On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

OSIRIS-REx Contamination Control Strategy and Implementation

OSIRIS-REx will return pristine samples of carbonaceous asteroid Bennu. This article describes how pristine was defined based on expectations of Bennu and on a realistic understanding of what is achievable with a constrained schedule and budget, and how that definition flowed to requirements and implementation. To return a pristine sample, the OSIRIS-REx spacecraft sampling hardware was maintained at level 100 A/2 and 2 of amino acids and hydrazine on the sampler head through precision cleaning, control of materials, and vigilance. Contamination is further characterized via witness material exposed to the spacecraft assembly and testing environment as well as in space. This characterization provided knowledge of the expected background and will be used in conjunction with archived spacecraft components for comparison with the samples when they are delivered to Earth for analysis. Most of all, the cleanliness of the OSIRIS-REx spacecraft was achieved through communication among scientists, engineers, managers, and technicians

The Antecedents and Outcomes of Online Knowledge-Sourcing Behavior: The Influence of Computer Attitude and Learning Styles

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Concentrações de imunoglobulinas G em colostro de vacas mestiças holandês-zebu Colostral immunoglobulin G concentrations in crossbred holstein-zebu dairy cows

Oitenta e oito vacas leiteiras mestiças holandês-zebu (HZ) foram distribuídas de acordo com a percentagem de grau de sangue holandês em quatro grupos: Grupo 1 = animais com menos de 70% de grau de sangue holandês (19 vacas); Grupo 2 = animais com 75% de grau de sangue holandês, que equivale a ¾ HZ (46 vacas); Grupo 3 = mestiços entre 80 e 90% de grau de sangue holandês, que corresponderam a 13/16 HZ e 7/8 HZ (11 vacas); Grupo 4 = vacas com mais de 90% de grau de sangue holandês (12 vacas). Após o parto, amostras de colostro da primeira ordenha foram colhidas e, posteriormente, submetidas à imunodifusão radial simples para determinações dos níveis de imunoglobulinas G (IgG). Os resultados obtidos permitiram concluir que as concentrações de IgG não são influenciadas pelos graus de sangue estudados e seus valores médios (145,94mg/m<img src="http:/img/fbpe/cr/v31n6/a19img01.gif">) são muito superiores aos relatados para animais de raças taurinas puras. Por esse motivo, não se justifica o emprego de métodos artificiais de fornecimento do colostro em se tratando de mestiços HZ. Ademais, o nível elevado de IgG observado no colostro sugere que a adoção da prática da mamada natural assistida seja adequada para assegurar que, na maioria das vezes, os neonatos não venham a apresentar falhas de transferência de imunidade passiva.<br>Eighty-eight healthy crossbred holstein-zebu (HZ) dairy cows were distributed in four groups as follow: Group 1 = less than 70% HZ (19 cows); Group 2 = 75% HZ animals, corresponding to ¾ HZ (46 cows); Group 3 = crossbred animals between 80 to 90% HZ, corresponding to 13/16 HZ and 7/8 HZ (11 cows); Group 4 = cows more than 90% HZ (12 animals). After birth, colostrum samples were obtained from each cow and than were analyzed for immunoglobulin G (IgG) concentration by single radial immunodifusion assay. IgG colostral concentrations were not influenced by group of crossbred HZ and its mean concentration (145.97mg/m<img src="http:/img/fbpe/cr/v31n6/a19img01.gif">) were higher than that related for purebreds Bos taurus dairy cows. Considering these results, it was concluded that artificial methods of feeding colostrum to crossbred HZ calves are not necessary. Probably, assisted natural sucking as soon after birth as possible is enough to get passive immune transfer