Parametric amplification and wavelength conversion in the 1040-1090 nm band by use of a photonic crystal fiber

International audienceHighly efficient parametric amplification and wavelength conversion have been demonstrated in the 1040-1090 nm band. A nonlinear photonic crystal fiber was used to provide the anomalous dispersion required for phase matching at 1 μm. A 40 dB maximum gain and +35 dB idler conversion efficiency have been achieved in the subnanosecond pulsed regime and by using a spectrally filtered supercontinuum source as a small signal

Effets spatiaux et effets réseau dans l’évaluation d’indicateurs sur les nœuds d’un réseau d’infrastructure

The quantitative study of an infrastructure network in geography often consists in assessing indicators on the network components (nodes and sections). In that respect, the network is modelled by a graph whose vertices and edges respectively correspond to the nodal and linear network infrastructures. Then, such a graph can be studied thanks to tools provided by the graph theory and mainly based on the shortest paths features. The most typical indicators are accessibility (closeness from a given vertex to the others graph vertices, computed in summarizing the shortest path lengths) and centrality or “betweenness” (contribution of a given vertex or edge to the origin-destination paths, computed in counting the shortest paths passing through this component). For this reason, accessibility and centrality features of a vertex depend on the shortest paths distribution on the network, and also on the relative location of the vertex inside the network. However, the spatial location of vertices predisposes them to be accessible and central, regardless of the relational potentialities provided by the network structure. Actually, a vertex located at the centre (resp. on the periphery) of the network area is more (resp. less) likely to be accessible and central. Therefore, it seems relevant to highlight how the network makes the vertices accessible and central, independently on the advantages only provided by their spatial location. Then, we show that it is possible to make allowances for the corresponding “network and spatial effects” by comparing the shortest paths traditionnally taken into account to compute these indicators with a set of optimal paths called “Delaunay paths”. Besides the study of accessibility and centrality indicators, our method can be extended to the study of any indicator (structural or not), as long as such an indicator is usually computed from shortest paths. It finally provides a useful tool to interpret indicators on a network and to understand the networks contribution to the phenomena described by these indicators

L’évaluation des réseaux de circulation en géographie quantitative

Les réseaux de circulation interviennent dans la manifestation de nombreux phénomènes spatiaux mettant en jeu des déplacements ou des mises en relation sur les territoires. L’analyse de ces phénomènes nécessite de disposer d’outils d’évaluation des réseaux, lesquels sont principalement des indicateurs fournis par la géographie quantitative. Néanmoins, ces indicateurs sont souvent définis dans le contexte d’études thématiques, et ne proposent donc pas d’approche générique qui permette d’extraire les propriétés intrinsèques des réseaux et d’élaborer de nouveaux indicateurs. Sur la base de ce constat, nous proposons dans cet article de développer un cadre d’étude fondé sur l’observation de la structure du réseau, c’est-à-dire de ses informations topologiques, géométriques et métriques. En focalisant l’analyse sur les chemins que le réseau offre pour réaliser les relations entre sommets origine et destination, ce cadre d’étude est adapté pour mettre en évidence les potentialités relationnelles du réseau, c’est-à-dire sa capacité à mettre en relation les lieux sur le territoire. Le processus d’élaboration des indicateurs présenté dans ce cadre permettent non seulement de reconstruire et d’expliciter les indicateurs traditionnels fournis par la géographie quantitative (accessibilité, centralité), mais également de construire de nouveaux indicateurs : à ce titre, nous détaillons la construction d’indicateurs descriptifs de la richesse des alternatives offertes par le réseau (nombre de chemins) et de la portée spatiale des relations auxquelles les sommets participent (rayon proximal). Ce processus peut être étendu à toute propriété observable à l’échelle des chemins.Circulation networks are often implied in spatial phenomena, since they highlight displacements or relationships of places on territories. To analyse such phenomena, specifics tools are needed, in particular indicators coming from quantitative geography. Nevertheless, these indicators are often defined in thematic studies, and do not put forward a generic approach which would help to extract the intrinsic network properties and to draw up new indicators. Making this observation, we propose to develop a framework based on the study of the network structure, combining its topological, geometrical and metrical information. In focusing on the analysis of the paths offered by the network to carry out the relations between origin and destination nodes, this framework is relevant to highlight the network relational potentialities, i.e. its ability to link the different places on the territory. The process we use to draw up structural indicators helps not only to rebuild and reinterpret the traditional indicators supplied by quantitative geography (accessibility, betweenness), but also to build new indicators: in that respect, we explain this process for two indicators, describing on the one hand the network paths supply (paths number) and on the other hand the spatial range of relations in which the network nodes are implied (proximal radius). This process can be extended to analyse any property observable at the path level

L’impact du voisinage géographique des pays dans l’attribution des votes au Concours Eurovision de la Chanson

The Eurovision Song Contest has been held every year since 1956. The originality of this contest lies in the points awarding system. There is no single jury but, on the contrary, each country is asked to award a given number of points to the countries which performed its favourite songs. Beyond the interest of such a system to collectively rank countries, it provides a long story of the swapped points between countries. Such information makes it possible to detect couples of countries {voter, performer} for whom votes are not exclusively guided by song quality. Currently the media covering the event regularly mention a bias in the votes distribution: according to them, this bias would be caused by geographical proximity and would lead to blocs of nearby countries which overwhelmingly vote for each other. In this article, we try to discuss this assumption. This latter requires to answer the following question: “how can we assess the influence of spatial proximity on the social ties formation?”. Besides this issue, several methodological challenges appear. First, we examine the votes of the 1993-2008 period and we identify the social ties of interest, that is the couples of countries {voter, performer} whose votes significantly diverge from the reference situation (i.e. a competition on song quality). Then, we compare the resulting social network with the spatial countries network by a well-suited statistical method to prove that “over-votes” concern nearby countries. Finally, we highlight clusters of countries tending to over-vote for each other and, in that respect, we define clustering criteria which make sense. We show that these blocs strongly structure the abnormally high votes of the 2009 event. This analysis method combines geographical and social networks and can be extended to the study of phenomena concerning relations between spatialised entities

Impact of relief accuracy on flood simulations and road network vulnerability analysis

The increased availability and accuracy of multi-sources data enhance the simulation quality of natural disasters (hazard). Moreover, it enables a better prediction of their impact on the territory (vulnerability). Numerical representation of relief (DTM) is a prime necessity in risk simulation, in particular in flood study. Integrating 2D objects into a DTM significantly improves the relief representation around each object. The aim of this paper is first to enrich the relief accuracy with the altimetric attributes of 2D vector objects, and then to assess the impact of these modifications within the context of a rise in the water level and its consequences on the road network vulnerability. The first part focuses on the integration of 2D vector data (e.g. roads) on a 2.5D digital terrain model. The integration of 2D vector data on a DTM usually raises data consistance issues. These data often stem from different acquisition modes ; moreover, their scale and their dimension (2D, 2.5D, 3D) vary according to their nature and the data capture. In order to overcome these problems, our approach consists in converting 2D vector data in 2.5D vector data by assigning them a width and computing their elevation. Then, these latter are integrated into the DTM and make it sharper, especially on the former interpolated areas. In a second part, we analyze the floods effects on the running of the road network in Orléans (France). In addition to the direct damages caused by the physical action of the water, the flood also leads to functional disruptions on the road network by forcing users to take detours. In a risk preventive viewpoint, the network administrator has first to consider a given flood scenario and consequently to identify the network components to be protected as a priority, in order to reduce to the minimum the costs induced by the detours. On account of both levels of precision considered in the original DTM and in the enriched DTM, we have to compare two damaging scenarios of the road network for a given flood hazard. To that end, we quantify the functionality of the network components with centrality measures and we compare the efficiency of the different configurations of damaged network with accessibility measures. The results of this study prove how much the flood of the road network, the induced functional disruptions and the associated preventive actions depend on the adopted precision in the representation of the terrain

La vulnérabilité structurelle comme outil de compréhension des mécanismes d'endommagement

L'exemple du risque de crue centennale en agglomération parisienne nous rappelle que la multiplicité des aléas et la grande variété de leurs impacts sur les territoires rendent difficile la compréhension de certains risques et des vulnérabilités associées. Pour dépasser cette complexité, nous proposons de construire une grille de lecture fondée non plus sur l'aléa, mais sur les enjeux et leur vulnérabilité. En nous appuyant sur le cas des réseaux de transport, nous distinguons d'abord la vulnérabilité matérielle de la vulnérabilité fonctionnelle. Puis, en isolant la vulnérabilité structurelle, nous faisons apparaître un niveau intermédiaire essentiel pour comprendre les mécanismes en jeu dans les chaînes d'endommagement induites par l'aléa initial. Nous pouvons alors généraliser cette méthode au territoire francilien et mettre en évidence le rôle de l'organisation spatiale comme facteur de vulnérabilité structurelle. Cette analyse ouvre de nouvelles pistes pour la gestion des risques.The case of flood risk in the Parisian urban area exemplifies that the analysis of hazardous processes and vulnerability can be very difficult, especially when the area under study is subject to a multiplicity of hazards, which may have very different impacts on different territories. In order to understand these intricate processes, we propose to build a new framework based on the elements at risk and their vulnerability, rather than on hazards. We study the case of risk in transport networks. This example enables us to distinguish material and functional damage, and link each form to a specific vulnerability. Then, we identify an intermediary scale, called structural vulnerability, which seems to be necessary to under-stand the chains of damage caused by the impacts of the initial hazard. This analysis suggests new ideas for better risk management, at both local and global scales

La géomatique au service de la caractérisation automatique des réseaux hydrographiques

L'analyse des phénomènes territoriaux est facilitée aujourd'hui par les Systèmes d'Information Géographique, lesquels permettent d'intégrer au sein d'une même plateforme les données géographiques et les données thématiques associées aux phénomènes d'intérêt. En pratique, les outils et les méthodes offerts par les SIG proposent d'analyser les phénomènes de manière intégrée, sans distinguer explicitement les facteurs explicatifs propres à la spatialisation des phénomènes et les facteurs explicatifs contextuels. Pour autant, les données géographiques ne se limitent pas à un simple support cartographique pour représenter les phénomènes territoriaux, mais contiennent en puissance des informations susceptibles de faire comprendre les mécanismes spatiaux qui sous-tendent ces phénomènes. En particulier, les données géographiques représentatives des réseaux hydrographiques décrivent la forme et la topologie de ces réseaux, et peuvent à ce titre fournir des informations complémentaires sur leurs types morphométriques. Sur la base de la typologie établie en géomorphométrie et des caractérisations géométriques fournies par la littérature, cet article montre qu'il est possible d'extraire l'information sémantique relative aux différents types de réseaux en automatisant leur reconnaissance, grâce à des indicateurs structurels quantitatifs construits sur leur représentation topographique. Cette démarche est mise en œuvre sur les réseaux de type parallèle, à partir de l'observation des angles formés par les tronçons hydrographiques au niveau des nœuds de confluence des réseaux. En considérant les directions moyennes empruntées par les tronçons autour de ces nœuds et en étudiant les distributions des angles qu'ils forment sur l'ensemble de la zone d'étude, il est alors possible d'élaborer une méthode de segmentation des réseaux hydrographiques, permettant de faire la part entre les réseaux de type parallèle et ceux relevant de types différents.Analyzing territorial phenomena is made easier today by Geographical Information Systems, which make it possible to integrate within the same platform geographical and thematic data related to the phenomena under study. In practice, tools and methods provided by GIS propose an integrated way to analyze the phenomena, without explicitly distinguishing the spatial from the contextual factors which explain the phenomena. Nonetheless, geographical data do not amount to a simple cartographic support representing the territorial phenomena, but potentially contain information making the undelying spatial mechanisms of these phenomena explicit. In particular, the geographical data related to the river networks describe the shape and topology of these networks and, for this reason, can provide additional details on their morphometric types. Thanks to the networks typology and the geometric characterizations provided by previous research in geomorphometry, this article shows that it is possible to extract semantic information relative to the various network types by automating their recognition, thanks to quantitative structural indicators built on their topographic representation. This process is implemented on parallel networks, starting from the observation of the angles formed by the networks edges around the junction nodes. By considering the average directions taken by the edges around these nodes, and by studying the angles distributions on the whole study area, it is possible to implement a segmentation method for hydrographic networks, dinstinguishing parallel networks from the other network types

Demonstration of a true single-shot 100 GHz bandwidth optical oscilloscope at 1053-1064 nm

International audienc