Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Advanced aero and power generation industry needs high-performance gas turbine. As key parts of gas turbine directionally solidified (DS) columnar grain and single crystal (SX) blades operate in heavy stress and high temperature conditions. The continuous demand for increasing turbine inlet temperature and aggressive environment has pushed alloy designers to develop DS and SX Ni-based blade alloys that contain high amount of alloying elements. DS process of blades using such alloys has become a challenging task. The small DS and SX blades are usually produced by high rate solidification (HRS) process. However, the growth of large DS and SX blades requires directional solidification with a sustained thermal gradient along the DS direction. By increasing the thermal gradient, the dendrites are refined, which results in a mechanically-superior DS and SX with reduced defects. One method to achieve consistent and higher thermal gradients is the utilization of the liquid metal cooling (LMC) process. In this method, heat extraction from the outer surface of the mold during DS relies on heat conduction rather than radiation in the conventional HRS process. The optimization of the LMC process is difficult and costly by experimental methods, especially for the complexly shaped industry gas turbine (IGT) blades because of the complicated process parameters associated with the technique. Numerical simulation is an efficient method to solve this problem. In this work, directionally solidified industry gas turbine hollow blades were prepared by high gradient LMC process. Liquid Sn was used as cooling medium. The temperature fields, macrostructures, primary dendrite arm spacing (PDAS) at various withdrawal rates during LMC process have been calculated with ProCAST software. The impact of withdrawal rate on formation of stray grains and freckles was predicted. The calculated results and the experimental observations agreed well. The solidification rates and cooling rates were found to increase with the increase of withdrawal rate. The axial thermal gradient was high and stable during the LMC process. It was found that stray grains would not block the growth of original grains at optimized withdrawal rate. No freckles were observed in the industry gas turbine hollow blades prepared by LMC technique due to the high cooling rate. Though the mean diameters of columnar grains in LMC blades were almost identical to that observed in HRS blades, the PDAS were more than 50% refined in LMC blades than those in HRS blades.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni- based single crystal superalloys have been widely used for blades and vanes in gas turbine. However, recrystallization (RX) induced by residual strain has been a serious problem for the application of single crystal superalloys. In previous work, effect of microstructure, such as g', g/g' eutectics and carbides, as well as heat treatment parameters, on the RX behavior have been studied. However, the effect of alloy elements on the RX behavior has rarely been reported. Therefore, in this work, the effect of the important solution strengthening elements, W and Re, on the deformation and RX of solution heat treated Ni-based single crystal superalloys was investigated. At first, two single crystal superalloys were prepared, and W and Re were added into one alloy among them. After solution heat treatment, these two single crystal superalloys were deformed by shot-peening or Brinell indentation. Then these deformed samples were heat treated to observe the microstructure of RX. It indicated that RX depth decreased with the addition of W and Re irrespective of deformation mode and heat treatment temperature. Short time heat treatment experiment of indented and shot-peened samples both indicated that incubation period of RX was prolonged and nucleation of RX was slowed with the addition of W and Re, which verified that RX was suppressed by W and Re. After shot-peening, micro-hardness of the alloy with W and Re increased, but the depth of deformation zone was obviously reduced. Higher density of dislocation was found in the single crystal superalloy with W and Re, and also lots of dislocation tangles were observed. So, in this alloy, dislocation annihilated slowly, that is, recovery was slowed down, which prolonged the incubation period of RX. During the process of RX grain growth, the maximum RX grain boundary migration velocity was reduced with the addition of W and Re. Moreover, the change of mean RX grain boundary migration velocity showed the same trend with the micro-hardness along the direction of RX depth.
Subjects: Biology >> Botany submitted time 2022-11-24 Cooperative journals: 《广西植物》
Abstract：
‘Hongxia’, a Yunnan flowering cheery cultivar blooming in March with semi-double to double pink petals, have been widely cultivated in central Yunnan thanks to its high ornamental value. It was regarded as the cultivar of Cerasus cerasoides var. rubea. However, it were clustered in C. campanulata based on molecular markers. Therefore, the phylogeny of these cultivars are doubtful, which is not conducive to their breeding and cultivation. In order to explore the origin of ‘Hongxia’,with leaf DNA of ‘Hongxia’ as materials, we used Illumina sequence, and then assembled, annotated, and analyzed by bioinformatic methods, Analysis of chloroplast genome characteristics was used by MISA and Genious R10. The phylogenetic tree of Cerasus was reconstructed by using RAxML 8.0. The phylogenetic relationship of ‘Hongxia’ in Cerasus was analyzed.. The results were as follows: (1) The chloroplast genome of ‘Hongxia’ was 157 832 bp in length, containing a pair of reverse repeat regions (Inverted Repeat Sequence，IR, 26 381 bp), which were separated by a small single copy region (Short Single Copy, SSC, 19 120 bp) and a large single copy region (Long Single Copy, LSC, 85 950 bp). A total of 128 genes were encoded, including 84 protein-coding genes, 36 tRNA genes and 8 rRNA ribosomal genes. The overall Guanine (G) and Cytosine (C) content of genome was 36.73%; (2) Based on the maximum likelihood phylogenetic tree analysis of 16 chloroplast genome of Cerasus, it was found that ‘Hongxia’ was formed as sister to C. subhirtella and C. yedoensis, and was far away from C. cerasoides. It has been reported that ‘ Hongxia ’ and similar cultivars were clustered in C. campanulata, rather than C. cerasoides based on the nuclear DNA. Therefore, we speculated that ‘ Hongxia ’ may be a hybrid cultivar of C. campanulata and C. subhirtella or C. yedoensis, rather than the cultivar of C. cerasoides. The above results will be useful for studies of the origination and genetic breeding of ‘ Hongxia ’ , as well as the cultivar identification and classification of C. cerasoides.
Subjects: Geosciences >> Other Disciplines of Geosciences submitted time 2019-09-11 Cooperative journals: 《干旱区地理》
Abstract：基于山西省24个气象站点1960—2016年逐日最高、最低、平均气温数据，运用线性倾向估计法、Mann-Kendall非参数检验法、Morlet小波分析等方法，分析了山西省近56 a“数九”时节气温的时空变化特征。结果表明：（1） 近56 a山西“数九”时节气温均呈上升趋势，其中平均最高气温上升趋势最大，约为0.5 ℃·（10 a）-1。就平均气温变化而言，“五九”变化趋势最大，约为0.703 ℃·（10 a）-1，就分布而言，“四九”值最低，“五九”开始回暖，“六九”回暖幅度最大。20世纪90年代前后各“九”各项平均气温对比发现，最低值延后，回暖时间提前，“数九”冷期缩短。（2） “数九”时节气温高值区主要集中在晋南山间盆地、河谷区，以运城盆地最为明显，低值区主要分布于以晋东北五台山为中心的山地丘陵区，增温幅度分布情况大致与此相反。（3） 在1990年左右气温均出现暖突变，平均最高气温突变前后变化最大，约为1.73 ℃。（4） 气温周期变化明显，均存在4~8 a短时间尺度周期。本研究填补山西省 对“数九”时节气温变化研究的空白，为山西省气候资源评价和农业生产布局提供科学依据。
Subjects: Medicine, Pharmacy >> Preclinical Medicine submitted time 2017-12-07 Cooperative journals: 《南方医科大学学报》
Abstract： Objective To establish a mouse model bearing human choriocarcinoma xenograft in severe combined immuno-deficient (SCID) beige mice and investigate the disease course and biological behaviors of the tumors．Methods Human choriocarcinoma JAR cells were injected in female SCID beige mice (3-5 weeks old) either subcutaneously (group A, n= 6) or via the tail vein (group B, n=6). Morphological studies, radioactive immunoassay, in vivo tumor imaging and histopathological examinations were performed to confirm JAR cell engraftment at the subcutaneous injection site and in the lungs of the mice. Results On day 28 after tumor cell inoculation, the mice in group A showed palpable subcutaneous nodules, and HE staining revealed morphological features of the nodules consistent with choriocarcinoma cells; in vivo imaging in group B showed single or multiple solid tumor masses in the lungs, and tissue biopsy examination demonstrated varying degrees of tumor cell infiltration. Compared with the control mice, peripheral blood β-HCG levels in both groups A and B increased significantly on day 14 after cell inoculation (P<0.05), and the increment was more conspicuous in group B (P<0.05). Conclusion Mouse models bearing human choriocarcinoma xenograft can be successfully established by injecting JAR cells either subcutaneously or via the tail vein to mimic the characteristics of epithelial solid tumors and lung metastasis of human choriocarcinoma.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用高温度梯度定向凝固-液态金属冷却(LMC)技术制备了重型燃机定向结晶空心高压涡轮叶片，采用ProCAST有限元模拟软件计算了LMC定向凝固工艺下，不同抽拉速率时空心定向结晶叶片凝固过程的温度场、晶粒组织以及一次枝晶间距(PDAS)，预测了抽拉速率对杂晶、雀斑等缺陷的影响。结果表明，模拟结果与实验结果吻合良好。随着抽拉速率增加，叶片的凝固速率、冷却速率均增加，远高于高速凝固法(HRS)的凝固速率、冷却速率；叶片不同部位达到最大纵向温度梯度时的抽拉速率不同，纵向温度梯度是评价定向工艺的有效方法；LMC工艺制备的燃机叶片消除了雀斑缺陷，PDAS远小于HRS工艺。
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： In order to choose the best detection efficiency of different formations, quantitative evaluation of different formations shall be employed. In this paper, the existing evaluation parameters of four-point cooperative detection are analyzed and summarized and then based on the definition of volumetric tensor, the five-point formation is divided into five tetrahedrons and one main tetrahedron plus a fifth point to evaluate the detection efficiency. Finally, orbit data of five-spacecraft in one orbit period is used to simulate and analyze the two methods, and result shows that the method works well in evaluating five-point formation.
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