Temperatures of aqueous alteration on carbonaceous chondrite parent bodies

Aqueous alteration of primitive meteorites is among the earliest and the most widespread geological processes in the solar system. A better understanding of these processes would help us constrain the early evolution condition of the solar system and test models of thermal and chemical evolution of planetesimals. In this study, we extended our previous work on CM chondrites by further applying carbonate clumped isotope thermometry to other types of carbonaceous chondrites (GRO 95577, CR1; Orgueil, CI; and Tagish Lake, ungrouped type 2) to determine the conditions of their aqueous alteration. Carbonate in GRO 95577 is almost exclusively calcite; both Orgueil and Tagish Lake contain complex mixtures of several carbonates, which necessitated stepped phosphoric acid digestion to separately analyze calcite, dolomite/ankerite and breunnerite. CO_2 gases derived from these acid digestions are exceptionally rich in sulfur and organic contaminants. While so far no consistent evidence suggests their influences on Δ_(47) after extensive purification, we are continuing working on this issue

The Aqueous Alteration of CR Chondrites: Experiments and Geochemical Modeling

CR carbonaceous chondrites are of major interest since they contain some of the most primitive organic matter known. However, aqueous alteration has more or less overprinted their original features in a way that needs to be assessed. This study was initiated by comparing the mineralogy and modal abundances of the most altered CR1 chondrite, GRO 95577, to a less altered CR2. Calculated element distributions imply that GRO 95577 may result from aqueous alteration of Renazzo by an isochemical process on their parent asteroid, whose mineralogical composition was estimated ( Unaltered CR shown included table)

Mineralogy and petrology of comet 81P/wild 2 nucleus samples

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk

Mineralogy and petrology of Comet Wild-2 nucleus samples - Final results of the preliminary examination team

Accepted versio

Mineralogy and petrology of Comet Wild-2 nucleus samples - Final results of the preliminary examination team

Accepted versio

Mineralogy and Petrology of Comet Wild 2 Nucleus Samples

The bulk of the Wild 2 samples appear to be weakly-constructed mixtures of nanometerscale grains with occasional much larger (>1{micro}m) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in Wild 2 require a wide range of formation conditions, probably reflecting different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and absence of hydrous phases indicate that Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require large-scale radial transport in the early protoplanetary disk. The nature of cometary solids is of fundamental importance to our understanding of the early solar nebula and protoplanetary history. Until now we have had to study comets from afar using spectroscopy, or settle for analyses of interplanetary dust particles (IDPs) of uncertain provenance. We report here mineralogical and petrographic analyses of particles derived directly from Comet Wild 2. All of the Wild 2 particles we have thus far examined have been modified in various ways by the capture process. All particles that may have been loose aggregates, ''traveling sand piles'', disaggregated into individual components with the larger, denser components penetrating more deeply into the aerogel. Individual grains experienced a wide range of heating effects that range from excellent preservation to melting (Fig. 1); such behavior was expected (1, 2 ,3). What is remarkable is the extreme variability of these modifications and the fact that severely modified and unmodified materials can be found within a micrometer of each other, requiring tremendous local temperature gradients. Fortunately, we have an internal gauge of impact collection heating. Fe-Ni sulfides are ubiquitous in the Wild 2 samples, are very sensitive indicators of heating, and accurate chemical analyses can reveal which have lost S, and which have not (and are therefore stoichiometric) (Fig. 2). Our surveys show that crystalline grains are found along the entire lengths of tracks, not just at track termini

Cooperative driving at isolated intersections based on the optimal minimization of the maximum exit time

Traditional traffic control systems based on traffic light have achieved a great success in reducing the average delay of vehicles or in improving the traffic capacity. The main idea of these systems is based on the optimization of the cycle time, the phase sequence, and the phase duration. The right-of-ways are assigned to vehicles of one or several movements for a specific time. With the emergence of cooperative driving, an innovative traffic control concept, Autonomous Intersection Management (AIM), has emerged. In the framework of AIM, the right-of-way is customized on the measurement of the vehicle state and the traffic control turns to determine the passing sequence of vehicles. Since each vehicle is considered individually, AIM faces a combinatorial optimization problem. This paper proposes a dynamic programming algorithm to find its optimal solution in polynomial time. Experimental results obtained by simulation show that the proper arrangement of the vehicle passing sequence can greatly improve traffic efficiency at intersections

LPE GROWTH AND CHARACTERIZATION OF CADMIUM AND BERYLLIUM DOPED InP AND In.7Ga.3As.6P.4

Cet article traite de l'étude des couches épitaxiales de InP et In.7Ga.3As.6P.4 réalisées sur substrat de InP par la technique à deux phases et dopées au beryllium et au cadmium. Après avoir décrit les conditions de croissance propres à l'emploi de ces dopants on analysera les propriétés électriques et optiques de ces couches épitaxiales à la lumière de résultats de mesures de photoluminescence (4,2 K - 300 K) et d'effet Hall (77 K - 300 K). On déterminera les énergies d'ionisation des niveaux accepteurs associés à ces impuretés. On analysera également la variation de la mobilité en fonction du dopage.Properties of cadmium and beryllium doped InP and In.7Ga.3As.6P.4 layers grown by liquid phase epitaxy by the two phase technique will be studied in this paper. Growth conditions related to the use of these dopants will be described. Electrical and optical properties of the grown layers will then be studied from photoluminescence (4.2 K - 300 K) and Hall effect measurements (77 K - 300 K). Ionization energies of the acceptor levels associated to these impurities will be determined. Mobility variation versus doping level will also be studied

EPITAXIE EN PHASE LIQUIDE DE DOUBLES HETEROSTRUCTURES LASER In1-xGaxAsyP1-y/InP (x ≈ 0,5y, y ≈ 0,9) EMETTANT AU VOISINAGE DE 1,55µm ET CARACTERISEES PAR UNE FAIBLE DENSITE DE COURANT DE SEUIL

Cette communication est relative aux problèmes liés à la croissance de doubles hétérostructures laser In1-xGaxAsyP1-y/InP (x ≈ 0,5y, y ≈ 0,9) émettant à une longueur d'onde voisine de 1,55 µm et caractérisées par de faibles densités de courant de seuil (J < 1,5 kA/cm2). On sait que la réalisation de telles structures se heurte principalement au problème de redissolution de la couche active de faible teneur en phosphore par la solution de la couche de confinement