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Wladyslaw Witold Szymanski 《Atmospheric Research》2002,62(3-4)
The performance of two different optical concentration-measuring techniques was investigated over a concentration range starting with about 102 cm−3 and extending over more than four decades. Both instruments are capable of real-time counting, however due to their particular design-single particle counter and ensemble particle-measuring system—they operate in overlapping, but different concentration ranges. The upper, coincidence-free counting limit for the single particle counter used in this study was established to be in the order of 104 cm−3. The ensemble technique was found to be functional and stable for concentrations of about 103 cm−3 and limited by the onset of multiple scattering at concentrations nearby 2×106 cm−3. Within the determined boundaries, both techniques proved to provide reliable aerosol concentration data. 相似文献
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Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa 总被引：1，自引：0，他引：1
Jzef Kazmierczak Wladyslaw Altermann Barbara Kremer Stephan Kempe Patrick G. Eriksson 《Precambrian Research》2009,173(1-4):79
The sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post-mortem silicification. Hitherto as an exception, sedimentary carbonate rocks from the Neoarchean Nauga Formation of South Africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria (Chroococcales and Pleurocapsales). Their remains, visible under the scanning electron microscope (SEM) after etching of polished rock samples, comprise capsular envelopes, mucilage sheaths, and groups of cells mineralized by calcium carbonate with an admixture of Al–K–Mg–Fe silicates. The capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the Neoarchean microbiota described and their modern analogues. The new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the Neoarchean, and offer a solution to the problem of the origin of Archean carbonate platforms, stromatolites and microbial reefs. 相似文献
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