Low temperature (39-298 K) kinetics study of the reactions of the C4H radical with various hydrocarbons observed in Titan's atmosphere

The reaction kinetics of the butadinyl radical, C₄H, with various hydrocarbons detected in the atmosphere of Titan (methane, ethane, propane, acetylene, ethene and methylacetylene) are studied over the temperature range of 39-298 K using the Rennes CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus. Kinetic measurements were made using the pulsed laser photolysis—laser induced fluorescence technique. The rate coefficients, except for the reaction with methane, all show a negative temperature dependence and can be fitted with the following expressions over the temperature range of this study: ; ; , , . These expressions are not intended to be physically meaningful but rather to provide an easy way to introduce experimental results in photochemical models. They are only valid over the temperature range of the experiments. Possible channels of these reactions are discussed as well as possible consequences of these results for the production of large molecules and hazes in the atmosphere of Titan. These results should also be considered for the photochemistry of Giant Planets.     

Intensity measures for probabilistic assessment of non‐structural components acceleration demand

A fundamental issue in the framework of seismic probabilistic risk analysis is the choice of ground motion intensity measures (IMs). Based on the floor response spectrum method, the present contribution focuses on the ability of IMs to predict non‐structural components (NSCs) horizontal acceleration demand. A large panel of IMs is examined and a new IM, namely equipment relative average spectral acceleration (E‐ASA_R), is proposed for the purpose of NSCs acceleration demand prediction. The IMs efficiency and sufficiency comparisons are based on (i) the use of a large dataset of recorded earthquake ground motions; (ii) numerical analyses performed on three‐dimensional numerical models, representing actual structural wall and frame buildings; and (iii) systematic statistical analysis of the results. From the comparative study, the herein introduced E‐ASA_R shows high efficiency with respect to the estimation of maximum floor response spectra ordinates. Such efficiency is particularly remarkable in the case of structural wall buildings. Besides, the sufficiency and the simple formulation allowing the use of existing ground motion prediction models make the E‐ASA_R a promising IMs for seismic probabilistic risk assessment. Copyright © 2015 John Wiley & Sons, Ltd.     

Chandra observations of Tycho’s supernova remnant

We present a newChandra observation of Tycho’s supernova remnant with the Advanced CCD Imaging Spectrometer. Multicolor Xray imaging reveals new details of the outer shock and ejecta. At energies between 4 and 6 keV, the outline of the outer shock is clearly revealed in X-rays for the first time. The distribution of the emission from lines of Si and Fe are confirmed to have a different morphology from each other, and the Si ejecta are shown to extend to the blast shock at several locations. Characteristic spectra of the outer shock and ejecta are also presented.     

X-Ray Emission From Comet Hale–Bopp

The discovery of X-ray emission from comets has created a number of questions about the physical mechanism producing the radiation. There are now a variety of explanations for the emission, from thermal bremsstrahlung of electrons off neutrals or dust, to charge exchange induced emission from solar wind ions, to scattering of solar X-rays from attogram dust, to reconnection of solar magnetic field lines. In an effort to understand this new phenomenon, we observed but failed to detect in the X-ray the very dusty and active comet C/Hale-Bopp 1995 O1 over a two year period, September 1996 to December 1997, using the ROSAT HRI imaging photometer at 0.1–2.0 keV and the ASCA SIS imaging spectrometer at 0.5–10.0 keV. The results of our Hale-Bopp non-detections, when combined with spectroscopic imaging 0.08–1.0 keV observations of the comet by EUVE and BeppoSAX, show that the emission has the same spectral shape and strong variability seen in other comets. Comparison of the ROSAT photometry of the comet to our ROSAT database of 8 comets strongly suggests that the overall X-ray faintness of the comet was due to an emission mechanism coupled to gas, and not dust, in the comet’s coma. This revised version was published online in July 2006 with corrections to the Cover Date.     

The content of some microelements in mineral waters from Covasna and Harghita Romanian districts

Using two analytical techniques, CSV/ASV and ICP–AES, the concentration of some microelements (lead, zinc, manganese) in mineral waters from the Covasna and Harghita districts of Romania were determined. The optimum parameters for the voltammetric determination of manganese, copper, zinc and lead were established (electrolyte, deposition time, pulse duration, pulse amplitude, etc.) and then the content of these elements in twelve samples of mineral water were determined. The results obtained by both techniques led to the conclusion that the concentration of microelements in mineral waters from Covasna and Harghita districts is connected to the mineral content underground.     

The Danube Delta: Geographical characteristics and ecological recovery

The Danube Delta is very large with diverse resources which have been intensively exploited during the modern period. It is now of great interest to conservationists with 280 species of birds (177 of which hatch in the delta). The origin of the delta is considered and its development is traced from the initial offshore bar, referring to the writings of the classical scholars and other sources. Modern developments involve the navigational work of the European Commission of the Danube (set up in 1856) and the more intensive exploitation of the reed beds, fisheries, agricultural lands and forests since 1950. Since the revolution of 1989 this programme has stopped and the delta (including the Razim-Sinoie lake complex) is now a Biosphere Reserve. The reserve is described and the principles for management are discussed.     

Circumstellar X-ray emission from SN1978K

We present the X-ray light curve in the 0.2–2.4 keV band based on fiveROSAT observations of SN1978K in NGC 1313. The X-ray emission is believed to arise from the interaction of the reverse shock and the expanding debris from the supernova. The reverse shock becomes established after the outgoing shock runs into circumstellar matter.     

Radionuclides transport at the site of a low- and intermediate-level waste repository,Saligny, Romania

The site of the future Saligny low- and intermediate-level waste repository presents a rather deep unsaturated zone consisting of a pile of loess and clay, underlain by a calcareous aquifer. Van Genuchten parameters were first estimated in laboratory on samples collected from all the horizons, at different depths. In a second kind of test, moisture parameters were estimated from the natural water content profiles, observed in some wells, by inversion of the unsaturated flow equation. Based on the solution of the inverse problem as well as of the sensitivity analyses a simple physical model of the vadose zone was determined, consisting of a layered sequence that was subjected to a constant infiltration flux. Radionuclide migration was simulated in a vertical cross section made along the most probable path from the repository towards the surface water discharge zone. For radionuclide release, a source term was evaluated by ensuring a conservative estimate of cell inventory during the cell-filling operation. According to the simulation results, for the medium half-life nuclides, the unsaturated zone is a perfect barrier, whereas the long half-life isotopes break through in the aquifer at significant concentrations.

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Resumen El sitio del futuro repositorio para desechos de nivel bajo e intermedio, denominado Saligny, presenta una zona no saturada bastante profunda, consistente en un depósito de loess y arcilla, subyacido por un acuífero calcáreo. Los parámetros de Van Genuchten se estimaron por primera vez en laboratorio, a partir de muestras recolectadas de todos los horizontes, a diferentes profundidades. En un segundo tipo de prueba se estimaron los parámetros de humedad a través de la inversión de la ecuación de flujo no saturado, a partir de los perfiles naturales que contienen agua, observados en algunos pozos. Con base en la solución del problema inverso, así como también en análisis de sensibilidad, se determinó un modelo físico simple de la zona vadosa, el cual consiste de una secuencia estratificada sometida a un flujo de infiltración constante. La migración del radioisótopo fue simulada en una sección vertical, hecha a lo largo del camino más probable entre el repositorio y la zona de descarga en el agua superficial. Para la liberación del radioisótopo se evaluó la fuente, asegurando un estimativo conservador del inventario de celdas durante la operación de llenado de celdas. De acuerdo con los resultados de la simulación, para los isótopos con vida media intermedia, la zona no saturada es una barrera perfecta; mientras que los isótopos con vida media larga irrumpen en el acuífero con concentraciones importantes.

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Résumé Le futur stockage de déchets radioactifs de faible et moyenne activité de Saligny est caractérisé par une zone non-saturée assez profonde qui consiste dans des dépôts de loess et dargile qui couvrent un aquifère calcaire. Dans une première étape, les paramètres de van Genuchten ont été déterminés en laboratoires sur des échantillons prélevés de toutes les couches, à des profondeurs différentes. Dans une seconde étape les mêmes paramètres ont été estimés, comme un solution du problème inverse à partir de profils de la saturation en eau, mesurés dans des forages. Les résultats du problème inverse, ainsi que l› analyse de sensibilité ont mené à un modèle multi- couches de la zone non-saturé, rechargé par un flux constant. On a simulé le transport des radionucléides dans une coupe verticale, construite au long du trajet le plus probable entre le stockage et les eaux de surface. Le flux de radionucléides relâchés a été estimé en considérant une valeur consevative pour la masse totale stocké. D› après les résultats de la simulation la zone non saturée forme une barrière presque parfaite pour les radionucléides de période moyenne, denvirons de 30 ans, tendis quelle est traversée avec des concentrations assez importantes par des isotopes à grande période.