185 research outputs found
DiversitÊ des mÊthodes utilisÊes par les laboratoires français pour la surveillance des infections à cytomÊgalovirus humain
Monitoring cytomegalovirus circulating viral load is an important parameter of the follow-up in immunocompromised patients. It can be measured either by DNAemia or by pp65 antigenemia. The French national reference center for cytomegaloviruses organized an investigation of practice in 37 teacher hospital virology laboratories to assess the situation in France in 2010.
Methods
A questionnaire was sent to collect following information: method used in routine for monitoring of circulating viral load of CMV, assay used, sample matrix and extraction method.
Results
Thirty-six over thirty-seven laboratories filled the questionnaire. Among these, 67% used the quantitative PCR in routine, 11% antigenemia and 22% antigenemia or quantitative PCR; 87% of the laboratories use whole blood for quantitative PCR, whereas 10% and 3% use plasma and leukocytes respectively. Among the laboratories using DNAemia, 100% used real-time PCR assays, 91% use an automated extraction and 9% a manual extraction.
Conclusion
Thus in France, measurement of DNAemia by real-time PCR is a tool, which gradually replaces the antigenemia for the monitoring of cytomegalovirus infection among immunocompromised patients. The very great diversity of the methods used justifies the installation of a national quality control on total blood, matrix used by 87% of the laboratories
The β pictoris circumstellar disk XXV: the ca ii absorption lines and the falling evaporating bodies model revisited using UHRF observations
We present here ultra high resolution observations
of the Ca ii K and H lines towards β Pictoris recorded over a
period of 3 years and a smaller set of calcium triplet data.
At the present resolution, the central Ca ii circumstellar absorption is complex, with several variable components, some
of them at very low velocity shifts (< 10 km sâ1) with respect
to the star, in addition to a very narrow stable component. The
stable component is analyzed and physical informations are derived. The variable components at low redshifts are analyzed,
and well modeled in the framework of the Falling Evaporating Bodies (FEB) scenario previously invoked to explain the
absorption features observed at higher redshifts.
We show that the very low redshift events are well simulated
by FEBs crossing the line of sight at somewhat larger distances
from the star than those responsible for the higher velocity redshift events. The implications of these new observations on the
dynamical process responsible for the FEB phenomenon are
discussed. In particular, they put strong constraints on the orbital parameters of the incoming bodies that appear in fact in
perfect agreement with an origin based on mean-motion resonances with a massive planet
Oscillatory dynamos and their induction mechanisms
Context: Large-scale magnetic fields resulting from hydromagnetic dynamo
action may differ substantially in their time dependence. Cyclic field
variations, characteristic for the solar magnetic field, are often explained by
an important omega-effect, i.e. by the stretching of field lines due to strong
differential rotation. Aims: The dynamo mechanism of a convective, oscillatory
dynamo model is investigated. Methods: We solve the MHD-equations for a
conducting Boussinesq fluid in a rotating spherical shell. For a resulting
oscillatory model, dynamo coefficients have been computed with the help of the
so-called test-field method. Subsequently, these coefficients have been used in
a mean-field calculation in order to explore the underlying dynamo mechanism.
Results: Although the rather strong differential rotation present in this model
influences the magnetic field, the omega-effect alone is not responsible for
its cyclic time variation. If the omega-effect is suppressed, the resulting
alpha^2-dynamo remains oscillatory. Surprisingly, the corresponding alpha-omega
dynamo leads to a non-oscillatory magnetic field. Conclusions: The assumption
of an alpha-omega mechanism does not explain the occurrence of magnetic cycles
satisfactorily
Variable strength of forest stand attributes and weather conditions on the questing activity of Ixodes ricinus ticks over years in managed forests
Given the ever-increasing human impact through land use and climate change on the environment, we crucially need to achieve a better understanding of those factors that influence the questing activity of ixodid ticks, a major disease-transmitting vector in temperate forests. We investigated variation in the relative questing nymph densities of Ixodes ricinus in differently managed forest types for three years (2008â2010) in SW Germany by drag sampling. We used a hierarchical Bayesian modeling approach to examine the relative effects of habitat and weather and to consider possible nested structures of habitat and climate forces. The questing activity of nymphs was considerably larger in young forest successional stages of thicket compared with pole wood and timber stages. Questing nymph density increased markedly with milder winter temperatures. Generally, the relative strength of the various environmental forces on questing nymph density differed across years. In particular, winter temperature had a negative effect on tick activity across sites in 2008 in contrast to the overall effect of temperature across years. Our results suggest that forest management practices have important impacts on questing nymph density. Variable weather conditions, however, might override the effects of forest management practices on the fluctuations and dynamics of tick populations and activity over years, in particular, the preceding winter temperatures. Therefore, robust predictions and the detection of possible interactions and nested structures of habitat and climate forces can only be quantified through the collection of long-term data. Such data are particularly important with regard to future scenarios of forest management and climate warming
Use of radiotracer techniques to study subcellular distribution of metals and radionuclides in bivalves from the Noumea Lagoon, New Caledonia
Relations between dynamo-region geometry and the magnetic behavior of stars and planets
The geo and solar magnetic fields have long been thought to be very different
objects both in terms of spatial structure and temporal behavior. The recently
discovered field structure of a fully convective star is more reminiscent of
planetary magnetic fields than the Sun's magnetic field (Donati J.-F. et al.,
Science, 311 (2006) 633), despite the fact that the physical and chemical
properties of these objects clearly differ. This observation suggests that a
simple controlling parameter could be responsible for these different
behaviors. We report here the results of three-dimensional simulations which
show that varying the aspect ratio of the active dynamo region can yield sharp
transition from Earth-like steady dynamos to Sun-like dynamo waves
Performance of the CMS Cathode Strip Chambers with Cosmic Rays
The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device
in the CMS endcaps. Their performance has been evaluated using data taken
during a cosmic ray run in fall 2008. Measured noise levels are low, with the
number of noisy channels well below 1%. Coordinate resolution was measured for
all types of chambers, and fall in the range 47 microns to 243 microns. The
efficiencies for local charged track triggers, for hit and for segments
reconstruction were measured, and are above 99%. The timing resolution per
layer is approximately 5 ns
Weak and Strong Field Dynamos: from the Earth to the stars
Observations of magnetism in very low mass stars recently made important
progress, revealing characteristics that are now to be understood in the
framework of dynamo theory. In parallel, there is growing evidence that dynamo
processes in these stars share many similarities with planetary dynamos. We
investigate the extent to which the weak \emph{vs} strong field bistability
predicted for the geodynamo can apply to recent observations of two groups of
very low mass fully-convective stars sharing similar stellar parameters but
generating radically different types of magnetic fields. Our analysis is based
on previously published spectropolarimetric and spectroscopic data. We argue
that these can be interpreted in the framework of weak and strong field
dynamos.Comment: 5 pages, 4 figures, accepted for publication in MNRAS letter
Performance and Operation of the CMS Electromagnetic Calorimeter
The operation and general performance of the CMS electromagnetic calorimeter
using cosmic-ray muons are described. These muons were recorded after the
closure of the CMS detector in late 2008. The calorimeter is made of lead
tungstate crystals and the overall status of the 75848 channels corresponding
to the barrel and endcap detectors is reported. The stability of crucial
operational parameters, such as high voltage, temperature and electronic noise,
is summarised and the performance of the light monitoring system is presented
Can we predict the global magnetic topology of a pre-main sequence star from its position in the Hertzsprung-Russell diagram?
ZDI studies have shown that the magnetic fields of T Tauri stars can be
significantly more complex than a simple dipole and can vary markedly between
sources. We collect and summarize the magnetic field topology information
obtained to date and present Hertzsprung-Russell (HR) diagrams for the stars in
the sample. Intriguingly, the large scale field topology of a given pre-main
sequence (PMS) star is strongly dependent upon the stellar internal structure,
with the strength of the dipole component of its multipolar magnetic field
decaying rapidly with the development of a radiative core. Using the
observational data as a basis, we argue that the general characteristics of the
global magnetic field of a PMS star can be determined from its position in the
HR diagram. Moving from hotter and more luminous to cooler and less luminous
stars across the PMS of the HR diagram, we present evidence for four distinct
magnetic topology regimes. Stars with large radiative cores, empirically
estimated to be those with a core mass in excess of ~40 per cent of the stellar
mass, host highly complex and dominantly non-axisymmetric magnetic fields,
while those with smaller radiative cores host axisymmetric fields with field
modes of higher order than the dipole dominant (typically, but not always, the
octupole). Fully convective stars stars above ~0.5 MSun appear to host
dominantly axisymmetric fields with strong (kilo-Gauss) dipole components.
Based on similarities between the magnetic properties of PMS stars and main
sequence M-dwarfs with similar internal structures, we speculate that a
bistable dynamo process operates for lower mass stars (<~0.5 MSun at an age of
a few Myr) and that they will be found to host a variety of magnetic field
topologies. If the magnetic topology trends across the HR diagram are confirmed
they may provide a new method of constraining PMS stellar evolution models.Comment: accepted for publication in the Ap
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