Le retour du tramway à Besançon

Plus de 60 ans après leur suppression, les tramways seront de retour dans la capitale comtoise, sans doute en 2014. Ce retour -- le premier dans une agglomération de moins de 200 000 habitants en France -- est le fruit d'une longue maturation liée à la prise de conscience de l'impasse du tout automobile commencée dans les années 1970. L'hypothèse d'un passage des autobus au tramway a été évoquée pour la première fois en 2000 lors de l'élaboration du premier plan de déplacements urbains (pdu) et c'est seulement le 18 décembre 2008 que le conseil de la Communauté d'Agglomération du Grand Besançon (CAGB) a validé le projet de tramway

Decadal prediction skill using a high-resolution climate model

The ability of a high-resolution coupled atmosphere–ocean general circulation model (with a horizontal resolution of a quarter of a degree in the ocean and of about 0.5° in the atmosphere) to predict the annual means of temperature, precipitation, sea-ice volume and extent is assessed based on initialized hindcasts over the 1993–2009 period. Significant skill in predicting sea surface temperatures is obtained, especially over the North Atlantic, the tropical Atlantic and the Indian Ocean. The Sea Ice Extent and volume are also reasonably predicted in winter (March) and summer (September). The model skill is mainly due to the external forcing associated with well-mixed greenhouse gases. A decrease in the global warming rate associated with a negative phase of the Pacific Decadal Oscillation is simulated by the model over a suite of 10-year periods when initialized from starting dates between 1999 and 2003. The model ability to predict regional change is investigated by focusing on the mid-90’s Atlantic Ocean subpolar gyre warming. The model simulates the North Atlantic warming associated with a meridional heat transport increase, a strengthening of the North Atlantic current and a deepening of the mixed layer over the Labrador Sea. The atmosphere plays a role in the warming through a modulation of the North Atlantic Oscillation: a negative sea level pressure anomaly, located south of the subpolar gyre is associated with a wind speed decrease over the subpolar gyre. This leads to a reduced oceanic heat-loss and favors a northward displacement of anomalously warm and salty subtropical water that both concur to the subpolar gyre warming. We finally conclude that the subpolar gyre warming is mainly triggered by ocean dynamics with a possible contribution of atmospheric circulation favoring its persistence

Caractérisation tribologique de films moléculaires d'acide phosphonique déposés sur une surface de cuivre

National audienceLa surface d'un substrat de cuivre a été fonctionnalisée grâce à une technique d'auto-assemblage d'une monocouche d'acide phosphonique. Après caractérisation de ce film, un excellent comportement tribologique est noté lorsqu'aucun nettoyage ultrasonore n'est effectué, pour des conditions de sollicitation de pression de 133 MPa et de vitesse de glissement de 1mm/s sur un tribomètre alternatif linéaire utilisant un frotteur en Si3N4 (μ = 0.12, durée de vie multipliée par 100). Des espèces physisorbées, sous formes d'amas de plusieurs μm3, présentes sur la monocouche semblent responsables de ce bon comportement. De premiers essais sur un tribomètre d'étirage-plan ont montré un réel potentiel de ce type de fonctionnalisation en emboutissage

Adaptación de un método de optimización multiobjetivo para modelos de pronóstico de inundaciones

Los métodos de optimización multi-objetivo tienen diversas aplicacionesen la ingeniería. En particular, en la hidrología son una herramienta de gran valor para encontrar un conjunto de soluciones de compromiso para dos objetivos hidrológicos cualesquiera en conflicto. Por su parte, los modelos de pronóstico hidrológico se emplean durante un evento lluvioso con el fin de predecir el caudal que se producirá en una sección de un río con un cierto tiempo de anticipación (horizonte de pronóstico).Como información de entrada suelen utilizar la lluvia y el caudal de la sección de interés, registrados en tiempo real. Sin embargo, durante un evento de gran magnitud, algunos sistemas de pronóstico experimentan una degradación en la calidad de los caudales observados en tiempo real, y en ciertos casos se produce incluso pérdida de dicha información. Cuando la cadena de transmisión de datos hidrometeorológicos (redpluviométrica e hidrométrica) a tiempo real falla, el desempeño del modelo puede decaer drásticamente respecto del esperado en un caso real. En particular, si lainformación a tiempo real del último caudal observado se pierde (daño en la estación hidrométrica, o en la red de comunicación, etc.) y no puede ser asimilado, el modelo hidrológico corre en una situación típica de simulación, ejercicio para el cual otro modelo (o el mismo, pero parametrizado de otro modo) podría conducir a resultados más confiables. Por esta razón, un método de optimización multi-objetivo puede ser empleado para encontrar soluciones de compromiso entre ambos criterios. En este trabajo fue llevada a cabo una optimización multi-objetivo del modelo GR4P, mediante el uso del algoritmo MOCOM-UA. Se observó que el método era incapaz de encontrar en todos los experimentos de manera robusta el mismo frente de Pareto, por lo quefueron llevadas a cabo un conjunto de modificaciones al método con el fin de mejorar la robustez. Finalmente, fue posible obtener una versión adaptada del algoritmo MOCOMUA con la cual se llega en los sucesivos experimentos a frentes de Pareto bien semejantes entre sí. Los trabajos fueron realizados sobre una cuenca pequeña de la Bretaña francesa

Quantifying the impact of early 21st century volcanic eruptions on global-mean surface temperature

Despite a continuous increase in well-mixed greenhouse gases, the global-mean surface temperature has shown a quasi-stabilization since 1998. This muted warming has been linked to the combined effects of internal climate variability and external forcing. The latter includes the impact of recent increase in the volcanic activity and of solar irradiance changes. Here we used a high-resolution coupled ocean–atmosphere climate model to assess the impact of the recent volcanic eruptions on the Earth’s temperature, compared with the low volcanic activity of the early 2000s. Two sets of simulations are performed, one with realistic aerosol optical depth values, and the other with a fixed value of aerosol optical depth corresponding to a period of weak volcanic activity (1998–2002). We conclude that the observed recent increase in the volcanic activity led to a reduced warming trend (from 2003 to 2012) of 0.08 °C in ten years. The induced cooling is stronger during the last five-year period (2008–2012), with an annual global mean cooling of 0.04 °C (+/-0.04 °C). The cooling is similar in summer (0.05 °C+/-0.04 °C cooling)than in winter (0.03 °C+/-0.04 °C cooling), but stronger in the Northern Hemisphere than in the Southern Hemisphere. Although equatorial and Arctic precipitation decreases in summer, the change in precipitation does not indicate robust changes at a local scale. Global heat content variations are found not to be impacted by the recent increase in volcanic activity

Caractérisation tribologique de monocouches auto-assemblées

L'auto-assemblage de monocouches ou SAMs (Self-Assembled Monolayers) permet la génération d'une surface fonctionnalisée basée sur le greffage, par réaction chimique, d'un film de molécules organiques en surface. Dans ce cadre, nous avons exploré les aptitudes tribologiques de diverses SAM's en sollicitation de contact « sec » et « lubrifié » après avoir optimisé leur « qualité » : adsorption, organisation, densité et stabilité

Deep mixed ocean volume in the Labrador Sea in HighResMIP models

Simulations from seven global coupled climate models performed at high and standard resolution as part of the high resolution model intercomparison project (HighResMIP) are analyzed to study deep ocean mixing in the Labrador Sea and the impact of increased horizontal resolution. The representation of convection varies strongly among models. Compared to observations from ARGO-floats and the EN4 data set, most models substantially overestimate deep convection in the Labrador Sea. In four out of five models, all four using the NEMO-ocean model, increasing the ocean resolution from 1° to 1/4° leads to increased deep mixing in the Labrador Sea. Increasing the atmospheric resolution has a smaller effect than increasing the ocean resolution. Simulated convection in the Labrador Sea is mainly governed by the release of heat from the ocean to the atmosphere and by the vertical stratification of the water masses in the Labrador Sea in late autumn. Models with stronger sub-polar gyre circulation have generally higher surface salinity in the Labrador Sea and a deeper convection. While the high-resolution models show more realistic ocean stratification in the Labrador Sea than the standard resolution models, they generally overestimate the convection. The results indicate that the representation of sub-grid scale mixing processes might be imperfect in the models and contribute to the biases in deep convection. Since in more than half of the models, the Labrador Sea convection is important for the Atlantic Meridional Overturning Circulation (AMOC), this raises questions about the future behavior of the AMOC in the models

Mineral magnetic characterization of the Upper Pleniglacial Nussloch loess sequence (Germany): an insight into local environmental processes

Presently, most loess/palaeosol magnetic susceptibility records are interpreted as following either the wind-vigour model or the pedogenic enhancement model. However redoxomorphic processes induced by waterlogging, often referred to gleying in the loess literature, are also known to alter loess deposits but their impact on loess/palaeosol magnetic susceptibility records has received little attention. The reported rock magnetic study aims to characterize the mineral magnetic response of loess to waterlogging-induced redoxomorphic processes, thus improving our understanding of mineral magnetic changes within loess deposits with respect to environmental and climate conditions. The Nussloch loess-palaeosol deposit (Rhine Valley, Germany) was targeted because it is one of the best-studied Pleniglacial deposits for Western Europe in which numerous tundra gley intervals have been identified. Moreover, a comprehensive high-resolution environmental magnetism study has never been undertaken for this site. Various rock magnetism experiments were conducted at both room and low temperatures to characterise the composition, concentration and relative magnetic grain size of the mineral magnetic assemblage. The relative changes in magnetic parameters within the investigated loess interval are primarily controlled by (1) varying concentrations of coarse-grained ferrimagnetic particles of detrital (aeolian) origin and (2) dissolution of fine-grained ferrimagnetic particles related to in situ post-depositional alteration promoted by waterlogging-induced redoxomorphic processes. Goethite is found to be ubiquitous throughout the studied interval and is argued to have both a primary (aeolian) and secondary (in situ) origin. We conclude, that redoxomorphic processes induced by waterlogging, if present, will hinder the interpretation of magnetic susceptibility variations within loess and palaeosol deposits following the expected relationships dictated by the wind-vigour and the pedogenic enhancement magnetism models