The first observations of the entire temperature-induced coil-globule transition in a single polystyrene polymer chain in cyclohexane is reported. The position of the coilglobule transition relative to the coexistence curve in the phase diagram of the system is also shown. The transition occurred at 32°C with a width of 5°C for 2.6×${10}^7$-molecularweight polystyrene with a sharp decrease in hydrodynamic radius from 1250 Å to 500 Å as the temperature was lowered.

It is suggested that the 2×1 and 7×7 reconstructions of Si(111) surfaces are inherently quite similar and propose a 7×7 structure based on ringlike arrangements of positively and negatively charged surface atoms. High-resolution angle-resolved photoemission data are shown to provide strong support for the buckled, (2×1)-like nature of the 7×7 surface.

Prolonged exposure to strongly absorbed light induces a large density of metastable defects in chalcogenide glasses. Observed properties of the new defects include light-in-duced ESR, extrinsic absorption below the band-gap energy and nonradiative recombination. The defect creation apparently underlies the well-known reversible photostructural change, and our data support a recent model of optically induced defect pairs.

The first magneto-optical transitions originating from a deep defect level in high-purity $n$-InSb are observed in the C${\mathrm{O}}_2$-laser-induced resonant photoconductivity at low magnetic fields. Another series of resonant structures is associated with three-LO-phonon-assisted spin-conserving cyclotron harmonic transitions.

The energies of substitutional deep $A_1$ impurity levels in zinc-blende semiconductors are predicted and related to the impurities' atomic energies and to host dangling bond (ideal vacancy) energies.

The first observation of Si(111) 7×7 intrinsic surface states that uses Auger electron spectroscopy as a valence band spectroscopy is reported. A global inversion method based upon the fast Fourier transform was used to self-deconvolve the Auger spectra. Subsequent oxygen chemisorption is shown to give rise to ${\mathrm{O}}_2$ electronic levels. Only at the beginning of the oxidation stage are the surface states completely removed.

This paper reports unusual structures in the x-ray photoelectron spectrum of the $5p$ level of thorium metal and proposes that the low-lying empty $5f$ levels are responsible for such a complicated $5p$ spectrum through two mechanisms: (i) fluctuation of the core hole between $5\mathit{p}$ and $5{\mathit{d}}^{2}5f$ configurations (underline denotes a hole level) and (ii) shakeup from filled valence levels to empty low-lying $5f$ levels.

A possibility of coexistence of antiferromagnetism and superconductivity is investigated theoretically. It is shown that a new superconducting pairing state is more stable than simple BCS pairing state under antiferromagnetic molecular field, which is similar to the Fulde-Ferrell state under ferromagnetic molecular field. We derive the critical value of this molecular field at which this new pairing state is completely quenched. Recent experiments on rare-earth ternary compounds of antiferromagnetic superconductors are interpreted in terms of this state.

Exciton dynamics in KMn${\mathrm{F}}_3$ at exciton densities up to ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are examined with time-resolved emission spectroscopy. The exciton emission line shifts and broadens with increasing exciton density. A nonlinear exciton decay channel is observed. These effects are found to be consistent with an exciton-exciton process. The shift scales with the exciton density and suggests that the effect is dominated by pairwise interactions up to the densities reached in these experiments.

This Letter shows how the well-known expressions for conductivity and Hall mobility in crystalline semiconductors can be extended to disordered systems with a simple reinterpretation of the concepts of electronic mass, velocity, and lifetime based on the density matrix approach.

The thermal stiffness derived from a realistic equation of state lies just in the range necessary for mass ejection in the collapse of the cores of heavy stars.

The velocity autocorrelation function is measured directly for the first time for one Brownian test particle in nitrogen at two different densities. The persistence of the autocorrelation is more pronounced than predicted on the basis of the modified Langevin equation. The measured distribution for the Brownian displacement shows a considerable departure from the Gaussian distribution at both densities.

The determination of the geometrical structure of the universe through the magnitude-vs-redshift relation in standard cosmology has not been very successful, mainly because of the intrinsic insensitivity of the $m-\mathrm{vs}-z$ relation to the deceleration parameter ${\overline{q}}_0$ which determines the spatial curvature and therefore the geometry. By relaxing the assumption usually made, i.e., the identity of gravitational and atomic clocks, sufficient sensitivity is achieved for the determination of ${\overline{q}}_0$. Existing observational evidence then leads one to conclude that the universe is open.

Parity nonconservation in $p-p$ scattering has been studied by comparing the cross sections ${\sigma }^{+}$, and ${\sigma }^{-}$ for longitudinally polarized 45-MeV protons of positive and negative helicity. The longitudinal analyzing power is found to be $A_z=-(3.2\mathrm{}\pm 1.1)\times {10}^{-7\mathrm{}}$. The quoted uncertainty includes the statistical error, the uncertainties of corrections applied, and estimates of systematic effects.

A way of avoiding the standard scenario (which many people find vexing on philosophical grounds) is suggested in which particles are in causal contact with only a limited number of other particles in the early universe.

The excitation of high-energy pions in the nuclear Coulomb field has been investigated. The data, analyzed assuming the presence of both electromagnetic and strong contributions to coherent production of ${\pi }^{-}{\pi }^0$ systems, yield a decay width for ${\rho }^{-}\to {\pi }^{-}\gamma$ of 67±7 keV.

Conclusions about weak interactions from nonleptonic $D^0$ decays are completely changed by strong final-state interactions. The suppression of $D^0\to {\overline{K}}^0{\pi }^0$ found in some models is completely reversed to $\Gamma (D^0\to {\overline{K}}^0{\pi }^0)=8\mathrm{}\Gamma (D^0\to K^{-}{\pi }^{+})$ by introduction of experimentally measured $K\pi$ scattering phase shifts in the exotic $I=\frac{3}{2}$ and nonexotic $I=\frac{1}{2}$ amplitudes. The $\frac{K^{+}{K}^{-}}{{\pi }^{+}{\pi }^{-}}$ ratio is very sensitive to meson resonances expected at the $D$ mass. Predictions less sensitive to final-state interactions are discussed.

The decay $\frac{J}{\psi }$ into $3\gamma$ final states has been studied. No evidence is found for the existence of the $X\left(2.83\right)\mathrm{}$ or any heavy narrow state (e.g., the ${\eta }_c$) decaying into two photons. Upper limits are given on the branching ratio $\frac{J}{\psi }\to {\eta }_c$, ${\eta }_c\to 2\gamma$ for ${\eta }_c$ masses in the 2.7-3.0-GeV region. In addition, the branching ratios $\frac{J}{\psi \to \gamma \eta }$, $\gamma {\eta }^{\prime }$ are measured. It is found that the ${\eta }^{\prime }$ branching ratio is higher than previously reported.

The electroinduced fission of ${}_{}{}^{182,184,186}{}_{}{}^{}\mathrm{W}$ has been investigated in the energy range from 35 to 55 MeV. The fission barriers, estimated by a statistical-model analysis of the measured cross sections, are compared with theoretical predictions and are only consistent with the assumption of a constant pairing strength.

The angular cross-correlation function of cross-section fluctuations in heavy-ion reactions is investigated. It is demonstrated that in general the coherence angle is much larger than commonly assumed. Consequences for the identification of heavy-ion resonances are discussed.