Région de la baie de San Francisco

La région de la baie de San Francisco (San Francisco Bay Area) est une aire urbaine aux particularités géographiques variées entourant la baie de San Francisco, en Californie du Nord. Elle accueille plus de huit millions d'habitants, ainsi que des municipalités à la taille diverse, des bases militaires, des technopoles dont la Silicon Valley, des aéroports, ainsi que des parcs nationaux, d'État ou locaux. Elle est parcourue par un réseau routier et ferroviaire très dense et s'étend sur les neuf comtés suivants : Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, et Sonoma auxquels s'ajoute parfois le comté de Santa Cruz. La région de « La Baie » (The Bay Area, comme les autochtones l'appellent généralement) diffère de la plupart des métropoles américaines par son intégration de plusieurs centres urbains et banlieues distincts. San José est ainsi la municipalité la plus peuplée de la région de La Baie depuis le début des années 1990, mais San Francisco

Spatial and Temporal Analysis of Congestion in Urban Transportation Networks

Yuxuan Ji

Research on congestion and propagation in large urban city networks has been mainly based on microsimulations of link-level traffic dynamics. However, both the unpredictability of travel behaviors and high complexity of accurate physical modeling remain challenging and simulation results may be far time consuming and not realistic. It has been recently shown that amacroscopic fundamental diagram (MFD) linking space-mean network flow, density and speed exists in the urban transportation networks under some conditions. An MFD is further well defined if the network is homogeneous with links of similar properties. This collective behavior concept can also be utilized to introduce simple control strategies to improve mobility in homogeneous city centers without the need for details in individual links. However many real urban transportation networks are heterogeneous with different levels of congestion. In order to study the existence of MFD and the feasibility of simple control strategies to improve network performance in heterogeneously congested networks, this thesis mainly focuses on three issues: (1) static partitioning of traffic networks, (2) congestion propagation and dynamic partitioning, and (3) the effect of network structure on congestion propagation. Firstly, we study the static partitioning of transportation networks based on the spatial features of congestion during a specific time period. A partitioning mechanism which consists of three consecutive algorithms, is designed to minimize the variance of link densities while maintaining the spatial compactness of the clusters. Secondly we explore the dynamics of traffic conditions and thus the corresponding dynamic partitioning scheme. We reveal the hidden information during the process of congestion formation by exploring empirical data from large-scale urban networks. Specifically, we aim at studying the spatiotemporal relation of congested links, observing congestion propagation from an macroscopic perspective, and finally identifying critical congestion regimes to aid the design of peripheral control strategies. Finally, we study the formation of traffic congestion by simulation in large scale cities with different network structures. A parsimonious model of congestion propagation is developed and validated by real data in San Francisco in US and Shenzhen in China (20000 taxis with 30 million logs per day). The effect of network structure on congestion propagation is investigated by simulations conducted in a variety of network structures.

EPFL2014

Scleractinian coral morphogenesis

Agathe Eliette Marie Lecointe

Metamorphosis is a crucial step in the life cycle of a scleractinian coral: The swimming coral larva, the planula, settles, and metamorphoses into a sessile calcifying primary polyp, which subsequently grows into an adult colony. Importantly, morphogenesis into a primary polyp involves the establishment of the skeletogenic cell layer, the so-called calicodermis, but the cellular mechanisms that support this process are not well understood. In the work presented here, calicodermis establishment was studied in two scleractinian corals, Pocillopora damicornis and Stylophora pistillata using cell proliferation and apoptosis assays, electron microscopy, molecular biology tools, and isotopic imaging using NanoSIMS. Cell proliferation during coral metamorphosis was evaluated with BrdU (5-bromo-2â-deoxyuridine) incuba-tion pulses (24 h). In the primary polyp stage, cell migration was observed in the chase phase for several days (48 to 64 h) after the incubation pulse. A number of key observations were made: 1) Right after settlement, during the earliest metamorphosis stage that includes initial skeletal formation and therefore requires a fully functional calicodermis, cell proliferation rate in this tissue layer is in fact not significantly higher than in the preceding planula larval stage. This indicates that calicodermis establishment is primarily happening through transdifferentiation of cells from the aboral pseudostratified epithelium of the planula into calicodermis cells. 2) Later, in the growing primary polyp local cell proliferation in the calicodermis remains low, indicating that these cells do not originate in the calicodermis itself. 3) At the same time, it is observed in S. pistillata that the pharynx is the most proliferative area with up to 19% of cells dividing, and that cells migrate from this area through pseudostratified epithelium and/or mesenterial filaments to reach the expanding calicodermis, which is actively forming skeleton at this stage. 4) In order to identify potential stem cells and calicodermis precursor cells locations, biological markers where developed. Potential stem cells expressing piwi genes were localized in the mesenteries and below tentacle tips of P. damicornis. These sites contain proliferative areas involved in gametogenesis and nematogenesis, respectively. 5) Pdcyst-rich is a protein localizedin the adult calicodermis and potentially involved in skeleton formation. The related gene was observed to be expressed at the early metamorphosis stage, when skeleton deposition commences. Preliminary results indicate that Pdcyst-rich proteins are also located in the calicodermis of the forming polyp and skeleton of the primary polyp stage. This suggests a role of Pdcyst-rich in skeletogenesis but it is not clear if it acts as a protein of the skeletal organic matrix or as an adhesion protein.

EPFL2016

Exploring the energy use drivers of 10 cities at microscale level

Aristide Henri Roger Athanassiadis, Franziska Meinherz, João Vitor Meirelles de Miranda

Cities are responsible for the predominant share of anthropogenic environmental pressures. Recently, consistent methodologies to measure the metabolism of cities have been developed in order to enhance comparability between case studies and enable cross-city comparisons at the macro-scale. This comparison illustrated potential factors and drivers explaining macro-scale differences between cities. However, such studies rely on very few data points and look at cities as homogenous entities omitting their complex functioning. When looking at the relationships between urban characteristics and metabolic flows at smaller spatial scales, drivers appear to be different than in macroscopic analyses, pointing towards the importance of taking microscale urban heterogeneity into account. The aim of this paper is to improve our understanding of these effects by analyzing the relationship between energy use and various urban indicators at a microscale level for ten cities (Brussels, Buenos Aires, Cape Town, Chicago, Glasgow, London, Los Angeles, Milan, New York City and San Francisco).