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The aggregation dynamics of fine sediments was analysed through laboratory tests using Couette and disk flocculators.It was shown that floc sizes tend to increase as concentrations grow both in fresh and salt water,in agreement with the aggregation theory,and that equilibrium diameters are slightly greater in salt environments for flocs developed either under shear stress or by differential sedimentation.Their transport and the aggregation processes were preliminarily studied in the estuary of the Paraiba do Sul River using a particle tracking model and field data.The floc breakup process by shear stress was included in the model.Yield stresses,which were determined by fractal dimensions and differential density,were accounted for.After the calibration of the collision efficiency coefficients,the numerical model was able to predict floc sizes comparable with those measured at the Paraiba do Sul estuary,which,in turn,were similar to those obtained during the laboratory experiments in the Couette flocculator. 相似文献
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Aquaculture, like terrestrial farming, cannot achieve economic and sustainable production without high performing genetic stocks tailored to the conditions under which they are grown. It is essential, therefore, that aquaculture investment includes genetics and biotechnology to adapt marine livestock to the novel conditions of intensive aquaculture and to the demanding markets into which they are sold. The return on investment in well-structured breeding programmes can be very high, and significant performance and economic gains have been demonstrated in multiple species. Many factors must be considered in designing a genetic improvement programme, including the reproductive biology of the species and the identification of realistic and commercially relevant breeding goals based on the resources and facilities available. This paper reviews the options available to aquaculturists and provides examples of how these are being applied to six aquaculture species in New Zealand: king salmon, hāpuku, kingfish, GreenshellTM mussels, Pacific oysters and pāua (abalone). 相似文献
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捷克Jílové金矿集区在中世纪时期曾是波希米亚地块最大、最富集金的地区,黄金开采已具有2000多年的悠久历史。最重要的矿床有Pepˇr、Bohuliby、Radlík和Rotlev,主要赋存于新元古界těchovice组火山-沉积岩和波希米亚花岗闪长岩深成岩体中。金矿化存在3种类型:脉状矿化、含金网脉状矿化、浸染状矿化。金矿床中的矿物组成已超过70种,包括Cu、Pb、Zn、Fe、As、Mo、Bi、Hg、Au和Ag的一些硫化物、硫盐、氧化物、氢氧化物、硫酸盐、碳酸盐、钨酸盐、硅酸盐,还有碲化物、卤化物和自然元素的矿物。笔者通过显微镜观察、电子探针和扫描分析等综合分析技术,确认金矿床中也存在一些硒矿物。金矿石中的矿物种类较多,组成复杂以及存在大量碲化物、自然金,构成Jílové金矿集区的一大特色。一般说来,亲硫环境越强,出现硒化物、碲化物这样的特殊矿物就越少。因此,金矿床中同时存在大量碲化物、硒化物矿物,表明金矿床的形成具有特殊的物理化学条件。在成矿早阶段,具有高f(S2)和低f(Se2)、f(Te2)、f(O2)的介质,且f(S2)/f(Se2)>1、f(S2)/f(Te2)>1,此时形成大量的黄铁矿、白铁矿、磁黄铁矿、黄铜矿、毒砂、方铅矿、闪锌矿等硫化物。而Se、Te有可能以类质同象的形式赋存于硫化物矿物中。在成矿晚阶段,随着硫化物的大量沉淀,具有f(Se2)/f(S2)、f(Te2)/f(S2)、f(O2)逐渐增高,有利于硒化物、碲化物的形成。根据金矿石中的硒矿物、碲矿物组合,获得在300℃成矿温度下形成硒化物、碲化物时的f(Se2)、f(Te2)分别为10-14.97～10-7.09和10-10.98～10-7.50。 相似文献
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