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91.
92.
Naomi Murdoch Patrick Michel Derek C. Richardson Kerstin Nordstrom Christian R. Berardi Simon F. Green Wolfgang Losert 《Icarus》2012,219(1):321-335
Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small-body evolution thus contributing to their geological properties.We demonstrate that the new adaptation of the parallel N-body hard-sphere code pkdgrav has the capability to model accurately the key features of the collective motion of bidisperse granular materials in a dense regime as a result of shaking. As a stringent test of the numerical code we investigate the complex collective ordering and motion of granular material by direct comparison with laboratory experiments. We demonstrate that, as experimentally observed, the scale of the collective motion increases with increasing small-particle additive concentration.We then extend our investigations to assess how self-gravity and external gravity affect collective motion. In our reduced-gravity simulations both the gravitational conditions and the frequency of the vibrations roughly match the conditions on asteroids subjected to seismic shaking, though real regolith is likely to be much more heterogeneous and less ordered than in our idealised simulations. We also show that collective motion can occur in a granular material under a wide range of inter-particle gravity conditions and in the absence of an external gravitational field. These investigations demonstrate the great interest of being able to simulate conditions that are to relevant planetary science yet unreachable by Earth-based laboratory experiments. 相似文献
93.
Abstract. The synaptid holothuroid Leptosynapta inhaerens has the ability to expel unwanted particles that enter its body cavity. Intracoelomic particles ( viz. experimentally injected carmine particles) are trapped either by a coelom-produced mucoid net or by specialized organs (the vibratile urnae) that occur in bands in some interradial areas. Whatever the trapping method, particles are incorporated into dense mucoid masses that move towards the posterior part of the body cavity, in the vicinity of the rectum. These aggregates then cross the rectal wall through rectal pores, mix with the faeces, and are eventually incorporated into the wall of the synaptid burrow. Clearance of foreign particles requires 2 to 3 days. The coelom-cleaning system of synaptids appears to be the most effective within the class Holothuroidea , being well designed for endofaunal organisms whose walls are delicate and easily rupture. 相似文献
94.
Organic carbon in oxidizable forms and nitrogen are the only elements among some 40 elements studied that are significantly enriched in terrestrial soils as compared to the crust. This enrichment is due to and reflecting life activity in soils, and is characterized by a unique profile distribution. It is suggested that these facts can constitute the basis for the future chemical-biological search for life in planetary soils. 相似文献
95.
Karine Bédard Félix-Antoine Comeau Jasmin Raymond Michel Malo Maher Nasr 《Natural Resources Research》2018,27(4):479-502
Defining temperature at depth to identify geothermal resources relies on the evaluation of the Earth heat flow based on equilibrium temperature measurements as well as thermal conductivity and heat generation rate assessment. Such high-quality geothermal data can be sparse over the region of interest. This is the case of the St. Lawrence Lowlands sedimentary basin covering 20,000 km2 to the south of Québec, Canada, and enclosing only three wells up to a depth of 500 m with equilibrium heat flow measurements. However, more than 250 oil and gas exploration wells have been drilled in this area, providing for this study (parce que c'est 93 sinon) 81 locations with bottom-hole temperature up to a depth of 4300 m, however, not at equilibrium. Analyzing these data with respect to the deep geothermal resource potential of this sedimentary basin requires evaluating the thermal conductivity and heat generation rate of its geological units to properly extrapolate temperature downward. This was done by compiling literature and recent thermal conductivity measurements in outcrop and core samples as well as new heat generation rate estimates from spectral gamma ray logs to establish a first thermal assessment of geological units deep down into the basin. The mean thermal conductivity of the thermal units varies from 2.5 to 6.3 W/m·K, with peak values in the basal sandstones, while the heat generation rate varies from 1.6 to 0.3 µW/m3, decreasing from the upper caprocks toward the base of the sequence. After correcting the bottom-hole temperatures for drilling disturbance with the Harrison correction and subsequently for paleoclimate variations, results indicate a mean geothermal gradient of 23.1 °C/km, varying from 14 to 40 °C/km. Evaluating the basin thermal state from oil and gas data is a significant challenge facilitated by an understanding of its thermal properties. 相似文献
96.
Direct measurements of plasma motions in the photosphere are limited to the line-of-sight component of the velocity. Several algorithms have therefore been developed to reconstruct the transverse components from observed continuum images or magnetograms. We compare the space and time averages of horizontal velocity fields in the photosphere inferred from pairs of consecutive intensitygrams by the LCT, FLCT, and CST methods and the DeepVel neural network in order to identify the method that is best suited for generating synthetic observations to be used for data assimilation. The Stein and Nordlund (Astrophys. J. Lett.753, L13, 2012) magnetoconvection simulation is used to generate synthetic SDO/HMI intensitygrams and reference flows to train DeepVel. Inferred velocity fields show that DeepVel performs best at subgranular and granular scales and is second only to FLCT at mesogranular and supergranular scales. 相似文献
97.
Christian Ferrarin Georg Umgiesser Andrea Cucco Tai-Wen Hsu Aron Roland Carl L. Amos 《Coastal Engineering》2008
Recognising the importance of understanding sediment dynamics to evaluate the status of a coastal lagoon environment, this work has been focused on the investigation of the hydrodynamic and sediment transport processes occurring in such basins. In order to describe the lagoon system, a modelling approach combining hydrodynamics, waves and sediment dynamics has been developed. The framework of the numerical model consists of a finite element hydrodynamic model, a third generation finite element spectral wave model and a sediment transport and morphodynamic model for both cohesive and non-cohesive sediments. The model adopts the finite element technique for spatial integration, which has the advantage to describe more accurately complicated bathymetry and irregular boundaries for shallow water areas. The developed model has been applied to test cases and to a very shallow tidal lagoon, the Venice Lagoon, Italy. Numerical results show good agreement with water level, waves and turbidity measurements collected in several monitoring stations inside the Lagoon of Venice. Such a model represents an indispensable tool in analysing coastal problems and assessing morphological impacts of human interference. 相似文献
98.
99.
Frdric Gazeau Stephen V. Smith Bernard Gentili Michel Frankignoulle Jean-Pierre Gattuso 《Estuarine, Coastal and Shelf Science》2004,60(4):673-694
The geomorphic, oceanographic, terrestrial and anthropogenic attributes of the European coastal zone are described and published data on ecosystem function (primary production and respiration) are reviewed. Four regions are considered: the Baltic Sea, Mediterranean Sea, Black Sea and the European Atlantic coast including the North Sea. The metabolic database (194 papers) suffers from a non-homogeneous geographical coverage with no usable data for the Black Sea which was therefore excluded from this part of our study. Pelagic gross primary production in European open shelves is, by far, the most documented parameter with an estimated mean of 41 mmol C m−2 d−1, the lowest value is reported in the Mediterranean Sea (21 mmol C m−2 d−1) and the highest one in the Atlantic/North Sea area (51 mmol C m−2 d−1). Microphytobenthic primary production, mostly measured in shallow areas, is extrapolated to the entire 0–200 m depth range. Its contribution to total primary production is low in all regions (mean: 1.5 mmol C m−2 d−1). Although macrophyte beds are very productive, a regional production estimate is not provided in this study because their geographical distribution along the European coastline remains unknown. Measurements of pelagic community respiration are clearly too sparse, especially below the euphotic zone, to yield an accurate picture of the fate of organic matter produced in the water column. With a mean value of 17 mmol C m−2 d−1, benthic community respiration consumes approximately 40% of the pelagic organic matter production. Estuaries generally exhibit high metabolic rates and a large range of variation in all parameters, except microphytobenthic primary production. Finally, the problem of eutrophication in Europe is discussed and the metabolic data obtained in the framework of the Land–Ocean Interactions in the Coastal Zone (LOICZ) project are compared with available direct measurements of net ecosystem production. 相似文献
100.
Michel Dupuy 《Journal of Geodesy》1952,26(3):345-357
Résumé La simplicité du calcul de la réduction au plan est une des qualités pratiques les plus importantes dans toute projection
géodésique. Comme les calculs sont à l'heure actuelle entièrement effectués en coordonnés rectangulaires, la réduction au
plan demande à être calculée exclusivement à partir des dits éléments: telle est bien du reste la situation en ce qui concerne
la projection de Mercator Transverse, communément employée.
Pour la projection conique conforme deLambert, officiellement employée pour la triangulation fran?aise, on obtient une formule commode en introduisant l'aire triangulaire
comprise entre le sommet de la projection conique (image du p?le) et les stations AB à relier. Le présent acticle justifie
cette formule, décrit son application par la section de Géodésie de l'Institut Géographique National, et spécifie les formules
de moyenne à employer: cette note forme un ensemble avec l'article suivant deM. Dufour.
Summary Simplicity of calculation in the plane is one of the most important characteristics of any surveyor's projection. Since all calculation is today carried out in terms of rectangular coordinates, any reduction to the plane should involve only these coordinates: and this is, in fact, the situation in the commonly employed Transverse Mercator projection. For theLambert Conical orthomorphic projection, officially used for the French triangulation, a convenient formula is obtained in terms of the area of the triangle formed by the two points concerned and the vertex of the projection (which represents the pole in the plane). This paper justifies the use of the formula; describes its application by the Institut Géographique National; and discusses the different mean value formulae which are suited to the various grades of accuracy desired. This paper should be considered together with that ofM. Dufour.
Zusammenfassung In jeder geod?tischen Projektion besteht das Haupterfordernis für eine praktische Durchführung darin, da? die Berechnung der Reduktionen auf die Ebene m?glichst einfach sei. Da gegenw?rtig alle Rechnungen mit Hilfe von rechtwinkligen Koordinaten durchgeführt werden, mu? die Reduktion auf die Ebene ausschlie?lich von den genannten Elementen ausgehen. So liegen jedenfalls die Dinge bei der gemeinhin verwendeten Transversalen Mercator-Projektion. Für die Lambertsche konforme Kegelprojektion, die amtliche Projektion für das franz?sische Dreiecksnetz, erh?lt man eine zweckdienliche Formel, wenn man die Dreiecksfl?che zwischen dem Scheitelpunkt der Kegelprojektion (Bildpunkt des Poles) und den zu verbindenden Stationen A B benutzt. Der vorliegende Artikel begründet diese Formel, beschreibt ihre Verwendung durch die Geod?tische Abteilung des Franz?sischen Instituts für Geographie (Section de Géodésie de l'Institut Géographique National) und erl?utert die zu verwendenden Mittelwert-Formeln. Der Aufsatz geh?rt mit dem folgenden vonM. Dufour geschriebenen eng zusammen.
Resumen La sencillez del cálculo de la reducción al plano es una de las condiciones prácticas más importantes en toda proyección geodésica. Como actualmente están efectuados los cálculos en coordenadas rectangulares, la reducción al plano exige ser calculada exclusivamente a partir de dichos elementos; tal es por lo demás la situación en lo que concierne a la proyección deMercator Transverse, comúnmente empleada. Para la proyección cónica conforme deLambert, oficialmente empleada para la triangulación francesa, se obtiene una fórmula cómoda introduciendo el área triangular comprendida entre el vértice de la proyección cónica (imagen del polo) y las estaciones A y B a enlazar. El presente articulo justifica esta fórmula, y describe su aplicación por la Sección de Geodesia del Instituto Geogróafico Nacional.
Sommario La semplicità del calcolo delle riduzioni al piano è una delle qualià pratiche più importanti in ogni proiezione geodetica. Poichè attualmente tutti i calcoli di una triangolazione vengono effettuati sul piano, in coordinate rettangolari, è essenziale che tali riduzioni possano avvenire facendo ricorso ai soli elementi piani; come accade in particolare per la proiezione trasversa di Mercatore. Per la proiezione conica conforme diLambert, usata ufficialmente uella triangolazione francese, si ottiene una formula comoda per la riduzione alla corda introducendo l'area del triangolo formalo dall' immagine del polo, e dai due punti da collegare. L'articolo giustifica questa formula, ne descrive la sua applicazione da parte della Sezione Geodetica dell' Istituto Geografico Nazionale, e precisa le formule da impiegare. Esso è collegato con l'articolo seguente del sig.Dufour, col quale forma un tutto unico.相似文献