608 research outputs found
Psuedo-isotropic upper critical field in cobalt-doped SrFe2As2 epitaxial films
The temperature and angular dependence of the upper critical field (Hc2) is
reported for cobalt-doped SrFe2As2 epitaxial films between Tc and 0.5 K in
pulsed magnetic fields up to 50 T. For H parallel c, Hc2 is close to a linear
function of temperature, while in the perpendicular direction there is
significant downward curvature that results in an Hc2 ratio (gamma =
Hc2(perpendicular)/Hc2(parallel) that decreases nearly linearly with
temperature, approaching gamma = 1 at low temperature with Hc2(0) = 47 T. We
measure the complete upper-critical field phase diagram including angular
dependence and model the data using a two band theory allowing us to determine
the anisotropy of both bands, their relative diffusivities, and the
relationship between BCS coupling constant matrix elements. We find an unusual
relationship between the diffusivities of the two bands, with two anisotropic
and opposite bands. This relationship is supported by the observation of a
local maximum for Hc2(parallel) at low temperature
Evidence for Anisotropic Vortex Dynamics and Pauli Limitation in the Upper Critical Field of FeSe1-xTex
We have determined HC2(T) for FeSe1-xTex (x=0.52) single crystals using
resistivity measurements at high static and pulsed magnetic field, as well as
specific heat measurements up to 9T. We find that the significant anisotropy of
the initial slope of HC2(T) determined from resistivity measurements, is not
present when HC2 is determined from the specific heat results. This suggests
that the thermodynamic upper critical field is almost isotropic, and that
anisotropic vortex dynamics play a role. Further evidence of anisotropic vortex
dynamics is found in the behaviour in pulsed field. We also find that Pauli
limiting must be included in order to fit the temperature dependence of HC2,
indicating probably higher effective mass in FeSe1-xTex than in other Fe
superconductors
Doping dependence of upper critical field and Hall resistivity in LaFeAsO1-xFx
The electrical resistivity (Rxx) and Hall resistivity (Rxy) of LaFeAsO1-xFx
have been measured over a wide fluorine doping range 0 =< x =< 0.14 using 60 T
pulsed magnets. While the superconducting phase diagram (Tc, x) displays the
classic dome-shaped structure, we find that the resistive upper critical field
(Hc2) increases monotonically with decreasing fluorine concentration, with the
largest Hc2 >= 75 T for x = 0.05. This is reminiscent of the composition
dependence in high-Tc cuprates and might correlate with opening of a pseudo-gap
in the underdoped region. Further, the temperature dependence of Hc2(T) for
superconducting samples can be understood in terms of multi-band
superconductivity. Rxy data for non-superconducting samples show non-linear
field dependence, which is also consistent with a multi-carrier scenario.Comment: 15 pages, 5 figures, Accepted by PR
Ir-Man: An Information Retrieval Framework for Marine Animal Necropsy Analysis
This paper proposes Ir-Man (Information Retrieval for Marine Animal Necropsies), a framework for retrieving discrete information from marine mammal post-mortem reports for statistical analysis. When a marine mammal is reported dead after stranding in Scotland, the carcass is examined by the Scottish Marine Animal Strandings Scheme (SMASS) to establish the circumstances of the animal's death. This involves the creation of a 'post-mortem' (or necropsy) report , which systematically describes the body. These semi-structured reports record lesions (damage or abnormalities to anatomical regions) as well as other observations. Observations embedded within these texts are used to determine cause of death. While a cause of death is recorded separately, many other descriptions may be of pathological and epidemiological significance when aggregated and analysed collectively. As manual extraction of these descriptions is costly, time consuming and at times erroneous, there is a need for an automated information retrieval mechanism which is a non-trivial task given the wide variety of possible descriptions, pathologies and species. The Ir-Man framework consists of a new ontology, a lexicon of observations and anatomical terms and an entity relation engine for information retrieval and statistics generation from a pool of necropsy reports. We demonstrate the effectiveness of our framework by creating a rule-based binary classifier for identifying bottlenose dolphin attacks (BDA) in harbour porpoise gross pathology reports and achieved an accuracy of 83.4%
Randomizing world trade. II. A weighted network analysis
Based on the misleading expectation that weighted network properties always
offer a more complete description than purely topological ones, current
economic models of the International Trade Network (ITN) generally aim at
explaining local weighted properties, not local binary ones. Here we complement
our analysis of the binary projections of the ITN by considering its weighted
representations. We show that, unlike the binary case, all possible weighted
representations of the ITN (directed/undirected, aggregated/disaggregated)
cannot be traced back to local country-specific properties, which are therefore
of limited informativeness. Our two papers show that traditional macroeconomic
approaches systematically fail to capture the key properties of the ITN. In the
binary case, they do not focus on the degree sequence and hence cannot
characterize or replicate higher-order properties. In the weighted case, they
generally focus on the strength sequence, but the knowledge of the latter is
not enough in order to understand or reproduce indirect effects.Comment: See also the companion paper (Part I): arXiv:1103.1243
[physics.soc-ph], published as Phys. Rev. E 84, 046117 (2011
Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions
We present a theoretical description of the thermopower due to
magnon-assisted tunneling in a mesoscopic tunnel junction between two
ferromagnetic metals. The thermopower is generated in the course of thermal
equilibration between two baths of magnons, mediated by electrons. For a
junction between two ferromagnets with antiparallel polarizations, the ability
of magnon-assisted tunneling to create thermopower depends on the
difference between the size of the majority and
minority band Fermi surfaces and it is proportional to a temperature dependent
factor where is the magnon Debye
energy. The latter factor reflects the fractional change in the net
magnetization of the reservoirs due to thermal magnons at temperature
(Bloch's law). In contrast, the contribution of magnon-assisted
tunneling to the thermopower of a junction with parallel polarizations is
negligible. As the relative polarizations of ferromagnetic layers can be
manipulated by an external magnetic field, a large difference results in a magnetothermopower effect. This
magnetothermopower effect becomes giant in the extreme case of a junction
between two half-metallic ferromagnets, .Comment: 9 pages, 4 eps figure
Presence of DNA from Chlamydia-like organisms in the nasal cavities of grey seal pups (Halichoerus grypus) and three different substrates present in a breeding colony
BackgroundChlamydia-like organisms (CLO) have been found to be present in many environmental niches, including human sewage and agricultural run-off, as well as in a number of aquatic species worldwide. Therefore, monitoring their presence in sentinel wildlife species may be useful in assessing the wider health of marine food webs in response to habitat loss, pollution and disease. We used nasal swabs from live (n?=?42) and dead (n?=?50) pre-weaned grey seal pups and samples of differing natal substrates (n?=?8) from an off-shore island devoid of livestock and permanent human habitation to determine if CLO DNA is present in these mammals and to identify possible sources.ResultsWe recovered CLO DNA from 32/92 (34.7%) nasal swabs from both live (n?=?17) and dead (n?=?15) seal pups that clustered most closely with currently recognised species belonging to three chlamydial families: Parachlamydiaceae (n?=?22), Rhabdochlamydiaceae (n?=?6), and Simkaniaceae (n?=?3). All DNA positive sediment samples (n?=?7) clustered with the Rhabdochlamydiaceae. No difference was found in rates of recovery of CLO DNA in live versus dead pups suggesting the organisms are commensal but their potential as opportunistic secondary pathogens could not be determined.ConclusionThis is the first report of CLO DNA being found in marine mammals. This identification warrants further investigation in other seal populations around the coast of the UK and in other areas of the world to determine if this finding is unique or more common than shown by this data. Further investigation would also be warranted to determine if they are present as purely commensal organisms or whether they could also be opportunistic pathogens in seals, as well as to investigate possible sources of origin, including whether they originated as a result of anthropogenic impacts, including human waste and agricultural run-off
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