4,333 research outputs found
A study of commuter air service
A regionally oriented overview of the commuter air service industry is provided. A framework for an eventual assessment of potential technology directions that may be of benefit to the industry is presented. Data are provided on the industry's market characteristics, service patterns, patronage characteristics, aircraft and airport needs, economic characteristics and institutional issues. Using personal interview and literature survey methods, investigation of a considerable cross-section of the industry was made
Efficient concepts for large erectable space structures
The status of Langley Research Center development of the nestable column concept is reviewed including results of member and truss component tests, and planned assembly studies. In addition, more recent studies of alternative member concepts are presented. Preliminary results on relative efficiency of several types of truss-type columns are compared and future test plans discussed
Critical behavior in a cross-situational lexicon learning scenario
The associationist account for early word-learning is based on the
co-occurrence between objects and words. Here we examine the performance of a
simple associative learning algorithm for acquiring the referents of words in a
cross-situational scenario affected by noise produced by out-of-context words.
We find a critical value of the noise parameter above which learning
is impossible. We use finite-size scaling to show that the sharpness of the
transition persists across a region of order about ,
where is the number of learning trials, as well as to obtain the
learning error (scaling function) in the critical region. In addition, we show
that the distribution of durations of periods when the learning error is zero
is a power law with exponent -3/2 at the critical point
Effect of Flushing and Gonadotropin on Ovulation Rate of Yearling Ewes on Range
Improvement of the reproduction rate of range ewes is of the utmost importance to the range sheep producer. Good grazing management and proper supplementation have been shown to be important. Flushing range ewes has given conflicting results. Gonadotrophic hormones have been used to increase ovulation rates but have been less successful with yearlings than with older ewes
Statistical Communication Theory
Contains research objectives and reports on five research projects.National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-04)National Aeronautics and Space Administration (Grant NsG-496
Arm & Interarm Star Formation in Spiral Galaxies
We investigate the relationship between spiral arms and star formation in the
grand-design spirals NGC 5194 and NGC 628 and in the flocculent spiral NGC
6946. Filtered maps of near-IR (3.6 micron) emission allow us to identify "arm
regions" that should correspond to regions of stellar mass density
enhancements. The two grand-design spirals show a clear two-armed structure,
while NGC 6946 is more complex. We examine these arm and interarm regions,
looking at maps that trace recent star formation - far-ultraviolet (GALEX NGS)
and 24 micron emission (Spitzer, SINGS) - and cold gas - CO (Heracles) and HI
(Things). We find the star formation tracers and CO more concentrated in the
spiral arms than the stellar 3.6 micron flux. If we define the spiral arms as
the 25% highest pixels in the filtered 3.6 micron images, we find that the
majority (60%) of star formation tracers occurs in the interarm regions; this
result persists qualitatively even when considering the potential impact of
finite data resolution and diffuse interarm 24 micron emission. Even with a
generous definition of the arms (45% highest pixels), interarm regions still
contribute at least 30% to the integrated star formation rate tracers. We look
for evidence that spiral arms trigger star or cloud formation using the ratios
of star formation rate (SFR, traced by a combination of FUV and 24 micron
emission) to H_2 (traced by CO) and H_2 to HI. Any enhancement of SFR / M(H_2)
in the arm region is very small (less than 10%) and the grand design spirals
show no enhancement compared to the flocculent target. Arm regions do show a
weak enhancement in H_2/HI compared to the interarm regions, but at a fixed gas
surface density there is little clear enhancement in the H_2/HI ratio in the
arm regions. Thus, it seems that spiral arms may only act to concentrate the
gas to higher densities in the arms.Comment: 11 pages, 9 Figures, accepted by Ap
EXPOSURE TIME OF ORAL RABIES VACCINE BAITS RELATIVE TO BAITING DENSITY AND RACCOON POPULATION DENSITY
Oral rabies vaccination (ORV) baiting programs for control of raccoon (Procyon lotor) rabies in the USA have been conducted or are in progress in eight states east of the Mississippi River. However, data specific to the relationship between raccoon population density and the minimum density of baits necessary to significantly elevate rabies immunity are few. We used the 22-km2 US National Aeronautics and Space Administration Plum Brook Station (PBS) in Erie County, Ohio, USA, to evaluate the period of exposure for placebo vaccine baits placed at a density of 75 baits/km2 relative to raccoon population density. Our objectives were to 1) estimate raccoon population density within the fragmented forest, old-field, and industrial landscape at PBS; and 2) quantify the time that placebo, Merial RABORAL V-RG* vaccine baits were available to raccoons. From August through November 2002 we surveyed raccoon use of PBS along 19.3 km of paved-road transects by using a forward-looking infrared camera mounted inside a vehicle. We used Distance 3.5 software to calculate probability of detection function by which we estimated raccoon population density from transect data. Estimated population density on PBS decreased from August (33.4 raccoons/km2) through November (13.6 raccoons/km2), yielding a monthly mean of 24.5 raccoons/km2. We also quantified exposure time for ORV baits placed by hand on five 1-km2 grids on PBS from September through October. An average 82.7% (SD=4.6) of baits were removed within 1 wk of placement. Given raccoon population density, estimates of bait removal and sachet condition, and assuming 22.9% nontarget take, the baiting density of 75/ km\u27 yielded an average of 3.3 baits consumed per raccoon anti the sachet perforated
Extremely Inefficient Star Formation in the Outer Disks of Nearby Galaxies
(Abridged) We combine data from The HI Nearby Galaxy Survey and the GALEX
Nearby Galaxy Survey to study the relationship between atomic hydrogen (HI) and
far-ultraviolet (FUV) emission outside the optical radius (r25) in 17 spiral
and 5 dwarf galaxies. In this regime, HI is likely to represent most of the ISM
and FUV emission to trace recent star formation with little bias due to
extinction, so that the two quantities closely trace the underlying
relationship between gas and star formation rate (SFR). The azimuthally
averaged HI and FUV intensities both decline with increasing radius in this
regime, with the scale length of the FUV profile typically half that of the HI
profile. Despite the mismatch in profiles, there is a significant spatial
correlation (at 15" resolution) between local FUV and HI intensities; near r25
this correlation is quite strong, in fact stronger than anywhere inside r25,
and shows a decline towards larger radii. The star formation efficiency (SFE) -
defined as the ratio of FUV/HI and thus the inverse of the gas depletion time -
decreases with galactocentric radius across the outer disks, though much
shallower than across the optical disks. On average, we find the gas depletion
times to be well above a Hubble time (~10^11 yr). We observe a clear
relationship between FUV/HI and HI column in the outer disks, with the SFE
increasing with increasing HI column. Despite observing systematic variations
in FUV/HI, we find no clear evidence for step-function type star formation
thresholds. When compared with results from inside r25, we find outer disk star
formation to be distinct in several ways: it is extremely inefficient
(depletion times of many Hubble times) with column densities and SFRs lower
than found anywhere inside the optical disks. It appears that the HI column is
one of, perhaps even the key environmental factor in setting the SFR in outer
galaxy disks.Comment: Accepted for Publication in The Astronomical Journa
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