7,419 research outputs found
Pressure and heat flux results from the space shuttle/external fuel tank interaction test at Mach numbers 16 and 19
Heat transfer rates and pressures were measured on a 0.0175-scale model of the space shuttle external tank (ET), model MCR0200. Tests were conducted with the ET model separately and while mated with a 0.0175-scale model of the orbiter, model 21-OT (Grumman). The tests were conducted in the AEDC-VKF Hypervelocity Wind Tunnel (F) at Mach numbers 16 and 19. The primary data consisted of the interaction heating rates experienced by the ET while mated with the orbiter in the flight configuration. Data were taken for a range of Reynolds numbers from 50,000 to 65,000 under laminar flow conditions
Hypersonic rarefied wake characterization
Results of a numerical study using the direct simulation Monte Carlo (DSMC) method are presented for hypersonic rarefied flow over an aeroassisted space transfer vehicle (ASTV). The emphasis of the study is the characterization of the near wake region which includes the ASTV payload. The study covered the transitional flow regime from near continuum to free molecular. Calculations show that the character of the near wake is significantly affected by the presence of the payload. Flow separation occurs when an afterbody is present throughout the transitional flow regime. In contrast, when no afterbody is present, no separation is observed until the flow approaches continuum
Covalent bonding and the nature of band gaps in some half-Heusler compounds
Half-Heusler compounds \textit{XYZ}, also called semi-Heusler compounds,
crystallize in the MgAgAs structure, in the space group . We report a
systematic examination of band gaps and the nature (covalent or ionic) of
bonding in semiconducting 8- and 18- electron half-Heusler compounds through
first-principles density functional calculations. We find the most appropriate
description of these compounds from the viewpoint of electronic structures is
one of a \textit{YZ} zinc blende lattice stuffed by the \textit{X} ion. Simple
valence rules are obeyed for bonding in the 8-electron compound. For example,
LiMgN can be written Li + (MgN), and (MgN), which is isoelectronic
with (SiSi), forms a zinc blende lattice. The 18-electron compounds can
similarly be considered as obeying valence rules. A semiconductor such as
TiCoSb can be written Ti + (CoSb); the latter unit is
isoelectronic and isostructural with zinc-blende GaSb. For both the 8- and
18-electron compounds, when \textit{X} is fixed as some electropositive cation,
the computed band gap varies approximately as the difference in Pauling
electronegativities of \textit{Y} and \textit{Z}. What is particularly exciting
is that this simple idea of a covalently bonded \textit{YZ} lattice can also be
extended to the very important \textit{magnetic} half-Heusler phases; we
describe these as valence compounds \textit{ie.} possessing a band gap at the
Fermi energy albeit only in one spin direction. The \textit{local} moment in
these magnetic compounds resides on the \textit{X} site.Comment: 18 pages and 14 figures (many in color
Virtual light-by-light scattering and the g factor of a bound electron
The contribution of the light-by-light diagram to the g factor of electron
and muon bound in Coulomb field is obtained. For electron in a ground state,
our results are in good agreement with the results of other authors obtained
numerically for large Z. For relatively small Z our results have essentially
higher accuracy as compared to the previous ones. For muonic atoms, the
contribution is obtained for the first time with the high accuracy in whole
region of Z.Comment: 10 pages, 3 figures, RevTe
Collective modes and correlations in one-component plasmas
The static and time-dependent potential and surface charge correlations in a
plasma with a boundary are computed for different shapes of the boundary. The
case of a spheroidal or spherical one-component plasma is studied in detail
because experimental results are available for such systems. Also, since there
is some knowlegde both experimental and theoretical about the electrostatic
collective modes of these plasmas, the time-dependent correlations are computed
using a method involving these modes.Comment: 20 pages, plain TeX, submitted to Phys. Rev.
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
A Quality Improvement Project to Standardize Surfactant Delivery in the Era of Noninvasive Ventilation.
Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOsSb
Transverse-field muon spin rotation (SR) experiments in the
heavy-fermion superconductor PrOsSb ( K) suggest that
the superconducting penetration depth is temperature-independent
at low temperatures, consistent with a gapped quasiparticle excitation
spectrum. In contrast, radiofrequency (rf) inductive measurements yield a
stronger temperature dependence of , indicative of point nodes in
the gap. This discrepancy appears to be related to the multiband structure of
PrOsSb. Muon Knight shift measurements in PrOsSb
suggest that the perturbing effect of the muon charge on the neighboring
Pr crystalline electric field is negligibly small, and therefore is
unlikely to cause the difference between the SR and rf results.Comment: 10 pages, 7 figure
Carbon Stars and other Luminous Stellar Populations in M33
The M33 galaxy is a nearby, relatively metal-poor, late-type spiral. Its
proximity and almost face-on inclination means that it projects over a large
area on the sky, making it an ideal candidate for wide-field CCD mosaic
imaging. Photometry was obtained for more than 10^6 stars covering a 74' x 56'
field centered on M33. Main sequence (MS), supergiant branch (SGB), red giant
branch (RGB) and asymptotic giant branch (AGB) populations are identified and
classified based on broad-band V and I photometry. Narrow-band filters are used
to measure spectral features allowing the AGB population to be further divided
into C and M-star types. The galactic structure of M33 is examined using star
counts, colour-colour and colour-magnitude selected stellar populations. We use
the C to M-star ratio to investigate the metallicity gradient in the disk of
M33. The C/M-star ratio is found to increase and then flatten with increasing
galactocentric radius in agreement with viscous disk formation models. The
C-star luminosity function is found to be similar to M31 and the SMC,
suggesting that C-stars should be useful distance indicators. The ``spectacular
arcs of carbon stars'' in M33 postulated recently by Block et al. (2004) are
found in our work to be simply an extension of M33's disk.Comment: 20 pages, 20 figures. Accepted for publication in The Astronomical
Journa
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