By use of depolarized laser relection microscopy, unique textural defects have been observed in thin tilted hexatic liquid-crystal films which result from their bond-orientational order. The temperature dependence of the bond-orientational elasticity can be deduced from these textural patterns and is in qualitative agreement with the theory of two-dimensional melting. The effects of molecular chirality and film thickness on the defect textures is also reported along with observations on the polygonization of the two-dimensional crystalline phase.

This paper derives an infinite class of quasiperiodic lattices, composed of incommensurately modulated sublattices with displacive modulations, whose diffraction patterns have icosahedral symmetry. The sublattice reference lattices, as well as the sublattice displacement fields, belong to the space group $R\overline{3}m$ and are equivalent under the icosahedral point group. These quasiperiodic lattices are fundamentally different from those constructed by the projection and grid methods. Nevertheless, a special displacement field reproduces a three-dimensional generalization of the Penrose tiling.

We have formed the icosahedral phase in ${\mathrm{Al}}_{86}$${\mathrm{Mn}}_{14}$, ${\mathrm{Al}}_{82}$${\mathrm{Mn}}_{18}$, and ${\mathrm{Al}}_{75.5}$${\mathrm{Mn}}_{20}$${\mathrm{Si}}_{4.5}$ alloys by the interdiffusion of elemental layers in the solid state. Annealing at 250-425°C produced the phase in times as short as 1 min with grains up to ∼ 14 nm in diameter. Continued annealing transformed the alloy layers into crystalline phases. These results demonstrate that the icosahedral phase nucleates in the solid state in preference to crystalline phases of lower free energy, even though the initial material does not have liquidlike icosahedral short-range order.

We generalize a surface ionization model due to Langmuir to liquid mixtures of polar and nonpolar components in contact with ionizable substrates. When a predominantly nonpolar mixture is near a miscibility gap, thick wetting layers of the conjugate polar phase form on the substrate. Such charged layers can be much thicker than similar wetting layers stabilized by dispersion forces. This model may explain the 0.4- to 0.6-μm-thick wetting layers formed in stirred mixtures of nitromethane and carbon disulfide in contact with glass.

In situ transmission-electron-microscopy experiments show that, as expected from previously measured transport properties, the production of Ni and Pd hydrides prepared by hydrogen implantation at 10-20 K does not destroy the host symmetry. However, contrary to their quasiequilibrium counterparts, both implanted hydrides are single phased up to $\frac{H}{M}=1\mathrm{}$. The lattice parameter varies linearly with $\frac{H}{M}$, and its value for implanted PdH is only half that of the high-pressure-charged hydride.

The survival probability of a random-walking particle is derived for hopping in a random distribution of traps of arbitrary radius and concentration. The single-center approximation is shown to be valid for times of physical interest even when the fraction of volume occupied by traps approaches unity. The theory is based on computation of the number of different potential trap regions sampled in a random walk and is confirmed by simulations on a simple-cubic lattice.

We report on the first observation of long-wavelength interface optical phonons in a GaAs/AlGaAs superlattice by high-resolution electron-energy-loss spectroscopy. The observed spectrum is well accounted for by scattering theory with material data taken from infrared spectroscopy.

Intersubband resonances and collective intraband plasmon resonances are the elementary dynamic excitations of a two-dimensional electronic system. By applying uniaxial stress to a Si(100) metal-oxide-semiconductor system we can tune and energetically match the two resonances. In the crossing regime we find a resonant interaction of the two excitations leading to an enhancement of the intersubband resonance amplitude and a splitting of the dispersion.

By studying a single crystal of polydiacetylene-toluene-sulfonate, we have made the first identification of the triplet excited state of a conjugated polymer. The basis for this identification is the magnetic field dependence of the excited-state lifetime, which is measured by time-resolved optical absorption. Additionally, we have detected the $\Delta m=\pm 1$ transitions between triplet sublevels by measuring microwave-induced changes in the triplet-state lifetime.

Current-voltage characteristics, voltage oscillations, and NMR on a ${\mathrm{Rb}}_{0.3}$Mo${\mathrm{O}}_3$ crystal at 77 K are presented. The ½, - ½ transition at ${\nu }_0=80\mathrm{}$ MHz of ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ nuclei, broadened by the charge-density-wave modulation, is motionally narrowed for bias currents exceeding threshold for nonlinear conduction. Calculation of the line shapes, on the assumption of a partial depinning of the sample, leads to excellent agreement with experiment. The ratio of average current density to voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. The phase-correlation time of single domains is deduced to be $\tau =200\mathrm{}$ μs.

We present results of conductance measurements of ultranarrow inversion layers in which averaging has resulted in what we believe to be a clear observation of a quasi one-dimensional density of states. A 0.2-μm-period grating gate is used to produce 250 inversion lines in parallel, each of which is Å50 nm wide and 10 μm long. Summing the conductance of these lines results in a signal-to-noise improvement of of $\sqrt{250}$ (Å16) which has enabled the observation of the quasi one-dimensional conductance oscillation.

Valence-band ultraviolet photoemission spectra of undoped poly(methylthiophene) show an extended $\pi$ bonding at 1.05 eV from the Fermi level, $E_F$. Doping with Cl${\mathrm{O}}_4^{-}$ proceeds through uniform extraction of $\pi$-bonding electrons resulting in (i) an extension of the $\pi$ band and (ii) an $E_F$ shift by 0.8 eV relative to this band and 0.5 eV relative to the core levels. Band-gap narrowing reduces the $\pi \to {\pi }^{*}$ shakeup energy of the x-ray photoemission spectroscopy Cl$s$ peak from 2.7 to 1.7 eV with a strong intensity enhancement.

Orthodeuterium of unprecedented purity $p-{\mathrm{D}}_2$ concentration $c_1=1.7\mathrm{}\times {10}^{-4\mathrm{}}$ has been produced, with spin-lattice relaxation time $T_1^{\mathrm{D}}\left({\mathrm{D}}_2\right)\simeq 0.5$ h at $T=4.2\mathrm{}$ K and $H=0.7\mathrm{}$ T. This suffices for retention of high spin polarization built up at millikelvin temperatures and use at 1-4 K as a highly spin-polarized $\uparrow {\mathrm{D}}_2$ solid. $T_1^{\mathrm{D}}\left({\mathrm{D}}_2\right)$ from 1 to 10 K and 0.01 to 0.70 T are compared with $T_1^{\mathrm{H}}\left(\mathrm{HD}\right)$ and $T_1^{\mathrm{D}}\left(\mathrm{HD}\right)$, allowing tests of current relaxation theories. Measurement of the $p-{\mathrm{D}}_2\to o-{\mathrm{D}}_2$ homogeneous conversion rate in ${\mathrm{D}}_2$ at 4.2 K for ${10}^{-4\mathrm{}}<c_1<{10}^{-3\mathrm{}}$ is found to be substantially in agreement with a previous determination for $0.20<\mathrm{}{c}_1<0.90\mathrm{}$.

We calculate the longitudinal ultrasonic attenuation $\alpha$ of clean anisotropic superconductors. The temperature dependence of $\alpha$ depends not only on the density of states and the sound orientation, but also on $R=\frac{T_c}{{2T}_F}$, where $T_c$ and $T_F$ are the transition and Fermi temperatures. Peaks in $\alpha \mathrm{}\left(T\right)\mathrm{}$ can occur for certain orientations if $R\ne 0$. The asymptotic low-temperature regime is only reached for $T<<R{T}_c$.

A half-life of 0.55 ± 0.02 s was measured for the neutron-rich fission-product nucleus ${}_{30}{}^{80}{}_{}{}^{}\mathrm{Zn}_{50}^{}{}_{}{}^{}$. A $Q_{\beta }$ value for the decay of ${}_{}{}^{80}{}_{}{}^{}\mathrm{Zn}$ of 7.15 ± 0.15 MeV and a level scheme for ${}_{}{}^{80}{}_{}{}^{}\mathrm{Ga}$ have also been deduced. The properties of this $N=50\mathrm{}$ waiting-point nucleus are significant for the evaluation of different models of $r$-process environments and exposure times.

The rich-cluster two-point correlation function is examined in a model where rich clusters of galaxies form at high peaks of primordial Gaussian mass-density fluctuations (averaged over a suitable volume). Particular attention is paid to the case when the primordial fluctuations have a Zel'dovich spectrum.

Under a certain assumption (which is satisfied whenever there is a dense infinite cluster in the half-space), we prove a differential inequality for the infinite-cluster density, $P_{\infty }\mathrm{}\left(p\right)\mathrm{}$, in Bernoulli percolation. The principal implication of this result is that if $P_{\infty }\mathrm{}\left(p\right)\mathrm{}$ vanishes with critical exponent $\beta$, then $\beta$ obeys the mean-field bound $\beta <~1$. As a corollary, we also derive an inequality relating the backbone density, the truncated susceptibility, and the infinite-cluster density.

Breakdown of time-reversal invariance can be detected in macroscopic samples as a magnetic alignment along an electric field. We show that both fundamental and practical limits to the detection of this effect in paramagnets correspond to measurement of electron electric dipole moments down to $d_e\sim {10}^{-28\mathrm{}}e·\mathrm{cm}$ on 50-g quantities of EuS near its Curie point; this compares to the current limit of $d_e<~{10}^{-24\mathrm{}}e·\mathrm{cm}$. Strategies for still greater sensitivity are outlined.

It is shown that there is a correspondence between the supersymmetric sine-Gordon theory in the vicinity of ${\beta }^2=4\mathrm{}\pi$ and an anisotropic $N=3\mathrm{}$ Ashkin-Teller model. Thus the latter model displays a line of first-order transition which turns into a line of continuous transition with varying critical exponents via a multicritical point of the Kosterlitz-Thouless type.

The location of a Hopf bifurcation in parameter space may be postponed or advanced by multiplicative colored noise depending on the interplay between the time scale of the noise and the rotation period of the phase variable.