1,245 research outputs found
What do we really know about Dark Energy?
In this paper I discuss what we truly know about dark energy. I shall argue
that up to date our single indication for the existence of dark energy comes
from distance measurements and their relation to redshift. Supernovae, CMB
anisotropies and observations of baryon acoustic oscillations, they all simply
tell us that the observed distance to a given redshift is larger than the one
expected from a Friedmann Lemaitre universe with matter only and the locally
measured Hubble parameter.Comment: invited talk at the meeting "Cosmological Tests of General
Relativity" at the Kavli Royal Society Center for the Advancement of Science
organized by Rachel Bean, Pedro Ferreira and Andy Taylor. 14p 2 figs. revised
version: updated to match version in print in Phil. Trans. R. Soc.
Evaluation of nickel-hydrogen battery for space application
Results of electrical space qualification tests of nickel-hydrogen battery type HR 23S are presented. The results obtained for the nickel-cadmium battery type VO 23S are similar except that the voltage level and the charge conservation characteristics vary significantly. The electrical and thermal characteristics permit predictions of the following optimal applications: charge coefficient in the order of 1.3 to 1.4 at 20C; charge current density higher than C/10 at 20C; discharge current density from C/10 to C/3 at 20C; maximum discharge temperature: OC; storage temperature: -20C
A {\mu}-TPC detector for the characterization of low energy neutron fields
The AMANDE facility produces monoenergetic neutron fields from 2 keV to 20
MeV for metrological purposes. To be considered as a reference facility,
fluence and energy distributions of neutron fields have to be determined by
primary measurement standards. For this purpose, a micro Time Projection
Chamber is being developed to be dedicated to measure neutron fields with
energy ranging from 8 keV up to 1 MeV. In this work we present simulations
showing that such a detector, which allows the measurement of the ionization
energy and the 3D reconstruction of the recoil nucleus, provides the
determination of neutron energy and fluence of these neutron fields
Vibrations on pulse tube based Dry Dilution Refrigerators for low noise measurements
Dry Dilution Refrigerators (DDR) based on pulse tube cryo-coolers have
started to replace Wet Dilution Refrigerators (WDR) due to the ease and low
cost of operation. However these advantages come at the cost of increased
vibrations, induced by the pulse tube. In this work, we present the vibration
measurements performed on three different commercial DDRs. We describe in
detail the vibration measurement system we assembled, based on commercial
accelerometers, conditioner and DAQ, and examined the effects of the various
damping solutions utilized on three different DDRs, both in the low and high
frequency regions. Finally, we ran low temperature, pseudo-massive (30 and 250
g) germanium bolometers in the best vibration-performing system under study and
report on the results
Directional detection of Dark Matter with MIMAC: WIMP identification and track reconstruction
Directional detection is a promising Dark Matter search strategy. Indeed,
WIMP-induced recoils present a direction dependence toward the Cygnus
constellation, while background-induced recoils exhibit an isotropic
distribution in the galactic rest frame. Taking advantage on these
characteristic features and even in the presence of a sizeable background, we
show for the first time the possibility to constrain the WIMP properties, both
from particle and galactic halo physics, leading to an identification of
non-baryonic Dark Matter. However, such results need highly accurate track
reconstruction which should be reachable by the MIMAC detector using a
dedicated readout combined with a likelihood analysis of recoiling nuclei.Comment: 8 pages, 5 figures, Proc. of the fifth international symposium on
large TPCs for low energy rare event detection, Paris, France, Dec. 2010. To
appear in Journal of Physic
D-SERINE CONTRIBUTES TO β-AMYLOID-DEPENDENT PATHOPHYSIOLOGYIN ALZHEIMER’S DISEASE
International audienceB fEPSP/PFV ra>o 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 WT 5xFAD 5xFAD/SR-/-+ D-s e ri n e + D-s e ri n e + D-s e ri n e Key regulators of the structural and funcFonal brain plasFcity, the N-methyl-D-aspartate subtype of glutamate receptors (NMDARs) requires the binding of the co-agonist D-serine to be acFvated. In Alzheimer's disease (AD), soluble oligomers of the beta-amyloid pepFde (Aßo) affect NMDARs possibly through mechanisms involving changes in D-serine levels since Aßo sFmulate in vitro the producFon of the co-agonist. In this study, we asked whether D-serine contributes in vivo to morpho-funcFonal NMDAR-related deregulaFons mediated by Aßo. Behavioral analysis combined to electrophysiological recordings at CA1/CA3 hippocampal synapses have been thus conducted in the 5xFAD transgenic mice model of amyloïdogenesis displaying marked increase in Aßo rates and compared to 5xFAD animals in which the homozygous gene of the serine racemase (SR) that synthesizes D-serine, has been jointly invalidated. Our results therefore show that deleFon of serine racemase prevents memory-related behavioral deficits observed in mice with prominent features of amyloidogenesis as well as impairment of NMDAR-dependent funcFonal plasFcity, suggesFng a significant contribuFon of D-serine in NMDAR-dependent β-amyloid-related pathophysiology of Alzheimer's disease. EXPERIMENTAL PROCEDURES 1) Behavioral analysis: 8-min spontaneous alternaFon test was performed in a Y maze apparatus to assess working memory performances in 10-12 months of aged mice. Successive entry of the three arms of the maze was considered as an alternaFon. The percentage of alternaFon was calculated as follows: number of alternaFons / (total number of arms visited-2) x 100. 2) Electrophysiology: Hippocampal slices (400 µm thickness) were cut from two groups of WT, 5xFAD/SR +/+ and 5xFAD/SR-/-mice aged 3-4 or 10-12 months. Field excitatory postsynapFc potenFals (fEPSPs) and presynapFc fiber volley (PFV) were extracellularly recorded in CA1 stratum radiatum aner electrical sFmulaFon of Schaffer collaterals. Input/output curves of the fEPSP/PFV raFo of isolated NMDAr-mediated fEPSPs were constructed in a low magnesium medium supplemented with the non-NMDAr antagonist NBQX (10µM) before and 15 min aner addiFon of D-serine (100 µM). High frequency (HFS)-induced long-term potenFaFon (LTP) was studied in control medium aner tetanic sFmulaFon consisFng in one train at 100 Hz delivered for 1 sec. TesFng sFmulaFon was then resumed for 60 min aner HFS. 3) Semi-quanFtaFve immunoblopng analysis: Hippocampal Fssue was homogenized in protein lysis buffer. The membranes were probed with anFbodiesaginst GluN1 (1:750
Orientation and Alignment Echoes
We present what is probably the simplest classical system featuring the echo
phenomenon - a collection of randomly oriented free rotors with dispersed
rotational velocities. Following excitation by a pair of time-delayed impulsive
kicks, the mean orientation/alignment of the ensemble exhibits multiple echoes
and fractional echoes. We elucidate the mechanism of the echo formation by
kick-induced filamentation of phase space, and provide the first experimental
demonstration of classical alignment echoes in a thermal gas of CO_2 molecules
excited by a pair of femtosecond laser pulses
Investigating Gaze of Children with ASD in Naturalistic Settings.
BACKGROUND: Visual behavior is known to be atypical in Autism Spectrum Disorders (ASD). Monitor-based eye-tracking studies have measured several of these atypicalities in individuals with Autism. While atypical behaviors are known to be accentuated during natural interactions, few studies have been made on gaze behavior in natural interactions. In this study we focused on i) whether the findings done in laboratory settings are also visible in a naturalistic interaction; ii) whether new atypical elements appear when studying visual behavior across the whole field of view.
METHODOLOGY/PRINCIPAL FINDINGS: Ten children with ASD and ten typically developing children participated in a dyadic interaction with an experimenter administering items from the Early Social Communication Scale (ESCS). The children wore a novel head-mounted eye-tracker, measuring gaze direction and presence of faces across the child's field of view. The analysis of gaze episodes to faces revealed that children with ASD looked significantly less and for shorter lapses of time at the experimenter. The analysis of gaze patterns across the child's field of view revealed that children with ASD looked downwards and made more extensive use of their lateral field of view when exploring the environment.
CONCLUSIONS/SIGNIFICANCE: The data gathered in naturalistic settings confirm findings previously obtained only in monitor-based studies. Moreover, the study allowed to observe a generalized strategy of lateral gaze in children with ASD when they were looking at the objects in their environment
Low energy electron/recoil discrimination for directional Dark Matter detection
Directional detection is a promising Dark Matter search strategy. Even though
it could accommodate to a sizeable background contamination, electron/recoil
discrimination remains a key and challenging issue as for direction-insensitive
detectors. The measurement of the 3D track may be used to discriminate
electrons from nuclear recoils. While a high rejection power is expected above
20 keV ionization, a dedicated data analysis is needed at low energy. After
identifying discriminant observables, a multivariate analysis, namely a Boosted
Decision Tree, is proposed, enabling an efficient event tagging for Dark Matter
search. We show that it allows us to optimize rejection while keeping a rather
high efficiency which is compulsory for rare event search.With respect to a
sequential analysis, the rejection is about 20 times higher with a multivariate
analysis, for the same Dark Matter exclusion limit.Comment: 20 pages, 20 figure
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