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排序方式: 共有334条查询结果,搜索用时 15 毫秒
71.
A high sensitivity, low volume HPLC method to determine soluble reactive phosphate in freshwater and saltwater 总被引:1,自引:0,他引:1
A reverse phase High Performance Liquid Chromatography (HPLC) method was developed to detect soluble reactive phosphate (SRP) in marine and freshwater samples. This technique is scalable over a range of sample volumes from 10 μl to 10 ml, requires minimal sample preparation, and responds linearly from 1 nM to 100 μM (R2>0.964). Standard Murphy–Riley molybdenum blue reagents were used to react with phosphate in samples for analysis. Solid phase extraction tubes were used to clean the mixed complexing reagent prior to combining the reagent with samples. The method was applied to freshwater samples collected in July 2001 along an Andean mountain stream located in the Eastern Cordillera (2400 m) of Peru and marine samples collected in January 2002 within the low marsh of the estuarine Nueces Delta System, Texas Coastal Bend. For method comparison, field samples were analyzed using a standard manual spectrophotometric method. Field sample phosphate concentrations produced from each method were nearly identical. This method offers the advantages of low sample volume (1 ml or less) with high sensitivity, precision, and potential automation. 相似文献
72.
The wave force on a seawater intake structure consisting of a perforated square caisson of 400 mm×400 mm size encircling a vertical suction pipe of 160-mm diameter is investigated using physical model studies. The porosity of caisson was varied from 1.6 to 16.9%. Regular and random waves of wide range of heights and periods were used. It is found that the force ratio (ratio of the force on perforated caisson to the force on caisson with zero percent porosity) reduces to an extent of up to 60% with increase in porosity of the caisson from 1.6 to 16.9%. The force ratio was found to increase with increase in relative wave height and reduces with increase in relative width. Multiple regression analysis of the measured data points was carried out and predictive equations for wave force ratios are obtained both for regular and random waves. The results of this investigation can be used in the hydrodynamic design of perforated caissons, which are widely used as seawater intake structures. 相似文献
73.
文章根据2013—2016年广西涠洲岛珊瑚礁海域水质实际调查情况,应用单因子污染指数评价法、富营养化指数法和有机污染指数法,对近年来涠洲岛珊瑚礁海域水质环境变化进行综合分析和评价。2013—2016年,广西涠洲岛珊瑚礁海域水质大部分符合国家第一类海水水质标准,满足珊瑚礁的正常生长要求,但悬浮物含量持续偏高,对珊瑚礁造成一定影响。涠洲岛海域水体虽未出现显著的污染,根据历史数据分析,人为排污已在一定程度上影响珊瑚礁的生长,持续的监测有助于及时发现水质环境质量的变化。 相似文献
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木构架承重-空斗墙围护民居大量分布在我国南方农村地区,该类民居整体性较差,历次地震中该类民居破坏较严重。采取高延性混凝土ECC面层加固围护空斗墙,扁钢、角钢及薄钢板增强木构架节点,穿墙钢筋捆绑木构架与围护墙体等加固措施。设计了1/2缩尺模型进行振动台试验,通过调整输入地震波峰值加速度来考虑不同水准地震烈度,分析了围护空斗墙损伤,探讨了模型频率与阻尼比变化特性,对比了围护空斗墙体与木构架加速度放大系数和位移包络值,并验证了二者在地震中的变形协调性。试验结果表明:(1)围护墙体仅在外侧出现明显裂缝,内侧ECC面层与墙体始终未脱离且未出现裂缝,围护墙整体性仍可得到一定保障;(2)木构架与钢加固件连接部位仅发生轻微破坏,木构架没有出现明显损伤;(3)木构架与围护墙体之间出现滑移,整体上二者协同抗震变形性能良好。该系列措施的加固效果较理想,适用于该类民居的抗震加固。 相似文献
76.
Pumping optimization of coastal aquifers based on evolutionary algorithms and surrogate modular neural network models 总被引:4,自引:0,他引:4
Pumping optimization of coastal aquifers involves complex numerical models. In problems with many decision variables, the computational burden for reaching the optimal solution can be excessive. Artificial Neural Networks (ANN) are flexible function approximators and have been used as surrogate models of complex numerical models in groundwater optimization. However, this approach is not practical in cases where the number of decision variables is large, because the required neural network structure can be very complex and difficult to train. The present study develops an optimization method based on modular neural networks, in which several small subnetwork modules, trained using a fast adaptive procedure, cooperate to solve a complex pumping optimization problem with many decision variables. The method utilizes the fact that salinity distribution in the aquifer, depends more on pumping from nearby wells rather than from distant ones. Each subnetwork predicts salinity in only one monitoring well, and is controlled by relatively few pumping wells falling within certain control distance from the monitoring well. While the initial control area is radial, its shape is adaptively improved using a Hermite interpolation procedure. The modular neural subnetworks are trained adaptively during optimization, and it is possible to retrain only the ones not performing well. As optimization progresses, the subnetworks are adapted to maximize performance near the current search space of the optimization algorithm. The modular neural subnetwork models are combined with an efficient optimization algorithm and are applied to a real coastal aquifer in the Greek island of Santorini. The numerical code SEAWAT was selected for solving the partial differential equations of flow and density dependent transport. The decision variables correspond to pumping rates from 34 wells. The modular subnetwork implementation resulted in significant reduction in CPU time and identified an even better solution than the original numerical model. 相似文献
77.
78.
79.
《Marine pollution bulletin》2013,72(1-2):29-40
Plans are being made to construct Dalian Offshore Airport in Jinzhou Bay with a reclamation area of 21 km2. The large-scale reclamation can be expected to have negative effects on the marine environment, and these effects vary depending on the reclamation techniques used. Water quality mathematical models were developed and biology resource investigations were conducted to compare effects of an underwater explosion sediment removal and rock dumping technique and a silt dredging and rock dumping technique on water pollution and fishery loss. The findings show that creation of the artificial island with the underwater explosion sediment removal technique would greatly impact the marine environment. However, the impact for the silt dredging technique would be less. The conclusions from this study provide an important foundation for the planning of Dalian Offshore Airport and can be used as a reference for similar coastal reclamation and marine environment protection. 相似文献
80.
The isolation of vibrations from the surroundings is one of the important problems in the design of machine foundations. The use of open trenches, infilled trenches, single and multiple pile rows have been widely studied. In this paper, the vibration screening efficiency of an inclined secant micro-pile wall positioned as an active vibration barrier is investigated. The study is performed using three-dimensional time domain finite element analyses. Various parameters such as barrier depth, inclination, barrier distance and load excitation frequency were studied. The results show that inclined secant micro-pile walls are a viable vibration isolation option for a multitude of vibration problems. It is shown that varying barrier inclination angle from 90° to 120° improved vibration isolation performance as high as 44% relative to the vertical barrier for the active isolation case. The effectiveness of the barrier increases as its depth increases and also as the excitation frequency increases. The orientation of the inclined barrier towards or against vibration source is shown to be a fundamental design consideration. 相似文献