Many spacetimes are known which should represent gravitational fields outside rotating sources, but for which no satisfactory sources have been found. We indicate that these spacetimes can arise as the metrics of counterrotating thin disks of finite mass, consisting of two streams of collisionless particles, circulating in opposite directions with different velocities. We show how such disks can act as exact sources of all types of the Kerr metric. In their central regions they can produce ergoregions, the velocities can approach that of light, and the redshifts can becomes arbitrarily large.

The dominant production mechanism for heavy-quark–antiquark bound states with large transverse momentum is fragmentation, the splitting of a high energy parton into a quarkonium state and other partons. We show that the fragmentation functions D(z,μ) describing these processes can be calculated using perturbative QCD. We calculate the fragmentation functions for a gluon to split into S-wave quarkonium states to leading order in the QCD coupling constant.

We compute the kaon B parameter on an ensemble of lattices which include the effects of dynamical quark loops. Comparing with our previous quenched calculations, we find that dynamical fermions have negligible effect.

We have measured the ${\mathit{B}}^0$B${\mathrm{¯}}^0$ mixing probability, ${\mathrm{\chi }}_{\mathit{d}}$, using a sample of 965 000 BB¯ pairs from Υ(4S) decays. Counting dilepton events, we find ${\mathrm{\chi }}_{\mathit{d}}$=0.157±0.016±0.${018}_{\mathrm{-}0.021}^{+0.028\mathrm{}}$. Using tagged ${\mathit{B}}^0$ events, we find ${\mathrm{\chi }}_{\mathit{d}}$=0.149±0.023±0.019±0.010. The first (second) error is statistical (systematic). The third error reflects a ±15% uncertainty in the assumption, made in both cases, that charged and neutral B pairs contribute equally to dilepton events. We also obtain a limit on the CP impurity in the ${\mathit{B}}_{\mathit{d}}^0$ system, ‖Re(${\mathrm{\epsilon }}_{\mathit{B}}^0$)‖<0.045 at 90% C.L.

This Letter reports the observation and mass measurement of fully reconstructed ${\mathit{B}}_{\mathit{s}}^0$ mesons through the decay chain ${\mathit{B}}_{\mathit{s}}^0$→J/ψ ψ, J/ψ→${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$, φ→${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{-}}$ using data obtained at the Collider Detector at Fermilab in p¯p collisions at √s =1.8 TeV. A signal of 14.0±4.7 events is observed. Comparison of the ${\mathit{B}}_{\mathit{s}}^0$ signal with the kinematically similar decays ${\mathit{B}}^{+}$→J/ψ ${\mathit{K}}^{+}$ and ${\mathit{B}}^0$→J/ψ ${\mathrm{K}}^{\mathrm{*}}$(892${)}^0$ is presented. The mass of the ${\mathit{B}}_{\mathit{s}}^0$ meson is determined to be 5383.3±4.5(stat)±5.0(syst) MeV/${\mathit{c}}^2$.

We have observed the 1 ${}_{}{}^1{}_{}{}^{}$S-2 ${}_{}{}^1{}_{}{}^{}$P resonance line of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at 58.4 nm (linewidth 0.3 ${\mathrm{cm}}^{\mathrm{-}1}$) in a laser-atomic-beam experiment. The coherent radiation is produced by fifth-harmonic generation of UV light from a frequency-doubled, pulsed dye laser at 584 nm in a pulsed expansion of acetylene gas. The frequency of the fundamental radiation is calibrated against the iodine absorption spectrum, resulting in a transition frequency of 171 134.89(3) ${\mathrm{cm}}^{\mathrm{-}1}$. From this value a Lamb shift for the ground state of +1.38(3) ${\mathrm{cm}}^{\mathrm{-}1}$ is extracted, in good agreement with the theoretical value of +1.3745 ${\mathrm{cm}}^{\mathrm{-}1}$

We present a nonperturbative, fully correlated calculation of the structure of ${\mathrm{H}}^{\mathrm{-}}$ in an intense laser field, based on the high-frequency Floquet theory. We show that, as the intensity increases at sufficiently high frequencies, the electron affinity manifests a peculiar behavior and can become substantially higher than its field-free value. Besides, ${\mathrm{H}}^{\mathrm{-}}$ acquires excited states, some of which are doubly excited and nonautodetaching. At high intensities ${\mathrm{H}}^{\mathrm{-}}$ undergoes stabilization, similarly to the H atom.

The ratio R of helium double-to-single ionization cross sections was measured for ${\mathrm{Ne}}^{10+}$ and ${\mathrm{Ni}}^{28+}$ projectiles at velocities of 0.39≤${\mathit{v}}_{\mathit{P}}$/c≤0.93 intending to explore the high-velocity limit of R for highly charged ion impact. For ${\mathrm{Ne}}^{10+}$ projectiles R was observed to become independent of ${\mathit{v}}_{\mathit{P}}$ for ${\mathit{v}}_{\mathit{P}}$/c≳0.73 and an asymptotic experimental value R=(2.57±0.10)×${10}^{\mathrm{-}3}$ has been established. This is in good agreement with experimental results for proton, antiproton, electron, and positron impact and in excellent accordance with the theoretical prediction of (2.59±0.03)×${10}^{\mathrm{-}3}$.

We report for the first time the calculation of Stokes parameters and state-to-state rovibrationally resolved differential cross sections for the excitation ${\mathit{X}}^1$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$(v=0, N=1)→${\mathit{d}}^3$${\mathrm{\Pi }}_{\mathit{u}}^{\mathrm{-}}$(v=0, N=1) in ${\mathrm{H}}_2$ by electron impact at 25 eV. Comparison with the only available experimental data is encouraging.

A new class of amplitude instabilities severely restricts the stability domain of the transverse patterns in a laser that takes the form of a continuum of waves traveling transverse to the laser axis. Linear stability analyses and numerical solution of the laser equations reveal that one of the instabilities, which should be manifest in a broad range of contexts for which traveling waves are the preferred pattern, results in the death of the traveling wave and its replacement by a wave traveling in the opposite direction which exhibits novel transient and asymptotic behavior.

We propose and analyze a nonlinear optical amplifier that is phase insensitive but has no additive noise. When the input field is in a coherent state, the noise figure is -6 dB when the gain is high. However, unlike conventional linear amplifiers with -3 dB noise figures, the detectibility of the amplified signal is not degraded. The amplifier is constructed simply, in principle, by the same type of nonlinear interferometer used in photon number quantum nondemolition measurements.

We present an alternative approach to statistical analysis of an intermittent ideal magnetohydrodynamics fluid in two dimensions, based on the hydrodynamic discrete vortex model applied to the Elsasser variables. The model contains negative temperature states which predict the formation of magnetic islands, but also includes a natural limit under which the equilibrium states revert to the familiar twin-vortex states predicted by hydrodynamic turbulence theories. Numerical dynamical calculations yield equilibrium spectra in agreement with the theoretical predictions.

Films of diblock copolymers with thicknesses less than a lamellar period on a noninteracting surface were found to be model systems for studying the late stages of two dimensional phase separation. It was found under conditions of constant surface coverage that the average particle size 〈R(t)〉, the inverse of the total number of particles N(t${)}^{\mathrm{-}1}$, and the correlation length ξ(t) varied as ${\mathit{t}}^{\mathrm{\alpha }}$, ${\mathit{t}}^{2\mathrm{\alpha }}$, and ${\mathit{t}}^{\mathrm{\alpha }}$, respectively, where α=0.23±0.03.

Scanning tunneling micrographs of cleaved (ET${)}_2$KHg(SCN${)}_4$ crystals [where ET is bi(ethylenedithio)tetrathiafulvalene] indicate two distinct types of surfaces. Scans of type I surfaces show a 2D lattice and packing arrangement characteristic of the ET molecular layer; these features are relatively insensitive to reversal of the tip polarity. By contrast, scans of type II surfaces show maxima consistent with either the positions of the K-Hg atoms or with the SCN groups, depending upon the polarity of the tip. This is the first demonstration that a cleaved crystal of this material can present at least two possible surfaces: a complete metallic cation layer, or a complete insulating anion layer.

Deformation and alignment of an N-bead chain (9≤N≤50) in good solvent undergoint steady shear flow of shear rate γ̇ are studied by molecular dynamics. The alignment angle depends on the reduced shear rate β=γ̇${\mathrm{\tau }}_{\mathit{N}}$ where ${\mathrm{\tau }}_{\mathit{N}}$ is the chain longest relaxation time. Along each principal axis α of the gyration tensor ssG, the scattering function and ${\mathit{G}}_{\mathrm{\alpha }}$ exhibit power laws S(${\mathit{k}}_{\mathrm{\alpha }}$)∼${\mathit{k}}_{\mathrm{\alpha }}^{\mathrm{-}1/\nu }$(β) and ${\mathit{G}}_{\mathrm{\alpha }}$∼${\mathit{N}}_{\mathrm{\alpha }}^{\nu }$(β). This result suggests the existence of anisotropic scaling laws at fixed β. In the extension direction, ${\nu }_{\mathrm{\alpha }}$ increases with β and it is ${\nu }_{\mathrm{\alpha }}$=0.69±0.01 at β=3.17, in agreement with experiment.

Aqueous solutions of triblock copolymers of poly(ethylene oxide) and poly(propylene oxide) aggregate at elevated temperatures into micelles which for polymer concentrations ≥20% or more make a hard sphere crystallization to a cubic micellar crystal. Structural studies show that pressure improves the solvent quality of water, thus resulting in decomposition of the micelles and consequent melting of the miceller crystal. The combined pressure and temperature dependence reveals that (decreasing pressure) the overall entropy increases through the inverted micellar crystallization characteristic.

We investigate the stability, bonding, and geometric structure of recently discovered metallocarbohedrenes by the use of density-functional calculations. It is found that the previously proposed ${\mathit{T}}_{\mathit{h}}$ dodecahedron structure is dynamically unstable. Instead, a new, stable, and more strongly bound structure with ${\mathit{D}}_{2\mathit{d}}$ symmetry is found. We find strong interactions between C-C and strong Ti-C covalent bonding. The stability of the ${\mathit{D}}_{2\mathit{d}}$ structure has been verified by calculating vibrational frequencies. The infrared spectrum of the ${\mathrm{Zr}}_8$${\mathrm{C}}_{12}$ cluster is predicted.

We report the observation of a β-decay-induced lattice site change after the decay of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Nb}$ (${\mathit{T}}_{1/2}$=14.6 h) to ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ in Fe. Samples of ${}_{}{}^{90}{}_{}{}^{}\mathit{Fe}$ were prepared by recoil implantation and cooled to temperatures of ∼10 mK. The lattice location before and after the β decay was monitored via nuclear magnetic resonance on oriented nuclei (NMR-ON) on ${}_{}{}^{90}{}_{}{}^{}\mathrm{Nb}$ and ${}_{}{}^{90\mathit{m}}{}_{}{}^{}\mathrm{Zr}$ (${\mathit{T}}_{1/2}$=0.8 s), respectively. With double-resonance NMR-ON measurements it could be shown that for a fraction of ∼0.14(3) of ${}_{}{}^{90\mathit{m}}{}_{}{}^{}\mathrm{Zr}$ a β-decay-induced lattice site change must have occurred.

We have determined for the first time the ‘‘electronic’’ specific heat coefficient γ(x,T) of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ for 0.16≤x≤0.97 between 1.8 and 300 K. Weakly superconducting behavior between x=0.43 and 0.8 progresses rapidly to BCS-like superconducting and metallic normal state behavior for x≥0.9. However, the continuous development of the entropy S(x,T) with x and T across the entire series suggests a progressive modification of the low energy spin spectrum with hole doping rather than a simple band model. Fermi statistics and k-space pairing are indicaed by the magnitude and T dependence of S(x,T).

We have directly imaged the evolution of surface cusps during strained-layer epitaxy. The cusps arise naturally as a result of gradients in the surface chemical potential. High stress concentrations at the cusp tip have important implications for strain relaxation in the film via dislocation nucleation.