Discrete event front tracking simulator of a physical fire spread model

International audienceSimulation of moving interfaces, like a fire front usually requires the resolution of a large scale and detailed domain. Such computing involves the use of supercomputers to process the large amount of data and calculations. This limitation is mainly due to the fact that large scale of space and time is usually split into nodes, cells or matrices, and the solving methods often require small time steps. This paper presents a novel method that enables the simulation of large scale/high resolution systems by focusing on the interface. Unlike the conventional explicit and implicit integration schemes, it is based on the discrete-event approach, which describes time advance in terms of increments of physical quantities rather than discrete time stepping. Space as well is not split into discrete nodes or cells, but we use polygons with real coordinates. The system is described by the behaviour of its interface, and evolves by computing collision events of this interface in the simulation. As this simulation technique is suited for a class of models that can explicitly provide rate of spread for a given configuration, we developed a specific radiation based propagation model of physical wildland fire. Simulations of a real large scale fire performed with an implementation of our method provide very interesting results in less than 30 seconds with a 3 metres resolution with current personal computers

An abrupt change in the African monsoon at the end of the Younger Dryas

International audienceHigh-resolution studies of variations in the elemental and stable carbon- and nitrogen-isotope composition of organic matter in cores from Lakes Malawi, Tanganyika, and Bosumtwi (tropical Africa) indicate an abrupt change in the wind-driven circulation of these lakes that, within the limits of available chronologies, was contemporaneous with the end of the Younger Dryas in the northern hemisphere. The change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of Africa. A range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics. Africa south of ~5°-10°S, on the other hand, initially suffered drought conditions. Together, the evidence suggests an abrupt northward translation of the African monsoon system at circa 11.5 ± 0.25 ka B.P. The data assembled here contribute to a growing body of work showing that the Younger Dryas was a major climatic excursion in tropical Africa. Furthermore, they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the Younger Drya

Exploitation of beehive products, plant exudates and tars in Corsica during the early Iron Age

International audienceIn the northwestern Mediterranean area, the first Iron Age is characterized by intense contacts and cultural interactions between populations. Archaeological remains such as ceramic vessels or metal and glass objects are usually good indicators of the nature and the intensity of these exchanges, but can also be used to determine the way in which these populations were living at their time. In contrast, organic substances, despite their importance in a wide variety of activities, are rarely investigated due to their low degree of preservation. The recent discovery of a series of amorphous organic residues with adhesive properties at the site of Cuciurpula provided a unique opportunity to address questions related to the types of natural substances exploited, their provenance, their uses and their informational input to intercultural relationships. Our results, based on GC and GC–MS analysis of organic residues preserved at the site of Cuciurpula, provide strong evidence for the most southern use of birch bark tar in Western Europe, and also for the simultaneous use of this substance with pine resin. Beeswax was also identified in some samples. The combined study of residue composition, aspect and location on ceramic sherds reveals a variety of uses, highlighting a complex technical system

The Origin of Primitive Cells, Nutrient Intake, and Non-Enzymatic Elongation of Encapsulated Nucleotides

Fatty acids and fatty alcohols are commonly found in experiments simulating the prebiotic 'soup'. These amphiphiles can be synthesized under prebiotic conditions, at least as long as the molecules are chemically relatively simple and do not need to be enantiomerically pure. In the context of topical origin-of-life theories, two distinct formation pathways for amphiphiles have been described; one related to geophysical sites, such as marine hydrothermal systems, and another to extraterrestrial sources, such as the proto-solar nebula, which was fed by interplanetary and interstellar nebulae. The chemical analysis of each provides individual characteristic challenges

Evolution of Endoscopic Lesions in Steroid-Refractory Acute Severe Ulcerative Colitis Responding to Infliximab or Cyclosporine

BACKGROUND/AIMS: Few data on the evolution of endoscopic findings are available in patients with acute severe ulcerative colitis (ASUC). The aim of this study was to describe this evolution in a prospective cohort. METHODS: Patients admitted for a steroid-refractory ASUC and included in a randomized trial comparing infliximab and cyclosporine were eligible if they achieved steroid-free clinical remission at day 98. Flexible sigmoidoscopies were performed at baseline, days 7, 42 and 98. Ulcerative colitis endoscopic index of severity (UCEIS) and its sub-scores - vascular pattern, bleeding and ulceration/erosion - were post-hoc calculated. Global endoscopic remission was defined by a UCEIS of 0, and partial endoscopic remission by any UCEIS sub-score of 0. RESULTS: Among the 55 patients analyzed (29 infliximab and 26 cyclosporine), 49 (83%) had UCEIS >= 6 at baseline at baseline. Partial endoscopic remission rates were higher for bleeding than for vascular pattern and for ulcerations/erosions at day 7 (20% vs. 4% and 5% (n = 55); p CONCLUSION: In steroid-refractory ASUC patients responding to a second-line medical therapy, endoscopic remission process started with bleeding remission and was not achieved in half the patients at day 98 for vascular pattern. Infliximab provided a higher endoscopic remission rate than cyclosporine at day 98.Peer reviewe

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure fl ux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defi ned as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium ) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the fi eld understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation it is imperative to delete or knock down more than one autophagy-related gene. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways so not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field

Sulfuration des lactones (accès aux sulfanylalcools et à leurs dérivés hétérocycliques)

Depuis la fin des années 70, les composés volatils soufrés ont bénéficié d une attention particulière en Chimie des arômes et des parfums. L ensemble des études analytiques d aliments, de végétaux et d autres matrices naturelles, a conduit à l identification de plusieurs centaines de composés soufrés volatils. La plupart d entre eux présentent généralement des propriétés organoleptiques remarquables, à travers des notes olfactives singulières et de faibles seuils de perception. De même, un des aspects principaux de ce domaine de recherche englobe aussi bien la synthèse des produits soufrés naturels que de leurs homologues purement synthétiques. Les 1,3-sulfanyalcools sont une famille majeure de composés volatils soufrés en raison de leur forte contribution à l arôme global de matrices naturelles telles que les vins et les fruits exotiques. Cependant, leurs homologues supérieurs, les 1,4-sulfanyalcools, n ont bénéficié à ce jour que de peu d attention. Dans ce travail, parallèlement à l étude de leurs caractéristiques organoleptiques, nous avons décidé de considérer ces molécules comme précurseurs d hétérocycles soufrés tels que les thiolanes et les sultines. De plus, la voie de synthèse que nous avons développée à partir des lactones, nous a permis d étudier plus particulièrement l étape de sulfuration offrant un accès à des lactones soufrés. A ce titre, un nouveau procédé de synthèse sous irradiation micro-ondes de thionolactones utilisant la combinaison du réactif de Lawesson et d hexaméthyldisiloxane a été développé. L ensemble du travail de synthèse nous a donné accès à une large variété de molécules soufrées couvrant un champ de notes olfactives relativement étendu.Volatile organosulfur compounds (VOSCs) have been of increasing interest in Flavour and Fragrance Chemistry since the late nineteen seventies. Analytical studies led to the chemical identification of several hundreds of volatile sulphur containing compounds in food, vegetables and many other natural matrices. Most of the compounds identified presented powerful organoleptic properties including olfactory notes combined with low odour thresholds. In addition, another part of this field of research comprises the synthesis of natural organosulfur compounds as well as their synthetic analogues. 1,3-sulfanyalcools are n outstanding class of VOSCs since they have been shown to provide a strong contribution to the aroma profile of natural matrices such as tropical fruits and wines. However, only fex work has been performed to study the organoleptic properties of their 1,4-analogues. In the present work, besides the study of the their organoleptic properties, we also considered 1,4-sulfanyalcools as synthetic precursors of heterocyclic compounds such as thiolanes and sultines. Moreover, our synthetic pathway to sulfanyalcools starting from lactones, led us to study the sulfarization step giving an access to lactone sulphur analogues such as thionolactones. As a part of our study, a new synthetic procedure of thionation including the use of a Lawesson s reagent/hexamethyldisiloxane combination under microwave irradiation was developed. The whole synthetic work led to the preparation of a large variety of sulphur containing compounds which revealed a broad and interesting spectrum to the preparation of a large variety of sulphur containing compounds which revealed a broad and interesting spectrum of olfactory notes.NICE-BU Sciences (060882101) / SudocSudocFranceF

New Pinane Derivatives Found in Essential Oils of Calocedrus decurrens

International audienc

Absolute Configuration of Aliphatic Hydrocarbon Enantiomers Identified by Gas Chromatography: Theorized Application for Isoprenoid Alkanes and the Search of Molecular Biosignatures on Mars

Acyclic saturated hydrocarbon enantiomers were resolved by gas chromatography using a β-cyclodextrin-based chiral stationary phase. The stereospecific synthesis of single enantiomers of 4-methyloctane allowed to assign the absolute stereochemical configuration to the resolved enantiomers. Data show that the (S)-4-methyloctane shows higher chromatographic retention as compared to the (R)-4-methyloctane due to stronger van der Waals interactions with the β-cyclodextrin chiral selector. This introductive research presents future prospects for the separation of stereoisomers of larger branched hydrocarbons. We discuss the importance of chiral hydrocarbons, more precisely the stereochemistry of the isoprenoid alkanes pristane and phytane, as potential biosignatures stable on geological timescales. The origins of pristane and phytane in Earth sediments are presented, and we detail the implications for the search of extinct or extant life on Mars. The data presented here will help to systematically investigate the chirality of hydrocarbon enantiomers in biological and nonbiological samples and in samples to be analyzed by the ESA’s ExoMars rover to trace the chiral precursors of life in 2023