14,023 research outputs found
Design outline for a new multiman ATC simulation facility at NASA-Ames Research Center
A new and unique facility for studying human factors aspects in aeronautics is being planned for use in the Man-Vehicle Systems Research Division at the NASA-Ames Research Center. This facility will replace the existing three cockpit-single ground controller station and be expandable to include approximately seven cockpits and two ground controller stations. Unlike the previous system, each cockpit will be mini-computer centered and linked to a main CPU to effect a distributed computation facility. Each simulator will compute its own flight dynamic and flight path predictor. Mechanical flight instruments in each cockpit will be locally supported and CRT cockpit displays of (e.g.) traffic and or RNAV information will be centrally computed and distributed as a means of extending the existing computational and graphical resources. An outline of the total design is presented which addresses the technical design options and research possibilities of this unique man-machine facility and which may also serve as a model for other real time distributed simulation facilities
A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283
Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron
capture processes: the s- and r-process. Metal-poor stars should contain fewer
isotopes that form via the s-process, according to currently accepted theory.
It has been shown in several investigations that theory and observation do not
agree well, raising questions on the validity of either the methodology or the
theory. We analyse the metal-poor star HD140283, for which we have a high
quality spectrum. We test whether a 3D LTE stellar atmosphere and spectrum
synthesis code permits a more reliable analysis of the iron abundance and
barium isotope ratio than a 1D LTE analysis. Using 3D model atmospheres, we
examine 91 iron lines of varying strength and formation depth. This provides us
with the star's rotational speed. With this, we model the barium isotope ratio
by exploiting the hyperfine structure of the singly ionised 4554 resonance
line, and study the impact of the uncertainties in the stellar parameters.
HD140283's vsini = 1.65 +/- 0.05 km/s. Barium isotopes under the 3D paradigm
show a dominant r-process signature as 77 +/- 6 +/- 17% of barium isotopes form
via the r-process, where errors represent the assigned random and systematic
errors, respectively. We find that 3D LTE fits reproduce iron line profiles
better than those in 1D, but do not provide a unique abundance (within the
uncertainties). However, we demonstrate that the isotopic ratio is robust
against this shortcoming. Our barium isotope result agrees well with currently
accepted theory regarding the formation of the heavy-elements during the early
Galaxy. The improved fit to the asymmetric iron line profiles suggests that the
current state of 3D LTE modelling provides excellent simulations of fluid
flows. However, the abundances they provide are not yet self-consistent. This
may improve with NLTE considerations and higher resolution models.Comment: 16 pages, 10 figures, 5 tables. Accepted for publication in A&
Beanie Babies: An Idea Whose Time Has Come - Or - A Craze Whose Time Has Almost Run?
TY Warner's objectives are the same as the company. It is a fad product which is usually adapted fast, peaks early and declines quickly, but Ty Warner kept reinventing the product. (Kotler
Solar Flare X-ray Source Motion as a Response to Electron Spectral Hardening
Context: Solar flare hard X-rays (HXRs) are thought to be produced by
nonthermal coronal electrons stopping in the chromosphere, or remaining trapped
in the corona. The collisional thick target model (CTTM) predicts that sources
produced by harder power-law injection spectra should appear further down the
legs or footpoints of a flare loop. Therefore, hardening of the injected
power-law electron spectrum during flare onset should be concurrent with a
descending hard X-ray source.
Aims: To test this implication of the CTTM by comparing its predicted HXR
source locations with those derived from observations of a solar flare which
exhibits a nonthermally-dominated spectrum before the peak in HXRs, known as an
early impulsive event.
Methods: HXR images and spectra of an early impulsive C-class flare were
obtained using the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI).
Images were reconstructed to produce HXR source height evolutions for three
energy bands. Spatially-integrated spectral analysis was performed to isolate
nonthermal emission, and to determine the power-law index of the electron
injection spectrum. The observed height-time evolutions were then fit with
CTTM-based simulated heights for each energy.
Results: A good match between model and observed source heights was reached,
requiring a density model that agreed well with previous studies of flare loop
densities.
Conclusions: The CTTM has been used to produce a descent of model HXR source
heights that compares well with observations of this event. Based on this
interpretation, downward motion of nonthermal sources should indeed occur in
any flare where there is spectral hardening in the electron distribution during
a flare. However, this would often be masked by thermal emission associated
with flare plasma pre-heating.Comment: 8 pages, 5 figure
The Exceptionally Soft X-ray Spectrum of the Low-mass Starburst Galaxy NGC 1705
NGC 1705 is one of the optically brightest and best studied dwarf galaxies.
It appears to be in the late stage of a major starburst and contains a young
super star cluster. Type II supernovae are therefore likely to have been a
major effect in the recent evolution of this galaxy and are likely to have
produced a superbubble whose affects on the low-density ambient interstellar
medium can be ideally studied. ROSAT PSPC observations of this galaxy reveal
two striking blobs of X-ray emission embedded in \Ha loops which can be
interpreted as both sides of the upper plumes of the same superbubble. These
sources are a surprise. They are much softer than those observed from other
starburst dwarf galaxies, and are so soft that they should have been blocked if
the observed Galactic HI column density were uniformly distributed across NGC
1705 or if the sources were embedded in the HI disk of NGC 1705. In addition,
the total X-ray luminosity in the ROSAT energy band of 1.2x10^{38} erg s^{-1}
is low in comparison to similar objects. We discuss possible models for the two
X-ray peaks in NGC 1705 and find that the sources most likely originate from
relatively cool gas of one single superbubble in NGC 1705. The implications of
the exceptional softness of these sources are addressed in terms of intrinsic
properties of NGC 1705 and the nature of the foreground Galactic absorption.Comment: 7 pages, 2 ps-figures, LATEX-file; accepted for publication in
ApJ.Letter
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