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1.
W.M. Schuh R.L. Cline M.J. Kosse D.W. Sletton 《Ground Water Monitoring & Remediation》1997,17(1):81-90
A field experiment was conducted to examine the effect of short-term (one minute) contact of pesticide-laden water with a polyvinyl chloride (PVC) bailer on quantitative laboratory measurements of seven pesticide concentrations in distilled water samples subsequently decanted from the bailer. Pesticides were tested at two initial concentrations (low. based on current FPA maximum contaminant levels, or MCL: and high, based on a multiple of approximately lour times the MCL). Pesticide species included bromoxynil, diclofop-m, dimethoate. MCPA, methyl parathion, propiconazole, and trifluralin. Dimethoate recoveries were poor for all treatments. For all other pesticides there was no systematic difference between pesticide concentrations measured before and after bailer contact. Effectiveness of bailer decontamination treatments consisting of distilled water rinse alone was related to water solubility (S) for each species. Distilled water samples decanted from a rigid PVC bailer following initial bailer contact with pesticide-spiked water, and after the bailer had been cleaned with a single distilled water rinse, had measured pesticide concentrations of less than 2 percent of the pesticide concentration in the initial pesticide-spiked water, regardless of S. A single distilled water rinse effectively removed all trace of contaminants having S> 500 mg/L. Multiple distilled water rinses, and multiple distilled water rinses followed by 15 bailings of a well, effectively removed all trace of contaminants having S> 50 mg/L. Below threshold S, cleaning effectiveness decreased as a power function of S. 相似文献
2.
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4.
Two long time series were analysed: the C01 series of the International Earth Rotation Service and the pole series obtained
by re-analysis of the classical astronomical observations using the HIPPARCOS reference frame. The linear drift of the pole
was determined to be 3.31 ± 0.05 milliarcseconds/year towards 76.1 ± 0.80° west longitude. For the least-squares fit the a priori correlations between simultaneous pole coordinates x
p
, y
p
were taken into account, and the weighting function was calculated by estimating empirical variance components. The decadal
variations of the pole path were investigated by Fourier and wavelet analysis. Using sliding windows, the periods and amplitudes
of the Chandler wobble and annual wobble were determined. Typical periods in the variable Chandler wobble and annual wobble
parameters were obtained from wavelet analyses.
Received: 21 January 2000 / Accepted: 28 August 2000 相似文献
5.
Summary For several years polar motion has been routinely monitored with the technique of geodetic Very Long Baseline Interferometry (VLBI) at five-day intervals. Here we present the results of the first two series of VLBI measurements for polar motion monitoring observed on a quasi daily basis employing only a single baseline. The high sensitivity of the long north-south baseline between radio telescopes at Wettzell in Germany and Hartebeesthock in South Africa for both components of polar motion permitted relatively short and inexpensive measurements of only two hours duration per session. The results of this series agree very well with the pole path determined with the IRIS network using 4 observatories in each observing session of 24 hour duration. With the polar motion results of the two series spanning about 35 days each, spectral analyses were performed which have shown a fortnightly period with a high degree of probability. These measurements demonstrate the potential of long north-south VLBI baselines for monitoring polar motion with very high temporal resolution for studies of short period fluctuations. 相似文献
6.
Modeling path delays in the neutral atmosphere for the analysis of Very Long Baseline Interferometry (VLBI) observations has
been improved significantly in recent years by the use of elevation-dependent mapping functions based on data from numerical
weather models. In this paper, we present a fast way of extracting both, hydrostatic and wet, linear horizontal gradients
for the troposphere from data of the European Centre for Medium-range Weather Forecasts (ECMWF) model, as it is realized at
the Vienna University of Technology on a routine basis for all stations of the International GNSS (Global Navigation Satellite
Systems) Service (IGS) and International VLBI Service for Geodesy and Astrometry (IVS) stations. This approach only uses information
about the refractivity gradients at the site vertical, but no information from the line-of-sight. VLBI analysis of the CONT02
and CONT05 campaigns, as well as all IVS-R1 and IVS-R4 sessions in the first half of 2006, shows that fixing these a priori
gradients improves the repeatability for 74% (40 out of 54) of the VLBI baseline lengths compared to fixing zero or constant
a priori gradients, and improves the repeatability for the majority of baselines compared to estimating 24-h offsets for the
gradients. Only if 6-h offsets are estimated, the baseline length repeatabilities significantly improve, no matter which a
priori gradients are used. 相似文献
7.
Temperature variations at very long baseline interferometry (VLBI) sites cause thermal deformations of the VLBI antennas and
corresponding displacements of the VLBI reference points. The thermal deformation effects typically contain seasonal and daily
signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending
on the design of the antenna structure, on the material, and on the environmental effects such as global station position,
station height and climatology effects. Simple methods to correct this effect use the difference of the environmental temperature
with respect to a defined reference temperature, the antenna dimensions, the elevation of the antenna, the material of antenna
structure. Applying these simple models for thermal deformation in the VLBI data analysis improves the baseline length repeatability
by 3.5%. A comparison of these simple models with local thermal deformation measurements at the antennas in Onsala and Wettzell
show that the local measurements and the modeled corrections agree well when the temperature of the antenna structure is used,
but agree less good when the surrounding air temperatures are used. To overcome this problem we present a method to model
temperature penetration into the antenna structures, that allows to model thermal deformation effects that agree with the
observed vertical deformation of the Onsala and Wettzell radio telescopes with a root mean square deviation of 0.07 and 0.13 mm,
respectively. Possible implementations in the VLBI analysis are presented, and the definition of an adequate reference temperature
is discussed. 相似文献
8.
S. Schuh 《Astronomische Nachrichten》2010,331(5):489-501
The disciplines of asteroseismology and extrasolar planet science overlap methodically in the branch of high‐precision photometric time series observations. Light curves are, amongst others, useful to measure intrinsic stellar variability due to oscillations, as well as to discover and characterize those extrasolar planets that transit in front of their host stars, periodically causing shallow dips in the observed brightness. Both fields ultimately derive fundamental parameters of stellar and planetary objects, allowing to study for example the physics of various classes of pulsating stars, or the variety of planetary systems, in the overall context of stellar and planetary system formation and evolution. Both methods typically also require extensive spectroscopic follow‐up to fully explore the dynamic characteristics of the processes under investigation. In particularly interesting cases, a combination of observed pulsations and signatures of a planet allows to characterize a system's components to a very high degree of completeness by combining complementary information. The planning of the relevant space missions has consequently converged with respect to science cases, where at the outset there was primarily a coincidence in instrumentation and techniques. Whether space‐ or ground‐based, a specific type of stellar pulsations can themselves be used in an innovative way to search for extrasolar planets. Results from this additional method at the interface of stellar pulsation studies and exoplanet hunts in a beyond‐mainstream area are presented (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
A shallow unconfined glaciofluvial aquifer in North Dakota (USA) has largest groundwater sulfate concentrations near the bottom boundary. A deltaic silt layer underlying the aquifer, at >16 m, is the modern proximate sulfate source for the aquifer. The original sulfate source was pyrite in the organic-rich shale component of the aquifer and silt grain matrix. An oxidizing event occurred during which grain-matrix pyrite sulfur was oxidized to sulfate. Thereafter the silt served as a “conserving” layer, slowly feeding sulfate into the lower part of the aquifer and the underlying till. A method was developed for estimating the approximate initial sulfate concentration in the source layer and the redistribution time since the oxidizing event, using a semi-generic convection–dispersion model. The convection–dispersion model and a model for the evolution of modern sulfate δ 34S in silt-layer pore water from the initial grain-matrix pyrite δ 34S, both estimated that the oxidizing event occurred several thousand years ago, and was likely related to the dry conditions of the Hypsithermal Interval. The silt layer also serves as an arsenic source. Results indicate that deltaic silts derived from organic-rich shale parent materials in a glacial environment can provide long-term sources for sulfate and arsenic and possibly other related oxidative weathering products. 相似文献
10.
Many geodetic applications require the minimization of a convex objective function subject to some linear equality and/or inequality constraints. If a system is singular (e.g., a geodetic network without a defined datum) this results in a manifold of solutions. Most state-of-the-art algorithms for inequality constrained optimization (e.g., the Active-Set-Method or primal-dual Interior-Point-Methods) are either not able to deal with a rank-deficient objective function or yield only one of an infinite number of particular solutions. In this contribution, we develop a framework for the rigorous computation of a general solution of a rank-deficient problem with inequality constraints. We aim for the computation of a unique particular solution which fulfills predefined optimality criteria as well as for an adequate representation of the homogeneous solution including the constraints. Our theoretical findings are applied in a case study to determine optimal repetition numbers for a geodetic network to demonstrate the potential of the proposed framework. 相似文献