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1. chinaXiv:202006.00194 [pdf]

常见遥感干旱监测指标在哈萨克斯坦的一致性分析

孙博; 钱静; 陈曦; 邢秀为; 周启鸣
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

利用主被动微波卫星(SMAP)土壤含水量数据,从相同空间尺度上对比了全球在运行系统中3种常见遥感干旱指数[距平植被指数(AVI)、植被健康指数(VHI)、植被供水指数(VSWI)]在哈萨克斯坦农业干旱监测上的一致性。通过皮尔森相关系数(r)和肯德尔秩相关系数(τ),分别检验干旱指数与土壤含水量及其在干旱等级判断上的相关性,以评估遥感在哈萨克斯坦作物生长季中后期干旱监测中的适用性。结果表明:不同干旱指数在该地区一致性不高。基于植被状况的遥感干旱指数与土壤含水量相关性较低,而结合植被和地表温度的综合指数具有显著正相关。不同土层比较上,VSWI指数与作物根区(0~100 cm)土壤含水具有较强相关性(r>0.6),表明其对植物生长季中后期的土壤含水状况有较好的响应能力。

submitted time 2020-06-21 From cooperative journals:《干旱区研究》 Hits53Downloads34 Comment 0

2. chinaXiv:201803.00958 [pdf]

PIK3CA and AKT2 mutations of gastric cancer in China

wenxiang cheng
Subjects: Biology >> Genetics

Mutations in PI3K and/or AKT have been reported in a variety of cancers. This indicates that the two pathways interact to cause cancer. We have therefore investigated their roles in gastric cancer (GC) in China. In our study, exons 9, 18 and 20 of PIK3CA gene and exons 6~14 of AKT2 gene were screened in 10 GC cell lines and 100 advanced primary GC together with matched normal tissues. Denaturing high performance liquid chromatography (DHPLC) and DNA sequencing were used to analyze the mutations in the two genes. Two point mutations in the PIK3CA gene were identified in 4 of 10 GC cell lines and in 4 of 100 GC primary tumors. Two polymorphisms in AKT2 were detected in 19 of 100 GC primary tumors. One point mutation in AKT2 was detected in 1 of 10 GC cell lines and 3 of 100 GC primary tumors, and no hot spot variation was detected. Our results indicate that PIK3CA and AKT2 mutations are found in GC, although not a common event, therefore they might still play an important role in mediating kinase activities towards gastric carcinogenesis.

submitted time 2018-03-16 Hits1418Downloads718 Comment 0

3. chinaXiv:201803.00577 [pdf]

Effects of tetracyclines on bone: an ambiguous question needs to be clarified

wenxiang cheng
Subjects: Biology >> Biochemistry

Tetracyclines have been widely used in bone histomorphometry to label new bone formation and apposition rate. However, most studies of tetracyclines have also shown their strong inhibitory action on osteoclasts and their effects on osteoblast activities as well. To even obtain the in-depth understanding on this issue, we have reviewed related studies in “Pubmed” by searching the keywords “tetracyclines and osteoclast”, “tetracyclines and osteoblast”, which retrieved 115 and 159 related documents, respectively. Among these papers, some described the application of tetracyclines as fluorescent marker in bone histomorphometry, while others discussed their role in protection of bone metabolism partly through inhibiting osteoclastogenesis or bone resorption and through enhancing osteogenesis. Based on the above mentioned, it seems that tetracyclines used as bone labeling markers may affect the results of bone histomorphometry to some extent. To even confirm the effect of tetracyclines on bone cells (osteoblast, osteoclast) and in vivo bone remodeling, related research work has been performed in our research team which indicated quite different results in vivo and in vitro. Therefore, the influence of tetracyclines on bone may differ in terms of different conditions which need to be further elucidated as well.

submitted time 2018-03-15 Hits1771Downloads721 Comment 0

4. chinaXiv:201803.00584 [pdf]

一种新型Micro-CT系统设计

张志诚; 梁晓坤; 朱轩玉; 李维振; 谢耀钦
Subjects: Engineering and technical science >> Biomedical Engineering

传统的 CT 设备由于受到系统架构的物理限制,导致最终扫描结果中运动伪影影响很大,本文依据碳纳米管的场致发射原理设计出一套工作在准静态模式下的显微CT。该系统采用 35 个碳纳米管 X 射线光源和 5 个探测器,相对于传统 CT,通过外部时序控制减少了机架的机械旋转次数和行程,大大降低了运动伪影的影响。由于重建角度是稀疏的,因此通过采用迭代重建算法模拟仿真验证了该系统的有效性。

submitted time 2018-03-15 Hits2902Downloads1488 Comment 0

5. chinaXiv:201803.00580 [pdf]

城市大气环境的高保真度数值模拟

Yan Zhengzheng
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

对于城市大气环境模拟问题,高保真度往往意味着庞大的计算量,几何多尺度、高雷诺数等因素致使其求解非常具有挑战性,对计算机的硬件与算法都有极高的要求。寻求稳定、可扩展的高效并行数值算法以获取时效性强且可置信的数值结果是数值模拟的关键所在。基于国产大规模计算系统平台,本文通过对大规模非线性系统进行高效求解器和预处理技术的研究,提出一种可扩展并行Newton-Krylov-Schwarz算法。非线性方程采用非精确Newton方法进行求解,在每个Newton步,Jacobian系统通过基于区域分解方法的限制加性Schwarz 预 条件子处理,然后使用以GMRES方法为代表的Krylov子空间迭代法作为线性求解器进行求解。作为应用,我们对深圳地王大厦附近约一平方公里区域进行大气流场进行计算。数值结果显示,本文的算法在扩展至万核处理器平台时仍具有非常良好的可扩展并行性能,为未来对整个城市区域进行高精度(如网格分辨率达到米级,未知数个数达十亿量级)的大气环境模拟提供了一种可参考的算法。

submitted time 2018-03-15 Hits5439Downloads839 Comment 0

6. chinaXiv:201803.00581 [pdf]

一种求解汽车外流问题的可扩展数值算法

Yan Zhengzheng
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

受车型复杂、雷诺数高等因素影响,汽车外流场流动的数值计算规模巨大且难以精确求解。发展高效并行算法以利用超级计算平台资源成为该领域的研究热点。本文提出一种全隐格式的可扩展并行Newton-Krylov-Schwarz算法对某真实汽车的外流场流动问题进行计算,并与商业软件计算结果进行对比。数值结果显示,本文的算法在超过2000个处理器规模下仍具有很好的并行可扩展性。

submitted time 2018-03-15 Hits3050Downloads743 Comment 0

7. chinaXiv:201803.00583 [pdf]

基于静息态fMRI的催眠控制呼吸研究

刘燕君; 李荣茂; 臧珊珊; 陈思宇; 谢耀钦
Subjects: Biology >> Neurobiology
Subjects: Engineering and technical science >> Biomedical Engineering

催眠是一种被证明有效的、无害的心理学上的呼吸控制方法。文章通过对 13 位有催眠背景的心理咨询师被试进行催眠控制呼吸实验,由催眠师引导被试进行催眠,运用静息态功能磁共振的方法来研究催眠控制呼吸状态下脑功能的异常。结果显示:在催眠状态下,脑活动在视觉皮层(枕叶)、感觉运动皮层(中央前回、中央后回、布洛德曼 4、6 区)、后扣带回以及颞中回上升;在背外侧前额皮层、小脑后叶以及缘上回下降,并且在全脑大规模静息态功能网络范围内相关关系增强(正常态 r=0.64,催眠态 r=0.80)。此外,催眠状态下视觉皮层与运动皮层之间的功能连接增强。研究结果表明,视觉皮层和运动皮层在催眠控制呼吸的神经机制中发挥了重要的作用,其神经机制也可能与认知处理和感知处理密切相关。本研究结合了心理学以及脑科学进行了研究,为催眠的研究提供了一个认知脑科学的研究新视觉。

submitted time 2018-03-15 Hits3634Downloads1902 Comment 0

8. chinaXiv:201803.00582 [pdf]

一种基于ROEWA算子的改进CV模型用于乳腺超声图像分割

刘磊; 温铁祥; 秦文健; 李凌; 辜嘉
Subjects: Biology >> Bioengineering

基于区域的几何活动轮廓(Chan-Vese, CV)模型是乳腺超声图像常用的一种分割算法。但传统的CV模型不能满足乳腺超声图像分割精度高、速度快的要求。因此,文章提出了一种基于指数加权平均比率(Ratio of Exponential Weighted Average,ROEWA)算子改进的CV模型,用于乳腺超声图像中病灶区域的分割。首先,计算乳腺超声图像的ROEWA算子。其次,基于图像的ROEWA算子构建边缘指示函数,用于代替CV模型中的Dirac项。最后,去除平滑项,从而提高曲线演化的速度。实验结果表明,文章提出的算法不仅能提高分割的精度,而且能显著提高分割的速度。

submitted time 2018-03-15 Hits1290Downloads727 Comment 0

9. chinaXiv:201803.00572 [pdf]

Analysis of Meshing Characteristics of Pins and Pin Housing Integral Structure in Cycloidal Planetary Drive-1.doc

王钰堃
Subjects: Mechanical Engineering >> Mechanical Design

Precision reducer is one of the key parts of an industrial robot, which generally incorporates cycloidal planetary drive. Engagement of the cycloidal wheel and the pins causes rolling friction between the wheel and the pins as well as sliding friction between the pins and the pin housing in the traditional cycloidal transmission of the reducer. In this paper, we present a new kind of design to make the pins and the pin housing a whole structure, thereby the cost of manufacturing and assembly can be significantly reduced. And in this new structure, we only need to consider sliding friction between the cycloidal wheel and the unibody of the pins and pin housing. The difference between the new structure and the conventional structure in the meshing properties was given. In addition, we used finite element method to analyze the friction and contact stress between the cycloidal wheel and the pins in the actual working condition, and compared it with the traditional structure. The simulation results proved the feasibility of the new structure and provided a theoretical basis for further design and manufacturing of this new kind of cycloidal planetary drive structure.

submitted time 2018-03-14 Hits1624Downloads909 Comment 0

10. chinaXiv:201803.00567 [pdf]

生物阻抗技术在手臂红外治疗中的初步应用研究

顾陈磊; 刘宇航; 李景振; 王磊; 聂泽东
Subjects: Biology >> Bioengineering

红外理疗采用红外光对人体部位进行照射,已在各种疾病的辅助治疗中得到了广泛的应用。红外理疗效果一般由医护人员的经验进行定性评估,目前鲜有关于红外理疗效果定量分析的报道。鉴于理疗身体部位血流信息的变化能反映红外理疗效果,实现无创、安全、实时监测红外理疗过程中的血流信息,将有助于引导红外理疗的疗程安排,提升红外理疗效果。文章提出了一种基于生物阻抗的方法来对手臂血流红外理疗效果进行评估。首先,选用BIOPAC生理信息记录仪为系统核心,利用二电极法测量人体心电信号,四电极法同步测量人体手臂在红外光照射前、中、后的生物阻抗变化;其次,通过小波变换进行基线漂移去除与特征提取分析,并运用朴素贝叶斯模型对特征点的稳定性进行评估。实验结果表明:手臂生物阻抗信号特征频率与心率变化趋势相同,平均数值误差在0.09%~1.60%;经红外光照射后,手臂生物阻抗单周期信号内次级波与主波比值上升,幅度为3.91%~13.05%,即生物阻抗信号能够反应手臂血流信息,且具有感知红外理疗过程中血流变化的灵敏性。

submitted time 2018-03-14 Hits1716Downloads927 Comment 0

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