6,684 research outputs found
Fuselage shell and cavity response measurements on a DC-9 test section
A series of fuselage shell and cavity response measurements conducted on a DC-9 aircraft test section are described. The objectives of these measurements were to define the shell and cavity model characteristics of the fuselage, understand the structural-acoustic coupling characteristics of the fuselage, and measure the response of the fuselage to different types of acoustic and vibration excitation. The fuselage was excited with several combinations of acoustic and mechanical sources using interior and exterior loudspeakers and shakers, and the response to these inputs was measured with arrays of microphones and accelerometers. The data were analyzed to generate spatial plots of the shell acceleration and cabin acoustic pressure field, and corresponding acceleration and pressure wavenumber maps. Analysis and interpretation of the spatial plots and wavenumber maps provided the required information on modal characteristics, structural-acoustic coupling, and fuselage response
Invariant Peano curves of expanding Thurston maps
We consider Thurston maps, i.e., branched covering maps
that are postcritically finite. In addition, we assume that is expanding in
a suitable sense. It is shown that each sufficiently high iterate of
is semi-conjugate to , where is equal to the
degree of . More precisely, for such an we construct a Peano curve
(onto), such that
(for all ).Comment: 63 pages, 12 figure
The Age Dependent Luminosities of the Red Giant Branch Bump, Asymptotic Giant Branch Bump, and Horizontal Branch Red Clump
Color-magnitude diagrams of globular clusters often exhibit a prominent
horizontal branch (HB) and may also show features such as the red giant branch
(RGB) bump and the asymptotic giant branch (AGB) bump. Stellar evolution theory
predicts that the luminosities of these features will depend on the metallicity
and age of the cluster. We calculate theoretical lines of 2 to 12 Gyr constant
age RGB-bumps and AGB-bumps in the V(HB-Bump)--[Fe/H] diagram, which shows the
brightness difference between the bump and the HB as a function of metallicity.
In order to test the predictions, we identify giant branch bumps in new Hubble
Space Telescope color-magnitude diagrams for 8 SMC clusters. First, we conclude
that the SMC cluster bumps are RGB-bumps. The data for clusters younger than ~6
Gyr are in fair agreement the relative age dependent luminosities of the HB and
RGB-bump. The V(HB-Bump)--[Fe/H] data for clusters older then ~6 Gyr
demonstrate a less satisfactory agreement with our calculations. We conclude
that ~6 Gyr is a lower bound to the age of clusters for which the Galactic
globular cluster, age independent V(HB-Bump)--[Fe/H] calibration is valid.
Application of the V(HB-bump)--[Fe/H] diagram to stellar population studies is
discussed.Comment: Accepted for publication in the Astrophysical Journal, 30 pages,
Latex aaspp4.sty, including 7 postscript figure
The Age and Metallicity Relation of Omega Centauri
We present a metallicity distribution based on photometry and spectra for 442
omega Cen cluster members that lie at the main sequence turnoff region of the
color-magnitude diagram. This distribution is similar to that found for the red
giant branch. The distribution shows a sharp rise to a mean of [Fe/H] = -1.7
with a long tail to higher metallicities. Ages have then been determined for
the stars using theoretical isochrones enabling the construction of an
age-metallicity diagram. Interpretation of this diagram is complicated by the
correlation of the errors in the metallicities and ages. Nevertheless, after
extensive Monte-Carlo simulations, we conclude that our data show that the
formation of the cluster took place over an extended period of time: the most
metal-rich stars in our sample ([Fe/H] ~ -0.6) are younger by 2-4 Gyrs than the
most metal-poor population.Comment: 53 pages, 20 figures, 5 tables, accepted for publication in Ap
A Planetary Mass Companion to the K0 Giant HD 17092
We report the discovery of a substellar-mass companion to the K0-giant HD
17092 with the Hobby-Eberly Telescope. In the absence of any correlation of the
observed 360-day periodicity with the standard indicators of stellar activity,
the observed radial velocity variations are most plausibly explained in terms
of a Keplerian motion of a planetary-mass body around the star. With the
estimated stellar mass of 2.3Msun, the minimum mass of the planet is 4.6MJ. The
planet's orbit is characterized by a mild eccentricity of e=0.17 and a
semi-major axis of 1.3 AU. This is the tenth published detection of a planetary
companion around a red giant star. Such discoveries add to our understanding of
planet formation around intermediate-mass stars and they provide dynamical
information on the evolution of planetary systems around post-main sequence
stars.Comment: 13 pages, 3 figures, 2 tables. Submitted to Ap
UHB demonstrator interior noise control flight tests and analysis
The measurement and analysis of MD-UHB (McDonnell Douglas Ultra High Bypass) Demonstrator noise and vibration flight test data are described as they relate to passenger cabin noise. The analyses were done to investigate the interior noise characteristics of advanced turboprop aircraft with aft-mounted engines, and to study the effectiveness of selected noise control treatments in reducing passenger cabin noise. The UHB Demonstrator is an MD-80 test aircraft with the left JT8D engine replaced with a prototype UHB engine. For these tests, the UHB engine was a General Electric Unducted Fan, with either 8x8 or 10x8 counter-rotating propeller configurations. Interior noise level characteristics were studied for several altitudes and speeds, with emphasis on high altitude (35,000 ft), high speed (0.75 Mach) cruise conditions. The effectiveness of several noise control treatments was evaluated based on cabin noise measurements. The important airborne and structureborne transmission paths were identified for both tonal and broadband sources using the results of a sound intensity survey, exterior and interior noise and vibration data, and partial coherence analysis techniques. Estimates of the turbulent boundary layer pressure wavenumber-frequency spectrum were made, based on measured fuselage noise levels
Cohesion, team mental models, and collective efficacy: Towards an integrated framework of team dynamics in sport
A nomological network on team dynamics in sports consisting of a multi-framework perspective is introduced and tested. The aim was to explore the interrelationship among cohesion, team mental models (TMM), collective-efficacy (CE), and perceived performance potential (PPP). Three hundred and forty college-aged soccer players representing 17 different teams (8 female and 9 male) participated in the study. They responded to surveys on team cohesion, TMM, CE and PPP. Results are congruent with the theoretical conceptualization of a parsimonious view of team dynamics in sports. Specifically, cohesion was found to be an exogenous variable predicting both TMM and CE beliefs. TMM and CE were correlated and predicted PPP, which in turn accounted for 59% of the variance of objective performance scores as measured by teams’ season record. From a theoretical standpoint, findings resulted in a parsimonious view of team dynamics, which may represent an initial step towards clarifying the epistemological roots and nomological network of various team-level properties. From an applied standpoint, results suggest that team expertise starts with the establishment of team cohesion. Following the establishment of cohesiveness, teammates are able to advance team-related schemas and a collective sense of confidence. Limitations and key directions for future research are outlined
Blue Stragglers in Galactic Open Clusters and the Integrated Spectral Energy Distributions
Synthetic integrated spectral properties of the old Galactic open clusters
are studies in this work, where twenty-seven Galactic open clusters of ages >=
1Gyr are selected as the working sample. Based on the photometric observations
of these open clusters, synthetic integrated spectrum has been made for the
stellar population of each cluster. The effects of blue straggler stars (BSSs)
on the conventional simple stellar population (SSP) model are analyzed on an
individual cluster base. It is shown that the BSSs, whose holding positions in
the color-magnitude diagrams (CMDs) cannot be predicted by the current
single-star evolution theory, present significant modifications to the
integrated properties of theoretical SSP model. The synthesized integrated
spectral energy distributions (ISEDs) of our sample clusters are dramatically
different from the SSPs based on isochrone only. The BSSs corrected ISEDs of
stellar populations show systematic enhancements towards shorter wavelength in
the spectra. When measured with wide-band colors in unresolvable conditions,
the age of a stellar population can be seriously under-estimated by the
conventional SSP model. Therefore, considering the common existence of BSS
component in real stellar populations, a considerable amount of alternations on
the conventional ISEDs should be expected when applying the technique of
evolutionary population synthesis (EPS) to more complicated stellar systems.Comment: 45 pages, 21 figures Accepted for publication in ApJ (Feburary 1,
2005 issue
A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
A revised near infrared classification scheme for T dwarfs is presented,
based on and superseding prior schemes developed by Burgasser et al. and
Geballe et al., and defined following the precepts of the MK Process. Drawing
from two large spectroscopic libraries of T dwarfs identified largely in the
Sloan Digital Sky Survey and the Two Micron All Sky Survey, nine primary
spectral standards and five alternate standards spanning spectral types T0 to
T8 are identified that match criteria of spectral character, brightness,
absence of a resolved companion and accessibility from both northern and
southern hemispheres. The classification of T dwarfs is formally made by the
direct comparison of near infrared spectral data of equivalent resolution to
the spectra of these standards. Alternately, we have redefined five key
spectral indices measuring the strengths of the major HO and CH bands
in the 1-2.5 micron region that may be used as a proxy to direct spectral
comparison. Two methods of determining T spectral type using these indices are
outlined and yield equivalent results. These classifications are also
equivalent to those from prior schemes, implying that no revision of existing
spectral type trends is required. The one-dimensional scheme presented here
provides a first step toward the observational characterization of the lowest
luminosity brown dwarfs currently known. Future extensions to incorporate
spectral variations arising from differences in photospheric dust content,
gravity and metallicity are briefly discussed. A compendium of all currently
known T dwarfs with updated classifications is presented.Comment: 52 pages, 11 figures; accepted for publication to Ap
An infinite genus mapping class group and stable cohomology
We exhibit a finitely generated group \M whose rational homology is
isomorphic to the rational stable homology of the mapping class group. It is
defined as a mapping class group associated to a surface \su of infinite
genus, and contains all the pure mapping class groups of compact surfaces of
genus with boundary components, for any and . We
construct a representation of \M into the restricted symplectic group of the real Hilbert space generated by the homology
classes of non-separating circles on \su, which generalizes the classical
symplectic representation of the mapping class groups. Moreover, we show that
the first universal Chern class in H^2(\M,\Z) is the pull-back of the
Pressley-Segal class on the restricted linear group
via the inclusion .Comment: 14p., 8 figures, to appear in Commun.Math.Phy
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