The single-particle states of compactified bosonic string theory are classified by a direct product of a fundamental representation of the Heisenberg algebra for the noncompact flat dimensions and an affine-$g$ Lie algebra, where the rank of its Lie subalgebra $g$ is the number of internal dimensions and its identity depends on their length scales. The operators that create these states are explicitly constructed in light-cone gauge. The massless particles lie in the adjoint representation of $g$.

We have observed underground cosmic-ray muons, corresponding to a secondary flux of ∼7×${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$, at a depth of 1800 m water equivalent, which appear to be initiated by Cygnus X-3. This identification is based on both direction and phase coherence. The existence of such secondary muons conflicts with the current understanding of photon cascades and/or the nature and location of Cygnus X-3.

The experimental consequences of a model that links $\mathrm{CP}$ nonconservation with horizontal interactions and is based on the gauge group $\mathrm{S}{\mathrm{U}}_L^W\mathrm{}\left(2\right)\mathrm{}\otimes \mathrm{S}{\mathrm{U}}_R^H\mathrm{}\left(2\right)\mathrm{}\otimes {\mathrm{U}}^Y\mathrm{}\left(1\right)\mathrm{}$ are investigated. The magnitude of the observed $\mathrm{CP}$ nonconservation and that of the $K_L-K_S$ mass difference constrain the horizontal gauge boson masses ($M_R$) such that $66 \mathrm{TeV}\gtrsim M_{\mathcal{R}}>5\mathrm{} \mathrm{TeV}$. The model implies an extremely small value for $\left|\frac{{\epsilon }^{\prime }}{\epsilon }\right|$. The branching ratio for $K_L\to \mu e(K\to \pi \mu e)$ could be greater than ≈ ${10}^{-10\mathrm{}}$ (≈ ${10}^{-12\mathrm{}}$). ${\Theta }_{\mathrm{QFD}}$ vanishes at the tree level. The contribution from the gauge sector, arising at two loops, is also discussed.

We show that the cascade in muonic atoms with $Z<\mathrm{}20\mathrm{}$ ejects sufficient atomic electrons to ionize an isolated muonic atom completely. In gases, the rates with which electrons refill the atomic shell can be accurately deduced from measured and calculated electron transfer cross sections. Thus, we can conclude that completely ionized muonic atoms can be prepared in gases, and that they remain isolated for long enough times at attainable pressures to facilitate studies of fundamental interactions in muonic atoms.

The observation of spectral and spatial diffusion of phonons in an ${\mathrm{Al}}_2$${\mathrm{O}}_3$ crystal containing both inelastic and resonance-elastic scattering centers (two different species of impurity ions) is reported. Phonons were generated by pulsed far-infrared excitation at a fixed frequency and monitored by time-resolved detection at a different frequency. Analysis of the data leads to the determination of the basic parameters of spectral and spatial diffusion.

The measured two-dimensional band structure of physisorbed molecular monolayers has been used to determine the structure of the ordered phase. For the previously reported ordered herringbone structure of ${\mathrm{N}}_2$ on graphite we observe a $k$-dependent splitting in the $3{\sigma }_g$ level which is a consequence of the intermolecular interaction of the two molecules per unit cell. Our measured dispersion is consistent with the structure proposed by recent LEED calculations and with a semi-empirical tight-binding calculation. For CO on Ag(111), which has not been studied by LEED, we find an orientationally ordered phase where there are two molecules per unit cell with the CO lying parallel to the surface.

Phase diagrams of cholesteric liquid crystals in relatively weak electric or magnetic fields are calculated. In very weak fields the helicoidal-phase region grows at the expense of the cubic blue phases. A new phase, having a two-dimensional structure, is shown to appear at physically realizable chiralities for fields exceeding $E\simeq \frac{70}{{\left(\Delta \epsilon \right)}^{\frac{1}{2}}}$ kV/cm and $H\simeq \frac{20}{{\left(\Delta \chi \right)}^{\frac{1}{2}}}$ Oe, where $\Delta \epsilon \left(\Delta \chi \right)$ is the dielectric (diamagnetic) anisotropy. This structure exists between the disordered and cubic-blue-phase regions in the phase diagram.

Metastable crystalline and amorphous phases were obtained by pulsed-laser quenching of thin Au-Ti and Cr-Ti films. Subsequent furnace annealing was found to convert metastable crystalline modifications into amorphous ones for certain compositions in both systems. In ${\mathrm{Cr}}_{1-x}{\mathrm{Ti}}_x$ ($x\sim 0.7$), a further annealing step at a higher temperature leads back to the initial metastable crystalline phase, thus making possible repeated crystalline to amorphous to crystalline transitions by simple thermal cycling. This phenomenon is unrelated to fast diffusion, but can be explained on the basis of free-energy considerations.

It is believed that covalent glasses can be divided into two classes: those with high average coordination (amorphous solids) and those with low average coordination (polymeric glasses). We present the first conclusive evidence that this division is correct by calculating the elastic properties of random networks with different average coordination $〈r〉$. The results show that the elastic constants depend predominantly on $〈r〉$ and go to zero when $〈r〉=2.4\mathrm{}$ with an exponent $f=1.5\mathrm{}\pm 0.2$.

It is shown that in GaAs-AlAs superlattices the confined longitudinal-optic Raman phonons created via either deformation-potential or Fröhlich electron-phonon interaction are different. This effect is demonstrated by comparison of resonance and off-resonance Raman spectra. Phonons of $A_1$ symmetry (point group $D_{2d}$) dominate in resonance, while $B_2$ phonons are stronger in the off-resonance case. The resonance profile of the $A_1$ modes is discussed. We also report the observation of confined transverse-optic phonons under extremely resonant conditions.

We report the observation of interface phonons by Raman scattering from GaAs-AlAs superlattices. These modes have frequencies close to the optical phonons of bulk GaAs and AlAs and resonate strongly for laser energies near the confined exciton levels of the GaAs quantum wells. The results are analyzed in terms of an electrostatic continuum model. In the long-wavelength limit this theory predicts the phonons of the layered media proposed by Merlin et al.

The temperature dependence of the internal stretch vibrational mode of CO adsorbed on Ni(111) has been studied by infrared spectroscopy. The results are successfully analyzed by a model for vibrational phase relaxation. It is found that anharmonic coupling between the C-O stretch mode and a low-frequency frustrated rotation gives the dominant contribution.

Silica spheres of 1600-Å diameter immersed in the binary fluid water+2-6-lutidine have been studied by light-scattering techniques. The scattered light was seen to be strongly dependent on temperature and concentration. This effect is due to the appearance of a lutidine layer on the spheres. The layer thickness dramatically increases near a transition line were the spheres aggregate as a result of attractive interactions. This transition exhibits all the features predicted for the prewetting transition between high and low adsorption of a fluid on a surface.

Singular vortex lines are predicted to occur in the rotating $A$ phase when the superfluid is confined in a parallel-plate geometry. A symmetry classification is introduced for the possible singly and doubly quantized axisymmetric vortices in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ in terms of the separate symmetries of the vortex hard-core and soft-core matters.

The thermodynamic Bethe-Ansatz equations for the isotropic ferromagnetic $S=\frac{1}{2}$ Heisenberg chain have been solved numerically. At low temperatures, I find a power-law dependence on $T$ for the specific heat and the susceptibility with critical exponents $\alpha =-0.49\mathrm{}\pm 0.02$, $\gamma =2.00\mathrm{}\pm 0.02$, and $\Delta \simeq \gamma$. The exponent $\alpha$ is compatible with effective spin waves and $\gamma$ and $\Delta$ are the exponents of the classical chain. Amplitudes and corrections to scaling are obtained and differences with previous results are discussed.

The technique of nuclear magnetic resonance on oriented nuclei has been applied for the first time to hexagonal Gd as host matrix. Radioactive ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ was mass-separator implanted into a Gd single crystal and nuclear magnetic resonance was detected via the anisotropy of the $\gamma$ radiation at temperatures of ∼ 10 mK. The magnetization properties of Gd, the anisotropy of the hyperfine field, the influence of the electric quadrupole interaction on the resonance structure, and the applicability of Gd to the detection of electric quadrupole interactions of heavy nuclei are discussed.

The correlation of Schottky-barrier height and microstructure has been investigated with three types of epitaxial Ni silicides, type-$A$ and -$B$ Ni${\mathrm{Si}}_2$ and NiSi, on Si(111) substrates. All these interfaces can be formed to yield a barrier height of 0.78 eV. This high barrier was obtained only for near-perfect interfaces; otherwise-less-perfect silicides yielded low barrier heights of 0.66 eV. This barrier height is controlled primarily by the structural perfection of the interface rather than by the specific type of epitaxy.

The superconductive and magnetic transition temperatures taken together are shown to provide a unique probe which separately determines both the magnitude and range of the Ruderman-Kittel interaction in the $R{\mathrm{Rh}}_4{\mathrm{B}}_4$ magnetic superconductors ($R=\mathrm{E}\mathrm{r},\mathrm{S}\mathrm{m}$). Experimentally, an unexpected peak is found in the antiferromagnetic-ordering temperature of Sm${\mathrm{Rh}}_4$${\mathrm{B}}_4$ versus electron mean free path, while for Er${\mathrm{Rh}}_4$${\mathrm{B}}_4$ the ferromagnetic-ordering temperature decreases monotonically. These qualitative features, as well as the quantitative differences between Sm${\mathrm{Rh}}_4$${\mathrm{B}}_4$ and Er${\mathrm{Rh}}_4$${\mathrm{B}}_4$, are in excellent agreement with calculations using a mean-free-path-dependent Ruderman-Kittel interaction.

High-resolution neutron-scattering measurements of the random-field Ising phase-transition behavior in ${\mathrm{Mn}}_{0.75}$${\mathrm{Zn}}_{0.25}$${\mathrm{F}}_2$ are reported. An abrupt, apparently discontinuous, transition at $T_{\mathrm{N}}\mathrm{}\left(H\right)\mathrm{}$ from history-independent to history-dependent behavior occurs; below $T_{\mathrm{N}}\mathrm{}\left(H\right)\mathrm{}$ all states with length scales between the field-cooled value and infinity are stable for indefinite lengths of times; logarithmic decay of the domain size in time may be ruled out. No existing theory accounts for this transition behavior.

Time-dependent spontaneous Raman spectra of optically pumped GaAs have been measured with subpicosecond time resolution. When the optically injected carrier density is less than ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$, we temporally resolve the growth of the optically induced nonequilibrium LO-phonon population and deduce an average electron-phonon scattering time of about 165 fs. For higher injected carrier densities, substantial time-dependent changes are observed in the spectra which result from screening of the LO phonons by the free carriers and the relaxation of the free carriers to the band edges.