783 research outputs found
Apport de la gravimétrie à la compréhension de la chaßne panafricaine dans l'Adrar des Iforas
The SVOM gamma-ray burst mission
We briefly present the science capabilities, the instruments, the operations,
and the expected performance of the SVOM mission. SVOM (Space-based multiband
astronomical Variable Objects Monitor) is a Chinese-French space mission
dedicated to the study of Gamma-Ray Bursts (GRBs) in the next decade. The SVOM
mission encompasses a satellite carrying four instruments to detect and
localize the prompt GRB emission and measure the evolution of the afterglow in
the visible band and in X-rays, a VHF communication system enabling the fast
transmission of SVOM alerts to the ground, and a ground segment including a
wide angle camera and two follow-up telescopes. The pointing strategy of the
satellite has been optimized to favor the detection of GRBs located in the
night hemisphere. This strategy enables the study of the optical emission in
the first minutes after the GRB with robotic observatories and the early
spectroscopy of the optical afterglow with large telescopes to measure the
redshifts. The study of GRBs in the next decade will benefit from a number of
large facilities in all wavelengths that will contribute to increase the
scientific return of the mission. Finally, SVOM will operate in the era of the
next generation of gravitational wave detectors, greatly contributing to
searches for the electromagnetic counterparts of gravitational wave triggers at
Xray and gamma-ray energies.Comment: 13 pages, 5 figures, published by PoS, proceedings of the conference
Swift: 10 Years of Discovery, 2-5 December 2014, La Sapienza University,
Rome, Ital
Preparation of Long-Lived, Non-Autoionizing Circular Rydberg States of Strontium
Alkaline earth Rydberg atoms are very promising tools for quantum
technologies. Their highly excited outer electron provides them with the
remarkable properties of Rydberg atoms and, notably, with a huge coupling to
external fields or to other Rydberg atoms while the ionic core retains an
optically active electron. However, low angular-momentum Rydberg states suffer
almost immediate autoionization when the core is excited. Here, we demonstrate
that strontium circular Rydberg atoms with a core excited in a metastable
level are impervious to autoionization over more than a few millisecond time
scale. This makes it possible to trap and laser-cool Rydberg atoms. Moreover,
we observe singlet to triplet transitions due to the core optical
manipulations, opening the way to a quantum microwave to optical interface
Numerical Investigation on Charring Ablator Geometric Effects: Study of Stardust Sample Return Capsule Heat Shield
Sample geometry is very influential in small charring ablative articles where 1D assumption might not be accurate. In heat shield design, 1D is often assumed since the nose radius is much larger than the thickness of charring. Whether the 1D assumption is valid for the heat shield is unknown. Therefore, the geometric effects of Stardust sample return capsule heat shield are numerically studied using a material response program. The developed computer program models material charring, conductive heat transfer, surface energy balance, pyrolysis gas transport and orthotropic material properties in 3D Cartesian coordinates. Simulation results show that the centerline temperatures predicted by 3D model are quite close to 1D model at the surface, but not the case inside the material. The pyrolysis surface gas blowing behaviors are quite similar but differences are observed at later time. Orthotropic model predicted a very different heat shield response to both the isotropic model and the 1D model
Numerical Investigation of Pyrolysis Gas Blowing Pattern and Thermal Response using Orthotropic Charring Ablative Material
An orthotropic material model is implemented in a three-dimensional material response code, and numerically studied for charring ablative material. Model comparison is performed using an iso-Q sample geometry. The comparison is presented using pyrolysis gas streamlines and time series of temperature at selected virtual thermocouples. Results show that orthotropic permeability affects both pyrolysis gas flow and thermal response, but orthotropic thermal conductivity essentially changes the thermal performance of the material. The effect of orthotropic properties may have practical use such that the material performance can be manipulated by altering the angle of orthotropic orientation
Neuron-to-neuron wild-type Tau protein transfer through a trans-synaptic mechanism: relevance to sporadic tauopathies.
BACKGROUND: In sporadic Tauopathies, neurofibrillary degeneration (NFD) is characterised by the intraneuronal aggregation of wild-type Tau proteins. In the human brain, the hierarchical pathways of this neurodegeneration have been well established in Alzheimer's disease (AD) and other sporadic tauopathies such as argyrophilic grain disorder and progressive supranuclear palsy but the molecular and cellular mechanisms supporting this progression are yet not known. These pathways appear to be associated with the intercellular transmission of pathology, as recently suggested in Tau transgenic mice. However, these conclusions remain ill-defined due to a lack of toxicity data and difficulties associated with the use of mutant Tau.
RESULTS: Using a lentiviral-mediated rat model of hippocampal NFD, we demonstrated that wild-type human Tau protein is axonally transferred from ventral hippocampus neurons to connected secondary neurons even at distant brain areas such as olfactory and limbic systems indicating a trans-synaptic protein transfer. Using different immunological tools to follow phospho-Tau species, it was clear that Tau pathology generated using mutated Tau remains near the IS whereas it spreads much further using the wild-type one.
CONCLUSION: Taken together, these results support a novel mechanism for Tau protein transfer compared to previous reports based on transgenic models with mutant cDNA. It also demonstrates that mutant Tau proteins are not suitable for the development of experimental models helpful to validate therapeutic intervention interfering with Tau spreading
Abrupt Convergence and Escape Behavior for Birth and Death Chains
We link two phenomena concerning the asymptotical behavior of stochastic
processes: (i) abrupt convergence or cut-off phenomenon, and (ii) the escape
behavior usually associated to exit from metastability. The former is
characterized by convergence at asymptotically deterministic times, while the
convergence times for the latter are exponentially distributed. We compare and
study both phenomena for discrete-time birth-and-death chains on Z with drift
towards zero. In particular, this includes energy-driven evolutions with energy
functions in the form of a single well. Under suitable drift hypotheses, we
show that there is both an abrupt convergence towards zero and escape behavior
in the other direction. Furthermore, as the evolutions are reversible, the law
of the final escape trajectory coincides with the time reverse of the law of
cut-off paths. Thus, for evolutions defined by one-dimensional energy wells
with sufficiently steep walls, cut-off and escape behavior are related by time
inversion.Comment: 2 figure
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