6,591 research outputs found
Developments in steady and unsteady aerodynamics for use in aeroelastic analysis and design
A review is given of seven research projects which are aimed at improving the generality, accuracy, and computational efficiency of steady and unsteady aerodynamic theory for use in aeroelastic analysis and design. These projects indicate three major thrusts of current research efforts: (1) more realistic representation of steady and unsteady subsonic and supersonic loads on aircraft configurations of general shape with emphasis on structural-design applications, (2) unsteady aerodynamics for application in active-controls analyses, and (3) unsteady aerodynamics for the frequently critical transonic speed range. The review of each project includes theoretical background, description of capabilities, results of application, current status, and plans for further development and use
The large scale distribution of warm ionized gas around nearby radio galaxies with jet-cloud interactions
Deep, narrow-band Halpha observations taken with the TAURUS Tunable Filter
(TTF) on the 4.2m WHT telescope are presented for two nearby radio galaxies
with strong jet-cloud interactions. Although the brightest emission line
components are closely aligned with the radio jets --- providing nearby
examples of the ``alignment effect'' most commonly observed in high redshift (z
> 0.5) radio galaxies --- lower surface brightness emission line structures are
detected at large distances (10's of kpc) from the radio jet axis. These latter
structures cannot be reconciled with anisotropic illumination of the ISM by
obscured quasar-like sources, since parts of the structures lay outside any
plausible quasar ionization cones. Rather, the distribution of the emission
lines around the fringes of the extended radio lobes suggests that the gas is
ionized either by direct interaction with the radio components, or by the
diffuse photoionizing radiation fields produced in the shocks generated in such
interactions. These observations serve to emphasise that the ionizing effects
of the radio components can extend far from the radio jet axes, and that deep
emission line imaging observations are required to reveal the true distribution
of warm gas in the host galaxies. We expect future deep imaging observations to
reveal similar structures perpendicular to the radio axes in the high-z radio
galaxies.Comment: 18 pages, 4 figures, to be published in MNRA
Tunable-filter imaging of quasar fields at z ~ 1. II. The star-forming galaxy environments of radio-loud quasars
We have scanned the fields of six radio-loud quasars using the Taurus Tunable
Filter to detect redshifted [OII] 3727 line-emitting galaxies at redshifts 0.8
< z < 1.3. Forty-seven new emission-line galaxy (ELG) candidates are found.
This number corresponds to an average space density about 100 times that found
locally and, at L([OII]) < 10^{42} erg s^{-1} cm^{-2}, is 2 - 5 times greater
than the field ELG density at similar redshifts, implying that radio-loud
quasars inhabit sites of above-average star formation activity. The implied
star-formation rates are consistent with surveys of field galaxies at z ~ 1.
However, the variation in candidate density between fields is large and
indicative of a range of environments, from the field to rich clusters. The ELG
candidates also cluster -- both spatially and in terms of velocity -- about the
radio sources. In fields known to contain rich galaxy clusters, the ELGs lie at
the edges and outside the concentrated cores of red, evolved galaxies,
consistent with the morphology-density relation seen in low-redshift clusters.
This work, combined with other studies, suggests that the ELG environments of
powerful AGN look very much the same from moderate to high redshifts, i.e. 0.8
< z < 4.Comment: 18 pages, 18 figures, uses emulateapj.cls. Accepted for publication
in A
NGC 300: an extremely faint, outer stellar disk observed to 10 scale lengths
We have used the Gemini Multi-object Spectrograph (GMOS) on the Gemini South
8m telescope in exceptional conditions (0.6" FWHM seeing) to observe the outer
stellar disk of the Sculptor group galaxy NGC 300 at two locations. At our
point source detection threshold of r' = 27.0 (3-sigma) mag, we trace the
stellar disk out to a radius of 24', or 2.2 R_25 where R_25 is the 25
mag/arcsec**2 isophotal radius. This corresponds to about 10 scale lengths in
this low-luminosity spiral (M_B = -18.6), or about 14.4 kpc at a cepheid
distance of 2.0 +/- 0.07 Mpc. The background galaxy counts are derived in the
outermost field, and these are within 10% of the mean survey counts from both
Hubble Deep Fields. The luminosity profile is well described by a nucleus plus
a simple exponential profile out to 10 optical scale lengths. We reach an
effective surface brightness of 30.5 mag/arcsec**2 (2-sigma) at 55%
completeness which doubles the known radial extent of the optical disk. These
levels are exceedingly faint in the sense that the equivalent surface
brightness in B or V is about 32 mag/arcsec**2. We find no evidence for
truncation of the stellar disk. Only star counts can be used to reliably trace
the disk to such faint levels, since surface photometry is ultimately limited
by nonstellar sources of radiation. In the Appendix, we derive the expected
surface brightness of one such source: dust scattering of starlight in the
outer disk.Comment: ApJ accepted -- 30 pages, 13 figures -- see
ftp://www.aao.gov.au/pub/local/jbh/astro-ph/N300 for full resolution figures
and preprin
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Correlated modal mineralogy, aqueous alteration and oxygen isotope composition of CM Chondrites
In this study we move beyond defining alteration sequences in CM chondrites towards understanding the relationship between modal mineralogy, the extent of aqueous alteration and O-isotope compositions
Tunable-filter imaging of quasar fields at z~1. I. A cluster around MRC B0450-221
Using a combination of multicolour broad- and narrow-band imaging techniques
and follow-up spectroscopy, we have detected an overdensity of galaxies in the
field of quasar MRC B0450-221, whose properties are consistent with a cluster
at the quasar redshift z=0.9. An excess of red galaxies (V-I>2.2, I-K'>3.8) is
evident within 1' of the quasar, with the colours expected for galaxies at
z=0.9 that have evolved passively for 3 Gyr or more. A number of line-emitting
galaxies (nine candidates with equivalent widths EW>70A) are also detected in
the field using the TAURUS Tunable Filter (TTF). Three have been confirmed
spectroscopically to indeed lie at z=0.9. The TTF candidates with the strongest
[O II] line emission cluster in a group which lies 200-700 kpc away from the
quasar and the red galaxy excess, and therefore most likely on the outskirts of
the cluster. These observations are the first in a series probing quasar
environments at z~1 with TTF.Comment: Accepted for publication in AJ. 25 pages, 24 figs (large files in jpg
or gif format), uses emulateapj.st
Discovery of a 500 pc shell in the nucleus of Centaurus A
Spitzer Space Telescope mid-infrared images of the radio galaxy Centaurus A
reveal a shell-like, bipolar, structure 500 pc to the north and south of the
nucleus. This shell is seen in 5.8, 8.0 and 24 micron broad-band images. Such a
remarkable shell has not been previously detected in a radio galaxy and is the
first extragalactic nuclear shell detected at mid-infrared wavelengths. We
estimate that the shell is a few million years old and has a mass of order
million solar masses. A conservative estimate for the mechanical energy in the
wind driven bubble is 10^53 erg. The shell could have created by a small few
thousand solar mass nuclear burst of star formation. Alternatively, the
bolometric luminosity of the active nucleus is sufficiently large that it could
power the shell. Constraints on the shell's velocity are lacking. However, if
the shell is moving at 1000 km/s then the required mechanical energy would be
100 times larger.Comment: submitted to ApJ Letter
Missing data in randomized controlled trials testing palliative interventions pose a significant risk of bias and loss of power: a systematic review and meta-analyses
Objectives To assess the risk posed by missing data (MD) to the power and validity of trials evaluating palliative interventions. Study Design and Setting A systematic review of MD in published randomized controlled trials (RCTs) of palliative interventions in participants with life-limiting illnesses was conducted, and random-effects meta-analyses and metaregression were performed. CENTRAL, MEDLINE, and EMBASE (2009-2014) were searched with no language restrictions. Results One hundred and eight RCTs representing 15,560 patients were included. The weighted estimate for MD at the primary endpoint was 23.1% (95% confidence interval [CI] 19.3, 27.4). Larger MD proportions were associated with increasing numbers of questions/tests requested (odds ratio [OR] , 1.19; 95% CI 1.05, 1.35) and with longer study duration (OR, 1.09; 95% CI 1.02, 1.17). Meta-analysis found evidence of differential rates of MD between trial arms, which varied in direction (OR, 1.04; 95% CI 0.90, 1.20; I 2 35.9, P = 0.001). Despite randomization, MD in the intervention arms (vs. control) were more likely to be attributed to disease progression unrelated to the intervention (OR, 1.31; 95% CI 1.02, 1.69). This was not the case for MD due to death (OR, 0.92; 95% CI 0.78, 1.08). Conclusion The overall proportion and differential rates and reasons for MD reduce the power and potentially introduce bias to palliative care trials
Direct observation of domain-wall configurations transformed by spin currents
Direct observations of current-induced domain-wall propagation by
spin-polarized scanning electron microscopy are reported. Current pulses move
head-to-head as well as tail-to-tail walls in sub-micrometer Fe_{20}Ni_{80}
wires in the direction of the electron flow, and a decay of the wall velocity
with the number of injected current pulses is observed. High-resolution images
of the domain walls reveal that the wall spin structure is transformed from a
vortex to a transverse configuration with subsequent pulse injections. The
change in spin structure is directly correlated with the decay of the velocity.Comment: 5 pages, 3 figure
Suppression of the near-infrared OH night sky lines with fibre Bragg gratings - first results
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.Comment: Accepted for publication in MNRAS. 15 pages, 18 figure
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