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S.W. Ihle B.B. Johnson T.A. Raven G.J. Sparrow 《International Journal of Mineral Processing》1983,11(4):239-253
Previous laboratory work indicated that the dewatering of suspensions of kaolin and fine quartz on a sand bed could be described by a simple two-term equation with one term for the drainage component and one for the evaporation component.Field tests have been carried out at three sand-washing operations in Victoria to determine if the equation is applicable in practice.The thickened suspensions were dewatered to a solid when they were ponded in shallow depths onto a sand bed. The changes in solids content during the dewatering confirmed that the dewatering equation could be used in practice.The dewatering equation is potentially very useful since it can be used to calculate optimum ponding depths, and therefore the area required to dewater a given production of tailing. 相似文献
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K.L. Kilminster D.I. Walker P.A. Thompson J.A. Raven 《Estuarine, Coastal and Shelf Science》2006,68(3-4):675
Essential nutrients for seagrass growth may be derived from benthic decomposition of organic matter. To test this idea, cores of Halophila ovalis (seagrass-vegetated) and unvegetated sediment (control) were amended with either particulate organic matter (POM) or dissolved organic matter (DOM) to test whether a positive feed-back loop exists, where increased organic matter results in increased seagrass nutrients. POM was added in the form of seagrass wrack (0, 1, 5, 12 g core−1) and DOM was added with sucrose diffusion tubes at the root zone (0, 0.8, 2.4, 5.2 g core−1). Cores were incubated under saturating light conditions (12 h light/12 h dark) at 18 °C, for 4 weeks. Results suggest a complex balance between positive and negative effects of organic matter enrichment. Whilst leaf molar concentrations of N and P of H. ovalis increased (by 15 and 30% respectively), plant growth declined (up to 50% relative to control) for both DOM and POM enrichments. Phosphate was removed from sediment porewater following POM addition and most likely translocated to the leaves. Stressors other than nutrient limitation (e.g. biogeochemical constraints) reduce growth and affect the nutrient dynamics of the seagrass and should be the focus of future work. 相似文献
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R.D. WolstencroftJ.A. Raven 《Icarus》2002,157(2):535-548
Although there are considerable technical challenges to be overcome during this decade, the prospects for the detection of Earth-like planets (ELPs) orbiting nearby stars are encouraging. If life has developed on some of the ELPs that may be discovered by sophisticated telescope systems, such as the Terrestrial Planet Finder, the detection of photosynthesis is an attractive possibility. Here we discuss the likely preconditions and subsequent events that have led to the occurrence of O2-producing photosynthesis on Earth and then extend this discussion to how this may have occurred on ELPs orbiting in the habitable zone of a variety of main-sequence stars from spectral type F0V to M0V. We point out how the need for liquid water and the need to avoid UV radiation have influenced the evolution of photosynthesis on Earth, how the absorption spectra of the dominant (chlorophyll) photosynthetic pigments may have been determined in natural selection, and how and when the evolution of the ability to use water as an electron donor took place. Models for the photosynthetic productivity of ELPs orbiting at the inner edge of the habitable zone are discussed both from aquatic and land-based photosynthesis, making some allowance for global cloud cover on the ELP. The photosynthetic generation of O2 is greatest on cloud-free planets with hot (e.g., F0V) parent stars, though the advantage over cooler stars depends on the fraction of the planet covered by oceans. The low O2 generation in ELPs orbiting cooler stars is due to the poor match between the parent star's spectral energy distribution and the assumption of terrestrial pigment properties. We discuss the possibility that a three- or four-photon mechanism might operate on such planets (as opposed to the two-photon system on Earth) and how it could influence the spectral properties of the ELP. We also emphasize the role of tectonic and other geological processes as well as biology in determining the O2 level on Earth and on ELPs. 相似文献