Albedo reduction by absorbing aerosols over China

Long-term observations with satellites show that absorbing aerosols have reduced the local planetary albedo (LPA) over China during the recent decade. While the reduction of air pollution was leading to an LPA decrease in Europe, an increase of pollution in China also lowered the LPA. The strong absorption in clouds is accompanied by a cloud lifetime effect over the Red Basin and surrounding areas in southern Chin

Gaming with eutrophication: Contribution to integrating water quantity and quality management at catchment level

The Metropolitan Region of Sao Paulo (MRSP) hosts 18 million inhabitants. A complex system of 23 interconnected reservoirs was built to ensure its water supply. Half of the potable water produced for MRSP's population (35 m3/s) is imported from a neighbour catchment, the other half is produced within the Alto Tietê catchment, where 99% of the population lives. Perimeters of land use restriction were defined to contain uncontrolled urbanization, as domestic effluents were causing increasing eutrophication of some of these reservoirs. In the 90's catchment committees and sub committees were created to promote discussion between stakeholders and develop catchment plans. The committees are very well structured "on paper". However, they are not very well organised and face a lack of experience. The objective of this work was to design tools that would strengthen their discussion capacities. The specific objective of the AguAloca process was to integrate the quality issue and its relation to catchment management as a whole in these discussions. The work was developed in the Alto Tietê Cabeceiras sub-catchment, one of the 5 sub catchments of the Alto-Tietê. It contains 5 interconnected dams, and presents competitive uses such as water supply, industry, effluent dilution and irrigated agriculture. A RPG was designed following a companion modelling approach (Etienne et al., 2003). It contains a friendly game-board, a set of individual and collective rules and a computerized biophysical model. The biophysical model is used to simulate water allocation and quality processes at catchment level. It articulates 3 modules. A simplified nutrient discharge model permits the estimation of land use nutrient exportation. An arc-node model simulates water flows and associated nutrient charges from one point of the hydrographical network to another. The Vollenweider model is used for simulating specific reservoir dynamics. The RPG allows players to make individual and collective decisions related to water allocation and the management of its quality. Impacts of these decisions are then simulated using the biophysical model. Specific indicators of the game are then updated and may influence player's behaviour (actions) in following rounds. To introduce discussions on the management of water quality at a catchment level, an issue that is rarely explicitly dealt with, four game sessions were implemented involving representatives of basin committees and water and sanitation engineers. During the game session, the participants took advantage of the water quality output of the biophysical model to test management alternatives such as rural sewage collection or effluent dilution. The biophysical model accelerated calculations of flows and eutrophication rates that were then returned to the game board with explicit indicators of quantity and quality. Players could easily test decisions impacting on qualitative water processes and visualize the simulation results directly on the game board that was representing a friendly, virtual and simplified catchment. The Agualoca game proved its ability to turn complex water processes understandable for a non totally initiated public. This experience contributed to a better understanding of multiple-use water management and also of joint management of water quality and quantity. (Résumé d'auteur

Recent visible light and metal free strategies in [2+2] and [4+2] photocycloadditions

When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as wellFinancial support was provided by the European Research Council (ERC-CoG, Contract Number: 647550), the Spanish Government (RTI2018-095038-B-I00), the ‘Comunidad de Madrid’ and European Structural Funds (S2018/NMT-4367). R. I. R thanks Fundación Carolina for a graduate fellowshi

Wetter und Klima

Der Beitrag beschreibt die gegenwärtigen Kenntnisse der Variabilität des Klimas in der jüngsten Vergangenheit, die beobachteten Veränderungen seit Jahrtausenden und die vom Verhalten der Menschheit abhängigen Klimazukünfte.Wobei auch immer über das zugehörige Wetter und dabei vor allem seine Extreme berichtet wird. Abschließend wird gezeigt, wie stark Wetter und Klima von winzigen Beimengungen in der Atmosphäre abhängen

Complexité structurelle et complexité de requête pour des problèmes totaux

Dans cette thèse, nous abordons des problèmes de complexité structurelle, traitant de la classification des problèmes en fonction de leurs difficultés relatives, et nous nous intéressons aussi à l'existence d'une solution à un problème plus concret d'algorithmique en-ligne. Suivant cette dichotomie, dans la première partie de cette thèse nous étudions des problèmes de la classe des problèmes totaux TFNP, à savoir les problèmes de Sperner et la recherche de minimum local. Nous montrons les complétudes de problèmes de Sperner localement 2-dimensionnels dans les classes d'arguments de parité PPA, PPAD et PPADS. Nous améliorons ainsi des résultats de Papadimitriou et Grigni. Nous étudions ensuite le nombre de requêtes, au sens classique et au sens quantique, nécessaires pour résoudre un problème de Sperner en dimension arbitraire sur une pseudo-variété ; nous prouvons une borne inférieure ainsi qu'une borne supérieure correspondant à la complexité d'un algorithme, cette dernière étant optimale pour un cas précédemment étudié par Crescenzi et Silvestri. Enfin, nous donnons deux algorithmes, un classique et un quantique, pour déterminer la position d'un minimum local d'une fonction définie sur les sommets d'un graphe. Les analyses de nos deux algorithmes sont fondées sur l'existence de séparateurs de petite taille dans les graphes, et nous montrons un tel résultat qui améliore un résultat antérieur de Gilbert, Hutchinson et Tarjan. Dans la seconde partie de la thèse, nous nous intéressons à l'existence d'un algorithme en-ligne sans mémoire pour le problème CNN. Notre résultat généralise et améliore un résultat antérieur de Koutsoupias et Taylor.In this thesis, we treat problems of structural complexity, which aims at classifying problems depending on their relative difficulty to be solved, and we also study the existence of an efficient solution to a more concrete problem of online algorithmics. Following this dichotomy, in the first part of this thesis we study some problems of the class TFNP, more specifically Sperner problems and the search for a local minimum. We prove completeness of locally 2-dimensional Sperner problems in the Parity Argument'' classes PPA, PPAD and PPADS. Thus, we improve results of Papadimitriou and Grigni. We also study the number of queries, both in the classical and the quantum settings, necessary to solve an arbitrary dimensional Sperner problem on a pseudo-manifold ; we prove a lower bound and an upper bound corresponding to the complexity of an algorithm, the latter being optimal for a particular case previously studied by Crescenzi and Grigni. Finally, we give a classical and a quantum algorithm for spotting a local minimum of a function defined over the vertices of a graph, and prove that they use fewer queries than previously known algorithms on large classes of graphs. The analyses of our two algorithms rely on the use of {\em separator theorems}, and we prove such a theorem which slightly improves an older result of Gilbert, Hutchinson and Tarjan. In the second part of this thesis, we study the existence of a memoryless online algorithm for the CNN problem. Our results generalize and improve a previous result of Koutsoupias and Taylor.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF