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摘要： Wise 天文台是由以色列特拉维夫大学 (Tel Aviv University)拥有并运营的天文研究机构.它位于以色列的内盖夫 (Negev)沙漠中,距离最近的城镇也有5 km;这种独特的地理位置意味着,这里的夜空全年大多数时间晴朗无云,并且远离光污染的影响.

关键词： 3D printing   additive manufacturing   composites   conducting polymers   mechanical properties  

摘要： 3D printed polylactic acid (PLA) composites reinforced with zinc oxide (ZnO) were successfully fabricated by attaching a ZnO dispenser beside a MendelMax RepRap Printer. Mechanical and electrical testings were performed to characterize the properties of PLA/ZnO and cPLA/ZnO composites. PLA polymer filament is a biodegradable material with the same strength and modulus as other plastic materials. This work emphasizes the effects of printing parameters (infill density and raster angle) on the mechanical properties and electrical conductivity of PLA/ZnO composites. The combination of 100% infill density and 0 degrees raster angle resulted in a substantial increase in the tensile strength and Young's modulus, but reduction in break elongation. As the infill density increased and shifted from 90 degrees to 0 degrees raster angle, the storage modulus was enhanced but the damping factor declined. Scanning electron microscope images proved ZnO was dispersed in the PLA matrix. Optical measurements showed a large air gap across the 35% compared to the 100% infill density. Conductive PLA composites (cPLA/ZnO) enhanced electrical conductivity when increasing infill density compared to PLA composites. Therefore, optimizing printing parameters could help manufacturers provide superior quality structure and cPLA composites for electrical and electronic applications due to good electrical conductivity.

关键词： Cavity ring down spectroscopy   Distributed feedback lasers   Laser induced fluorescence   Laser systems   Tunable lasers   Ultraviolet lasers  

摘要： We report the development of an optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) instrument for OH detection at 2.8 mu m using a DFB diode laser. Two different approaches, symmetry analysis and wavelength modulation, were performed to achieve laser frequency locking to the cavity mode. Compared with the symmetry analysis method, the wavelength modulation method continuously locked the laser frequency to the cavity mode and eliminated decoupling the laser from the cavity mode. A detection sensitivity of 1.7x10(-9) cm(-1) was achieved in a 25 s sampling time and was about 3 times better than that of the symmetry analysis method. The corresponding OH detection limit was similar to 2x10(8) molecule/cm(3). Further improvement can be achieved by using higher reflectivity mirrors and other high-sensitivity approaches, such as frequency modulation spectroscopy and Faraday rotation spectroscopy. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： 脑白质高信号   扩散张量成像   异质性  

摘要： 目的 探讨使用扩散张量成像(DTI)辨别不同类型的脑白质高信号(WMH).方法 对73例WMH患者和18例健康志愿者(对照组)行DTI检查,比较额叶、枕叶、顶叶脑室旁和额顶叶半卵圆中心正常脑白质和WMH的各DTI参数.结果 不同部位DTI参数的变化幅度有差异,与正常脑白质相比,额叶Fazekas 1级WMH的部分各向异性(FA)值降低更明显,平均扩散率(MD)、纵向扩散率(AD)和径向扩散率(RD)的增高也更明显,其中RD的变化程度高于AD.结论 DTI可显示不同部位WMH的异质性,额叶WMH与其他部位的有明显的不同.

关键词： Liquid crystal devices  

ISBN: (数字)9781119667940 ISBN: (纸本)9781119667919

摘要： LIQUID CRYSTAL DISPLAYS THE NEW EDITION OF THE GOLD-STANDARD IN TEACHING AND REFERENCING THE FUNDAMENTALS OF LCD TECHNOLOGIES This book presents an up-to-date view of modern LCD technology. Offering balanced

关键词： 课堂内外   征文比赛   我们去哪儿   期末考试   旅游   优秀作品   好奇   秘密  

摘要： 本文为课堂内外“创星小作家”活动2022年1月征文比赛优秀作品期末考试考完就放寒假了。我一直对妈妈之前的话念念不忘——她说,放了寒假就带我和弟弟一起去旅游。但妈妈没说带我们去哪儿旅游,这让我非常好奇。一考完试,我就死缠烂打地问妈妈我们到底去哪儿旅游,妈妈总是笑着说:“这是个秘密。”为了研究这个“秘密”,我暗地里展开了调查。

关键词： 光强模拟   杨氏双缝干涉   MATLAB仿真  

摘要： 从双光束叠加原理和傅里叶光学的角度分析了杨氏双缝干涉实验中光强分布的计算方法,从傅里叶光学的角度运用MATLAB对光强分布进行了模拟计算。结果表明,在近场条件和远场条件下,菲涅耳衍射公式模拟结果与实验现象相吻合,双光束干涉的光强公式模拟结果只有满足远场的条件下与实验现象一致。通过对缝宽与缝间距的设置,进一步明确了干涉与衍射的联系。

关键词： 1/4对称度量联络   Kenmotsu流形   Eisenhart问题  

摘要： 利用张量分析方法,结合Kenmotsu流形的结构方程,考虑关于1/4对称度量联络平行的对称(0,2)型张量场的Eisenhart问题,在适当条件下证明该张量场必为度量张量的常数倍,并给出一个Ricci对称的Kenmotsu流形为Einstein流形的充要条件.