8,401 research outputs found
Estimating Sighting Proportions of American Alligator Nests during Helicopter Survey
Proportions of American alligator (Alligator mississippiensis) nests sighted
during aerial survey in Florida were estimated based upon multiple surveys by different
observers. We compared sighting proportions across habitats, nesting seasons, and observer
experience levels. The mean sighting proportion across all habitats and years was
0.736 (SE=0.024). Survey counts corrected by the mean sighting proportion reliably
predicted total nest counts (R2=0.933). Sighting proportions did not differ by habitat
type (P=0.668) or year P=0.328). Experienced observers detected a greater proportion
of nests (P<O.OOOl) than did either less experienced or inexperienced observers. Reliable
estimates of nest abundance can be derived from aerial counts of alligator nests
when corrected by the appropriate sighting proportion
The Organic Research Centre - Elm Farm:Bulletin 87
Bulletin 87 with coverage of Avian Influenza H5N1 in Suffolk,commentary on Biofuels, a paper on the organic "transition to sustainable resilience",paper on participatory approach to agronomy trials,update on evolutionary breeding of wheat project,article on formation of new growers alliance in UK
A comparison of minimum distance and maximum likelihood techniques for proportion estimation
The estimation of mixing proportions P sub 1, P sub 2,...P sub m in the mixture density f(x) = the sum of the series P sub i F sub i(X) with i = 1 to M is often encountered in agricultural remote sensing problems in which case the p sub i's usually represent crop proportions. In these remote sensing applications, component densities f sub i(x) have typically been assumed to be normally distributed, and parameter estimation has been accomplished using maximum likelihood (ML) techniques. Minimum distance (MD) estimation is examined as an alternative to ML where, in this investigation, both procedures are based upon normal components. Results indicate that ML techniques are superior to MD when component distributions actually are normal, while MD estimation provides better estimates than ML under symmetric departures from normality. When component distributions are not symmetric, however, it is seen that neither of these normal based techniques provides satisfactory results
Noise of fan designed to reduce stator lift fluctuations
An existing fan stage was redesigned to reduce stator lift fluctuations and was acoustically tested at three nozzle sizes for reduced noise generation. The lift fluctuations on the stator were reduced by increasing the stator cord, adjusting incidence angles, and adjusting the rotor velocity diagrams. Broadband noise levels were signficantly reduced in the middle to high frequencies. Blade passage tone sound power was not lessened, but decreases in the harmonics were observed. Aerodynamic improvements in both performance and efficiency were obtained
Effects of installation caused flow distortion on noise from a fan designed for turbofan engines
Far-field noise measurements were taken for three different installations of essentially the same fan. The installation with the most uniform inlet flow resulted in fan-blade-passage tone sound pressure levels more than 10 dB lower than the installation with more nonuniform inflow. Perceived noise levels were computed for the various installations and compared. Some measurements of inlet flow distortion were made and used in a blade-passage noise generation theory to predict the effects of distortion on noise. Good agreement was obtained between the prediction and the measured effect. Possible origins of the distortion were identified by observation of tuft action in the vicinity of the inlet
Fan noise reduction achieved by removing tip flow irregularities behind the rotor - forward arc test configurations
The noise source caused by the interaction of the rotor tip flow irregularities (vortices and velocity defects) with the downstream stator vanes was studied. Fan flow was removed behind a 0.508 meter (20 in.) diameter model turbofan through an outer wall slot between the rotor and stator. Noise measurements were made with far-field microphones positioned in an arc about the fan inlet and with a pressure transducer in the duct behind the stator. Little tone noise reduction was observed in the forward arc during flow removal; possibly because the rotor-stator interaction noise did not propagate upstream through the rotor. Noise reductions were maded in the duct behind the stator and the largest decrease occurred with the first increment of flow removal. This result indicates that the rotor tip flow irregularity-stator interaction is as important a noise producing mechanism as the normally considered rotor wake-stator interaction
Reduction of fan noise in an anechoic chamber by reducing chamber wall induced inlet flow disturbances
The difference between the flight and ground static noise of turbofan engines presents a significant problem in engine noise testing. The additional noise for static testing has been attributed to inlet flow disturbances or turbulence interacting with the fan rotor. In an attempt to determine a possible source of inflow disturbances entering fans tested in the Lewis Research Center anechoic chamber, the inflow field was studied using potential flow analysis. These potential flow calculations indicated that there was substantial flow over the wall directly behind the fan inlet that could produce significant inflow disturbances. Fan noise tests were run with various extensions added to the fan inlet to move the inlet away from this backwall and thereby reduce the inlet flow disturbances. Significant noise reductions were observed with increased inlet length. Over 5 db reduction of the blade passage tone sound power level was observed between the shortest and longest inlets at 90% fan speed and the first overtone was reduced 9 db. High frequency broadband noise was also reduced
Survival and Growth of American Alligator (Alligator mississippiensis) hatchlings after artificial incubation and repatriation
Hatchling American Alligators (Alligator mississippiensis) produced from artificially incubated
wild eggs were returned to their natal areas (repatriated). We compared artificially incubated and
repatriated hatchlings released within and outside the maternal alligator’s home range with naturally
incubated hatchlings captured and released within the maternal alligator’s home range on Lake Apopka,
Lake Griffin, and Orange Lake in Florida. We used probability of recapture and total length at approximately
nine months after hatching as indices of survival and growth rates. Artificially incubated hatchlings released
outside of the maternal alligator’s home range had lower recapture probabilities than either naturally
incubated hatchlings or artificially incubated hatchlings released near the original nest site. Recapture
probabilities of other treatments did not differ significantly. Artificially incubated hatchlings were
approximately 6% shorter than naturally incubated hatchlings at approximately nine months after hatching.
We concluded that repatriation of hatchlings probably would not have long-term effects on populations
because of the resiliency of alligator populations to alterations of early age-class survival and growth rates of
the magnitude that we observed. Repatriation of hatchlings may be an economical alternative to repatriation
of older juveniles for population restoration. However, the location of release may affect subsequent survival
and growth
Alligator Diet in Relation to Alligator Mortality on Lake Griffin, FL
Alligator mississippiensis (American Alligators) demonstrated low hatchrate
success and increased adult mortality on Lake Griffin, FL, between 1998 and
2003. Dying Lake Griffin alligators with symptoms of poor motor coordination were
reported to show specific neurological impairment and brain lesions. Similar lesions
were documented in salmonines that consumed clupeids with high thiaminase levels.
Therefore, we investigated the diet of Lake Griffin alligators and compared it with
alligator diets from two lakes that exhibited relatively low levels of unexplained
alligator mortality to see if consumption of Dorosoma cepedianum (gizzard shad)
could be correlated with patterns of mortality. Shad in both lakes Griffin and Apopka
had high levels of thiaminase and Lake Apopka alligators were consuming greater
amounts of shad relative to Lake Griffin without showing mortality rates similar to
Lake Griffin alligators. Therefore, a relationship between shad consumption alone
and alligator mortality is not supported
Design and development of a multi-layer memory system Final report, 28 Jan. 1966 - 27 Jan. 1967
Design and development of multilayer memory syste
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