduced to be 139 567.5±0.9 keV, leading to an improved value for the $\mu$-neutrino mass of ${m_{{\nu }_{\mu }}}^2$=0.102±0.119 ${\mathrm{MeV}}^2$; $m_{{\nu }_{\mu }}<0.52\mathrm{}$ MeV, at 90% confidence level.

Enhancement of nonleptonic decays of the $D^0$ meson is explained by unitarity sum of quark diagrams with gluon productions, which is expressed by a diagram with nonexotic intermediate states. Experimental values, $\frac{{\Gamma }_{\mathrm{tot}}\left(D^0\right)}{{\Gamma }_{\mathrm{tot}}\left(D^{+}\right)}\approx 10$, are reasonably understood in our model and the enhancement of Cabbibo-suppressed decay of the $D^{+}$ meson is also explained. Our enhancement mechanism leads to the enhancement of $\Delta I=\frac{1}{2}$ amplitudes in nonleptonic decays of $K$ mesons.

The Franzini-Radicati mass relationship between isobars is reexamined to find out whether it provides a good test of the Wigner SU(4) symmetry in nuclei. It is found that the mass ratio is an extremely insensitive function of the symmetry mixing.

The technique of average resonance neutron capture can lead to the disclosure of sets of nuclear levels known to be complete for certain spin, parity, and excitation-energy ranges. This perceived completeness contains hitherto unrecognized consequences which are shown to present a powerful new tool for nuclear structure studies.

Both the magnitude and alignment of the transferred angular momentum in the reaction ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$+${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ have been measured as a function of $Q$ value via continuum $\gamma$-ray multiplicity and anisotropy techniques. Two regimes are observed: A low—$Q$-value regime where the aligned angular momentum component dominates over the random components, and a large—$Q$-value regime where the random components dominate and decrease the spin alignment.

Two independent emulsion experiments using Bevalac beams of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ at ∼2 GeV/nucleon find with > 99.7% confidence that the reaction mean-free paths of projectile fragments, $3<~Z<~26$, are shorter for a few centimeters after their emission than at larger distances, or than predicted from experiments on beam nuclei. This effect, which is enhanced in later generations of fragments, can be interpreted by the relatively rare occurrence of fragments that interact with an unexpectedly large cross section.

It is shown here how to map the problem with pseudospin $J$ into an equivalent one in which $\frac{1}{J}$ plays the role of $\hslash$ and canonical variables exist at the classical level. Bohr-Sommerfeld quantization of the equivalent theory is found to produce a spectrum in very good agreement with the exact results for the Lipkin-Meshkov-Glick model at $J=15\mathrm{} \mathrm{and} 25$. The method readily extends to the $\mathrm{SU}\mathrm{}\left(n\right)\mathrm{}$ case.

From a numerical analysis of the energy-level structure for hydrogen in a uniform magnetic field, evidence is found for an approximate dynamical symmetry which is effectively exact for many highly excited states. Identification of this approximate symmetry is expected to lead to new physical insights and to new calculational methods.

This paper reports narrowing and splitting of 7-ps-duration pulses from a mode-locked color-center laser by a 700-m-long, single-mode silica-glass fiber, at a wavelength (1.55 μm) of loss and large but negative group-velocity dispersion. At certain critical power levels, the observed behavior is characteristic of solitons.

Optical coherent transients are reported here for the first time in a pure, optically concentrated material (Eu${\mathrm{P}}_5$${\mathrm{O}}_{14}$). Qualitatively new behavior is found in the form of a systematic variation of the homogeneous dephasing time $T_2$ (∼ 20 μsec) across the inhomogenously broadened line. This is interpreted as evidence for delocalization of the excitation. In contrast, the dilute impurity system ${\mathrm{Eu}}^{3+}$: YAl${\mathrm{O}}_3$ shows narrower lines and no frequency dependence of $T_2$.

The beam-driven current produced by neutral injection into the DITE tokamak has been measured. The variation of this current with electron density and gas current has also been investigated. Good agreement is found between experiment and a model in which the Fokker-Planck equation describes the fast-ion distribution and a magnetic field diffusion equation gives the time dependence of the electromagnetic fields.

In a hydrogen plasma ($T_e=2.5\mathrm{}$ eV, $T_i=1.5\mathrm{}$ eV), excitation of ion Bernstein waves by an externally placed electrostatic antenna has been investigated for $\omega \simeq 2{\Omega }_i$. Mode transformation of the electron plasma wave at $\omega \simeq {\omega }_{\mathrm{pi}}$ without observable reflection was observed, followed by strong excitation of the ion Bernstein wave. Detailed measurements of $k_{\perp }(\omega ,k_{\parallel })$ and of the wave-packet trajectory show excellent agreement with theory.

The electron-density profile in the corona of 40-μm-diam glass spheres irradiated by 100-GW, 50-ps pulses from a Nd-glass laser was measured. Critical density scale lengths of 1.5 μm have been observed at rather low intensity (3×${10}^{14}$ ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$). At high irradiance (${10}^{15}$ ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$) variation of density is sufficient to blur the interferograms. This observation is correlated with an increase of fast-ion emission.

Structure-dependent $\mathrm{Si}\mathrm{}\left(2p\right)\mathrm{}$ surface core-level shifts and $2p$ photothreshold spectra which yield new surface geometry information are reported. For Si(100)-(2×1), ∼0.5 monolayer of surface atoms are found shifted to smaller binding energy (-0.5 eV) relative to the bulk; this rules out symmetric pairing models. Si(111)-(7×7) and Si(111)-(2×1) show different surface $2p$ core-level spectra (e.g., $\frac{1}{6}$ layer shifted -0.7 eV versus ½ layer shifted - 0.4 eV), suggesting different geometries. Si(111)-(1×1)H exhibits first-layer (+ 0.26 eV) and second-layer (+ 0.15 eV) shifts.

A particular example of impurity diffusion in a solid is calculated and it is noted that the usual assumptions for Brownian-motion theory are invalid in this case.

Raman scattering measurements are reported in amorphous boron-rich alloys of Y and La which indicate cagelike or in-band resonant modes not previously observed in noncrystalline solids. Low-frequency, intense Raman peaks indicate weak metal-boron bonding that is significantly reduced in the Y system. This is similar to the recent results in superconducting crystalline hexaborides and suggests that the anomalous transition temperature of Y${\mathrm{B}}_6$ is a consequence of general bonding trends that persist in the amorphous state.

The absoulte spin susceptibility of As${\mathrm{F}}_5$-doped trans-polyacetylene, ${\left[\mathrm{CH}{\left(\mathrm{As}{\mathrm{F}}_5\right)}_y\right]}_x$, was determined by spin resonance techniques for $0.0004<~y<~0.138$. The Curie-law contribution decreases above $y=0.001\mathrm{}$ to a level less than 1 ppm in the highly conducting regime. The temperature-independent Pauli term is small (≤5×${10}^{-8\mathrm{}}$ emu/mole) for $y<\mathrm{}0.01\mathrm{}$, remains small up to $y=0.05\mathrm{}$, and shows an abrupt increase near $y=0.07\mathrm{}$ to a value of ∼ 3 × ${10}^{-6\mathrm{}}$ emu/mole at higher concentrations. The results are consistent with the soliton doping mechanism.

Optical absorption measurements on very pure CuCl single crystals, prepared by a novel process, show the exponential drop of the direct optical absorption edge to continue below an absorption coefficient $K\sim {10}^{-2\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. This rules out unambiguously the existence of an indirect-gap absorption below 3 eV, which is not only consistent with band-structure calculations but also excludes pure CuCl from being a suitable candidate for intrinsic high-$T_c$ superconductivity (on the grounds of existing theories).

The phase diagram of the ternary system potassium laurate-1-decanol-D${}_2{}^{}{}_{}{}^{}\mathrm{O}$ was studied over concentration ranges where nematic phases are likely to occur. Two uniaxial nematic phases which are separated by a biaxial nematic phase are found. In limited concentration range the following phase sequence may be observed reversibly on heating and on cooling: isotropic-uniaxial nematic (positive optical anisotropy)-biaxial nematic-uniaxial nematic (negative optical anisotropy)-biaxial nematic-uniaxial nematic (positive optical anisotropy)-isotropic.

An ab initio calculation for the solid-solid phase transformation, static structural properties, and the lattice dynamics of Si is presented. A density-functional pseudopotential scheme is used with the atomic number as the only input. The detailed properties of the diamond to $\beta$-tin transition are accurately reproduced. The phonon frequencies and mode-Grüneisen parameters at $\Gamma$ and $X$, along with the lattice constant, bulk modulus, and cohesive energy, are calculated and found to be in excellent agreement with experiment.