We derive the Mollwo-Ivey power-law relation between optical absorption energy and lattice constant for defects in ionic solids from the spatial scaling of the defect’s electronic charge distribution. Our starting point is the Vinti sum rule, which relates the rms size of the electronic ground state to the absorption spectrum. We treat F centers and impurity ions in alkali halides in detail, but the general theory should be widely applicable.

The negative ion fractions of oxygen directly recoiled from a Ni{100}-c(2×2)-O surface have been measured as a function of both azimuthal and exit angles. The data show a pronounced angular dependence of the ion fractions. A theoretical analysis suggests that the probability for charge transfer between an oxygen atom and the surface varies strongly with lateral position. The experiments provide a 3D map of the local electron tunneling rates within the surface unit cell.

On the basis of the neutralization of low-energy (${\mathit{E}}_0$=50 eV) ${\mathrm{D}}^{+}$ ions, the nature of bonding of potassium on metal and semiconductor surfaces has been studied in a low-coverage region (Θ<0.2). It is concluded that the K adatoms on the Si(100) surface are highly ionic while those on the Pt(111) and W(110) surfaces are characterized by covalent or metallic bonding. The ionic nature of potassium can be ascribed to the existence of the empty dangling-bond states and/or the bulk band gap of the semiconductor substrate.

Polar angle x-ray photoelectron diffraction (XPD) curves are presented for the Ir(001) 5${\mathit{p}}_{3/2}$, 4${\mathit{f}}_{7/2}$, 4${\mathit{d}}_{5/2}$, 4${\mathit{p}}_{3/2}$, and 4${\mathit{s}}_{1/2}$ core levels, as well as for the valence band. The core-level XPD intensity enhancements along the [001] and [011] crystallographic directions show a substantial dependence on the initial-state orbital angular momentum ${\mathit{l}}_{\mathit{i}}$. XPD from regions within the Ir valence band correlate well with core-level XPD of the same ${\mathit{l}}_{\mathit{i}}$. This correlation indicates that ${\mathit{l}}_{\mathit{i}}$-dependent XPD can influence the angular dependence of spectral intensities within angle-resolved x-ray photoemission valence-band spectra.

We present a realistic simulation of the reaction of fluorine with Si(100). Isothermal molecular dynamics simulations, using an analytic many-body potential fit to first-principles quantum mechanical adsorbate-surface and experimental gas phase data, show the initial buildup of the fluorosilyl layer necessary for etching. Several aspects of the microscopic mechanism are revealed. These simulations represent the first time that first-principles-derived surface reaction dynamics have been carried out; we show that this approach is critical to obtaining physically correct results.

Recent experiments have demonstrated the existence of standing waves for the catalytic reaction CO+O→${\mathrm{CO}}_2$ on a Pt (110) surface. We study this reaction by adding spatial coupling terms to a kinetic reaction scheme originally proposed by Eiswirth, Krischer, and Ertl. We argue that the standing waves arise from a novel mechanism involving the parametric driving of finite-wave-vector waves via a globally oscillating reaction rate. This interaction is possible because of the (near) resonance of these two modes.

We discuss the implications of the classical Gauss-Bonnet formula to foam in two and three dimensions. For a two-dimensional foam it gives a generalization of the von Neumann law for the coarsening of foams to curved surfaces. As a consequence of this we find that the stability properties of stationary bubbles of such a froth depend on the Gaussian curvature of the surface. For three-dimensional foam we find a relation between the average Gaussian curvature of a soap film and the average number of vertices for each face.

The problem of whether there is a constraint on the number of flavors for quark confinement in QCD is numerically investigated on a lattice with Wilson fermions as quarks. It is shown that even in the strong coupling limit, when the number of flavors exceeds 7, quarks are not confined and chiral symmetry is not spontaneously broken for light quarks.

Studying the decay of a Z’ to ${\mathrm{\tau }}^{+}$${\mathrm{\tau }}^{\mathrm{-}}$ at a future hadron collider will allow its polarization asymmetry to be measured, and will provide direct information about its leptonic couplings. It has not previously been appreciated that this measurement was possible. If this measurement is to be performed, detectors at the Superconducting Super Collider and Large Hadron Collider must be able to trigger on high-energy τ’s.

An analysis of proton-antiproton collisions at √s =1.8 TeV recorded with the Collider Detector at Fermilab (CDF) yields σ(pp¯→WX)B(W→μν)=2.21±0.22 nb and σ(pp¯→ZX)B(Z →${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-})}$=0.226±0.032 nb. The ratio is ${\mathit{R}}_{\mathrm{\mu }}$=${\mathrm{\sigma }}_{\mathit{W}}$B(W→μν)/${\mathrm{\sigma }}_{\mathit{Z}}$B(Z→${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$)=9.8±1.2. Combining with previous CDF electron results gives ${\mathrm{\sigma }}_{\mathit{W}}$B(W→lν)=2.20±0.20 nb, ${\mathrm{\sigma }}_{\mathit{Z}}$B(Z→${\mathit{l}}^{+}$${\mathit{l}}^{\mathrm{-}}$)=0.214±0.023 nb, and ${\mathit{R}}_{\mathit{l}}$=10.0±0.8. We extract the ratios of the coupling constants ${\mathit{g}}_{\mathrm{\mu }}$/${\mathit{g}}_{\mathit{e}}$ and ${\mathit{g}}_{\mathrm{\tau }}$/${\mathit{g}}_{\mathrm{\mu }}$. Using standard model assumptions we deduce the inverse branching ratio ${\mathit{B}}^{\mathrm{-}1}$(W→lν), the width Γ(W), and a decay-mode-independent lower bound on the top quark mass of 45 GeV/${\mathit{c}}^2$ (95% C.L.).

We consider the motion of a classical particle in (1+1)-dimensional space-time. Four probability distributions govern the trajectory of the particle; these give the probability of moving to the left or right in space while moving backwards or forwards in time. If these probabilities are randomly distributed and if the probability of moving backwards in time is related to the probability of moving forwards in time in a prescribed manner, then the master equations for these probabilities give rise to the Dirac equation without recourse to direct analytic continuation. In contrast, when a particle always moves forward in time, an analytic continuation is required to recover the Dirac equation.

The leading contribution to the electric and the chromoelectric dipole moments of the top quark is calculated in Higgs-boson-exchange models of CP nonconservation. The dipole moments are typically of the order of ${10}^{\mathrm{-}20}$ e cm and ${10}^{\mathrm{-}20}$ g cm, respectively and arise at one-loop order through neutral-Higgs-boson exchange. Several two-loop contributions are estimated to be smaller by about 2 orders of magnitude for the electric case and about 1 order of magnitude smaller for the chromoelectric case. The ${\mathit{q}}^2$ dependence of the dipole moment form factor is given for possible application to experimental searches.

We give a parameter-free microscopic description of the α decay of the ground state of ${}_{}{}^{212}{}_{}{}^{}\mathrm{Po}$ by expanding the parent wave function over a basis containing shell-model- as well as cluster-model-type elements. The resulting decay width agrees with experiment well within the range of the uncertainty inherent in the input of the model. The amount of core +α clustering in the parent state is found much higher (30%) than former microscopic estimates (∼1%), which shows the soundness of assuming the existence of preformed α particles with appreciable probability in the initial state.

Inclusive electron scattering cross sections for ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}$ have been measured in the quasielastic region at electron energies between 0.9 and 4.3 GeV, and scattering angles of 15° and 85°. Longitudinal (${\mathit{R}}_{\mathit{L}}$) and transverse (${\mathit{R}}_{\mathit{T}}$) response functions have been extracted using a Rosenbluth separation at constant ‖q‖ of 1.050 GeV/c. The ratio of the longitudinal to the transverse reduced response functions in the negative y region reaches unity.

Nuclear fragmentation may show specific features such as intermittency which induces self-similarity at all scales in final mass or charge distributions. We test this property on specific rate-equation models which are aimed at describing sequential decay processes. We use analytical arguments which are corroborated by numerical calculations in order to show that the generic structure of these equations does not allow for the presence of intermittency.

We observe transitions of laser-cooled Rb between vibrational levels in subwavelength-sized optical potential wells, using high-resolution spectroscopy of resonance fluorescence. We measure the spacing of the levels and the population distribution, and find the atoms to be localized to 1/15 of the optical wavelength. We find up to 60% of the population of trapped atoms in the vibrational ground state. The dependence of the spectrum on the parameters of the optical field provides detailed information about the dynamics of laser-cooled atoms.

Asymptotic formulas for the probability of finding exactly n eigenvalues in an interval of length s, for large s and fixed n, are given for random matrices taken from the Gaussian ensembles (β=1,2,4). These exact results are compared with the predictions of a continuum Coulomb gas model due to Dyson.

Convergence as a function of the number of states is studied and demonstrated for the Poet-Temkin model of electron-hydrogen scattering. In this Coulomb three-body problem only the l=0 partial waves are treated. By taking as many as thirty target states, obtained by diagonalizing the target Hamiltonian in a Laguerre basis, complete agreement with the smooth results of Poet is obtained at all energies. We show that the often-encountered pseudoresonance features in the cross sections are simply an indication of an inadequate target state representation.

We report the formation of positronium hydride (PsH), in collisions between positrons and methane. A preliminary value of 1.1±0.2 eV for the binding energy of PsH is obtained.

Polyampholytes are polymers composed of positive and negative charges randomly quenched along the chain. We examine configurations of such macromolecules by Monte Carlo simulations and analytical arguments. Polyampholytes with an overall constraint of charge neutrality are found to collapse into compact globules. Without such a constraint, on lowering temperature, the chain initially reduces its size and then becomes stretched due to a net charge imbalance. Experimental preparation conditions (water or organic solvent) determine if the polymer is overall neutral or randomly charged.