We report the first observation of a critical-temperature and coexistence-curve dependence on film thickness for a binary fluid mixture (methanol-cyclohexane). The data suggest long-range interactions with mean-field exponent $\beta =\frac{1}{2}$ for film thicknesses, $L$, in the range $1 \mu \mathrm{m}\lesssim L\lesssim 6 \mu \mathrm{m}$.

We show that longitudinal optical (LO) vibrational modes account for several previously unexplained peaks in the Raman spectra of vitreous Ge${\mathrm{O}}_2$ and Si${\mathrm{O}}_2$. Identification of LO modes in these and other glasses reduces the complexity of the spectra that must be explained by simple structural models. It also follows that long-range (Coulomb) forces should be included in complete theories of the vibrational properties of many glasses.

The existence of "critical" slowing down at the roughening transition in Monte Carlo simulations of both the kinetic solid-on-solid model and discrete Gaussian model is reported. Comparison with critical behavior at the more usual second-order phase transitions shows both similarities and differences that shed light on the nature of the roughening transition. The roughening temperature is found to be $k_B{T}_R=(1.15\mathrm{}\pm 0.05)\epsilon$ for the solid-on-solid model.

Using light-scattering techniques we have measured the correlation function of a binary liquid near the critical point with a precision of 0.2%. The data cover a range $0.18<k\xi <26\mathrm{}$ in terms of the scaling variable $k\xi$ and yield critical-exponent values in close agreement with recent theoretical calculations for the Ginzburg-Landau-Wilson model.

We report the first measurements of the stability of persistent currents in unsaturated ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films in an open geometry. Persistent currents are generated without rotation and exhibit several features which place strong restrictions on models of thermally activated dissipation in thin films.

A joint experimental-theoretical effort combining low-temperature electron-nuclear double-resonance measurements and a pseudopotential calculation was undertakent to determine the main contributing factors to the pressure shifts in the $F$ center hyperfine interaction parameters in KCl. The results indicate that the signs of the pressure shifts beyond shell I are primarily determined by the changes in the indirect overlap contributions to the $F$-electron wave function which result from the requirement of orthogonality of the ion core states at a given site to those on neighboring sites.

Relaxation rates of the ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$ nuclear resonance in $\mathrm{Au}\mathrm{Yb}$ have been measured in the low-temperature local-moment regime (${\omega }_{e}T_2^{}{}_{}{}^e\gg 1$). The measured rates can be accounted for by virtual transitions of the ${\mathrm{Yb}}^{3+}$ moment within the ${\Gamma }_7$ doublet caused by exchange interactions with host conduction electrons. The absence of significant contributions to the high-field ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$ relaxation rates from virtual transitions to the ${\Gamma }_8$ quartet requires an anisotropic form for the exchange.

The electronic structure of both the bare W(001) surface and one with a saturation coverage of H atoms has been calculated for a sixteen-layer slab using a parametrized linear combination of atomic orbitals (LCAO) model. The results permit an identification of H-induced structures that have been observed in recent angle-resolved photoemission experiments.

Angle-resolved photoemission spectra of the molecular obritals of chemisorbed CO on Pt(111) and Ni(111) substrates show a strong angular variation of the peak intensity ratio. Comparison with Davenport's $X\alpha$ calculations establishes that CO stands up on these substrates, with the carbon atom bonded to the substrate. The $\mathrm{Pt} 5d\left(t_{2g}\right)$ orbitals are found to be strongly involved in chemisorption bonding to CO.

An experimental study of electrical transport phenomena in TTF-TCNQ in the low-temperature ($T<\mathrm{}4.2\mathrm{}$ K) dielectric regime is reported. The current-voltage curves are nonlinear with conductance increasing with increasing voltage. The observed nonlinearity is insensitive to radiation-induced defects at the fraction of a percent level. The data are discussed in terms of electric field depinning of the incommensurate charge-density wave with a critical electric field of approximately 1.5 × ${10}^2$ V/cm.

A model is presented for the structure and properties of active centers in lone-pair semiconductors, based on the possibility of unique bonding configurations which can arise from the presence of nonbonding orbitals. It is shown that the lowest-energy neutral center is unstable towards the creation of different positively and negatively charged centers, thus resulting in a negative effective correlation energy. These centers yield gap states which explain the unusual properties of lone-pair semiconductors.

A new type of phase diagram for the metal-insulator transition in $n$-type semiconductors and related systems is proposed. By starting from the Herzfeld criterion for the polarization instability, it is argued that an intermediate ferroelectric phase may arise. The ferroelectric and excitonic phases are shown to be complementary structures.

We report measurements of the specific heat, Mössbauer effect, and electrical resistivity of Np${\mathrm{Sn}}_3$, which identify its weak antiferromagnetism ($T_{\mathrm{N}}=9.5\mathrm{}$ K) as arising from itinerant $5f$ electrons. This is the first known verification of itinerant $f$-electron antiferromagnetism in any system.

Evidence is given for the existence of a heretofore undetected low-density critical point in a classical fluid of charged hard spheres.

It is pointed out that the recently measured difference in $p_T$ spectrum between ${\pi }^{\pm }p\to {\pi }^{0}X$ and $\mathrm{pp}\to {\pi }^{0}X$, with a large-$p_T {\pi }^0$, seems to be a consequence only of the smaller number of quarks per projectile in a pion beam.

We report results on the production of muon pairs in the mass range 2.5 to 20 GeV in 400-GeV proton-nucleus collisions. A total of 159 events are observed in the mass range 5.5 to 11 GeV with a cross section which is in agreement with the previous observation of a high-mass dielectron continuum signal in this interval. Details on the production dynamics and comparisons with parton-model predictions are presented. Within limitations of resolution and continuum uncertainty, the dimuon mass spectrum provides no evidence for fine structure above 5 GeV.

A procedure is given to estimate the decay probability of a metastable vacuum state in quantum field theory. As an application, in the Weinberg-Salam model the lower bound (for ${\theta }_{\mathrm{W}}=35\mathrm{}°$) on the Higgs mass can be reduced from 4.9 GeV, corresponding to effective stability of a metastable vacuum.

We have measured 29 pionic-atom transitions in eight elements. From the best twelve transitions, we obtain $m_{{\pi }^{-}}=139\mathrm{}568.6\pm 2.0$KeV/${\mathit{c}}^2$.

The influence of the laser fluctuations on resonance fluorescence is treated exactly within the framework of multiplicative stochastic processes. For the phase diffusion model of the laser, I find that, in the limit of strong fields, the ratios of the width and height of the central peak to the side peak are, respectively, $\frac{2}{3x}$ and $3x$, where $x=\frac{(\gamma +{\gamma }_c)}{(\gamma +2\mathrm{}{\gamma }_c)}$. The envelope of the intensity correlations is found to decay at the rate $\frac{(3\mathrm{}\gamma +{\gamma }_c)}{2}$.

I develop a nonperturbative relaxation theory appropriate for an atom subjected to strong finite-bandwidth radiation fields. The partial coherence implied by the finite bandwidth is modeled by simple phase and amplitude correlation functions. Modifications of the Mollow theory of resonance fluorescence are calculated as an example. The finite bandwidth of the applied field does not have a simply additive effect on the predicted fluorescence spectrum.