Uses and Misuses of Agricultural Pesticides in Africa: Neglected Public Health Threats for Workers and Population

Pesticides are use in agriculture for their capacity to reduce pest and protect foods. Since their introduction in Africa by colonial masters, the use of these chemicals is constantly growing. Herbicides and insecticides are the two dominant categories. Although they are used in small quantities by farmers who own small exploitation, the frequency of their use, as well as overuses and misuses, constitutes serious factors of exposure and health risks. Farm workers are more vulnerable to occupational effects from pesticide inhalation and skin contacts. Failure to wear protective equipment and observe good agricultural practices explained health symptoms that are frequently experienced: eye and skin irritation, nausea, vomiting, and headache. Population is subject to chronic health effects due to repeated dietary intake of pesticides. Most consumed staple foods on the continent (cereals, vegetables, and fruits) have been found to be contaminated by one or multiple residues of pesticides. The level of residues is often higher than regulatory limits. Organization of surveillance programs to monitor concentration of pesticide residues remains inexistent in most countries, same for toxicovigilance systems to documented poisoning cases. Current data underline the need to carry out pesticide health risk assessment in order to appreciate the threats they pose for public health

Protonolysis of a Ruthenium–Carbene Bond and Applications in Olefin Metathesis

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru–MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicated a rate-determining protonation step in the generation of the metathesis-active species. The activity of the NHC/MIC catalyst was found to exceed those of current commercial ruthenium catalysts

Oil Contracts, Progressive Taxation and Government Take in the Context of Uncertainty in Crude Oil Prices: The Case of Chad

Etudes & documentsConcession Contracts (CC) and Production Sharing Contracts (PSC) have quite different implications for Government Take and the properties of the tax system, such as progressivity. In general, taxation via CC introduces significant distortions in activity, particularly due to the balance of royalties which tax production irrespective of the profitability of the project. So CC is normally regressive while PSC is normally progressive, because PSC taxation depends more directly on the profitability of the project. Chad has the distinction of having introduced PSC in the 2007 Chad oil code, while maintaining a royalty on production. Despite this feature, we show with a Cash Flow model and Monte Carlo simulations that the application of the 2007 oil code introduced more progressivity into taxation. This feature is particularly interesting in the current context of falling crude oil prices, because it maintains a favorable tax regime for exploration and exploitation by multinational oil companies. As a result, the Chad government should reactivate a counter-cyclical policy of oil revenue reserves when the crude oil price increases again

Synthesis of Highly Stable 1,3-Diaryl-1H-1,2,3-triazol-5-ylidenes and Their Applications in Ruthenium-Catalyzed Olefin Metathesis

The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions

Construction et analyse des signaux non-stationnaires adaptés à la caractérisation des phénomènes turbulents

National audienceDans ce papier nous proposons une approche hybride signal-physique pour la détection de la présence de la turbulence dans un fluide. L'idée est de construire une forme d'onde capable de porter, de manière robuste, l'information sur la turbulence et de mettre en place le traitement qui permettra l'extraction des paramètres liés à ce phénomène. Il est donc nécessaire de réaliser une correspondance entre les grandeurs qui caractérisent les écoulements turbulents et les signaux acoustiques. Nous allons montrer que l'utilisation des signaux avec une loi de fréquence instantanée polynomiale est potentiellement porteuse de l'information de turbulence que nous pouvons extraire à partir de l'estimation de la déformation de cette loi

Isolation of cationic and neutral (allenylidene)(carbene) and bis(allenylidene)gold complexes.

The one-electron reduction of a cationic (allenylidene)[cyclic(alkyl) (amino)carbene]gold(i) complex leads to the corresponding neutral, paramagnetic, formally gold(0) complex. DFT calculations reveal that the spin density of this highly robust coinage metal complex is mainly located on the allenylidene fragment, with only 1.8 and 3.1% on the gold center and the CAAC ligand, respectively. In addition, the first homoleptic bis(allenylidene)gold(i) complex has been prepared and fully characterized