Formulation and characterization of suRNA LNC

National audienc

Deconstructing classical water models at interfaces and in bulk

Using concepts from perturbation and local molecular field theories of liquids we divide the potential of the SPC/E water model into short and long ranged parts. The short ranged parts define a minimal reference network model that captures very well the structure of the local hydrogen bond network in bulk water while ignoring effects of the remaining long ranged interactions. This deconstruction can provide insight into the different roles that the local hydrogen bond network, dispersion forces, and long ranged dipolar interactions play in determining a variety of properties of SPC/E and related classical models of water. Here we focus on the anomalous behavior of the internal pressure and the temperature dependence of the density of bulk water. We further utilize these short ranged models along with local molecular field theory to quantify the influence of these interactions on the structure of hydrophobic interfaces and the crossover from small to large scale hydration behavior. The implications of our findings for theories of hydrophobicity and possible refinements of classical water models are also discussed

Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run

Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society

Etude par diffusion de Huang des auto-interstitiels dans un alliage ordonné Fe-40 at % Al irradié aux électrons

A single crystal of Fe-40 at % A1 ordered alloy has been irradiated with 2.5 NIeV electrons at liquid hydrogen temperature, and diffuse X-ray scattering (MoKα1) near Bragg reflections has been studied after annealing the sample up to 300 K. The characteristic diffuse scattering from point defects with weak displacement fields (Huang diffusion) has been observed near the (200) Bragg reflection in the directions [011] and [100] and near the (110) reflection in the directions [ 110] and [110]. This Huang scattering has been attributed to self interstitials since under the same irradiation conditions, electrical resistivity measurements indicate that the long range migration of self interstitials by annihilation at vacancies would occur only for temperatures higher than 300 K. The comparison of the experimental results with the different simple interstitial configurations proposed for b.c.c. crystals suggests that the most probable configuration should be the [110] split interstitial with orthorhombic symmetry.Un monocristal d'alliage ordonné Fe-40 at % A1 a été irradié avec des électrons de 2,5 MeV à la température de l'hydrogène liquide et l'on a étudié la diffusion des rayons X (MoKα 1) au voisinage des pics de Bragg après un recuit de l'échantillon jusqu'à 300 K. La diffusion caractéristique de défauts ponctuels à faible champ de déplacement (diffusion de Huang) a été mise en évidence au voisinage de la tache de Bragg (200) dans les directions [011] et [100] et au voisinage de la tache de Bragg (110) dans les directions [110] et [110]. Cette diffusion de Huang a été attribuée à la présence d'auto-interstitiels puisque dans les mêmes conditions d'irradiation, des mesures de résistivité électrique indiquent que la migration à grande distance des auto-interstitiels avec annihilations sur les lacunes ne se produirait que pour des températures supérieures à 300 K. La comparaison des résultats expérimentaux avec les différentes configurations simples d'interstitiels proposées pour les cristaux cubiques centrés suggère que la configuration la plus probable serait l'interstitiel dissocié selon [110] à symétrie orthorhombique

Macroscopic Model of Arc Roots and its Limits

Experimental study: - low current (2 - 5 A): Ag, Cu, W. - high current (100 - 2000 A): AgNi, AgWC, AgCdO, AgZnO, AgSnO2.A macroscopic model based on Mackeown's (for the electric field) and Murphy's theories (for electron current density) is used to calculate the characteristic parameters of the arc roots at atmospheric pressure in the whole range of current covering largely the experimental field (0.1 - 8500 A). A comparison between some theoretical and experimental electrode parameters is presented