Pour une localisation optimale des centres de transbordement intermodaux entre réseaux de transport: formulation et extensions

La localisation des centres de transbordement où s'opère le changement de mode ou de réseau de transport intervient de façon déterminante dans la compétitivité du transport multimodal. L'objet de cette contribution est de discuter cette problématique en l'envisageant sous l'angle particulier de la théorie de la localisation. Ainsi, la localisation de centres de transbordement entre réseaux est définie comme un problème de type discret qui cherche à localiser des unités (équipements techniques) permettant le transfert dun réseau à un autre avec pour objectif de réduire les coûits de transport totaux. Une formulation mathématique de ce problème, reposant sur de la programmation linéaire en nombres entiers, est proposée et argumentée. La souplesse de cette formulation autorise plusieurs extensions qui peuvent être combinées de manière à représenter diverses situations rencontrées dans la pratique.     

The Design and Development of a Closed Chamber for the in‐situ Quantification of Dryland Soil Carbon Dioxide Fluxes

This paper describes the design features and capabilities of a portable automated in‐situ closed chamber (ISCC) for the quantification of CO₂ fluxes in dryland soils where both photosynthetic and respiratory components may be associated with a cyanobacterial crust. The processes of CO₂ flux in dryland soils are briefly described in order to clarify the conditions that make quantification of these fluxes problematic. The instrumentation currently available for in‐situ soil CO₂ flux measurements is then reviewed demonstrating their inadequacies for the dryland environment. The ISCC described here is a member of the closed or enrichment class of soil respiration chambers. The ISCC, however, features an optical window possessing high (>90%) transmission in the photosynthetic active region (PAR) of the solar irradiance spectrum, permitting observations of photosynthesis. The ISCC possesses automatic venting and purging so that gaseous concentrations inside the chamber do not change from ambient sufficiently to significantly affect diffusion. The ISCC features both active and passive cooling employing internal solid‐state Peltier coolers and external aluminised Mylar respectively. This avoids severe disturbance of the microclimate within the chamber due to admission of high fluxes of PAR and permits in‐situ operation under a wide range of ambient field temperatures (~ ?5 to 40°C). Sensors internal to the chamber monitor temperature, relative humidity, irradiance and pressure. In this implementation the ISCC is coupled to a portable gas chromatograph (Agilent GC‐3000) to sample the chamber atmosphere. Indicative data for Kalahari Sand soils of Botswana are presented as an illustration of the general performance characteristics.     

The UN and the African Union in Mali and beyond: a shotgun wedding?

The United Nations (UN) and the African Union (AU) have collaborated in building a viable African Peace and Security Architecture and have worked together in a number of armed conflicts over the past decade. Examples include the peace operations in Burundi and Somalia, and the hybrid peace operation in Sudan's Darfur region which is perhaps the most prominent illustration of this collaboration. Although the UN Security Council authorized the intervention in Libya, which was approved by leading regional organizations (the Arab League, the Organization of the Islamic Conference and the Gulf Cooperation Council), it was opposed initially by the AU although the three African states in the Security Council voted for it. Relations cooled as a result and have grown colder still as the UN snubbed the AU and its initial efforts to engage in post‐conflict stabilization in Mali. While the AU sought to prove itself as a capable security provider and partner on the continent with its operation AFISMA, France's Opération Serval and the UN's peace operation for Mali, MINUSMA, bypassed the African Union. This article explores the underlying fault‐lines between the two organizations by examining interactions between the UN and AU since the latter's launch in 2002, but focusing on the Mali case. The fault‐lines emerging from the analysis are different capabilities, risk‐averse vs risk‐assuming approaches to casualties, diverging geopolitics and leadership rivalry.