3,341 research outputs found
Phase-dependent X-ray observations of the beta Lyrae system: No eclipse in the soft band
We report on observations of the eclipsing and interacting binary beta Lyrae
from the Suzaku X-ray telescope. This system involves an early B star embedded
in an optically and geometrically thick disk that is siphoning atmospheric
gases from a less massive late B II companion. Motivated by an unpublished
X-ray spectrum from the Einstein X-ray telescope suggesting unusually hard
emission, we obtained time with Suzaku for pointings at three different phases
within a single orbit. From the XIS detectors, the softer X-ray emission
appears typical of an early-type star. What is surprising is the remarkably
unchanging character of this emission, both in luminosity and in spectral
shape, despite the highly asymmetric geometry of the system. We see no eclipse
effect below 10 keV. The constancy of the soft emission is plausibly related to
the wind of the embedded B star and Thomson scattering of X-rays in the system,
although it might be due to extended shock structures arising near the
accretion disk as a result of the unusually high mass-transfer rate. There is
some evidence from the PIN instrument for hard emission in the 10-60 keV range.
Follow-up observations with the RXTE satellite will confirm this preliminary
detection.Comment: to appear in A&A Letter
Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves
Transport currents can alter alter order parameter dynamics and change steady
states in superconductors, in ferromagnets, and in hybrid systems. In this
article we present a scheme for fully microscopic evaluation of order parameter
dynamics that is intended for application to nanoscale systems. The approach
relies on time-dependent mean-field-theory, on an adiabatic approximation, and
on the use of non-equilibrium Greens function (NEGF) theory to calculate the
influence of a bias voltage across a system on its steady-state density matrix.
We apply this scheme to examine the spin-transfer torques which drive
magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic
torques are peaked near Co/Cu interfaces, in agreement with most previous
pictures, but suprisingly act mainly on Co transition metal -orbitals rather
than on -orbitals as generally supposed.Comment: 9 pages, 5 figure
A three-season comparison of match performances among selected and unselected elite youth rugby league players
This is an author's accepted manuscript of an article published in Journal of Sports Sciences, 28 February 2014, available online: http:www.tandfonline.com/10.1080/02640414.2014.889838This study compared technical actions, movements, heart rates and perceptual responses of selected and unselected youth rugby league players during matches (under-15 to under-17). The players’ movements and heart rates were assessed using 5 Hz Global Positioning Systems (GPS), while their technical actions were analysed using video analysis. The maturity of each player was predicted before each season for statistical control. There were no differences (P > 0.05) between selected and unselected players in the under-15 or the under-17 age groups for any variables. However, in the under-16 group, the selected players (57.1 ± 11.9 min) played for longer than the unselected players (44.1 ± 12.3 min; P = 0.017; ES = 1.08 ± CI = 0.87), and covered more distance (5,181.0 ± 1063.5 m cf. 3942.6 ± 1,108.6m, respectively; P = 0.012; ES = 1.14 ± CI = 0.88) and high intensity distance (1,808.8 ± 369.3 m cf. 1,380.5 ± 367.7 m, respectively; P = 0.011; ES = 1.16 ± CI = 0.88). Although successful carries per minute was higher in the selected under-15 group, there were no other differences (P > 0.05) in match performance relative to playing minutes between groups. Controlling for maturity, the less mature, unselected players from the under-16 group performed more high-intensity running (P < 0.05). Our findings question the use of match- related measurements in differentiating between selected and unselected players, showing that later maturing players were unselected, even when performing greater high-intensity running during matches
Ab-initio GMR and current-induced torques in Au/Cr multilayers
We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and
current-induced-torques (CITs) in Cr/Au multilayers that is based on
non-equilibrium Green's functions and spin density functional theory. We find
substantial GMR due primarily to a spin-dependent resonance centered at the
Cr/Au interface and predict that the CITs are strong enough to switch the
antiferromagnetic order parameter at current-densities times smaller
than typical ferromagnetic metal circuit switching densities.Comment: 8 pages, 6 figure
Higher Spin Gravitational Couplings and the Yang--Mills Detour Complex
Gravitational interactions of higher spin fields are generically plagued by
inconsistencies. We present a simple framework that couples higher spins to a
broad class of gravitational backgrounds (including Ricci flat and Einstein)
consistently at the classical level. The model is the simplest example of a
Yang--Mills detour complex, which recently has been applied in the mathematical
setting of conformal geometry. An analysis of asymptotic scattering states
about the trivial field theory vacuum in the simplest version of the theory
yields a rich spectrum marred by negative norm excitations. The result is a
theory of a physical massless graviton, scalar field, and massive vector along
with a degenerate pair of zero norm photon excitations. Coherent states of the
unstable sector of the model do have positive norms, but their evolution is no
longer unitary and their amplitudes grow with time. The model is of
considerable interest for braneworld scenarios and ghost condensation models,
and invariant theory.Comment: 19 pages LaTe
BPS black holes, quantum attractor flows and automorphic forms
We propose a program for counting microstates of four-dimensional BPS black
holes in N >= 2 supergravities with symmetric-space valued scalars by
exploiting the symmetries of timelike reduction to three dimensions. Inspired
by the equivalence between the four dimensional attractor flow and geodesic
flow on the three-dimensional scalar manifold, we radially quantize stationary,
spherically symmetric BPS geometries. Connections between the topological
string amplitude, attractor wave function, the Ooguri-Strominger-Vafa
conjecture and the theory of automorphic forms suggest that black hole
degeneracies are counted by Fourier coefficients of modular forms for the
three-dimensional U-duality group, associated to special "unipotent"
representations which appear in the supersymmetric Hilbert space of the quantum
attractor flow.Comment: 9 pages, revtex; v2: references added and typos correcte
X-ray emission from the double-binary OB-star system QZ Car (HD 93206)
X-ray observations of the double-binary OB-star system QZ Car (HD 93206)
obtained with the Chandra X-ray Observatory over a period of roughly 2 years
are presented. The orbit of systems A (O9.7 I+b2 v, PA = 21 d) and B (O8 III+o9
v, PB = 6 d) are reasonably well sampled by the observations, allowing the
origin of the X-ray emission to be examined in detail. The X-ray spectra can be
well fitted by an attenuated three temperature thermal plasma model,
characterised by cool, moderate, and hot plasma components at kT ~ 0.2, 0.7,
and 2 keV, respectively, and a circumstellar absorption of ~ 0.2 x 10^22 cm-2.
Although the hot plasma component could be indicating the presence of wind-wind
collision shocks in the system, the model fluxes calculated from spectral fits,
with an average value of ~ 7 x 10^-13 erg s-1 cm-2, do not show a clear
correlation with the orbits of the two constituent binaries. A semi-analytical
model of QZ Car reveals that a stable momentum balance may not be established
in either system A or B. Yet, despite this, system B is expected to produce an
observed X-ray flux well in excess of the observations. If one considers the
wind of the O8 III star to be disrupted by mass transfer the model and
observations are in far better agreement, which lends support to the previous
suggestion of mass-transfer in the O8 III + o9 v binary. We conclude that the
X-ray emission from QZ Car can be reasonably well accounted for by a
combination of contributions mainly from the single stars and the mutual
wind-wind collision between systems A and B.Comment: 11 pages, 7 figures. Accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
leas
Efficacy of an 8-Week Concurrent Strength and Endurance Training Programme on Hand Cycling Performance
The aim of the present study was to investigate the effects of an 8-week concurrent strength and endurance training programme in comparison to endurance training only on several key determinants of hand cycling performance. Five H4 and five H3 classified hand cyclists with at least one year’s hand cycling training history consented to participate in the study. Subjects underwent a battery of tests to establish body mass, body composition, VO2peak, maximum aerobic power, gross mechanical efficiency, maximal upper body strength, and 30 km time trial performance. Subjects were matched into pairs based upon 30 km time trial performance and randomly allocated to either a concurrent strength and endurance or endurance training only, intervention group. Following an 8-week training programme based upon a conjugated block periodisation model, subjects completed a second battery of tests. A mixed model, 2-way analysis of variance (ANOVA) revealed no significant changes between groups. However, the calculation of effect sizes (ES) revealed that both groups demonstrated a positive improvement in most physiological and performance measures with subjects in the concurrent group demonstrating a greater magnitude of improvement in body composition (ES -0.80 vs. -0.22) maximal aerobic power (ES 0.97 vs. 0.28), gross mechanical efficiency (ES 0.87 vs. 0.63), bench press 1 repetition maximum (ES 0.53 vs. 0.33), seated row 1 repetition maximum (ES 1.42 vs. 0.43), and 30 km time trial performance (ES -0.66 vs. -0.30). In comparison to endurance training only, an 8-week concurrent training intervention based upon a conjugated block periodisation model appears to be a more effective training regime for improving the performance capabilities of hand cyclists
Multi-serotype pneumococcal nasopharyngeal carriage prevalence in vaccine naïve Nepalese children, assessed using molecular serotyping.
Invasive pneumococcal disease is one of the major causes of death in young children in resource poor countries. Nasopharyngeal carriage studies provide insight into the local prevalence of circulating pneumococcal serotypes. There are very few data on the concurrent carriage of multiple pneumococcal serotypes. This study aimed to identify the prevalence and serotype distribution of pneumococci carried in the nasopharynx of young healthy Nepalese children prior to the introduction of a pneumococcal conjugate vaccine using a microarray-based molecular serotyping method capable of detecting multi-serotype carriage. We conducted a cross-sectional study of healthy children aged 6 weeks to 24 months from the Kathmandu Valley, Nepal between May and October 2012. Nasopharyngeal swabs were frozen and subsequently plated on selective culture media. DNA extracts of plate sweeps of pneumococcal colonies from these cultures were analysed using a molecular serotyping microarray capable of detecting relative abundance of multiple pneumococcal serotypes. 600 children were enrolled into the study: 199 aged 6 weeks to <6 months, 202 aged 6 months to < 12 months, and 199 aged 12 month to 24 months. Typeable pneumococci were identified in 297/600 (49.5%) of samples with more than one serotype being found in 67/297 (20.2%) of these samples. The serotypes covered by the thirteen-valent pneumococcal conjugate vaccine were identified in 44.4% of samples containing typeable pneumococci. Application of a molecular serotyping approach to identification of multiple pneumococcal carriage demonstrates a substantial prevalence of co-colonisation. Continued surveillance utilising this approach following the introduction of routine use of pneumococcal conjugate vaccinates in infants will provide a more accurate understanding of vaccine efficacy against carriage and a better understanding of the dynamics of subsequent serotype and genotype replacement
Trouble in Paradise - A disabled person's right to the satisfaction of a self-defined need:Some conceptual and practical problems
This paper questions the usefulness of the rights-based approach to ameliorating the social situation of disabled people in Britain and advances two criticisms. First, that rights and self-de? ned needs have been under-theorised by disability theorists to the extent that they have insuf? ciently appreciated the problems that these approaches pose. The paper suggests that rights to appropriate resources to satisfy self-de? ned needs will generate vast numbers of competing rights claims and that the resulting tendency of rights to con? ict has been under-appreciated. Secondly, that there has been little consideration of how these con? icts might be reconciled. The ? rst two sections of the paper look at the concepts of ascribed and self-de? ned needs, respectively, whilst the ? nal one looks at some of the problems of the rights approach and some of the dif? culties of making self-de? ned need the basis of rights claims
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