Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： As a solid state technology, friction stir welding (FSW) has been used to join titanium alloys for avoiding the fusion welding defects. So far, many previous studies have attempted to elucidate the microstructure characteristics and evolution during the FSW process of titanium alloy, but few are about the mechanism of microstructure transformation along the thickness direction of joint. For solving this problem, in this work, 2 mm thick TC4 titanium alloy is successfully welded by FSW. On the basis of numerical simulation, the effects of temperature distribution on the microstructure along the weld thickness direction and the tensile strength of welding joint were investigated. The results show that the peak temperatures of material close to weld surface exceed β phase transus temperature under the rotational speed of 300 r/min and the welding speed of 50 mm/min. With the increase of distance away from the weld surface, the peak temperature decreases. The peak temperature of weld bottom near the backing board is difficult to be higher than β phase transus temperature owing to quick heat radiation. The region, where the peak temperature is higher than b phase transus temperature, consists of primary a, lath-shape a and residual β phases. The size of lath-shape a inside the weld is larger than that near the weld surface. Primary a and b phases with smaller size are attained in the weld bottom owing to the dynamic recrystallization, and the distribution of b phase on primary a matrix is more homogeneous. When the rotational speed reaches 350 r/min, the area where the peak temperature is higher than β phase transus temperature becomes wider along the thickness direction, which makes the size and quantity of lath-shape a phase increase and then the lath-shape a clump appears. Lathshape a phase with different orientations hinder the propagation of crack and be beneficial for the tensile strength of FSW joint.
Subjects: Astronomy >> Astrophysical processes submitted time 2020-05-06 Cooperative journals: 《天文研究与技术》
Abstract： 为充分利用丽江2.4米望远镜有限的卡焦接口，提高观测效率，研制了一个双视场天文观测终端，在2.4米望远镜上实现不同视场和图像比例尺等参数，进行快速测光和高分辨成像等天文观测，以满足天文学家的不同观测需求。针对该终端对滤光片轮精度和大视场光路与小视场光路切换的精度要求，以及对EMCCD相机图像采集的速度要求，本文采用三层电机闭环控制以及多线程并发执行等技术，实现了该终端中滤光片轮、大视场光路与小视场光路切换的精确控制，以及EMCCD相机图像的快速采集与存储。最后在实验室进行了详细测试，结果表明所设计的控制与图像采集能满足该终端的各项性能指标和功能指标的要求。
Subjects: Biology >> Botany >> Applied botany submitted time 2019-02-25 Cooperative journals: 《广西植物》
Abstract：随着全球气候变化加重，干旱强度和持续时间逐渐增加，严重影响植物生长和作物产量。喀斯特为典型的干旱和高钙生境，植物叶片富集大量的草酸钙晶体，而该晶体与植物的耐旱性之间的关系并不清楚。该文以喀斯特适生植物堇菜（Viola verecumda）为材料，土壤进行自然干旱，分析堇菜叶片的草酸钙晶体变化特征与水分之间的关系。结果表明，在土壤自然干旱条件下，堇菜主要通过细胞内束缚水的游离，维持细胞内水分平衡；而在干旱后期，叶片通过关闭气孔，将部分自由水转变为束缚水，防止水分流失。此外，草酸钙晶体的数量与束缚水含量具有极其显著的强正相关线性回归关系（r=0.825 3，P<0.000 1），意味着草酸钙晶体担当主要的束缚水物质。因此，堇菜植物在耐旱过程中可能协调草酸钙晶体和气孔的生理行为忍耐干旱胁迫。
Subjects: Biology >> Bioengineering submitted time 2018-07-15 Cooperative journals: 《中国生物工程杂志》
Abstract：星形胶质细胞上调基因-1（astrocyte elevated gene-1，AEG-1）在多种肿瘤中过表达，参与肿瘤的形成、转移等过程。本实验利用CRISPR/Cas9技术敲除AEG-1基因并研究其在胶质瘤细胞转移过程中的作用。首先设计构建sgRNA/Cas9二合一表达载体并转染到人胶质瘤U251细胞中，通过TA克隆测序鉴定sgRNA的活性；然后筛选建立稳定的AEG-1敲除U251细胞系，并利用Western blot实验检测AEG-1的敲除效率；最后利用Transwell小室、划痕实验评价AEG-1敲除后对肿瘤细胞迁移能力的影响。结果显示，成功构建靶向敲除AEG-1基因的sgRNA/Cas9二合一表达载体，所构建的载体与实验设计相一致，通过TA克隆测序鉴定sgRNA有活性；成功建立稳定的AEG-1敲除U251细胞系，Western blot实验结果表明敲除效率高达98％；Transwell小室实验、划痕实验结果表明AEG-1敲除U251细胞系的转移能力明显降低。
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