1,355 research outputs found
Sizing Tool for Quadrotor Biplane Tailsitter UAS
The Quadrotor-Biplane-Tailsitter (QBT) configuration is the basis for a mechanically simplistic rotorcraft capable of both long-range, high-speed cruise as well as hovering flight. This work presents the development and validation of a set of preliminary design tools built specifically for this aircraft to enable its further development, including: a QBT weight model, preliminary sizing framework, and vehicle analysis tools. The preliminary sizing tool presented here shows the advantage afforded by QBT designs in missions with aggressive cruise requirements, such as offshore wind turbine inspections, wherein transition from a quadcopter configuration to a QBT allows for a 5:1 trade of battery weight for wing weight. A 3D, unsteady panel method utilizing a nonlinear implementation of the Kutta-Joukowsky condition is also presented as a means of computing aerodynamic interference effects and, through the implementation of rotor, body, and wing geometry generators, is prepared for coupling with a comprehensive rotor analysis package
A Survey of 10-Micron Silicate Emission from Dust around Young Sun-Like Stars
We obtained low resolution (R = 100) mid-infrared (8-13 micron wavelengths)
spectra of 8 nearby young main sequence stars with the Keck 1 telescope and
Long-Wavelength Spectrometer (LWS) to search for 10 micron silicate (Si-O
stretch) emission from circumstellar dust. No stars exhibited readily apparent
emission: Spectra were then analyzed by least-squares fitting of a template
based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to
constrain the level of silicate emission to a threshold ten times below what
was previously possible from space. We found one star, HD 17925, with a
spectrum statistically different from its calibrator and consistent with a
silicate emission peak of 7% of the photosphere at a wavelength of 10 microns.
Excess emission at 60 microns from this star has already been reported.Comment: 19 total pages, 5 Postscript figures, 2 tables, Late
Infrared study of the eta Chamaeleontis cluster and the longevity of circumstellar discs
We have analyzed JHKL observations of the stellar population of the ~9
Myr-old eta Chamaeleontis cluster. Using infrared (IR) colour-colour and
colour-excess diagrams, we find the fraction of stellar systems with near-IR
excess emission is 0.60 pm 0.13 (2_sigma). This results implies considerably
longer disc lifetimes than found in some recent studies of other young stellar
clusters. For the classical T Tauri (CTT) and weak-lined T Tauri (WTT) star
population, we also find a strong correlation between the IR excess and H_alpha
emission. The IR excesses of these stars indicate a wide range of star-disc
activity; from a CTT star showing high levels of accretion, to CTT - WTT
transition objects with evidence for some on-going accretion, and WTT stars
with weak or absent IR excesses. Of the 15 known cluster members, 4 stars with
IR excesses delta(K-L) > 0.4 mag are likely experiencing on-going accretion
owing to strong or variable optical emission. The resulting accretion fraction
(0.27 pm 0.13; 2_sigma) shows that the accretion phase, in addition to the
discs themselves, can endure for at least ~10 Myr.Comment: 7 pages, 4 figures, accepted for MNRA
Evolved Stars in the Core of the Massive Globular Cluster NGC 2419
We present an analysis of optical and ultraviolet Hubble Space Telescope
photometry for evolved stars in the core of the distant massive globular
cluster NGC 2419. We characterize the horizontal branch (HB) population in
detail including corrections for incompleteness on the long blue tail. We
present a method for removing (to first order) lifetime effects from the
distribution of HB stars to facilitate more accurate measurements of helium
abundance for clusters with blue HBs and to clarify the distribution of stars
reaching the zero-age HB. The population ratio R = N_HB / N_RGB implies there
may be slight helium enrichment among the EHB stars in the cluster, but that it
is likely to be small (dY < 0.05). An examination of the upper main sequence
does not reveal any sign of multiple populations. Through comparisons of
optical CMDs, we present evidence that the EHB clump in NGC 2419 contains the
end of the canonical horizontal branch, and that the boundary between the
normal HB stars and blue hook stars shows up as a change in the density of
stars in the CMD. This corresponds to a spectroscopically-verified gap in NGC
2808 and an "edge" in omega Cen. The more clearly visible HB gap at V = 23.5
appears to be too bright.(Abridged)Comment: 27 pages, 25 figures (some bitmapped), uses emulateapj, accepted to
Astronomical Journa
Visual Prosody: Facial Movements Accompanying Speech
As we articulate speech, we usually move the head and exhibit various facial expressions. This visual aspect of speech aids understanding and helps communicating additional information, such as the speaker's mood. We analyze quantitatively head and facial movements that accompany speech and investigate how they relate to the text's prosodic structure. We recorded several hours of speech and measured the locations of the speakers' main facial features as well as their head poses. The text was evaluated with a prosody prediction tool, identifying phrase boundaries and pitch accents. Characteristic for most speakers are simple motion patterns that are repeatedly applied in synchrony with the main prosodic events. Direction and strength of head movements vary widely from one speaker to another, yet their timing is typically well synchronized with the spoken text. Understanding quantitatively the correlations between head movements and spoken text is important for synthesizing photo-realistic talking heads. Talking heads appear much more engaging when they exhibit realistic motion pattern
The Removal Kinetics of Dissolved Organic Matter and the Optical Clarity of Groundwater
Concentrations of dissolved organic matter (DOM) and ultraviolet/visible light absorbance decrease systematically as groundwater moves through the unsaturated zones overlying aquifers and along flowpaths within aquifers. These changes occur over distances of tens of meters (m) implying rapid removal kinetics of the chromophoric DOM that imparts color to groundwater. A one-compartment input-output model was used to derive a differential equation describing the removal of DOM from the dissolved phase due to the combined effects of biodegradation and sorption. The general solution to the equation was parameterized using a 2-year record of dissolved organic carbon (DOC) concentration changes in groundwater at a long-term observation well. Estimated rates of DOC loss were rapid and ranged from 0.093 to 0.21 micromoles per liter per day (ÎŒM dâ1), and rate constants for DOC removal ranged from 0.0021 to 0.011 per day (dâ1). Applying these removal rate constants to an advective-dispersion model illustrates substantial depletion of DOC over flow-path distances of 200 m or less and in timeframes of 2 years or less. These results explain the low to moderate DOC concentrations (20â75 ÎŒM; 0.26â1 mg Lâ1) and ultraviolet absorption coefficient values (a 254â\u3câ5 mâ1) observed in groundwater produced from 59 wells tapping eight different aquifer systems of the United States. The nearly uniform optical clarity of groundwater, therefore, results from similarly rapid DOM-removal kinetics exhibited by geologically and hydrologically dissimilar aquifers
Hes-6, an inhibitor of Hes-1, is regulated by 17ÎČ-estradiol and promotes breast cancer cell proliferation
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Leveraging population admixture to characterize the heritability of complex traits.
Despite recent progress on estimating the heritability explained by genotyped SNPs (h(2)g), a large gap between h(2)g and estimates of total narrow-sense heritability (h(2)) remains. Explanations for this gap include rare variants or upward bias in family-based estimates of h(2) due to shared environment or epistasis. We estimate h(2) from unrelated individuals in admixed populations by first estimating the heritability explained by local ancestry (h(2)γ). We show that h(2)γ = 2FSTCΞ(1 - Ξ)h(2), where FSTC measures frequency differences between populations at causal loci and Ξ is the genome-wide ancestry proportion. Our approach is not susceptible to biases caused by epistasis or shared environment. We applied this approach to the analysis of 13 phenotypes in 21,497 African-American individuals from 3 cohorts. For height and body mass index (BMI), we obtained h(2) estimates of 0.55 ± 0.09 and 0.23 ± 0.06, respectively, which are larger than estimates of h(2)g in these and other data but smaller than family-based estimates of h(2)
Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like stars
We present the discovery of debris systems around three solar mass stars
based upon observations performed with the Spitzer Space Telescope as part of a
Legacy Science Program, ``the Formation and Evolution of Planetary Systems''
(FEPS). We also confirm the presence of debris around two other stars. All the
stars exhibit infrared emission in excess of the expected photospheres in the
70 micron band, but are consistent with photospheric emission at <= 33 micron.
This restricts the maximum temperature of debris in equilibrium with the
stellar radiation to T < 70 K. We find that these sources are relatively old in
the FEPS sample, in the age range 0.7 - 3 Gyr. Based on models of the spectral
energy distributions, we suggest that these debris systems represent materials
generated by collisions of planetesimal belts. We speculate on the nature of
these systems through comparisons to our own Kuiper Belt, and on the likely
planet(s) responsible for stirring the system and ultimately releasing dust
through collisions. We further report observations of a nearby star HD 13974 (d
=11 pc) that is indistinguishable from a bare photosphere at both 24 micron and
70 micron. The observations place strong upper limits on the presence of any
cold dust in this nearby system (L_IR/L_* < 10^{-5.2}).Comment: 31 pages, 9 figures, accepted for publication in Ap
Formation and Evolution of Planetary Systems: Placing Our Solar System in Context with Spitzer
We summarize the progress to date of our Legacy Science Program entitled "The
Formation and Evolution of Planetary Systems" (FEPS) based on observations
obtained with the Spitzer Space Telescope during its first year of operation.
In addition to results obtained from our ground-based preparatory program and
our early validation program, we describe new results from a survey for
near-infrared excess emission from the youngest stars in our sample as well as
a search for cold debris disks around sun-like stars. We discuss the
implications of our findings with respect to current understanding of the
formation and evolution of our own solar system.Comment: 8 postscript pages including 3 figures. To appear in "Spitzer New
Views of the Cosmos" ASP Conference Series, eds. L. Armus et al. FEPS website
at http://feps.as.arizona.ed
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