计算三维恒定磁场的等效磁荷法

本文从磁化强度Ｍ出发，利用等效磁荷模型推导了以等效磁荷面密度σｍ为未知变量的边界积分方程，同时与全标量位ψ为未知变量的边界积分方程进行了对比分析，指出了它们各自的优越点。实测结果证明了本文的数学模型与所编计算程序的正确性。以此为基础，可以计算工程实际中的电磁装置的场分布和其他所需要的电磁参数。     

水稻边际优势利用栽培增产的生态原因研究

对大小垄栽培群体和30cm等行距栽培群体不同层次的光照强度、群体行间温、湿度等生态因子及每穴穗数、每穗实粒数和单穴生产力三个产量性状和不同分蘖时期每穴茎数的边际效应指数进行了研究。结果表明,大小垄栽培群体下部的光照强度和透光率显著增加,行间温、湿度降低,使群体内部的光、温条件得到改善。每穴穗数、每穗实粒数和单穴生产力及不同分蘖时期每穴茎数的边际效应指数降低,说明实行大小垄种植后,群体内部的长势与边行的差距缩小,群体内部个体的生长优势得到发挥,达到了利用边际优势增产的目的。     

利用WRF模拟兰州城市边界层

利用WRF中尺度模式对兰州城市边界层进行了模拟,结果表明,WRF在兰州地区模拟效果较好,可用于研究山谷城市的大气边界层情况。     

Vertical distribution of sand-dust aerosols and the relationships with atmospheric environment

The vertical distribution of aerosols in the troposphere is important for determining their effects on climate.The vertical distribution of aerosols under different atmospheric conditions in the free troposphere was directly observed using a surface micro-pulse LIDAR(MPL) and a TP/WVP-3000 microwave radiometer at the Semi-Arid Climate & Environment Observatory of Lanzhou University(SACOL,35.95°N,104.10°E) in the western Loess Plateau,China,in the spring of 2008.The results showed two possible transportation paths of a sandstorm from May 1 to May 4 in 2008.In one path,sand-dust aerosols were transported toward the east from the Taklimakan Desert to the Badain Jaran Desert and the Tengger Desert by a westerly wind and then toward the southeast to Jingtai and Lanzhou.A weak aerosol index(AI) indicated another possible transport path toward the east from the Taklimakan Desert to the Qaidam Basin and through the Tibetan Plateau eastward to SACOL.The aerosol profile of sandstorm processes over the SACOL area displayed three patterns:a single peak distribution under stable atmospheric conditions,indicating urban aerosol distribution;an exponential decrease under unstable atmospheric conditions in the presence of a sandstorm;and a slight change in the mixed layer during the first and last stages of the sandstorm,indicative of thorough mixing during lifting and deposition stages.Analyses of the aerosol layer height(ALH) showed that there are two types of ALH diurnal variation.The ALH during the first sandstorm stage was complex and disordered,and affected by atmospheric circulation.While the ALH had obvious diurnal variation in the other stage,the ALH and aerosol extinction coefficient(AEC) had a single peak,and was higher in the afternoon and lower in the morning.In the second case the ALH was in agreement with the atmospheric boundary layer height(BLH) variation.As a result of the development of the atmospheric boundary layer(ABL) during day and maintenance at night,ALH during sandstorm-free days showed obvious diurnal variations.Multiple vertical distribution patterns of sand-dust aerosols will result in different climate effects;therefore,the vertical distribution patterns can be used to parameterize climate and aerosol models.     

开孔农用隐蔽式通信电缆屏蔽效应分析(英文)

以农用隐蔽式信号电缆的开孔屏蔽壳体为研究对象,应用线性边界元法计算了屏蔽体上开有不同对称/非对称孔型时对屏蔽效能的影响。根据工程实例计算表明:对于双芯屏蔽电缆,当孔深较浅时屏蔽电缆的耦合电容影响不大,随着孔洞深度的增加,对称/非对称劈形孔耦合电容变化幅度最小;而不同形状孔洞的宽窄对耦合电容影响不太明显。     

植物水分利用效率的影响因子研究综述

在概述植物水分利用效率(WUE)及其层次和测定、计算方法的基础上,介绍了影响植物WUE的内部因素(包括植物种类和品种、叶片解剖结构及生理生化特征等)和外部因素(包括气象、土壤、生物因素等),以及各自的作用机理,尤其是对气孔不均匀关闭、影响Δ13C在田间条件下表现较差的原因、冠层和叶边界层对植物WUE产生的效应及其作用原理进行了探讨,并提出了今后植物WUE研究的重点和方向。     

Service Life Prediction of Concrete Structures under Chloride Environment

The problems rendered from the conventional time marching, referring to stepwise time marching scheme (STMS) adopted in boundary element method (BEM) for chloride diffusion in concrete structures, were investigated, and a new time marching, referring to initial time marching scheme (ITMS) in BEM, was developed for evaluation of service life of the concrete structures under chloride environment. Results of the numerical examples show that the ITMS-BEM proposed can eliminate domain integral and simplify the computational model, so that the stability in iteration process can be improved, resulting in better efficiency and accuracy, compared with the STMS-BEM. It can also be concluded that the dimensions of the diffusion of chloride can affect the service life of the concrete structure significantly, which should be taken into account in structural design.     

气候变暖对华北冬小麦种植界限及生育期的影响

为了揭示冬小麦的物候变化态势及其对气候变化的响应程度,以气温的空间变化替代其时间变化,分析了不同升温幅度对华北冬小麦生育期,尤其是对升温较为明显的秋冬季生育期的影响.结果表明,随着气候变暖,冬小麦冬前生育期呈推迟趋势,而越冬之后各生育期呈提早趋势,越冬期缩短.当气温升高1℃时,冬小麦播种时间将推迟4d左右,越冬开始时间由11月底推迟到12月中旬,返青时间由3月初提前到2月中旬,越冬开始至返青的间隔时间将缩短40 d左右;当气温升高1.5℃时,播种时间将推迟10 d左右,越冬时间将由11月底推迟到12月底,个别暖冬年份将推迟至第二年1月初,返青时间提前至2月上中旬,越冬开始至返青的间隔时间将缩短50 d左右;若气温继续上升,越冬开始至返青的间隔时间可能仍会持续地缩短,但缩短的幅度将可能减小.     

Yield gap and production constraints of mango (Mangifera indica) cropping systems in Tianyang County,China

Mango is an important cash crop in the tropics and subtropics. Determining the yield gap of mango and production constraints can potentially promote the sustainable development of the mango industry. In this study, boundary line analysis based on survey data from 103 smallholder farmers and a yield gap model were used to determine the yield gap and production constraints in mango plantations in the northern mountain, central valley and southern mountains regions of Tianyang County, Guangxi, China. The results indicated that the yield of mango in three representing regions of Tianyang County,Northern Mountains, Central Valley and Southern Mountains, was 18.3, 17.0 and 15.4 t ha~(–1) yr~(–1), with an explainable yield gap of 10.9, 6.1 and 14.8 t ha~(–1) yr~(–1), respectively. Fertilization management, including fertilizer N, P_2O_5 and K_2O application rates, and planting density were the main limiting factors of mango yield in all three regions. In addition, tree age influenced mango yield in the Northern Mountains(11.1%) and Central Valley(11.7%) regions. Irrigation time influenced mango yield in the Northern Mountains(9.9%) and Southern Mountains(12.2%). Based on a scenario analysis, the predicted yield would increase by up to 50%, and fertilizer N use would be reduced by as much as approximately 20%. An improved understanding of production constraints will aid in the development of management strategy measures to increase mango yield.     

Identifying the limiting factors driving the winter wheat yield gap on smallholder farms by agronomic diagnosis in North China Plain

North China Plain(NCP) is the primary winter wheat production region in China, characterized by smallholder farming systems. Whereas the winter wheat average yield of smallholder farmers is currently low, the yield potential and limiting factors driving the current yield gap remain unclear. Therefore, increasing the wheat yield in NCP is essential for the national food security. This study monitored wheat yield, management practices and soil nutrient data in 132 farmers' fields of Xushui County, Baoding City, Hebei Province during 2014–2016. These data were analyzed using variance and path analysis to determine the yield gap and the contribution of yield components(i.e., spikes per hectare, grain number per spike and 1 000-grain weight) to wheat yield. Then, the limiting factors of yield components and the optimizing strategies were identified by a boundary line approach. The results showed that the attainable potential yield for winter wheat was 10 514 kg ha~(–1). The yield gaps varied strongly between three yield groups(i.e., high, middle and low), which were divided by yield level and contained 44 farmers in each group, and amounted to 2 493, 1 636 and 814 kg ha~(–1), respectively. For the three yield components, only spikes per hectare was significantly different(P0.01) among the three yield groups. For all 132 farmers' fields, correlation between yield and spikes per hectare(r=0.51, P0.01), was significantly positive, while correlations with grain number per spike(r=–0.16) and 1 000-grain weight(r=–0.10) were not significant. The path analysis also showed that the spikes per hectare of winter wheat were the most important component to the wheat yield. Boundary line analysis showed that seeding date was the most limiting factor of spikes per hectare with the highest contribution rate(26.7%), followed by basal N input(22.1%) and seeding rate(14.5%), which indicated that management factors in the seeding step were the most important for affecting spikes per hectare. For desired spikes per hectare(6.598×10~6 ha~(–1)),the seeding rate should range from 210–300 kg ha~(–1), seeding date should range from 3th to 8th October, and basal N input should range from 90~(–1)80 kg ha~(–1). Compared to these reasonable ranges of management measures, most of the farmers' practices were not suitable, and both lower and higher levels of management existed. It is concluded that the strategies for optimizing yield components could be achieved by improving wheat seeding quality and optimizing farmers' nutrient management practices in the NCP.