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Evasion from first- and second-order streams in a watershed may be a significant factor in the atmospheric recycling of volatile pollutants such as mercury; however, methods developed for the determination of Hg evasion rates from larger water bodies are not expected to provide satisfactory results in highly turbulent and morphologically complex first- and second-order streams. A new method for determining the Hg evasion rates from these streams, involving laboratory gas-indexing experiments and field tracer tests, was developed in this study to estimate the evasion rate of Hg from Gossan Creek, a first-order stream in the Upsalquitch River watershed in northern New Brunswick, Canada. Gossan Creek receives Hg-contaminated groundwater discharge from a gold mine tailings pile. Laboratory gas-indexing experiments provided the ratio of gas-exchange coefficients for zero-valent Hg to propane (tracer gas) of 0.81+/-0.16, suggesting that the evasion mechanism in highly turbulent systems can be described by the surface renewal model with an additional component of enhanced gas evasion probably related to the formation of bubbles. Deliberate field tracer tests with propane and chloride tracers were found to be a reliable and practical method for the determination of gas-exchange coefficients for small streams. Estimation of Hg evasion from the first 1 km of Gossan Creek indicates that about 6.4 kg of Hg per year is entering the atmosphere, which is a significant fraction of the regional sources of Hg to the atmosphere.  相似文献
2.
D. Don) veneers. Spectral data obtained from 1.2×2.4 m veneer sheets was corellated against stiffness data obtained from 6-ply mini-LVL panels prepared from the sheet. This paper describes the method used to prepare the mini-LVL test pieces and the results of multivariate regression of NIR spectra with the test piece stiffness. The results show the potential for using NIR spectroscopy for on-line assessment of veneer stiffness prior to layup of plywood or LVL panels. Selection of high stiffness veneers for layup would enable engineered panels of high uniform stiffness to be produced.  相似文献
3.
This study was to examine the effect of end pressure on the mechanical properties and delamination resistance of structural black spruce (Picea mariana) finger-joined lumber made of a short (12.7-mm-long) finger profile. End pressures used were 2.00, 3.43, 6.00 and 8.00 MPa. 8.00 MPa yielded the greatest 5th percentile ultimate tensile strength, but caused cracks at tips of a joint. It was recommended that 2.00 MPa be used as the optimized end pressure from the viewpoint of energy saving.  相似文献
4.
BACKGROUND: Knowledge of the fat content in dairy products is important for both industry and consumers. A new procedure for rapid and non‐destructive determination of the fat content in dairy products using unilateral nuclear magnetic resonance (NMR) is proposed. The sample magnetisation is prepared using either T1 suppression or diffusion editing, and read out via a Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence. RESULTS: A linear correlation between the measured NMR signal from the fat component and the declared fat content in the tested products validated both approaches as viable instrumental methods. The shortest measurement time was about 7 s. CONCLUSION: Advantages of the unilateral NMR method, including hardware simplicity and accommodation of commercially packaged products, make it attractive for routine use in industry. Copyright © 2008 Society of Chemical Industry  相似文献
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Cold caustic extraction has potential applications in the production of dissolving-grade pulps due to its ability to selectively remove hemicellulose from lignocellulosic materials.In this study,we demonstrate the conversion of paper-grade kraft pulp into dissolving pulp by a single-stage cold caustic extraction.Under the extraction conditions of 12 wt% NaOH lye,11% pulp consistency,a temperature of 35℃,and 2 h,a paper-grade softwood kraft pulp was purified to high-grade dissolving pulp with 97.1% α-cellulose content,1.2% pentosane content,and narrowed molecular weight distribution.The resulting extraction filtrate was concentrated by nano-filtration to obtain the hemicellulose content of 59.0 g/L,while the permeate was a clear NaOH solution with 10.9 wt% concentration.A process configuration was also proposed,integrating this cold caustic extraction process with existing pulp and paper production and multi-purpose utilization of the extraction filtrate.  相似文献
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