527 research outputs found

    The Impact of Climate and Transport on the Compositions and Textures of Heavy Minerals in Modern Rivers of New Zealand

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    The types, abundances and textures of heavy minerals in the 63-125 ÎŒm fraction of modern river sands were investigated in order to assess the controls of climate, tectonic setting, source composition, recycling, transport and diagenesis on the nature of sedimentary systems. Two rivers on the South Island of New Zealand were selected for detailed study; the Haast is a high-flow river located in the high precipitation region near the west coast, whereas the Ahuriri River has lower flow rates and is located in a drier region in the central South Island. In both river systems, the Zircon-Tourmaline-Rutile (ZTR) index increases downstream, illustrating that chemical and mechanical weathering gradually degraded the more unstable mineral species relative to ultrastable zircon. Point counting of the light mineral fractions indicates a downstream increase in quartz compared with feldspar, further suggesting chemical and mechanical weathering processes. Although the Chemical Index of Alteration (CIA) values are not high (average 55 for each river system), the heavy and light mineral data, combined with major element results illustrating an increase in SiO2 with decreasing Al2O3, MgO and Fe2O3 downstream, all indicate a weathering signal. Highly fluctuating patterns in mineralogical and geochemical data suggest bar-to-bar variations consistent with mixing from tributary input. Four heavy mineral types were chosen for textural investigations and include garnet, zircon, titanite and tourmaline. Roundness and etching values for each mineral produced no downstream trends. This discrepancy is attributed to the recycled nature of the source rocks, which are schistose and wacke deposits, as well as input of new source material downstream via tributaries, alluvial fans and erosion of Quaternary and Tertiary deposits. Detailed investigations of sediment sampled from a longitudinal bar in the Haast River show that surface samples have lower roundness and etching values than sediment 10 cm below the surface. This result suggests that mineral alteration takes place within the water-laden bar through diagenetic processes rather than from subaerial chemical weathering

    Analyse de la formation des phases du systĂšme cuivre-germanium par diffraction des rayons X sur des Ă©chantillons d'Ă©paisseur nanoscopique

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    Avec la miniaturisation incessante des circuits dans le domaine de la microĂ©lectronique, pour des raisons de performance et de diminution de coĂ»ts, de nouveaux matĂ©riaux doivent ĂȘtre introduits dans leur fabrication pour pallier diffĂ©rents problĂšmes. La liste des dĂ©fis Ă  relever pour l'avancement de l'industrie de la microĂ©lectronique est tenue par l'ITRS (International Technology Roadmap for Semiconductors), qui met Ă  jour rĂ©guliĂšrement les pistes de solution envisagĂ©es pour chacun des domaines d'intĂ©rĂȘt dans la fabrication de circuits intĂ©grĂ©s, que ce soit la mĂ©tallisation globale ou locale, la largeur de la grille des transistors, l'Ă©paisseur de l'isolant de la grille et les matĂ©riaux la constituant, etc. Un des dĂ©fis majeurs pour les prochaines gĂ©nĂ©rations de dispositifs microĂ©lectroniques est de dĂ©velopper un nouveau matĂ©riau pour remplacer le cuivre dans les interconnexions globales et locales, le cuivre Ă©tant actuellement le principal matĂ©riau conducteur utilisĂ© dans les interconnexions des dispositifs de derniĂšre gĂ©nĂ©ration. Aux dimensions de dispositifs Ă  venir, le cuivre possĂšde certains dĂ©savantages liĂ©s Ă  sa grande diffusivitĂ© dans le silicium, ce qui force l'utilisation de barriĂšres de diffusion d'une Ă©paisseur minimale excessive dans les dispositifs rĂ©cents. Un des matĂ©riaux prometteurs pour remplacer le cuivre est en fait un des composĂ©s binaires du systĂšme cuivre-germanium, soit la phase Δ1-Cu3Ge. À l'Ă©poque oĂč l'industrie cherchait un remplaçant Ă  l'aluminium dans les interconnexions dans les annĂ©es 1990, des travaux avaient rĂ©vĂ©lĂ© sa trĂšs faible rĂ©sistivitĂ© d'environ 5.5ΌΩ∙cm Ă  la tempĂ©rature de la piĂšce [1], sa stabilitĂ© en contact avec le silicium et l'oxyde de silicium [2] et sa stabilitĂ© aux cours de recuits [3]. À l'Ă©poque, le cuivre avait Ă©tĂ© choisi Ă  cause de son avantage au niveau de ses performances Ă©lectriques dues Ă  sa trĂšs faible rĂ©sistivitĂ© de 1.68ΌΩ∙cm Ă  la tempĂ©rature de la piĂšce[4]. L'objectif de ce mĂ©moire est d'Ă©tudier plus en dĂ©tail la formation des phases du systĂšme cuivre germanium, et plus prĂ©cisĂ©ment la phase Δ1-Cu3Ge, pour des applications dans l‟industrie de la microĂ©lectronique. Les tests effectuĂ©s reposent sur l'utilisation de trois techniques de diffraction des rayons X avec source synchrotron, soit la diffraction des rayons X in situ pendant recuit avec mesure simultanĂ©e de la rĂ©sistance par une sonde Ă  quatre pointes, dans le but d'analyser la formation des phases, les balayages Ξ-2Ξ pour obtenir les pics de diffraction des phases prĂ©sentes sur une large plage d'angles de diffraction suite Ă  des trempes et finalement la----------abstract With the miniaturization of electronic devices, driven by cost reduction and performance increase, new materials have to be introduced in their fabrication process to solve many emerging problems. These challenges are brought forth by the ITRS (International Technology Roadmap for Semiconductors), a comity in charge of listing the technological needs for the upcoming generations of integrated circuits. Many fields of interest require new technological developments, from global to local interconnections, the transistor gate, the gate insulator thickness, etc. One of the major challenges mentioned in the ITRS roadmap is the need for a new interconnection material. Indeed, the need for a diffusion barrier for the copper lines in local and global interconnections of integrated circuits, the main technology in today‟s devices, is becoming more hindering with the decrease of the metallization lines‟ cross-section. In the 90‟s, a binary compound of copper and germanium, known as the Δ1-Cu3Ge phase, was investigated as a replacement for aluminum because of its low resistivity, that can reach as low as 5.5ΌΩ∙cm [1], its stability in contact with both silicon and silicon oxide [2] as well as its thermal stability during anneals [3]. However, copper proved to be a better choice at the time because of its low bulk resistivity of 1.68ΌΩ∙cm at room temperature[4]. The objective of this master thesis is to re-examine the copper-germanium system, and more specifically the Δ1-Cu3Ge, for future applications in the microelectronics industry. Different X ray diffraction techniques were used to obtain more information on the system, including in situ X ray diffraction during 3°C/s anneals in an inert helium atmosphere with simultaneous resistance measurement, Ξ-2Ξ scans to detect diffraction peaks of the present phases after sample quenching as well as partial acquisition of the reciprocal space of quenched samples which allowed to obtain pole figures for d-spacings of interest. Results obtained on germanium and copper bilayers of total thicknesses between 20nm and 89nm deposited on an inert silicon nitride layer using magnetron sputtering in an MRC-673 show that with an atomic copper concentration between 72 and 87%, the Δ1-Cu3Ge phase starts to form between 180°C and 210°C during a 3°C/s ramp anneal. At 72% at. copper (50nm thickness) and 75% at. copper (20nm thickness), the Δ1-Cu3Ge phase is stable above 500°C. However, the measured resistance of the 50nm sample is low between 220°C and 500°C whil

    Spin-Orbit induced phase-shift in Bi2_{2}Se3_{3} Josephson junctions

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    The transmission of Cooper pairs between two weakly coupled superconductors produces a superfluid current and a phase difference; the celebrated Josephson effect. Because of time-reversal and parity symmetries, there is no Josephson current without a phase difference between two superconductors. Reciprocally, when those two symmetries are broken, an anomalous supercurrent can exist in the absence of phase bias or, equivalently, an anomalous phase shift φ0\varphi_0 can exist in the absence of a superfluid current. We report on the observation of an anomalous phase shift φ0\varphi_0 in hybrid Josephson junctions fabricated with the topological insulator Bi2_2Se3_3 submitted to an in-plane magnetic field. This anomalous phase shift φ0\varphi_0 is observed directly through measurements of the current-phase relationship in a Josephson interferometer. This result provides a direct measurement of the spin-orbit coupling strength and open new possibilities for phase-controlled Josephson devices made from materials with strong spin-orbit coupling

    Quantum confinement effects in Pb Nanocrystals grown on InAs

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    In the recent work of Ref.\cite{Vlaic2017-bs}, it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a quantum constriction of the electronic wave-function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this manuscript, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by quantum confinement effects in the Pb nanocrystals. We identified three distinct regimes of quantum confinement. For the largest nanocrystals, quantum confinement effects appear through the formation of quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomic-like electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave-functions with a random spatial structure are observed, as expected from Random Matrix Theory.Comment: Main 12 pages, Supp: 6 page

    Ordonnancement de tùches sous contraintes sur des métiers à tisser

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    Dans une usine de production de textile, il y a des mĂ©tiers Ă  tisser. Ces mĂ©tiers Ă  tisser peuvent ĂȘtre configurĂ©s de diffĂ©rentes façons. Des tĂąches doivent ĂȘtre exĂ©cutĂ©es sur ces mĂ©tiers Ă  tisser et le temps d’exĂ©cution d’une tĂąche est fonction du mĂ©tier sur lequel elle est effectuĂ©e. De plus, chaque tĂąche est seulement compatible avec les mĂ©tiers Ă  tisser Ă©tant configurĂ©s de certaines façons. Un temps de mise en course peut permettre de configurer ou prĂ©parer un mĂ©tier Ă  tisser pour l’exĂ©cution d’une tĂąche. Le temps de mise en course est dĂ©pendant de la tĂąche qui prĂ©cĂšde et de celle qui suit. Nous souhaitons alors crĂ©er un horaire pour minimiser les temps de fabrication et les retards. Toutefois, certaines contraintes doivent ĂȘtre respectĂ©es. Lorsque des prĂ©parations surviennent sur des mĂ©tiers diffĂ©rents en mĂȘme temps, le nombre d’employĂ©s doit ĂȘtre suffisant. Un mĂ©tier ne peut faire qu’une seule action Ă  la fois. L’ordonnancement d’une seule machine est un problĂšme NP-Difficile. Dans ce projet, il faut ordonnancer environ 800 tĂąches sur 90 machines dans un horizon de deux semaines, tout en respectant les contraintes de personnel. Des Ă©vĂšnements stochastiques doivent ĂȘtre pris en compte pour obtenir un meilleur horaire. Le bris d’un fil n’étant pas un Ă©vĂšnement rare, l’occurrence des bris est donnĂ©e sous la forme d’une loi de Poisson. Nous proposons alors une approche de rĂ©solution utilisant une heuristique de branchement basĂ©e sur le problĂšme du commis voyageur. Cette approche permet d’obtenir de bonnes solutions pour le problĂšme d’ordonnancement explorĂ©. Les solutions trouvĂ©es sont 5 Ă  30% meilleures en termes de fonction objectif qu’une heuristique semblable Ă  celle utilisĂ©e par l’équipe de planification de notre partenaire industriel. Nous prĂ©sentons aussi un algorithme pour garantir la robustesse d’un horaire. Notre algorithme permet de gĂ©nĂ©rer des horaires plus rĂ©alistes et qui rĂ©sistent bien aux Ă©vĂšnements imprĂ©vus. La combinaison de ces deux pratiques mĂšne Ă  l’intĂ©gration et l’utilisation du produit final par notre partenaire industriel.In a textile factory, there are looms. Workers can configure the looms to weave different pieces of textiles. A loom can only weave a piece of textiles if the piece of textiles is compatible with its loom configuration. To change its configuration, a loom requires a setup. The setups are performed manually by workers. There are also sequence-dependent setups to prepare a loom for the upcoming piece of textiles. We wish to minimize the setups duration and the lateness. A solution must satisfy some constraints. The problem is subject to cumulative resources. The quantity of workers simultaneously configuring machines can’t exceed the total number of employees. A loom can only weave a piece of textiles at a time. Scheduling tasks on a single loom is an NP-Hard problem. In this project, we must schedule tasks an average of 800 tasks on 90 looms with a two-week horizon. Stochastic events might occur and must be accounted for. We must design an algorithm to create robust schedules under uncertainty. As a thread breaking during the weaving process isn’t a rare occurrence, a better schedule could greatly impact the performances of a company when applying the schedule to a real situation. We formulate that the number of breaks per task follows a Poisson distribution. First, we propose a branching heuristic based on the traveling salesperson problem in order to leverage computation times. The solutions found are 5 to 30% better according to their objective function than the ones of a greedy heuristic similar to what our industrial partner uses. We also present a filtering algorithm to guarantee robustness of solutions in respect to a confidence level. This algorithm improves robustness and creates more realist schedules. The algorithm is also efficient in computation time by achieving bound consistency in linear time. Combining both these techniques leads to the integration of our research in the decision system of our industrial partner

    Ecosystem service framework and typology for an ecosystem approach to aquaculture

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    International audienceThe ecosystem approach to aquaculture (EAA) considers ecosystem services (ES) important but does not provide a conceptual framework or a typology to integrate and assess them. To supplement the EAA, a literature review of the ES conceptual framework and ES typologies was combined with selected criteria from the EAA and ES literature. Eight criteria of transition from a conventional approach to aquaculture to the EAA were used as selection criteria to choose a conceptual framework of ES relevant with the EAA. To select a typology, we determined that ES must be distinguished from benefits, be a part of nature, be usable directly and indirectly, and not contain support or habitat ES. The conceptual framework of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) is the most compatible with the EAA but does not provide an ES typology. The Common International Classification of Ecosystem Services (CICES) provides the ES typology most consistent with EAA criteria to supplement the conceptual framework. We identified 10 provisioning ES, 20 regulation and maintenance ES, and 11 cultural ES. Integration of the IPBES conceptual framework with the CICES typology preserves the generic approach of the EAA. This integration could highlight the main interactions among an aquaecosystem, its ES supply, its management, and its relevant stakeholders at multiple spatial and temporal scales. Moreover, it fulfils the three main goals of the EAA by identifying them in a clear and common framework

    Two-Connected Graphs with Given Diameter

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    The problem we study in this work is an extremal problem arising from graph theory : what is the minimum number of edges of a 2-connected graph satisfying diameter conditions. This problem deals with survivable netowrk design when the network is subjected to satisfy grade of service constraints. One way to provide networks working when some failures arise is to provide a sufficient connectivity to the networks. Due to equipment robustness 2-connectivity or 2-edge-connectivity will be sufficient. Notice that k-connected networks, k≄\geq3, will provide too expensive networks. Another important parameter is the crossing-delay, ie the total amount of time spent in the network by some data packet to reach its destination from its origin. In order to keep this crossing-delay under reasonable values one can bound the number of hops of a routing path. This leads to bound the diameter of the underlying graph. We prove the following bounds : if GG is 2-(vertex)-connected, then |E|\geq\lceil\fracnD-(2D+1){D-1}\rceil, if GG is 2-edge-connected of odd diameter, then |E|\geq\lceil\fracnD-(2D+1){- D-1}\rceil, if GG is 2-edge-connected of even diameter, then |E|\geq min(\lceil\fracnD-(2D+1){D-1}\rceil,\lceil\frac{(n-1)(D+1)}{D}\rceil)