884 research outputs found
Augmentor emissions reduction technology program
Technology to reduce pollutant emissions from duct-burner-type augmentors for use on advanced supersonic cruise aircraft was investigated. Test configurations, representing variations of two duct-burner design concepts, were tested in a rectangular sector rig at inlet temperature and pressure conditions corresponding to takeoff, transonic climb, and supersonic cruise flight conditions. Both design concepts used piloted flameholders to stabilize combustion of lean, premixed fuel/air mixtures. The concepts differed in the flameholder type used. High combustion efficiency (97%) and low levels of emissions (1.19 g/kg fuel) were achieved. The detailed measurements suggested the direction that future development efforts should take to obtain further reductions in emission levels and associated improvements in combustion efficiency over an increased range of temperature rise conditions
Preliminary comparison of natural versus model-predicted recovery of vessel-generated seagrass injuries in Florida Keys National Marine Sanctuary
Each year, more than 500 motorized vessel groundings cause widespread damage to seagrasses in Florida Keys National Marine Sanctuary (FKNMS). Under Section 312 of the National Marine Sanctuaries Act (NMSA), any party responsible for the loss, injury, or destruction of any Sanctuary resource, including seagrass, is liable to the United States for response costs and resulting damages. As part of the damage assessment process, a cellular automata model is utilized to forecast seagrass recovery rates. Field validation of these forecasts was accomplished by comparing model-predicted percent recovery to that which was observed to be occurring naturally for 30 documented vessel grounding sites. Model recovery forecasts for both Thalassia testudinum and Syringodium filiforme exceeded natural recovery estimates for 93.1% and 89.5% of the sites, respectively. For Halodule wrightii, the number of over- and under-predictions by the model was similar. However, where under-estimation occurred, it was often severe, reflecting the well-known extraordinary growth potential of this opportunistic species. These preliminary findings indicate that the recovery model is consistently generous to Responsible Parties in that the model forecasts a much faster recovery than was observed to occur naturally, particularly for T. testudinum, the dominant seagrass species in the region and the species most often affected. Environmental setting (i.e., location, wave exposure) influences local seagrass landscape pattern and may also play a role in the recovery dynamics for a particular injury site. An examination of the relationship between selected environmental factors and injury recovery dynamics is currently underway. (PDF file contains 20 pages.
Characterising exo-ringsystems around fast-rotating stars using the Rossiter-McLaughlin effect
Planetary rings produce a distinct shape distortion in transit lightcurves.
However, to accurately model such lightcurves the observations need to cover
the entire transit, especially ingress and egress, as well as an out-of-transit
baseline. Such observations can be challenging for long period planets, where
the transits may last for over a day. Planetary rings will also impact the
shape of absorption lines in the stellar spectrum, as the planet and rings
cover different parts of the rotating star (the Rossiter-McLaughlin effect).
These line-profile distortions depend on the size, structure, opacity,
obliquity and sky projected angle of the ring system. For slow rotating stars,
this mainly impacts the amplitude of the induced velocity shift, however, for
fast rotating stars the large velocity gradient across the star allows the line
distortion to be resolved, enabling direct determination of the ring
parameters. We demonstrate that by modeling these distortions we can recover
ring system parameters (sky-projected angle, obliquity and size) using only a
small part of the transit. Substructure in the rings, e.g. gaps, can be
recovered if the width of the features () relative to the size of the
star is similar to the intrinsic velocity resolution (set by the width of the
local stellar profile, ) relative to the stellar rotation velocity (
sin, i.e. sin/). This opens up a new
way to study the ring systems around planets with long orbital periods, where
observations of the full transit, covering the ingress and egress, are not
always feasible.Comment: Accepted for publication in MNRA
All NIRspec needs is HST/WFC3 pre-imaging? The use of Milky Way Stars in WFC3 Imaging to Register NIRspec MSA Observations
The James Webb Space Telescope (JWST) will be an exquisite new near-infrared
observatory with imaging and multi-object spectroscopy through ESA's NIRspec
instrument with its unique Micro-Shutter Array (MSA), allowing for slits to be
positioned on astronomical targets by opening specific 0.002"-wide micro
shutter doors.
To ensure proper target acquisition, the on-sky position of the MSA needs to
be verified before spectroscopic observations start. An onboard centroiding
program registers the position of pre-identified guide stars in a Target
Acquisition (TA) image, a short pre-spectroscopy exposure without dispersion
(image mode) through the MSA with all shutters open.
The outstanding issue is the availability of Galactic stars in the right
luminosity range for TA relative to typical high redshift targets. We explore
this here using the stars and candidate galaxies identified in the
source extractor catalogs of Brightest of Reionizing Galaxies survey
(BoRG[z8]), a pure-parallel program with Hubble Space Telescope Wide-Field
Camera 3.
We find that (a) a single WFC3 field contains enough Galactic stars to
satisfy the NIRspec astrometry requirement (20 milli-arcseconds), provided its
and the NIRspec TA's are AB in WFC3 F125W, (b) a single WFC3
image can therefore serve as the pre-image if need be, (c) a WFC3 mosaic and
accompanying TA image satisfy the astrometry requirement at AB mag in
WFC3 F125W, (d) no specific Galactic latitude requires deeper TA imaging due to
a lack of Galactic stars, and (e) a depth of AB mag in WFC3 F125W is
needed if a guide star in the same MSA quadrant as a target is required.
We take the example of a BoRG identified candidate galaxy and
require a Galactic star within 20" of it. In this case, a depth of 25.5 AB in
F125W is required (with 97% confidence).Comment: 17 pages, 15 figures, to appear in the Journal of Astronomical
Instrumentatio
Joint Report of Peer Review Panel for Numeric Nutrient Criteria for the Great Bay Estuary New Hampshire Department of Environmental Services June, 2009
This peer review was authorized through a collaborative agreement sponsored by the New Hampshire Department of Environmental Services (DES) and the Cities of Dover, Rochester and Portsmouth, New Hampshire. The purpose was to conduct an independent scientific peer review of the document entitled, “Numeric Nutrient Criteria for the Great Bay Estuary,” dated June, 2009 (DES 2009 Report)
Research Notes: Recurrent selection for yield in soybeans
Recurrent selection procedures have had limited application in soybean improvement (Kenworthy, 1976). Despite the procedural difficulties, theoretical considerations suggest an advantage for recurrent selection in supplementing standard breeding procedures. We present here a preliminary report of the yield response realized from several cycles of selection
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