1,405 research outputs found
Solar Ellerman Bombs in 1D Radiative Hydrodynamics
Recent observations from the Interface Region Imaging Spectrograph (IRIS)
appear to show impulsive brightenings in high temperature lines, which when
combined with simultaneous ground based observations in H, appear
co-spatial to Ellerman Bombs (EBs). We use the RADYN 1-dimensional radiative
transfer code in an attempt to try and reproduce the observed line profiles and
simulate the atmospheric conditions of these events. Combined with the MULTI/RH
line synthesis codes, we compute the H, Ca II 8542~\AA, and Mg II h \&
k lines for these simulated events and compare them to previous observations.
Our findings hint that the presence of superheated regions in the photosphere
(10,000 K) is not a plausible explanation for the production of EB
signatures. While we are able to recreate EB-like line profiles in H,
Ca II 8542~\AA, and Mg II h \& k, we cannot achieve agreement with all of these
simultaneously.Comment: Accepted into ApJL. 4 Figures, 1 Tabl
Bi2Te1.6S1.4 - a Topological Insulator in the Tetradymite Family
We describe the crystal growth, crystal structure, and basic electrical
properties of Bi2Te1.6S1.4, which incorporates both S and Te in its Tetradymite
quintuple layers in the motif -[Te0.8S0.2]-Bi-S-Bi-[Te0.8S0.2]-. This material
differs from other Tetradymites studied as topological insulators due to the
increased ionic character that arises from its significant S content.
Bi2Te1.6S1.4 forms high quality crystals from the melt and is the S-rich limit
of the ternary Bi-Te-S {\gamma}-Tetradymite phase at the melting point. The
native material is n-type with a low resistivity; Sb substitution, with
adjustment of the Te to S ratio, results in a crossover to p-type and resistive
behavior at low temperatures. Angle resolved photoemission study shows that
topological surface states are present, with the Dirac point more exposed than
it is in Bi2Te3 and similar to that seen in Bi2Te2Se. Single crystal structure
determination indicates that the S in the outer chalcogen layers is closer to
the Bi than the Te, and therefore that the layers supporting the surface states
are corrugated on the atomic scale.Comment: To be published in Physical Review B Rapid Communications 16 douuble
spaced pages. 4 figures 1 tabl
Hydrogen Balmer Line Broadening in Solar and Stellar Flares
The broadening of the hydrogen lines during flares is thought to result from
increased charge (electron, proton) density in the flare chromosphere. However,
disagreements between theory and modeling prescriptions have precluded an
accurate diagnostic of the degree of ionization and compression resulting from
flare heating in the chromosphere. To resolve this issue, we have incorporated
the unified theory of electric pressure broadening of the hydrogen lines into
the non-LTE radiative transfer code RH. This broadening prescription produces a
much more realistic spectrum of the quiescent, A0 star Vega compared to the
analytic approximations used as a damping parameter in the Voigt profiles. We
test recent radiative-hydrodynamic (RHD) simulations of the atmospheric
response to high nonthermal electron beam fluxes with the new broadening
prescription and find that the Balmer lines are over-broadened at the densest
times in the simulations. Adding many simultaneously heated and cooling model
loops as a "multithread" model improves the agreement with the observations. We
revisit the three-component phenomenological flare model of the YZ CMi
Megaflare using recent and new RHD models. The evolution of the broadening,
line flux ratios, and continuum flux ratios are well-reproduced by a
multithread model with high-flux nonthermal electron beam heating, an extended
decay phase model, and a "hot spot" atmosphere heated by an ultrarelativistic
electron beam with reasonable filling factors: 0.1%, 1%, and 0.1% of the
visible stellar hemisphere, respectively. The new modeling motivates future
work to understand the origin of the extended gradual phase emission.Comment: 31 pages, 13 figures, 2 tables, accepted for publication in the
Astrophysical Journa
LaRC design analysis report for National Transonic Facility for 304 stainless steel tunnel shell. Volume 4S: Thermal analysis
For abstract, see N76-33552
LaRC design analysis report for National Transonic Facility for 304 stainless steel tunnel shell. Volume 7S: Special studies
For abstract, see N76-33552
LaRC design analysis report for national transonic facility for 9% nickel tunnel shell. Volume 7: Special studies
For abstract, see N76-33543
LaRC design analysis report for National Transonic Facility for 9% nickel tunnel shell. Volume 3: Finite element analysis of plenum region including side access reinforcement, side access door and angle of attack penetration
For abstract, see N76-33543
Extreme Sensitivity of Superconductivity to Stoichiometry in FeSe (Fe1+dSe)
The recently discovered iron arsenide superconductors, which display
superconducting transition temperatures as high as 55 K, appear to share a
number of general features with high-Tc cuprates, including proximity to a
magnetically ordered state and robustness of the superconductivity in the
presence of disorder. Here we show that superconductivity in Fe1+dSe, the
parent compound of the superconducting arsenide family, is destroyed by very
small changes in stoichiometry. Further, we show that non-superconducting
Fe1+dSe is not magnetically ordered down to low temperatures. These results
suggest that robust superconductivity and immediate instability against an
ordered magnetic state should not be considered as intrinsic characteristics of
iron-based superconducting systems, and that Fe1+dSe may present a unique
opportunity for determining which materials characteristics are critical to the
existence of superconductivity in high Tc iron arsenide superconductors and
which are not.Comment: Updated to reflect final version and include journal referenc
New York's Southern Tier Landowners' Management for Early Successional Forest Habitat: Attitudes, Barriers and Motivations
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