2,234 research outputs found
Calculated and flight measured handling- qualities factors of three subsonic jet transports
Calculated and flight measured handling quality factors of three subsonic jet transport
A simulator and flight study of yaw coupling in turning maneuvers of large transport aircraft
Piloted simulator study of yaw coupling in turning maneuvers of supersonic transport compared with flight test data on large variable stability jet transpor
Charge Exchange Spectra of Hydrogenic and He-like Iron
We present H-like Fe XXVI and He-like Fe XXV charge-exchange spectra
resulting from collisions of highly charged iron with N2 gas at an energy of 10
eV/amu in an electron beam ion trap. Although individual high-n emission lines
are not resolved in our measurements, we observe that the most likely level for
Fe25+ --> Fe24+ electron capture is n~9, in line with expectations, while the
most likely value for Fe26+ --> Fe25+ charge exchange is significantly higher.
In the Fe XXV spectrum, the K-alpha emission feature dominates, whether
produced via charge exchange or collisional excitation. The K-alpha centroid is
lower in energy for the former case than the latter (6666 versus 6685 eV,
respectively), as expected because of the strong enhancement of emission from
the forbidden and intercombination lines, relative to the resonance line, in
charge-exchange spectra. In contrast, the Fe XXVI high-n Lyman lines have a
summed intensity greater than that of Ly-alpha, and are substantially stronger
than predicted from theoretical calculations of charge exchange with atomic H.
We conclude that the angular momentum distribution resulting from electron
capture using a multi-electron target gas is significantly different from that
obtained with H, resulting in the observed high-n enhancement. A discussion is
presented of the relevance of our results to studies of diffuse Fe emission in
the Galactic Center and Galactic Ridge, particularly with ASTRO-E2/Suzaku.Comment: 16 pages, 4 figures (3 color), accepted by Ap
A search for L dwarf binary systems
We present analysis of HST Planetary Camera images of twenty L dwarfs
identified in the course of the Two Micron All-Sky Survey. Four of the targets
have faint, red companions at separations between 0.07 and 0.29 arcseconds (1.6
to 7.6 AU). In three cases, the bolometric magnitudes of the components differ
by less than 0.3 magnitudes. Since the cooling rate for brown dwarfs is a
strong function of mass, similarity in luminosities implies comparable masses.
The faint component in the 2M0850 system, however, is over 1.3 magnitudes
fainter than the primary in the I-band, and ~0.8 magnitudes fainter in M(bol).
Indeed, 2M0850B is ~0.8 magnitudes fainter in I than the lowest luminosity L
dwarf currently known, while the absolute magnitude we deduce at J is almost
identical with M_J for Gl 229B. Theoretical models indicate a mass ratio of
\~0.75. The mean separation of the L dwarf binaries in the current sample is
smaller by a factor of two than amongst M dwarfs. We discuss the implications
of these results for the temperature scale in the L/T transition region and for
the binary frequency amongst L dwarfs.Comment: 38 pages, 11 figures; accepted for A
Hidden in plain sight: The importance of cryptic interactions in marine plankton
Here, we present a range of interactions, which we term “cryptic interactions.” These are interactions that occur throughout the marine planktonic foodweb but are currently largely overlooked by established methods, which mean large‐scale data collection for these interactions is limited. Despite this, current evidence suggests some of these interactions may have perceptible impacts on foodweb dynamics and model results. Incorporation of cryptic interactions into models is especially important for those interactions involving the transport of nutrients or energy. Our aim is to highlight a range of cryptic interactions across the plankton foodweb, where they exist, and models that have taken steps to incorporate these interactions. Additionally, it is discussed where additional research and effort is required to continue advancing our understanding of these cryptic interactions. We call for more collaboration between ecologists and modelers in order to incorporate cryptic interactions into biogeochemical and foodweb models
Precision measurements of large scale structure with future type Ia supernova surveys
Type Ia supernovae are currently the best known standard candles at
cosmological distances. In addition to providing a powerful probe of dark
energy they are an ideal source of information about the peculiar velocity
field of the local universe. Even with the very small number of supernovae
presently available it has been possible to measure the dipole and quadrupole
of the local velocity field out to z~0.025. With future continuous all-sky
surveys like the LSST project the luminosity distances of tens of thousands of
nearby supernovae will be measured accurately. This will allow for a
determination of the local velocity structure of the universe as a function of
redshift with unprecedented accuracy, provided the redshifts of the host
galaxies are known. Using catalogues of mock surveys we estimate that future
low redshift supernova surveys will be able to probe sigma-8 to a precision of
roughly 5% at 95% C.L. This is comparable to the precision in future galaxy and
weak lensing surveys and with a relatively modest observational effort it will
provide a crucial cross-check on future measurements of the matter power
spectrum.Comment: 18 pages, 9 figures, submitted to JCA
The Substellar Mass Function: A Bayesian Approach
We report our efforts to constrain the form of the low-mass star and brown
dwarf mass function via Bayesian inference. Recent surveys of M, L, and T
dwarfs in the local solar neighborhood are an essential component of our study.
Uncertainties in the age distribution of local field stars make reliable
inference complicated. We adopt a wide range of plausible assumptions about the
rate of galactic star formation and show that their deviations from a uniform
rate produce little effect on the resulting luminosity function for a given
mass function. We use a Bayesian statistical formalism to evaluate the
probability of commonly used mass functions in light of recent discoveries. We
consider three functional forms of the mass function, include a two-segment
power law, a single power law with a low-mass cutoff, and a log-normal
distribution. Our results show that, at a 60% confidence level, the power-law
index, , for the low-mass arm of a two-segment power law has a value
between -0.5 and 0.5 for objects with masses between and . The best-fit index is at the 60% confidence
level for a single-segment mass function. Current data require this function
extend to at least with no restrictions placed on a lower mass
cutoff. Inferences of the parameter values for a log-normal mass function are
virtually unaffected by recent estimates of the local space density of L and T
dwarfs. We find no preference among these three forms using this method. We
discuss current and future capabilities that may eventually discriminate
between mass-function models and refine estimates of their associated parameter
values.Comment: 40 pages, 15 figures, 3 tables, accepted for publication in The
Astrophysical Journa
Constructing a WISE High Resolution Galaxy Atlas
After eight months of continuous observations, the Wide-field Infrared Survey
Explorer (WISE) mapped the entire sky at 3.4 {\mu}m, 4.6 {\mu}m, 12 {\mu}m and
22 {\mu}m. We have begun a dedicated WISE High Resolution Galaxy Atlas (WHRGA)
project to fully characterize large, nearby galaxies and produce a legacy image
atlas and source catalogue. Here we summarize the deconvolution technique used
to significantly improve the spatial resolution of WISE imaging, specifically
designed to study the internal anatomy of nearby galaxies. As a case study, we
present results for the galaxy NGC 1566, comparing the WISE super-resolution
image processing to that of Spitzer, GALEX and ground-based imaging. The is the
first paper in a two part series; results for a much larger sample of nearby
galaxies is presented in the second paper.Comment: Published in the AJ (2012, AJ, 144, 68
In-Depth Global Analysis of Transcript Abundance Levels in Porcine Alveolar Macrophages Following Infection with Porcine Reproductive and Respiratory Syndrome Virus
Porcine reproductive and respiratory syndrome virus (PRRSV) is a major pathogen of swine worldwide and causes considerable economic loss. Identifying specific cell signaling or activation pathways that associate with variation in PRRSV replication and macrophage function may lead to identification of novel gene targets for the control of PRRSV infection. Serial Analysis of Gene Expression (SAGE) was used to create and survey the transcriptome of in vitro mock-infected and PRRSV strain VR-2332-infected porcine alveolar macrophages (PAM) at 0, 6, 12, 16, and 24 hours after infection. The transcriptome data indicated changes in transcript abundance occurring in PRRSV-infected PAMs over time after infection with more than 590 unique tags with significantly altered transcript abundance levels identified (P < .01). Strikingly, innate immune genes (whose transcript abundances are typically altered in response to other pathogens or insults including IL-8, CCL4, and IL-1β) showed no or very little change at any time point following infection
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