In situ TEM study of twin boundary migration in sub-micron Be fibers

Deformation twinning in hexagonal crystals is often considered as a way to palliate the lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in-situ in a transmission electron microscope (TEM) deform by a $\{ 10\bar{1}2 \}$ $\langle 10\bar{1}1 \rangle$ twin thickening. The propagation speed of the twin boundary seems to be entirely controlled by the nucleation of twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of twinning dislocations. We demonstrate that the activation volume ($V$) associated with the twin boundary propagation can be retrieved from the measure of the twin boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of $V \approx 8.3 \pm 3.3 \times 10^{-29}m^3$ is comparable to the value expected from surface nucleation.Comment: 13 pages, 9 figure

Fabrication de chikwangue au Congo

Ce rapport fait état, d'une part, des résultats obtenus dans le cadre de recherches entreprises pour définir les contextes dans lesquels il est prévu de diffuser un produit nouveau, la "chiwangue Agricongo", ainsi que les procédés et les équipements mis au point de fabrication et, d'autre part, des actions menées à l'échelle pilote en vue d'assurer la diffusion de ces innovations. A partir d'enquêtes réalisées, à Brazzaville et sur toute l'étendue du territoire, les modalités de consommation de la chikwangue au Congo ont été décrites et son importance dans la ration alimentaire des congolais précisée. Les préférences exprimées et le comportement des consommateurs de chikwangue vis-à vis de leur aliment de base ont été analysés. Si la chikwangue reste l'aliment de base préféré des congolais, l'importance de sa consommation varie en fonction de certains facteurs éco-socioéconomiques. D'autres enquêtes réalisées dans le même temps ont permis d'inventorier et de décrire les variantes et les innovations endogènes apparues dans les procédés de fabrication de la chikwangue en zones rurales et le mode de fonctionnement des ateliers urbains de fabrication. Le rendement des transformations et la durée et la pénibilité des différentes étapes ont été mesurés. Les procédés et les équipements mis au point à partir de 1987 par Agricongo sont décrits ainsi que, en comparaison avec les systèmes traditionnels, le système de production du groupement de producteurs agricoles dans lequel une ligne de fabrication a été installée en 1991. Les études réalisées pour évaluer le réseau mis en place pour assurer la distribution du produit et l'acceptabilité des produits, des procédés et des équipements montrent que le produit est très bien accepté et que le choix de le commercialiser dans un réseau de petits commerces est judicieux. Malheureusement, les équipements se sont révélés mal adaptés aux contextes socio-économiques, insuffisamment analysés au moment du démarrage du projet. D'autre part, le coût de l'amortissement des machines et la cherté de la matière première en ville ne permet pas d'envisager d'installer des lignes de fabrication en zones urbaines. D'autre part, une fiabilité encore insuffisante des machines rend aléatoire leur installation près des zones de production en raison des problèmes de maintenance. Par ailleurs, la diffusion des équipements pris séparément est difficile, compte tenu de leur coût et du faible niveau habituel d'investissement des ateliers traditionnels. Toutefois, la description rigoureuse des modalités de consommation et de transformation de la chikwangue existant actuellement au Congo permet à Agricongo, promoteur du projet, de dresser un cahier des charges précis pour les aménagements à faire subir aux procédés et aux équipements en vue de les rendre complètement adaptés aux contestes technologiques et économiques qui prévalent au Congo. (Résumé d'auteur

Injection of insect membrane in Xenopus oocyte: An original method for the pharmacological characterization of neonicotinoid insecticides

Insect nicotinic acetylcholine receptors (nAChRs) represent a major target of insecticides, belonging to the neonicotinoid family. However, the pharmacological profile of native nAChRs is poorly documented, mainly because of a lack of knowledge of their subunit stoichiometry, their tissue distribution and the weak access to nAChR-expressing cells. In addition, the expression of insect nAChRs in heterologous systems remains hard to achieve. Therefore, the structure–activity characterization of nAChR-targeting insecticides is made difficult. The objective of the present study was to characterize insect nAChRs by an electrophysiological approach in a heterologous system naturally devoid of these receptors to allow a molecular/cellular investigation of the mode of action of neonicotinoids

Call centers with a postponed callback offer

We study a call center model with a postponed callback option. A customer at the head of the queue whose elapsed waiting time achieves a given threshold receives a voice message mentioning the option to be called back later. This callback option differs from the traditional ones found in the literature where the callback offer is given at customer’s arrival. We approximate this system by a two-dimensional Markov chain, with one dimension being a unit of a discretization of the waiting time. We next show that this approximation model converges to the exact one. This allows us to obtain explicitly the performance measures without abandonment and to compute them numerically otherwise. From the performance analysis, we derive a series of practical insights and recommendations for a clever use of the callback offer. In particular, we show that this time-based offer outperforms traditional ones when considering the waiting time of inbound calls

Peri-urban Farn ing Systems and Food Processing in the Congo

Abstract AGRICONGO (Institut de recherche et d'appui pour le développement agricole en Zones tropicales) developed a project entitled new farming systems (NSF). This project is intended to implement peri-urban agriculture for city dwellers who want to go into small farm businesses. Because the Congo is importing a large part of its food, the project's first goal was to identify products for development. A basic project assumption was that the best way to reduce these imports was to modernize traditional foods. There was also a need to develop appropriate technologies in agronomy and food science. Work was done to design both a 1.5 ha NFS farm and an integrated food processing facility. Farming techniques were tested at the research station level and the study included socioeconomic issues and farmer-level implementation of product marketing and commercialization. This report presents preliminary findings from 20 pilot NFS farms that were tested near Brazzaville. Food processing lines and their management are also described. Processed products made available to urban markets through the project were chikwangue (cassava bread) and cassava-based mixed flour for infant food

Accessing the soot-related radiative heat feedback in a flame spreading in microgravity: Optical designs and associated limitations

Novel, high-fidelity results related to soot from microgravity flames were obtained by an international topical team on fire safety in space. More specifically, embedded optical techniques for evaluation of the soot-related radiative feedback to the base material from a spreading non-premixed flame in microgravity were developed. The configuration used a non-buoyant axisymmetric flame propagating in an opposed laminar stream over a Low Density PolyEthylene coating of an electrical wire. Within this context, both the standard Broadband Two Color Pyrometry (B2CP) and its recent extension Broadband Modulated Absorption/Emission (BMAE) technique can be deployed to measure the spatial distribution of soot temperature and volume fraction within the flame. Both fields are then processed to establish the field of local radiative balance attributed to soot within the flame, and ultimately the soot contribution to the radiative flux to the wire. The present study first assesses the consistency of the methodology contrasting an experimental frame and a synthetic one, the latter being produced by a signal modeling that processes fields delivered by a numerical simulation of the configuration as inputs. Using the synthetic signals obtained, the fields of local radiative balance within the flame are then computed and significant discrepancies were disclosed locally between the fields originating from the synthetic BMAE and B2CP inputs. Nevertheless, the subsequent evaluation of the soot-related radiative heat feedback to the wire shows that a weak deviation among the techniques implemented is expected. This finding is corroborated by similar evaluations conducted with experimental BMAE and B2CP measurements obtained in parabolic flights. As BMAE is implemented in an ISS configuration within the SCEM rig, BMAE and B2CP will soon provide long-duration soot observations in microgravity. In order to contrast the upcoming results, this current study quantifies discrepancies originating from the post-processing regarding soot temperature and volume fraction, and shows that the radiative feedback evaluation from both methods should be consistent