136 research outputs found
CAUVIN, Colette, ESCOBAR, Francisco et SERRADJ, Aziz (2008) Cartographie thématique 4. Des transformations renouvelées. Paris, Hermès, 198 p. (ISBN 978-2-7462-2207-6)
Stanford, Q.H., éd. (1992) Canadian Oxford World Atlas. Toronto, Oxford University Press, 216 p. (ISBN 0-19-540897-7)
Barnes, Trevor J. & Hayter, Roger, eds (1997) Troubles in the Rainforest : British Columbia’s Forest Economy in Transition. Victoria, Western Geograhical Press (Coll. « Geographical Series », no 33), 303 p. (ISBN 0-919838-23-5)
Fortunel, Frédéric (2000) Le café au Viêt Name. De la colonisation à l’essor d’un grand producteur mondial. Paris, L’Harmattan (Coll. « Points sur l’Asie »), 172 p. (ISBN 2-7384-9158-8)
L’enneigement et la dynamique du pergélisol : l’exemple du détroit de Manitounuk, Québec nordique
Le régime nival d'un plateau de pergélisol situé le long du rivage du détroit de Manitounuk, au Québec subarctique, a été étudié en détail pendant plusieurs hivers consécutifs. Ce régime nival dépend surtout du régime éolien, lequel détermine le patron d'accumulation de la neige en conjonction avec les conditions de surface, notamment le relief et le couvert végétal. Un modèle de potentiel d'enneigement, établi en fonction des pentes, des orientations et de la forme des versants, ainsi que du couvert végétal, est proposé. Ce modèle, entériné à partir des valeurs observées, a permis de faire ressortir le lien entre la végétation arbustive et le régime éolien et leur effet sur les variations locales du couvert nival. On peut donc envisager de produire, à partir d'éléments tels que les données sur les vents, la cartographie du couvert végétal et la modélisation de la topographie, un modèle de prévision de l'enneigement dans les régions subarctiques devenues instables en raison de l'équilibre thermique précaire du pergélisol et de la dynamique des populations végétales.The snow cover regime over a permafrost plateau located along the shore of the Manitounuk Strait was monitored in detail for several winters. The pattern of snow accumulation and distribution depends essentially upon wind direction and speed, in conjunction with surface conditions, particularly topography and vegetation cover. A snow accumulation potential model was built, based on slope, aspect and shape, and on structure of the vegetation cover. Results of this model illustrate the strong link between winds and vegetation cover and their combined impact on snowdrifting. Using wind speed and direction data as well as a detailed mapping of vegetation cover, it is useful to apply such an accumulation model in subarctic regions where permafrost is highly sensitive to any modification of the surface conditions.Man hat die Schneever-hà ltnisse auf einem là ngs des Ufers der Meerenge von Manitounouk gelegenen Permafrostboden-Plateau im subarktischen Québec wâhrend mehrerer aufeinanderfolgenden Winter im Detail studiert. Dies System der Schneeakkumulation ist vor allem vom Windsystem abhângig, welches zusammen mit den Oberflachenbedingungen, vor allem dem Relief und der Pflanzendecke, das Muster der Schneeakkumulation bestimmt. Es wird ein Modell der potentiellen Schneeakkumulation vorgeschlagen, das in Abhân-gigkeit von den Hângen, der Orientierung und der Form der Abhânge sowie der Pflanzendecke erstellt wurde, dies aufgrund der beobachteten Werte erstellte Modell hat es ermôglicht, die Beziehung zwischen der Buschvegetation und dem Windsystem und ihre Auswirkung auf die ôrtlichen Variationen der Schneedecke hervorzuheben. Es ist also môglich, ausgehend von Elementen wie den Daten zu Winden, der Kartographie der Pflanzendecke und der Modellierung der Topographie, ein Modell zur Voraussage der Schneeakkumulation in den subarktischen Regionen zu erstellen, welche wegen des unsicheren thermischen Gleichgewichts des Permafrostbodens und der Dynamik der Vegetationspopulationen schwankend geworden sind
L’urbanisation de la ville de Ninh Binh dans le delta du fleuve rouge (Vietnam) : Mise en perspective des forces et faiblesses de la gestion du risque d’inondation
Les problèmes associés à la gestion des risques d’inondation sont une question d’actualité, mais aussi source de polémique. En effet, la manière dont ces risques sont gérés suscite généralement des avis très tranchés, les uns très positifs, les autres mettant uniquement l’accent sur les aspects négatifs. Le cas du delta du fleuve Rouge, au Vietnam, régulièrement soumis aux risques d’inondations, est à cet égard particulièrement parlant et le présent article a pour objet de montrer les points forts et les faiblesses dans la manière dont ces risques sont gérés. Pour ce faire, nous nous appuierons sur les observations effectuées au cours d’une recherche menée dans la province de Ninh Binh, dans le sud-ouest du delta, entre 2002 et 2005. Ces observations ont notamment mis en lumière les contradictions en matière de gestion du risque d’inondation existant dans le delta du fleuve Rouge. Elles soulignent les caractéristiques culturelles inhérentes au contexte vietnamien et confirment que les contradictions observées répondent en fait à une logique de préservation des intérêts financiers d’une région en plein essor économique et démographique où les espaces non exposés aux inondations sont rares.Flood risk management is becoming an issue that is both relevant and sensitive. Even though no one argues about the need for flood risk management, the practices used are often challenged and subject to controversy. This is particularly the case in the Red River Delta, in Vietnam. Flood risks are very important in the area and so they have been for centuries, but the management practices are often considered as being either very positive or very negative. This paper intends to give a full picture on the strengths and weaknesses of current flood risk management practices in the Red River Delta, through the example of the province of Ninh Binh, where fieldwork has been done from 2002 to 2005. Data and observations collected in this province located in the southwestern tip of the Delta underline the contradictions of flood risk management practices in the Red River Delta. The driving force behind these contradictions seems to be a fast economic and demographic development involving short term planning in a region where areas unexposed to flood risk are not many
Transport Length Scales in Disordered Graphene-based Materials: Strong Localization Regimes and Dimensionality Effects
We report on a numerical study of quantum transport in disordered two
dimensional graphene and graphene nanoribbons. By using the Kubo and the
Landauer approaches, transport length scales in the diffusive (mean free path,
charge mobilities) and localized regimes (localization lengths) are computed,
assuming a short range disorder (Anderson-type). In agreement with localization
scaling theory, the electronic systems are found to undergo a conventional
Anderson localization in the zero temperature limit. Localization lengths in
weakly disordered ribbons are found to differ by two orders of magnitude
depending on their edge symmetry, but always remain several orders of magnitude
smaller than those computed for 2D graphene for the same disorder strength.
This pinpoints the role of transport dimensionality and edge effects.Comment: 4 pages, Phys. rev. Lett. (in press
Transport properties of 2D graphene containing structural defects
We propose an extensive report on the simulation of electronic transport in
2D graphene in presence of structural defects. Amongst the large variety of
such defects in sp carbon-based materials, we focus on the Stone-Wales
defect and on two divacancy-type reconstructed defects. First, based on ab
initio calculations, a tight-binding model is derived to describe the
electronic structure of these defects. Then, semiclassical transport properties
including the elastic mean free paths, mobilities and conductivities are
computed using an order-N real-space Kubo-Greenwood method. A plateau of
minimum conductivity () is progressively
observed as the density of defects increases. This saturation of the decay of
conductivity to is associated with defect-dependent
resonant energies. Finally, localization phenomena are captured beyond the
semiclassical regime. An Anderson transition is predicted with localization
lengths of the order of tens of nanometers for defect densities around 1%.Comment: 17 pages, 17 figures, submitted to Phys. Rev.
La radicalización islámica. Causas y procesos: casos de Francia y Bélgica
Fac. de Ciencias PolÃticas y SociologÃaFALSEpu
Atomistic Boron-Doped Graphene Field Effect Transistors: A Route towards Unipolar Characteristics
We report fully quantum simulations of realistic models of boron-doped
graphene-based field effect transistors, including atomistic details based on
DFT calculations. We show that the self-consistent solution of the
three-dimensional (3D) Poisson and Schr\"odinger equations with a
representation in terms of a tight-binding Hamiltonian manages to accurately
reproduce the DFT results for an isolated boron-doped graphene nanoribbon.
Using a 3D Poisson/Schr\"odinger solver within the Non-Equilibrium Green's
Functions (NEGF) formalism, self-consistent calculations of the gate-screened
scattering potentials induced by the boron impurities have been performed,
allowing the theoretical exploration of the tunability of transistor
characteristics. The boron-doped graphene transistors are found to approach
unipolar behavior as the boron concentration is increased, and by tuning the
density of chemical dopants the electron-hole transport asymmetry can be finely
adjusted. Correspondingly, the onset of a mobility gap in the device is
observed. Although the computed asymmetries are not sufficient to warrant
proper device operation, our results represent an initial step in the direction
of improved transfer characteristics and, in particular, the developed
simulation strategy is a powerful new tool for modeling doped graphene
nanostructures.Comment: 7 pages, 5 figures, published in ACS Nan
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