Search results for "Rust"
showing 10 items of 1659 documents
Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordo…
2001
Abstract This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in the Eastern Erzgebirge region. Metamorphism has strongly disturbed the primary petrological genetic characteristics of the rocks. We compare geological, geochemical, and petrological data, and zircon populations as well as isotope and geochronological data for the major gneiss units of the Eastern Erzgebirge; (1) coarse- to medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer Grey Gneiss”, and (3) “Red Gneiss”. The Inner and Outer Grey Gneiss units (MP–MT overprinted) have very similar geochemical and mineralogical compositions, but they contain different zircon populations…
Recycling in the subduction factory: Archaean to Permian zircons in the oceanic Cretaceous Caribbean island-arc (Hispaniola)
2018
Abstract Little mineralogical evidence is left of the recycling of continental and oceanic crust into the mantle at subduction zones. Zircon, because of its exceptional robustness, is probably the only surviving phase and the best mineral tracer of this global-scale process. This article combines new in-situ U-Pb dating and O and Hf isotope analyses on Cretaceous (co-magmatic) and pre-Cretaceous (inherited) zircons separated from Albian-Aptian arc-related igneous rocks from the Dominican Republic. The O and Hf systematics of Cretaceous zircons reflect derivation from predominantly juvenile sources and variable mixing with evolved melts, as expected for an oceanic island-arc. Inherited zirco…
Cold plumes trigger contamination of oceanic mantle wedges with continental crust-derived sediments: Evidence from chromitite zircon grains of easter…
2018
The origin of zircon grains, and other exotic minerals of typical crustal origin, in mantle-hosted ophiolitic chromitites are hotly debated.We report a population of zircon grains with ages ranging from Cretaceous (99 Ma) to Neoarchean (2750 Ma), separated from massive chromitite bodies hosted in the mantle section of the supra-subduction (SSZ)-type Mayarí-Baracoa Ophiolitic Belt in eastern Cuba. Most analyzed zircon grains (n = 20, 287 +/- 3 Ma to 2750 +/- 60 Ma) are older than the early Cretaceous age of the ophiolite body, show negative εHf(t) (+/-26 to +/-0.6) and occasional inclusions of quartz, K-feldspar, biotite, and apatite that indicate derivation from a granitic continental crust…
Zvaigžņotā Debess: 2007, Rudens
2007
Latvijas Zinātnes padome, Latvijas Universitāte
3D Geosynchronous Transfer of a Satellite: Continuation on the Thrust
2003
The minimum-time transfer of a satellite from a low and eccentric initial orbit toward a high geostationary orbit is considered. This study is preliminary to the analysis of similar transfer cases with more complicated performance indexes (maximization of payload, for instance). The orbital inclination of the spacecraft is taken into account (3D model), and the thrust available is assumed to be very small (e.g. 0.3 Newton for an initial mass of 1500 kg). For this reason, many revolutions are required to achieve the transfer and the problem becomes very oscillatory. In order to solve it numerically, an optimal control model is investigated and a homotopic procedure is introduced, namely cont…
Energy minimization of single input orbit transfer by averaging and continuation
2006
AbstractThis article deals with the transfer between Keplerian coplanar orbits using low propulsion. We focus on the energy minimization problem and compute the averaged system, proving integrability and relating the corresponding trajectories to a three-dimensional Riemannian problem that is analyzed in details. The geodesics provide approximations of the extremals of the energy minimization problem and can be used in order to evaluate the optimal trajectories of the time optimal and the minimization of the consumption problems with continuation methods. In particular, minimizing trajectories for transfer towards the geostationary orbit can be approximated in suitable coordinates by straig…
Time Versus Energy in the Averaged Optimal Coplanar Kepler Transfer towards Circular Orbits
2015
International audience; The aim of this note is to compare the averaged optimal coplanar transfer towards circular orbits when the costs are the transfer time transfer and the energy consumption. While the energy case leads to analyze a 2D Riemannian metric using the standard tools of Riemannian geometry (curvature computations, geodesic convexity), the time minimal case is associated to a Finsler metric which is not smooth. Nevertheless a qualitative analysis of the geodesic flow is given in this article to describe the optimal transfers. In particular we prove geodesic convexity of the elliptic domain.
On the optimal control of the circular restricted three body problem
2011
The context of this work is space mechanics. More precisely, we aim at computing low thrust transfers in the Earth-Moon system modeled by the circular restricted three-body problem. The goal is to calculate the optimal steering of the spacecraft engine with respect to two optimization criteria: Final time and fuel consumption. The contributions of this thesis are of two kinds. Geometric, first, as we study the controllability of the system together with the geometry of the transfers (structure of the command) by means of geometric control tools. Numerical, then, different homotopic methods being developed. A two-three body continuation is used to compute minimum time trajectories, and then …
Time minimization versus energy minimization in the one-input controlled Kepler problem with weak propulsion
2014
International audience
Vitesse et cyclicité de fonctionnement des failles normales de rift : implication sur le remplissage stratigraphique des bassins et sur les modalités…
2002
Les objectifs de ce travail sont les suivants. 1- Reconstitution de la géométrie syn-rift du demi-graben de Bourg-d 'Oisans 2- Quantification des vitesses de fon ctionnement des failles normales syn-rift 3- Relation entre vitesse de fonctionnement et processus de croissance des failles normales dans la croûte continentale 4- Reconstitution de la géométrie profonde des failles normales 5- Caractérisation des facteurs de contrôle de l'étirement crustal en contexte de rift 6- Variabilité spatiale et temporelle de l'étirement sur une paléomarge. Secteur d'étude Pour répondre aux différentes problématiques évoquées ci-dessus, le choix du secteur d'étude s'est porté sur le bassin de Bourg-d'Oisan…