空间五杆机构的可动性分析

机构的第2类可动性。是机构分析与综合所要探讨的基本问题之一。本文对一般形式的空间RRRSR五杆机构的可动性进行分析。通过拆开运动副,分析运动轨迹,根据其雅可比矩阵奇异获得各位形分支的边界后,采用拓朴变换原理,讨论得出该机构的装配条件和连架杆的运动情况。为空间多杆机构的第2类可动性分析,提供了一条方便、实用的途径。     

Absolute configuration of arylglycerol-β-aryl ethers obtained by asymmetric reduction of the correspondingα-ketonic compound with intactFusarium solani cells

When (±)--oxo-guaiacylglycerol--(vanillic acid) ether (1) is degraded byFusarium solani M-13-1, the-ketone is initially reduced to giveerythro andthreo guaiacylglycerol--(vanillic acid) ethers (2), arylglycerol--aryl ethers, both of which are enantiomerically pure. The absolute configuration in each2 was determined by Mosher's method; the products were converted to,-di-(R)--methoxy--trifluoromethylphenylacetates (MTPA esters) (3) oferythro (-)- andthreo (+)-veratrylglycerol--(methyl vanillate) ethers (3), whose¹H nuclear magnetic resonance (NMR) spectra were examined and compared with those of four di-(R)-MTPA ester (3) diastereomers from chemically synthesizederythro (±)-3 andthreo (±)-3. To assign the- and-MTPA-OCH₃ peaks, the¹H NMR scans of several compounds that have substructures of 3 and their 3,4,5-trimethoxyphenyl analogues were examined. When a racemic alcohol reacts with (R)-MTPA to give a pair of (R)-MTPA ester diastereomers, the value was defined as the absolute value of the difference in the¹H chemical shifts of the peak between the diastereomers. It was found that the values of-MTPA-OCH₃ were larger than those of-MTPA-OCH₃ owing to a shielding effect of the veratryl ring located on the-MTPA-OCH₃, and that the-MTPA-OCH₃ peaks in the 3,4,5-trimethoxyphenyl compounds shifted downfield relative to those in the veratryl compounds. On the basis of the¹h NMR data of (R)-MTPA esters, the absolute configuration of the four chemically prepared diastereomers (3) were determined. The catabolicerythro 3 [fromerythro (-)-3] andthreo 3 [fromthreo (+)-3] were identical to (R, S, R)-erythro 3 and (R, S, S)- threo 3, respectively. An hydrogen species in the fungal reduction would attack the-ketone fromre-face of both (R)-1 and (S)-1, givingerythro (S, R)-2 andthreo (S, S)-2, respectively.Part of this paper was presented at the 33rd Lignin Symposium, Tsukuba, November 1988     

宁夏生态经济型林业发展初探

文章在分析宁夏生态经济型林业发展现状的基础上,以生态学、恢复生态学和生态经济学为理论基础,围绕“生态”“经济”两条主线,以林业资源保育和增加植被盖度为切入点,由北向南将宁夏构建为3个林业生态功能区,即宁夏干旱带贺兰山及引黄灌溉绿洲生态网络体系建设区、宁夏中部干旱风沙带灌草配置区、宁夏南部半干旱带水土保持和水源涵养林区,实行多林种、树种,多序列的资源优化配置,以期形成产出效益的多样性和受益的社会性。     

城市园林绿化中植物生态配置研究

从分析我国城市园林植物配置的现状出发,阐述了园林植物生态配置的内涵、特点和原则,提出了园林植物生态配置应以构建人工顶级植物群落为园林设计"立意在先"的基础、以地带性植物作为绿化植物材料选择的依据、以模仿植物的自然组合作为园林植物的主要配置形式等三个方面来合理地配置植物,使城市园林绿化达到最佳的综合效果。     

东莞国家城市湿地公园植物生态化管理与利用研究

东莞国家城市湿地公园是人工修复重建型湿地的典型代表。针对湿地公园内植物构建成效,在实地调查和查找文献资料的基础上,分析湿地公园内植物的类型、分布以及植物构建现状和存在的问题,提出了湿地公园植物生态化管理与利用的对策建议。     

云南师范大学校园植物受冻害调查与植物合理配置分析

2012年末至2013年初,昆明出现的极端低温和持续低温天气,导致云南师范大学校园的部分植物遭受冻害。对受冻害植物进行调查,包括云南师范大学呈贡校区内的植物,总计71科178种。划分植物受冻害级别,分析不同受害级别植物的数量与受害程度,对冻害原因进行分析和讨论,提出植物合理配置和植物防冻害保护建议。     

Beware of changes: Conservation of Indo‐Pacific humpback dolphins in disturbed habitats

1. Protecting critical habitats of the Indo‐Pacific humpback dolphin, Sousa chinensis, is a hot topic of discussion for marine biodiversity conservation in China and many Southeast Asian countries. In practice, sound habitat protection action (HPA) planning often suffers from information gaps in macroscopic habitat configurations and changes in the habitat conditions of humpback dolphins.
2. Recent publications in the journal Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) have served to advance humpback dolphin conservation in Chinese waters by resolving such habitat configurations and indicating significant changes in distribution patterns and habitat characteristics under intense coastal anthropogenic activity.
3. We highlight an integrative research framework to investigate habitat configuration and long‐term habitat changes when planning a holistic HPA programme for humpback dolphins. When constructing habitat configuration baselines, field surveys should be designed and conducted in a systematic manner to ensure survey efforts cover diverse environments equally, in either a spatially stratified or gridded pattern, to minimize potential spatial sampling biases. Long‐term habitat changes can be revealed by comparing satellite images from different decades. Changes in habitat preferences and habitat characteristics can be explored through questionnaire surveys on local ecological knowledge, associating historical occurrences with coastline features and projecting historical habitat configuration by species distribution modelling exercises.
4. A lack of good communication and sharing of information between research and management sectors can still be an obstacle to the implementation of sound conservation practices, however, even though there is robust scientific evidence to fill knowledge gaps in distribution and habitat baselines. We have addressed the need to establish a mechanism to improve and streamline information sharing between research teams, management sectors, and stakeholder groups.

     

黄金宝树幼龄木枝系构型特征及影响因素

为分析黄金宝树(Melaleuca bracteata)幼龄木不同生长高度的枝系构型特征及影响因素,通过统计分析不同高度阶段的枝系构型指标,并采用主成分分析法分析影响枝系构型的因素。结果表明:随着高度的增加,树高、地径、冠幅均值、树冠体积、逐步分枝率1,2与枝径均值对枝系构型的影响趋于上升;总体分枝率、逐步分枝率2,3、逐步分枝率3,4与枝条倾角均值对枝系构型的影响则增减不一。第1主成分的贡献率在23.61%~60.32%间,当高度小于60 cm时,树冠体积、枝径均值及冠幅均值是影响枝系构型的主要影响因素;高度在60~80 cm时,树冠体积和冠幅均值是主要影响因素;高度在80~100cm时,逐步分枝率1,2和总体分枝率是该阶段的主要影响因素;高度在100~120 cm时,逐步分枝率1,2、冠幅均值及枝径均值为主要影响因素。高度超过120 cm时,逐步分枝率1,2的绝对值最大,说明其为该阶段影响枝系构型的主要因素。     

不同植物配置模式对人工边坡减流减沙效益的影响

[目的] 探讨不同植物模式（混草、花草、灌草、乔草）及配置比例对生产建设项目人工边坡水土流失的影响,为人工边坡植被恢复提供参考。[方法] 采用径流小区定位观测法,记录2019年1—12月自然降雨,研究4种植物模式的产流产沙特点,揭示4种植物模式的减流减沙效益。[结果] ①观测期内总降雨量为1 052.73 mm,总降雨历时为845.1 h,7月降雨量最大,2月降雨历时最长,降雨集中在1—7月,以中雨、大雨、暴雨为主。②每场降雨产流差异大,产流月季差异大,集中在2—4月及7月,多发生在中雨、大雨和暴雨情况。③每场降雨及月、季降雨之间产沙差异大,3月产沙最大,产沙集中在2—4月及7月,多发生中雨、大雨和暴雨。④以花草模式为对照,每场降雨条件下灌草模式的减流率最大,乔草模式的减沙率最大,月降雨累计条件下,混草模式减流率最大,乔草模式减沙率最大,不同降雨等级累积和全年累积条件下,乔草模式的减流减沙率最大。[结论] 植被恢复初期,受植被覆盖度差异影响,乔草模式、混草模式的减流减沙率较大,具有较好的固土保持效益。     

黄丘区小流域暴雨径流动力特征对淤地坝配置的响应

为定量揭示淤地坝措施配置对黄丘区小流域暴雨径流形成及演进过程的影响,采用室内小流域人工模拟降雨试验,对不同淤地坝措施布设情景下（无坝、单坝、双坝）小流域不同断面径流的水动力、侵蚀动力特征进行研究。结果表明：径流量与含沙量整体均随时间推移而增大,无淤地坝布设情景下径流量增幅为114.60 cm3/s,双坝情景的径流量增幅仅有70.11 cm3/s;淤地坝对小流域暴雨径流演进过程的影响显著,淤地坝布设后径流流态由主要的紊流-缓流变为以层流-缓流为主,雷诺数Re减小幅度达到12.04%～85.85%;动力参数中径流功率ω和雷诺数Re可以被认为是能够较好描述不同淤地坝布设下侵蚀产沙的动力因子。研究结果对于揭示流域暴雨径流过程及成灾机理具有重要现实意义,可为科学评价水土保持措施调控径流过程的效应提供理论依据。