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排序方式: 共有4130条查询结果,搜索用时 15 毫秒
991.
992.
To date, farming fish in recirculating aquaculture systems (RAS) is one of the most environmentally friendly ways of producing fish. However, with the trend towards intensification, and consequently decrease in water exchange rates, these systems may accumulate substances, such as heavy metals, in the water and fish. Inductively-coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectroscope (ICP-MS) were used to determine Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn, in the water and fish (Nile tilapia Oreochromis niloticus). Three RAS were used, differing in daily water exchange rates (30, 70 and 1500 l/kg feed/d). The concentrations of As, Fe, Mn, Ni and Zn in the water increased with decreasing water exchange rates, suggesting an accumulation of heavy metals as more water was re-used. Such accumulation in the water was, however, not translated into accumulation in the liver and muscle. Accumulation of heavy metals was always higher in the liver than in the muscle; however, As reached 1.61 mg/kg wet weight in the muscle of fish farmed in RAS-70 l/kg feed/d. However, these levels are considerably lower than permissible safety levels for human consumption. 相似文献
993.
994.
According to the thermodynamic and kinectic theory, considering variation of bulk free energy and superficial energy after nucleation as well as migration of atom, we study deeply planar nucleation and crystallization that relate to two possible transition mechanism in the process of annealing of ion implanted Si. 1) Liquid/Solid transition: critical nucleation work is a half of increased superficial energy and inversely proportional to the supercooling . Compared with bulk nucleation, the radius of critical nucleus decrease by a half, nucleation rate attain its maximum at T=1/2Tm; 2) Amorphous/Crystal transition: atoms containing in critical nucleus and on its surface, as well as critical nucleation work are all directly proportional to the height of nucleus, nucleation barrier is a half of superficial energy too. Taking SiGe semiconductor as an example, we calculate that the value of its elastic strain energy is 0.03eV/atom, and get more reasonable result after taking its effect to transition into account.
In one word, we reach such a conclusion through calculation: for annealing of ion implanted Si, no matter what transition way—liquid or solid, the planar nucleation and recrystallization process is actually carried out layer by layer on crystal substrate, probability forming “rod-like”nucleus is much larger than probability of “plate-like”nucleus. 相似文献
995.
996.
YEJian-song CHANGHong-bing TYHsu 《钢铁研究学报(英文版)》2004,11(6):33-36
A novel model of the evolution of microstructure during continuous cooling with the formation of proeutectoid ferrite in steel was proposed from a Voronoi construction for the austenite grains, based on the Rappaz‘s integral nucleation model and the assumption that the ferrite nucleates at the edges of the original austenite grains and the successive growth of the ferrite grain is radial. The model can be used to calculate the fraction of ferrite as a function of time or temperature during continuous cooling, and to determine the microstructure of ferrite. The calculated results are in agreement with experimental results investigated in 0.38C-0.28Si-0.55Mn-0.92Cr-0.20Mo steel under continuous cooling using a Gleeble 1500 thermomechanical simulator. 相似文献
997.
ZHAIQi-jie LIUGuo-jun ZHAIHuaying LIZu-qi 《钢铁研究学报(英文版)》2004,11(3):41-43
The bainite ductile cast iron with given comppasition was quenched to get bainite strueture. The nucleating position of bainite and the distrihution of alloying elements in the matrix were measured. The results show thai the bainite nucleates at the interface between graphite and austenite during quenching. Based on the experimental results and thermodynamics, the nucleating tnechanism of bainite in ductile iron was analyzed. 相似文献
998.
采用RF辅助加热CVD方法,在76mm硅衬底上生长了β-SiC薄膜。设备为电容耦合式RF(13.56MHz)等离子体装置,反应气体为甲烷(CH4);通过控制反应系统内碳原子成核生长的条件,实现了大面积β-SiC薄膜的生长。对样品进行了XRD、AFM检查;退火后整个样片膜厚均匀、一致性好、应力低、与衬底的粘附性好。 相似文献
999.
1000.
The paper presents an entropy generation analysis for steady conduction in a slab with temperature‐dependent volumetric internal heat generation. The slab experiences asymmetric convective cooling on its two faces. The exact analytical solution for the temperature distribution is used to compute dimensionless local and total entropy generation rates in the slab. The total entropy generation rate depends on five dimensionless parameters: reference heat generation temperature Q, the heat generation–temperature variation parameter a, the temperature asymmetry parameter λ, and Biot numbers Bi1 and Bi2. Graphs illustrating the effect of these five parameters on the local and total entropy generation rates are presented and discussed. It is found that the total entropy generation in the slab can be minimized with a suitable choice of the cooling parameters. The paper corrects the flawed entropy results published recently. The present results for the special case of uniform internal heat generation confirm the results presented in a 2003 paper. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20404 相似文献