液压机械无级变速传动拖拉机虚拟试验平台设计

采用计算虚拟试验技术搭建无级变速拖拉机虚拟试验平台,缓解液压机械无级变速器(HMCVT)研究中实物试验存在的成本高、周期长及试验场地限制问题.以模块化和参数化建模的方法,将拖拉机系统划分为发动机模块、HMCVT模块、中央传动模块及行走机构模块,搭建了虚拟试验平台.采用神经网络建立发动机模型,采用动力学方程建立液压机械无...     

茶叶生产格局演变及空间集聚效应研究——以广东省为例

明确茶叶生产格局的演变特征和集聚效应,对广东省茶叶产业规划布局具有重要意义。引入空间重心模型,运用GIS技术和空间自相关分析方法分析广东省茶叶生产格局的演变过程、演变特征,采用空间自相关分析探究茶叶生产的空间集聚效应,研究结果表明：（1）1992—2017年广东省茶叶种植面积和茶叶产量稳步提升,2008年以后增速较为明显;（2）茶叶生产空间差异明显。粤北和粤东地区茶叶种植总面积占到广东全省的85%以上,茶叶产量占到83%以上,粤西和珠三角缩减较为明显;（3）广东省茶叶生产重心具有整体向东偏北迁移的趋势。茶园面积和茶叶产量重心的东移反映出广东省茶叶生产已呈现逐渐向粤东和粤北地区集聚的态势;（4）广东省茶叶生产空间极化和空间溢出作用显著,已经形成了以饶平、潮安、大埔、丰顺、五华、兴宁、英德、东源等县区的茶叶生产集聚区,构成了广东省茶叶生产的“热点区”,并对周边县市产生带动和刺激效应;（5）地理环境等自然因素是茶园规模扩张的基础,政府的政策激励和支持是茶叶产业形成的重要驱动力,巨大的市场消费力是茶叶产业迅速发展的直接因素,新品种和新技术的应用和推广是茶园面积扩张的重要原因。广东省茶叶生产空间集聚效应进一步增强,应根据地区自然资源、地理条件、种植传统等因素,推进茶叶生产区域集群化发展,提升广东茶叶的市场竞争力。     

Using fishers' anecdotes, naturalists' observations and grey literature to reassess marine species at risk: the case of the Gulf grouper in the Gulf of California, Mexico

Designing fishing policies without knowledge of past levels of target species abundance is a dangerous omission for fisheries management. However, as fisheries monitoring started long after exploitation of many species began, this is a difficult issue to address. Here we show how the ‘shifting baseline’ syndrome can affect the stock assessment of a vulnerable species by masking real population trends and thereby put marine animals at serious risk. Current fishery data suggest that landings of the large Gulf grouper (Mycteroperca jordani, Serranidae) are increasing in the Gulf of California. However, reviews of historical evidence, naturalists’ observations and a systematic documentation of fishers’ perceptions of trends in the abundance of this species indicate that it has dramatically declined. The heyday for the Gulf grouper fishery occurred prior to the 1970s, after which abundance dropped rapidly, probably falling to a few percent of former numbers. This decline happened long before fishery statistics were formally developed. We use the case of the Gulf grouper to illustrate how other vulnerable tropical and semi‐tropical fish and shellfish species around the world may be facing the same fate as the Gulf grouper. In accordance with other recent studies, we recommend using historical tools as part of a broad data‐gathering approach to assess the conservation status of marine species that are vulnerable to over‐exploitation.     

花椒杂草系统地下生物量的空间分配格局

农林复合系统中,地下生物量的分配格局是目的物种和间作作物竞争的结果,因而可以看作是模式物种选择及系统设计的依据。在花椒杂草系统模式更新改造中,为了达到间作作物选择和行间配置的合理性,采用壕沟法研究了系统地下生物量的空间分配现状。结果表明：（1）花椒杂草系统地下生物量总量248．57g·m^-2,杂草生物量占82％,花椒仅占18％;（2）该系统地下生物量总量和杂草生物量在水平空间上呈均匀分配,而在垂直空间上随土层加深呈负指数分配,其表达式分别是Y=1024．6exp^-0.5254x（R^2=0．9688,x为土层深度,cm）和Y=1187．2exp^-0.6889（R^2=0．9989,x为土层深度,cm）;花椒根量均匀分配于垂直空间,而在水平空间上呈负指数式分配,其表达式为Y=118．3exp^-0.3817x（R^2=0．8215,x为距树干距离）;（3）花椒吸水根生物量均匀分配于地下空间,杂草吸水根生物量的分配呈现出明显的分层现象,其吸水根总量的81．11％分配于0～15cm土层,而15cm以下土层仅占18．89％;（4）所研究的256个500cm^3的取样单元中,花椒和杂草吸水根的重合率50．4％,非重合率49．6％;然而在127个吸水根非重合单元中,花椒吸水根仅占29．1％,杂草吸水根却占了70．9％。文中根据花椒和杂草地下空间生物量的分配现状,讨论了四川盆地丘陵区退耕还林地花椒模式更新中间作物选择、行间配置和水肥管理应注意的问题．     

基于离散元法的茶叶抖筛机结构参数优化与试验

茶叶抖筛机是茶叶精加工的关键装备,传统抖筛装备主要通过经验设计,筛分性能较差,主要表现在筛净率较低、误筛率较高。该研究结合抖筛机的筛分原理,运用solidworks构建虚拟样机,利用EDEM软件建立茶叶颗粒离散元仿真模型,通过单因素仿真试验对茶叶颗粒进行动力学分析,结果表明,连杆长度、曲柄半径和筛面倾角是茶叶抖筛机筛分性能的主要影响因素。以筛净率、误筛率为评价指标,设计三因素三水平二次旋转正交试验,并运用Design-Expert软件对试验数据进行回归分析,当连杆长度为1 977 mm、曲柄半径为25 mm、筛面倾角为2.8 °时,茶叶筛净率为94.5%、误筛率为4.61%,筛分性能最优。以最优结构参数进行验证试验,筛净率为93.8%,误筛率为4.73%,生产效率为319kg/h,较优化前筛净率提高3.42%,误筛率降低7.62%,生产效率提高8.87%。该研究结果可为茶叶筛分装备的优化提供理论依据。     

不同治理措施对流动沙地天然植被恢复效果的影响

流动沙地采取不同治理措施7 a后,天然植被恢复效果不同。①生态垫阻断了天然植被的正常演替规律,植被盖度和物种丰富度只有4.31%和3种。同期营造的人工林中,小叶锦鸡儿和侧柏林地的植被盖度和物种丰富度最高,均大大超过同期封育的流动沙地,新疆杨和欧美杨84林地的植被盖度和物种丰富度最低,沙枣和榆树林地居于中间位置。②新疆杨和欧美杨84林地植被一年生草本占绝对优势,榆树和沙枣林地多年生草本和灌木数量有所增加,侧柏和小叶锦鸡儿林地物种生活型结构已趋于多样化。③集沙观测表明,生态垫、侧柏和小叶锦鸡儿林地均无风蚀现象,欧美杨84和新疆杨林地风蚀较为严重,榆树和沙枣林地风蚀较轻。     

8℃相变蓄冷技术

指出了自“十二五”规划以来,可持续发展和能源结构转型成为我国政府工作的重中之重,合理利用能源为人类社会创造更加美好的现代生活已经成为社会的共识。蓄冷技术能够按需实现能量的存储和释放,从宏观上起到“移峰填谷”平衡电网的作用;我国电力系统实行分时计价政策,从微观上可以利用峰谷电价差为用户节省制冷系统的运行费用。8℃相变蓄冷技术兼备了传统水蓄冷和冰蓄冷的优点,具有蓄冷密度大、系统简单的突出优点,是当前蓄冷技术研究和应用的前沿方向,市场前景十分广阔。     

塔克拉玛干沙漠腹地建立农业生态体系的初步研究

塔克拉玛干沙漠腹地生态条件恶劣 ,建立农业生态体系需采取特别的措施。两年试验表明 ,供试 71种作物大部分适应性较差 ,蔬菜产量相对较低 ;能量的产投比低 ,养分的利用率低。因此 ,在塔克拉玛干沙漠腹地建立农业生态体系时 ,应采取科学的田间管理措施 ,充分利用地力     

Effect of alley cropping on soil aggregate stability of a tropical Alfisol

The beneficial effect of organic matter on soil aggregate stability is well documented. Alley cropping has been suggested as a possible alternative to maintain soil organic matter content in cropping systems without fallowing the land. The objective of this study was to asses the effect of alley cropping on dry and wet soil aggregate stability on land degraded by shifting cultivation. The aggregate size distribution by dry sieving, aggregate stability by wet sieving, soil organic Carbon content and soil bulk density were measured following two and three years of alley cropping with Gliricedia (Gliricidia sepium) and Pigeon pea (Cajanas cajan) in a tropical Rhodustalf. Alley cropping increased the mean aggregate diameter and water stability of soil aggregates. The mean aggregate diameter obtained from dry sieving increased from 1.3 mm of the control to 2.68 and 3.11 mm after three years in Pigeon pea and Gliricidia alley cropped plots, respectively. This is an indication of resistance to wind erosion in alley cropped plots. The wet aggregate stability which shows the resistance to erosion by water also increased in alley cropped plots. These increases were significant after three years of hedge row establishment. The increase in soil organic C in alley cropped plots contributed to the higher dry and wet aggregate stability, and decreased soil bulk density. The improvement was higher in plots alley cropped with Gliricidia than Pigeon pea. This study shows the importance of ally cropping in increasing aggregate stability of degraded sandy soils which in return reduce erosion by wind and water.     

Forest villages: an agroforestry approach to rehabilitating forest land degraded by shifting cultivation in Thailand

The Forest village scheme was introduced by the Forest Industries Organisation (FIO) of Thailand in 1967 as an attempt to stop further spread of the fast increasing shifting cultivation and deforestation in the country. The underlying princple of the scheme is to relate reforestation with social welfare of the people involved. It is essentially a modification of the traditional taungya method of plantation establishment.The salient aspect of the scheme is to induce the shifting cultivators to settle down in villages where each family is given tenure over a plot of land to construct a house and develop a homegarden around it. The farmers are required to help establish and maintain forest plantations, in which they are permitted to raise agricultural crops during the first three years of its establishment. The farmers are also given free medical and educational facilities, and technical advice on crop and livestock husbandry. They can also earn cash rewards for successful plantation establishment.Although the scheme has not achieved its full target in terms of area covered and number of families settled, it is proving to be a successful method of luring people away from destructive shifting cultivation. The approach is applicable to other countries and regions with similar land-use problems and socio-cultural background.The paper also examines the constraints to the effective working of the scheme, provides some simple suggestions for improving its functioning and identies some of the issues that can easily be tackled by research.