Production And Studies Of Photocathodes For High Intensity Electron Beams

For short, high-intensity electron bunches, alkali-tellurides have proved to be a reliable photo-cathode material. Measurements of lifetimes in an RF gun of the CLIC Test Facility II at field strengths greater than 100 MV/m are presented. Before and after using them in this gun, the spectral response of the Cs-Te and Rb-Te cathodes were determined with the help of an optical parametric oscillator. The behaviour of both materials can be described by Spicer's 3-step model. Whereas during the use the threshold for photo-emission in Cs-Te was shifted to higher photon energies, that of Rb-Te did not change. Our latest investigations on the stoichiometric ratio of the components are shown. The preparation of the photo-cathodes was monitored with 320 nm wavelength light, with the aim of improving the measurement sensitivity. The latest results on the protection of Cs-Te cathode surfaces with CsBr against pollution are summarized. New investigations on high mean current production are presented.Comment: Submission to LINAC2000 conference, Paper number MOB08, 3 pages, 6 figure

Ethnic Entrepreneurship In OECD Countries: A Systematic Review Of Performance Determinants Of Ethnic Ventures

This paper seeks to examine the evolution of determinants under scrutiny by academics publishing on performance of ethnic companies in Organisation for Economic Co-operation and Development (OECD) countries. Using the systematic literature review method, we first provide a descriptive analysis of articles gathered, and then make an in-depth examination of the determinants focused on. A database of 40 papers published between 2002 and 2011 was collected – the topic was precise enough to yield only a few articles – from a wide range of journals. We provide a systemized summary of the current status of this body of work, examine areas where research is lacking, and explain why further study of the role of cultural and ethical values as determinants of ethnic entrepreneurship is critical

Effects of oxygen depletion on soot production, emission and radiative heat transfer in opposed-flow flame spreading over insulated wire in microgravity

This paper investigates experimentally and numerically pressure effects on soot production and radiative heat transfer in non-buoyant opposed-flow flames spreading over wires coated by Low Density PolyEthylene (LPDE). Experiments, conducted in parabolic flights, consider pressure levels ranging from 50.7 kPa to 121.6 kPa and an oxidizer flowing parallel to the wire's axis at a velocity of 150 mm/s and composed of 20% O2/80% N2 in volume. The numerical model includes a detailed chemistry, a two-equation smoke-point based soot production model, a radiation model coupling the Full-Spectrum correlated-k method with the finite volume method and a simple degradation model for LDPE. An analysis of the experimental data shows that the spread rate, the pyrolysis mass flow rate, and the residence time for soot formation are independent of pressure whereas the soot formation rate is third-order in pressure. The model reproduces quantitatively the effects of pressure on soot production and captures the transition from non-smoking to smoking flames. The radiant fraction increases with pressure because of an enhancement in soot radiation whereas the contribution of radiating gases remains approximately constant over the range of pressures considered. In addition, gas radiation dominates at pressure lower than 75 kPa whereas soot radiation prevails at higher-pressure levels. Consistently with the data obtained at normal gravity, the smoke-point transition is found to occur for a radiant fraction of about 0.3 and the soot oxidation freezing temperature is estimated in the range 1350-1450K. Eventually, whatever the pressure considered, the surface re-radiation from the wire is higher than the incident radiative flux from the flame to the surface along the entire wire. This shows that radiative heat transfer contributes negatively to the heating of the unburnt LDPE and to the heat balance along the pyrolysing surface

Etude clinique et épidémiologique du paludisme en zone urbaine d'Afrique soudano-sahélienne (Pikine-Sénégal)

Pour des raisons de coût et de tolérance, la chimiothérapie présomptive repose toujours essentiellement sur la chloroquine, malgré l'apparition, il y a dix ans en Afrique de l'Est, de souches de #Plasmodium falciparum$ résistantes à la chloroquine et leur extension à l'ensemble de l'Afrique intertropicale. Dans le cas des zones urbaines, plusieurs particularités épidémiologiques du paludisme suggèrent qu'à partir de certains niveaux de chimiorésistance d'autres stratégies de lutte anti paludique pourraient être développées avec un meilleur rapport coût/efficacité. Dans une première approche de cette question, une recherche a été faite à Pikine, à savoir s'il existait des paramètres cliniques ou épidémiologiques, faciles à obtenir chez un enfant consultant pour fièvre, qui permettraient de choisir entre trois attitudes possibles : abstention thérapeutique, traitement présomptif, confection d'une goutte épaiss

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

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