Use of the 15N natural abundance technique to quantify biological nitrogen fixation by woody perennials

Biological nitrogen fixation (BNF) associated with trees and shrubs plays a major role in the functioning of many ecosystems, from natural woodlands to plantations and agroforestry systems, but it is surprisingly difficult to quantify the amounts of N₂ fixed. Some of the problems involved in measuring N₂ fixation by woody perennials include: (a) diversity in occurrence, and large plant-to-plant variation in growth and nodulation status of N₂-fixing species, especially in natural ecosystems; (b) long-term, perennial nature of growth and the seasonal or year-to-year changes in patterns of N assimilation; and (c) logistical limitations of working with mature trees which are generally impossible to harvest in their entirety. The methodology which holds most promise to quantify the contributions of N₂ fixation to trees is the so-called `¹⁵N natural abundance' technique which exploits naturally occurring differences in ¹⁵N composition between plant-available N sources in the soil and that of atmospheric N₂. In this review we discuss probable explanations for the origin of the small differences in ¹⁵N abundance found in different N pools in both natural and man-made ecosystems and utilise previously published information and unpublished data to examine the potential advantages and limitations inherent in the application of the technique to study N₂ fixation by woody perennials. Calculation of the proportion of the plant N derived from atmospheric N₂ (%Ndfa) using the natural abundance procedure requires that both the ¹⁵N natural abundance of the N derived from BNF and that derived from the soil by the target N₂-fixing species be determined. It is then assumed that the ¹⁵N abundance of the N₂-fixing species reflects the relative contributions of the N derived from these two sources. The ¹⁵N abundance of the N derived from BNF (B) can vary with micro-symbiont, plant species/provenance and growth stage, all of which create considerable difficulties for its precise evaluation. If the%Ndfa is large and the ¹⁵N abundance of the N acquired from other sources is not several ¹⁵N units higher or lower than B, then this can be a major source of error. Further difficulties can arise in determining the ¹⁵N abundance of the N derived from soil (and plant litter, etc.) by the target plant as it is usually impossible to predict which, if any, non-N₂-fixing reference species will obtain N from the same N sources in the same proportions with the same temporal and spatial patterns as the N₂-fixing perennial. The compromise solution is to evaluate the ¹⁵N abundance of a diverse range of neighbouring non-N₂-fixing plants and to compare these values with that of the N₂-fixing species and the estimate of B. Only then can it be determined whether the contribution of BNF to the target species can be quantified with any degree of confidence. This review of the literature suggests that while the natural abundance technique appears to provide quantitative measures of BNF in tree plantation and agroforestry systems, particular difficulties may arise which can often limit its application in natural ecosystems.     

紫草在柞丝绸织物染色中的应用

对紫草用于柞蚕丝织物的染色性能进行了探讨。用乙醇提取紫草色素,选取染液体积分数、pH值、温度和时间4个因素,通过正交试验及单因素分析试验,优化出紫草上染柞蚕丝织物的最佳工艺条件为:浴比1∶40,染液体积分数8%,pH 6,温度80℃,时间60 min。通过不同媒染剂(Al3+、Fe2+、Cu2+)媒染处理,得到不同颜色的织物。通过对染色织物耐水洗及耐摩擦色牢度的检测得出,紫草上染柞蚕丝织物色牢度优良,直接染色和媒染均达到3级以上。     

基于本体的网络空间决策支持系统研究*

为了不同的空间决策,往往需要建立相应的空间决策支持系统,在这些空间决策支持系统中,大量的空间数据和模型是可以被重复使用的,因此提出了一种基于本体的空间决策支持系统。该系统能够高效、自动地利用互联网中存在的各类异构空间信息与分析资源来支持空间决策;此外,本系统还提出了一种灵活的体系架构来解决空间决策中存在的语义问题。     

Research on the Control Strategy of Variable Nozzle Turbocharger for Natural Gas Engine

A variable nozzle turbocharger (VNT) was applied to a 2.2-liter L4 natural gas engine,and a VNT control system was designed to operate it.Based on VNT matching test results,a VNT control strategy was studied,in which VNT adjustment is carried out through pre-calibrated VNT handling rod position,combined with a closed-loop target boost pressure feedback using proportional-integral-derivative(PID) algorithm.Experimental results showed that the VNT control system presented in this thesis can lead to optimized ...     

烟气冷凝热能回收利用装置烟气流动方式优化研究

烟气冷凝热能回收利用装置中烟气的分布与流动对换热起着重要作用,为优化烟气冷凝热能回收利用装置,保证烟气能够在装置中分布均匀、充分换热,分别设计两种烟气流动方式,采用CFD软件Fluent模拟了烟气冷凝热能回收利用装置中的流场及温度场,并将其分别应用于实际工程进行现场实测.结果表明,采用渐变断面设计的烟气流动方式,烟气在换热面上分布更均匀,更有利于强化换热,阻力更小,节能率比采用等高断面最大可提高3.25%,可有效降低和消除噪音.     

水处理中超滤膜不能去除水中溶解态有机物

根椐天然水中有机物的形态和分子量分布状况,对比水处理中常用的超滤膜截留分子量,认为给水处理中超滤不能去除天然水中溶解态有机物.     

天然气管道事故严重度评价体系研究

为解决由于天然气管道管材的老化、腐蚀以及外力破坏引发事故的评价问题,以目标层、准则层和指标层3层结构体系,构建了天然气管道事故严重度评价体系,该体系从管道类型、事故类型、事故发生地点和事故已有损失4个方面来评价事故的严重程度,采用百分制权重加和法得到事故严重度指标值G,依据G值大小将事故分为3个等级,评估结果可以为管理层提供参考,为制定天然气管道事故抢修抢险方案起到导向作用.     

Characterization of NOM and THM formation potential in eutrophic reservoir water

Resin adsorption technique with XAD-8 and XAD-4 was used to characterize the raw water from Erlong reservoir in Jilin province of China. The NOM chemical composition sequences of four organic fractions in the raw water,from high to low,are fulvic acid (FA) fraction,hydrophilic non-acid (HPINA) fraction,hydrophilic acid (HPIA) fraction,and humic acid (HA) fraction. Experimental results show that FA is the main precursor of THMFP among the four organic fractions. However,HA or hydrophobic acid exhibits the highest chlorination activity in forming THMs. It is also found that the value of FI/DOC or SUVA and the specific THMFP have better positive correlation. It is implied that certain source water has unique nature of NOM and DBPs.     

无信号交叉口交通流有序运行实现方法研究

为改善无信号交叉口交通运行现状,基于自然排队思想,采用路中时间提醒装置使驾驶员获取无信号交叉口通行信息,对车速进行主动调整,达到自然排队的效果,在交叉口形成有序的交通流．运用不完全停车理论分析了此种方法对延误的降低,同时剖析了自然排队对交叉口交通的改善．实施方法的采取可以显著改善无信号交叉口的交通秩序,提高其通行能力．     

风力发电机锥筒型塔架的模态分析

应用SAP2000有限元分析软件对某定型风力发电机组塔架建模并进行模态分析,研究了有无门洞两种塔架的固有频率及其与风轮转动频率的关系,通过对塔架固有频率影响因素的探讨,得到了一些基础性结论.分析表明：塔架的固有频率每两阶基本相等;门洞对塔架固有频率的影响很小;塔架一阶固有频率与机头质量基本呈线性关系递减;能否引起塔架与风轮激励的共振主要取决于塔架的低阶频率.研究成果可为风力发电机锥筒型塔架的设计提供参考.