1,128 research outputs found
Development of 2 underseat energy absorbers for application to crashworthy passenger seats for general aviation aircraft
This report presents the methodology and results of a program conducted to develop two underseat energy absorber (E/A) concepts for application to nonadjustable crashworthy passenger seats for general aviation aircraft. One concept utilizes an inflated air bag, and the other, a convoluted sheet metal bellows. Prototypes of both were designed, built, and tested. Both concepts demonstrated the necessary features of an energy absorber (load-limiter); however, the air bag concept is particularly encouraging because of its light weight. Several seat frame concepts also were investigated as a means of resisting longitudinal and lateral loads and of guiding the primary vertical stroke of the underseat energy absorber. Further development of a seat system design using the underseat energy absorbers is recommended because they provide greatly enhanced crash survivability as compared with existing general aviation aircraft seats
Luminosity Distributions within Rich Clusters - III: A comparative study of seven Abell/ACO clusters
We recover the luminosity distributions over a wide range of absolute
magnitude (-24.5 < M_{R} < -16.5) for a sample of seven rich southern galaxy
clusters. We find a large variation in the ratio of dwarf to giant galaxies,
DGR: 0.8\le \le 3.1. This variation is shown to be inconsistent with a
ubiquitous cluster luminosity function. The DGR shows a smaller variation from
cluster to cluster in the inner regions (r \ls 0.56 Mpc). Outside these regions
we find the DGR to be strongly anti-correlated with the mean local projected
galaxy density with the DGR increasing towards lower densities. In addition the
DGR in the outer regions shows some correlation with Bautz-Morgan type. Radial
analysis of the clusters indicate that the dwarf galaxies are less centrally
clustered than the giants and form a significant halo around clusters. We
conclude that measurements of the total cluster luminosity distribution based
on the inner core alone are likely to be severe underestimates of the dwarf
component, the integrated cluster luminosity and the contribution of galaxy
masses to the cluster's total mass. Further work is required to quantify this.
The observational evidence that the unrelaxed, lower density outer regions of
clusters are dwarf-rich, adds credence to the recent evidence and conjecture
that the field is a predominantly dwarf rich environment and that the dwarf
galaxies are under-represented in measures of the local field luminosity
function.Comment: 31 pages including 11 figures. Also available from
http://star-www.st-and.ac.uk/~spd3/bib.htm
Model-independent measurement of internal stellar structure in 16 Cygni A and B
We present a method for measuring internal stellar structure based on
asteroseismology that we call "inversions for agreement." The method accounts
for imprecise estimates of stellar mass and radius as well as the relatively
limited oscillation mode sets that are available for distant stars. By
construction, the results of the method are independent of stellar models. We
apply this method to measure the isothermal sound speeds in the cores of the
solar-type stars 16 Cyg A and B using asteroseismic data obtained from Kepler
observations. We compare the asteroseismic structure that we deduce against
best-fitting evolutionary models and find that the sound speeds in the cores of
these stars exceed those of the models.Comment: Accepted for publication in The Astrophysical Journa
Luminosity Distributions within Rich Clusters - II: Demonstration and Verification via Simulation
We present detailed simulations of long exposure CCD images. The simulations
are used to explore the validity of the statistical method for reconstructing
the luminosity distribution of galaxies within a rich cluster i.e. by the
subtraction of field number-counts from those of a sight-line through the
cluster. In particular we use the simulations to establish the reliability of
our observational data presented in Paper 3. Based on our intended CCD
field-of-view (6.5 by 6.5 arcmins) and a 1-sigma detection limit of 26 mags per
sq arcsecond, we conclude that the luminosity distribution can be robustly
determined over a wide range of absolute magnitude (-23 < M_{R} < -16)
provided:
(a) the cluster has an Abell richness 1.5 or greater,
(b) the cluster's redshift lies in the range 0.1 < z < 0.3,
(c) the seeing is better than FWHM 1.25'' and
(d) the photometric zero points are accurate to within Delta m = \pm 0.12.
If these conditions are not met then the recovered luminosity distribution is
unreliable and potentially grossly miss-leading. Finally although the method
clearly has limitations, within these limitations the technique represents an
extremely promising probe of galaxy evolution and environmental dependencies.Comment: 24 pages, 8 figures accepted for publication in MNRAS also available
from http://star-www.st-and.ac.uk/~spd3/bib.htm
On the Stellar Kinematics and Mass of the Virgo Ultra-Diffuse Galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultra-diffuse
galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager
(KCWI). We confirm VCC 1287's association both with the Virgo cluster and its
globular cluster (GC) system, measuring a recessional velocity of $1116 \pm 2\
\mathrm{km\ s^{-1}}19 \pm 6\
\mathrm{km\ s^{-1}}1.11^{+0.81}_{-0.81}
\times 10^{9} \ \mathrm{M_{\odot}}13^{+11}_{-11}$)
within the half light radius (4.4 kpc). This places VCC 1287 slightly above the
well established relation for normal galaxies, with a higher mass to light
ratio for its dynamical mass than normal galaxies. We use our dynamical mass,
and an estimate of GC system richness, to place VCC 1287 on the GC number --
dynamical mass relation, finding good agreement with a sample of normal
galaxies. Based on a total halo mass derived from GC counts, we then infer that
VCC 1287 likely resides in a cored or low concentration dark matter halo. Based
on the comparison of our measurements to predictions from simulations, we find
that strong stellar feedback and/or tidal effects are plausibly the dominant
mechanisms in the formation of VCC 1287. Finally, we compare our measurement of
the dynamical mass with those for other UDGs. These dynamical mass estimates
suggest relatively massive halos and a failed galaxy origin for at least some
UDGs.Comment: 13 pages, 10 figures with an additional 5 pages and 5 figures in
appendices. Accepted for publication in MNRAS. v2: with small updates from
publication formatting and a minor plotting fix for Fig. 1
Asymmetrical Force Production in the Maneuvering Flight of Pigeons
Downstroke force produced by Rock Doves (Columba livia) as they negotiated an obstacle course was measured using in vivo recordings of delto-pectoral crest strain. During this slow , maneuvering flight, pigeons produced a series of four to six successive wingbeats in which the wing on the outside of the turn produced greater peak force than the wing on the inside of the turn, suggesting that the birds maneuvered in a saltatory manner during slow flight. This asymmetrical downstroke force may be used to increase or reestablish bank lost during upstroke, or it may be directed as thrust to compensate for adverse yaw or create excess yaw to alter the bird\u27s direction of flight. Continuous production of asymmetrical downstroke force through a turn differs from the traditional model of maneuvering flight, in which asymmetrical force is used only to initiate a bank, the forces are briefly reversed to arrest the momentum of the roll and then equalized to maintain the established bank, and the redirected lift of the wings then effects a turn. Although this traditional model probably describes most turns initiated during fast and gliding flight in birds, it underestimates the complexity of maneuvering during slow, flapping flight, where sophisticated kinematics and neuromuscular control are needed to change direction effectively
The assembly history of the nearest S0 galaxy NGC 3115 from its kinematics out to six half-light radii
Using new and archival data, we study the kinematic properties of the nearest
field S0 galaxy, NGC 3115, out to half-light radii ()
from its stars (integrated starlight), globular clusters (GCs) and planetary
nebulae (PNe). We find evidence of three kinematic regions with an inner
transition at from a dispersion-dominated bulge
() to a fast-rotating disk (), and then an additional transition from the disk to a slowly rotating
spheroid at , as traced by the red GCs and PNe (and
possibly by the blue GCs beyond ). From comparison with
simulations, we propose an assembly history in which the original progenitor
spiral galaxy undergoes a gas-rich minor merger that results in the embedded
kinematically cold disk that we see today in NGC 3115. At a later stage, dwarf
galaxies, in mini mergers (mass-ratio 1:10), were accreted building-up the
outer slowly rotating spheroid, with the central disk kinematics largely
unaltered. Additionally, we report new spectroscopic observations of a sample
of ultra-compact dwarfs (UCDs) around NGC 3115 with the Keck/KCWI instrument.
We find that five UCDs are inconsistent with the general rotation field of the
GCs, suggesting an \textit{ex-situ} origin for these objects, i.e. perhaps the
remnants of tidally stripped dwarfs. A further seven UCDs follow the GC
rotation pattern, suggesting an \textit{in-situ} origin and, possibly a GC-like
nature.Comment: 22 pages (including 3 pages of Appendix material), 14 figures,
published in MNRA
Spectroscopic evolution of dusty starburst galaxies
By using a one-zone chemical and spectrophotometric evolution model of a disk
galaxy undergoing a dusty starburst, we investigate, numerically, the optical
spectroscopic properties in order to explore galaxy evolution in distant
clusters. We adopt an assumption that the degree of dust extinction
(represented by ) depends on the ages of starburst populations in such a
way that younger stars have larger (originally referred to as selective
dust extinction by Poggianti & Wu 2000). In particular, we investigate how the
time evolution of the equivalent widths of [OII]3727 and H is
controlled by the adopted age dependence. This leads to three main results: (1)
If a young stellar population (with the age of yr) is more
heavily obscured by dust than an old one ( yr), the galaxy can show
an ``e(a)'' spectrum characterized by strong H absorption and
relatively modest [OII] emission. (2) A dusty starburst galaxy with an e(a)
spectrum can evolve into a poststarburst galaxy with an a+k (or k+a) spectrum
0.2 Gyr after the starburst and then into a passive one with a k-type spectrum
1 Gyr after the starburst. This result clearly demonstrates an evolutionary
link between galaxies with different spectral classes (i.e., e(b), e(a), a+k,
k+a, and k). (3) A dusty starburst galaxy can show an a+k or k+a spectrum even
in the dusty starburst phase if the age-dependence of dust extinction is rather
weak, i.e., if young starburst populations with different ages (
yr) are uniformly obscured by dust.Comment: 27 pages 12 figures,2001,ApJ,in pres
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