A sensitivity study of the neutral-neutral reactions C + C3 and C + C5 in cold dense interstellar clouds

Chemical networks used for models of interstellar clouds contain many reactions, some of them with poorly determined rate coefficients and/or products. In this work, we report a method for improving the predictions of molecular abundances using sensitivity methods and ab initio calculations. Based on the chemical network osu.2003, we used two different sensitivity methods to determine the most important reactions as a function of time for models of dense cold clouds. Of these reactions, we concentrated on those between C and C3 and between C and C5, both for their effect on specific important species such as CO and for their general effect on large numbers of species. We then used ab initio and kinetic methods to determine an improved rate coefficient for the former reaction and a new set of products, plus a slightly changed rate coefficient for the latter. Putting our new results in a pseudo-time-dependent model of cold dense clouds, we found that the abundances of many species are altered at early times, based on large changes in the abundances of CO and atomic C. We compared the effect of these new rate coefficients/products on the comparison with observed abundances and found that they shift the best agreement from 3e4 yr to (1-3)e5 yr

Review of the late Quaternary stratigraphy of the northern Gulf of Cadiz continental margin:New insights into controlling factors and global implications

Over the past decades, the northern Gulf of Cadiz has been the focus of a wide range of late Quaternary seismic and sequence stratigraphic studies, either addressing the slope contourite depositional system (CDS), or the development of the continental shelf. Yet, high-resolution seismic data bridging between these domains and age information have remained sparse. This study, based on new high-resolution reflection seismic profiles calibrated to IODP Expedition 339 sites U1386/U1387, now presents an updated stratigraphic framework, that integrates (for the first time) the late Quaternary records of the northern Gulf of Cadiz middle slope to shelf off the Guadiana River. Seismic stratigraphic analysis of the stacking, depocenter distribution, stratal architecture and facies of the seismic (sub-)units reveals the influence of similar to 100 kyr sea-level variations paced by Milankovitch (eccentricity) cycles, tectonics (manifesting as two pulses of uplift and margin progradation), sediment supply and bottom current activity. This work furthermore contributes to the application and understanding of high-resolution, late Quaternary sequence stratigraphy. Firstly, the proposed sequence stratigraphic interpretation shows that adaptations to the basic models are required to integrate the shelf and slope record, and to account for the presence of a significant alongslope (bottom current-controlled) component. Secondly, the results confirm that the sequences are dominantly composed of regressive deposits, whereas the preservation of transgressive to highstand deposits is more irregular. Significantly, the common assumption that successive major glacial lowstands are consistently recorded as well-marked, shelf-wide erosional unconformities, is demonstrated to be occasionally invalid, as tectonics can obliterate this one-to-one relationship

Autoantibodies against type I IFNs in patients with life-threatening COVID-19

Interindividual clinical variability in the course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is vast. We report that at least 101 of 987 patients with life-threatening coronavirus disease 2019 (COVID-19) pneumonia had neutralizing immunoglobulin G (IgG) autoantibodies (auto-Abs) against interferon-w (IFN-w) (13 patients), against the 13 types of IFN-a (36), or against both (52) at the onset of critical disease; a few also had auto-Abs against the other three type I IFNs. The auto-Abs neutralize the ability of the corresponding type I IFNs to block SARS-CoV-2 infection in vitro. These auto-Abs were not found in 663 individuals with asymptomatic or mild SARS-CoV-2 infection and were present in only 4 of 1227 healthy individuals. Patients with auto-Abs were aged 25 to 87 years and 95 of the 101 were men. A B cell autoimmune phenocopy of inborn errors of type I IFN immunity accounts for life-threatening COVID-19 pneumonia in at least 2.6% of women and 12.5% of men

Kinetics of 1,6-hydrogen migration in alkyl radical reaction class

The kinetics of the 1,6-intramolecular hydrogen migration in the alkyl radical reaction class has been studied using the reaction class transition state theory (RC-TST) combined with the linear energy relationship (LER) and the barrier height grouping (BHG) approach. The RC-TST/LER, where only reaction energy is needed, and RC-TST/BHG, where no other information is needed, are found to be promising methods for predicting rate constants for any reaction in the 1,6-intramolecular H migration in alkyl radicals reaction class. Direct comparison with available experimental data indicates that the RC-TST/LER, where only reaction energy is needed, can predict rate constants for any reaction in this reaction class with satisfactory accuracy

Mise au point chimiluminescences pouvant se produire dans les phénomènes de combustion

Les émissions de chimiluminescence se produisent par le canal de réactions élémentaires vérifiant des conditions bien précises, dont une assez grande exoénergéticité. Ces conditions sont assez fréquemment réunies au cours de combustions, dont évidemment celle des hydrocarbures. Mais, sauf à très basse pression, la relaxation collisionnelle efface rapidement les distributions de population produites par les réactions élémentaires ; les états radiatifs sont désactivés, le système réagissant est "thermalisé” et les émissions lumineuses deviennent de ce fait de nature essentiellement thermique. Néanmoins, dans les cas les plus favorables, les émissions de chimiluminescence ne disparaissent pas totalement. On peut les mettre en évidence et déduire des lois qui les régissent des indications, souvent très significatives, sur le mécanisme cinétique. On essaie, dans le présent mémoire, de faire le point sur les conditions théoriques d'apparition des phénomènes de chimiluminescence, puis de présenter ceux connus en combustion, en définitive assez peu nombreux, dont la nature chimiluminescente paraît prouvée. On considère tant le cas des systèmes statiques (régime "explosif") que celui des systèmes dynamiques (c'est à dire en écoulement) signalés dans les différentes publications, notamment dans les communications présentées à l'occasion des symposiums internationaux sur la combustion

Réactions des radicaux chlorofluorométhyl péroxyles avec no : étude cinétique dans le domaine de température compris entre 230 et 430 K

Les constantes de vitesse absolues des réactions d'une série de radicaux chlorofluoromethyl peroxyles CX3O2 avec NO ont été déterminées pour des températures comprises entre 230 et 430 K, par photolyse laser pulsée et spectrométrie de masse résolue dans le temps. Les réactions sont rapides, environ deux fois plus rapides que la réaction équivalente de CH3O2 et présentent un coefficient négatif de température. Les expressions des constantes de vitesse sont les suivantes, les unités étant exprimées en cm3 molecule-1.s-1 : [math] Aucun effet de pression significatif n'a pu être détecté entre 1 et 10 Torr. Des mesures de rendements de NO3 ont montré que CX3O et NO3 sont les produits principaux de la réaction dans le domaine de pression étudié

Photochemistry of C3Hp hydrocarbons in Titan's stratosphere revisited

The description of C3 hydrocarbon chemistry in current photochemical models of Titan's atmosphere is found to be far from complete. We have carefully investigated the photochemistry involving C3Hp compounds in the atmosphere of Titan (considering both photolysis and neutral reactions), which considerably impacts the abundances of many other hydrocarbon species (including C2 compounds). Model results indicate that three species (C3, c-C3H2 and C3H3) could be abundant enough to be present in the Cassini/INMS data. Because the error bars on predicted C3-hydrocarbon abundances are considerably larger than those of the observational data, new experimental and theoretical studies targeting the measurement of low-temperature reaction rate constants and product branching ratios are required to reduce current model uncertainties. In particular, we highlight 30 "key reactions", the uncertainty factors of which should be lowered to improve the quality of photochemical models involving C3Hp molecules

The neutral photochemistry of nitriles, amines and imines in the atmosphere of Titan

The photochemistry of N2 and CH4 in the atmosphere of Titan leads to a very rich chemistry which is not well understood. The aim of our study is to improve our understanding of the production of nitrogen compounds and to predict the abundances of those with high molar mass with better accuracy. We have made a careful investigation of the neutral nitrogen photochemistry to improve current chemical schemes including the most abundant species and the most efficient reactions. We also studied the propagation of uncertainties on rate constants in our model and determined the key reactions from a global sensitivity analysis. Our photochemical model contains 124 species, 60 of which are nitrogen containing compounds, and 1141 reactions. Our results are in reasonable agreement with Cassini/INMS data in the higher atmosphere but our model overestimates the mole fractions of several nitriles in the lower stratosphere. New species such as CH3C3N and C3H7CN could be relatively abundant in Titan's atmosphere. Uncertainties on some nitrogen compounds are important and further studies of the key reactions that we have identified are needed to improve the predictivity of photochemical models. Meridional transport is expected to be an efficient process to govern the abundances of several nitriles in the lower stratosphere