33,433 research outputs found
All-sky Relative Opacity Mapping Using Night Time Panoramic Images
An all-sky cloud monitoring system that generates relative opacity maps over
many of the world's premier astronomical observatories is described.
Photometric measurements of numerous background stars are combined with
simultaneous sky brightness measurements to differentiate thin clouds from sky
glow sources such as air glow and zodiacal light. The system takes a continuous
pipeline of all-sky images, and compares them to canonical images taken on
other nights at the same sidereal time. Data interpolation then yields
transmission maps covering almost the entire sky. An implementation of this
system is currently operating through the Night Sky Live network of CONCAM3s
located at Cerro Pachon (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT
(South Africa) and the Canary Islands (Northwestern Africa).Comment: Accepted for publication in PAS
Pharmacokinetics and efficacy of oral versus intravenous mixed-micellar phylloquinone (vitamin K-1) in severe acute liver disease
Background/Aims: In patients with severe acute liver dysfunction, i.v. phylloquinone (vitamin K-1) may be given to exclude vitamin K deficiency, rather than impaired hepatic synthesis of coagulation factors alone, as the cause of the coagulopathy. However, there have been no studies of the pharmacokinetics or efficacy of i.v. or oral K-1 in such patients.Methods: 49 adults with severe acute liver disease were randomised double-blind to a single 10 mg dose of i.v. or oral mixed-micellar K-1, or placebo. Serum levels of phylloquinone and undercarboxylated prothrombin (PIVKA-II) were assessed before and after treatment.Results: At admission, 13 patients (27 %) had either low serum K-1 levels or elevated PIVKA-II concentrations, indicative of subclinical vitamin K deficiency. In the 16 patients who received i.v. K-1, there was one (6 %) treatment failure (K-1 rise < 10 ng/ml above baseline), compared with 12 of the 15 (80 %) who received oral K, (P < 0.0001). One patient in the placebo group developed overt vitamin K deficiency.Conclusions: A minority of patients with severe acute liver dysfunction have subclinical vitamin K deficiency at the time of presentation, which is corrected by a single dose of i.v. K-1. The intestinal absorption of mixed-micellar K, is unreliable in adults with severe acute liver dysfunction. (c) 2004 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved
Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets
Using a model of nonmagnetic impurity potential, we have examined the
behavior of planar vortex solutions in the classical two-dimensional XY
ferromagnets in the presence of a spin vacancy localized out of the vortex
core. Our results show that a spinless atom impurity gives rise to an effective
potential that repels the vortex structure.Comment: 6 pages, 2 figures, RevTex
The role of damped Alfven waves on magnetospheric accretion models of young stars
We examine the role of Alfven wave damping in heating the plasma in the
magnetic funnels of magnetospheric accretion models of young stars. We study
four different damping mechanisms of the Alfven waves: nonlinear, turbulent,
viscous-resistive and collisional. Two different possible origins for the
Alfven waves are discussed: 1) Alfven waves generated at the surface of the
star by the shock produced by the infalling matter; and 2) Alfven waves
generated locally in the funnel by the Kelvin-Helmholtz instability. We find
that, in general, the damping lengths are smaller than the tube length. Since
thermal conduction in the tube is not efficient, Alfven waves generated only at
the star's surface cannot heat the tube to the temperatures necessary to fit
the observations. Only for very low frequency Alfven waves ~10^{-5} the ion
cyclotron frequency, is the viscous-resistive damping length greater than the
tube length. In this case, the Alfven waves produced at the surface of the star
are able to heat the whole tube. Otherwise, local production of Alfven waves is
required to explain the observations. The turbulence level is calculated for
different frequencies for optically thin and thick media. We find that
turbulent velocities varies greatly for different damping mechanisms, reaching
\~100 km s^{-1} for the collisional damping of small frequency waves.Comment: 29 pages, 12 figures, to appear in The Astrophysical Journa
Magnetic states of linear defects in graphene monolayers: effects of strain and interaction
The combined effects of defect-defect interaction and of uniaxial or biaxial
strains of up to 10\% on the development of magnetic states on the
defect-core-localized quasi-one-dimensional electronic states generated by the
so-called 558 linear extended defect in graphene monolayers are investigated by
means of {\it ab initio} calculations. Results are analyzed on the basis of the
heuristics of the Stoner criterion. We find that conditions for the emergence
of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel
strains (along the defect direction) at both limits of isolated and interacting
558 defects. Parallel strains are shown to lead to two cooperative effects that
favor the emergence of itinerant magnetism: enhancement of the DOS of the
resonant defect states in the region of the Fermi level and tuning of the Fermi
level to the maximum of the related DOS peak. A perpendicular strain is
likewise shown to enhance the DOS of the defect states, but it also effects a
detunig of the Fermi level that shifts away from the maximum of the DOS of the
defect states, which inhibts the emergence of magnetic states. As a result,
under biaxial strains the stabilization of a magnetic state depends on the
relative magnitudes of the two components of strain.Comment: 9 pages 8 figure
Geometric Aspects of the Dipolar Interaction in Lattices of Small Particles
The hysteresis curves of systems composed of small interacting magnetic
particles, regularly placed on stacked layers, are obtained with Monte Carlo
simulations. The remanence as a function of temperature, in interacting
systems, presents a peak that separates two different magnetic states. At low
temperatures, small values of remanence are a consequence of antiferromagnetic
order due to the dipolar interaction. At higher values of temperature the
increase of the component normal to the lattice plane is responsible for the
small values of remanence. The effect of the number of layers, coordination
number and distance between particles are investigated.Comment: 5 pages, 7 figure
Runoff at the micro-plot and slope scale following wildfire, central Portugal
Through their effects on soil properties and vegetation/litter cover, wildfires can strongly enhance overland flow generation and accelerate soil erosion [1] and, thereby, negatively affect land-use sustainability as well as downstream aquatic and flood zones. Wildfires are a common phenomenon in present-day Portugal, devastating in an average year some 100.000 ha of forest and woodlands and in an exceptional year like 2003 over 400.000 ha. There therefore exists a clear need in Portugal for a tool that can provide guidance to post-fire land management by predicting soil erosion risk, on the one hand, and, on the other, the mitigation effectiveness of soil conservation measures. Such a tool has recently been developed for the Western U.S.A. [3: ERMiT] but its suitability for Portuguese forests will need to be corroborated by field observations.
Testing the suitability of existing erosion models in recently burned forest areas in Portugal is, in a nutshell, the aim of the EROSFIRE projects. In the first EROSFIRE project the emphasis was on the prediction of erosion at the scale of individual hill slopes. In the ongoing EROSFIRE-II project the spatial scope is extended to include the catchment scale, so that also the connectivity between hill slopes as well as channel and road processes are being addressed. Besides ERMiT, the principal models under evaluation for slope-scale erosion prediction are: (i) the variant of USLE [4] applied by the Portuguese Water Institute after the wildfires of 2003; (ii) the MorganâMorganâFinney model (MMF) [5]; (iii) MEFIDIS [6]. From these models, MEFIDIS and perhaps MMF will, after successful calibration at the slope scale, also be applied for predicting catchment-scale sediment yields of extreme events
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