Influence of the angular scattering of electrons on the runaway threshold in air

International audienceThe runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy electrons that run away in electric fields associated with thunderstorms. In this paper, we discuss the runaway threshold definition with a particular interest in the influence of the angular scattering for electron energy close to the threshold. In order to understand the mechanism of runaway, we compare the outcome of different FokkerPlanck and Monte Carlo models with increasing complexity in the description of the scattering. The results show that the inclusion of the stochastic nature of collisions smooths the probability to run away around the threshold. Furthermore, we observe that a significant number of electrons diffuse out of the runaway regime when we take into account the diffusion in angle due to the scattering. Those results suggest using a runaway threshold energy based on the FokkerPlanck model assuming the angular equilibrium that is 1.6 to 1.8 times higher than the one proposed by [1, 2], depending on the magnitude of the ambient electric field. The threshold also is found to be 5 to 26 times higher than the one assuming forward scattering. We give a fitted formula for the threshold field valid over a large range of electric fields. Furthermore, we have shown that the assumption of forward scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation

Study of the Stability of a Selective Solar Absorber Coating under Air and High Temperature Conditions

Abstract Selective solar absorber material is one of the major components in the Concentrated Solar Power (CSP) technologies. Its optical properties determine the efficiency of the energy conversion from the concentrated sun irradiation to the heat recovered by the heat transfer fluid. Development of the CSP requires costs reduction for this technology. To achieve this goal, one way is the increase of the work temperature up to 400 – 500 °C or more. For economic reasons, the bankable of CSP technology requires a lifetime over 25 years for components and so for solar absorbers. The development of solar receiver, able to operate under air, instead of vacuum conditions, is a challenge to reduce the costs. Along the 25 years of a CSP plant lifetime, solar absorber material is daily exposed to high levels of stresses: high solar flux, high thermal gradient. As the oxidation is one of the main factors involved in degradation processes air stability of the absorber coating under high temperatures should be studied as it could be a critical point in the solar field maintainability in case of accidental vacuum loss. In this article we present a durability study of selective solar absorber from Archimede Solar Energy (ASE) exposed in air at high temperature (up to 500 °C). The results show a good stability of this materials up to 450 °C during 3000h without change of solar absorptance and emittance. An analysis of the degradation process at higher temperature is presented

Antirhea borbonica Aqueous Extract Protects Albumin and Erythrocytes from Glycoxidative Damages

Diabetes constitutes a major health problem associated with severe complications. In hyperglycemic conditions, chronically increased oxidation and glycation of circulating components lead to advanced glycation end-products (AGEs) formation, a key contributor in diabetes complication progression. In line with literature documenting the beneficial properties of herbal teas, this study evaluates the antioxidant/glycant properties of Antirhea borbonica (Ab). Ab aqueous extract effects were tested on human albumin or erythrocytes submitted to methyl glyoxal-mediated glycoxidative damages. By using mass spectrometry, Ab aqueous extracts revealed to be rich in polyphenols. All tested biomarkers of oxidation and glycation, such as AGE, ketoamine, oxidized thiol groups, were decreased in albumin when glycated in the presence of Ab aqueous extract. Ab extract preserve erythrocyte from methylglyoxal (MGO)-induced damages in terms of restored membrane deformability, reduced oxidative stress and eryptosis phenomenon. Antioxidant capacities of Ab extract on erythrocytes were retrieved in vivo in zebrafish previously infused with MGO. These results bring new evidences on the deleterious impacts of glycation on albumin and erythrocyte in diabetes. Furthermore, it reveals antioxidant and antiglycant properties of Ab that could be used for the dietary modulation of oxidative stress and glycation in hyperglycemic situations

Quantifying loopy network architectures

Biology presents many examples of planar distribution and structural networks having dense sets of closed loops. An archetype of this form of network organization is the vasculature of dicotyledonous leaves, which showcases a hierarchically-nested architecture containing closed loops at many different levels. Although a number of methods have been proposed to measure aspects of the structure of such networks, a robust metric to quantify their hierarchical organization is still lacking. We present an algorithmic framework, the hierarchical loop decomposition, that allows mapping loopy networks to binary trees, preserving in the connectivity of the trees the architecture of the original graph. We apply this framework to investigate computer generated graphs, such as artificial models and optimal distribution networks, as well as natural graphs extracted from digitized images of dicotyledonous leaves and vasculature of rat cerebral neocortex. We calculate various metrics based on the Asymmetry, the cumulative size distribution and the Strahler bifurcation ratios of the corresponding trees and discuss the relationship of these quantities to the architectural organization of the original graphs. This algorithmic framework decouples the geometric information (exact location of edges and nodes) from the metric topology (connectivity and edge weight) and it ultimately allows us to perform a quantitative statistical comparison between predictions of theoretical models and naturally occurring loopy graphs.Comment: 17 pages, 8 figures. During preparation of this manuscript the authors became aware of the work of Mileyko at al., concurrently submitted for publicatio

An Introduction To Marine Invasive Species

Countless marine species are invading new environments with devastating effects on the ecosystem, the local and global economy, and on human health. The frequency of marine invasions has been increasing in recent decades with a respective raised interest of invasive species in the scientific community, and the general public. The Aquatic Invasive Species class (MAR442) at the University of New England offers an informative overview of invasive species, targeting educated readers with a general interest in invasive species biology. Students in the MAR 442 class have worked on identifying the most important topics on marine invasive species, have reviewed the respective literature and written chapters that provide both a broad overview of the general aspects on marine invasions, as well as a set of individual case studies that illustrate different specific aspects of marine invasions. The class, comprised of fifteen junior and senior marine biology students, selected the different topics, presented the material, wrote the drafts, edited the drafts and assembled the final versions into this book. With a wealth of information on invasive species assembled in peer-reviewed articles, books, other literature, websites, data-bases and more, this book cannot claim to be all inclusive. However, we think that this book will provide an excellent broad overview of the most important aspects of marine invasion biology, and will furthermore provide very specific information on selected topics.https://dune.une.edu/marinesci_studproj/1000/thumbnail.jp

Socioeconomic and geographic determinants of survival of patients with digestive cancer in France

Using a multilevel Cox model, the association between socioeconomic and geographical aggregate variables and survival was investigated in 81 268 patients with digestive tract cancer diagnosed in the years 1980–1997 and registered in 12 registries in the French Network of Cancer Registries. This association differed according to cancer site: it was clear for colon (relative risk (RR)=1.10 (1.04–1.16), 1.10 (1.04–1.16) and 1.14 (1.05–1.23), respectively, for distances to nearest reference cancer care centre between 10 and 30, 30 and 50 and more than 90 km, in comparison with distance of less than 10 km; P-trend=0.003) and rectal cancer (RR=1.09 (1.03–1.15), RR=1.08 (1.02–1.14) and RR=1.12 (1.05–1.19), respectively, for distances between 10 and 30 km, 30 and 50 km and 50 and 70 km, P-trend=0.024) (n=28 010 and n=18 080, respectively) but was not significant for gall bladder and biliary tract cancer (n=2893) or small intestine cancer (n=1038). Even though the influence of socioeconomic status on prognosis is modest compared to clinical prognostic factors such as histology or stage at diagnosis, socioeconomic deprivation and distance to nearest cancer centre need to be considered as potential survival predictors in digestive tract cancer

First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength

We present the first observation of Self-Amplified Spontaneous Emission (SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width and intensity fluctuations all corroborate the existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]