喀斯特原生天坑垂直梯度上植物多样性特征——以云南沾益天坑为例

规模宏大的地表负地形——喀斯特天坑具有巨大的容积和陡峭圈闭的岩壁,在坑底形成异于坑外的独特微生境,是研究物种组成和多样性的理想场所,但目前鲜少对喀斯特天坑植物群落的生态过程及其空间变化特征进行探讨。本研究以云南沾益大毛寺原生天坑植物群落为研究对象,通过游动分割窗技术以及边缘效应值、边缘效应强度和β多样性指数的计算,对原生天坑\"坑边缘—坑壁—坑底\"的生态交错带进行定量判定,探讨垂直环境梯度上植物群落物种多样性变化特征及天坑内外物种多样性边缘效应特征。研究结果表明,原生天坑\"坑边缘—坑壁—坑底\"垂直梯度上的生态交错带出现在坑壁中域位置,宽度大约为40 m,是连接天坑内外生态系统的一个特殊生态过渡带;天坑内外植物群落在坑壁出现\"断裂\",存在不同于一般生态交错带的\"边缘负效应\";基于β多样性指数,垂直环境梯度上植物物种更替率总体呈上升趋势,坑底与坑边缘的植物群落物种组成存在较大差异,坑底拥有更高的物种丰富度和多样性,具有重要的物种多样性保护库价值

喀斯特原生天坑植物群落空间格局特征——以云南沾益天坑为例

以云南沾益大毛寺原生天坑为例,获取坑内植物群落林木个体相对位置信息,进行角尺度、混交度、林层指数等林木空间结构参数与坑底植物群落空间格局分析,并运用点格局分析方法进行单个种群的空间分布特征以及不同种群间的空间关联性分析.结果表明:大毛寺原生天坑坑底植物群落在空间分布上呈现随机分布,林木物种呈中度混交,林木垂直分层虽较简单,但结构稳定,具有发育成熟的顶极森林群落的空间分布特征;坑底植物群落的种群主要呈聚集分布,种群间呈负关联,且处于同一垂直层次上种群间空间负相关性更强,垂直层次相差越大,空间竞争性越小,而随着空间范围的增大,空间负关联越弱;坑内生态系统具有较高的稳定性,是难得的物种自然栖息地和生态避难所,独特生境中形成的稳定植物群落结构在喀斯特地区生态恢复研究中具有重要的借鉴意义和导向作用.国家重点研发计划项目(2016YFC0502900)资助~

A STUDY ON THE STRUCTURE AND SPATIAL PATTERNS of CYCLOBALANOPSIS GLAUCA POPULATIONS IN WESTERN HUANGSHAN

黄山西坡青冈种群结构与分布格局研究陈小勇，张庆费，吴化前，宋永昌（华东师范大学环境科学系，上海，200062）ASTudyOnTHESTruCTurEAndSPATIAlPATTErnSOfCyClObAlAnOPSISglAuCAPOPulATIO...国家自然科学基

Preparation of the Polycrystalline Alumina Fubers by Sol-gel Progress

以铝粉和六水氯化铝为主要原料、水为溶剂,采用溶胶-凝胶法制备了稳定的多晶氧化铝纤维.结合IR,TG-DTA,XRD等研究手段推测凝胶纤维的化学结构和凝胶的烧结过程,以SEM对凝胶纤维热处理后的显微形貌进行观察.研究表明溶胶在1 200℃热处理后可得到-αAl2O3多晶纤维,且微量氯化镁随铝粉同时加入AlCl3.6H2O水溶液中能显著改善纤维的显微形貌,减少裂纹的产生;而直接将氯化镁加到溶胶中则无法得到光洁的纤维形貌.Sol-gel process is a promising method for making ceramic materials.In this paper,Al_2O_3 precursor sols were synthesized by refluxing Al powder and aqueous AlCl_3·6H_2O solution.After a series of hydrolysis-condensation reactions,stable and transparent precursor sols were formed.PVA was then added as fiber forming aid.Precursor fibers were produced by dry-spinning.After heat-treatment,the gel fibers were transformed into ceramic fibers.The chemical structure of the gels was characterized by IR spectroscopy.The sintering process of the alumina fibers was analyzed through DTA-TG and XRD.The morphology of the fibers was examined by SEM.The research shows that the polycrystalline alpha alumina fibers could be attained after heat treatment in air and at 1200℃.The addition of MgCl_2 would significantly improve the microstructure of the fibers,reducing the number density of cracks,when it was added together with Al powder and AlCl_3·6H_2O,but the same beneficial effects were not obtained when it was directly introduced into the Al_2O_3 precursor sols.The underlining reasons were discussed

Preparation and Thermal Shock Property of Si_3N_4 Ceramic Reinforced by Orientation SiC Whiskers

[中文文摘]通过SiC晶须在载体纤维中定向挤出和热压烧结工艺制备了高度定向SiC晶须增韧Si_3N_4复合材料,利用SEM观察了晶须的定向方向和复合材料的断口形貌. 实验结果表明,70％以上SiC晶须的定向角在0～10°之间,具有较好的方向性.过高的烧结温度和晶须含量使材料抗弯强度降低。晶须定向方向的断裂韧性(单迫切口垂直于定向晶须)比横向方向高出20％.1000和500℃温差的热震实验表明,定向SiC晶须复合材料比随机SiC晶须复合材料的抗热震性能高得多.[英文文摘] A highly orientation SiC whisker reinforced Si_3N_4 composite was fabricated by fiber extrusion and hot-pressing technique, which SiC whiskers were unidirectional oriented in the ex- truded carrier fiber. Microstructure of the composites was observed by SEM. Whisker directions were image-processed to quantify SiC whisker orientation in the extruded fibers and the compos- ites. Effects of sintering temperature and SiC whisker content on the flexural strength and fracture toughness of the composites were investigated.The experimental results show that the flexural strength and fractrue toughness of the orientation SIC whisker toughened Si_3N_4 composites are higher than that of the random SiC whisker toughened Si_3N_4 complsites after thermal shock experiment,in temperature difference of 1000℃ and 500℃

Design of a novel capacitor: multifiber ceramic capacitor

［中文文摘］提出了一种新型多纤维陶瓷电容器(MFC)。MFC由众多纤维电容器并联而成,而每根纤维电容器由内电极(导电纤维)、介电层和外电极构成。理论分析表明,当纤维直径与介电层厚度相匹配时,MFC的电容比多层电容器(MLC)的电容大,而且MFC也具有更优异的抗击穿性能。［英文文摘］Based on the fundamental principles of ceramic capacitor, a new type of capacitor designated as multifiber capacitor (MFC) is proposed. It is made up of fiber capacitors (elements) connected in parallel and bonded together with a binder. Each element consists of fiber core (inner electrode), dielectric coating and outer electrode. Theoretical analysis indicates that MFC has the optimum and greater capacitance in comparison with multilayer capacitor (MLC), when the diameter of fiber core is carefully　matched with the thickness of dielectric coating.MFC also has better resistance to dielectric breakdown

Effects of Sintering Conditions on the Liquid-phase Sintering of SiC-Y_2O_3-Al_2O_3 System

研究SiC-Al2O3-Y2O3体系在无压液相烧结过程中,不同的埋粉、烧结温度和保温时间对致密化过程的影响规律以及发生的主要物理化学变化.通过对烧结体失重率、线收缩率和密度的测量和断面形貌的观察发现,以BN为惰性埋粉时,烧结助剂挥发严重,密度低;以Y2O3为埋粉时,烧结过程中Y2O3从埋粉扩散进入坯体,造成烧结体质量增加,实际上未促进烧结;Al2O3和60%(-βSiC)-25%Al2O3-15%Y2O3埋粉有利于烧结,这是由于埋粉中Al2O3的含量较试样中的Al2O3含量高,具有较高的Al2O分压,能有效抑制烧结助剂的挥发.埋粉相同时,由于烧结和挥发的竞争,密度随烧结温度的升高或保温时间的增长先增加后降低.SiC ceramics were sintered using Al_2O_3 and Y_2O_3 as sintering additives.The effects of the powder bed,sintering temperature and sintering time on the densification and microstructure were investigated.The weight loss,linear shrinkage,relative densities and chemical compositions of the sintered samples were measured.And the crystal phase compositions was characterized by X-Ray Diffraction,and the microstructures was observed by SEM.It was found that the BN powder bed could not promote the densification effectively;With Y_2O_3 as the powder bed,large amount of Y_2O_3 diffused into the sample,but the materials did not densify;With Al_2O_3 or 60%(β-SiC)-25%Al_2O_3-15%Y_2O_3 as the beds,much improved densification was obtained,the density were up to 3.07 g/cm~3、3.08 g/cm~3 respectively,higher than with the BN powder bed,because the weight loss of the sintering aids was suppressed or the shrinkage was improved.And it was found that β-SiC could transform into α-SiC with the holding time.The final density increased initially with sintering temperature or holding time,but dropped then due to the evaporation of the additives.国家自然科学基金(50472056);; 福建省重大科技专项(200314007);; 国家“863”计划(2002AA305101)资

Effects of Sintering Additives on the Liquid-phase Sintering of SiC

研究了以Al2O3、Y2O3、Al2O3-Y2O3、SiO2-YAG为烧结助剂时,SiC液相烧结行为以及烧结过程中发生的主要物理化学变化.与传统固相烧结相比,液相烧结使SiC陶瓷性能显著提高.通过对烧结体失重率、线收缩率及密度的测量和断面形貌的观察发现:Al2O3对坯体致密化的促进效果较差;Y2O3为助剂烧结时,由于高温下剧烈挥发,不能有效促进致密化;不同配比的Al2O3-Y2O3助剂能有效促进坯体致密,当配比满足形成YAG的化学计量比要求时,最有利于SiC的烧结.同时对SiC的液相烧结机理也进行了探索.Silicon carbide ceramics have been widely used in petroleum chemical,automotive,mechanical and aerospace industries because of their excellent resistance to thermal shock,high temperatures,oxidation and chemical corrosion.In this paper liquid phase sintered silicon carbide ceramics were prepared with A_2O_3、Y_2O_3、A_2O_3-Y_2O_3 and SiO_2-YAG as sintering additives respectively.Compared with solid state sintered silicon carbide ceramics,the liquid phase sintered one exhibits superior performance.The effects of different additives on the densification and microstructure were also investigated by the measurement of weight loss,linear shrinkage and relative density as well as X-ray diffraction(XRD) and scanning electron microscopy(SEM) analysis.It is found that A_2O_3 was not effective sintering additive due to its high evaporation rate at the sintering temperature.With Y_2O_3 as the sintering additive,large amount of Y_2O_3 from the powder bed diffused into the sample,but the materials did not densify,so Y_2O_3 could not improved the densification of silicon carbide effectively.However,different ratios of A_2O_3-Y_2O_3 significantly promote the sintering,and much improved densification were obtained.With the best result for A_2O_3-Y_2O_3 ratio right for the formation of YAG,the final density was 3.03 g/cm~3,and SEM showed the densification of this sample was highest.The liquid-phase sintering mechanisms of SiC were also studied.国家自然科学基金(50472056);; 福建省重大科技专项(200314007);; 国家“863”计划(2002AA305101)资

纯母乳喂养新生儿低血糖影响因素研究

【目的】探讨纯母乳喂养新生儿血糖变化及低血糖的影响因素。【方法】在出生后1、4、8、12 、24、48 、72 h 对纯母 乳喂养的新生儿306 例进行血糖系列监测。【结果】新生儿出生后1 h 的平均血糖浓度较低为(2.8±0.95)mmol/ L, 4 h 后升 高并逐渐稳定为(3.22±1.03)mmol/ L;有糖代谢异常母亲的新生儿、巨大儿、低体重儿, 其出生3 天内低血糖的发生率分别 为22.4 %(11/49)、36.9%(31/ 84)、29.6 %(8/27), 显著高于无以上并发症的正常新生儿(11.6 %, 17/ 146)。【结论】纯母乳喂 养儿出生1 h 血糖偏低, 有糖代谢异常母亲的新生儿、巨大儿、低体重儿, 出生3 天内低血糖发生率较高, 应给予严密监测, 以 预防有症状的低血糖发生

空间智能软体机械臂动力学建模与控制

空间智能软体机械臂因其结构轻巧、灵活可变、可折叠收缩等特性，在航天器在轨服务任务中，将具有广阔的应用前景。首先提出了一种全向驱动的模块化软体机械臂设计方案，利用刚柔耦合动力学理论建立了气控驱动的软体机械臂动力学模型，基于深度回归卷积神经网络理论建立了空间非合作目标检测与识别算法，为空间软体机械臂智能控制奠定了技术基础。进一步地，设计并研制了软体机械臂地面原理样机及其试验系统，通过地面试验，对软体机械臂的自主运动控制和识别算法进行了初步验证