The lime–silicate question

Hikers passing through nature easily recognize that the vegetation on limestone (calcareous soils) and silicate (acidic soils) is very different. This is not so much the case with trees but with herbs, particularly in grasslands. These differences in the vegetation on both soil types, referred to as the lime–silicate question, were recognized as early as the 18th century. Even so, fairly little is known about why this occurs. The current paucity of information exists mainly because the determinants that govern the formation of plant communities on either lime or acid soils mainly reside below-ground, in the root-surface area, and these complex below-ground interactions are almost impossible to explore through experimental approaches and direct measurements. Element availability or toxicity and interactions with microorganisms are both equally important. The calcium cation, for example, is not only an essential growth component but can be severely toxic to plants in unbalanced concentrations. Plants also vary in their ability to acquire iron and phosphorus. Aluminium toxicity affects plant growth, particularly in acid soils, and acid-tolerant plants have acquired the capability to cope with high levels of Al in soils. Mainly saprophytic fungi serve to degrade litter in acid soils and liberate nutrients for plant growth. In calcareous soils, bacteria and small animals, such as earthworms and their inhabitant bacteria, are the main decomposers of litter and contribute significantly to the fertility of the soils. Arbuscular mycorrhizal fungi (AMF) have a particularly significant role in calcareous soils, where they are believed to determine the competitiveness of plants in lime meadows. Physical factors also impact the different composition of plant communities in acid and calcareous soils.     

马铃薯动态分级系统中多目相机同步采集方法

针对马铃薯动态分级系统中的图像同步采集问题,提出了基于千兆以太网的三目相机同步采集方法.采用3台相机分别从待测马铃薯3 个方向进行同步采集,利用LM358 设计一级同相电压放大电路将STM32 产生的PWM 信号放大来控制3 部相机同步工作,使用C++语言在Visual Studio 2013 平台上进行二次设计与开发...     

水平定向钻施工数据采集及处理系统

目前水平定向钻施工中的数据长期依赖人工记录,容易出现人为误差、漏记现象,造成所记录的数据不能直观反映施工状况,不能科学高效地指导下一级扩孔施工.水平定向钻施工数据采集及处理系统通过压力变送器将扩孔扭矩、拉力、泥浆压力等施工数据进行实时采集,并将数据进行处理,提取出每根钻杆的最大扭矩、最大拉力、扩孔有效时间等参数,同时自动将这些数据绘制成对比曲线,直观反映定向钻穿越施工情况,科学预测下级扩孔可能出现的问题,从而提前制定预防措施.该系统的应用可降低施工风险,提高施工效率.     

基于无线传输的稻田灌溉监控系统

为实现稻田环境的监控和节水灌溉,该文设计了基于无线传输的稻田灌溉监控系统,其中包括1个主站和18个基站,采用日精ND250A数传电台进行无线数据通信。基站可按设定的时间间隔自动采集稻田水温、土壤湿度、稻田水位等参数,并当接到主站指令时通过无线传输将数据上传到主站;基站供电采用太阳能蓄电池,以满足传感器运行及无线通讯的能耗需求。PLC控制灌溉设备的运行,运用组态软件设计人机交互界面,可自动或手动进行灌溉操作;工控机可运行基于Web的信息管理系统,监控灌溉现场的运行情况并在显示器上动态显示各种实时操作。该系统运行稳定,能够实现准确的无线数据采集,适用于稻田灌溉的实时监控。     

氮磷钾配施对小麦植株养分吸收利用和产量的影响

采用大田试验,研究了不同氮水平与磷、钾配施对小麦植株氮磷钾含量、土壤速效氮磷钾含量和产量的影响。结果表明,在低氮（135kg N/hm ²）、中氮（225kg N/hm ²）和高氮（315kg N/hm ²）与2个磷钾用量（P₂O₅-K₂O,90-120、135-180kg/hm ²）处理组合中,各处理不同生育时期植株干重、氮钾含量、氮钾累积量随供氮水平提高而增高;等氮条件下,增施磷钾使植株含氮量降低,植株氮、磷和钾累积量随磷钾用量增加而增多。各施肥处理生育期间土壤碱解氮含量呈波动性变化,表现为起身期较冬前降低,起身至开花期不断增高,开花期至灌浆期明显下降,灌浆期至成熟期有所回升的特征。随生育进程,各处理土壤速效磷含量不断降低,土壤速效钾含量呈“V”字形变化,在开花期达到谷底。高氮水平各生育时期的土壤速效磷、钾含量低于低氮处理;等氮水平下增施磷、钾肥处理的土壤速效磷、钾含量提高。单位面积穗数随供氮增多而增加,穗粒数和千粒重以中氮处理最高;产量表现与穗数相似,但中、高氮处理差异较小。等氮水平下,增施磷钾可明显改善各产量构成因素和产量。随供氮增多,单位氮素生产子粒能力降低,氮肥利用率下降;单位磷、钾素生产子粒能力随氮素用量增多呈低—高—低变化。研究表明,中氮（225kg N/hm ²）配施磷钾（P₂O₅-K₂O,90-120kg/hm ²或135-180kg/hm ²）有利于调节生育期间土壤养分供应,改善植株养分吸收、干物质生产和产量形成能力。     

Study of Acquisition in a Rake Receiver Based on Digital Matched-filter

The Rake receiver based on digital matched filter(DMF) is studied extensively in order to investigate the performance of the PN code acquisition.By using the state transition diagram,the authors derive the analytic expressions of the mean acquisition time of the Rake receiver based on DMF over frequency-selective channel.Numerical analysis is also given.It is shown that the proposed Rake receiver based on DMF can accelerate the process of PN code acquisition.Because there are many resolved multipath components over frequency-selective channel,the detection probability of Rake receiver is larger than the conventional receiver.If more fingers of Rake receiver are available,then the mean acquisition time is longer and the threshold of detector can be set more widely.     

图书馆开展知识服务的冷思考

本文从不同方面探讨了现阶段知识服务研究中的不足之处，并提出了改进方法。     

ARM的温室图像采集设计

介绍了一种基于S3C2440硬件平台和嵌入式WinCE操作系统的USB温室作物图像采集系统的总体设计方案,并详细分析了系统的总体结构和各模块功能特点。对USB驱动模块进行了详细论述,对其他USB摄像头和USB设备在WinCE上的实现具有一定的参考价值。     

基于ontology的地理信息系统构建中的信息共享

针对现在不同GIS系统中数据交换和数据共享困难的现状,提出将ontology引入GIS系统中,如地理on-tology的构建,通过不同本体之间的交互解决信息和知识的共享问题,以及ODGIS中不同功能模块类的实现方法。     

基于知识生产模式视角的农科发展的实然困境与应然向度

学科建设应遵循知识生产模式的演变规律。在新一轮科技革命与产业变革背景下,农科同社会经济发展的不相适应与发展转型的应循之道成为焦点。知识生产模式历经三次变革,知识生产模式I在一定程度上造成了农科发展的实然困境,而知识生产模式I与II的结合则为农林院校新农科发展的应然向度提供了角度,即实现学科建设现代化、基础科学研究应成为重要内容、与时俱进的新农科人才培养观、凝练特色并形成优势,以及学科质量控制多元化等。