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

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

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

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

A lower bound for the BCS functional with boundary conditions at infinity

We consider a many-body system of fermionic atoms interacting via a local pair potential and subject to an external potential within the framework of BCS theory. We measure the free energy of the whole sample with respect to the free energy of a reference state which allows us to define a BCS functional with boundary conditions at infinity. Our main result is a lower bound for this energy functional in terms of expressions that typically appear in Ginzburg-Landau functionals.Comment: 32 page

D-­‐SERINE IS INVOLVED IN THE β-­‐AMYLOID-­‐RELATED PATHOPHYSIOLOGYIN ALZHEIMER’S DISEASE

International audienc

Positronium chemistry studied by AMOC measurements using a relativistic positron beam

Beam-based Age-Momentum Correlation (β+γΔE AMOC) measurements using an MeV positron beam have become a powerful tool to study chemical reactions of positronium by time-domain observations of the different positron states tagged by the Doppler-broadening (ΔE) characteristics of the 511 keV annihilation radiation. As an example, the investigation of the spin-conversion reaction in the system HTEMPO/methanol is reported. The experimental data for small HTEMPO concentrations can be fitted quite well to a rate-equation model containing the conversion rate as the only adjustable parameter. This model can presumably be applied not only to spin conversion but also to other chemical reactions and to inhibition of positronium. Possible effects of oxidation, complex formation, and inhibition are discussed by way of examples