4,665 research outputs found
A First Step Towards Automatically Building Network Representations
To fully harness Grids, users or middlewares must have some knowledge on the
topology of the platform interconnection network. As such knowledge is usually
not available, one must uses tools which automatically build a topological
network model through some measurements. In this article, we define a
methodology to assess the quality of these network model building tools, and we
apply this methodology to representatives of the main classes of model builders
and to two new algorithms. We show that none of the main existing techniques
build models that enable to accurately predict the running time of simple
application kernels for actual platforms. However some of the new algorithms we
propose give excellent results in a wide range of situations
The Carrington event not observed in most ice core nitrate records
The Carrington Event of 1859 is considered to be among the largest space weather events of the last 150 years. We show that only one out of 14 well-resolved ice core records from Greenland and Antarctica has a nitrate spike dated to 1859. No sharp spikes are observed in the Antarctic cores studied here. In Greenland numerous spikes are observed in the 40 years surrounding 1859, but where other chemistry was measured, all large spikes have the unequivocal signal, including co-located spikes in ammonium, formate, black carbon and vanillic acid, of biomass burning plumes. It seems certain that most spikes in an earlier core, including that claimed for 1859, are also due to biomass burning plumes, and not to solar energetic particle (SEP) events. We conclude that an event as large as the Carrington Event did not leave an observable, widespread imprint in nitrate in polar ice. Nitrate spikes cannot be used to derive the statistics of SEPs
Comment on “Low time resolution analysis of ice cores cannot detect impulsive nitrate events” by D. F. Smart et al.
Smart et al. (2014) suggested that the detection of nitrate spikes in polar ice cores from solar energetic particle (SEP) events could be achieved if an analytical system with sufficiently high resolution was used. Here we show that the spikes they associate with SEP events are not reliably recorded in cores from the same location, even when the resolution is clearly adequate. We explain the processes that limit the effective resolution of ice cores. Liquid conductivity data suggest that the observed spikes are associated with sodium or another nonacidic cation, making it likely that they result from deposition of sea salt or similar aerosol that has scavenged nitrate, rather than from a primary input of nitrate in the troposphere. We consider that there is no evidence at present to support the identification of any spikes in nitrate as representing SEP events. Although such events undoubtedly create nitrate in the atmosphere, we see no plausible route to using nitrate spikes to document the statistics of such events
Atmospheric nitrogen oxides (NO and NO2) at Dome C, East Antarctica, during the OPALE campaign
Mixing ratios of the atmospheric nitrogen oxides NO and NO2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands & Export) campaign at Dome C, East Antarctica (75.1 degrees S, 123.3 degrees E, 3233 m), during December 2011 to January 2012. Profiles of NOx mixing ratios of the lower 100m of the atmosphere confirm that, in contrast to the South Pole, air chemistry at Dome C is strongly influenced by large diurnal cycles in solar irradiance and a sudden collapse of the atmospheric boundary layer in the early evening. Depth profiles of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO2 and is a sink of gas-phase ozone (O-3). First-time observations of bromine oxide (BrO) at Dome C show that mixing ratios of BrO near the ground are low, certainly less than 5 pptv, with higher levels in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO2 radicals are too low to explain the large NO2 : NO ratios found in ambient air, possibly indicating the existence of an unknown process contributing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011-2012, NOx mixing ratios and flux were larger than in 2009-2010, consistent with also larger surface O-3 mixing ratios resulting from increased net O-3 production. Large NOx mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mixing height and significant NOx emissions by surface snow (F-NOx). During 23 December 2011-12 January 2012, median F-NOx was twice that during the same period in 20092010 due to significantly larger atmospheric turbulence and a slightly stronger snowpack source. A tripling of F-NOx in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO3- concentrations in the snow skin layer, and only to a secondary order by decrease of total column O-3 and associated increase in NO3- photolysis rates. A source of uncertainty in model estimates of F-NOx is the quantum yield of NO3- photolysis in natural snow, which may change over time as the snow ages
Hypercalcémie majeure révélatrice d’une sarcoïdose induite par étanercept
Introduction
The principal secondary effects of anti-TNF alpha therapy are now well understood, particularly the risk of opportunistic infections. Other paradoxical effects have been described much more occasionally such as the developement of sarcoid-like granulomatous reactions.
Case report
We report here the case of a woman of 39 years treated for severe rheumatoid arthritis for five years with etanercept. She was admitted to hospital as an emergency with vomiting and diffuse abdominal pain. Investigations revealed severe hypercalcaemia and acute renal failure. After correction of the metabolic disturbances with rehydration and biphosphonates, CT scanning of the abdomen, pelvis and thorax showed bilateral interstitial infiltration and splenomegaly. The diagnosis of sarcoidosis was confirmed by endoscopic bronchial biopsies. Progress was satisfactory following withdrawal of the etanercept and corticosteroid therapy in reducing dosage.
Conclusion
The risk of induced sarcoidosis should be understood in patients receiving anti-TNF therapy and should be considered in cases of hypercalcaemia and/or splenomegaly
Preference and usage of pasture versus free-stall housing by lactating dairy cattle
The aim of the current study was to assess if cows preferred pasture or indoor housing, and how diurnal and environmental factors affected this preference. Lactating dairy cows (n = 5 groups, each containing 5 cows) were sequentially housed either in a free-stall barn on pasture, or given the choice between the 2 environments. Each group was tested 3 times under each condition, for a total of 21 d, to assess the effects of varying climatic conditions (outdoor temperature ranged from 9.9 to 28.2°C and daily rainfall from 0 to 65 mm/d over the course of the experiment). When provided the choice, cows spent on average (± SD) 13.0 ± 0.6 h/d on pasture, mainly at night. The time cows spent on pasture during the day decreased with the temperature-humidity index (R2 = 0.55); time on pasture at night decreased with rainfall (R2 = 0.12). When provided a choice, cows spent more of their lying time on pasture (69.4 ± 0.02% of the total lying time/d) than indoors in the free-stalls. Cows also spent more time in total lying down when provided a choice than when confined to pasture [0.6 h/d more lying time; standard error of the difference (SED) = 0.21 h/d] and spent even more time lying down when confined indoors (1.1 h/d more time; SED = 0.21 h/d). Cows used the indoor housing especially for feeding; feeder use peaked when cows returned from morning and afternoon milkings. However, cows with free access to pasture spent 1.0 h/d (SED = 0.09 h/d) less time eating the TMR available indoors, resulting in a decline in intake of 2.9 kg of dry matter/d (SED = 0.36 kg of dry matter/d). How cows used the indoor housing differed when cows were provided a choice; for example, cows spent a greater percentage of their time indoors at the feed alley both during the day (47% of the total time spent indoors, versus 41% for cows confined indoors, SED = 0.02%) and at night (22 vs. 5%, SED = 0.04%). In conclusion, under the housing and environmental conditions tested, cows showed a strong preference for access to pasture at night and for access to indoor housing during the day when temperature and humidity increased
Hydrogenation of CO on a silica surface: an embedded cluster approach
The sequential addition of H atoms to CO adsorbed on a siliceous edingtonite surface is studied with an embedded cluster approach, using density functional theory for the quantum mechanical (QM) cluster and a molecular force field for the molecular mechanical (MM) cluster. With this setup, calculated QM/MM adsorption energies are in agreement with previous calculations employing periodic boundary conditions. The catalytic effect of the siliceous edingtonite (100) surface on CO hydrogenation is assessed because of its relevance to astrochemistry. While adsorption of CO on a silanol group on the hydroxylated surface did not reduce the activation energy for the reaction with a H atom, a negatively charged defect on the surface is found to reduce the gas phase barriers for the hydrogenation of both CO and H2C = O. The embedded cluster approach is shown to be a useful and flexible tool for studying reactions on (semi-)ionic surfaces and specific defects thereon. The methodology presented here could easily be applied to study reactions on silica surfaces that are of relevance to other scientific areas, such as biotoxicity of silica dust and geochemistry
Abundances in the Neutral Interstellar Medium of I Zw 18 from FUSE Observations
We report on new FUSE far-UV spectroscopy of the most metal-poor blue compact
dwarf galaxy I Zw 18. The new data represent an improvement over previous FUSE
spectra by a factor of 1.7 in the signal-to-noise. Together with a larger
spectral coverage (917-1188 angstroms), this allows us to characterize
absorption lines in the interstellar medium with unprecedented accuracy. The
kinematics averaged over the large sampled region shows no clear evidence of
gas inflows or outflows. The H I absorption is interstellar with a column
density of 2.2 (+0.6,-0.5} * 10^21 cm^(-2). A conservative 3 sigma upper limit
of 5.25 * 10^(14) cm^(-2) is derived for the column density of diffuse H_2.
From a simultaneous fitting of metal absorption lines in the interstellar
medium, we infer the following abundances: [Fe/H] = -1.76 +/- 0.12, [O/H] =
-2.06 +/- 0.28, [Si/H] = -2.09 +/- 0.12, [Ar/H] = -2.27 +/- 0.13, and [N/H] =
-2.88 +/- 0.11. This is in general several times lower than in the H II
regions. The only exception is iron, whose abundance is the same. The abundance
pattern of the interstellar medium suggests ancient star-formation activity
with an age of at least a Gyr that enriched the H I phase. Around 470 SNe Ia
are required to produce the iron content. A more recent episode that started 10
to several 100 Myr ago is responsible for the additional enrichment of
alpha-elements and nitrogen in the H II regions.Comment: 48 pages including 3 tables (Latex) and 7 figures (postscript).
Accepted for publication in the Astrophysical Journa
Water adsorption on amorphous silica surfaces: A Car-Parrinello simulation study
A combination of classical molecular dynamics (MD) and ab initio
Car-Parrinello molecular dynamics (CPMD) simulations is used to investigate the
adsorption of water on a free amorphous silica surface. From the classical MD
SiO_2 configurations with a free surface are generated which are then used as
starting configurations for the CPMD.We study the reaction of a water molecule
with a two-membered ring at the temperature T=300K. We show that the result of
this reaction is the formation of two silanol groups on the surface. The
activation energy of the reaction is estimated and it is shown that the
reaction is exothermic.Comment: 12 pages, 6 figures, to be published in J. Phys.: Condens. Matte
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