253 research outputs found
Aerodynamic Study of Stability and Control of Straight Flying-Wings
The bell-spanload, or bell-shaped lift distribution, gives proverse yaw for outer aileron deflections, a key factor in controlling a tailless vehicle. Study of bell-spanload applications have been limited to swept wings with elevon control schemes, relying on a well-tuned proverse yaw response for a differential elevon deflection. In examining unswept wings, symmetric outer control surface deflections have minimal associated pitching moment, allowing their use in adjusting the lift distribution to optimize for a wide range of flight conditions. Lateral-directional control of bell-spanloads can be improved by the use of an additional set of ailerons inboard of the mid-span vortices. The inboard ailerons provide traditional adverse yaw which serves as a linearly independent control vector relative to the existing proverse yaw outer surfaces; the two vectors are sufficient to define a parallelogram-shaped controllable region in the roll-yaw control space
Seyfert Galaxies in the Local Universe: Analysis of Spitzer Spectra of a Complete Sample
The Spitzer high resolution spectra of 72 Seyfert galaxies from the 12m
Galaxy Sample are presented and discussed. The presence of starburst components
in these galaxies can be quantified by powerful mid-IR diagnostics tools (i.e.
11.25m PAH feature equivalent width and the H emission line
intensity), as well as the AGN dominance can be measured by specific fine
structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The two types of
Seyfert galaxies do not show any statistical difference in our diagnostic
tools. However, the Seyfert 2's showing hidden Broad Line Regions in
spectro-polarimetric observations have on average an higher AGN dominance, a
weaker star formation component and a warmer [60 - 25] spectral index than
those without broad emission lines.Comment: Proceedings of the Conference "The central kiloparsec. Active
Galactic Nuclei and their hosts, 4-6 June 2008, Ierapetra, Crete, Greec
Examination of Proverse Yaw in Bell-Shaped Spanload Aircraft
Recent developments in the bell-shaped spanload have shown the existence of proverse yaw control power via induced thrust at the wingtips. With no need for vertical control surfaces, new types of aircraft designs are possible. Via the use of traditional roll and proverse yaw control power, a lateral directional control space can be created for flying wings where no sweep is required for lateral directional stability and control. These straight tapered flying wings have increased efficiency and performance compared to traditional aircraft. In order to maintain stability and control, straight tapered flying wings require adequate proverse yaw control power. This paper investigated the connection between aircraft geometry and proverse yaw control power while applying the bell spanload. A straight tapered flying wing Biomimetic Aircraft was used for the initial aircraft geometry. By varying taper ratio, wing chord, wing length, twist distribution, and outboard wing control surface (OWCS) size, several relationships between aircraft geometry and proverse yaw control power are determined. Proverse yaw control power is a function of the change in lift over a region of upwash as well as the change in localized downwash. As the OWCS area increases due to larger chord lengths, proverse yaw control power increases. Additionally, increasing the region of upwash via a longer wingspan or twist distribution leads to improved proverse yaw control power. However, increasing the span fraction of the OWCS does not necessarily result in increased proverse yaw control power as it is tied to localized downwash. Varying the lift distribution due to an OWCS deflection can positively affect this downwash decreasing proverse yaw control power. The Biomimetic Aircraft with 10% more span and 10% more twist at the wingtips has 16 times more proverse yaw control power than the original Biomimetic Vehicle. With this increase in proverse yaw control power, straight tapered flying wings are controllable through all necessary flight regimes
Stellar Populations of UV-Selected Active Galactic Nuclei Host Galaxies at z ~ 2 - 3
We use stellar population synthesis modeling to analyze the host galaxy
properties of a sample of 33 UV-selected, narrow-lined active galactic nuclei
(AGNs) at z ~ 2 - 3. In order to quantify the contribution of AGN emission to
host galaxy broadband spectral energy distributions (SEDs), we use the
subsample of 11 AGNs with photometric coverage spanning from rest-frame UV
through near-IR wavelengths. Modeling the SEDs of these objects with a linear
combination of stellar population and AGN templates, we infer the effect of the
AGN on derived stellar population parameters. We also estimate the typical bias
in derived stellar populations for AGNs lacking rest-frame near-IR wavelength
coverage, and develop a method for inferring the true host galaxy properties.
We compare AGN host galaxy properties to those of a sample of UV-selected,
star-forming non-AGNs in the same redshift range, including a subsample
carefully matched in stellar mass. Although the AGNs have higher masses and
SFRs than the full non-active sample, their stellar population properties are
consistent with those of the mass-selected sample, suggesting that the presence
of an AGN is not connected with the cessation of star-formation activity in
star-forming galaxies at z ~ 2 - 3. We suggest that a correlation between M_BH
and galaxy stellar mass is already in place at this epoch. Assuming a roughly
constant Eddington ratio for AGNs at all stellar masses, we are unable to
detect the AGNs in low-mass galaxies because they are simply too faint.Comment: 30 pages, 16 figures, ApJ accepted. Replaced with accepted versio
Weighing Obscured and Unobscured Quasar Hosts with the Cosmic Microwave Background
We cross-correlate a cosmic microwave background (CMB) lensing map with the projected space densities of quasars to measure the bias and halo masses of a quasar sample split into obscured and unobscured populations, the first application of this method to distinct quasar subclasses. Several recent studies of the angular clustering of obscured quasars have shown that these objects likely reside in higher-mass halos compared to their unobscured counterparts. This has important implications for models of the structure and geometry of quasars, their role in growing supermassive black holes, and mutual quasar/host galaxy evolution. However, the magnitude and significance of this difference has varied from study to study. Using data from \planck, \wise, and SDSS, we follow up on these results using the independent method of CMB lensing cross-correlations. The region and sample are identical to that used for recent angular clustering measurements, allowing for a direct comparison of the CMB-lensing and angular clustering methods. At z∼1, we find that the bias of obscured quasars is bq=2.57±0.24, while that of unobscured quasars is bq=1.89±0.19. This corresponds to halo masses of log(Mh/M⊙h−1)=13.24+0.14−0.15 (obscured) and log(Mh/M⊙h−1)=12.71+0.15−0.13 (unobscured). These results agree well with with those from angular clustering (well within 1σ), and confirm that obscured quasars reside in host halos ∼3 times as massive as halos hosting unobscured quasars. This implies that quasars spend a significant portion of their lifetime in an obscured state, possibly more than one half of the entire active phase
New CO detections of lensed submillimeter galaxies in A2218: Probing molecular gas in the LIRG regime at high redshift
Context: Submillimeter galaxies (SMGs) are distant, dusty galaxies undergoing
star formation at prodigious rates. Recently there has been major progress in
understanding the nature of the bright SMGs (i.e. S(850um)>5mJy). The samples
for the fainter SMGs are small and are currently in a phase of being built up
through identification studies. Aims: We study the molecular gas content in two
SMGs, SMMJ163555 and SMMJ163541, at z=1.034 and z=3.187 with unlensed submm
fluxes of 0.4mJy and 6.0mJy. Both SMGs are gravitationally lensed by the
foreground cluster A2218. Methods: IRAM Plateau de Bure Interferometry
observations at 3mm were obtained for the lines CO(2-1) for SMMJ163555 and
CO(3-2) for SMMJ163541. Additionally we obtained CO(4-3) for the candidate
z=4.048 SMMJ163556 with an unlensed submm flux of 2.7mJy. Results: CO(2-1) was
detected for SMMJ163555 at z=1.0313 with an integrated line intensity of
1.2+-0.2Jy km/s and a line width of 410+-120 km/s. From this a gas mass of
1.6x10^9 Msun is derived and a star formation efficiency of 440Lsun/Msun is
estimated. CO(3-2) was detected for SMMJ163541 at z=3.1824, possibly with a
second component at z=3.1883, with an integrated line intensity of 1.0+-0.1 Jy
km/s and a line width of 280+-50 km/s. From this a gas mass of 2.2x10^10 Msun
is derived and a star formation efficiency of 1000 Lsun/Msun is estimated. For
SMMJ163556 the CO(4-3) is undetected within the redshift range 4.035-4.082 down
to a sensitivity of 0.15 Jy km/s. Conclusions: Our CO line observations confirm
the optical redshifts for SMMJ163555 and SMMJ163541. The CO line luminosity
L'_CO for both galaxies is consistent with the L_FIR-L'_CO relation. SMMJ163555
has the lowest FIR luminosity of all SMGs with a known redshift and is one of
the few high redshift LIRGs whose properties can be estimated prior to ALMA.Comment: 7 pages, 4 figures. A&A in pres
Submillimeter galaxies behind the Bullet Cluster (1E 0657-56)
Clusters of galaxies are effective gravitational lenses able to magnify
background galaxies and making it possible to probe the fainter part of the
galaxy population. Submillimeter galaxies, which are believed to be
star-forming galaxies at typical redshifts of 2 to 3, are a major contaminant
to the extended Sunyaev-Zeldovich (SZ) signal of galaxy clusters. For a proper
quantification of the SZ signal the contribution of submillimeter galaxies
needs to be quantified. The aims of this study are to identify submillimeter
sources in the field of the Bullet Cluster (1E 0657-56), a massive cluster of
galaxies at z~0.3, measure their flux densities at 870 micron, and search for
counterparts at other wavelengths to constrain their properties. We carried out
deep observations of the submillimeter continuum emission at 870 micron using
the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment
(APEX) telescope. Several numerical techniques were used to quantify the noise
properties of the data and extract sources. In total, seventeen sources were
found. Thirteen of them lie in the central 10 arcminutes of the map, which has
a pixel sensitivity of 1.2 mJy per 22 arcsec beam. After correction for flux
boosting and gravitational lensing, the number counts are consistent with
published submm measurements. Nine of the sources have infrared counterparts in
Spitzer maps. The strongest submm detection coincides with a source previously
reported at other wavelengths, at an estimated redshift z~2.7. If the submm
flux arises from two images of a galaxy magnified by a total factor of 75, as
models have suggested, its intrinsic flux would be around 0.6 mJy, consistent
with an intrinsic luminosity below 10^12 L_sun.Comment: Accepted by A&A, 15 pages, 11 figure
The Physical Conditions of a Lensed Star-forming Galaxy at z=1.7
We report rest-frame optical Keck/NIRSPEC spectroscopy of the bright lensed
galaxy RCSGA 032727-132609 at z=1.7037. From precise measurements of the
nebular lines, we infer a number of physical properties: redshift, extinction,
star formation rate, ionization parameter, electron density, electron
temperature, oxygen abundance, and N/O, Ne/O, and Ar/O abundance ratios. The
limit on [O III]~4363 A tightly constrains the oxygen abundance via the
"direct" or electron temperature method, for the first time in an
average-metallicity galaxy at z~2. We compare this result to several standard
"bright-line" O abundance diagnostics, thereby testing these
empirically-calibrated diagnostics in situ. Finally, we explore the positions
of lensed and unlensed galaxies in standard diagnostic diagrams, and explore
the diversity of ionization conditions and mass--metallicity ratios at z=2.Comment: ApJ in press. 15 pages, 7 figure
A Potential Galaxy Threshing System in the Cosmos Field
We report on the discovery of a new potential galaxy threshing system in the
COSMOS 2 square degree field using the prime-focus camera, Suprime-Cam, on the
8.2 m Subaru Telescope. This system consists of a giant elliptical galaxy with
and a tidally disrupted satellite galaxy with at a photometric redshift of . This redshift is
consistent with the spectroscopic redshift of 0.079 for the giant elliptical
galaxy obtained from the Sloan Digital Sky Survey (SDSS) archive. The
luminosity masses of the two galaxies are
and , respectively. The distance between the
two galaxies is greater than 100 kpc. The two tidal tails emanating from the
satellite galaxy extend over 150 kpc. This system would be the second
well-defined galaxy threshing system found so far.Comment: 17 pages, 7 figures, accepted for the COSMOS special issue of ApJ
General Approach for Combining Diverse Rare Variant Association Tests Provides Improved Robustness Across a Wider Range of Genetic Architectures
The widespread availability of genome sequencing data made possible by way of next-generation technologies has yielded a flood of different gene-based rare variant association tests. Most of these tests have been published because they have superior power for particular genetic architectures. However, for applied researchers it is challenging to know which test to choose in practice when little is known a priori about genetic architecture. Recently, tests have been proposed which combine two particular individual tests (one burden and one variance components) to minimize power loss while improving robustness to a wider range of genetic architectures. In our analysis we propose an expansion of these approaches, yielding a general method that works for combining any number of individual tests. We demonstrate that running multiple different tests on the same dataset and using a Bonferroni correction for multiple testing is never better than combining tests using our general method. We also find that using a test statistic that is highly robust to the inclusion of non-causal variants (Joint-infinity) together with a previously published combined test (SKAT-O) provides improved robustness to a wide range of genetic architectures and should be considered for use in practice. Software for this approach is supplied. We support the increased use of combined tests in practice-- as well as further exploration of novel combined testing approaches using the general framework provided here--to maximize robustness of rare-variant testing strategies against a wide range of genetic architectures
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