Mössbauer ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ spectra of $1T$-Ta${\mathrm{Se}}_2$ at 300 K show only two of three Ta sites predicted by 6:6:1 charge-density-wave models. They have equal amplitude and are separated by a shift the authors calibrate as 0.34(0.17) electrons. The unseen site is experimentally excluded from the region between ${\mathrm{Ta}}^{4+}$ and ${\mathrm{Ta}}^{5+}$. Site linewidths limit possible secondary splittings by interlayer effects to 0.018 of the primary splitting. The $2H$-Ta${\mathrm{Se}}_2$ data at 52 K are consistent with an orthorhombic charge-density wave with three equal Ta sites at -0.049(0.020), +0.033(0.016), and +0.023(0.011) electrons relative to ${\mathrm{Ta}}^{4+}$.

A simple extension of the SU(5) Higgs system is presented and shown to yield a satisfactory inflationary scenario.

The inertial frame of reference in the neighborhood of a test body provided by the construction of Fermi normal coordinates is generalized to include the effect of the body's gravitational field. The metric obtained provides a simple physical description of relativistic corrections to the orbital motion of a satellite of the Earth. The main correction is the nonlinear Schwarzschild field of the Earth; in these coordinates there are also three much smaller terms arising from the solar tidal influence.

Time dependence of the fundamental "constants" is examined within the framework of Kaluza-Klein theories. Relationships among low-energy couplings and masses are derived. It is suggested that detection of a time variation in any of these parameters may provide evidence for extra space dimensions. Experimental bounds are reviewed and new measurements advocated.

The inclusive reactions $p+A\to p+X$ are studied in the framework of an evolution process in momentum degradation. All measured inclusive cross sections between C and Pb for all $x$ values can be understood in terms of one basic degradation function which involves only one adjustable parameter. The inferred degradation length in nuclear matter is 17 fm.

At certain combinations of temperature and density, nuclear matter may exist as a liquid-gas mixture exhibiting phase instabilities, a characteristic signature of which may be found in the emission of intermediate-mass fragments in nuclear collisions. The present analysis of fragment distributions from proton- and heavy-ion-induced reactions, in the framework of a theory of condensation, is suggestive of the occurrence of such phase transitions with a critical exponent $k\sim 1.7$ and a critical temperature $T_c\sim 12$ MeV.

The exchange of a virtual nuclear collective mode is shown to have an important effect on the isobar-nucleon-hole interaction. A numerical estimate for the Landau parameter in the isobar-nucleon sector is given by solving the fully coupled Babu-Brown equation in a simple model.

The levels of ${}_{}{}^{225}{}_{}{}^{}\mathrm{Ac}$ are reliably assigned by detailed measurements of the radiations associated with the $\alpha$ decay of ${}_{}{}^{229}{}_{}{}^{}\mathrm{Pa}$ and the $\beta$ decay of ${}_{}{}^{225}{}_{}{}^{}\mathrm{Ra}$. Extremely large enhancements of $E1\mathrm{}$ transition rates are found in ${}_{}{}^{225}{}_{}{}^{}\mathrm{Ac}$. The adequacy of a single-particle description of strong octupole correlations is examined.

High-resolution, low-background, two-dimensional $\gamma$-ray energy correlations $E\left({\gamma }_1\right)$ vs $E\left({\gamma }_2\right)$ have been measured at high spin in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ with the spectrometer TESSA2. Ridges characteristic of rotational behavior are observed for $\gamma$-ray energies $0.8<~E\left(\gamma \right)<~1.35$ MeV. The separation of the ridges gives a dynamical moment of inertai ${{\mathcal{I}}_{\mathrm{band}}}^{\mathrm{}\left(2\right)\mathrm{}}=(85\mathrm{}\pm 2){\hslash }^2$ Me${\mathrm{V}}^{-1\mathrm{}}$ indicating a quadrupole deformation of $\epsilon \approx 0.51$ for a rigid body assuming $\gamma =0\mathrm{}$.

It is shown that the elastic scattering of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in the center-of-mass energy range $6<E<\mathrm{}31\mathrm{}$ MeV exhibits forward glory enhancement. Semiclassical analysis of the quantity $\Delta {\sigma }_T\equiv {\sigma }_R-\int \left[\frac{d{\sigma }_{\mathrm{Ruth}}}{d\Omega }-\frac{d{\sigma }_{\mathrm{el}}}{d\Omega }\right] d\Omega$ indicates that the best candidate for a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ interaction potential is a small-radius, deep Woods-Saxon potential, in qualitative agreement with the results obtained from recent analyses of $\frac{d{\sigma }_{\mathrm{e}1}}{d\Omega }$ done at higher energies.

Results are presented from an electronic experiment to check directly the anomalous mean-free-path phenomena observed in high-energy heavy-ion collisions. The mean-free-path measurements presented are based on interactions of 1.25 × ${10}^5$ secondary fragments produced by interactions of $1.8A$-GeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ in Lucite. The result is consistent with no anomalon phenomena and rules out (95% confidence limit) anomalons being more than 2% abundant if they have interaction lengths between 0.4 and 3 cm.

The emission of electrons in the forward direction in collisions of ${\mathrm{Au}}^{15+}$ with He has been studied in coincidence with final projectile charge state. The large transfer-ionization cross section observed can be accounted for by transfer of two electrons to a highly correlated state on the ion followed by loss of one electron to the continuum. Autoionization lines are observed which are due to transfer plus excitation.

It is shown that the efficiency of classical gas-dynamic isotope separation can be strongly improved with the aid of a relatively weak cw infrared laser. Irradiation in the collisional region of a free jet of S${\mathrm{F}}_6$ diluted in argon with a 20-W C${\mathrm{O}}_2$ laser leads to an increase in the overall enrichment factor $\alpha$ from about 1.01 to nearly 2, at conditions that have not yet been completely optimized. Efficient isotopically selective condensation is demonstrated for the first time, the inhibition of homogeneous condensation being due to the selective vibrational excitation of one S${\mathrm{F}}_6$ isotopomer.

An optical ring cavity is considered in which the propagation of an envelope pulse is described by the nonlinear Schrödinger equation. This cavity is pumped by a coherent train of pulses. As the pump intensity is increased a sequence of period-doubling bifurcations is followed by an inverse sequence (chaotic band structure). The global (moment) and local (field) properties of the pulse sequences have the same dynamical behavior. Bistability and the merging of two chaotic branches have also been observed.

A powerful new approach to the study of particle transport and helium ash confinement in high-temperature fusion plasmas is demonstrated by charge-exchange recombination spectroscopy of ${\mathrm{He}}^{++}$ in Ohmically heated PDX discharges. Time- and space-resolved measurements of ${\mathrm{He}}^{++}$ density following a short puff of helium gas into the plasma edge are fitted with use of a diffusive/convective transport model with coefficients $D=(2.1\mathrm{}\pm 0.9)\times {10}^4$ ${\mathrm{cm}}^2$ ${\mathrm{s}}^{-1\mathrm{}}$ and $\frac{v\left(r\right)\mathrm{}}{D}=\frac{(0.8\mathrm{}\pm 0.3)\partial \left(\ln n_e\right)}{\partial r}$.

Multistep processes involving excited atomic states are found to produce a substantial increase in the stopping cross section for a neutral hydrogen beam injected into a plasma, and thus to reduce the beam penetration. For typical plasma and beam parameters of current large tokamak experiments, the stopping-cross-sectional enhancement is found to vary from 25% to 50%, depending on the beam energy, plasma density, and impurity level. For neutral hydrogen beams with energies ≳ 500 keV, envisioned in tokamak and mirror reactor designs, the enhancement can be as large as 80%-90%.

A new technique is reported for in-situ, nonintrusive, and sensitive measurement of plasma electric fields with high spatial resolution (≲${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^3$). Fields as small as 40 V/cm are measured by spectral resolution of laser-induced fluorescence from Stark-mixed parity levels. The technique is demonstrated by excitation of the $A{}_{}{}^1{}_{}{}^{}\Pi -X{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ band system of BCl, produced in an rf discharge through B${\mathrm{Cl}}_3$. The absolute measurement of sheath fields, which has been elusive, is now possible.

Normal shear modes of axial symmetry were excited in polycrystalline samples of blue phase I. An average shear modulus, $E$, is determined from the frequencies of these modes. $E$ is found to vary by nearly two orders of magnitude throughout the blue-phase temperature range. The authors report the first observation of faceted single crystals of blue phase I growing from the isotropic phase. These have enabled them to determine the blue phase I lattice constant.

The first electron-spin-resonance observation of positive ions in liquid helium is reported. Experiments were performed in pure ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures. The signals exhibit an anomalous $g$ shift and a temperature-dependent linewidth. These data are tentatively interpreted in terms of the "snowball" model.

Molecular hydrogen in amorphous Si: H films prepared by glow discharge is detected calorimetrically at low temperatures from the heat release associated with the ortho-to-para conversion. The ${\mathrm{H}}_2$ concentration is much higher in samples prepared at 250°C (6.4 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$) than in those prepared at room temperature (2.4 × ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$). These results support a recent model of ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ nuclear spin relaxation via interaction with ${\mathrm{H}}_2$ molecules in $a$-Si: H and, in addition, give new insight into the structure of $a$-Si: H.