We report a new value for the universal gas constant $R:8.314471\mathrm{}\pm 0.000014$ J ${\mathrm{mol}}^{-1\mathrm{}}$ ${\mathrm{K}}^{-1\mathrm{}}$. The standard error of $R$ has been reduced by a factor of 5, to 1.7 ppm. $R$ was determined from the speed of sound in argon contained within a thick, spherical shell at the temperature of the triple point of water $T_t$. The volume of the shell was measured by our weighing the mercury required to fill it at $T_t$. The molar mass of the argon was determined relative to that of a standard with accurately known chemical and isotopic composition by use of speed-of-sound data.

The calculation of rapidly converging lower and upper bounds to the ground-state energy, $E_g$, of hydrogenic atoms in superstrong magnetic fields ($B\gtrsim {10}^9$ G) has been an important theoretical problem for the past twenty-five years. Much effort has gone into reconciling the many different estimates for $E_g$ predicted by an assortment of techniques. On the basis of recently developed eigenvalue moment methods, a precise solution involving rapidly converging bounds to $E_g$ for arbitrary superstrong magnetic field strengths, is now possible.

We study, by means of numerical simulations, the most fundamental issue of cosmic-string evolution: the existence of a scaling solution. We find strong evidence that a scaling solution does indeed exist. This justifies the main assumption on which the cosmic-string theories of galaxy formation are based. Our main conclusion coincides with that of Albrecht and Turok in previous work, but our results are not consistent with theirs. In fact, our results indicate that the details of string evolution are very different from the standard dogma.

A procedure is described for obtaining new exact solutions for the purely cubic form of Witten's bosonic string field theory. These solutions do not correspond to conformally invariant $\sigma$ models. Some of them have no tachyons in their spectrum of linearized fluctuations (but may have negative-norm states). Others make no reference to a space-time metric.

A consistency condition for anomalous gauge theories is used to show that the usual form of the chiral anomaly is inadmissible and that a different but equivalent form yields Faddeev's Schwinger term.

Studies of the Schwinger-Dyson equation for the gluon propagator in the pure gauge sector have shown it to be strongly enhanced at low momenta. This enhancement in turn generates a severe suppression of the fermion propagator for massless quarks at the same low momenta, killing the pole at $p=0\mathrm{}$. Here we compute how loops of such quarks affect the gluon propagator and find they reduce the gluon's infrared enhancement by an amount out of proportion to their relative insignificance in the perturbative short-distance regime, indicating their unquenchable importance.

We show that new aspects of the physics of microclusters can be investigated accurately with ab initio molecular dynamics. We present results on a number of properties of ${\mathrm{Si}}_N$ aggregates ($N$ up to 10) at both zero and finite temperatures. The results of dynamical simulated annealing for the ground state point to a complex growth sequence. Simulations at finite temperatures show the existence of two regimes, solidlike and liquidlike, with substantially different electronic and structural properties.

Inner-shell autoionization spectra obtained with synchrotron radiation are reported for mercury clusters ${\mathrm{Hg}}_n$, $n\le 40$. For the small clusters $n\le 12$ the spectral behavior as a function of size is interpreted in terms of an excitonic model. For larger cluster sizes a gradual deviation from van der Waals bonding is observed. The asymmetry occuring in the line profiles reflects the progressive construction of the $\mathrm{sp}$ conduction band.

A three-wave, free-electron laser was operated with a powerful 8.4-GHz electromagnetic "pump" wave replacing the usual magnetostatic wiggler. The presence of a uniform axial magnetic field $B_0$ produced cyclotron-harmonic "idler" waves. Peaks in the emission spectrum corresponding to cyclotron harmonics were observed covering a frequency range from 16.5 to 130 GHz. The frequency spectrum of this novel free-electron laser mechanism was tuned continuously by variation of $B_0$.

We have performed an extensive level-resolved experimental study of vibrotationally inelastic collisions in this system ${\mathrm{Li}}_2^{*}(v_i,j_i)+\mathrm{Ne}\to {\mathrm{Li}}_2^{*}(v_f=v_i+\Delta v,j_f=j_i+\Delta j)+\mathrm{Ne}$, with $8\le j_i\le 76$. At high $j_i$, the rate of vibrational transfer is large, exceeding the purely rotationally inelastic rate, and extremely specific, populating only a few rotational levels per $\Delta v$. The most probable $\Delta j$ obeys the rule $\Delta j=-4\mathrm{}\Delta v$. These effects are enhanced at low collision velocity and are quite insensitive to $v_i$ and the target gas. Classical trajectory calculations reproduce these results.

The transition to spatiotemporal intermittency has been experimentally studied in Rayleigh-Bénard convection in an annular cell. The dynamics of the system has been analyzed by computation of the statistical distribution of turbulent and laminar regions. The results, which display features typical of phase transitions, are similar to those found in systems of coupled maps and in partial differential equations.

A hierarchy of fractal geometrical exponents $D\left(l\right)\mathrm{}$, based upon $l$-rank orientational fluctuations, is proposed; $D\left(0\right)=D$ is the usual fractal dimension. The first three $D\left(l\right)\mathrm{}$ are calculated via computer simulation for a growth model with a tunable fractal dimension for several values in the range $3>D>\mathrm{}1\mathrm{}$, and for bond percolation. The new exponents are used to discuss fractal structure. The second-order light-scattering intensity is evaluated for the growing fractal clusters, and is shown to be sensitive to the higher-order $D\left(l\right)\mathrm{}$.

Effects of high-power ion-Bernstein-wave heating on the PLT tokamak plasmas have been investigated with up to 650 kW of rf power coupled to the plasma. A significant improvement in the deuterium particle confinement (as much as 300%) during high-power ion-Bernstein-wave heating has been observed. Associated with it, a longer injected-impurity-confinement time, reduced drift-wave turbulence activity, frequency shifts of drift-wave turbulence, and development of a large negative edge potential were observed. The ion heating efficiency, $\frac{\Delta T_i\mathrm{}\left(0\right)\mathrm{}{\overline{n}}_e}{P_{\mathrm{rf}}}=6\mathrm{}\times {10}^{13}$ eV ${\mathrm{cm}}^{-3\mathrm{}}$/kW, without high-energy tail ions, is relatively constant up to the maximum rf power.

Plasma heating by directly launched ion Bernstein waves is investigated in the Alcator C tokamak at densities ${\overline{n}}_e\gtrsim 1\times {10}^{20}$ ${\mathrm{m}}^{-3\mathrm{}}$. For injected rf powers $P_{\mathrm{rf}}\lesssim 180$ kW, bulk-ion-temperature increases of $\Delta T_i\lesssim 380$ eV, as well as improvements in global particle and central impurity confinement times by a factor of 2-3, are observed. In certain regimes, the energy-confinement time improves relative to the initial Ohmic value. At higher densities (${\overline{n}}_e\gtrsim 2\times {10}^{20}$ ${\mathrm{m}}^{-3\mathrm{}}$), the heating ceases to be efficient.

We have developed a new technique to study superfluidity in saturated liquid-${}_{}{}^3{}_{}{}^{}\mathrm{He}$ films. Using the enhanced sensitivity of this new method, we directly observe the suppression of the film's transition temperature $T_c^F$ as the film thickness decreases. We also measure a well-defined maximum critical film current which scales with temperature as ${(1-\frac{T}{T_c^F})}^a$, where $a=1.5\mathrm{}\pm 0.17$.

We have measured the magnetization of 2.5 atomic layers of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ adsorbed on graphite to 0.7 mK. The magnetization is well described by the exact high-temperature 2D Heisenberg expansion for $T>J=2.1\mathrm{}$ mK, the highest direct nuclear exchange constant ever reported. At lower temperatures, an exponential increase in susceptibility followed by a linear approach to saturation is seen, consistent with present theories for a 2D Heisenberg ferromagnet. The absence of a phase transition is confirmed for temperatures as low as $\frac{J}{3}$.

We have calculated the dynamical matrix for an aluminum slab bounded by a pair of (110) surfaces using a self-consistent implementation of pseudopotential perturbation theory. The screening response of the conduction electrons to the field of the ions is obtained within the local-density approximation of density-functional theory. Both relaxed and unrelaxed geometries are treated. We present numerical results for the dispersion curves of surface phonons. Comparison is made with recent theoretical and experimental results.

Local-density-functional calculations have been employed to study the energies of the epitaxial (111) interfaces ${\mathrm{S}\mathrm{i}-\mathrm{N}\mathrm{i}\mathrm{S}\mathrm{i}}_2$ and ${\mathrm{S}\mathrm{i}-\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{i}}_2$. For ${\mathrm{NiSi}}_2$, the widely accepted interface structure with sevenfold-coordinated Ni has the lowest energy. For ${\mathrm{CoSi}}_2$, however, a new structure with eightfold-coordinated Co has the lowest energy, and the widely discussed fivefold structure is seen to be extremely unfavorable.

We consider a Green's-function formulation of directional solidification. We develop a numerical scheme which suppresses logarithmic singularities and makes the asymptotic behavior explicit. This one is characterized by a new parameter $\lambda$. At zero surface tension, we obtain solutions for any choice of $\alpha$ and $\lambda$. With surface tension, we find that the wavelength remains arbitrary while discrete $\lambda$ values are allowed, in agreement with the work of Dombre and Hakim. Their results are generalized to arbitrary surface tension.

The lattice location of deuterium diffused into boron-doped silicon has been studied by means of channeling. After removal of a 0.2-μm-thick surface layer, it is found that 87% of the deuterium atoms occupy near-bond-center sites, whereas the remaining 13% are located close to tetrahedral sites. It is argued that the near-bond-center sites are related to boron-deuterium pairs, and the structure of these is discussed.