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)

The time course of perceptual grouping in natural scenes.

Visual perception starts with localized filters that subdivide the image into fragments that undergo separate analyses. The visual system has to reconstruct objects by grouping image fragments that belong to the same object. A widely held view is that perceptual grouping occurs in parallel across the visual scene and without attention. To test this idea, we measured the speed of grouping in pictures of animals and vehicles. In a classification task, these pictures were categorized efficiently. In an image-parsing task, participants reported whether two cues fell on the same or different objects, and we measured reaction times. Despite the participants’ fast object classification, perceptual grouping required more time if the distance between cues was larger, and we observed an additional delay when the cues fell on different parts of a single object. Parsing was also slower for inverted than for upright objects. These results imply that perception starts with rapid object classification and that rapid classification is followed by a serial perceptual grouping phase, which is more efficient for objects in a familiar orientation than for objects in an unfamiliar orientation

Reducing glucose infusion safely prevents hyperglycemia in post-surgical children

SummaryBackground & aimsTo investigate the effects of two different glucose infusions on glucose homeostasis and amino acid metabolism in post-surgical children.MethodsThis randomized crossover study evaluated glucose and amino acid metabolism in eight children (age 9.8 ± 1.9 months, weight 9.5 ± 1.1 kg) admitted to a pediatric intensive care unit in a tertiary university hospital after surgical correction for non-syndromal craniosynostosis. Patients were randomized to receive low (LG; 2.5 mg kg−1 min−1) and standard (SG; 5.0 mg kg−1 min−1) glucose infusion in a crossover setting. After a bolus (4 g kg−1) of deuterium oxide, we conducted a primed, constant, 8 h tracer infusion with [6,6-2H2]Glucose, [1-13C]Leucine, [ring-2H5]Phenylalanine and [3,3-2H2]Tyrosine.ResultsSG resulted in hyperglycemia (defined as > 6.1 mmol L−1), while during LG plasma glucose levels were normoglycemic (5.9 ± 0.6 vs. 7.5 ± 1.7 mmol L−1; LG vs. SG respectively, p = 0.02). Hypoglycemia did not occur during LG infusion. Endogenous glucose production was not fully suppressed during the hyperglycemic state under SG and increased with reduced glucose infusion (2.6 ± 1.5 vs. 1.1 ± 1.4 mg kg−1 min−1; LG vs. SG; p = 0.05). Whole body protein balance derived from leucine and phenylalanine kinetics was slightly negative but not further affected with a decrease in glucose infusion.ConclusionsThe current recommended glucose infusion induces hyperglycemia in post-surgical children. A reduced glucose infusion safely reduced high glucose levels, while children were capable to sustain normoglycemia with increased endogenous glucose production. The reduced glucose infusion did not exacerbate the mild catabolic state in which the patients were