First and second order magnetic and structural transitions in BaFe2(1−x)_{2(1-x)}Co2x_{2x}As2_{2}

We present here high resolution magnetization measurements on high-quality BaFe$_{2(1-x)}$Co$_{2x}$As$_{2}$, 0$\leq$x$\leq$0.046 as-grown single crystals. The results confirm the existence of a magnetic tricritical point in the ($x$,$T$) plane at x$^{m}_{tr}$$\approx$0.022 and reveal the emergence of the heat capacity anomaly associated with the onset of the structural transition at x$^{s}$$\approx$0.0064. We show that the samples with doping near x$^{m}_{tr}$ do not show superconductivity, but rather superconductivity emerges at a slightly higher cobalt doping, x$\approx$0.0315Comment: 4 pages, 5 figure

Pair distribution functions calculated from interatomic potential models using the General Utility Lattice Program.

A new module has been developed for the widely used General Utility Lattice\ud Program (GULP). The phonon-based theory developed by Chung & Thorpe\ud [Phys. Rev. B (1999), 59, 4807–4812] to calculate pair distribution function\ud (PDF) peak widths has been utilized to give a selection of commonly used\ud correlation functions. A numerical library of neutron scattering information is\ud now available within GULP, and is used to produce results that can be\ud compared with neutron scattering experimental data. The influence of different\ud phonon modes on the PDF can be assessed by excluding modes above or below\ud a cut-off frequency. Results are presented for sample crystallographic systems,\ud MgO, SrTiO3 and -cristobalite, as well as CaxSr1xTiO3 at x = 0.5, which makes\ud use of the capability to handle partial occupancies to compare different Ca/Sr\ud ordering arrangements with a disordered model in which every Ca/Sr site has\ud 50% occupancy of both species

Monitoring the Short-Term Variability of Cyg X-1: Spectra and Timing

We present first results from the spectral and temporal analysis of an RXTE monitoring campaign of the black hole candidate Cygnus X-1 in 1999. The timing properties of this hard state black hole show considerable variability, even though the state does not change. This has previously been noted for the power spectral density, but is probably even more pronounced for the time lags. From an analysis of four monitoring observations of Cyg X-1, separated by 2 weeks from each other, we find that a shortening of the time lags is associated with a hardening of the X-ray spectrum, as well as with a longer characteristic ``shot time scale''. We briefly discuss possible physical/geometrical reasons for this variability of the hard state properties.Comment: 5 pages, 2 figures, Proc. of the 5th Compton Symposium, AIP, in pres

RXTE Observations of LMC X-1 and LMC X-3

Of all known persistent stellar-mass black hole candidates, only LMC X-1 and LMC X-3 consistently show spectra that are dominated by a soft, thermal component. We present results from long (170ksec) Rossi X-ray Timing Explorer (RXTE) observations of LMC X-1 and LMC X-3 made in 1996 December. The spectra can be described by a multicolor disk blackbody plus an additional high-energy power-law. Even though the spectra are very soft (Gamma is about 2.5), RXTE detected a significant signal from LMC X-3 up to energies of 50keV, the hardest energy at which the object was ever detected. Focusing on LMC X-3, we present results from the first year of an ongoing monitoring campaign with RXTE which started in 1997 January. We show that the appearance of the object changes considerably over its ~200d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.Comment: 4 pages, 5 figures, also available at http://aitzu3.ait.physik.uni-tuebingen.de/publications/preprints1998.html to be published in "Highlights of X-Ray Astronomy, a symposium in honour of Joachim Truemper" (B. Aschenbach et al., eds.), MPE Repor

The ferroelectric transition in YMnO3_3 from first principles

We have studied the structural phase transition of multiferroic YMnO$_3$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic study of the energy surface around the prototypic phase. We find a single instability at the zone-boundary which couples strongly to the polarization. This coupling is the mechanism that allows multiferroicity in this class of materials. Our results imply that YMnO$_3$ is an improper ferroelectric. We suggest further experiments to clarify this point.Comment: published version, PRB (rapid comm), slight change in presentatio

Path integral Monte Carlo simulations of silicates

We investigate the thermal expansion of crystalline SiO$_2$ in the $\beta$-- cristobalite and the $\beta$-quartz structure with path integral Monte Carlo (PIMC) techniques. This simulation method allows to treat low-temperature quantum effects properly. At temperatures below the Debye temperature, thermal properties obtained with PIMC agree better with experimental results than those obtained with classical Monte Carlo methods.Comment: 27 pages, 10 figures, Phys. Rev. B (in press

Collaborative care model versus usual care for people with musculoskeletal conditions and co-existing anxiety and depression: protocol for a feasibility mixed-methods randomised controlled trial.

In the UK 17.8 million people have musculoskeletal pathophysiology, which becomes universal with age. Levels of discomfort and incapability correlate with symptoms of anxiety and depression. People with sufficient symptoms who seek care can benefit from collaborative diagnosis and treatment of mental and physical health organised by a case manager. This paper presents the protocol for a feasibility trial of collaborative care in an orthopaedic setting. To determine the feasibility and acceptability of providing collaborative care for patients with musculoskeletal conditions and co-existing symptoms of anxiety and depression identified on a screening tool in a physical and occupational therapy out-patient setting. A two-arm parallel-group randomised controlled trial will recruit 40 adult out-patients with at least moderate anxiety and depression, who have been referred for physiotherapy and occupational therapy. Participants will be allocated on a 1:1 ratio to collaborative care or to usual care. Co-primary outcomes will be key feasibility indicators collected at baseline and at 6 months. A qualitative study will be conducted post-intervention to explore the acceptability and potential improvements to the collaborative care model. This study will investigate the use of the collaborative care model for patients with musculoskeletal and co-existing moderate or severe levels of anxiety or depression. The results will provide important evidence to determine a future trial

The Escape of Ionizing Photons from OB Associations in Disk Galaxies: Radiation Transfer Through Superbubbles

By solving the time-dependent radiation transfer problem of stellar radiation through evolving superbubbles within a smoothly varying HI distribution, we estimate the fraction of ionizing photons emitted by OB associations that escapes the HI disk of our Galaxy into the halo and intergalactic medium (IGM). We consider both coeval star-formation and a Gaussian star-formation history with a time spread sigma_t = 2 Myr. We consider both a uniform H I distribution and a two-phase (cloud/intercloud) model, with a negligible filling factor of hot gas. We find that the shells of the expanding superbubbles quickly trap or attenuate the ionizing flux, so that most of the escaping radiation escapes shortly after the formation of the superbubble. For the coeval star-formation history, the total fraction of Lyman Continuum photons that escape both sides of the disk in the solar vicinity is f_esc approx 0.15 +/- 0.05. For the Gaussian star formation history, f_esc approx 0.06 +/- 0.03, a value roughly a factor of two lower than the results of Dove & Shull (1994), where superbubbles were not considered. For a local production rate of ionizing photons Psi_LyC = 4.95 X 10^7 cm^{-2} s^{-1}, the flux escaping the disk is Phi_LyC approx (1.5-3.0) X 10^6 cm^{-2} s^{-1} for coeval and Gaussian star formation, comparable to the flux required to sustain the Reynolds layer.Comment: Revised version (expanded), accepted for publication by ApJ, 38 pages, 8 figures, aasms4.sty and aabib.sty files include

Grid tool integration within the eMinerals Project

In this article we describe the eMinerals mini grid, which is now running in production mode. Thisis an integration of both compute and data components, the former build upon Condor, PBS and thefunctionality of Globus v2, and the latter being based on the combined use of the Storage ResourceBroker and the CCLRC data portal. We describe how we have integrated the middleware components,and the different facilities provided to the users for submitting jobs within such an environment. We willalso describe additional functionality we found it necessary to provide ourselves