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排序方式: 共有659条查询结果,搜索用时 562 毫秒
571.
针对宁夏电网新能源占比不断升高,常规水、火电机组出力逐步减少,电网调频裕量日显不足,且直流大功率闭锁进一步加剧电网频率安全运行风险的现状,提出了一种适用于宁夏电网的新能源电站快速频率研究方法。通过开展试点研究,掌握光伏电站、风电场参与电网频率调节的特性,结合日常电网运行频率波动情况和试点场站挂网实测响应效果,制定了快速频率响应参数设置策略,西北全网试验验证了该方法的可行性。 相似文献
572.
窦洪云 《中国环境管理干部学院学报》2008,18(1):98-100
提出了一种测定水中氟化物电极的洗涤方法,实验结果表明:利用稀盐酸代替蒸馏水对氟电极和参比电极进行洗涤,可以缩短电极的洗涤时间,提高工作效率3~4倍.同时对用稀盐酸洗涤电极法测定水中氟化物浓度的影响因素进行了分析. 相似文献
573.
McDowell RW Dou Z Toth JD Cade-Menun BJ Kleinman PJ Soder K Saporito L 《Journal of environmental quality》2008,37(3):741-752
An experiment was conducted to examine how potential phosphorus (P) bioavailability (inferred from speciation) differs in feed and feces collected in spring from four dairy herds representing different management systems: (i) total confinement with cows fed total mixed ration (TMR), (ii) total confinement with TMR plus P mineral supplement, (iii) a hybrid of confinement with TMR and pastoral grazing, and (iv) predominantly grazing with supplemental grains. A treatment was included that air dried feces to simulate conditions after dung deposition. Wet chemical techniques and solution (31)P nuclear magnetic resonance spectroscopy ((31)P-NMR) were used to identify P concentrations and compounds present in water (a surrogate for P in overland flow), dilute acid (0.012 M HCl, an estimate of P utilization by cattle), or NaOH-EDTA (a solution that maximizes the organic P extraction) extracts of feed and feces. In general, P concentration in feces paralleled P in feed. Air drying feces decreased water-extractable P by 13 to 61% largely due to a decrease in orthophosphate, whereas NaOH-EDTA-extractable P increased by 18 to 48%. Analysis of dilute HCl was unsuccessful due to orthophosphate precipitation when pH was adjusted to 12 for (31)P-NMR. In water extracts, more P was in bioavailable diester-P forms, undetectable by colorimetry, than in NaOH-EDTA extracts. In feed, orthophosphate dominated (46-70%), but myo-IHP varied with feed (<10% in forage samples but 43% in a TMR sample). The proportion of myo-IHP decreased in feces compared with feed via mineralization but decreased less in systems with a greater proportion of available P input (e.g., orthophosphate and phospholipids). Feed and drying effect the concentrations and forms of P in feces and their potential impact on soil and water quality. Although bioavailable P in feces from pasture-based and confined systems can be similar in spring, dung-P is distributed on a lower kg P ha(-1) rate in grazing systems. The best method to mitigate P loss from feces is to decrease P in feed. 相似文献
574.
The composition of chlorinated hydrocarbon DNAPLs (dense non-aqueous phase liquids) from field sites can be substantially different than the material originally purchased for use as a solvent. Waste management practices at the U.S. Department of Energy's (DOE) Savannah River Site (SRS) included co-disposal of a wide range of organic and inorganic wastes. In 1991, a clear, orange-colored DNAPL was found in two wells near the SRS M-area settling basin. Waste effluent from the fuel and target fabrication facilities that were discharged to this settling basin included acids, caustics, metals and chlorinated solvents. The characterization of the SRS DNAPL suggests that numerous constituents partitioned into the DNAPL during its use as a solvent, co-disposal and ultimate migration through the subsurface. Trace constituents in the DNAPL include metals, from processing operations or co-disposal practices and subsurface minerals, high molecular weight hydrocarbons and alkyl esters, and acids. This complex mixture results in DNAPL-water interfacial properties that are substantially different than would be expected from a simple mixture of PCE and TCE. Under conditions when there is a high DNAPL to water volume ratio, a semi-rigid film accumulates on water droplets suspended in the DNAPL. It is concluded that the array of precipitated metal species comprising this film contributes to the interfacial tension that is over an order of magnitude lower than expected for a "clean" PCE/TCE mixture. 相似文献
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岩质边坡在地震作用下稳定性的计算一般采用拟静力法和有限单元法,拟静力法因应用简便而得到大量应用,至今广泛应用于边坡的抗震计算。建立了某溢洪道引渠左侧整体边坡三维有限元模型,选用ADINA软件并采用拟静力法对三维模型进行了抗震稳定性计算和分析,结合有限元分析的结果,提出溢洪道引渠左侧整体边坡抗震措施和建议。 相似文献
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吴建军 《生态与农村环境学报》1993,(4)
本文采用综合评价法,对高产淡水鱼生产区——浙江省湖州市菱湖镇郊15个农户的综合功能效益作了调查研究。结果表明,仅有少数农户综合功能效益水平较高,具有生产资料较完备,充分利用系统内部资源及各业之间密切配合,生产技术和经营水平较高,注意闲季户外收入等特点;大多数农户的综合功能效益水平则较低,尚有较大的潜力。池塘水体富营养化、水体污染及市场影响是所有农户的共同问题,急需采取有效措施加以解决。 相似文献