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Exploring the Molecular Structure of Imidazolium-Silica-Based Nanoparticle Networks by Combining Solid-State NMR Spectroscopy and First-Principles Calculations
No full textInternational audienceA DFT-based molecular model for imidazolium-silica-based nanoparticle networks (INNs) is presented. The INNs were synthesized and characterized by using small-angle X-ray scattering (SAXS), NMR spectroscopy, and theoretical ab initio calculations. B-11 and P-31 HETCOR CP MAS experiments were recorded. Calculated (FNMR)-F-19 spectroscopy results, combined with the calculated anion-imidazolium (IM) distances, predicted the IM chain density in the INN, which was also confirmed from thermogravimetric analysis/mass spectrometry results. The presence of water molecules trapped between the nanoparticles is also suggested. First considerations on possible - stacking between the IM rings are presented. The predicted electronic properties confirm the photoluminescence emissions in the correct spectral domain
H.E.S.S. Observations of the Crab during its March 2013 GeV Gamma-Ray Flare
No full textContext. On March 4, 2013, the Fermi-LAT and AGILE reported a flare from the direction of the Crab Nebula in which the high-energy (HE; E > 100 MeV) flux was six times above its quiescent level. Simultaneous observations in other energy bands give us hints about the emission processes during the flare episode and the physics of pulsar wind nebulae in general. Aims. We search for variability of the emission of the Crab Nebula at very-high energies (VHE; E > 100 GeV), using contemporaneous data taken with the H.E.S.S. array of Cherenkov telescopes. Methods. Observational data taken with the H.E.S.S. instrument on five consecutive days during the flare were analysed concerning the flux and spectral shape of the emission from the Crab Nebula. Night-wise light curves are presented with energy thresholds of 1 TeV and 5 TeV. Results. The observations conducted with H.E.S.S. on 2013 March 6 to March 10 show no significant changes in the flux. They limit the variation on the integral flux above 1 TeV to less than 63% and the integral flux above 5 TeV to less than 78% at a 95% confidence level
Evolution of genes neighborhood within reconciled phylogenies: an ensemble approach
No full textInternational audienceReconstruction of the evolutionary history of genomic characters along a given species tree is a long-standing problem in computational biology, with efficient algorithms to compute parsimonious scenarios for many types of characters, as in the cases of genes and genomes sequences, gene content, and gene family evolution. Recently, Bérard et al. extended the corpus of such results to syntenic characters, as they introduced the notion of adjacency forest, that models the evolution of gene adjacencies within a phylogeny, and described an efficient dynamic programming (DP) algorithm, called DeCo (Berard et al, ECCB 2012), to compute parsimonious adjacency evolutionary histories. Applying the classical parsimony-based approach of DeCo to a dataset of over 6,000 pairs of mammalian gene trees yielded a significant number of ancestral genes involved in more than two adjacencies, which correspond to syntenic inconsistencies.Recently, more general approaches for parsimony problems have been analyzed, either exploring a wider range of parameters, or considering several alternate histories for a given instance. Our work seeks to address the syntenic inconsistencies of DeCo by extending their DP scheme toward an exploration of the whole solution space of adjacency histories, under the Boltzmann probability distribution, that assigns a probability to each solution defined in terms of its parsimony score. This principle has been applied in several contexts and is sometimes known as the “Boltzmann ensemble approach”.While this Boltzmann ensemble approach has been used for a long time in RNA structure analysis, to the best of our knowledge it is not the case in comparative genomics, where exact probabilistic models have been favored as increasing computational capacities allow them to handle realistic datasets. However, such a probabilistic model does not exist so far for gene adjacencies, which motivates our work.We first show that by sampling adjacencies histories under a Boltzmann distribution that favors co-optimal histories and conserving only frequent ancestral adjacencies, we can reduce significantly the number of syntenic inconsistencies. We also implement a inside/outside variant for DeCo, that computes the actual probabilities of each individual adjacency considered under the Boltzmann distribution
Linear and nonlinear stationary ac response of nanomagnets in the presence of thermal agitation and spin-transfer torques
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Possible Influence of Venus Topography on the Zonal Wind and UV albedo at Cloud Top Level
No full textInternational audienceWe investigate the possible existence of planetary stationary waves generated by the interaction of the super-rotating zonal wind with the mountains of Venus. If a stationary gravity wave is generated, as on the Earth with cloud-forming downstream of the mountain, then it may propagate upward, depending on the vertical wind profile and stability profile. The possible break-up of the waves at cloud top level or just below could have a significant effect on the magnitude of the zonal wind, and also on vertical transport of the still-unknown UV absorber which is responsible for the UV contrast in UV images of the ubiquitous Venus cloud cover
Matched asymptotic expansion method for an homogenized interface model
No full textInternational audienceOur aim is to demonstrate the effectiveness of the matched asymptotic expansion method in obtaining a simpli ed model for the influence of small identical heterogeneities periodically distributed on an internal surface on the overall response of a linearly elastic body. The results of some numerical experiments corroborate the precise identi cation of the di fferent steps, in particular of the outer/inner regions with their normalized coordinate systems and the scale separation, leading to the model
Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures
No full textInternational audienceMatrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecularradicals. However, the isolation matrices, usually composed of noble gases or small diamagnetic molecules,are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin.Here we report on the successful isolation of CH3 radicals in the cages of a nearly inert clathrate–SiO2matrix. This host is found to exhibit a comparable inertness with respect to that of most conventionalnoble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to thecovalent nature of the host material and gives the opportunity to study the confined radicals from a fewdegrees of Kelvin up to at least room temperature. Thanks to this advantage we were able to explore withcontinuity for the first time the CH3 rotor properties by electron paramagnetic resonance spectroscopy,starting from the quantum rotations which are observable only at the lowest temperatures (T E 4 K), goingthrough the gradual transition to the classical motion (4 K o T o 30 K), and ending with the properties ofthe fully classical rotor (T 4 30 K). The method of isolation presented here is found to be very effectiveand promising, as it is expected to be applicable to a large variety of different molecular radicals
Compact 180-kV Marx generator triggered in atmospheric air by femtosecond laser filaments
No full textInternational audienceWe developed a compact Marx generator triggered in atmospheric air by a single femtosecond laser beam undergoing filamentation. Voltage pulses of 180 kV could be generated with a subnanosecond jitter. The same laser beam was also used to initiate simultaneously guided discharges up to 21 cm long at the output of the generator
ICRF-3: Roadmap to the Next Generation International Celestial Reference Frame
No full textInternational audienceWe propose a 3rd generation radio-based International Celestial Reference Frame (ICRF-3) to improve upon the highly successful ICRF-2. Our goals are to improve the precision, spatial and frequency coverages relative to the ICRF-2 by 2018. This date is driven by the desire to create radio frames early enough to test the Gaia optical frame during its construction. Several specific actions are underway. A collaboration has been started to improve S/X-band precision of the 2200+ VLBA Calibrator Survey sources which are typically 5 times less precise than the rest of the ICRF-2. S/X-band southern precision improvements are planned from observations with southern antennas such as the AuScope and HartRAO, S. Africa. We seek to improve radio frequency coverage with X/Ka and K-band work. An X/Ka frame of 654 sources now has full sky coverage from the addition of a 2nd southern station in Argentina which should strengthen the southern hemisphere in general. A K-band collaboration has formed with similar coverage and southern precision goals. On the analysis front, special attention will be given to combination techniques both of VLBI catalogs and of multiple data types (e.g. VLBI+GPS). Finally, work is underway to identify and pinpoint sources bright enough in both radio and optical to allow for a robust frame tie between VLBI and Gaia optical frames
Numerical simulations of maternal blood flows in the human placenta: estimation of the wall shear stress exerted on the syncytiotrophoblast
No full textInternational audienceThe primary culture of syncytiotrophoblast (ST) is a model of the human placental endocrinian functions. In vivo the ST is submitted to the fluid shear stress generated by maternal blood flows. Our hypothesis is that the shear stress could modulate the secretory functions of the ST. The aim of this study is to determine the gradients of wall shear stress exerted in vivo by the maternal blood flows on the ST