Isotopic and spin selectivity of H_2 adsorbed in bundles of carbon nanotubes

Due to its large surface area and strongly attractive potential, a bundle of carbon nanotubes is an ideal substrate material for gas storage. In addition, adsorption in nanotubes can be exploited in order to separate the components of a mixture. In this paper, we investigate the preferential adsorption of D_2 versus H_2(isotope selectivity) and of ortho versus para(spin selectivity) molecules confined in the one-dimensional grooves and interstitial channels of carbon nanotube bundles. We perform selectivity calculations in the low coverage regime, neglecting interactions between adsorbate molecules. We find substantial spin selectivity for a range of temperatures up to 100 K, and even greater isotope selectivity for an extended range of temperatures,up to 300 K. This isotope selectivity is consistent with recent experimental data, which exhibit a large difference between the isosteric heats of D_2 and H_2 adsorbed in these bundles.Comment: Paper submitted to Phys.Rev. B; 17 pages, 2 tables, 6 figure

Energy aware approach for HPC systems

International audienceHigh‐performance computing (HPC) systems require energy during their full life cycle from design and production to transportation to usage and recycling/dismanteling. Because of increase of ecological and cost awareness, energy performance is now a primary focus. This chapter focuses on the usage aspect of HPC and how adapted and optimized software solutions could improve energy efficiency. It provides a detailed explanation of server power consumption, and discusses the application of HPC, phase detection, and phase identification. The chapter also suggests that having the load and memory access profiles is insufficient for an effective evaluation of the power consumed by an application. The available leverages in HPC systems are also shown in detail. The chapter proposes some solutions for modeling the power consumption of servers, which allows designing power prediction models for better decision making.These approaches allow the deployment and usage of a set of available green leverages, permitting energy reduction

Computer simulation of flow-dependent absorption in microperfused short Henle's loop of rats.

With computer simulation we examined the extent to which current theories and experimental data explain function of single microperfused superficial Henle's loops in rats. In the model standard phenomenological equations describe transport; two sets of transport parameters labeled rat and rabbit were taken from published experiments; Michaelis-Menten kinetics in the ascending thick limb were adjusted arbitrarily; tubular radius is either constant or depends on luminal pressure with compliance based on experimental observations; the interstitium is an infinite sink with salt and urea concentrations constant in the cortex and exponentially increasing in the outer medulla; concentrations resemble those found in hydropenic or saline diuretic rats. The following predictions were obtained. The model with rabbit parameters does not recirculate urea and will not operate with high medullary urea concentrations; with rat parameters too much urea recirculates an the results of perfusion with equilibrium solution are not reproduced. Using a compromise between rat and rabbit parameters, the model reproduces water absorption, salt reabsorption, and urea recirculation as observed in vivo in rat loops perfused at 5-40 nl/min. It also simulates perfusion with saline, equilibrium solution, saline plus furosemide, and 300 mM mannitol. When the model includes a short early distal segment, effluent salt concentration reaches a minimum at a 15 nl/min perfusion rate as observed in vivo; however, concentration at the macula densa is a monotonically increasing function of flow. When permeation rate is a function of wall surface area and thickness a better fit to experimental results is produced. However, the effect is small: water absorption alters by 4% or less and effluent salt concentration is reduced by up to 10% at low perfusion rates. Comparison of rigid and compliant loops shows no relationship between transit time per se and reabsorption

Flavaglines Stimulate Transient Receptor Potential Melastatin Type 6 (TRPM6) Channel Activity.

Contains fulltext : 155293.PDF (publisher's version ) (Open Access)Magnesium (Mg2+) is essential for enzymatic activity, brain function and muscle contraction. Blood Mg2+ concentrations are tightly regulated between 0.7 and 1.1 mM by Mg2+ (re)absorption in kidney and intestine. The apical entry of Mg2+ in (re)absorbing epithelial cells is mediated by the transient receptor potential melastatin type 6 (TRPM6) ion channel. Here, flavaglines are described as a novel class of stimulatory compounds for TRPM6 activity. Flavaglines are a group of natural and synthetic compounds that target the ubiquitously expressed prohibitins and thereby affect cellular signaling. By whole-cell patch clamp analyses, it was demonstrated that nanomolar concentrations of flavaglines increases TRPM6 activity by approximately 2 fold. The stimulatory effects were dependent on the presence of the alpha-kinase domain of TRPM6, but did not require its phosphotransferase activity. Interestingly, it was observed that two natural occurring TRPM6 mutants with impaired insulin-sensitivity, TRPM6-p.Val1393Ile and TRPM6-p.Lys1584Glu, are not sensitive to flavagline stimulation. In conclusion, we have identified flavaglines as potent activators of TRPM6 activity. Our results suggest that flavaglines stimulate TRPM6 via the insulin receptor signaling pathway