1,257 research outputs found
Age- and length-at-maturity of female arrowtooth flounder (Atheresthes stomias) in the Gulf of Alaska
Arrowtooth flounder (Atheresthes stomias) has had the highest abundance of any groundfish species in the Gulf
of Alaska since the 1970s (Matarese et al., 2003; Turnock et al., 2005; Blood et al., 2007); however, commercial
catches have been restricted because Pacific halibut (Hippoglossus stenolepis) are caught as bycatch in the fishery. Arrowtooth flounder plays a key role in the ecosystem because it is a dominant organism within the
food web, both as an apex predator of fish and invertebrates, as well as an important prey for walleye pollock (Theragra chalcogramma; Aydin et al., 2002). Walleye pollock is the dominant groundfish in the Bering
Sea, a principal groundfish in the Gulf of Alaska, and the primary prey for marine mammals. The distribution of arrowtooth flounder extends from Cape Navarin and the eastern Sea of Okhotsk in Russia, across the Bering Sea, Aleutian Islands, Gulf of Alaska, and south to the coast of
central California (Shuntov, 1964; Britt and Martin, 2001; Chetvergov, 2001; Weinberg et al., 2002; Zenger, 2004). Because of the importance of arrowtooth flounder in the marine ecosystem of A laska, a maturity study of this species was undertaken to determine age-at-maturity, which
is essential for age-based stock management models. Before these results, management has had to rely upon a length-at-maturity-based estimate (Zimmermann, 1997) to manage stocks in the Gulf of Alaska (GOA), Bering Sea, and Aleutian Islands. The central GOA was selected as the location for this maturity study Age- and length-at-maturity of female arrowtooth flounder (Atheresthes stomias) in the Gulf of Alaska because it contains approximately 70% of the total Gulf of Alaska arrowtooth flounder biomass (1.9Ă106 t, age
3 and older)â the highest percentage in the world (Shuntov, 1964; Britt and Martin, 2001; Weinberg et al., 2002;
Wilderbuer and Nichol, 2006)
Impacts of wastewater discharge to Fountain Creek on nitrate contamination in the Widefield aquifer
February 1990.Includes bibliographical references.Grant no. 14-08-0001-G1214, Project no. G1214-07
Geographic and seasonal variations in maturation and growth of female Pacific cod (Gadus macrocephalus) in the Gulf of Alaska and Bering Sea
This study investigates the temporal stability of length- and age-at-maturity estimates for female Pacific cod (Gadus macrocephalus) in the Gulf of Alaska and eastern Bering Sea. Females reached 50% maturity (A50) at 4.4 years in the
Gulf of Alaska and at 4.9 years in the eastern Bering Sea. Total body length at 50% maturity (LT50) was significantly smaller (503 mm) in the Gulf of Alaska than in the eastern
Bering Sea (580 mm). The estimated length- and age-at-maturity did not differ significantly between winter and spring in either the Gulf of Alaska (1999) or Bering Sea (2003) areas. The results of this study raised the
spawning biomass estimate of female Alaskan Pacific cod from 298Ă103 t for 2005 to 499Ă103 t for 2006. The
increased spawning biomass estimate resulted in an increased over-fishing limit for Pacific cod
Dense, Parsec-Scale Clumps near the Great Annihilator
We report on Combined Array for Research in Millimeter-Wave Astronomy (CARMA)
and James Clerk Maxwell Telescope (JCMT) observations toward the Einstein
source 1E 1740.7-2942, a LMXB commonly known as the "Great Annihilator." The
Great Annihilator is known to be near a small, bright molecular cloud on the
sky in a region largely devoid of emission in 12-CO surveys of the Galactic
Center. The region is of interest because it is interior to the dust lanes
which may be the shock zones where atomic gas from HI nuclear disk is converted
into molecular gas. We find that the region is populated with a number of dense
(n ~ 10^5 cm^-3) regions of excited gas with small filling factors, and
estimate that up to 1-3 x 10^5 solar masses of gas can be seen in our maps. The
detection suggests that a significant amount of mass is transported from the
shock zones to the GC star-forming regions in the form of small, dense bundles.Comment: 26 pages, 7 figures, accepted for publication by the Astrophysical
Journal, abstract abridge
The Baryon Content of Cosmic Structures
We make an inventory of the baryonic and gravitating mass in structures
ranging from the smallest galaxies to rich clusters of galaxies. We find that
the fraction of baryons converted to stars reaches a maximum between M500 =
1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright
galaxies in groups. The fraction of baryons detected in all forms deviates
monotonically from the cosmic baryon fraction as a function of mass. On the
largest scales of clusters, most of the expected baryons are detected, while in
the smallest dwarf galaxies, fewer than 1% are detected. Where these missing
baryons reside is unclear.Comment: ApJ Letters, in pres
encephalitis in Florida
Background: Eastern Equine Encephalitis virus (EEEV) is an alphavirus with high pathogenicity in both humans and horses. Florida continues to have the highest occurrence of human cases in the USA, with four fatalities recorded in 2010. Unlike other states, Florida supports year-round EEEV transmission. This research uses GIS to examine spatial patterns of documented horse cases during 2005â2010 in order to understand the relationships between habitat and transmission intensity of EEEV in Florida. Methods: Cumulative incidence rates of EEE in horses were calculated for each county. Two cluster analyses were performed using density-based spatial clustering of applications with noise (DBSCAN). The first analysis was based on regional clustering while the second focused on local clustering. Ecological associations of EEEV were examined using compositional analysis and Euclidean distance analysis to determine if the proportion or proximity of certain habitats played a role in transmission. Results: The DBSCAN algorithm identified five distinct regional spatial clusters that contained 360 of the 438 horse cases. The local clustering resulted in 18 separate clusters containing 105 of the 438 cases. Both the compositional analysis and Euclidean distance analysis indicated that the top five habitats positively associated with horse cases were rural residential areas, crop and pastureland, upland hardwood forests, vegetated non-forested wetlands, an
Nighttime removal of NOx in the summer marine boundary layer
The nitrate radical, NO3, and dinitrogen pentoxide, N2O5, are two important components of nitrogen oxides that occur predominantly at night in the lower troposphere. Because a large fraction of NO2 reacts to form NO3 and N2O5 during the course of a night, their fate is an important determining factor to the overall fate of NOx (=NO and NO2). As a comprehensive test of nocturnal nitrogen oxide chemistry, concentrations of O3, NO, NO2, NO3, N2O5, HNO3 and a host of other relevant compounds, aerosol abundance and composition, and meteorological conditions were measured in the marine boundary layer from the NOAA research vessel Ronald H. Brown off the East Coast of the United States as part of the New England Air Quality Study (NEAQS) during the summer of 2002. The results confirm the prominent role of NO3 and N2O5 in converting NOx to HNO3 at night with an efficiency on par with daytime photochemical conversion. The findings demonstrate the large role of nighttime chemistry in determining the NOx budget and consequent production of ozone. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollutionâurban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphereâcomposition and chemistry. Citation: Brown, S. S., et al. (2004), Nighttime removal of NOx in the summer marine boundary layer, Geophys. Res. Lett., 31, L07108, doi:10.1029/2004GL01941
The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO)
AST/RO, a 1.7 m diameter telescope for astronomy and aeronomy studies at
wavelengths between 200 and 2000 microns, was installed at the South Pole
during the 1994-1995 Austral summer. The telescope operates continuously
through the Austral winter, and is being used primarily for spectroscopic
studies of neutral atomic carbon and carbon monoxide in the interstellar medium
of the Milky Way and the Magellanic Clouds. The South Pole environment is
unique among observatory sites for unusually low wind speeds, low absolute
humidity, and the consistent clarity of the submillimeter sky. Four heterodyne
receivers, an array receiver, three acousto-optical spectrometers, and an array
spectrometer are installed. A Fabry-Perot spectrometer using a bolometric array
and a Terahertz receiver are in development. Telescope pointing, focus, and
calibration methods as well as the unique working environment and logistical
requirements of the South Pole are described.Comment: 57 pages, 15 figures. Submitted to PAS
A Lyman Break Galaxy Candidate at z~9
We report the discovery of a z~9 Lyman Break Galaxy (LBG) candidate, selected
from the NICMOS Parallel Imaging Survey as a J-dropout with J110 - H160 = 1.7.
Spitzer/IRAC photometry reveals that the galaxy has a blue H160 - 3.6 um color,
and a spectral break between 3.6 and 4.5 um. We interpret this break as the
Balmer break, and derive a best-fit photometric redshift of z~9. We use Monte
Carlo simulations to test the significance of this photometric redshift, and
show a 96% probability of z>7. We estimate a lower limit to the comoving number
density of such galaxies at z~9 of phi > 3.8 x 10^{-6} Mpc^{-3}. If the high
redshift of this galaxy is confirmed, this will indicate that the luminous end
of the rest-frame UV luminosity function has not evolved substantially from z~
9 to z~3. Still, some small degeneracy remains between this z~9 model and
models at z~2-3; deep optical imaging (reaching I ~ 29 AB) can rule out the
lower-z models.Comment: Accepted to ApJ Letter
Expanding the search for galaxies at z ~7-10 with new NICMOS Parallel Fields
We have carried out a search for galaxies at z ~ 7-10 in ~14.4 sq. arcmin of
new NICMOS parallel imaging taken in the Great Observatories Origins Deep
Survey (GOODS, 5.9 sq. arcmin), the Cosmic Origins Survey (COSMOS, 7.2 sq.
arcmin), and SSA22 (1.3 sq. arcmin). These images reach 5 sigma sensitivities
of J110 = 26.0-27.5 (AB), and combined they increase the amount of deep
near-infrared data by more than 60% in fields where the investment in deep
optical data has already been made. We find no z>7 candidates in our survey
area, consistent with the Bouwens et al. (2008) measurements at z~7 and 9 (over
23 sq. arcmin), which predict 0.7 galaxies at z~7 and <0.03 galaxies at z~9. We
estimate that 10-20% of z>7 galaxies are missed by this survey, due to
incompleteness from foreground contamination by faint sources. For the case of
luminosity evolution, assuming a Schecter parameterization with a typical phi*
= 10^-3 Mpc^-3, we find M* > -20.0 for z~7 and M* > -20.7 for z~9 (68%
confidence). This suggests that the downward luminosity evolution of LBGs
continues to z~7, although our result is marginally consistent with the z~6 LF
of Bouwens et al.(2006, 2007). In addition we present newly-acquired deep
MMT/Megacam imaging of the z~9 candidate JD2325+1433, first presented in Henry
et al. (2008). The resulting weak but significant detection at i' indicates
that this galaxy is most likely an interloper at z~2.7.Comment: Accepted to ApJ. Replacement includes updated discussion of
incompleteness from foreground contaminatio
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