93 research outputs found

    Experimental investigation of paraffin-based fuels for hybrid rocket propulsion

    Get PDF
    Solid fuels for hybrid rockets were characterized in the framework of a research project aimed to develop a new generation of solid fuels, combining at the same time good mechanical and ballistic properties. Original techniques were implemented in order to improve paraffin-based fuels. The first strengthening technique involves the use of a polyurethane foam (PUF); a second technique is based on thermoplastic polymers mixed at molecular level with the paraffin binder. A ballistic characterization of paraffin-based hybrid rocket solid fuels was performed, considering pure wax-based fuels and fuels doped with suitable metal additives. Nano-Al powders and metal hydrides (magnesium hydride (MgH2), lithium aluminum hydride (LiAlH4 )) were used as fillers in paraffin matrices. The results of this investigation show a strong correlation between the measured viscosity of the melted paraffin layer and the regression rate: a decrease of viscosity increases the regression rate. This trend is due to the increasing development of entrainment phenomena, which strongly increase the regression rate. Addition of LiAlH4 (mass fraction 10%) can further increase the regression rate up to 378% with respect to the pure HTPB regression rate, taken as baseline reference fuel. The highest regression rates were found for the Solid Wax (SW) composition, added with 5% MgH2 mass fraction; at 350 kg/(m2s) oxygen mass flux, the measured regression rate, averaged in space and time, was 2.5 mm/s, which is approximately five times higher than that of the pure HTPB composition. Compositions added with nanosized aluminum powders were compared with those added with MgH2, using gel or solid wax

    Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

    Get PDF
    The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota

    Smithian (Early Triassic) ammonoid faunas from exotic blocks from Oman: taxonomy and biochronology

    Full text link
    Ammonoid-rich exotic bocks of Hallstatt facies in Jebel Safra, in Wadi Musjah and at Baid (Oman Mountains) have yielded several well preserved and highly diversified Smithian (Early Triassic) ammonoid faunas (Baidites hermanni fauna, Rohillites omanensis fauna, Flemingites rursiradiatus fauna, Nammalites pilatoides fauna, Owenites koeneni fauna and Anasibirites multiformis fauna). The comparison of these assemblages with data from other Tethyan basins such as the Salt Range, Spiti, Tibet and South China shows that nearly all known Smithian ammonoid faunal assemblages are present in the exotic blocks from Oman. The new Oman data strengthens the remarkably uniform biogeographic distribution of the Smithian ammonoid faunas within the Tethys. One new ammonoid family (Galfettitidae), five new genera (Baidites, Goudemandites, Lucasites, Omanites, Safraites), and twelve new species (Baidites hermanni, Galfettites kyrae, G. omani, Goudemandites sinensis, Kashmirites baidi, Lucasites involutus, L. evolutus, Omanites musjahensis, Paranannites baudi, Pseudaspidites planus, Rohillites omanensis, Safraites simplex) are described. Additionally, a new early Spathian (late Early Triassic) species (Procolumbites safraensis) is described

    New latest Permian foraminifers from Laren (Guangxi Province, South China): palaeobiogeographic implications

    Full text link
    Microfacies analyses performed on the latest Permian Wujiaping Formation at Laren (Guangxi Province, South China) show that the bioclastic-rich limestones of Late Permian age contain a rich and well-diversified foraminiferal fauna. This fauna is here revised in order to be compared with time-equivalent levels of southern Iran and southern Turkey. Some new and unexpected phylogenetic trends are highlighted among the biseriamminoids. The new or poorly known genera Retroseptellina, Septoglobivalvulina, Paraglobivalvulinoides, Dagmarita?, Bidagmarita nov. gen., Louisettita, Paradagmaritopsis nov. gen. and Paradagmarita? are concerned. Nevertheless, these newly appeared biseriamminoids are subordinate to abundant Tetrataxis and Climacammina, ultimate survivors of the families Palaeotextulariidae and Tetrataxidae, appeared as old as the Early Carboniferous (“Mississippian”). Algae, miliolids, and nodosarioids are poorly represented. Two genera and four species are here newly described: Globivalvulina curiosa nov. sp., Louisettita ultima nov. sp., Bidagmarita nov. gen., Bidagmarita sinica nov. gen. nov. sp., Paradagmaritopsis nov. gen., Paradagmaritopsis kobayashii nov. gen. nov. sp. The palaeogeographic distribution of these foraminifers is interpreted to be typically of Neo-Tethyan regions, ranging from southern Turkey (Hazro) to South China (Laren) and up to Japan for some species (i.e., Paradagmaritopsis). At Laren, Late Permian strata are generally characterized by Reichelina ex gr. simplex Sheng. Isolated samples of packstones, collected in Tsoteng region (Guangxi Province, South China), contain Sphaerulina sp. together with various smaller foraminifers and numerous representatives of the new species G. curiosa nov. sp. In this study we demonstrate that the regions of Zagros (Iran), Taurus (Turkey), South China and even Japan shared similar foraminiferal assemblages and represented intermittently connected palaeobiogeographic provinces during Late Permian times. = Dans la rĂ©gion de Laren (Province du Guangxi, Chine du Sud), des microfaciĂšs calcaires bioclastiques renferment jusqu’à la limite Permo-triasique (PTB) de riches faunes de foraminifĂšres. Elles sont rĂ©visĂ©es taxonomiquement afin d’ĂȘtre comparĂ©es aux Ă©lĂ©ments des associations du Sud de l’Iran et du Sud de la Turquie. Des tendances Ă©volutives insoupçonnĂ©es se rĂ©vĂšlent, surtout parmi les bisĂ©riamminoĂŻdes, avec des genres nouveaux ou peu connus : Retroseptellina, Septoglobivalvulina, Paraglobivalvulinoides, Bidagmarita nov. gen., Louisettita, Paradagmaritopsis nov. gen. et Paradagmarita ? Ces taxons inhabituels sont cependant subordonnĂ©s Ă  d’abondants survivants d’autres superfamilles (Palaeotextularioidea et Tetrataxoidea) apparues dĂšs le CarbonifĂšre infĂ©rieur (« Mississippien »), tels que Tetrataxis et Climacammina. Algues, miliolides et nodosarioĂŻdes sont peu reprĂ©sentĂ©s. Six nouveaux taxons sont dĂ©crits : Globivalvulina curiosa nov. sp., Louisettita ultima nov. sp., Bidagmarita nov. gen., Bidagmarita sinica nov. gen. nov. sp., Paradagmaritopsis nov. gen. et Paradagmaritopsis kobayashii nov. gen. nov. sp. La rĂ©partition palĂ©ogĂ©ographique de ces foraminifĂšres est typiquement nĂ©o-tĂ©thysienne, du Sud de la Turquie (Hazro) au Sud de la Chine, voire jusqu’au Japon avec Paradagmaritopsis. Des Ă©chantillons isolĂ©s de packstones collectĂ©s dans une autre rĂ©gion (Tsoteng, Province du Guangxi, Chine du Sud) contiennent Sphaerulina sp. ainsi que de petits foraminifĂšres variĂ©s et de nombreux spĂ©cimens de l’espĂšce nouvelle G. curiosa nov. sp. Dans cette Ă©tude, il est dĂ©montrĂ© qu’au cours du Permien supĂ©rieur, le Zagros (Iran), le Taurus (Turquie), la Chine du Sud (bassin de Nanpanjiang) et mĂȘme le Japon partagent des associations de foraminifĂšres similaires et que ces diverses provinces palĂ©obiogĂ©ographiques Ă©taient pĂ©riodiquement interconnectĂ©es

    Latest Permian calcisponges of Laren, Guangxi Province, South China

    Full text link
    • 

    corecore