1,245 research outputs found
Synchrotron radiation from a runaway electron distribution in tokamaks
The synchrotron radiation emitted by runaway electrons in a fusion plasma
provides information regarding the particle momenta and pitch-angles of the
runaway electron population through the strong dependence of the synchrotron
spectrum on these parameters. Information about the runaway density and its
spatial distribution, as well as the time evolution of the above quantities,
can also be deduced. In this paper we present the synchrotron radiation spectra
for typical avalanching runaway electron distributions. Spectra obtained for a
distribution of electrons are compared to the emission of mono-energetic
electrons with a prescribed pitch-angle. We also examine the effects of
magnetic field curvature and analyse the sensitivity of the resulting spectrum
to perturbations to the runaway distribution. The implications for the deduced
runaway electron parameters are discussed. We compare our calculations to
experimental data from DIII-D and estimate the maximum observed runaway energy.Comment: 22 pages, 12 figures; updated author affiliations, fixed typos, added
a sentence at the end of section I
Differences in intestinal size, structure, and function contributing to feed efficiency in broiler chickens reared at geographically distant locations
The contribution of the intestinal tract to differences in residual feed intake (RFI) has been inconclusively studied in chickens so far. It is also not clear if RFI-related differences in intestinal function are similar in chickens raised in different environments. The objective was to investigate differences in nutrient retention, visceral organ size, intestinal morphology, jejunal permeability and expression of genes related to barrier function, and innate immune response in chickens of diverging RFI raised at 2 locations (L1: Austria; L2: UK). The experimental protocol was similar, and the same dietary formulation was fed at the 2 locations. Individual BW and feed intake (FI) of chickens (Cobb 500FF) were recorded from d 7 of life. At 5 wk of life, chickens (L1, n = 157; L2 = 192) were ranked according to their RFI, and low, medium, and high RFI chickens were selected (n = 9/RFI group, sex, and location). RFI values were similar between locations within the same RFI group and increased by 446 and 464 g from low to high RFI in females and males, respectively. Location, but not RFI rank, affected growth, nutrient retention, size of the intestine, and jejunal disaccharidase activity. Chickens from L2 had lower total body weight gain and mucosal enzyme activity but higher nutrient retention and longer intestines than chickens at L1. Parameters determined only at L1 showed increased crypt depth in the duodenum and jejunum and enhanced paracellular permeability in low vs. high RFI females. Jejunal expression of IL1B was lower in low vs. high RFI females at L2, whereas that of TLR4 at L1 and MCT1 at both locations was higher in low vs. high RFI males. Correlation analysis between intestinal parameters and feed efficiency metrics indicated that feed conversion ratio was more correlated to intestinal size and function than was RFI. In conclusion, the rearing environment greatly affected intestinal size and function, thereby contributing to the variation in chicken RFI observed across locations
Gravitational Properties of Monopole Spacetimes Near the Black Hole Threshold
Although nonsingular spacetimes and those containing black holes are
qualitatively quite different, there are continuous families of configurations
that connect the two. In this paper we use self-gravitating monopole solutions
as tools for investigating the transition between these two types of
spacetimes. We show how causally distinct regions emerge as the black hole
limit is achieved, even though the measurements made by an external observer
vary continuously. We find that near-critical solutions have a naturally
defined entropy, despite the absence of a true horizon, and that this has a
clear connection with the Hawking-Bekenstein entropy. We find that certain
classes of near-critical solutions display naked black hole behavior, although
they are not truly black holes at all. Finally, we present a numerical
simulation illustrating how an incident pulse of matter can induce the
dynamical collapse of a monopole into an extremal black hole. We discuss the
implications of this process for the third law of black hole thermodynamics.Comment: 23 pages, 4 figures RevTe
Hollow pellet injection for magnetic fusion
Precise delivery of mass to burning plasmas is a problem of growing interest
in magnetic fusion. The answers to how much mass is necessary and sufficient
can vary depending on parameters such as the type of atoms involved, the type
of applications, plasma conditions, mass injector, and injection timing.
Motivated by edge localized mode (ELM) control in H-mode plasmas, disruption
mitigation and other applications in magnetic fusion, we report progress and
new possibilities in mass delivery based on hollow pellets. Here, a hollow
pellet refers to a spherical shell mass structure with a hollow core. Based on
an empirical model of pellet ablation, coupled with BOUT++ simulations of ELM
triggering threshold, hollow pellets are found to be attractive in comparison
with solid spheres for ELM control. By using hollow pellets, it is possible to
tailor mass delivery to certain regions of edge plasmas while minimizing core
contamination and reducing the total amount of mass needed. We also include
experimental progress in mass delivery experiments, in-situ diagnostics and
hollow pellet fabrication, and emphasize new experimental possibilities for ELM
control based on hollow pellets. A related application is the disruption
mitigation scheme using powder encapsulated inside hollow shells. Further
experiments will also help to resolve known discrepancies between theoretical
predictions and experiments in using mass injection for ELM control and lead to
better predictive models for ELM stability and triggering.Comment: Manuscript prepared for reviews by {\it Nuclear Fusion}, following
the initial presentation in the 27th IAEA FEC, Gandhinagar, India, Oct. 22 -
27, 201
Intermittent compared to continuous real-time fMRI neurofeedback boosts control of amygdala activity
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