Radiative spacetimes approaching the Vaidya metric

We analyze a class of exact type II solutions of the Robinson-Trautman family which contain pure radiation and (possibly) a cosmological constant. It is shown that these spacetimes exist for any sufficiently smooth initial data, and that they approach the spherically symmetric Vaidya-(anti-)de Sitter metric. We also investigate extensions of the metric, and we demonstrate that their order of smoothness is in general only finite. Some applications of the results are outlined.Comment: 12 pages, 3 figure

The Effect of a Restraint Reduction Program on Physical Restraint Rates in Rehabilitation Settings in Hong Kong

Background. In view of the adverse effects of using restraints, studies examining the use of restraint reduction programs (RRPs) are needed. Objectives. To investigate the effect of an RRP on the reduction of physical restraint rates in rehabilitation hospitals. Methods. A prospective quasi-experimental clinical trial was conducted. Demographic data, medical and health-related information on recruited patients from two rehabilitation hospitals, as well as facility data on restraint rates were collected. Results. The increase in the restraint rate in the control site was 4.3 times greater than that in the intervention site. Changes in the restraint mode, from continuous to intermittent, and the type of restraint used were found between the pre- and postintervention periods in both the control site and the intervention site. Discussion. Compared with that in the control site, the RRP in the intervention site helped arrest any increase in the restraint rate although it had no effect on physical restraint reduction. The shift of restraint mode from continuous to intermittent in the intervention site was one of the positive outcomes of the RRP

Low-Energy Charge-Density Excitations in MgB2_{2}: Striking Interplay between Single-Particle and Collective Behavior for Large Momenta

A sharp feature in the charge-density excitation spectra of single-crystal MgB$_{2}$, displaying a remarkable cosine-like, periodic energy dispersion with momentum transfer ($q$) along the $c^{*}$-axis, has been observed for the first time by high-resolution non-resonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-$q$ collective mode residing in the single-particle excitation gap of the B $\pi$ bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB$_{2}$.Comment: 5 pages, 4 figures, submitted to PR

Commensurability oscillations in the rf conductivity of unidirectional lateral superlattices: measurement of anisotropic conductivity by coplanar waveguide

We have measured the rf magnetoconductivity of unidirectional lateral superlattices (ULSLs) by detecting the attenuation of microwave through a coplanar waveguide placed on the surface. ULSL samples with the principal axis of the modulation perpendicular (S_perp) and parallel (S_||) to the microwave electric field are examined. For low microwave power, we observe expected anisotropic behavior of the commensurability oscillations (CO), with CO in samples S_perp and S_|| dominated by the diffusion and the collisional contributions, respectively. Amplitude modulation of the Shubnikov-de Haas oscillations is observed to be more prominent in sample S_||. The difference between the two samples is washed out with the increase of the microwave power, letting the diffusion contribution govern the CO in both samples. The failure of the intended directional selectivity in the conductivity measured with high microwave power is interpreted in terms of large-angle electron-phonon scattering.Comment: 8 pages, 5 figure

Predictions for s-Wave and p-Wave Heavy Baryons from Sum Rules and Constituent Quark Model (I): Strong Interactions

We study the strong interactions of the L=1 orbitally excited baryons with one heavy quark in the framework of the Heavy Hadron Chiral Perturbation Theory. To leading order in the heavy mass expansion, the interaction Lagrangian describing the couplings of these states among themselves and with the ground state heavy baryons contains 46 unknown couplings. We derive sum rules analogous to the Adler-Weisberger sum rule which constrain these couplings and relate them to the couplings of the s-wave heavy baryons. Using a spin 3/2 baryon as a target, we find a sum rule expressing the deviation from the quark model prediction for pion couplings to s-wave states in terms of couplings of the p-wave states. In the constituent quark model these couplings are related and can be expressed in terms of only two reduced matrix elements. Using recent CLEO data on $\Sigma_c^{*}$ and $\Lambda_{c1}^+$ strong decays, we determine some of the unknown couplings in the chiral Lagrangian and the two quark model reduced matrix elements. Specific predictions are made for the decay properties of all L=1 charmed baryons.Comment: 50 pages, REVTeX with 4 included figures; predictions for additional decay modes included; 1 reference adde

Vertical transport and electroluminescence in InAs/GaSb/InAs structures: GaSb thickness and hydrostatic pressure studies

We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness between 0-1200 \AA. A negative differential resistance (NDR) is observed for all DHETs with GaSb thickness $>$ 60 \AA below which a dramatic change in the shape of the I-V and a marked hysteresis is observed. The temperature dependence of the I-V is found to be very strong below this critical GaSb thickness. The I-V characteristics of selected DHETs are also presented under hydrostatic pressures up to 11 kbar. Finally, a mid infra-red electroluminescence is observed at 1 bar with a threshold at the NDR valley bias. The band profile calculations presented in the analysis are markedly different to those given in the literature, and arise due to the positive charge that it is argued will build up in the GaSb layer under bias. We conclude that the dominant conduction mechanism in DHETs is most likely to arise out of an inelastic electron-heavy-hole interaction similar to that observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding, and not out of resonant electron-light-hole tunnelling as proposed by Yu et al. A Zener tunnelling mechanism is shown to contribute to the background current beyond NDR.Comment: 8 pages 12 fig

THERMODYNAMICS OF A BROWNIAN BRIDGE POLYMER MODEL IN A RANDOM ENVIRONMENT

We consider a directed random walk making either 0 or $+1$ moves and a Brownian bridge, independent of the walk, conditioned to arrive at point $b$ on time $T$. The Hamiltonian is defined as the sum of the square of increments of the bridge between the moments of jump of the random walk and interpreted as an energy function over the bridge connfiguration; the random walk acts as the random environment. This model provides a continuum version of a model with some relevance to protein conformation. The thermodynamic limit of the specific free energy is shown to exist and to be self-averaging, i.e. it is equal to a trivial --- explicitly computed --- random variable. An estimate of the asymptotic behaviour of the ground state energy is also obtained.Comment: 20 pages, uuencoded postscrip