282 research outputs found
The Effect of Magnetic Variability on Stellar Angular Momentum Loss II: The Sun, 61 Cygni A, Eridani, Bootis A and Bootis A
The magnetic fields of low-mass stars are observed to be variable on decadal
timescales, ranging in behaviour from cyclic to stochastic. The changing
strength and geometry of the magnetic field should modify the efficiency of
angular momentum loss by stellar winds, but this has not been well quantified.
In Finley et al. (2018) we investigated the variability of the Sun, and
calculated the time-varying angular momentum loss rate in the solar wind. In
this work, we focus on four low-mass stars that have all had their surface
magnetic fields mapped for multiple epochs. Using mass loss rates determined
from astrospheric Lyman- absorption, in conjunction with scaling
relations from the MHD simulations of Finley & Matt (2018), we calculate the
torque applied to each star by their magnetised stellar winds. The variability
of the braking torque can be significant. For example, the largest torque for
Eri is twice its decadal averaged value. This variation is
comparable to that observed in the solar wind, when sparsely sampled. On
average, the torques in our sample range from 0.5-1.5 times their average
value. We compare these results to the torques of Matt et al. (2015), which use
observed stellar rotation rates to infer the long-time averaged torque on
stars. We find that our stellar wind torques are systematically lower than the
long-time average values, by a factor of ~3-30. Stellar wind variability
appears unable to resolve this discrepancy, implying that there remain some
problems with observed wind parameters, stellar wind models, or the long-term
evolution models, which have yet to be understood.Comment: 15 pages + 8 figures, accepted for publication to Ap
Further evidence of the link between activity and metallicity using the flaring properties of stars in the Kepler field
The magnetic activity level of low-mass stars is known to vary as a function
of the physical properties of the star. Many studies have shown that the
stellar mass and rotation are both important parameters that determine magnetic
activity levels. In contrast, the impact of a star's chemical composition on
magnetic activity has received comparatively little attention. Data sets for
traditional activity proxies, e.g. X-ray emission or calcium emission, are not
large enough to search for metallicity trends in a statistically meaningful
way. Recently, studies have used the photometric variability amplitude as a
proxy for magnetic activity to investigate the role of metallicity because it
can be relatively easily measured for large samples of stars. These studies
find that magnetic activity and metallicity are positively correlated. In this
work, we investigate the link between activity and metallicity further by
studying the flaring properties of stars in the Kepler field. Similar to the
photometric variability, we find that flaring activity is stronger in more
metal-rich stars for a fixed mass and rotation period. This result adds to a
growing body of evidence that magnetic field generation is correlated with
metallicity.Comment: 6 pages, 5 figures, accepted for publication in MNRA
Insurance Perspectives on Federal Financial Regulatory Reform: Addressing Misunderstandings and Providing a View from A Different Paradigm
Conformational changes in alpha 7 acetylcholine receptors underlying allosteric modulation by divalent cations
Abstract Allosteric modulation of membrane receptors is a widespread mechanism by which endogenous and exogenous agents regulate receptor function. For example, several members of the nicotinic receptor family are modulated by physiological concentrations of extracellular calcium ions. In this paper, we examined conformational changes underlying this modulation and compare these with changes evoked by ACh. Two sets of residues in the α7 acetylcholine receptor extracellular domain were mutated to cysteine and analyzed by measuring the rates of modification by the thiol-specific reagent 2-aminoethylmethane thiosulfonate. Using Ba2+ as a surrogate for Ca2+, we found a divalent-dependent decrease the modification rates of cysteine substitutions at M37 and M40, residues at which rates were also slowed by ACh. In contrast, Ba2+ had no significant effect at N52C, a residue where ACh increased the rate of modification. Thus divalent modulators cause some but not all of the conformational effects elicited by agonist. Cysteine substitution of either of two glutamates (E44 or E172), thought to participate in the divalent cation binding site, caused a loss of allosteric modulation, yet Ba2+ still had a significant effect on modification rates of these residues. In addition, the effect of Ba2+ at these residues did not appear to be due to direct occlusion. Our data demonstrate that modulation by divalent cations involves substantial conformational changes in the receptor extracellular domain. Our evidence also suggests the modulation occurs via a binding site distinct from one which includes either (or both) of the conserved glutamates at E44 or E172
Potentially modifiable dementia risk factors in all Australians and within population groups: an analysis using cross-sectional survey data
Background:
Dementia is the second leading cause of disease burden in Australia. We aimed to calculate the population attributable fractions (PAFs) of dementia attributable to 11 of 12 previously identified potentially modifiable health and social risk factors (less education, hearing loss, hypertension, obesity, smoking, depression, social isolation, physical inactivity, diabetes, alcohol excess, air pollution, and traumatic brain injury), for Australians overall and three population groups (First Nations, and those of European and Asian ancestry).
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Methods:
We calculated the prevalence of dementia risk factors (excluding traumatic brain injury) and PAFs, adjusted for communality, from the cross-sectional National Aboriginal and Torres Strait Islander Health Survey (2018–19), National Aboriginal and Torres Strait Islander Social Survey (2014–15), National Health Survey (2017–18), and General Social Survey (2014) conducted by the Australian Bureau of Statistics. We conducted sensitivity analyses using proxy estimates for traumatic brain injury (12th known risk factor) for which national data were not available.
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Findings:
A large proportion (38·2%, 95% CI 37·2–39·2) of dementia in Australia was theoretically attributable to the 11 risk factors; 44·9% (43·1–46·7) for First Nations Australians, 36·4% (34·8–38·1) for European ancestry, and 33·6% (30·1–37·2) for Asian ancestry. Including traumatic brain injury increased the PAF to 40·6% (39·6–41·6) for all Australians. Physical inactivity (8·3%, 7·5–9·2), hearing loss (7·0%, 6·4–7·6), and obesity (6·6%, 6·0–7·3) accounted for approximately half of the total PAF estimates across Australia, and for all three population groups.
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Interpretation:
Our PAF estimates indicate a substantial proportion of dementia in Australia is potentially preventable, which is broadly consistent with global trends and results from other countries. The highest potential for dementia prevention was among First Nations Australians, reflecting the enduring effect of upstream social, political, environmental, and economic disadvantage, leading to greater life-course exposure to dementia risk factors. Although there were common dementia risk factors across different population groups, prevention strategies should be informed by community consultation and be culturally and linguistically appropriate.
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Funding:
Australian National Health and Medical Research Council and University College London Hospitals’ National Institute for Health Research (NIHR) Biomedical Research Centre, and North Thames NIHR Applied Research Collaboration
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