92 research outputs found
Status of NASA/Army rotorcraft research and development piloted flight simulation
The status of the major NASA/Army capabilities in piloted rotorcraft flight simulation is reviewed. The requirements for research and development piloted simulation are addressed as well as the capabilities and technologies that are currently available or are being developed by NASA and the Army at Ames. The application of revolutionary advances (in visual scene, electronic cockpits, motion, and modelling of interactive mission environments and/or vehicle systems) to the NASA/Army facilities are also addressed. Particular attention is devoted to the major advances made in integrating these individual capabilities into fully integrated simulation environment that were or are being applied to new rotorcraft mission requirements. The specific simulators discussed are the Vertical Motion Simulator and the Crew Station Research and Development Facility
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
Filling in the Gaps in the 4.85 GHz Sky
We describe a 4.85 GHz survey of bright, flat-spectrum radio sources
conducted with the Effelsberg 100 m telescope in an attempt to improve the
completeness of existing surveys, such as CRATES. We report the results of
these observations and of follow-up 8.4 GHz observations with the VLA of a
subset of the sample. We comment on the connection to the WMAP point source
catalog and on the survey's effectiveness at supplementing the CRATES sky
coverage.Comment: 13 pages, 3 figures, 2 tables. Accepted for publication in the
Astronomical Journal. Tables available in electronic form:
http://astro.stanford.edu/gaps
Exploring the Bone Proteome to Help Explain Altered Bone Remodeling and Preservation of Bone Architecture and Strength in Hibernating Marmots
Periods of physical inactivity increase bone resorption and cause bone loss and increased fracture risk. However, hibernating bears, marmots, and woodchucks maintain bone structure and strength, despite being physically inactive for prolonged periods annually. We tested the hypothesis that bone turnover rates would decrease and bone structural and mechanical properties would be preserved in hibernating marmots (Marmota flaviventris). Femurs and tibias were collected from marmots during hibernation and in the summer following hibernation. Bone remodeling was significantly altered in cortical and trabecular bone during hibernation with suppressed formation and no change in resorption, unlike the increased bone resorption that occurs during disuse in humans and other animals. Trabecular bone architecture and cortical bone geometrical and mechanical properties were not different between hibernating and active marmots, but bone marrow adiposity was significantly greater in hibernators. Of the 506 proteins identified in marmot bone, 40 were significantly different in abundance between active and hibernating marmots. Monoaglycerol lipase, which plays an important role in fatty acid metabolism and the endocannabinoid system, was 98-fold higher in hibernating marmots compared with summer marmots and may play a role in regulating the changes in bone and fat metabolism that occur during hibernation
Multifrequency radio continuum observations of NGC 1569: Evidence for a convective wind
We present high-sensitivity radio continuum observations with the VLA and
Ryle Telescope at 1.5, 4.9, 8.4 and 15.4 GHz of the dwarf irregular galaxy NGC
1569. The radio data show an extended, irregularly-shaped halo with filamentary
structure around the galaxy. The spectral index maps reveal an unusually patchy
distribution with regions of flat spectral index extending into the halo. The
data allow us to perform a spatially-resolved spectral fitting analysis of the
continuum emission from which we derive maps of the thermal and synchrotron
emission. The thermal radio emission is concentrated towards the brightest \hii
region west of the super star clusters A and B whereas the distribution of the
synchrotron emission peaks in a bar-like structure in the disk extending
between the two clusters. The total flux density of the thermal radio emission
allows us to derive the integrated synchrotron spectrum and we confirm the
break in the spectrum that was found by \citet{isr-deb88}. We discuss various
possibilities that could produce such a break and conclude that the only
mechanism able to fit the radio data and being consistent with data at other
wavelengths is a convective wind allowing cosmic ray electrons to escape from
the halo.Comment: Accepted for publication in MNRAS, 10 pages, 12 figure
The Arecibo Galaxy Environment Survey III: Observations Toward the Galaxy Pair NGC 7332/7339 and the Isolated Galaxy NGC 1156
Two 5 square degree regions around the NGC 7332/9 galaxy pair and the
isolated galaxy NGC 1156 have been mapped in the 21-cm line of neutral hydrogen
(HI) with the Arecibo L-band Feed Array out to a redshift of ~0.065
km/s) as part of the Arecibo Galaxy Environment Survey. One of the aims of this
survey is to investigate the environment of galaxies by identifying dwarf
companions and interaction remnants; both of these areas provide the potential
for such discoveries. The neutral hydrogen observations were complemented by
optical and radio follow-up observations with a number of telescopes. A total
of 87 galaxies were found, of which 39 (45 per cent) were previously cataloged
and 15 (17 per cent) have prior redshifts. Two dwarf galaxies have been
discovered in the NGC 7332 group and a single dwarf galaxy in the vicinity NGC
1156 . A parallel optical search of the area revealed one further possible
dwarf galaxy near NGC 7332.Comment: 18 pages, 17 figures, uses emulateap
The spiral structure of our Milky Way Galaxy
The spiral structure of our Milky Way Galaxy is not yet known. HII regions
and giant molecular clouds are the most prominent spiral tracers. We collected
the spiral tracer data of our Milky Way from the literature, namely, HII
regions and giant molecular clouds (GMCs). With weighting factors based on the
excitation parameters of HII regions or the masses of GMCs, we fitted the
distribution of these tracers with models of two, three, four spiral-arms or
polynomial spiral arms. The distances of tracers, if not available from stellar
or direct measurements, were estimated kinetically from the standard rotation
curve of Brand & Blitz (1993) with =8.5 kpc, and =220 km
s or the newly fitted rotation curves with =8.0 kpc and
=220 km s or =8.4 kpc and =254 km s. We
found that the two-arm logarithmic model cannot fit the data in many regions.
The three- and the four-arm logarithmic models are able to connect most
tracers. However, at least two observed tangential directions cannot be matched
by the three- or four-arm model. We composed a polynomial spiral arm model,
which can not only fit the tracer distribution but also match observed
tangential directions. Using new rotation curves with =8.0 kpc and
=220 km s and =8.4 kpc and =254 km s for
the estimation of kinematic distances, we found that the distribution of HII
regions and GMCs can fit the models well, although the results do not change
significantly compared to the parameters with the standard and
.Comment: 34 Pages, 10 Figures, 5 Tables. Accepted for publication in A&A.
Edited
The precision of large radio continuum source catalogues- An application of the SPECFIND tool
The accuracy in position and flux density of 19 large radio continuum source
catalogues has been determined using SPECFIND, a new tool recently made
available through the CDS. The ~67000 radio continuum spectra with three or
more frequencies produced by SPECFIND were used to cross-correlate sources from
different catalogues and to calculate offsets in right ascension and
declination in the various catalogues with respect to the positions given in
the NRAO VLA Sky Survey (NVSS) catalogue, which was adopted as a reference. The
flux densities reported in the catalogues were compared to those predicted by
the composite spectra, enabling us to assess the quality of the flux density
calibration of the different catalogues.Comment: 6 pages, 1 figure. Accepted for publication in A&A; erroneous entries
in the DEC of the MRC input file detected; the article is changed accordingl
A 22-year Southern Sky Survey for Transient and Variable Radio Sources using the Molonglo Observatory Synthesis Telescope
We describe a 22-year survey for variable and transient radio sources,
performed with archival images taken with the Molonglo Observatory Synthesis
Telescope (MOST). This survey covers 2775 \unit{deg^2} of the sky south of
at an observing frequency of 843 MHz, an angular
resolution of 45 \times 45 \csc | \delta| \unit{arcsec^2} and a sensitivity
of 5 \sigma \geq 14 \unit{mJy beam^{-1}}. We describe a technique to
compensate for image gain error, along with statistical techniques to check and
classify variability in a population of light curves, with applicability to any
image-based radio variability survey. Among radio light curves for almost 30000
sources, we present 53 highly variable sources and 15 transient sources. Only 3
of the transient sources, and none of the variable sources have been previously
identified as transient or variable. Many of our variable sources are suspected
scintillating Active Galactic Nuclei. We have identified three variable sources
and one transient source that are likely to be associated with star forming
galaxies at , but whose implied luminosity is higher than the
most luminous known radio supernova (SN1979C) by an order of magnitude. We also
find a class of variable and transient source with no optical counterparts.Comment: Accepted for publication in MNRAS. 34 pages, 30 figures, 7 table
Global Physical Conditions of the Interstellar Medium in Nearby Galaxies
Far-infrared spectra (43-197um) of 34 nearby galaxies obtained by the Long
Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory (ISO) were
analyzed to investigate the general properties of interstellar matter in
galaxies. The line fluxes of [CII]158um and [NII]122um relative to the total
far-infrared flux (FIR) decrease as the far-infrared color becomes bluer, while
the ratio of the [OI]63um flux to FIR does not show a systematic trend with the
color. The [OIII]88um to FIR ratio shows a large scatter with a weak trend of
increase with the color. We estimate the physical conditions of
photodissociation regions (PDRs) in the sample galaxies, such as the
far-ultraviolet radiation field intensity Go and the gas density n by assuming
that all the observed [OI]63um and far-infrared continuum emissions come from
PDRs. The present analysis suggests that the decrease in [CII]158um/FIR with
the far-infrared color may not be accounted for by the decrease in the
photoelectric heating efficiency owing to the increase in positive charges of
dust grains because a measure of the efficiency, Go/n, is found to stay
constant with the far-infrared color. Instead the decrease can be interpreted
in terms of either the increase in the collisional de-excitation of the [CII]
transition due to the increase in the gas density or the decrease in the
ionized component relative to the far-infrared intensity suggested by the
decrease in [NII]122um/FIR. Based on the present analysis, we derive average
relations of the far-infrared color with Go and n in galaxies, which can be
applied to the investigation of interstellar matter in distant galaxies.Comment: to apear in A&
- …