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1.
针对采用FCT +FST的自动无功补偿装置的晶闸管的保护及续流问题 ,提出一种受保护及续流晶闸管控制的R -C旁路电路 ,将其与电抗器并联而不是与晶闸管并联的保护及续流方法 ,给出了R、C参数的计算方法。具有保护及续流灵敏完全、电抗器电流基本连续的优点 ,并可减少对交流电源侧的谐波污染  相似文献   
2.
Drip irrigation system has been one of the technical means to improve water use efficiency. In India, this system is gaining popularity among fruit growers and in water scarced area but a substantial area is being covered annually under vegetables crops. One of the major concerns raised by farmers about this system is its economic viability. In present study, the economic viability of drip irrigation system for growing capsicum crop based on discounted cash flow technique (Net present worth and Benefit cost ratio) was explored. Eight irrigation treatments were laid under drip with and without plastic mulch. The irrigation levels were taken as 1, 0.8 and 0.6 of the crop evapotranspiration. The pan evaporation method was used for estimation of reference evapotranspiration and Water Balance Approach was used for irrigation scheduling. The average amount of water supplied under treatment VD (100% irrigation requirement supplied with drip) was found to be 415 mm for whole growing season of the crop. Similarly the amount of water was found to be 332 mm and 249 mm for the treatment 0.8VD (80% irrigation requirement supplied with drip) and 0.6VD (60% irrigation requirement supplied with drip) respectively. Highest yield was recorded in case of treatment VD + PM (100% irrigation requirement supplied with drip plus plastic mulch) followed by VD. Yield under treatments 0.8VD, 0.6VD, 0.8VD + PM and 0.6VD + PM were significant while treatments VD, VF and VF + PM were at par with the treatment VD + PM. Net Present Worth (NPW) was found to be positive for all the treatments. The highest NPW was obtained under treatment VD as Rs. 309,734.90 and lowest was in case of 0.6VD + PM as Rs. 144,172.24. The yield per mm of water used was reported to be at higher side as 35 in both the treatments VD and VD + PM. But the yield per mm of water used was found to be lowest as 18.07 and 19 in case of VF and VF + PM respectively.  相似文献   
3.
A slightly modified three-step sequential extraction procedure proposed by the Community Bureau of Reference (BCR) for analysis of sediments was successfully applied to soil samples. Contaminated soil samples from the lead and zinc mining area in the Mezica valley (Slovenia) and natural soils from a non-industrial area were analysed. The total concentrations of Cd, Pb and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry (FAAS, ETAAS). Total metal concentrations in natural soils ranged from 0.3 to 2.6 mg kg-1 for Cd, from 20 to 45 mg kg-1 for Pb and from 70 to 140 mg kg-1 for Zn, while these concentrations ranged from 0.5 to 35 mg kg-1 for Cd, from 200 to 10000 mg kg-1 for Pb and from 140 to 1500 mg kg-1 for Zn in soils from contaminated areas. The results of the partitioning study applying the slightly modified BCR three-step extraction procedure indicate that Cd, Pb and Zn in natural soils prevails mostly in sparingly soluble fractions. Cd in natural soils is bound mainly to Fe and Mn oxides and hydroxides, Pb to organic matter, sulphides and silicates, while Zn is predominantly bound to silicates. In contaminated soils, Cd, Pb and Zn are distributed between the easily and sparingly soluble fractions. Due to the high total Cd, Pb and Zn concentrations in contaminated soil close to the smelter, ! and their high proportions in the easily soluble fraction (80% of Cd, 50% of Pb and 70% of Zn), the soil around smelters represents an environmental hazard.  相似文献   
4.
渭河(咸阳段)表层沉积物中重金属形态分布特征   总被引:3,自引:0,他引:3  
采用欧共体修正BCR四步连续提取法对渭河(咸阳段)的表层沉积物的重金属(Pb,Cr,Cu,Ni,Mn和Zn)形态进行了研究.结果表明,Cr,Ni和Zn主要以残渣态的形式存在,分别为97.91%,66.36%和73.68%,表现出很高的稳定性.而Pb和Mn仅在乙酸提取态含量分别达27.66%和38.49%时表现出一定的生物有效性和潜在危害性."非稳定态"重金属的空间分布特征是沣河渭河交汇处上游位含量最高,其次为渭河3号桥下,沣河渭河交汇处下游含量最低.  相似文献   
5.
针对铬污染土壤不易处置的难题,文章通过室内模拟实验,采用振荡淋洗的方法研究了猪粪源沼液对铬污染土壤中铬的淋洗效果,优化了固液比、淋洗时间和淋洗次数等影响土壤中总铬和六价铬洗脱效果的因子,并研究了猪粪源沼液淋洗前后土壤中铬形态分布及DOM的变化。结果表明,当环境温度为20℃,振荡速度200 r·min^-1时,沼液洗脱土壤铬的最优条件为:固液比1∶10,振荡6 h,淋洗1次。该条件下,当土壤总铬浓度为121.54 mg·kg^-1(六价铬浓度为119.9 mg·kg^-1)时,其总铬和六价铬洗脱率分别为43.27%,48.99%;当土壤总铬浓度为941.9 mg·kg^-1(六价铬浓度为856.9 mg·kg^-1)时,洗脱率达84.89%,96.32%。猪粪源沼液对水溶态、弱酸提取态和残渣态铬有较好的洗脱效果,有效削减了土壤环境风险。紫外-可见光谱和三维荧光光谱显示:淋洗后土壤DOM芳香性物质及疏水性物质减少,类腐殖酸类还原性物质增多,使得沼液对铬污染土壤有解毒效果。该研究可为铬污染土壤淋洗修复提供一定的参考价值。  相似文献   
6.
生物质炭对单一与复合污染土壤中铜、铅、铬的钝化作用   总被引:2,自引:0,他引:2  
外源投加重金属硝酸盐制得铜、铅、铬单一和复合三级污染土壤(800 mg kg~(-1)、1000 mg kg~(-1)、800 mg kg~(-1)),以热解制备的生物炭为钝化剂,根据重金属钝化率对钝化剂投加量进行优化,并通过改进的BCR(European Communities Bureau of Referent)分级提取方法研究最佳钝化剂投加量下土壤中重金属形态变化。结果表明:施入生物质炭后,单一与复合污染土壤重金属有效浓度均显著降低,确定2%和10%为单一和复合最佳投加量。最佳投加量下,单一与复合过程Cu、Pb、Cr钝化率分别为26.2%、10.9%、36.5%与12.7%、6.0%、37.6%。生物质炭的施入能促进金属离子从可交换态向残渣态和可还原态转变,比较单一与复合污染,Cu、Pb、Cr可交换态减少量分别从18.4%、20.5%、37.5%变为10.5%、18.2%、46.5%,残渣态增加量分别从138.1%、64.2%、41.6%变为37.4%、58.5%、48.2%。生物炭对土壤中Cr的钝化效果最佳,在复合污染土壤中更为明显。  相似文献   
7.
分别采用BCR法和Maiz法两种连续提取法,对蔗田土壤样品中重金属元素Cu、Zn、Pb、Cd和Ni进行了形态分析。结果表明:Cu、Zn、Pb、Cd和Ni均主要以残渣态的形式赋存,具有较低的潜在生物有效性;Pb主要以可还原态或螯合态的形式存在,具有一定的潜在生物有效性;BCR法得到的重金属回收率高于Maiz法的,但是Maiz法测得的有效态Cu、Zn、Pb、Cd和Ni的量均高于BCR法测得的弱酸提取态的量。  相似文献   
8.
凤凰铅锌矿区土壤铅的化学形态及污染特征   总被引:2,自引:1,他引:1  
以湘西凤凰铅锌矿区土壤为对象,基于BCR三步法和ICP-MS技术,研究了该矿区土壤中Pb的化学形态及污染特征。结果表明,矿区土壤中Pb以残渣态为主,其次为有机-硫化物结合态,酸交换态和Fe-Mn氧化物结合态所占比例较少,各形态Pb的分配系数依次为:残渣态(44.0%)>有机-硫化物结合态(29.3%)≈Fe-Mn氧化物结合态(24.3)>酸交换态(2.4%);矿区土壤中各形态Pb含量存在明显的空间分异,并因土地利用类型不同而差异明显;土壤理化性质影响土壤Pb的形态分配,各形态Pb含量与砂粒含量正相关,并随土壤pH升高而增加,这与人为排放输入的含Pb物质以类似于土壤砂粒形式存在有关。人类活动引起的外源输入性Pb污染对矿区土壤中Pb的污染特征产生了重要影响。  相似文献   
9.
磷矿粉和活化磷矿粉修复Cu污染土壤   总被引:5,自引:0,他引:5  
为了比较磷矿粉和活化磷矿粉对铜污染土壤的修复效果,在实验室将实际铜污染土壤和模拟污染土壤与不同质量分数(0、0.1%、0.5%、1%、4%、8%等)的磷矿粉和活化磷矿粉混合培养,运用欧共体标准物质局提出的改进的三步连续提取法(简称BCR法)分析了土壤中铜的各种形态及其含量的变化。结果表明:2种含磷材料都具有一定的修复土壤铜污染的作用;培养10 d后,2种土壤在磷矿粉8%用量下可溶态铜含量降幅分别为25.8%和40.0%,氧化态和还原态变化趋势不同,残渣态含量增幅达到77.1%和41.3%,有效地降低了土壤中铜的活性。而施用经草酸活化的磷矿粉后,实际污染土壤中可溶态铜含量有所增加,模拟污染土壤中可溶态铜含量基本无变化;实际污染的红壤和模拟污染的土壤中残渣态铜含量分别增加了82.6%和17.0%,其他形态铜的变化差异不显著。该研究可为磷矿的综合利用和重金属污染的土壤的原位修复提供参考。  相似文献   
10.
杨亚鸽  崔立强  严金龙  丁成 《安徽农业科学》2013,41(5):2044-2046,2057
以不同生物质炭添加量修复稻田土壤为研究对象,采取三步连续提取法对3年来土壤中镉元素的形态分布特征及其变异规律进行了系统分析。结合土壤理化性质,探讨了镉污染稻田生物质炭修复的化学稳定机制。结果表明,在生物质炭修复2、3年后,与对照相比土壤pH分别提高了0.16~0.65单位和0.26~0.60单位;土壤有机质分别提高了26.2%~50.4%和29.2%~51.2%;镉的赋存形态由有效态向潜在有效态或无效态转变,酸溶态分别降低了5.9%~37.6%和21.7%~27.3%;40 t/hm2处理强度土壤镉的氧化态和残渣态分别升高了126.7%和64.2%,显著降低镉污染的生物可利用性和生态毒性。该研究结果能够为深入探讨生物质炭修复机制提供理论依据,并且为生物质炭在重金属污染土壤中的农业应用提供技术支撑。  相似文献   
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