Theoretical Fluctuations of Conductance in Stretched Monatomic Nanowire

Recent experiments showed that the last, single channel conductance step in monatomic gold contacts exhibits significant fluctuations as a function of stretching. From simulations of a stretched gold nanowire linked to deformable tips, we determine the distribution of the bond lengths between atoms forming the nanocontact and analyze its influence on the electronic conductance within a simplified single channel approach. We show that the inhomogeneous distribution of bond lengths can explain the occurrence and the 5% magnitude of conductance fluctuations below the quantum conductance unit $g_{o}= 2e^2/h$

Clathration of Volatiles in the Solar Nebula and Implications for the Origin of Titan's atmosphere

We describe a scenario of Titan's formation matching the constraints imposed by its current atmospheric composition. Assuming that the abundances of all elements, including oxygen, are solar in the outer nebula, we show that the icy planetesimals were agglomerated in the feeding zone of Saturn from a mixture of clathrates with multiple guest species, so-called stochiometric hydrates such as ammonia hydrate, and pure condensates. We also use a statistical thermodynamic approach to constrain the composition of multiple guest clathrates formed in the solar nebula. We then infer that krypton and xenon, that are expected to condense in the 20-30 K temperature range in the solar nebula, are trapped in clathrates at higher temperatures than 50 K. Once formed, these ices either were accreted by Saturn or remained embedded in its surrounding subnebula until they found their way into the regular satellites growing around Saturn. In order to explain the carbon monoxide and primordial argon deficiencies of Titan's atmosphere, we suggest that the satellite was formed from icy planetesimals initially produced in the solar nebula and that were partially devolatilized at a temperature not exceeding 50 K during their migration within Saturn's subnebula. The observed deficiencies of Titan's atmosphere in krypton and xenon could result from other processes that may have occurred both prior or after the completion of Titan. Thus, krypton and xenon may have been sequestrated in the form of XH3+ complexes in the solar nebula gas phase, causing the formation of noble gas-poor planetesimals ultimately accreted by Titan. Alternatively, krypton and xenon may have also been trapped efficiently in clathrates located on the satellite's surface or in its atmospheric haze.Comment: Accepted for publication in The Astrophysical Journa

Variability of the methane trapping in martian subsurface clathrate hydrates

Recent observations have evidenced traces of methane CH4 heterogeneously distributed in the martian atmosphere. However, because the lifetime of CH4 in the atmosphere of Mars is estimated to be around 300-600 years on the basis of photochemistry, its release from a subsurface reservoir or an active primary source of methane have been invoked in the recent literature. Among the existing scenarios, it has been proposed that clathrate hydrates located in the near subsurface of Mars could be at the origin of the small quantities of the detected CH4. Here, we accurately determine the composition of these clathrate hydrates, as a function of temperature and gas phase composition, by using a hybrid statistical thermodynamic model based on experimental data. Compared to other recent works, our model allows us to calculate the composition of clathrate hydrates formed from a more plausible composition of the martian atmosphere by considering its main compounds, i.e. carbon dioxyde, nitrogen and argon, together with methane. Besides, because there is no low temperature restriction in our model, we are able to determine the composition of clathrate hydrates formed at temperatures corresponding to the extreme ones measured in the polar caps. Our results show that methane enriched clathrate hydrates could be stable in the subsurface of Mars only if a primitive CH4-rich atmosphere has existed or if a subsurface source of CH4 has been (or is still) present.Comment: Accepted for publication in Planetary and Space Scienc

DNA Sequencing by MALDI-TOF MS using alkali cleavage of RNA / DNA Chimera

International audienc

MathematicaStan

MathematicaStan is a package to interact with CmdStan from Mathematica. It is developed under Linux and is compatible with Mathematica v11+. It should work under MacOS and also under Window

Optimization of SMES and superconducting magnets with a derivative free deterministic method

International audienceThis article presents a constrained optimization method, based on the duality theory, which does not need the gradients. The method is used to optimize superconducting devices. In order to reduce the computing effort, the initial optimization problem is divided into two coupled optimization problems. One manages the geometrical parameters, the other finds the best current densities for a given geometrical configuration

Human Milk Fortification for Preterm Infants: A Review

International audienceNo abstract availabl

Superconducting coils quench simulation, the Wilson's method revisited

International audienceThis paper describes a new numerical method which analyzes adiabatic quench of superconducting coils.The method is a generalization of the Wilson's older method. With this new method the resistive front is not restricted to be an ellipsoid and can evolve with an arbitrary velocity at its border. The evolution of the resistive front is efficiently controlled by the introduction of the level-set method. The two-dimensional version presented here leads to a fast simulation code of the quench proces