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31.
The estuarine turbidity maximum (ETM) is an important nursery area for anadromous fish where early-life stages can be retained
in high prey concentrations and favorable salinities. Episodic freshwater flow and wind events could influence the transport
of striped bass (Morone saxatilis) eggs to the ETM. This hypothesis was evaluated with regression analysis of observational data and with a coupled biological-physical
model of a semi-idealized upper Chesapeake Bay driven by observed wind and freshwater flow. A particle-tracking model was
constructed within a numerical circulation model (Princeton Ocean Model) to simulate the transport of fish eggs in a 3-dimensional
flow field. Particles with the sinking speed of striped bass eggs were released up-estuary of the salt front in both 2-d event-scale
and 60-d seasonal-scale scenarios. In event scenarios, egg-like particles with observed specific gravities (densities) of
striped bass eggs were transported to the optimum ETM nursery area after 2 d, the striped bass egg-stage duration. Wind events
and pulses in river discharge decreased the number of egg-like particles transported to the ETM area by 20.9% and 13.2%, respectively,
compared to nonevent conditions. In seasonal scenarios, particle delivery to the ETM depended upon the timing of the release
of egg-like particles. The number of particles transported to the ETM area decreased when particles were released before and
during wind and river pulse events. Particle delivery to the ETM area was enhanced when the salt front was moving up-estuary
after river pulse events and as base river flow receded over the spawning season. Model results suggest that the timing of
striped bass spawning in relation to pulsed events may have a negative (before or during events) or positive (after river
flow events) effect on egg transport. Spawning after river flow events may promote early-stage survival by taking advantage
of improved transport, enhanced turbidity refuge, and elevated prey production that may occur after river pulse events. In
multiple regression analysis of observed data, mean spring freshwater flow rates and the number of pulsed freshwater flow
events during the striped bass spawning season explained 71% of the variability in striped bass juvenile abundance in upper
Chesapeake Bay from 1986 to 2002. Positive parameter estimates for these effects support the hypothesis that pulsed freshwater
flow events, coupled with spawning after the events, may enhance striped bass early-stage survival. Results suggest that episodic
events may have an important role in controlling fish recruitment. 相似文献
32.
J. P. McKean I. W. A. Browne N. J. Jackson L. V. E. Koopmans M. A. Norbury T. Treu † T. D. York A. D. Biggs R. D. Blandford A. G. de Bruyn C. D. Fassnacht S. Mao S. T. Myers T. J. Pearson P. M. Phillips A. C. S. Readhead D. Rusin P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2005,356(3):1009-1016
We present observations of CLASS B2108+213, the widest separation gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact components separated by 4.56 arcsec with a faint third component in between which we believe is emission from a lensing galaxy. 5-GHz VLBA observations reveal milliarcsecond-scale structure in the two lensed images that is consistent with gravitational lensing. Optical emission from the two lensed images and two lensing galaxies within the Einstein radius is detected in Hubble Space Telescope imaging. Furthermore, an optical gravitational arc, associated with the strongest lensed component, has been detected. Surrounding the system is a number of faint galaxies which may help explain the wide image separation. A plausible mass distribution model for CLASS B2108+213 is also presented. 相似文献
33.
Nikhil Padmanabhan David J. Schlegel Uro Seljak Alexey Makarov Neta A. Bahcall Michael R. Blanton Jonathan Brinkmann Daniel J. Eisenstein Douglas P. Finkbeiner James E. Gunn David W. Hogg eljko Ivezi Gillian R. Knapp Jon Loveday Robert H. Lupton Robert C. Nichol Donald P. Schneider Michael A. Strauss Max Tegmark Donald G. York 《Monthly notices of the Royal Astronomical Society》2007,378(3):852-872
34.
MUHAMMAD SHARAF GARY ARROY RON PERKINS Spectra-Physics Inc. North First Street San Jose CA U.S.A. 《地理学报(英文版)》1991,(3)
Ratio measurements are commonly used to address a variety of analytical problems in environmental,forensic and pharmaceutical laboratories.In absorbance ratioing techniques,analytical chemists rely onthe spectral features of the analyte(s)of interest.The absorbances at two wavelengths are monitored andthe ratio of these two absorbances is computed.This ratio is then used to confirm the identity of theanalyte(s)of interest,the purity of a product or the overlap of chromatographic peaks.These decisionsoften have far-reaching consequences(e.g.the identification of the source,biogenic or petrogenic,ofhydrocarbons in biological tissues or water).Given the cost and the liabilities associated with suchdecisions,it is unfortunate that these ratios are seldom reported with any statistical confidence.Thepurpose of this study is to delineate the parameters that affect absorbance ratio measurements.Themodels that can be used to estimate the statistical confidence in these measurements are derived andevaluated experimentally.The results show that these models can estimate the relative standard deviationsin absorbance ratios accurately.They can also estimate the effect of signal-to-noise ratio and the choiceof wavelengths on the precision of absorbance ratios. 相似文献
35.
It was found earlier from OAO-2 data (Bless and Savage, 1972) that considerable variability with direction in space is present in both the shape and level (relative toB-V color excess) of the interstellar extinction curve in the far ultraviolet. The star σ Sco was shown to be a case of extremely low UV extinction, but there was some question of whether this could be due to scattered nebular light entering the large entrance slit of the Wisconsin spectrometer aboard OAO-2. We have obtained UV data on σ Sco usingCopernicus (OAO-3), which has an entrance slit on the order of 103 times smaller in projected area than that of OAO-2, so that the contribution to the signal from scattered nebular light would be correspondingly smaller. We find very good agreement with the extinction curve of Bless and Savage, confirming the low UV extinction in the line of sight to σ Sco. The curve is extended down to 100 Å, showing a continued rise towards short wavelengths. 相似文献
36.
The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data
Tsvetanov ZI Golimowski DA Zheng W Geballe TR Leggett SK Ford HC Davidsen AF Uomoto A Fan X Knapp GR Strauss MA Brinkmann J Lamb DQ Newberg HJ Rechenmacher R Schneider DP York DG Lupton RH Pier JR Annis J Csabai I Hindsley RB Ivesic Z Munn JA Thakar AR Waddell P 《The Astrophysical journal》2000,531(1):L61-L65
We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (hereafter SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8 and 2.5 μm is dominated by strong absorption bands of H2O and CH4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (hereafter SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the Sun. The ratio of flux at 2.1 μm to that at 1.27 μm is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 deg2 and a detection limit of z*=19.8, we estimate a space density of 0.05 pc-3 for methane brown dwarfs with Teff approximately 1000 K in the 40 pc3 volume of our search. This estimate is based on small-sample statistics and should be treated with appropriate caution. 相似文献
37.
To understand the electrical structure of the Sulu(苏鲁) terrane,we analyzed the resis-tivity logs of the Chinese Continental Scientific Drilling main hole(CCSD-MH) and obtained the statis-tical characteristics of the resistivity log of ultrahigh-pressure(UHP) metamorphic rocks.To check the logs' quality,we compared the resistivity log data with the core test data.The two datasets show a good coherence.On the whole,the resistivity of the UHP metamorphic rocks from the CCSD-MH is very high(mostly higher than 1... 相似文献
38.
ZHAO Shunbo Ass. Prof. North China Institute of Water Conservancy Hydroelectric Power Zhengzhou P. R. China. 《中国海洋工程》1998,(4)
An experimental program was carried out to study the shear behavior of the reinforced con-crete composite beam(RCCB)subjected to two-phase uniformly distributed load.A total of 12 reinforcedconcrete composite beams were tested:10 of them were the RCCB subjected to two-phase uniformly dis-tributed load,the other 2 were the comparative reinforced concrete beams cast at the same time as theRCCB subjected to one-phase uniformly distributed load.The interface of precast unit and recast concretewas natural and rough.The test range of the main composite factors:the ratio of precast section depth tocomposite section depth was from 0.35 to 0.65,the ratio of first-phase load moment to precast section ulti-mate bearing moment was from 0.25 to 0.65.Based on the test results,the stresses of the longitudinal rein-forcements and stirrups,the load-bearing properties of the interface,the crack state and the failure charac-teristics of the RCCB under uniformly distributed load are discussed.The effects of the stirrups,the 相似文献
39.
P. F. L. Maxted T. R. Marsh U. Heber L. Morales-Rueda R. C. North W. A. Lawson 《Monthly notices of the Royal Astronomical Society》2002,333(1):231-240
We present light curves of four binary subdwarf B stars (sdB), Ton 245, Feige 11, PG 1432+159 and PG 1017−086. We also present new spectroscopic data for PG 1017−086 from which we derive its orbital period, P =0.073 d , and the mass function, f m =0.0010±0.0002 M⊙ . This is the shortest period for an sdB binary measured to date. The values of P and f m for the other sdB binaries have been published elsewhere. We are able to exclude the possibility that the unseen companion stars to Ton 245, Feige 11 and PG 1432+159 are main-sequence stars or subgiant stars from the absence of a sinusoidal signal, which would be caused by the irradiation of such a companion star, i.e. they show no reflection effect. The unseen companion stars in these binaries are likely to be white dwarf stars. In contrast, the reflection effect in PG 1017−086 is clearly seen. The lack of eclipses in this binary combined with other data suggests that the companion is a low-mass M-dwarf or, perhaps, a brown dwarf. 相似文献
40.