Signatures of quantum effects on radiation reaction in laser-electron-beam collisions

Two signatures of quantum effects on radiation reaction in the collision of a GeV electron beam with a high intensity (>3×1020Wcm-2]]>) laser pulse have been considered. We show that the decrease in the average energy of the electron beam may be used to measure the Gaunt factor for synchrotron emission. We derive an equation for the evolution of the variance in the energy of the electron beam in the quantum regime, i.e. quantum efficiency parameter . We show that the evolution of the variance may be used as a direct measure of the quantum stochasticity of the radiation reaction and determine the parameter regime where this is observable. For example, stochastic emission results in a 25% increase in the standard deviation of the energy spectrum of a GeV electron beam, 1 fs after it collides with a laser pulse of intensity 1021W cm-2. This effect should therefore be measurable using current high-intensity laser systems

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)

Eating attitudes in young teenage girls: Parental management of "fussy" eating

A large number of young children are “fussy” about their eating, refusing particular foods. Several behavioral programs have been advanced for making those foods more desirable. However, these programs ignore the function that this fussiness can serve for the child. Children may refuse food as a way of asserting some control over their environment—for example, by changing their parents behavior. It is also not clear to what extent parental efforts to change children's eating patterns may lead to later difficulties associated with eating. This retrospective study examined the possibility that parents' use of behavioral approaches to food refusal might be related to the child's general food fussiness. Associations between recalled parental behaviors, child fussiness, and the child's eating behavior were examined in considering possible causation. In a sample of 92 teenage girls, it was found that positive and negative reinforcement were ineffective, while early reported use of modeling was related to the children's being mted as more fussy in later childhood. Food fissiness showed some association with eating patterns measured by the Bulimic Inueat@tory Test, supporting the clinical utility of investigating “ffirsJiness.” This outcome suggests that food fusiness should be treated not in isolation but in the context of family relations, and that parents should be aduised accordingly. Such treatment of fissiness may play an important role in the development of adult eatingpsychopathology

Imaginary companions and young children’s responses to ambiguous auditory stimuli: Implications for typical and atypical development

Background: Previous research has reported a link between imaginary companions (ICs) in middle childhood and the perception of verbal material in ambiguous auditory stimuli. These findings have been interpreted in terms of commonalities in the cognitive processes underlying children's engagement with ICs and adults’ reporting of imaginary verbal experiences such as auditory verbal hallucinations. The aim of the present study was to examine these relations using improved methodology and a younger sample of children for whom engagement with ICs would be expected to be particularly salient. Method: Data on young children's (age range: 4–8 years) reporting of ICs were gathered in two studies (total N = 80). Responses to ambiguous auditory stimuli were investigated using the new Jumbled Speech task, which measures participants’ likelihood of perceiving words in meaningless but speech-like auditory stimuli. Results: Reporting hearing words in the Jumbled Speech task was associated with having a parentally corroborated IC. Hearing words on the task and having an IC were unrelated to age, gender, verbal ability, and understanding of the stream of consciousness. Conclusions: Findings are consistent with the hypothesis that engaging with ICs is one aspect of a general susceptibility to imaginary verbal experiences. We consider the implications for the assumption of continuity in psychopathological experiences between childhood and adulthood