1,720,974 research outputs found
Les travertins du Moyen Dadès (cuvette de Ouarzazate, Maroc)
No full textAkdim Brahim. Les travertins du Moyen Dadès (cuvette de Ouarzazate, Maroc). In: Méditerranée, troisième série, tome 57, 1-2-1986. Travertins LS et évolution des paysages holocènes dons le domaine méditerranéen. pp. 180-183
Les dolines d'effondrement et les dolines-lacs des Causses du SW du Moyen Atlas (Maroc)
No full textKarstic geosystems of the Causses in SW Middle Atlas (Morocco) : Interference between geomorphologic and hydrogeologic factors.
The karstic geosystems of the Causses in the Middle Atlas present a number of old and present karstic landforms. The interference between karstic geomorphology and the process of deep karstification find expression in an important development of sinkholes and collapse zones. Inventory and spatial distribution of these superficial karstic landforms show a very close relationship with the apparition of saline springs.
Water chemistry and the exported rock tonnage are analysed and point out the importance of caveming which takes place in gypsum and salt triassic formations.Les Causses du SW du Moyen Atlas présentent un grand nombre de phénomènes karstiques où prédominent les dépressions fermées et plus particulièrement les dolines d'effondrement. L'interférence entre la géomorphologie karstique de surface et les processus de karstification profonde se traduit par une morphologie de surface caractérisée par un développement important des dolines d'effondrement. L'inventaire de ces morphologies de surface et l'étude de leur répartition spatiale montrent une relation très étroite avec l'apparition des sources salées. La chimie et le tonnage rocheux exporté sont analysés et montrent l'importance du cavernement qui s'effectue au sein des formations gypso-salifères du Trias sous-jacent.El Khalki Yahia, Akdim Brahim. Les dolines d'effondrement et les dolines-lacs des Causses du SW du Moyen Atlas (Maroc). In: Karstologia : revue de karstologie et de spéléologie physique, n°38, 2e semestre 2001. Formations superficielles du Larzac central et Traçages dans les Alpes de Berchtesgaden. pp. 19-24
Impacts des cônes latéraux sur le fonctionnement hydrodynamique et morphosédimentaire actuel des fonds de vallées prérifaines : cas de l'Oued Larbâa (Maroc) / Impact of lateral fans on the current hydrodynamic and morphosedimentary characteristics of valley bottoms : the case of the Larbâa wadi (Morocco)
No full textAbstract : Impact of lateral fans on the current hydrodynamic and morphosedimentary characteristics of valley bottoms : the case of the Larbâa wadi (Morocco). Situated in a marly formation, in a region which is semi-arid and particularly sensitive to erosion processes, the valley bottom of the Larbâa wadi is marked by the presence of several lateral outwash fans of different ages. These fans operate intermittently, under the influence of exceptional rainfall events that may occur annually. With heavy rainfall, the fans invade the bed of the wadi thereby hindering its longitudinal flow. Under the pressure of heavy liquid and solid flows injected into the river by the fans, the main stream migrates across the valley bottom. As a result, the morphogenic dynamic processes show reverse trends in the meanders, leading to bank erosion and slipping on the slopes. These morphogenic processes warrant careful examination if we are to understand the present-day dynamic processes affecting deposition within fans, the changing state of fans in the valley bottom, and the flood risks they generate. The present survey analyses these impacts based on the observed relationship between climatic factors (rainfall), hydrodynamic aspects (lateral erosion, slope destabilization, etc.), sedimentary processes (granulometry, lithology and stratigraphy of deposits) and morphological aspects (types and measurements of fans, and their geometric relationship with the present alluvial plain and the actual bed of the wadi).Résumé : Situé dans un domaine marneux, semi-aride et très sensible aux processus d'érosion, le fond de vallée de l'Oued Larbâa est marqué par la présence de plusieurs cônes de déjection latéraux d'âges différents. Ces cônes fonctionnent actuellement de manière temporaire à l'occasion d'événements pluviométriques exceptionnels qui peuvent se produire annuellement. Au moment des grosses averses, ils envahissent le lit de l'Oued et entrent en jeu pour entraver son écoulement longitudinal, inverser la dynamique morphogénique des méandres et même favoriser le sapement des berges et activer des glissements sur les versants. Sous la pression des forts débits liquides et solides injectés dans le système fluvial par les cônes, l'Oued Larbâa adopte un comportement très instable sur le plan spatial. Sa morphologie se trouve souvent, après les grandes crues, profondément modifiée. Ces processus méritent une attention particulière en raison du rôle majeur qu'ils peuvent jouer dans la dynamique actuelle d'alluvionnement et les risques d'inondation affectant les plaines alluviales des Oueds prérifains. La présente étude analyse ces impacts, à travers des indicateurs météorologiques (pluviométrie), hydrodynamiques (sapement des berges, déstabilisation des versants par l'érosion latérale), sédimentologiques (faciès et organisation sédimentaires, granulométrie) et morphologiques (types et dimensions des cônes, leur relation géométrique avec la plaine alluviale actuelle et le lit actif de l'Oued).Taous Ali, Tribak Abdelletif, Laaouane Mohamed, Akdim Brahim. Impacts des cônes latéraux sur le fonctionnement hydrodynamique et morphosédimentaire actuel des fonds de vallées prérifaines : cas de l'Oued Larbâa (Maroc) / Impact of lateral fans on the current hydrodynamic and morphosedimentary characteristics of valley bottoms : the case of the Larbâa wadi (Morocco). In: Revue de géographie alpine, tome 92, n°1, 2004. De part et d'autre du Sahara, sous la direction de Ibrahim Bouzou-Moussa . pp. 17-28
Genèse des carbonates terrestres dans la dépression de Quarzazate (Maroc méridional).
No full textThe carbonate encrusting process and its consequent products (crusts, tufa and travertine) in the southern Morocco (Ouarzazate) are studied in this thesis. A detailed inventory of the carbonate deposits is given. The dynamic aspects of carbonate precipitation and dissolution are considered from an environmental point of view. The main factors influencing their genesis are discussed on the basis of a multidisciplinary investigation. Among the accumulated carbonates, caliches are the most abundant. Their genesis invokes a changing environment where sedimentation has the same importance as the biogenic and pedogenic processes. Dated by the Uranium/Thorium method, these caliches are older than 300 ka. They indicate that the encrusting process is ancient. These deposits have become progressively rare during the Quaternary period except for the important hydrothermal travertine of Skoura. Only a few accumulations are still forming nowadays (Ait Arbi and Ifesfas). Their absence in present day water, especially in rivers is interpreted as indicating an environmental change. It is hypothesised that a desequilibrium affects the incrusting process. A comparative study between rivers and sources in different settings is carried out. The saturation degree of water, its chemical composition, especially in elements that may have particular origins (potassium, nitrate, sulfate, etc.) and its bacteriological characteristics are investigated in the thesis. Results seem to indicate that differences exist between the calcite - precipitating waters of some sources (not affected by human activities) and the sterile waters of rivers (Dades and M'goun). The latter are polluted by chemical fertilizers or turbulent, such that no carbonate deposits are permitted. The conclusion is that the reduced incrusting phenomena indicate an environmental change. A progressively drier climate and progressively reduced discharge make the deposits more limited in space and rare. The human impact on the quality of water must be considered to explain the limited extend of present day encrusting processes
Genèse des carbonates terrestres dans la dépression de Quarzazate (Maroc méridional).
No full textThe carbonate encrusting process and its consequent products (crusts, tufa and travertine) in the southern Morocco (Ouarzazate) are studied in this thesis. A detailed inventory of the carbonate deposits is given. The dynamic aspects of carbonate precipitation and dissolution are considered from an environmental point of view. The main factors influencing their genesis are discussed on the basis of a multidisciplinary investigation. Among the accumulated carbonates, caliches are the most abundant. Their genesis invokes a changing environment where sedimentation has the same importance as the biogenic and pedogenic processes. Dated by the Uranium/Thorium method, these caliches are older than 300 ka. They indicate that the encrusting process is ancient. These deposits have become progressively rare during the Quaternary period except for the important hydrothermal travertine of Skoura. Only a few accumulations are still forming nowadays (Ait Arbi and Ifesfas). Their absence in present day water, especially in rivers is interpreted as indicating an environmental change. It is hypothesised that a desequilibrium affects the incrusting process. A comparative study between rivers and sources in different settings is carried out. The saturation degree of water, its chemical composition, especially in elements that may have particular origins (potassium, nitrate, sulfate, etc.) and its bacteriological characteristics are investigated in the thesis. Results seem to indicate that differences exist between the calcite - precipitating waters of some sources (not affected by human activities) and the sterile waters of rivers (Dades and M'goun). The latter are polluted by chemical fertilizers or turbulent, such that no carbonate deposits are permitted. The conclusion is that the reduced incrusting phenomena indicate an environmental change. A progressively drier climate and progressively reduced discharge make the deposits more limited in space and rare. The human impact on the quality of water must be considered to explain the limited extend of present day encrusting processes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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