The paper briefly describes an electro-optical system for counting of dust particles, which is based on the scattering phenomena.Utilizing the scattering of light by various size particles present in the environment, various particle counting techniques have been developed in order to measure the scattered intensity of light. Light scatters in all directions but much more in the so-called near forward direction 17∘ off axis, at 163∘ from the light source in the visible range.On the basis of two techniques, the right angle and forward angle scattering, opto-mechanical systems have been developed which measure scattered intensity and particulate matter. The forward scattering Nephelometer is more sensitive and therefore is more suitable for pollution monitoring than the right angle scattering Nephelometer. Whereas the right angle scattering Nephelometer has the utility in extremely low concentration in ppb level owing to the excellent light trap efficiency in comparison to forward scattering Nephelometer. In this paper measurement techniques and measurement results associated with design and development of a real time particle analyser are also discussed. 相似文献
13C CP-MAS NMR spectroscopy is a technique that has proved to be useful in studying soil organic matter (SOM). Nevertheless, NMR spectra exhibit a weak signal and have very low resolution due to: the low natural abundance of 13C (1.1 % of C) in SOM, the generally low SOM content of soils, and the presence of paramagnetic impurities. This paper studies the effects of soil chemical pre-treatments on 13CP-MAS NMR spectra quality and spectra representativity i.e. soil C mass balance.
After chemical pre-treatment to increase total organic carbon (TOC) content and C/Fe ratio, eight soils characterized by different levels of organic carbon content and C/Fe ratios were studied using 13CP-MAS NMR. Moreover, where chemical treatments were not applicable due to high carbon losses, the number of 13CP-MAS NMR scans was increased in order to obtain satisfactory spectra.
Results show that chemical pre-treatment of soils with C/Fe > 1 caused high C losses. Bulk soils were therefore studied by increasing the number of 13CP-MAS NMR scans. Acceptable spectra were obtained from 8K scans (1K = 1024 transient). On the other hand, even when a large number of scan (32K) are used, soil with C/Fe < 1 cannot be studied. As these soils are characterized by low C losses after HCl treatments (range of 2.9–25.4%), a pre-treatment of at least 1.39 mol l−1 HCl removes excess Fe and at the same time increases C/Fe ratio resulting in 32K scans providing good spectra. 相似文献
Abstract: The impacts of runoff events on external suspended solids loading to Schoharie Reservoir, New York, and patterns of light scattering and sediment deposition in this reservoir are assessed. The assessment is based on monitoring of suspended solids concentrations in the reservoir's primary tributary, detailed vertical profiles of optical backscattering (a surrogate measure of light scattering) in the reservoir water column, and analysis of sediment trap collections, over a seven-month interval of high runoff. These impacts are reported to be tightly temporally coupled and strongly positively related to the magnitude of runoff events. The primary tributary entered the reservoir as a plunging inflow during runoff events, causing conspicuous subsurface peaks in light scattering, with vertical patterns that varied strongly for different events. Deposition quantified by near-bottom trap deployments is reported to be more representative than results from metalimnetic deployments that were generally within, rather than below, the turbid layers. Direct inputs of sediment, transported by density currents, are found to drive deposition, rather than resuspension/redeposition. More than 50 percent of the reported deposition occurred in less than 15 percent of the study period, associated with the four largest runoff events. 相似文献