We consider a simple quantum model with a surface and prove the existence of a surface density of states. We show that the energy spectrum of the model is the union of the support of the bulk densities of states of the media forming the surface and the support of the surface density of states.

We report measurements of ${\pi }^{\pm }{K}^{\pm }$, and $p$, $\overline{p}$ inclusive cross sections and fractions in $e^{+}{e}^{-}$ annihilation at $\sqrt{s}=29\mathrm{}$ GeV, for the momentum interval $0.01<z=\frac{p}{p_{\mathrm{beam}}}<0.90\mathrm{}$. The analysis is based on approximately 70 ${\mathrm{pb}}^{-1\mathrm{}}$ of data collected with the $\frac{\mathrm{TPC}}{2\gamma }$ detector facility at the SLAC storage ring PEP. Detector upgrades result in significantly improved momentum coverage and precision of the data, compared to previous measurements.

We observe that the recent results on $\frac{{\epsilon }^{\prime }}{\epsilon }$ enable us to place a lower bound on the left-right mixing parameter $\xi$ in pseudomanifest left-right-symmetric models: $tan\xi \ge 2.0\times {10}^{-6\mathrm{}}$. We give the complete expression for the neutron electric dipole moment $D_n$ and show that it satisfies $D_n<7.6\mathrm{}\times {10}^{-24\mathrm{}}e \mathrm{cm}$. In a particular model, due to Chang, we can relate $D_n$ to $\frac{{\epsilon }^{\prime }}{\epsilon }$ and place limits on $D_n: 1.9\times {10}^{-26\mathrm{}}\ge \left|D_n\right|\ge 1.9\times {10}^{-27\mathrm{}}e \mathrm{cm}$.

Several examples of the production of electron-positron pairs were found in the interactions with emulsion of fragments resulting from the collision of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ projectiles of 4.5 and $4.2 \frac{\mathrm{GeV}}{c}$ per nucleon, respectively with emulsion nuclei. Taking into account the effect of the background, the results seem to suggest the existence of new neutral boson with mass $1.60\pm 0.59 \frac{\mathrm{MeV}}{c}$ and a lifetime (0.15 ± 0.01) × ${10}^{-14\mathrm{}}$ sec.

Electron-positron pairs apparently resulting from the decay of light intermediate neutral particles emitted in relativistic heavy-ion collisions have been reported by El-Nadi and Badawy. The events, observed in nuclear emulsions, are similar to data from 35 years ago that caused the ${\pi }^0$ lifetime estimate to be wrong by almost 2 orders of magnitude for about a decade. The data are consistent with the production and subsequent decay of short-lived neutral bosons with masses around 1.1, 2.1, and 9 MeV and with lifetimes of the order of ${10}^{-16\mathrm{}}$-${10}^{-15\mathrm{}}$ s.

Plasmas with densities of $6\times {10}^{22}\frac{e}{{\mathrm{cm}}^3}$ and temperatures of 10 eV have been created by means of capillary discharge. These parameters indicate that the plasmas are partially degenerate and strongly coupled. By measuring the size of the plasma, the current, and the voltage, one can infer the resistivity of the plasma and compare it with calculated values from various transport theories. The results of this experiment show that theories that do not accurately model the complete electron-ion interaction within this regime can be inaccurate by as much as a factor of 200.

Ab initio total-energy calculations indicate that the formation of a new defect complex, a vacancy surrounded by four arsenic atoms, is responsible for electrical deactivation and for structural changes seen in measurements of extended x-ray-absorption fine structure when heavily arsenic-doped silicon is annealed. The $v-{\mathrm{As}}_4$ complex is energetically favored over both substitutional, isolated As in Si and substitutional $\mathrm{S}\mathrm{i}-{\mathrm{As}}_4$ configurations, and it is neutral and electrically inactive. The formation of such defects may be a widespread occurrence in silicon and in other semiconductors.

We report the results of measurements of the propagation of classical waves in thin helium films adsorbed on silicon substrates with two different scattering patterns. Periodic scattering patterns show band structure; random scattering patterns show classical wave localization in one dimension consistent with theoretical predictions.

We study the effects of excess thermalized electron and hole populations on femtosecond carrier thermalization in optically excited GaAs quantum wells. In modulation-doped samples we find that the presence of 3×${10}^{11}$ ${\mathrm{cm}}^{-2\mathrm{}}$ electrons produces an extraordinarily fast carrier thermalization (faster than 10 fs); however, the presence of the same density of holes yields a thermalization time close to that of undoped samples (≅60 fs). These results give the first direct evidence that electron-electron interactions yield the dominant contributions to carrier thermalization in GaAs and also show that the electron distribution function itself influences thermalization dynamics.

We find that the transport coefficients ${\rho }_{\mathrm{xy}}$ and ${\rho }_{\mathrm{xx}}$ of two-dimensional electrons in InGaAs/InP show a characteristic power-law dependence on $T$. In the range $0.1 \mathrm{K} \lesssim T\lesssim 4.2 \mathrm{K}$, the maximum of $\frac{d{\rho }_{\mathrm{xy}}}{\mathrm{dB}}$ diverges like $\sim T^{-\kappa }$ with $\kappa =0.42\mathrm{}\pm 0.04$, for Landau levels $N=0\mathrm{}\downarrow$, $1\uparrow$, and $1\downarrow$, and the half-width $\Delta B$ for ${\rho }_{\mathrm{xx}}$ vanishes as $\Delta B\sim T^{\kappa }$. These results confirm the prediction of the scaling theory that the characteristic power-law behavior in the transport coefficients is a universal feature of delocalization in the integral quantum Hall effect.

The transition between localized and extended eigenstates in the integral quantum Hall regime is observable as a scaling phenomenon in the magnetoresistance tensor as a function of temperature and applied magnetic field strength. Field-theoretic studies on the quantum Hall effect are used to derive the scaling functions. The scaling behavior is shown to involve only a single critical exponent ($\mu$) which is the ratio between the inelastic-scattering exponent ($p$) and twice the localization length exponent ($\nu$). The results have recently been confirmed experimentally.

We report the first observation of quadrupole-interaction-resolved nuclear magnetic resonance on oriented nuclei in a hexagonal Co host. The radioactive isotopes ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{199}{}_{}{}^{}\mathrm{Au}$ were mass-separator implanted into a hcp Co single crystal and nuclear magnetic resonance was detected via the anisotropy of the $\gamma$ radiation at temperatures of ∼10 mK. These experiments have shown that hcp Co might be the best host matrix for the determination of the electric quadrupole moments of heavy radioactive nuclei with resonance precision.

Measurements of the far-infrared reflectance of ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ between 10 and 720 ${\mathrm{cm}}^{-1\mathrm{}}$ have been made at temperatures from 2 to 90 K. Above the coherence temperature the optical conductivity increases monotonically with increasing frequency and at lower temperatures the development of the narrow mode responsible for the high dc conductivity is clearly observed. In the antiferromagnetic state an energy gap with a size between 46 and 65 ${\mathrm{cm}}^{-1\mathrm{}}$ is observed whose shape is reminiscent of the energy gap observed in the spin-density-wave state of Cr.

Intermultiplet transitions with energies up to 810 meV in praseodymium metal have been observed by neutron spectroscopy. Both dipolar (${}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}H_5^{}{}_{}{}^{}$) and, for the first time, nondipolar, interterm (${}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}F_{2,3,4}^{}{}_{}{}^{}$) transitions have been identified. The energies of the interterm transitions are significantly reduced by approximately 50 meV from their free-ion values. This gives direct evidence of conduction-electron screening of the (on-site) Coulomb interaction between $4f$ electrons in rare-earth metals.

We present results for the reflectivity, $R$ of two bulk crystals of ${\mathrm{Ba}}_2\mathrm{Y}{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ which, below the superconducting transition at $T_c$, show behavior consistent with perfect reflectivity up to an energy of $\mathrm{}(3-4)\mathrm{}{k}_{\mathrm{B}}{T}_c$. We interpret the reproducibility and high $R$ values (especially $R\sim 1$ below $T_c$) as indicative of intrinsic behavior in the highly conducting crystal planes probed by the light. Results above $T_c$ show that the charge carriers have an enhanced effective mass and low scattering rate at low frequency and temperature, indicating a strong interaction with some excitation.

A large single crystal (7 × 7 × 3 ${\mathrm{mm}}^3$) of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.2}$ has been grown and its magnetic excitations have been observed by neutron-scattering techniques. A two-dimensional magnetic ridge, similar to that observed for ${\mathrm{La}}_2\mathrm{Cu}{\mathrm{O}}_{4-y}$, has been clearly identified by triple-axis measurements. The slope of the dispersion curve for spin-wave excitations is very large (≳0.5 eV Å), consistent with the result of spinpair Raman scattering by Lyons et al.

Evidence is presented for the role of excited conduction electrons in the laser-induced desorption of NO from Pt(111). State-specific detection of the desorbed NO establishes that the rotational distributions are non-Boltzmann, that the spin-orbit population is inverted, and that both the translational and vibrational distributions are uncorrelated with the laser-induced surface-temperature jump. The role of optically excited substrate electrons in driving the desorption process is evidenced by a dramatic dependence of the vibrational and translation energy distributions on the desorption-laser wavelength.

The diffusion of a Brownian particle is investigated for a class of potentials (soft bistable) which resist conventional techniques. A new method of solution based on supersymmetric quantum mechanics is shown to provide, with minimal effort, an accurate determination of the small eigenvalue of the relevant Fokker-Planck equation. The reciprocal of the small eigenvalue compares very closely with a refined definition of mean first-passage time.

We give necessary and sufficient conditions for the existence of trapped surfaces in spherically symmetric spacetimes. These conditions show that the formation of trapped surfaces depends on both the degree of concentration and the average flow of the matter. The result can be considered as a partial validation of the cosmic-censorship hypothesis.

One of the few experimental handles on unified theories of gravity with other interactions comes from possible time variation of coupling constants over the Hubble time: $H_0^{}{}_{}{}^{-1\mathrm{}}\simeq {(7.67\mathrm{}\times {10}^{-11\mathrm{}} {\mathrm{yr}}^{-1\mathrm{}})}^{-1\mathrm{}}$. We present a new theory-independent estimate (consistent with zero) of the time variation of Newton's gravitational constant derived from the timing of the binary pulsar PSR 1913+16: $\frac{{\dot{G}}_0}{G_0}=(1.0\mathrm{}\pm 2.3)\times {10}^{-11\mathrm{}}$ ${\mathrm{yr}}^{-1\mathrm{}}$. We anticipate that this estimate will become sharper as more data are acquired.