Dynamics of Nutrient Accumulation in Maize Plants Under Different Water and N Supply Conditions

The dynamics of accumulations of plant dry matter, nutrient uptake and N fertilizer recoverywere studied with different water and N supply, using summer maize (Zea mays L. var. Shandang) as an indi-cator crop. The total dry matter (including roots) and N, P, K uptake amounts were continuously increasedwith plant growth, and their accumulations with time during plant-growing period were shaped in S curves thatcould be described by exponential regression equations. Differentiating the regression equations fitting thecurves over time for first derivatives, the momentary rate was obtained of the dry matter and nutrient uptake.Results show that the dry matter and the nutrient uptake were not in the same rate at all time, but changedfrom one time to another. Usually, the rate increased rapidly at early stages, and gradually decreased afterreaching their peak. Of N, P and K, the uptake rate of N and K was higher, and their increase and decreasewere both fast while P was reversed. The time of the maximum absorptive rate appeared earlier for K, fol-lowed by N, and then by P. In any case, the maximum nutrient uptake rate appeared earlier than did the drymatter. The momentary N recovery rate was similar in trend to those of dry matter and N uptake, and its max-imum recovery rate occurred almost at the same time as its maximum uptake rate. Supplemental irrigationraised the cumulative and momentary rates of N. Although water and N supplies increased dry matter and nu-trient uptake rates, they did not alter their changing trends during the plant-growing period.     

Dynamics of viral spread in bluetongue virus infected calves

The kinetics of viremia and sites of viral replication in bluetongue virus (BTV) infected calves were characterized by virus isolation, serology and immunofluorescence staining procedures. In addition, the role of the regional lymph node and lymphatics draining inoculated skin in the pathogenesis of BTV infection was determined by analyzing efferent lymph collected from indwelling cannulas. Viremia persisted for 35 to 42 days after inoculation (DAI) and virus co-circulated with neutralizing antibodies for 23 to 26 days. Virus was first isolated from peripheral blood mononuclear (PBM) cells at 3 DAI, after stimulation of PBM cells with interleukin 2 and mitogen. BTV was frequently isolated from erythrocytes, platelets and stimulated PBM cells but never from granulocytes and rarely from plasma during viremia. Virus was consistently isolated from erythrocytes late in the course of veremia. Interruption of efferent lymph flow by cannulation delayed the onset of viremia to 7 DAI. BTV was infrequently isolated from lymph cells, and few fluorescence positive cells were observed after lymph and PBM cells were labelled with a BTV-specific monoclonal antibody. Virus was isolated from spleen by 4 DAI and most tissues by 6 DAI, whereas virus was isolated from bone marrow only at 10 DAI. Virus was not isolated from any tissue after termination of viremia. It is concluded that primary viral replication occurred in the local lymph node and BTV then was transported in low titer to secondary sites of replication via infected lymph and PBM cells. We speculate that virus replication in spleen resulted in release of virus into the circulation and non-selective infection of blood cells which disseminated BTV to other tissues. Virus association with erythrocytes likely was responsible for prolonged viremia, although infected erythrocytes eventually were cleared from the circulation and persistent BTV infection of calves did not occur.     

五轴全轮转向汽车动力学模型分析

为提高多轴汽车操纵稳定性,针对五轴全轮转向汽车的高速同相位转向工况,进行了受力分析,建立了运动微分方程,利用Fiala轮胎模型建立了轮胎的力学模型,利用LabVIEW软件建立了整车的动力学仿真程序。通过虚拟试验仿真分析,发现采用全轮转向,可以使后轴车轮较早地参与转向,从而提高了汽车的转向响应速度,并使车身侧倾角由7．5°减小为4°。     

曲轴-轴承系统动力学摩擦学和弹性力学耦合分析

以四缸柴油机为研究对象,采用自编程序和ADAMS、ANSYS相结合的办法,耦合分析研究了曲轴-轴承系统的动力学特性、摩擦学特性和弹性力学特性,并将损伤积累理论应用于曲轴疲劳强度计算。分析结果表明：这种耦合分析结果和传统的非耦合分析结果有很大不同;对曲轴-轴承系统同时发生的机械行为进行耦合分析,对于提高内燃机工作可靠性,改善性能是必要的。     

澳门1977~2004年生态足迹动态研究

运用生态足迹理论和方法,对澳门1977~2004年的生态足迹和生态承载力进行计算和动态分析,探寻影响澳门可持续发展的关键因子,结果表明:1977~2004年,随着经济的变化,澳门人均生态足迹和人均生态赤字呈先升后降然后再上升的趋势;人均生态足迹由1997年的2.123 hm2增加到2004年的4.210 hm2,净增2.087 hm2;人均生态赤字从2.108 hm2增加至2004年的4.198 hm2,年平均增长率达2.49%。28年间澳门万元GDP的生态足迹呈下降趋势,资源利用效率不断提高。     

一株磷降解菌的生长性能及水体中磷降解动力学

[目的]利用微生物修复受磷污染的水体。[方法]采用富集培养的方法从吉林农业大学人工湖底泥中培养出一株对磷有吸收能力的细菌。[结果]供试菌培养0.5d进入稳定生长期,菌株生长过程中体系pH值由7.0下降到4.2。水体中磷的消失过程符合一级反应动力学方程Ct=C0e-kt,相关系数0.894~0.977。将湖水进行灭菌处理与未灭菌处理,未灭菌湖水中磷的消失反应表观活化能由25.9kJ/mol降为10.32 kJ/mol,反映了生物转化的特点。[结论]所培养的微生物具有吸磷作用,在受污水体中有很大的应用价值。     

人为活动对云南纳帕海湿地土壤碳氮变化的影响

以纳帕海湿地原生沼泽作为参照 ,选择人为干扰下的沼泽化草甸 ,草甸和排干湿地开垦的耕地作为研究对象 ,研究人为干扰对纳帕海湿地土壤碳氮变化的影响。两年的定位研究结果表明 :沼泽土壤C/N值较高 ;人为干扰下纳帕海湿地土壤空间结构上土壤有机质 0～ 2 0cm表层与 2 0～ 4 0cm下层相差 4倍 ,水平分布上则随人为干扰加强、沼泽化过程减弱而降低 ,下降幅度高达 2 2 .92 %～ 6 9.6 4 %;土壤全氮及其空间分布呈现与有机质相同趋势 ,两者相关系数r=0 .98;NH 4 N、NO-3 N与全氮和水解氮相关系数分别为r=- 0 .74、r=- 0 .6 5 ,r=- 0 .81、r=- 0 .76。表明了纳帕海湿地沼泽土壤较低的矿化量和对碳的固定及较大的氮累积量 ,以及人为活动干扰后湿地土壤碳氮养分的释放变化。     

落叶松人工林土壤养分与微生物群落的变化动态

利用稀释平板法和B iolog检测技术,分析了落叶松人工林土壤微生物群落的时间动态,并测定了土壤养分的月份变化动态。结果表明:在土壤微生物群落中,细菌数量占绝对优势,放线菌次之,真菌最少。5—10月,表层与上层(0~10 cm)细菌数量为先增后减,下层(10~20 cm)为持续减少;表层真菌数量呈增加趋势,其余土层真菌的数量变化无明显规律;表层放线菌数量呈递减趋势,其余土层放线菌的数量变化无明显规律。相关分析结果表明:速效钾的质量分数与细菌数量呈负相关,速效钾和有效磷的质量分数与放线菌数量存在显著正相关性。B iolog Eco微平板的碳源平均颜色变化率随月份变化而不同,8月份最高。5—10月,表层与上层(0~10 cm)土壤微生物群落的多样性指数、丰富度指数、均匀度指数以及下层(10~20 cm)土壤的多样性指数、丰富度指数均呈先增后减的趋势,下层(10~20 cm)的均匀度指数呈先减后增的变化趋势。     

Comparison of finite element and finite volume methods for simulation of natural ventilation in greenhouses

This article aims to contribute to the discussion on the efficiency of two different discretization methods used as computational fluid dynamics (CFD) solvers for the simulation of natural ventilation in greenhouses. The focus is not on a general use of CFD, but rather on its specific application to simulate airflow in naturally ventilated greenhouses. After a short review of the basic model and its extensions, we compare the accuracy and computational efficiency of two simulation codes based on the Finite Element Method (FEM) and the Finite Volume Method (FVM) for two-dimensional incompressible turbulent flow in naturally ventilated greenhouses. FVM software (ANSYS/FLUENT v 6.3.) is the most frequently used CFD code in ventilation research, but few papers using FEM software (ANSYS/FLOTRAN v. 11.0) have been published. CFD simulations have been compared to experimental data for 12 cases corresponding to three greenhouse types. The experimental greenhouses were chosen to represent a large range of ventilation situations: buoyancy effect in a mono-span greenhouse with adiabatic walls, buoyancy and wind effect in a multi-span greenhouse and ventilation in an Almería-type greenhouse under conditions of large temperature gradient and high wind speeds. The data from simulations and field experiments were compared using different parameters to analyze the effectiveness of experimental data in the validations of CFD models.The possibility of repeating simulations with different discretization methods and commercial software has been tested, as well as the type of experimental data needed to ensure correct validation of CFD models for use in greenhouse ventilation studies. To this end, temperature distribution measurements are preferable to set-point measurements and the use of visualization techniques (laser sheets) or the measurement of velocity vectors (anemometer) are more indicative than ventilation rates.The computational capacity of these approaches has also been analyzed, comparing their performance in terms of the overall database space necessary to store the numerical models and the necessary CPU time to compute one step of the convergence process. On average, the FEM required twice as much computing time per cell and step as FVM, and the amount of required memory storage was approximately 10 times greater for the FEM.     

河南省南湾水库浮游蓝藻动态特征研究

按照规范方法,对河南省南湾水库2008年2月～2009年1月的浮游蓝藻时间与分布动态进行了监测研究。结果表明,南湾水库浮游蓝藻在6～10月易于形成优势,其中微囊藻属种类比较多见,仲冬到初春浮游蓝藻比较少见;库区浮游蓝藻分布不均匀,受河流影响大的库区浮游蓝藻动态与河流中的浮游蓝藻动态存在正向关联性,春季在饮用水源一级保护区的边界处监测到较高数量的微囊藻;6～12月,应警惕浮游蓝藻可能污染饮用水源。