15,605 research outputs found
Investigating the Rotational Phase of Stellar Flares on M dwarfs Using K2 Short Cadence Data
We present an analysis of K2 short cadence data of 34 M dwarfs which have
spectral types in the range M0 - L1. Of these stars, 31 showed flares with a
duration between 10-90 min. Using distances obtained from Gaia DR2
parallaxes, we determined the energy of the flares to be in the range
erg. In agreement with previous studies
we find rapidly rotating stars tend to show more flares, with evidence for a
decline in activity in stars with rotation periods longer than 10 days.
The rotational modulation seen in M dwarf stars is widely considered to result
from a starspot which rotates in and out of view. Flux minimum is therefore the
rotation phase where we view the main starspot close to the stellar disk
center. Surprisingly, having determined the rotational phase of each flare in
our study we find none show any preference for rotational phase. We outline
three scenarios which could account for this unexpected finding. The
relationship between rotation phase and flare rate will be explored further
using data from wide surveys such as NGTS and TESS.Comment: Accepted main Journal MNRA
Existing motor state is favored at the expense of new movement during 13-35 Hz oscillatory synchrony in the human corticospinal system
Oscillations in local field potentials in the β-frequency band (13-35 Hz) are a pervasive feature of human and nonhuman primate motor cortical areas. However, the function of such synchronous activity across populations of neurons remains unknown. Here, we test the hypothesis that β activity may promote existing motor set and posture while compromising processing related to new movements. Three experiments were performed. First, healthy subjects were instructed to make reaction time movements of the outstretched index finger in response to imperative cues triggered by transient increases in corticospinal synchrony, as evidenced by phasic elevations of β-frequency band microtremor and intermuscular synchrony. Second, healthy subjects were instructed to resist a stretch to the index finger triggered in the same way. Finger acceleration in the reaction time task and transcortical components of the stretch reflex were measured and compared with those elicited by random cue or stretch presentation. Finally, we sought a correlation between finger acceleration in the reaction time task and cortical synchrony directly measured from the electrocorticogram in two patients undergoing functional neurosurgery. We demonstrate that movements are slowed and transcortical responses to stretch are potentiated during periods of elevated β-band cortical synchrony. The results suggest that physiological periods of β synchrony are associated with a cortical state in which postural set is reinforced, but the speed of new movements impaired. The findings are of relevance to Parkinson's disease, in which subcortical and cortical β-band synchronization is exaggerated in the setting of increased tone and slowed movements
LABOR PRODUCTIVITY WITHIN THE AFRICAN AGRICULTURAL HOUSEHOLD: THE HOUSEHOLD PRODUCTION MODEL REVISITED
The benchmark concept is used to understand changes in farm household response to development dynamics. 1996-97 cropping seasons data from Cameroon is used to develop and test a "separate spheres" household model. Labor productivity for men and women is discussed, along with their implications for research and resource management policies.agriculture, labor productivity, gender, production, consumption, Consumer/Household Economics, Labor and Human Capital,
Effects of resonant magnetic perturbations on turbulence and transport in DIII-D L-mode plasmas
In this paper we show that resonant magnetic perturbations (RMPs) affect the L- to H-mode power threshold. We find that during the L-mode phase, RMPs cause the particle pinch to reverse from traditionally inward to outward. As a result, the density at the plasma edge increases, while the density in the plasma core is reduced. Linear stability calculations indicate that the plasma transitions from an ion temperature gradient (ITG) to trapped electron mode (TEM) regime at the plasma edge. If the applied RMP current is below the threshold for penetration and island formation, we find that the changes in the edge radial electric field are minimal, while the carbon toroidal rotation brakes over the whole minor radius. Once the RMP field penetrates and the screening plasma response dissappears, the spin-up of the toroidal rotation at the plasma edge results in a positive radial electric field inside the separatrix
A Chondritic Solar Neighborhood
A persistent question in exoplanet demographics is whether exoplanetary
systems form from similar compositional building blocks to our own. Polluted
white dwarf stars offer a unique way to address this question as they provide
measurements of the bulk compositions of exoplanetary material. We present a
statistical analysis of the rocks polluting oxygen-bearing white dwarfs and
compare their compositions to rocks in the Solar System. We find that the
majority of the extrasolar rocks are consistent with the composition of typical
chondrites. Measurement uncertainties prevent distinguishing between chondrites
and bulk Earth, but do permit detecting the differences between chondritic
compositions and basaltic or continental crust. We find no evidence of crust
amongst the polluted white dwarfs. We show that the chondritic nature of
extrasolar rocks is also supported by the compositions of local stars. While
galactic chemical evolution results in variations in the relative abundances of
rock-forming elements spatially and temporally on galaxy-wide scales, the
current sample of polluted white dwarfs are sufficiently young and close to
Earth that they are not affected by this process. We conclude that exotic
compositions are not required to explain the majority of observed rock types
around polluted white dwarfs, and that variations between exoplanetary
compositions in the stellar neighborhood are generally not due to significant
differences in the initial composition of protoplanetary disks. Nonetheless,
there is evidence from stellar observations that planets formed in the first
several billion years in the Galaxy have lower metal core fractions compared
with Earth on average.Comment: Accepted to PS
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