26,504 research outputs found
Mach-Zehnder optical configuration with Brewster window and two quarter-wave plates
Configuration is improvement because of the following: It provides higher efficiency. It reduces or eliminates feedthrough of untranslated local oscillator, which would produce a beat signal at shifted frequency of translator. When used without translator and with low-power detector, telescope secondary mirror reflects portion of output to local oscillator
Low speed and angle of attack effects on sonic and near-sonic inlets
Tests of the Quiet, Clean Short-Haul Experimental Engine (QCSEE) were conducted to determine the effects of forward velocity and angle of attack on sonic and near-sonic inlet aerodynamic performance penalties and acoustic suppression characteristics. The tests demonstrate that translating centerbody and radial vane sonic inlets, and QCSEE high throat Mach number inlets, can be designed to operate effectively at forward speed and moderate angle of attack with good performance and noise suppression capability. The test equipment and procedures used in conducting the evaluation are described. Results of the tests are presented in tabular form
The Status of the United States Population of Night Shark, Carcharhinus signatus
Night sharks, Carcharhinus signatus, are an oceanic species generally occurring in outer continental shelf waters in the western North Atlantic Ocean including the Caribbean Sea and Gulf of Mexico. Although not targeted, night sharks
make up a segment of the shark bycatch in the pelagic longline fishery. Historically, night sharks comprised a significant proportion of the artisanal Cuban shark
fishery but today they are rarely caught. Although information from some fisheries has shown a decline in catches of night sharks, it is unclear whether this decline is due to changes in fishing tactics, market, or species identification. Despite the uncertainty in the decline, the night shark is currently listed as a species of concern due
to alleged declines in abundance resulting from fishing effort, i.e. overutilization.
To assess their relevance to the species of concern list, we collated available information on the night shark to provide an analysis of its status. Night shark landings were
likely both over- and under-reported and thus probably did not reflect all commercial and recreational catches, and overall they have limited relevance to the current status
of the species. Average size information has not changed considerably since the 1980’s based on information from the pelagic longline fishery when corrected for gear bias.
Analysis of biological information indicates night sharks have intrinsic rates of increase (r) about 10% yr–1 and have moderate rebound potential and an intermediate generation time compared to other sharks. An analysis of trends in relative abundance from four data sources gave conflicting results, with one series in decline, two series
increasing, and one series relatively flat. Based on the analysis of all currently available information, we believe the night shark does not qualify as a species of concern
but should be retained on the prohibited species list as a precautionary approach to management until a more comprehensive stock assessment can be conducted
Simulated lumped-parameter system reduced-order adaptive control studies
Two methods of interpreting the misbehavior of reduced order adaptive controllers are discussed. The first method is based on system input-output description and the second is based on state variable description. The implementation of the single input, single output, autoregressive, moving average system is considered
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Extragalactic Radio Sources and the WMAP Cold Spot
We detect a dip of 20-45% in the surface brightness and number counts of NVSS
sources smoothed to a few degrees at the location of the WMAP cold spot. The
dip has structure on scales of approximately 1-10 degrees. Together with
independent all-sky wavelet analyses, our results suggest that the dip in
extragalactic brightness and number counts and the WMAP cold spot are
physically related, i.e., that the coincidence is neither a statistical anomaly
nor a WMAP foreground correction problem. If the cold spot does originate from
structures at modest redshifts, as we suggest, then there is no remaining need
for non-Gaussian processes at the last scattering surface of the CMB to explain
the cold spot. The late integrated Sachs-Wolfe effect, already seen
statistically for NVSS source counts, can now be seen to operate on a single
region. To create the magnitude and angular size of the WMAP cold spot requires
a ~140 Mpc radius completely empty void at z<=1 along this line of sight. This
is far outside the current expectations of the concordance cosmology, and adds
to the anomalies seen in the CMB.Comment: revised version, ApJ, in pres
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