377 research outputs found
Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem
The impulsive phase of a solar flare marks the epoch of rapid conversion of
energy stored in the pre-flare coronal magnetic field. Hard X-ray observations
imply that a substantial fraction of flare energy released during the impulsive
phase is converted to the kinetic energy of mildly relativistic electrons
(10-100 keV). The liberation of the magnetic free energy can occur as the
coronal magnetic field reconfigures and relaxes following reconnection. We
investigate a scenario in which products of the reconfiguration - large-scale
Alfven wave pulses - transport the energy and magnetic-field changes rapidly
through the corona to the lower atmosphere. This offers two possibilities for
electron acceleration. Firstly, in a coronal plasma with beta < m_e/m_p, the
waves propagate as inertial Alfven waves. In the presence of strong spatial
gradients, these generate field-aligned electric fields that can accelerate
electrons to energies on the order of 10 keV and above, including by repeated
interactions between electrons and wavefronts. Secondly, when they reflect and
mode-convert in the chromosphere, a cascade to high wavenumbers may develop.
This will also accelerate electrons by turbulence, in a medium with a locally
high electron number density. This concept, which bridges MHD-based and
particle-based views of a flare, provides an interpretation of the
recently-observed rapid variations of the line-of-sight component of the
photospheric magnetic field across the flare impulsive phase, and offers
solutions to some perplexing flare problems, such as the flare "number problem"
of finding and resupplying sufficient electrons to explain the impulsive-phase
hard X-ray emission.Comment: 31 pages, 6 figure
No effect of 24 h severe energy restriction on appetite regulation and ad libitum energy intake in overweight and obese males
Background/Objectives: Long-term success of weight loss diets might depend on how the appetite regulatory system responds to energy restriction (ER). This study determined the effect of 24 h severe ER on subjective and hormonal appetite regulation, subsequent ad libitum energy intake and metabolism.
Subjects/Methods: In randomised order, eight overweight or obese males consumed a 24 h diet containing either 100% (12105 (1174 kJ; energy balance; EB) or 25% (3039 (295) kJ; ER) of estimated daily energy requirements (EER). An individualised standard breakfast containing 25% of EER (3216 (341) kJ) was consumed the following morning and resting energy expenditure, substrate utilisation and plasma concentrations of acylated ghrelin, glucagon-like peptide-1 (GLP-17–36), glucose-dependant insulinotropic peptide (GIP1–42), glucose, insulin and non-esterified fatty acid (NEFA) were determined for 4 h after breakfast. Ad libitum energy intake was assessed in the laboratory on day 2 and via food records on day 3. Subjective appetite was assessed throughout.
Results: Energy intake was not different between trials for day 2 (EB: 14946 (1272) kJ; ER: 15251 (2114) kJ; P=0.623), day 3 (EB: 10580 (2457) kJ; 10812 (4357) kJ; P=0.832) or day 2 and 3 combined (P=0.693). Subjective appetite was increased during ER on day 1 (P0.381). Acylated ghrelin, GLP-17–36 and insulin were not different between trials (P>0.104). Post-breakfast area under the curve (AUC) for NEFA (P<0.05) and GIP1–42 (P<0.01) were greater during ER compared with EB. Fat oxidation was greater (P<0.01) and carbohydrate oxidation was lower (P<0.01) during ER, but energy expenditure was not different between trials (P=0.158).
Conclusions: These results suggest that 24 h severe ER does not affect appetite regulation or energy intake in the subsequent 48 h. This style of dieting may be conducive to maintenance of a negative EB by limiting compensatory eating behaviour, and therefore may assist with weight loss
Residential mobility:Towards progress in mobility health research
Research into health disparities has long recognized the importance of residential mobility as a crucial factor in determining health outcomes. However, a lack of connectivity between the health and mobility literatures has led to a stagnation of theory and application on the health side, which lacks the detail and temporal perspectives now seen as critical to understanding residential mobility decisions. Through a critical re-think of mobility processes with respect to health outcomes and an exploitation of longitudinal analytical techniques, we argue that health geographers have the potential to better understand and identify the relationship that residential mobility has with health.“The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 615159 (ERC Consolidator Grant DEPRIVEDHOODS, Socio-spatial inequality, deprived neighbourhoods, and neighbourhood effects)”OLD Urban Renewal and Housin
The decline and rise of neighbourhoods: the importance of neighbourhood governance
There is a substantial literature on the explanation of neighbourhood change. Most of this literature concentrates on identifying factors and developments behind processes of decline. This paper reviews the literature, focusing on the identification of patterns of neighbourhood change, and argues that the concept of neighbourhood governance is a missing link in attempts to explain these patterns. Including neighbourhood governance in the explanations of neighbourhood change and decline will produce better explanatory models and, finally, a better view about what is actually steering neighbourhood change
Exploring effects of exercise on the functional connectome in patients with schizophrenia [Abstract]
Estimates of Densities and Filling Factors from a Cooling Time Analysis of Solar Microflares Observed with RHESSI
We use more than 4,500 microflares from the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) microflare data set (Christe et al., 2008, Ap.
J., 677, 1385) to estimate electron densities and volumetric filling factors of
microflare loops using a cooling time analysis. We show that if the filling
factor is assumed to be unity, the calculated conductive cooling times are much
shorter than the observed flare decay times, which in turn are much shorter
than the calculated radiative cooling times. This is likely unphysical, but the
contradic- tion can be resolved by assuming the radiative and conductive
cooling times are comparable, which is valid when the flare loop temperature is
a maximum and when external heating can be ignored. We find that resultant
radiative and con- ductive cooling times are comparable to observed decay
times, which has been used as an assumption in some previous studies. The
inferred electron densities have a mean value of 10^11.6 cm^-3 and filling
factors have a mean of 10^-3.7. The filling factors are lower and densities are
higher than previous estimates for large flares, but are similar to those found
for two microflares by Moore et al. (Ap. J., 526, 505, 1999).Comment: Published in Ap.
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