273 research outputs found
Status of MICROSCOPE, a mission to test the Equivalence Principle in space
MICROSCOPE is a French Space Agency mission that aims to test the Weak
Equivalence Principle in space down to an accuracy of . This is two
orders of magnitude better than the current constraints, which will allow us to
test General Relativity as well as theories beyond General Relativity which
predict a possible Weak Equivalence Principle violation below . In
this communication, we describe the MICROSCOPE mission, its measurement
principle and instrument, and we give an update on its status. After a
successful instrument's commissioning, MICROSCOPE is on track for on-schedule
launch, expected in 2016.Comment: Proceedings of LISA Symposium X; accepted for publication in Journal
of Physics: Conference Serie
Quantum theory of fluctuations in a cold damped accelerometer
We present a quantum network approach to real high sensitivity measurements.
Thermal and quantum fluctuations due to active as well as passive elements are
taken into account. The method is applied to the analysis of the capacitive
accelerometer using the cold damping technique, developed for fundamental
physics in space by ONERA and the ultimate limits of this instrument are
discussed. It is confirmed in this quantum analysis that the cold damping
technique allows one to control efficiently the test mass motion without
degrading the noise level.Comment: 10 pages, 6 figures, RevTeX; Minor change
Dealing with missing data: An inpainting application to the MICROSCOPE space mission
Missing data are a common problem in experimental and observational physics.
They can be caused by various sources, either an instrument's saturation, or a
contamination from an external event, or a data loss. In particular, they can
have a disastrous effect when one is seeking to characterize a
colored-noise-dominated signal in Fourier space, since they create a spectral
leakage that can artificially increase the noise. It is therefore important to
either take them into account or to correct for them prior to e.g. a
Least-Square fit of the signal to be characterized. In this paper, we present
an application of the {\it inpainting} algorithm to mock MICROSCOPE data; {\it
inpainting} is based on a sparsity assumption, and has already been used in
various astrophysical contexts; MICROSCOPE is a French Space Agency mission,
whose launch is expected in 2016, that aims to test the Weak Equivalence
Principle down to the level. We then explore the {\it inpainting}
dependence on the number of gaps and the total fraction of missing values. We
show that, in a worst-case scenario, after reconstructing missing values with
{\it inpainting}, a Least-Square fit may allow us to significantly measure a
Equivalence Principle violation signal, which is
sufficiently close to the MICROSCOPE requirements to implement {\it inpainting}
in the official MICROSCOPE data processing and analysis pipeline. Together with
the previously published KARMA method, {\it inpainting} will then allow us to
independently characterize and cross-check an Equivalence Principle violation
signal detection down to the level.Comment: Accepted for publication in Physical Review D. 12 pages, 6 figure
Carotid Atherosclerotic Markers in CADASIL
Purpose: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a cerebral small vessel disease caused by mutations of the NOTCH3 gene. Marked variations in disease severity have raised the hypothesis that non-genetic factors may modulate the expressivity of the phenotype. The aim of the current study was to evaluate whether atherosclerosis, assessed by carotid duplex ultrasonography, is associated with variations in the clinical and MRI phenotype of CADASIL. Methods: Data from 144 consecutive patients enrolled in an ongoing prospective cohort study were collected. Degree of disability was assessed by the modified Rankin Scale, that of cognitive impairment by the Mattis Dementia Rating Scale (MDRS). The total volume of the brain, of lacunar lesions and of white matter hyperintensities, the number of cerebral microhemorrhages, and parameters derived from histograms of apparent diffusion coefficient were measured on cerebral MRI. Atherosclerosis was evaluated by B-mode ultrasonography of carotid arteries. Both the carotid intima-media thickness cIMT) and the presence of carotid plaques or stenosis were recorded. Results: Higher cIMT was found to be independently associated with lower MDRS scores when this score was less than the quartile limit (p = 0.02). Only a trend for a positive association was detected between cIMT and the Rankin score (p = 0.06). There was no significant association between carotid markers and the occurrence of stroke or MRI parameters except for diffusion data. The mean and peak values of MRI diffusion histograms were found positively associated with the presence of plaques (p < 0.01). Conclusion: The results suggest that the severity of atherosclerosis may relate to cognitive decline in CADASIL and that this effect is possibly related to the degree of microstructural cerebral tissue lesions. Longitudinal studies are needed to confirm these results. Copyright (C) 2010 S. Karger AG, Base
Variété et distribution des sujets d'actualité sur Internet: Une analyse quantitative de l'information en ligne
http://mots.revues.org/19832International audienceThe pluralism of news is supposed to be ensured by the multiplicity of the sources on the Internet. Based on thousands articles from all categories of websites, the Âlexicometric analysis of the titles and the identification of topical issues both highlight a more uneven reality. While websites deal with a wide diversity of issues during a whole day, they simultaneously focus on a few major issues, which treatment and wordings are often quite redundant.Sur Internet, la multiplicité des sources est censée garantir le pluralisme de l'information. Portant sur des milliers d'articles issus de toutes catégories de sites, l'analyse lexicométrique des titres et l'identification des sujets de l'actualité donnent à voir une réalité plus contrastée. La grande variété des sujets abordés sur la toile se traduit simutanément par une concentration sur quelques sujets majeurs, souvent traités de façon redondante jusque dans leur formulation
Equivalence Principle tests, Equivalence theorems and New long-range forces
We discuss the possible existence of new long-range forces mediated by spin-1
or spin-0 particles. By adding their effects to those of gravity, they could
lead to apparent violations of the Equivalence Principle. While the vector part
in the couplings of a new spin-1 U boson involves, in general, a combination of
the B and L currents, there may also be, in addition, an axial part as well. If
the new force has a finite range \lambda, its intensity is proportional to
1/(\lambda^2 F^2), F being the extra U(1) symmetry-breaking scale.
Quite surprisingly, particle physics experiments can provide constraints on
such a new force, even if it is extremely weak, the corresponding gauge
coupling being extremely small (<< 10^-19 !). An ``equivalence theorem'' shows
that a very light spin-1 U boson does not in general decouple even when its
gauge coupling vanishes, but behaves as a quasimassless spin-0 particle, having
pseudoscalar couplings proportional to 1/F. Similarly, in supersymmetric
theories, a very light spin-3/2 gravitino might be detectable as a quasi
massless spin-1/2 goldstino, despite the extreme smallness of Newton's
gravitational constant G_N, provided the supersymmetry-breaking scale is not
too large.
Searches for such U bosons in \psi and \Upsilon decays restrict F to be
larger than the electroweak scale (the U actually becoming, as an axion, quasi
``invisible'' in particle physics for sufficiently large F). This provides
strong constraints on the corresponding new force and its associated EP
violations. We also discuss briefly new spin-dependent forces.Comment: 19 page
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