2,856 research outputs found
Parameterizations of Chromospheric Condensations in dG and dMe Model Flare Atmospheres
The origin of the near-ultraviolet and optical continuum radiation in flares
is critical for understanding particle acceleration and impulsive heating in
stellar atmospheres. Radiative-hydrodynamic simulations in 1D have shown that
high energy deposition rates from electron beams produce two flaring layers at
T~10^4 K that develop in the chromosphere: a cooling condensation (downflowing
compression) and heated non-moving (stationary) flare layers just below the
condensation. These atmospheres reproduce several observed phenomena in flare
spectra, such as the red wing asymmetry of the emission lines in solar flares
and a small Balmer jump ratio in M dwarf flares. The high beam flux simulations
are computationally expensive in 1D, and the (human) timescales for completing
NLTE models with adaptive grids in 3D will likely be unwieldy for a time to
come. We have developed a prescription for predicting the approximate evolved
states, continuum optical depth, and the emergent continuum flux spectra of
radiative-hydrodynamic model flare atmospheres. These approximate prescriptions
are based on an important atmospheric parameter: the column mass (m_ref) at
which hydrogen becomes nearly completely ionized at the depths that are
approximately in steady state with the electron beam heating. Using this new
modeling approach, we find that high energy flux density (>F11) electron beams
are needed to reproduce the brightest observed continuum intensity in IRIS data
of the 2014-Mar-29 X1 solar flare and that variation in m_ref from 0.001 to
0.02 g/cm2 reproduces most of the observed range of the optical continuum flux
ratios at the peaks of M dwarf flares.Comment: 29 pages, 9 figures, accepted for publication in the Astrophysical
Journa
Optical Spectral Observations of a Flickering White-Light Kernel in a C1 Solar Flare
We analyze optical spectra of a two-ribbon, long duration C1.1 flare that
occurred on 18 Aug 2011 within AR 11271 (SOL2011-08-18T15:15). The impulsive
phase of the flare was observed with a comprehensive set of space-borne and
ground-based instruments, which provide a range of unique diagnostics of the
lower flaring atmosphere. Here we report the detection of enhanced continuum
emission, observed in low-resolution spectra from 3600 \AA\ to 4550 \AA\
acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small,
0''.5 ( cm) penumbral/umbral kernel brightens repeatedly in
the optical continuum and chromospheric emission lines, similar to the temporal
characteristics of the hard X-ray variation as detected by the Gamma-ray Burst
Monitor (GBM) on the Fermi spacecraft. Radiative-hydrodynamic flare models that
employ a nonthermal electron beam energy flux high enough to produce the
optical contrast in our flare spectra would predict a large Balmer jump in
emission, indicative of hydrogen recombination radiation from the upper flare
chromosphere. However, we find no evidence of such a Balmer jump in the
bluemost spectral region of the continuum excess. Just redward of the expected
Balmer jump, we find evidence of a "blue continuum bump" in the excess emission
which may be indicative of the merging of the higher order Balmer lines. The
large number of observational constraints provides a springboard for modeling
the blue/optical emission for this particular flare with radiative-hydrodynamic
codes, which are necessary to understand the opacity effects for the continuum
and emission line radiation at these wavelengths.Comment: 54 pages, 13 figures, accepted for publication in the Astrophysical
Journa
A Unified Computational Model for Solar and Stellar Flares
We present a unified computational framework which can be used to describe
impulsive flares on the Sun and on dMe stars. The models assume that the flare
impulsive phase is caused by a beam of charged particles that is accelerated in
the corona and propagates downward depositing energy and momentum along the
way. This rapidly heats the lower stellar atmosphere causing it to explosively
expand and dramatically brighten. Our models consist of flux tubes that extend
from the sub-photosphere into the corona. We simulate how flare-accelerated
charged particles propagate down one-dimensional flux tubes and heat the
stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative
transfer is included so that model predictions can be directly compared with
observations. The flux of flare-accelerated particles drives return currents
which additionally heat the stellar atmosphere. These effects are also included
in our models. We examine the impact of the flare-accelerated particle beams on
model solar and dMe stellar atmospheres and perform parameter studies varying
the injected particle energy spectra. We find the atmospheric response is
strongly dependent on the accelerated particle cutoff energy and spectral
index.Comment: Accepted for publication by the Astrophysical Journa
Correlation Between Time to Peak Torque and Peak Torque to Vertical Jump in College Age Athletes
The vertical jump is an essential part of athletics to gain an advantage over the opponent. Isokinetic testing provides quantitative data to determine power and how fast power or peak torque is achieved. In this study, after 20 NCAA Div. II athletes were measured for three trials of maximal vertical jump, they completed an isokinetic test of knee extension at speeds of 60, 180, and 300°/sec. The results showed a significant correlation (p\u3c0.05) between peak torque at a speed of 300°/sec and vertical jump p\u3c=0.019. As a result of this study it was found that the vertical jump test is a test of muscle power generated by the quadriceps muscle group, and relates to peak torque values documented by isokinetic testing at 300°/sec of knee extension
Modeling Mg II h, k and Triplet Lines at Solar Flare Ribbons
Observations from the \textit{Interface Region Imaging Spectrograph}
(\textsl{IRIS}) often reveal significantly broadened and non-reversed profiles
of the Mg II h, k and triplet lines at flare ribbons. To understand the
formation of these optically thick Mg II lines, we perform plane parallel
radiative hydrodynamics modeling with the RADYN code, and then recalculate the
Mg II line profiles from RADYN atmosphere snapshots using the radiative
transfer code RH. We find that the current RH code significantly underestimates
the Mg II h \& k Stark widths. By implementing semi-classical perturbation
approximation results of quadratic Stark broadening from the STARK-B database
in the RH code, the Stark broadenings are found to be one order of magnitude
larger than those calculated from the current RH code. However, the improved
Stark widths are still too small, and another factor of 30 has to be multiplied
to reproduce the significantly broadened lines and adjacent continuum seen in
observations. Non-thermal electrons, magnetic fields, three-dimensional effects
or electron density effect may account for this factor. Without modifying the
RADYN atmosphere, we have also reproduced non-reversed Mg II h \& k profiles,
which appear when the electron beam energy flux is decreasing. These profiles
are formed at an electron density of
and a temperature of K, where the source function slightly
deviates from the Planck function. Our investigation also demonstrates that at
flare ribbons the triplet lines are formed in the upper chromosphere, close to
the formation heights of the h \& k lines
Anti-Scientific Currents in American Thought
Multifarious forces have surrounded science and continue their—sometimes separate, sometimes coordinated—attempts to supplant a scientific approach to an explanation of important questions about us and the world we inhabit. We focus here on questions pertaining to biology and medicine, but no aspect of the scientific enterprise is immune from attack; and not all of the forces aligned against it are represented. The ones considered are: religion, neoliberalism, postmodernism, the “back-to-nature” movement, bioethical obstructionism, and the current POTUS, Donald Trump. We sit in amazement that at the amount of vitriol that has been leveled at science, but try to maintain civility in response. We would be irenic, not polemic; promoting true dialogue between respected scholars holding somewhat differing views. This is not as difficult as some would have you believe
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