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GEOSUR: Mesozoic to Quaternary evolution of Tierra del Fuego and neighbouring austral regions II
No full textGEOSUR2004: Mesozoic to Quaternary evolution of Tierra del Fuego and neighboring austral regions I
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Structural geology of the Fuegian Andes and Magallanes fold-and-thrust belt – Tierra del Fuego Island
Full text linkA synthesis of the structural geology of the Tierra del Fuego Island, which integrates a new data set derived from field surveys and literature data of the last few years, is here presented. The main geological features of the region developed during the Mesozoic-Cenozoic Andean orogenic cycle that started in the Middle to Late Jurassic with a back-arc extension, crustal stretching and widespread volcanism, related to the break-up of Gondwanaland. An extensional fault system deriving from the mechanical and thermal subsidence led the evolution of the Rocas Verdes marginal basin, which hosts the upper Jurassic volcanoclastic rocks, the lower Cretaceous turbiditic sequences and few isolated elongated ophiolitic complexes. From the Late Cretaceous onward, the orogenic cycle of the Fuegian Andes continued with the shortening and inversion of the back-arc margin through horizontal contraction and crustal thickening. The uplift of the Cordillera, the emplacement of plutonic rocks, and the intracontinental polyphase deformation resulted from thick-skinned tectonics. The thrust system developed from its deeper roots, where the Palaeozoic basement was involved in compressional deformation, and propagated to the shallower stratigraphic levels of the northward verging Magallanes fold-and-thrust belt. The Magallanes foreland basin developed in front of the orogenic wedge that records at least four syntectonic angular unconformities from Late Cretaceous to Lower Miocene. During the Late Cretaceous Andean compression, three distinct phases of penetrative ductile deformation defined by low-greenschist facies assemblages took place, both in the basement and in the cover units. These deformations are related to a single metamorphic event with foliation development, as observed from microscopic analysis of the schist in the Ushuaia area. The first foliation S1 is preserved either as relic sericite microfolds between microlithons of the dominant S2, or as early refolded veins of recrystallized quartz. The S2 foliation is defined by oriented white mica. The crenulation of S2, which is related to D3 and occurs in most strained zones, becomes a pressure solution S3 spaced foliation, lined by opaque minerals. From the Palaeogene to the present, EW sinistral wrench tectonics affected the region as a component of the relative motion between South America and the Antarctic Peninsula. This strike-slip activity is well documented from the Carbajal valley to the Canal de Beagle region south of the Magallanes-Fagnano transform fault system. Restraining bends and overlapping step-over geometry characterize few sectors of the strike-slip faults with pop-ups, pressure ridges and uplifted slivers of crust. Releasing step-over along the transform fault system, both in on-shore and off-shore zones, formed several elongated pull-apart basins with many tens of km in length and a few km in width. The Lago Fagnano represents the main morphotectonic expression of this structural setting. A N-S geological cross-section through the Fuegian Andes synthesizes all the geological and geophysical data. The major stacks of internal thick-skinned basement involved in the thrusting are high-grade Upper Palaeozoic to Lower Tertiary metamorphic rocks. The geometry of the thrust complex is an upright, south plunging monocline of moderately tilted sedimentary cover strata, as well as related thrusts, faults and chevron folds involving the Upper Jurassic and Cretaceous rocks. The orogenic shortening of the Fuegian Andes, including the Cordillera and the Magallanes fold-and-thrust belt, reaches few hundred kilometers with a left-lateral wrenching component of many tens of meters. The Tierra del Fuego Island is characterized by low magnitude (M<3.5) and shallow crustal earthquakes. The southern part presents strong morphological evidence of Quaternary activity, related to the E-W left-lateral strike-slip faults. The actual deformation pattern presents a horizontal slip component of about 6 mm/year. Moreover, the northern sector of the Island is affected by extensional tectonics related to the normal fault systems of the eastern arms of the Magallanes Strait
Influence of PbLi hydraulic path and integration layout on MHD pressure losses
No full textA critical point in the design of liquid metal blankets for fusion reactors is the accurate estimate of magnetohydrodynamic (MHD) pressure losses caused by the interaction between flowing breeder and magnetic field. In the Water-Cooled Lithium Lead (WCLL), the liquid metal (PbLi) is used as tritium breeder and carrier, whereas power extraction is delegated to water, thus allowing to minimize the breeder velocity. However, pressure drop for the PbLi loop is expected to remain significant due to high field intensity and direct electrical contact at fluid/wall interface. In this study, a comparative analysis between four alternative WCLL-DEMO configurations is performed to investigate the influence of blanket layout and piping system integration on this variable. Empirical and semi-empirical correlations, supported by numerical simulation results, have been used to estimate the baseline MHD loss, thus neglecting secondary contributions from viscous, inertial, and coupling effects. The larger contribution has been observed in the connection pipes, which are characterized by extensive length, high velocity, and large field gradients. Integration scheme with DEMO reactor is also a key factor, whereas breeding zone and manifold layout play secondary, albeit significant, roles in determining overall MHD loss. Adopting insulating elements in feeding and draining pipes should be carefully considered to reduce PbLi pumping requirements. Further numerical and experimental characterization of 3D MHD flow in manifolds and for coupling phenomena is vigorously suggested to reduce the uncertainty about blanket flow distribution and pressure loss estimate
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dystonia: Are animal models relevant in therapeutics?
No full textDystonia refers to a heterogeneous group of movement disorders characterized by involuntary, sustained muscle contractions leading to repetitive twisting movements and abnormal postures. A better understanding of the etiology, pathogenesis and molecular mechanisms underlying dystonia may be obtained from animal models. Indeed, while studies in vitro using cell and tissue models are helpful for investigating molecular pathways, animal models remain essential for studying the pathogenesis of these disorders and exploring new potential treatment strategies. To date, the mouse is the most common choice for mammalian models in most laboratories, particularly when manipulations of the genome are planned. Dystonia animal models can be classified into two categories, etiological and symptomatic, although neither is able to recapitulate all features of these disorders in humans. Nevertheless, etiological and symptomatic animal models have advantages and limitations that should be taken into consideration according to the specific proposed hypothesis and experimental goals. Etiological mouse models of inherited dystonia can reproduce the etiology of the disorder and help to reveal biochemical and cellular alterations, although a large majority of them lack motor symptoms. Conversely, symptomatic models can partially mimic the phenotype of human dystonia and test novel pharmacological agents, and also identify the anatomical and physiological processes involved, although the etiology remains unknown. Thus, our brief survey aims to review the state of the art as regards most of the commonly used animal models available for dystonia research. (C) 2018 Elsevier Masson SAS. All rights reserved
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