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51.
52.
J. H. M. Scholten 《Nutrient Cycling in Agroecosystems》1992,33(2):107-114
To increase the fertilizer-N efficiency in lowland rice (Oryza sativa L.) cultivation, new management practices are needed. Main cause of the present low efficiency is the low N recovery by plants, as a considerable part of the N applied is lost; deep placement techniques improve the recovery. A pneumatic injector, with which urea prills can be point-placed at a depth of 5–10 cm in paddy soils, was tested in 38 on-farm trials in 1989/90, mostly during the wet season. The experiments, located in Africa and Asia, focussed on differences in grain yield between conventional methods of broadcasting urea and injection by the pneumatic injector, at recommended N-rates. The study shows that the pneumatic injector is effective as a tool to improve the N fertilizer efficiency. The average yield increases per region, resulting from the use of the injector, ranged from about 250 to 1300 kg grain ha–1. The value of the yield increase would allow most farmers to recover the costs of the injector within one season, even if labour was hired to carry out the injections. The average labour requirement of the injector was 40 hours ha–1. In Indonesia, injection of prilled urea gave yields similar to those obtained with urea briquettes. 相似文献
53.
为了研究变异行为对病毒传播的影响,提出了一个病毒发生变异的疾病传播模型,在模型中考虑了两种病毒相互转换的过程,计算机模拟结果表明,两种病毒的稳态感染比例与它们之间的相互转换概率γ1和γ2有关,当γ1>0且γ2=0时,I1型感染者将消失,当γ1与γ2都大于0时,I1/I2与γ1/γ2成反比,且与α1/β1和α2/β2的取值无关.研究还发现病毒变异时由于缺乏对应的治疗药物和措施而出现一段真空期,这导致变异病毒的感染比例快速增加,但真空期的出现只能增加感染者的瞬时感染比例,而对稳态感染比例没有影响.该研究对人们深入理解病毒传播机理具有启发作用. 相似文献
54.
Oscillating heat pipes (OHPs) are very promising cooling devices. Their heat transfer performance is affected by many factors, and the form of the relationship between the performance and the factors is complex and non-linear. In this paper, the effects of charging ratio, inclination angle, and heat input and their interaction effects on heat transfer performance of a looped copper-water OHP are analyzed. First, suppose that the relationship between the response and the variables approximates a second-order model. And use the central composite design to arrange the experiment. Then, the method of least squares is used to estimate the parameters in the second-order model. Finally, multivariate variance analysis is used to analyze the model. The results show that the assumption is right, that is to say, the re- lationship is well modeled by a second-order function. Among the three main effect variables, the effect of inclination angle is the most significant, but their interaction effects are not significant. In the range of the considered factors, both the optimum charging ratio and the optimum inclination angle increase as the heating water flow rate increases. 相似文献
55.
本文综合论证了玻璃纤维及其主要用途的复合材料工业概况,指出我国玻璃纤维复合材料工业已经进入一个新的发展时期.过去是以发展速度为主要特征,现在则以产品应用、质量提高为重要标志.本文对新时期我国玻璃纤维复合材料的技术方向和行业管理提出建议. 相似文献
56.
为实现胸鳍摆动推进模式鱼类的游动,模仿牛鼻鲼构建了仿生鱼.首先,基于摆动胸鳍的生物学特征和运动规律,提出了具有主/被动复合柔性变形能力的仿生胸鳍原理模型.然后通过ADAMS运动学仿真验证了设计方案的可行性,并构建仿生样机.自由游动实验表明,仿生鱼游速可达0.46m/s,约1倍身长比,且具有原地转弯能力,最大转弯速度达60?/s.与国内外其他同类机器鱼相比,在游速和机动性方面均表现出明显的优势.基于准稳态叶素理论,提出了仿生胸鳍水动力简化计算模型.构建水动力实验平台,验证了计算模型的有效性,并通过一系列水动力实验研究了仿生胸鳍的水动力特性.实验结果表明,仿生胸鳍能够产生周期性变化的推、升力,且变化趋势与胸鳍运动控制参数密切相关. 相似文献
57.
58.
波浪要素的观测及分析对港口码头设计、航道建设、围垦工程等都尤为重要。为研究台州东部新区临时航道疏浚工程对周边涉水工程的影响,采用SZF型波浪浮标,在工程海域进行为期一年的波浪观测,并对实测的波浪要素进行统计分析。结果表明:台州湾全年以东北向波浪居多,东向浪最大,可高达5 m。波高主要集中在0.5 m~1.0 m范围,波周期集中在3.0 s~4.0 s范围。春季浪向分散,夏季浪向集中在S向,秋冬季浪向相似,N为主波向。受台风影响,夏秋季有大浪出现。 相似文献
59.
Stavros?LalasEmail author Vassilis?Dourtoglou 《Journal of the American Oil Chemists' Society》2003,80(6):579-583
The effect of using a rosemary extract on the stability of oil used for frying potato chips has been evaluated. Sliced potatoes
were fried intermittently in soybean oil containing a natural extract from rosemary. The conditions used for frying were 185°C
for 90 s. Two separate experiments, with and without replenishment of oil, were carried out. Oil samples were taken each day,
not only from the frying pans but also by extraction with hexane from the chips. Changes in the induction period of the oil
samples (Rancimat method) were determined. The induction period decreased as frying progressed. The reduction in the induction
period was higher in the oil free of rosemary extract, and the chips were much darker in color. The oil containing the extract
showed greater antioxidant activity, and reduced darkening and rancidity of the oil. Potato chips fried in the oil with added
rosemary extract were more acceptable than chips fried in oil containing no extract until the last frying. The free radical
scavenging activity of rosemary extract in comparison to other natural antioxidants was also determined by the reduction of
O2
.- in a hypoxanthine/xanthine oxidase system. 相似文献
60.
The initial transformation of methanol over HZSM-5 catalyst was investigated by a consecutive pulse reaction system. The reactant–catalyst contact time influenced the initial methanol transformation and the performances implied methanol reaction in induction period or under steady-state condition. The induction period, in which an organic-free HZSM-5 catalyst could be transferred to a working catalyst, were directly observed. The analysis result of the product stream predicted hydrogen-deficient species deposition over catalyst surface at the beginning of MTO reaction. The hydrogen transfer level of steady-state MTO reaction also varied with reaction contact time. 相似文献