6,938 research outputs found
Anisotropic thermal expansion of Fe1.06Te and FeTe0.5Se0.5 single crystals
Heat capacity and anisotropic thermal expansion was measured for Fe1.06Te and
FeTe0.5Se0.5 single crystals. Previously reported phase transitions are clearly
seen in both measurements. In both cases the thermal expansion is anisotropic.
The uniaxial pressure derivatives of the superconducting transition temperature
in FeTe0.5Se0.5 inferred from the Ehrenfest relation have opposite signs for
in-plane and c-axis pressures. Whereas the Gruneisen parameters for both
materials are similar and only weakly temperature-dependent above ~ 80 K, at
low temperatures (in the magnetically ordered phase) the magnetic contribution
to the Gruneisen parameter in Fe1.06Te is significantly larger than electron
and phonon contributions combined
SUSY vertex algebras and supercurves
This article is a continuation of math.QA/0603633 Given a strongly conformal
SUSY vertex algebra V and a supercurve X we construct a vector bundle V_X on X,
the fiber of which, is isomorphic to V. Moreover, the state-field
correspondence of V canonically gives rise to (local) sections of these vector
bundles. We also define chiral algebras on any supercurve X, and show that the
vector bundle V_X, corresponding to a SUSY vertex algebra, carries the
structure of a chiral algebra.Comment: 50 page
Circular dichroism of cholesteric polymers and the orbital angular momentum of light
We explore experimentally if the light's orbital angular momentum (OAM)
interacts with chiral nematic polymer films. Specifically, we measure the
circular dichroism of such a material using light beams with different OAM. We
investigate the case of strongly focussed, non-paraxial light beams, where the
spatial and polarization degrees of freedom are coupled. Within the
experimental accuracy, we cannot find any influence of the OAM on the circular
dichroism of the cholesteric polymer.Comment: 3 pages, 4 figure
Sub-Pixel Response Measurement of Near-Infrared Sensors
Wide-field survey instruments are used to efficiently observe large regions
of the sky. To achieve the necessary field of view, and to provide a higher
signal-to-noise ratio for faint sources, many modern instruments are
undersampled. However, precision photometry with undersampled imagers requires
a detailed understanding of the sensitivity variations on a scale much smaller
than a pixel. To address this, a near-infrared spot projection system has been
developed to precisely characterize near-infrared focal plane arrays and to
study the effect of sub-pixel non uniformity on precision photometry.
Measurements of large format near-infrared detectors demonstrate the power of
this system for understanding sub-pixel response.Comment: 9 pages, 13 figures, submitted to PAS
Ab initio parametrised model of strain-dependent solubility of H in alpha-iron
The calculated effects of interstitial hydrogen on the elastic properties of
alpha-iron from our earlier work are used to describe the H interactions with
homogeneous strain fields using ab initio methods. In particular we calculate
the H solublility in Fe subject to hydrostatic, uniaxial, and shear strain. For
comparison, these interactions are parametrised successfully using a simple
model with parameters entirely derived from ab initio methods. The results are
used to predict the solubility of H in spatially-varying elastic strain fields,
representative of realistic dislocations outside their core. We find a strong
directional dependence of the H-dislocation interaction, leading to strong
attraction of H by the axial strain components of edge dislocations and by
screw dislocations oriented along the critical slip direction. We
further find a H concentration enhancement around dislocation cores, consistent
with experimental observations.Comment: part 2/2 from splitting of 1009.3784 (first part was 1102.0187),
minor changes from previous version
On-the-Job Training
Firms in the U.S. invest billions of dollars annually in workforce training. Growing evidence of the effects of this training on worker productivity, wages, hiring and turnover has led researchers to gradually incorporate the role of training into their analyses. Barron, Berger and Black advance this line of research by offering new evidence on the amount of training provided to workers during the first three months on the job, and the characteristics of those workers who received that training.https://research.upjohn.org/up_press/1070/thumbnail.jp
Assessing the Positional Planimetric Accuracy of DBpedia Georeferenced Resources
International audienceAssessing the quality of the main linked data sources on the Web like DBpedia or Yago is an important research topic. The existing approaches for quality assessment mostly focus on determining whether data sources are compliant with Web of data best practices or on their completeness, semantic accuracy, consistency, relevancy or trustworthi-ness. In this article, we aim at assessing the accuracy of a particular type of information often associated with Web of data resources: direct spatial references. We present the approaches currently used for assessing the planimetric accuracy of geographic databases. We explain why they cannot be directly applied to the resources of the Web of data. Eventually , we propose an approach for assessing the planimetric accuracy of DBpedia resources, adapted to the open nature of this knowledge base
On the accuracy of the melting curves drawn from modelling a solid as an elastic medium
An ongoing problem in the study of a classical many-body system is the
characterization of its equilibrium behaviour by theory or numerical
simulation. For purely repulsive particles, locating the melting line in the
pressure-temperature plane can be especially hard if the interparticle
potential has a softened core or contains some adjustable parameters. A method
is hereby presented that yields reliable melting-curve topologies with
negligible computational effort. It is obtained by combining the Lindemann
melting criterion with a description of the solid phase as an elastic
continuum. A number of examples are given in order to illustrate the scope of
the method and possible shortcomings. For a two-body repulsion of Gaussian
shape, the outcome of the present approach compares favourably with the more
accurate but also more computationally demanding self-consistent harmonic
approximation.Comment: 25 pages, 7 figure
The effect of alongcoast advection on pacific northwest shelf and slope water properties in relation to upwelling variability
The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin-scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N-50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well-explained (R2=0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large-scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large-scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale
Is Option B+ the best choice?
The success of prevention of mother-to-child transmission (PMTCT) programmes (Options A and B) in middle-income countries, together with clinical trial data on antiretroviral (ARV) treatment as prophylaxis, has emboldened UN agencies to aggressively promote lifelong ARVs for PMTCT (Option B+). Unsubstantiated claims submit that Option B+ is cost-effective at population-level, will protect HIV-negative male partners, improve maternal and infant health, and increase ARV coverage. We provide counterfactual arguments about the ethics, medical safety, programme feasibility and economic benefits of Option B+.Option B+ offers no advantage to PMTCT and there are social hazards associated with privileging pregnant woman for treatment over men and non-pregnant women, especially with the absence of data to suggest that discordant relationships are more frequent among pregnant women or that they contribute disproportionately to the horizontal HIV transmission. The benefits and safety of long-term ARVs – including adherence and resistance – in mothers who do not need treatment for their own health, need to be considered, as well as, crucially, health service costs. The assumption that a decrease in efficiency caused by inappropriate targeting is compensated for by lower recruitment costs, is untested. Lives could be saved instead with appropriately targeted interventions. Countries should make individual decisions based on their HIV epidemiology, resources, priorities and local evidence.S Afr J HIV Med 2013;14(1):8-10. DOI:10.7196/SAJHIVMED.898This article is reprinted from The Lancet, with permission from Elsevier: Coutsodis A, Goga A, Desmond C, Barron P, Black V, Coovadia H. Is Option B+ the best choice? Lancet 2013;381(9863):269-271. [http://dx/doi.org/10.1016/S0140-6736(12)61807-8
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