7,826 research outputs found
TTF: a flexible approach to narrowband imaging
The Taurus Tunable Filter (TTF) is a tunable narrowband interference filter
covering wavelengths from 6300 A to the sensitivity drop-off of conventional
CCDs (9600 A), although a blue `arm' (3700-6500 A) is to be added by the end of
1997. The TTF offers monochromatic imaging at the cassegrain foci of both the
Anglo-Australian and William Herschel Telescopes, with an adjustable passband
of between 6 and 60 A. In addition, frequency switching with the TTF can be
synchronized to movement of charge (charge shuffling) on the CCD which has many
important applications in astrophysics. Here we review different modes of TTF.
We maintain a web site at http://msowww.anu.edu.au/~dhj/ttf.html describing all
aspects of TTF and its operation. In addition to general use, the instrument is
available in AAT service time. Details can be found at
http://www.aao.gov.au/local/www/jmc/service/service.html.Comment: 8 pages; Latex; 5 encapsulated postscript figures. Invited talk at
the "AAO/UKST Galactic Plane H-alpha Survey", International Workshop, Sydney,
Australi
Astrochemistry and Astrophotonics for an Antarctic Observatory
Due to its location and climate, Antarctica offers unique conditions for
long-period observations across a broad wavelength regime, where important
diagnostic lines for molecules and ions can be found, that are essential to
understand the chemical properties of the interstellar medium. In addition to
the natural benefits of the site, new technologies, resulting from
astrophotonics, may allow miniaturised instruments, that are easier to
winterise and advanced filters to further reduce the background in the
infrared.Comment: 4 pages, to be published in EAS Publications Series, Vol. 40, Proc.
of 3rd ARENA conferenc
Flow instabilities in transonic small disturbance theory
The dynamics of unsteady transonic small disturbance flows about two-dimensional airfoils is examined, with emphasis on the behavior in the region where the steady state flow is nonunique. It is shown that nonuniqueness results from an extremely long time scale instability which occurs in a finite Mach number and angle of attack range. The similarity scaling rules for the instability are presented and the possibility of similar behavior in the Euler equations is discussed
Ecological characterization of the Florida springs coast: Pithlachascotee to Waccasassa Rivers
This report covers the upper coast of west-central Florida. This region includes the drainage basins and nearshore waters of the west coast of Florida between, but not including, the Anclote River basin and the Suwannee River basin. The name Springs Coast wash chosen because this area contains a multitude of springs, both named and too small or inaccessible to have been names. Much of the area is karstic limestone. Most recognizable among the springs are the famous Crystal river, Weeki Wachee, and Homosassa. This territory includes large expanses of
marsh and wetland and, along its shores, the southern end of the largest area of seagrass beds in the state -- the Florida Big Bend Seagrass Beds preserve. It also possesses numerous spring-fed rivers and streams along the coast, whose constant discharges provide unique, relatively stable estuarine environments. This document is a summary of the available
information on the Springs Coast area of Florida, for
use by planners, developers, regulatory authorities,
and other interested parties. An understanding of the
factors affecting their plans and the possibly unexpected
impacts of their actions on others will, it is
hoped, promote intelligent development in areas
capable of supporting it. We have tried to provide a
clear, coherent picture of what is currently known
about how the physical, chemical, and biological
factors of the environment interact. (343 pp.
The Taurus Tunable Filter Field Galaxy Survey: Sample Selection and Narrowband Number-Counts
Recent evidence suggests a falling volume-averaged star-formation rate (SFR)
over z ~ 1. It is not clear, however, the extent to which the selection of such
samples influences the measurement of this quantity. Using the Taurus Tunable
Filter (TTF) we have obtained an emission-line sample of faint star-forming
galaxies over comparable lookback times: the TTF Field Galaxy Survey. By
selecting through emission-lines, we are screening galaxies through a quantity
that scales directly with star-formation activity for a given choice of initial
mass function. The scanning narrowband technique furnishes a galaxy sample that
differs from traditional broadband-selected surveys in both its volume-limited
nature and selection of galaxies through emission-line flux. Three discrete
wavelength intervals are covered, centered at H-alpha redshifts z = 0.08, 0.24
and 0.39.
Galaxy characteristics are presented and comparisons made with existing
surveys of both broadband and emission-line selection. When the number-counts
of emission-line objects are compared with those expected on the basis of
existing H-alpha surveys, we find an excess of ~ 3 times at the faintest
limits. While these detections are yet to be independently confirmed,
inspection of the stronger subsample of galaxies detected in both the line and
continuum (line-on-continuum subsample; 13 %) is sufficient to support an
excess population. This increase in the emission-line field population implies
higher star-formation densities over z ~ 0.4. However, further study in the
form of multi-object spectroscopic follow-up is necessary to quantify this and
confirm the faintest detections in the sample.Comment: 48 pages, 12 figures. To appear in the Astrophysical Journal. An
abridged version of the Abstract is shown her
Cohort Profile: Mamanengane or the Africa Centre Vertical Transmission Study
How did the study come about? From the mid-1990s, the success of antiretroviral prophylaxis to reduce HIV RNA viral load in plasma and avoidance of breastfeeding provided the real possibility that mother-to-child transmission (MTCT) of HIV-1 could be markedly reduced, 1 with an implicit understanding that these measures could be effectively applied to all HIV-infected women in developing countries. 2,3 The latter constitute the overwhelming majority of HIV-positive pregnancies resulting in approximately half a million new infant infections annually. 4 However, the inappropriate use of formula milks amongst impoverished populations resulted in major adverse effects; without the nutritiona
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