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991.
992.
Mailloux BJ Fuller ME Rose GF Onstott TC DeFlaun MF Alvarez E Hemingway C Hallet RB Phelps TJ Griffin T 《Ground water》2003,41(6):816-827
Ground water injection and sampling systems were developed for bacterial transport experiments in both homogenous and heterogeneous unconsolidated, surficial aquifers. Two types of injection systems, a large single tank and a dynamic mixing tank, were designed to deliver more than 800 L of amended ground water to the aquifer over 12 hours, without altering the ground water temperature, pH, Eh, or dissolved gas composition. Two types of multilevel samplers (MLSs) were designed and installed. Permanent MLSs performed well for the homogenous surficial aquifer, but their installation procedure promoted vertical mixing, which could obfuscate experimental data obtained from vertically stratified, heterogeneous aquifers. A novel, removable MLS was designed to fit in 2- and 4-inch wells. Expandable O-rings between each sampling port hydraulically isolated each port for sample collection when a nut was tightened at the land surface. A low-cost vacuum manifold system designed to work with both MLS designs used 50 mL centrifuge tubes to efficiently sample 12 MLS ports with one peristaltic pump head. The integrated system was developed and used during four field campaigns over a period of three years. During each campaign, more than 3000 ground water samples were collected in less than one week. This system should prove particularly useful for ground water tracer, injection, and push-pull experiments that require high-frequency and/or high-density sampling. 相似文献
993.
Duke NC Bell AM Pederson DK Roelfsema CM Bengtson Nash S 《Marine pollution bulletin》2005,51(1-4):308-324
Herbicides, particularly diuron, were correlated with severe and widespread dieback of the dominant mangrove, Avicennia marina (Forsk.) Vierh. var. eucalyptifolia (Val.) N.C. Duke (Avicenniaceae), its reduced canopy condition, and declines in seedling health within three neighbouring estuaries in the Mackay region of NE Australia. This unusual species-specific dieback, first observed in the early 1990s, had gotten notably worse by 2002 to affect >30 km(2) of mangroves in at least five adjacent estuaries in the region. Over the past century, agricultural production has responded well to the demands of increasing population with improvements in farm efficiency assisted by significant increases in the use of agricultural chemicals. However, with regular and episodic river flow events, these chemicals have sometimes found their way into estuarine and nearshore water and sediments where their effects on marine habitats have been largely unquantified. Investigations over the last three years in the Mackay region provide compelling evidence of diuron, and possibly other agricultural herbicides, as the most likely cause of the severe and widespread mangrove dieback. The likely consequences of such dieback included declines in coastal water quality with increased turbidity, nutrients and sediment deposition, as well as further dispersal of the toxic chemicals. The implications of such findings are immense since they describe not only the serious deterioration of protected and beneficial mangrove habitat but also the potential for significant direct and indirect effects on other highly-valued estuarine and marine habitats in the region, including seagrass beds and coral reefs of the Great Barrier Reef lagoon. This article reviews all key findings and observations to date and describes the essential correlative and causative evidence. 相似文献
994.
995.
On the redshift cut-off for steep-spectrum radio sources 总被引:1,自引:0,他引:1
Matt J. Jarvis Steve Rawlings Chris J. Willott Katherine M. Blundell Steve Eales Mark Lacy 《Monthly notices of the Royal Astronomical Society》2001,327(3):907-917
We use three samples (3CRR, 6CE and 6C*) selected at low radio frequency to constrain the cosmic evolution in the radio luminosity function (RLF) for the 'most luminous' steep-spectrum radio sources. Though intrinsically rare, such sources give the largest possible baseline in redshift for the complete flux-density-limited samples currently available. Using parametric models to describe the RLF, incorporating distributions in radio spectral shape and linear size, as well as the usual luminosity and redshift, we find that the data are consistent with a constant comoving space density between and . We find that this model is favoured over a model with similar evolutionary behaviour to that of optically selected quasars (i.e., a roughly Gaussian distribution in redshift) with probability ratios of and for spatially flat cosmologies with and respectively. Within the uncertainties, this evolutionary behaviour may be reconciled with the shallow decline preferred for the comoving space density of flat-spectrum sources by Dunlop & Peacock and Jarvis & Rawlings, in line with the expectations of unified schemes. 相似文献
996.
Chris Koen 《Monthly notices of the Royal Astronomical Society》2005,360(3):1132-1142
The results of more than 100 h of CCD photometric monitoring of 10 L dwarfs and two T dwarfs are presented. Reasonable evidence is shown for I C band variability in DENIS 0255−4700, DENIS 1705−0516 and 2M 2104−1037. Substantial brightening of the T dwarf binary ε Indi Bab was observed over the course of 3.6 h; it is unlikely that this could have been caused by surface spots. No unequivocal variability could be detected in the R C band. 相似文献
997.
Christopher Thom Chris Flynn Michael S. Bessell Jyrki Hänninen Timothy C. Beers Norbert Christlieb Dionne James Johan Holmberg Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,360(1):354-359
Large samples of field horizontal branch (FHB) stars make excellent tracers of the Galactic halo; by studying their kinematics, one can infer important physical properties of our Galaxy. Here we present the results of a medium-resolution spectroscopic survey of 530 FHB stars selected from the Hamburg/ESO survey. The stars have a mean distance of ∼7 kpc and thus probe the inner parts of the Milky Way halo. We measure radial velocities from the spectra in order to test the model of Sommer-Larsen et al., who suggested that the velocity ellipsoid of the halo changes from radially dominated orbits to tangentially dominated orbits as one proceeds from the inner to the outer halo. We find that the present data are unable to discriminate between this model and a more simple isothermal ellipsoid; we suggest that additional observations towards the Galactic Centre might help to differentiate them. 相似文献
998.
999.
Tropospheric corrections to SAR interferometry from GPS observations 总被引:10,自引:0,他引:10
Interferometric synthetic aperture radar (InSAR) techniques have been recognized as an ideal tool for many ground deformation monitoring applications. However, the spatially and temporally variable delay of the radar signal propagating through the atmosphere is a major limitation to accuracy. The dominant factor to be considered is the tropospheric heterogeneity, which can lead to misinterpretation of InSAR results. In this paper, a between-site (BS) and between-epoch (BE) double-differencing algorithm for the generation of tropospheric corrections to InSAR results based on GPS observations is tested. In order to correct the radar results on a pixel-by-pixel basis, the GPS-derived corrections have to be interpolated. Using experimental data it has been found that the inverse distance weighted and kriging interpolation methods are more suitable than the spline interpolation method. Differential corrections as large as several centimeters may have to be applied in order to ensure sub-centimeter accuracy for the InSAR result. The algorithm and procedures described in this paper could easily be implemented in a continuous GPS network data center. The interpolated image of BS, single-differenced tropospheric delays can be derived as a routine product to assist radar interferometry. 相似文献
1000.