共查询到20条相似文献，搜索用时 46 毫秒
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Many authors have explained the Gibraltar arc in various manners. It is our purpose to set up an explanation which takes into account the recent geological discoveries about the Geology of this region, and the concept of Plate Tectonics. Stratigraphic, metamorphic and structural arguments support the fundamental opposition between internal and external zones in the Betic-Rif mountain system. Internal zones, clearly showing an arcuate structure, were built before Miocene. External zones, on the contrary, were folded mainly during Middle Miocene. Both zones have been involved in important shortening (with strike-slip faulting) just before Messinian (late Miocene). Taking into account the later deformations, we can assume that the internal zones constituted, at the beginning of the Miocene, the sub-plate of Alboran, which separated, eastwards from the Azores transform-fault, the European and African plates. According to this model, we can suppose the Alboran sub-plate to be fixed, whereas the European and African plates move eastwards. So, tectonic structures oblique to the direction of drift, like folds and thrusts along a transcurrent-fault, appear along the north-western and south-western margins of the Alboran sub-plate; along its western margin, N-S structures form, thrusting towards the west. Our geometrical model is able to account for peculiar and unexplained structures of this region. Because of its simplicity, we are conscious of the limits of our explanation, but it seems to us to be a valuable working hypothesis, which needs further geophysical and geological tests. 相似文献
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The evolution of the trophic state of a part of the Lake of Neuchâtel was investigated by means of a study of 4 parameters (temperature, dissolved oxygen, total phosphorus and nitrates) in the waters of the Auvernier Bay (fig. 1). Each year is composed of a stratification period (June to November) and a circulation period (December to May) (fig. 2). Notwithstanding the heavy consumption of oxygen in the metalimnion during the stratification period, the waters are sufficiently abundant in dissolved oxygen (fig. 3). As a matter of fact, over the 12-year period studied, no decrease in the oxygen content was observed at any depth (fig. 4). On the other hand, the quantities of nutrients were enriched in nitrates (30%) and phosphorus (230%) (fig. 5–8). The Auvernier Bay may be thought to have evolved from an oligotrophic state in 1963 to an eutrophic state in 1972 if we consider only these latter two criteria. 相似文献
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Dr Par Claude Lang 《Aquatic Sciences - Research Across Boundaries》1986,48(1):64-70
Zoobenthic communities were used to indicate the trophic state of three mountain lakes of western Switzerland. In these lakes,
the macrobenthos was constituted mainly by oligochaetes and chironomid larvae;Tubifex tubifex was the most abundant worm species. In Lakes Lioson and Hongrin, the abundance of zoobenthos did not change or increased
slightly with depth andStylodrilus heringianus was present. In Lake Chavonnes, zoobenthos decreased strongly with depth and it consisted mainly ofTubifex tubifex. These data, compared with those from other oligotrophic lakes, indicated that Lake Chavonnes was eutrophic whereas Lakes
Lioson and Hongrin were oligotrophic. However, Lake Hongrin—an artificial lake made in 1968—constituted a special case. Its
water comes in part from mountain rivers and in part from Lake Geneva. Consequently, some benthic species of Lake Geneva have
colonized Lake Hongrin and its water is warmer than in a typical mountain lake.
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Prof. Dr. P. L. Mercanton 《Pure and Applied Geophysics》1950,18(1):170-174
Summary Thirty years ago, when no easy and efficient process of sounding could reveal them the true depth of a glacier,C. Somigliana tried to help the glaciologist with a formula giving them the maximal thickness of any transverse section. Requisites were: breadth, maximal velocity, slope and coefficient of internal friction to be known. Commanding condition: no gliding of the ice on the glacier-bed. Numerous recent soundings of Swiss ice-streams did afford the opportunity of verifying the pertinency of the formula. Therefore the writer selected sixteen of the most reliable soundings and reckoned the values of the coefficient of viscosity . The results have been deceptive: if however the mean value of differs not much from 1014 CGS usually accepted (afterLagally), the divergencies are very great, extending from less than the half to almost the double (The same is been shown for the recent formulae ofHaefeli andKoechlin). Therefore no secure number can be derived for the required depth. The condition of no gliding is mostly not realized and the are therefore lessened. If however the real value of for the ice can ever be ascertained it will be possible to reckon the velocity of the up to now unmeasured gliding of the ice on the bed. 相似文献
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Whitefish larvae (Coregonus sp.) were caught at regular intervals in 1986 and 1987 in oligotrophic Lake Sarnen, and in 1987 in eutrophic Lake Hallwil.The food spectra of the larvae in each lake were directly related to the available prey organisms.The causes for the important decrease of the larval catches in Lake Sarnen observed in 1987 are examined.There was no significant difference in the abundance and size distribution of the principal zooplankton taxa between the 1986 and 1987 samples. The effects of a sudden cooling of the surface water layer on the survival of cold-bred whitefish larvae are discussed. 相似文献
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Prof. Antonio Gião 《Pure and Applied Geophysics》1957,37(1):237-267
Résumé Le but de ce mémoire est de démontrer quelques nouvelles propriétés générales d'une classe de fonctions (les ondes de surface) très importante par son rôle en physique et en géophysique.On commence par la démontration d'un théoréme fondamental qui établit l'identité de l'ensemble des ondes de surface et de l'ensemble des fonctions pour lesquelles, à tout instantt
0 et en tout pointA
0 de leur domaine d'existence, on peut écrire une proportionnalité entre intervalles de temps (situés, en général asymétriquement, de part et d'autre det
0) et rayons des domaines circulaires centrés enA
0, telle que les moyennes temporelles et spatiales correspondantes soient égales. Ce théorème permet d'écrire, en termes finis, la solution des équations aux dérivées partielles de toute onde de surface.On applique ensuite les résultats généraux: 1° à la variation diurne de la pression lce qui permet de voir que ce phénomène peut être considéré comme une onde de surface et donne la loi fondamentale en cos3 ( latitude) pour l'amplitude de l'onde semidiurne progressive]; 2° aux ondes de variation de la pression synoptique. Pour ces ondes de variation on établit les relations qui existent entre leurs paramètres caractéristiques et on détermine finalement leur configuration théorique.
Communication faite le 23 Avril 1957 à la Cinquième Assemblée de la «Società Italiana di Geofisica e Meteorologia» (Genova, 23–25 Avril 1957). 相似文献
Summary The aim of this paper is to give the proof of some new general properties of a class of functions (the surface waves) which is very important in physics and geophysics.We first give the proof of a fundamental theorem establishing the identity of the set of all surface waves and the set of functions for which, at any momentt 0 and at any pointA 0 of their domain, there exists a proportionality between time intervals comprisingt 0 (asymmetrically, in the general case) and the radius of the circular domains centered onA 0, such that the corresponding temporal and spatial means are equal. This theorem allows to write in finite terms the solution of the partial differential equations of any surface wave.The general results are then applied: 1° to the diurnal pressure variation, showing that this phenomenon can be considered as a surface wave and giving the fundamental law cos3 ( latitude) for the amplitude of the progressive or travelling 12-hourly wave; 2° to the waves of the synoptic pressure variations. For these waves the relations between their characteristic parameters is first established and finally their theoretical spatial configuration or pattern is deduced.
Communication faite le 23 Avril 1957 à la Cinquième Assemblée de la «Società Italiana di Geofisica e Meteorologia» (Genova, 23–25 Avril 1957). 相似文献
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Le coefficient de compacité de Gravelius: analyse critique d'un indice de forme des bassins versants
Résumé Les classiques de l'hydrologie proposent, pour caractériser la géométrie d'un bassin versant, différents indices de forme destinés à comparer les bassins voire à estimer certaines de leurs caractéristiques hydrologiques. L'indice auquel il est le plus communément fait référence est l'indice de compacité, dit de Gravelius. Il est défini comme le rapport du périmètre du bassin étudié à celui d'un cercle de même surface. L'approche par la géométrie fractale amène à s'interroger sur la validité de cet indice. En effet, dans la définition précédente, seule la surface du bassin est une grandeur bien définie. Sa mesure est bien sûr entachée d'une incertitude mais il est possible d'en déterminer par exemple un minorant et un majorant. Le périmètre est par contre totalement dépendant de sa jauge de mesure et n'a donc aucun caractère objectif, ce qui retire toute signification à l'indice ainsi construit. 相似文献
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The behaviour and estimation of pollutant transport with water in an aquifer are based on the determination of displacement parameters (velocity field, dispersion tensor, kinematic porosity, etc.). We consider the one-dimensional and isothermal displacement of two miscible fluids through an isotropic and homogeneous porous medium in mechanical dispersion. An in situ measurement technique coupled with an impulse response method is used to verify the theoretical solution in the error function (trace case). With viscosity and density gradients, experimental and numerical (application of instability criterion) results are in good agreement. For a quasi-stable displacement, we have shown an asymptotic dispersion regime. The localization of a pollutant front in the studied configuration, is discussed.
Abstract
Le transfert d'un polluant par l'eau dans un milieu naturel repose sur la détermination des paramètres de déplacement (champ des vitesses tenseur de dispersion, porosité cinematique, ...). On considère un écoulement unidimensionnel et isotherme de deux fluides miscibles dans un milieu poreux homogène et isotrope en régime de dispersion mécanique. Une technique de mesure in situ couplée avec une méthode de réponse impulsionnelle a permis de vérifier la solution analytique en fonction erreur (cas du traceur). Dans le cas d'un déplacement avec contrastes de densité et de viscosité, les résultats expérimentaux et numériques (application d'un critère d'instabilité) concordent. Pour un déplacement quasi-stable, nous avons mis en évidence un régime de dispersion asymptotique. Nous analysons, ensuite, la localisation d'un front de pollution dans la configuration étudiée. 相似文献
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Resume La convection de la vapeur d'eau formée en profondeur dans une zone fumerollienne crée en surface une anomalie hydrique, thermique et électrique, cette dernière pouvant être la plus sensible à une variation de l'activité thermique profonde. L'amplitude des anomalies dépend de la position du site par rapport à la configuration de l'activité magmatique, mais aussi des conditions hydrogéologiques locales. La surveillance spatiale et temporelle des éruptions à partir du phénomène convectif hydrique doit tenir compte de ces conditions.
The water steam convection existing below a fumarolic area creates hydraulic, thermal and electric anomalies, the electric anomaly being probably the most correlated to a change of the deep thermal activity. The anomaly range depends on the position of the site connected with the configuration of the magmatic activity, but also on the local hydrogeologic conditions. The spatial and temporal surveillance of the eruptions based on these convective data should take into consideration these conditions.相似文献
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Par Raffaele Peduzzi Antonella Demarta 《Aquatic Sciences - Research Across Boundaries》1986,48(2):161-170
The spreading of bacteria of the genusAeromonas in intensive fish rearing tanks was analyzed during one year. Lysotyping has established epidemiologic correlations between
the strains ofAeromonas isolated from the aquatic environment and those of clinical (human) origin.
Dédié à Wolfgang Geiger 相似文献
Dédié à Wolfgang Geiger 相似文献
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Ch. Linder 《Aquatic Sciences - Research Across Boundaries》1941,9(1-2):81-107
Sans résumé
Avec 2 illustrations 相似文献
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Rev. A. Romañá 《Pure and Applied Geophysics》1950,18(1):148-154
Summary A comparative study of the geomagnetic bays at the Observatories of Cuajimalpa and Teoloyucan (Mexico) and Tortosa, shows: 1) that the grouping of the bays into a certain number of fundamental types, and that the tendency of their frequency maxima to recur in a cyclical order during the day, are general features of geomagnetic bays, at least for all middle geomagnetic latitudes; 2) that the relative importance of the different types and the hour of their maxima varies according to the geomagnetic latitude of the Observatory where the bays are recorded.
Résumé En comparant les baies géomagnétiques enregistrées aux Observatoires de Cuajimalpa et Teoloyucan (Mexique) avec celles observées à Tortosa, on examine la validité générale de la classification des baies établie à l'Observatoire de l'Ebre et de la loi de succession des différents types le long du jour. L'on arrive aux conclusions suivantes: 1o La classification des baies géomagnétiques en un certain nombre de types fondamentaux, de même que la tendence à l'apparition de leurs maxima de fréquence dans un ordre cyclique pendant la journée, a un caractère général, tout au moins pour les latitudes géomagnétiques moyennes; 2o L'importance relative des différents types et l'heure d'apparition de leurs maxima varie d'un Observatoire à l'autre, d'après leur latitude géomagnétique.相似文献