Subjects: Geosciences >> Geography submitted time 2024-05-20 Cooperative journals: 《干旱区地理》
Abstract：为明晰荒漠草原优势植物的植物生物量与土壤养分关系，研究选取祁连山北麓肃北区域荒漠草原骆驼蓬（Peganum harmala）、狗尾草（Setaria viridis）、中华羊茅（Festuca sinensis）、碱茅（Puccinellia distans）和冰草（Agropyron cristatum）5种优势植物，测定该其生物量和根际土壤养分，探究其植物生物量分配及其与土壤养分间的关系。结果表明：（1）5种优势植物间总生物量和根冠比差异显著（P冰草>中华羊茅>骆驼蓬>狗尾草。（2）5种植物根际土壤有机碳、碱解氮、速效钾、全氮、全磷、全钾及其化学计量特征均存在显著差异（P狗尾草>冰草>骆驼蓬>中华羊茅。（3）不同植物生物量、根冠比及土壤养分变异性不一致，骆驼蓬、狗尾草和中华羊茅的根际土壤全钾与碱茅和冰草的根际土壤含水量等均为弱变异，而土壤养分及其化学计量特征为中等变异。5 种优势植物的生物量与根际土壤碱解氮和全钾呈正相关性（P<0.05）。可见荒漠草原生态系统中植物生物量分配和根际土壤养分在生活史和物种间的差异较大，今后应根据不同优势植物养分需求，合理施肥来修复退化的荒漠生态系统。
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： Three high- entropy alloys Co1.5CrFeNi1.5Ti0.5Mo0.1, AlCoCrFeNiSi0.1 and TaNbHfZrTi were prepared by arc melting. Their phase structure, microstructure and chemical composition were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). A commercial alloy 690TT was used as the contrast material. The repassivation kinetics of the three high entropy alloys in high temperature pressurized water was investigated by means of electrochemical test. The results show that Co1.5CrFeNi1.5Ti0.5Mo0.1, AlCoCrFeNiSi0.1 and TaNbHfZrTi high entropy alloys are all composed of single phase. The crystallographic structure of Co1.5CrFeNi1.5Ti0.5Mo0.1 alloy is fcc, while that of the alloys AlCoCrFeNiSi0.1 and TaNbHfZrTi is bcc. The SEM results show that the Co1.5CrFeNi1.5Ti0.5Mo0.1 alloy showed a typical dendritic microstructure, of which the dendrite riches in Cr and Fe, but the interdendrite zone riches in Ti and Ni. There is no obvious element segregation observed in the AlCoCrFeNiSi0.1 alloy. The TaNbHfZrTi alloy also exhibited a dendritic microstucture, of which the dendrite riches in Ta and Nb, and the interdendrite zone riches in Hf, Zr and Ti. The repassivation rates of these four alloys in high-temperature pressurized water may be ranked as the following sequence: TaNbHfZrTi＞Co1.5CrFeNi1.5Ti0.5Mo0.1＞690TT＞AlCoCrFeNiSi0.1.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The dissimilar metal weld joint (DMWJ) in primary water system of pressurized water reactors (PWRs) has been proven to be a vulnerable component owing to its proneness to different type of flaws. Thus, maintaining integrity of such joint in case of defect presence is of great importance to the design and safe management of nuclear power plants (NPPs). For a reliable integrity analysis of DMWJ, it is essential to understand the microscopic characteristics in all regions of the joint. In this work, OM, TEM, SEM, durometer, AFM, MFM and SKPFM were utilized to investigate the microstructure, micro-hardness and the distribution of main elements, grain boundary characteristic and residual strain in the A508/52M/316L DMWJ that used for connecting the pipe safeend and the nozzle of reactor pressure vessel in PWRs, and a comparative analysis about the microstructure and property along the radical direction of the DMWJ was obtained. The results showed that there was no region that differed from the other part of the weldment in terms of the microstructure and micro-hardness dramatically. A layer of fine grain resulting from unmelted filler metal was found in the backing weld part of the joint. The residual strain in the heat affected zone (HAZ) of 316L was higher than that in other regions. Meanwhile, drastic variations in the microstructure, chemical composition distribution and grain boundary character distribution (GBCD) in both the 316L/52Mw and the 52Mb/A508 interface regions were observed. The analyses using TEM and MFM test showed that a large number of chromium and molybdenum-rich precipitates particles distributed both along the grain boundaries and inside grains in the 316L base metal, which were identified to be precipitates with complex elementary composition rather than the normal string delta ferrite in 316L austenitic stainless steel. The SKPFM test result indicated that these precipitates were more prone to be corroded than the base metal. Therefore, further investigation about the cause of deformation and the impacts to the corrosion resistance, particularly the stress corrosion cracking (SCC) sensitivity of the precipitates needs to be carried out.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The electropolished (EP) alloy 690TT samples were first oxidized in the simulated B and Li containing primary water with 2.5 mg/L H2 at 325 ℃ and 15.6 MPa for 720 h, and then half of the samples were continuously immersed in this solution with 2.0 mg/L O2 for another 720 h. The microstructures and chemical composition of the oxide films formed under the above two conditions were analyzed. The results show that the dual layered oxide film formed under the single hydrogen water chemistry is mainly composed of spinel oxides. The outer layer is composed of big oxide particles rich in Ni and Fe and the underlying loose needle-like oxides rich in Ni. The inner layer is continuous Cr-rich oxides. The oxide film formed on EP alloy 690TT under the hydrogen/oxygen water chemistry also shows a dual layered structure. The surface morphology and chemical composition of the outer layer are similar to the oxide film formed under the hydrogen water chemistry. However, the inner layer is changed to the nano-sized NiO. The stable phase region in the potential-pH diagram for the Ni oxides is enlarged by the later dissolved oxygen. As a result, the oxygen promotes the fast growth of the outer needle-like oxides rich in Ni. Further, the oxygen promotes the dissolution of the inner Cr-rich oxides formed under the hydrogen water chemistry and increases the corrosion rate of the EP alloy 690TT. Electropolishing treatment can not reduce the corrosion rate of alloy 690TT in the simulated primary water with sequentially dissolved hydrogen and oxygen.
Subjects: Biology >> Ecology submitted time 2018-05-29 Cooperative journals: 《生态学报》
Abstract：植物群落高度是反映植物群落特征的重要指标，植物群落高度的测定能给植物群落多样性分析、生物量估算、功能形状研究提供重要的数据基础。传统的森林调查主要由生态调查工作者通过目测或者利用激光测高仪对每个个体进行逐一测定，因此劳动强度大，耗时费力，并且难以进行大面积的植物群落高度调查。近年来，随着无人机（Unmanned Aerial Vehicle，UAV）技术的飞速发展，催生了无人机低空摄影测量和遥感技术，该技术已被应用于农作物植株高度测定和生物量估测等。然而针对植被类型多样、树木种类繁多且地形复杂的山区如何精确的获取植物群落高度仍然是一个较大挑战。以缓坡地形的云南大学呈贡校区为研究区，选取校区内人工种植的雪松（Cedrus deodara（Roxb.） G.Don）林为研究对象，利用无人机搭载可见光相机平台获取研究区近地面航空影像，利用高分辨的影像匹配加密获得的点云数据生成数字表面模型（Digital Surface Model，DSM）。依据点云分类提取非植物类点，消除少数因植被与非植被相接的边缘模糊而错分类的部分，内插后生成数字地面模型（Digital Terrain Model，DTM）。将DSM和DTM叠加相减得到树木高度变化模型（Canopy Height Model，CHM），即获得研究区各个雪松的高度。然后利用激光测距仪测定研究样地内100棵雪松的高度，将此测定的树高与无人机航测技术生成的CHM模型测定的树高值进行精度检验。结果表明无人机测定的树高值与激光测距仪测定的树高值线性拟合度较高，r2值在0.904以上。此方法基于无人机影像生成空间模型，提取树高，受外界环境因素影响较小，且成本较传统测树方法低廉，可广泛运用于各种植物群落的调查研究当中，有极好的应用前景。
Subjects: Materials Science >> Materials Science (General) submitted time 2017-03-31 Cooperative journals: 《金属学报》
Abstract：采用数值模拟方法对核电站316L不锈钢弯头的应力腐蚀裂纹扩展行为进行了研究。首先针对不锈钢厚壁弯头(外径355.6 mm，内径275.6mm)进行有限元建模,在弯头内壁上创建出与实际裂纹相符的半椭圆状3D缺陷作为裂纹形状,其裂纹张开位移 (δi) 由Dugdale模型计算确定;然后根据有限元计算结果,建立裂纹应力强度因子 (K) 随裂纹深度 (d) 及附加应力 (P) 变化的拟合公式,结合实验数据得到管材在两种冷变形量下的应力腐蚀裂纹扩展速率 (da/dt) 拟合公式,利用迭代方法计算了裂纹穿透管壁所需的时间，为核电站安全评估提供了有效依据.研究显示，当弯头部位的冷变形量较小（硬度为230~245 HV）且在理想情况下 (无初始附加应力) 弯头被应力腐蚀裂纹穿透耗时最长 (约57 a)，当初始附加应力增加至200 MPa此失效时间约缩减至前者的1/5 (无应力释放)、2/7 (应力释放一半) 以及3/7 (应力完全释放)；保持初始附加应力不变(200 MPa)并提高弯头部位冷加工变形量(由硬度为230~245 HV提高到275~300 HV)，弯头的大变形部位被穿透时间约缩短至小变形部位失效时间的2/5（无应力释放）、3/8 (应力释放一半)以及1/3 (应力完全释放)，由此可见应力释放程度的降低和冷加工变形量的增加均导致了核电站316L不锈钢弯头剩余寿命的缩短。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：利用光学显微镜、扫描电子显微镜（配有能谱仪及背散射电子衍射附件）、显微硬度仪、微小试样拉伸试验及慢应变速率拉伸实验对国产带热丝隔离层核电安全端焊接件不同部位的微观结构及局部的力学性能和应力腐蚀敏感性进行了分析研究。发现，在SA508-52Mb界面处的52Mb中具有大量的对应力腐蚀敏感的I型晶界及II型晶界，导致此界面具有最高的应力腐蚀敏感性；SA508热影响区存在明显的组织过渡；316LN热影响区中随着距熔合线距离的增加，CSL的数量分数逐渐增大，Σ3晶界与理想的Σ3晶界的偏差角减小，残余应变逐渐减小，残余应变的最高值出现在对接焊底焊位置处的316LN热影响区中，导致316LN的热影响区也具有较高的应力腐蚀敏感性。焊接件不同部位的性能存在较大的差异，主要是由不同部位的微观结构差异引起的。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用金相显微镜、透射电镜(TEM)、扫描电镜(SEM)、显微硬度仪、原子力显微镜(AFM)、磁力显微镜(MFM)、扫描开尔文探针(SKPFM)等微观分析手段，分析了先进压水堆核电站反应堆压力容器安全端异种金属焊接接头A508/52M/316L的金相组织、显微硬度、主要合金元素、晶界类型以及残余应变的分布，并对比了整个焊接接头不同厚度上的组织和性能。研究结果表明焊缝深度方向上组织和硬度没有显著差别，底焊位置出现一层因动态再结晶形成的细小等轴晶，在316L母材热影响区（HAZ）内残余应变较焊接件其他位置高，熔合线附近具有复杂的微观结构、显微硬度、晶界类型、元素成分和残余应变分布。TEM和MFM分析表明母材316L基体内有富Cr、Mo元素的颗粒状析出相，SKPFM的结果显示该析出相伏打电势较基体更负，因而更不耐腐蚀。析出相的形成原因以及对安全端耐蚀性能的影响，尤其是对应力腐蚀（SCC）敏感性的影响有待进一步研究。
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