Superconductivity in Heavy Alkaline-Earths Intercalated Graphites

We report the discovery of superconductivity below 1.65(6) K in Sr-intercalated graphite SrC6, by susceptibility and specific heat (Cp) measurements. In comparison with CaC6, we found that the anisotropy of the upper critical fields for SrC6 is much reduced. The Cp anomaly at Tc is smaller than the BCS prediction indicating an anisotropic superconducting gap for SrC6 similar to CaC6. The significantly lower Tc of SrC6 as compared to CaC6 can be understood in terms of "negative" pressure effects, which decreases the electron-phonon coupling for both in-plane intercalant and the out-of-plane C phonon modes. We observed no superconductivity for BaC6 down to 0.3 K.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

Impact of Human Immunodeficiency Virus Infection on the Outcome of Treatment and Survival of Tuberculosis Patients in Mwanza, Tanzania.

Little is known about the outcome of tuberculosis (TB) treatment and subsequent survival of human immunodeficiency virus (HIV) infected patients treated under routine programme conditions in a developing country. We followed a cohort of HIV-positive and HIV-negative tuberculosis patients during therapy and assessed their vital and tuberculosis status 3 years after completion of treatment in Mwanza, Tanzania. Newly diagnosed and relapse tuberculosis cases consecutively registered over a 6-month period were enrolled into an epidemiological study of TB/HIV. Treatment outcome was based on information in tuberculosis treatment registers. Patients surviving treatment were assessed 3 years later by personal interview. Cause of death was determined by verbal autopsy. Of 561 patients enrolled into the study, 505 patients alive at completion of treatment were eligible for assessment at 3 years. Except for mortality, HIV infection was not statistically associated with differing treatment outcomes. At time of follow-up, the overall mortality was 19% and was associated with HIV infection (hazard ratio [hr] 3.7, 95% confidence interval [CI] 2.6-5.2) and age 35 years and over (hr 1.5, 95% CI 1.02-2.1), but not with type of tuberculosis, gender, or initial drug resistance. By life table analysis, probability of survival at 4 years was 35% for HIV-positive patients compared to 90% for HIV-negative patients. Although no relapse cases were diagnosed, verbal autopsy suggested equivalent low rates of relapse in both groups. These results demonstrate the effectiveness of the current approach to the treatment of tuberculosis patients regardless of HIV status. However, HIV-related mortality remains high both during and following completion of treatment, and further studies are needed to determine if this mortality might be reduced by simple interventions which are feasible in developing countries.\u

Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines

The similarity of quasar line spectra has been taken as an indication that the emission line clouds have preferred parameters, suggesting that the environment is subject to a fine tuning process. We show here that the observed spectrum is a natural consequence of powerful selection effects. We computed a large grid of photoionization models covering the widest possible range of cloud gas density and distance from the central continuum source. For each line only a narrow range of density and distance from the continuum source results in maximum reprocessing efficiency, corresponding to ``locally optimally-emitting clouds'' (LOC). These parameters depend on the ionization and excitation potentials of the line, and its thermalization density. The mean QSO line spectrum can be reproduced by simply adding together the full family of clouds, with an appropriate covering fraction distribution. The observed quasar spectrum is a natural consequence of the ability of various clouds to reprocess the underlying continuum, and can arise in a chaotic environment with no preferred pressure, gas density, or ionization parameter.Comment: 9 pages including 1 ps figure. LaTeX format using aaspp4.st

Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: II. 1D hydrodynamical models of wind driven shocks

Following the early Swift X-ray observations of the latest outburst of the recurrent nova RS Ophiuchi in February 2006 (Paper I), we present new 1D hydrodynamical models of the system which take into account all three phases of the remnant evolution. The models suggest a novel way of modelling the system by treating the outburst as a sudden increase then decrease in wind mass-loss rate and velocity. The differences between this wind model and previous Primakoff-type simulations are described. A more complex structure, even in 1D, is revealed through the presence of both forward and reverse shocks, with a separating contact discontinuity. The effects of radiative cooling are investigated and key outburst parameters such as mass-loss rate, ejecta velocity and mass are varied. The shock velocities as a function of time are compared to the ones derived in Paper I. We show how the manner in which the matter is ejected controls the evolution of the shock and that for a well-cooled remnant, the shock deceleration rate depends on the amount of energy that is radiated away.Comment: 9 pages, 5 figure

Six months of mass outflow and inclined rings in the ejecta of V1494 Aql

V1494 Aql was a very fast nova which reached a visual maximum of mv≃ 4.0 by the end of 1999 December 3. We report observations from 4 to 284 d after discovery, including submillimetre- and centimetre-band fluxes, a single MERLIN image and optical spectroscopy in the 410 to 700 nm range. The extent of the radio continuum emission is consistent with a recent lower distance estimate of 1.6 kpc. We conclude that the optical and radio emission arises from the same expanding ejecta. We show that these observations are not consistent with simple kinematical spherical shell models used in the past to explain the rise and fall of the radio flux density in these objects. The resolved remnant structure is consistent with an inclined ring of enhanced density within the ejecta. Optical spectroscopy indicates likely continued mass ejection for over 195 d, with the material becoming optically thin in the visible sometime between 195 and 285 d after outburst

Self-pulsation at 480 GHz from a two-color discrete mode laser diode

A discrete mode Fabry-Pérot laser is designed and fabricated to achieve two-color lasing. We demonstrate beating between the two laser modes and self-pulsation at 480 GHz

Simulation-assisted control in building energy management systems

Technological advances in real-time data collection, data transfer and ever-increasing computational power are bringing simulation-assisted control and on-line fault detection and diagnosis (FDD) closer to reality than was imagined when building energy management systems (BEMSs) were introduced in the 1970s. This paper describes the development and testing of a prototype simulation-assisted controller, in which a detailed simulation program is embedded in real-time control decision making. Results from an experiment in a full-scale environmental test facility demonstrate the feasibility of predictive control using a physically-based thermal simulation program