We describe an x-ray scattering study of the commensurate-incommensurate transition in monolayer Kr films physisorbed onto basal planes of $z-y-x$ exfoliated graphite. At temperatures of 80.0 and 89.3 K there appears to be a single hexagonal-commensurate-to-hexagonal-incommensurate transition which is at least nearly second order with mean exponent $\beta =0.30\mathrm{}\pm 0.06$. In the incommensurate phase we directly observe domainwall superlattice effects.

For $e^{+}{e}^{-}$ annihilation, a quantity is constructed which contains information about the distribution of charges in the final states of the process but which, like other jet variables discussed extensively in the literature, is expected to be free of mass singularities. Unlike predictions of other variables, however, this perturbative result is not physically sensible. Confinement effects ruin the prediction, yet there is no indication of this in the form of infrared divergences in the calculation.

A wall-induced birefringence in a nematic liquid crystal above the nematic-isotropic phase transition point has been observed for the first time. It is expected that this phenomenon will provide a useful tool to study the nature of aligning forces at liquid-crystal-solid interfaces.

Along the (100) direction of tungsten, interband transitions induced by circularly polarized light of energy $1.5 \mathrm{eV}<~h\nu <~4.1 \mathrm{eV}$ lead to spin polarization of the excited conduction electrons. This is observed by measuring the spin polarization of the photoelectrons emitted from a cesiated crystal surface. The measured polarization values depend sensitively on the $s$-, $p$-, and $d$-hybridization properties of the conduction bands. Excited-state lifetimes are obtained from the widths of the polarization structures.

For the first time, structure has been found in the electron tunneling characteristics of a metal-oxide-semiconductor tunnel junction of an amorphous semiconductor. In the present study the amorphous semiconductor is phosphorus-doped hydrogenated amorphous silicon. The results have been analyzed to determine the surface density of states over part of the forbidden gap. The basic features of the density-of-states distribution are in agreement with the results of field-effect measurements reported for this material.

Through neutron polarization-analysis experiments at 9.9 K, we have determined that certain satellites in the neutron diffraction pattern of Nd are not caused by a lattice distortion, but rather by a modulated moment component in the basal plane and perpendicular to ${\overrightarrow{\mathrm{b}}}_1$. The magnetic structure is thus even more complicated than hitherto proposed, and there is now no direct experimental evidence to support the "triple-$\overrightarrow{\mathrm{q}}$" model.

A combined x-ray and neutron diffraction study has shown that the so-called "triple-$\overrightarrow{\mathrm{q}}$" structure is not the correct model of the magnetic structure of neodymium. The x-ray data showed only the Bragg reflections originating from the double-hcp lattice. Hence, all additional reflections observed below $T_N$ by neutrons are of magnetic origin. Additional neutron-diffraction data have shown that the magnetic structure must be described by modulation wave vectors with components both parallel and perpendicular to the $〈100〉$ axes.

The lowering of the Fermi energy in stage-1 Fe${\mathrm{Cl}}_3$-intercalated graphite is directly measured in the spectrum of electronic excitations from carbon $1s$ core states to empty carbon $2p$ states which appear after intercalation. The shape of the core exciton spectrum is related to the initial distribution of empty states in a formulation of the core exciton problem which includes the effect of electronic relaxation near the core hole.

A background continuum in the Raman spectrum of adsorbed molecules at a silverelectrolyte interface is observed experimentally. This background continuum is potential dependent on the Stokes and anti-Strokes of the spectrum and fits a Fermi distribution function on the anti-Stokes side of the spectrum. The continuum is interpreted in terms of radiative recombination of adsorbed molecular ions produced by photoionization.

We present an analytical expression for the dynamical spin-correlation function of the $S=\frac{1}{2}$ linear Heisenberg antiferromagnet based on the fact that the spectrum is dominated by a double continuum of spin-wave excitations. Our expression is not exact, but exact sum rules show that the degree of approximation is small. We predict that in a uniform magnetic field the spectral weight function will display a double-peaked structure. Such a feature is observed in recent neutron-scattering experiments.

The continuous-transfer-matrix technique, together with the dilute-gas approximation, is used to study the thermodynamics and static properties of the linear-chain planar model. Explicit analytic expressions for the free-energy and spin-spin correlation functions, as a function of temperature, symmetry-breaking fields, and density of solitons, are given. The correlation length is predicted to increase exponentially as the temperature goes to zero. This result should be seen in elastic neutron scattering experiments on CsNi${\mathrm{F}}_3$.

It is proposed to measure the deep-inelastic longitudinal structure function $F_L(x,Q^2)$, or moments thereof, in order to determine the $Q^2$ dependence of the gluon distribution. In contrast to $F_2(x,Q^2)$, the theoretical predictions for the $Q^2$ evolution of the moments of the gluon density depend critically on the gluon self-couplings and thus provide us with a sensitive test of the Yang-Mills structure of quantum chromodynamics.

We present a very accurate determination of the valence bands of copper along $\Gamma \mathrm{KX}$. This is obtained with high-resolution angle-resolved photoemission spectroscopy, using synchrotron radiation in the $15<~\hslash \omega <~100$ eV photon energy range. In addition the data yield inverse lifetime measurements for the $3d$ hole at the top and the bottom of the $d$ band which have a value much smaller (< 50 and 250 meV) than recently reported.

A hollow cylinder of a hysteretic type-II superconductor allows applied axial flux to enter the hole smoothly while sustaining trapped azimuthal flux until $H_{c2\mathrm{}}$ is attained showing clearly that flux cutting occurs. A comparison of the evolution of the axial flux, with and without trapped azimuthal flux in the wall, yields data on the energy associated with fluxcutting events. Our technique lends itself to a study of the role of many pertinent parameters in this phenomenon.

In a broadband neutrino exposure of the Fermilab 15-ft bubble chamber, we observe the production of the ${{\Sigma }_c}^{++}\mathrm{}\left(2426\right)\mathrm{}$ charmed baryon followed by its decay to ${{\Lambda }_c}^{+}\mathrm{}\left(2260\right)\mathrm{}$ and ${\pi }^{+}$. We find the mass of the ${{\Lambda }_c}^{+}$ to be 2257±10 MeV and the $m\left({{\Sigma }_c}^{++}\right)-m\left({{\Lambda }_c}^{+}\right)$ mass difference to be 168±3 MeV. Previously unseen two-body decay modes of the ${{\Lambda }_c}^{+}\mathrm{}\left(2260\right)\mathrm{}$ are observed.

Recent elastic $p-p$ $C_{\mathrm{LL}}$ measurements and other $p-p$ data indicate the existence of ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}F_3^{}{}_{}{}^{}$, and ${}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$ resonances at energies of about 2140, 2260, and 2430 MeV, respectively. These resonances accurately correspond to nuclear-physics-type rotational levels of a virtual $\mathrm{pp}\pi \mathrm{}\left(2020\right)\mathrm{}$ bound state.

Kinematically complete experiments have been performed on the three-body exit channels in 7.5 MeV/amu ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ on ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. The bulk of the events (>99%) can be interpreted as sequential fission following deeply inelastic collisions. From the angular correlations, oriented-spin values up to $45\hslash$ are deduced for the heavy fissioning fragment. Their constancy at large energy losses points to strong fluctuations in the correlation between energy loss and angular momentum.

Measurement of x-ray-x-ray and x-ray—$\gamma$-ray coincidence yields indicates that two to three $K$ x rays are emitted, on the average, during the deexcitation of neutron-poor Tl and Pb isotopes populated by (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$,$\mathrm{xn}$) reactions. Experimental constraints suggest that approximately two x rays arise from a narrow region of spin ($12\lesssim J\lesssim 20$) dominated by low-energy $M1\mathrm{}$ transitions. Measurement of the singles yield as well as the mean multiplicity of the $K$ x rays provides a useful new method for determining absolute evaporation-residue cross sections.

Observation of linewidths narrower than the natural width with use of a two-step resonant scattering scheme in ${\mathrm{I}}_2$ is reported. The 80-kHz-wide hyperfine lines obtained for the $B{0_{\mathrm{u}}}^{+}\to X{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}\mathrm{}(43,11)\mathrm{}$ $R\left(15\right)\mathrm{}$ transition are used and as high-resolution probes for collisional studies. Applications to frequency standards are considered. Also included are high-resolution measurements of the ac Stark effect in a folded Doppler-broadened system in ${\mathrm{I}}_2$.

We show that superfluorescent pulses fluctuate singificantly in shape notwithstanding their classical dynamical behavior. These fluctuations can be understood as originating from the quantum mechanical uncertainty of the initial polarization.