57 research outputs found
New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
(abridged) The heating mechanism at high densities during M dwarf flares is
poorly understood. Spectra of M dwarf flares in the optical and
near-ultraviolet wavelength regimes have revealed three continuum components
during the impulsive phase: 1) an energetically dominant blackbody component
with a color temperature of T 10,000 K in the blue-optical, 2) a smaller
amount of Balmer continuum emission in the near-ultraviolet at lambda 3646
Angstroms and 3) an apparent pseudo-continuum of blended high-order Balmer
lines. These properties are not reproduced by models that employ a typical
"solar-type" flare heating level in nonthermal electrons, and therefore our
understanding of these spectra is limited to a phenomenological interpretation.
We present a new 1D radiative-hydrodynamic model of an M dwarf flare from
precipitating nonthermal electrons with a large energy flux of erg
cm s. The simulation produces bright continuum emission from a
dense, hot chromospheric condensation. For the first time, the observed color
temperature and Balmer jump ratio are produced self-consistently in a
radiative-hydrodynamic flare model. We find that a T 10,000 K
blackbody-like continuum component and a small Balmer jump ratio result from
optically thick Balmer and Paschen recombination radiation, and thus the
properties of the flux spectrum are caused by blue light escaping over a larger
physical depth range compared to red and near-ultraviolet light. To model the
near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer
lines, we include the extra Balmer continuum opacity from Landau-Zener
transitions that result from merged, high order energy levels of hydrogen in a
dense, partially ionized atmosphere. This reveals a new diagnostic of ambient
charge density in the densest regions of the atmosphere that are heated during
dMe and solar flares.Comment: 50 pages, 2 tables, 13 figures. Accepted for publication in the Solar
Physics Topical Issue, "Solar and Stellar Flares". Version 2 (June 22, 2015):
updated to include comments by Guest Editor. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11207-015-0708-
Trade-offs between reducing complex terminology and producing accurate interpretations from environmental DNA: Comment on “Environmental DNA: What’s behind the term?” by Pawlowski et al. (2020)
Observational Consequences of Evolution of Primordial Fluctuations in Scalar-Tensor Cosmology
Evolution of primordial fluctuations in a Brans-Dicke type scalar-tensor
gravity theory is comprehensively investigated. The harmonic attractor model,
in which the scalar field has its harmonic effective potential in the Einstein
conformal frame and the theory relaxes toward Einstein gravity with time, is
considered. The evolution of adiabatic initial perturbations in flat SCDM
models is examined from the radiation-dominated epoch up to the present. We
discuss how the scalar-tensor gravity affects the evolution of metric and
matter perturbations, mainly focusing on the observational consequences, i.e.,
the matter power spectrum and the power spectrum of cosmic microwave background
temperature. We find that the early time deviation is characterized only by the
large static gravitational constant while the late time behavior is
qualitatively different from that in Einstein gravity because the time
variation of the gravitational constant and its fluctuation have non-negligible
effects. The attracting scalar-tensor gravity affects only small scale modes
due to its attracting nature, the degree of which is far beyond the
post-Newtonian deviation at the present epoch.Comment: 18 page
Gravitationally violated U(1) symmetry and neutrino anomalies
The current searches for neutrino oscillations seem to suggest an approximate
L_e-L_\m-L_{\tau} flavor symmetry. This symmetry implies a pair of degenerate
neutrinos with mass and large leptonic mixing. We explore the possibility
that gravitational interactions break this global symmetry. The Planck scale
suppressed breaking of the L_e-L_\m-L_{\tau} symmetry is shown to lead to the
right amount of splitting among the degenerate neutrinos needed in order to
solve the solar neutrino problem. The common mass of the pair can be
identified with the atmospheric neutrino scale. A concrete model is proposed in
which smallness of and hierarchy in the solar and atmospheric neutrino
scales get linked to hierarchies in the weak, grand unification and the Planck
scales.Comment: 12 pages, LATE
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Long-term outcome after atrial correction for transposition of the great arteries
Objective This study assessed adult survival and morbidity patterns in patients who underwent atrial correction according to Mustard or Senning for transposition of the great arteries (TGA).Methods In 76 adult patients with TGA (59% male) after atrial correction, long-term survival and morbidity were investigated in three periods: early (30 years postoperatively).Results The Mustard technique was performed in 41 (54%) patients, and the Senning technique was performed in 35 (46%) patients aged 3.1 (IQR: 2.1-3.8) and 1.0 (IQR: 0.6-3.1; p= 2 in 34 (48%) patients. Bradyarrhythmia, SVT and ventricular arrhythmia were associated with depressed RV function (OR: 4.47, 95% CI 1.50 to 13.28, p<0.01; OR: 3.74, 95% CI 1.26 to 11.14, p=0.02; OR: 14.40, 95% CI 2.80 to 74.07, p<0.01, respectively) and worse functional capacity (OR: 2.10, 95% CI 0.75 to 5.82, p=0.16; OR: 2.87, 95% CI 1.06 to 7.81, p=0.04; OR: 8.47, 95% CI 1.70 to 42.10, p<0.01, respectively).Conclusions In adult patients with TGA, survival was 82% at 39.7 (IQR: 35.9-42.4) years after atrial correction. Morbidity was high and included SVT as most frequent adverse event. Ventricular arrhythmias, heart failure and surgical reinterventions were common during late follow-up. Adverse events were associated with depressed right ventricle function and reduced functional class.Cardiolog
Pump Speed Optimization in Stable Patients with a Left Ventricular Assist Device
Cardiolog
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