BiPo prototype for SuperNEMO radiopurity measurements

The BiPo project is dedicated to the measurement of extremely low radioactive contaminations of SuperNEMO beta-beta source foils (208Tl < 2 microBq/kg and 214Bi < 10 microBq/kg). A modular BiPo1 prototype with its 20 modules and its shielding test facility is running in the Modane Underground Laboratory since February, 2008. The goal of this prototype is to study the backgrounds and particularly the surface contamination of plastic scintillators. After 2 months, a preliminary upper limit on the sensitivity of a 10 m2 BiPo detector in 208Tl contamination of selenium source foils can be extrapolated to: A(208Tl) < 7.5 microBq/kg (90 % C.L.).Comment: 4 pages, 10 figures, Moriond EW 2008 proceedin

Results of the NEMO-3 Double Beta Decay Experiment

The NEMO-3 experiment is searching for neutrinoless double beta decay for 2 main isotopes (100Mo and 82Se) and is studying the two-neutrino double beta decay of seven isotopes. The experiment has been taking data since 2003 and, up to the end of 2009, showed no evidence for neutrinoless double beta decay. Two 90 % CL lower limits on the half-lives of the transitions were obtained : T_{1/2}^{0\nu} > 1.0 10^{24} yr for 100Mo and T_{1/2}^{0\nu} > 3.2 10^{23}$ yr for 82Se. The corresponding limits on the effective Majorana neutrino mass are respectively | m_nu | < 0.47 - 0.96 eV and | m_nu | < 0.94 - 2.5 eV. The measurements of the two-neutrino double beta decays for all the isotopes have also reached the highest precision to date.Comment: Proceeding - 22nd Rencontres de Blois - 201

BiPo prototype measurements for SuperNEMO

International audienceThe BiPo pro ject is dedicated to the measurement of extremely low radioactive contaminations of SuperNEMO ββ source foils ( 208 Tl < 2 µBq/kg and 214 Bi < 10 µBq/kg). A modular BiPo1 prototype with its 20 modules and its shielding test facility is running in the Modane Underground Laboratory since February, 2008. The goal of this prototype is to study the back-grounds and particularly the surface contamination of plastic scintillators. After 2 months, a preliminary upper limit on the sensitivity of a 10 m 2 BiPo detector in 208 Tl contamination of selenium source foils can be extrapolated to: A( 208 Tl) < 7.5 µBq/kg (90 % C.L.)

Membrane dynamics shape TCR-generated signaling

Despite intensive investigation, the mechanisms of T cell receptor (TCR)-mediated signal generation remain poorly understood. Here we review various dynamic processes at the cell membrane that might critically control this signaling. Firstly, we summarize recent reports providing new information on the sensitivity of TCR/ligand interaction to the membrane environment and particularly to applied forces. Secondly, we review recent evidence that forces and displacements are continuously generated at cell surfaces. Thirdly, we summarize recent experimental evidence demonstrating the capacity of forces to generate signals. Lastly, we provide a quantitative model to exemplify the capacity of dynamic processes to modulate TCR properties such as specificity that were previously difficult to explain with conventional models. It is concluded that the described dynamic processes must be integrated into current models of TCR signaling

Biomolecule association rates do not provide a complete description of bond formation.: Biomolecule association rates

International audienceThe efficiency of many cell-surface receptors is dependent on the rate of binding soluble or surface-attached ligands. Much effort was exerted to measure association rates between soluble molecules (three-dimensional k(on)) and, more recently, between surface-attached molecules (two-dimensional [2D] k(on)). According to a generally accepted assumption, the probability of bond formation between receptors and ligands is proportional to the first power of encounter duration. Here we provide new experimental evidence and review published data demonstrating that this simple assumption is not always warranted. Using as a model system the (2D) interaction between ICAM-1-coated surfaces and flowing microspheres coated with specific anti-ICAM-1 antibodies, we show that the probability of bond formation may scale as a power of encounter duration that is significantly higher than 1. Further, we show that experimental data may be accounted for by modeling ligand-receptor interaction as a displacement along a single path of a rough energy landscape. Under a wide range of conditions, the probability that an encounter of duration t resulted in bond formation varied as erfc[(t(0)/t)(1/2)], where t(0) was on the order of 10 ms. We conclude that the minimum contact time for bond formation may be a useful parameter to describe a ligand-receptor interaction, in addition to conventional association rates

Instruction(s) en famille. Explorations sociologiques d’un phénomène émergent

Depuis son instauration en France par la loi Ferry du 28 mars 1882, l’instruction obligatoire peut être donnée, plutôt que dans les établissements scolaires publics ou privés, dans les familles. Cette option n’a pourtant été que très peu utilisée au cours du siècle, et les familles concernées n’ont qu’exceptionnellement suscité l’intérêt de la recherche. La généralisation et l’allongement de la fréquentation scolaire, naturalisée par l’idée et l’expression, juridiquement fausses, d’une « écol..