1,258 research outputs found
The Radiated Energy Budget of Chromospheric Plasma in a Major Solar Flare Deduced From Multi-Wavelength Observations
This paper presents measurements of the energy radiated by the lower solar
atmosphere, at optical, UV, and EUV wavelengths, during an X-class solar flare
(SOL2011-02-15T01:56) in response to an injection of energy assumed to be in
the form of nonthermal electrons. Hard X-ray observations from RHESSI were used
to track the evolution of the parameters of the nonthermal electron
distribution to reveal the total power contained in flare accelerated
electrons. By integrating over the duration of the impulsive phase, the total
energy contained in the nonthermal electrons was found to be
erg. The response of the lower solar atmosphere was measured in the free-bound
EUV continua of H I (Lyman), He I, and He II, plus the emission lines of He II
at 304\AA\ and H I (Ly) at 1216\AA\ by SDO/EVE, the UV continua at
1600\AA\ and 1700\AA\ by SDO/AIA, and the WL continuum at 4504\AA, 5550\AA, and
6684\AA, along with the Ca II H line at 3968\AA\ using Hinode/SOT. The summed
energy detected by these instruments amounted to erg;
about 15% of the total nonthermal energy. The Ly line was found to
dominate the measured radiative losses. Parameters of both the driving electron
distribution and the resulting chromospheric response are presented in detail
to encourage the numerical modelling of flare heating for this event, to
determine the depth of the solar atmosphere at which these line and continuum
processes originate, and the mechanism(s) responsible for their generation.Comment: 14 pages, 18 figures. Accepted for publication in Astrophysics
Journa
LaRC design analysis report for National Transonic Facility for 304 stainless steel tunnel shell. Volume 4S: Thermal analysis
For abstract, see N76-33552
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
LaRC design analysis report for National Transonic Facility for 304 stainless steel tunnel shell. Volume 7S: Special studies
For abstract, see N76-33552
Si IV Resonance Line Emission During Solar Flares: Non-LTE, Non-equilibrium, Radiation Transfer Simulations
The Interface Region Imaging Spectrograph (IRIS) routinely observes the Si IV
resonance lines. When analyzing observations of these lines it has typically
been assumed they form under optically thin conditions. This is likely valid
for the quiescent Sun, but this assumption has also been applied to the more
extreme flaring scenario. We used 36 electron beam driven radiation
hydrodynamic solar flare simulations, computed using the RADYN code, to probe
the validity of this assumption. Using these simulated atmospheres we solved
the radiation transfer equations to obtain the non-LTE, non-equilibrium
populations, line profiles, and opacities for a model Silicon atom, including
charge exchange processes. This was achieved using the `minority species'
version of RADYN. The inclusion of charge exchange resulted in a substantial
fraction of Si IV at cooler temperatures than those predicted by ionisation
equilibrium. All simulations with an injected energy flux
erg cm s resulted in optical depth effects on the Si IV emission,
with differences in both intensity and line shape compared to the optically
thin calculation. Weaker flares (down to erg cm
s) also resulted in Si IV emission forming under optically thick
conditions, depending on the other beam parameters. When opacity was
significant, the atmospheres generally had column masses in excess of
g cm over the temperature range to kK, and
the Si IV formation temperatures were between and kK. We urge caution
when analyzing Si IV flare observations, or when computing synthetic emission
without performing a full radiation transfer calculation.Comment: Accepted in the Astrophysical Journal, 23 pages (3 appendices, 15
figures
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
An inexpensive economical solar heating system for homes
A low-cost solar home heating system to supplement existing warm-air heating systems is described. The report is written in three parts: (1) a brief background on solar heating, (2) experience with a demonstration system, and (3) information for the homeowner who wishes to construct such a system. Instructions are given for a solar heating installation in which the homeowner supplies all labor necessary to install off-the-shelf components estimated to cost $2,000. These components, which include solar collector, heat exchanger, water pump, storage tank, piping, and controls to make the system completely automatic, are available at local lumber yards, hardware stores, and plumbing supply stores, and are relatively simple to install. Manufacturers and prices of each component used and a rough cost analysis based on these prices are included. This report also gives performance data obtained from a demonstration system which was built and tested at the Langley Research Center
Electron doped Ca10(Pt3As8)(Fe2As2)5 and Ca10(Pt4As8)(Fe2As2)5 - High Tc superconductors with skutterudite intermediary layers
It has been argued that the very high transition temperatures of the highest
Tc cuprate superconductors are facilitated by enhanced CuO2 plane coupling
through the (Bi,Tl,Hg)-O intermediary layers. Whether enhanced coupling through
intermediary layers can also influence Tc in the iron arsenide superconductors
has never been tested due the lack of appropriate systems for study. Here we
report the crystal structures and properties of two iron arsenide
superconductors, Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase) and
Ca10(Pt4As8)(Fe2As2)5 (the 10-4-8 phase). Based on -Ca-(PtnAs8)-Ca-Fe2As2-
layer stacking, the most important difference in the structures lies in the
structural and electronic characters of the intermediary platinum arsenide
layers. Electron doping through partial substitution of Pt for Fe in the Fe2As2
layers leads to Tc of 11 K in the 10-3-8 phase and 25 K in the 10-4-8 phase.
Using the chemical concepts of Zintl ion electron counting and the stability of
Pt in the 5d8 configuration we argue that the dramatic difference in Tc arises
because the intermediary layer is semiconducting in the 10-3-8 phase but
metallic in the 10-4-8 phase, leading to enhanced interlayer coupling in the
10-4-8 phase. The results suggest that metallic intermediary layers may offer a
new road to higher Tc in iron arsenide superconductors
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