1,428 research outputs found
LaRC design analysis report for National Transonic Facility for 304 stainless steel tunnel shell. Volume 4S: Thermal analysis
For abstract, see N76-33552
Symmetry of re-entrant tetragonal phase in Ba1-xNaxFe2As2: Magnetic versus orbital ordering mechanism
Magneto-structural phase transitions in Ba1-xAxFe2As2 (A = K, Na) materials
are discussed for both magnetically and orbitally driven mechanisms, using a
symmetry analysis formulated within the Landau theory of phase transitions.
Both mechanisms predict identical orthorhombic space-group symmetries for the
nematic and magnetic phases observed over much of the phase diagram, but they
predict different tetragonal space-group symmetries for the newly discovered
re-entrant tetragonal phase in Ba1-xNaxFe2As2 (x ~ 0.24-0.28). In a magnetic
scenario, magnetic order with moments along the c-axis, as found
experimentally, does not allow any type of orbital order, but in an orbital
scenario, we have determined two possible orbital patterns, specified by
P4/mnc1' and I4221' space groups, which do not require atomic displacements
relative to the parent I4/mmm1' symmetry and, in consequence, are
indistinguishable in conventional diffraction experiments. We demonstrate that
the three possible space groups are however, distinct in resonant X-ray Bragg
diffraction patterns created by Templeton & Templeton scattering. This provides
an experimental method of distinguishing between magnetic and orbital models
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
Technology, design, simulation, and evaluation for SEP-hardened circuits
This paper describes the technology, design, simulation, and evaluation for improvement of the Single Event Phenomena (SEP) hardness of gate-array and SRAM cells. Through the use of design and processing techniques, it is possible to achieve an SEP error rate less than 1.0 x 10(exp -10) errors/bit-day for a 9O percent worst-case geosynchronous orbit environment
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
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
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
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