A Novel Tunable Dual-frequency Laser with Large Frequency Difference

This paper proposed a novel tunable dual frequency laser with large frequency difference,which used LD to pump the Nd∶YAG microchip in the end surface and put the liquid pressure on the radial direction of the crystal by a pressure-transporting thin film. As a result of the stress birefringence, there was a mode splitting phenomenon of the microchip laser longitudinal mode. Both theoretical analysis and experiments indicated that there is a directly proportional relation between the frequency difference and the pressure, so the tunable frequency difference could be obtained when the pressure was changed. A large frequency difference of about 3.4 GHz with linear tunable relation was achieved in the experiment,so it can be a practical light source for the absolute distance interferometry.     

从不纯样品的光谱中提取单一组分和结构的拉曼谱

X射线衍射谱和拉曼光谱均证实所用的SiC和GaN样品为不纯的非晶样品。通过新采取的减去经加权的“杂质”光谱的方法,从不纯的非晶样品的拉曼光谱中获取了纯非晶SiC和GaN的拉曼光谱,并由理论计算的声子态密度与减去“杂质”光谱的拉曼光谱很好相符,进一步证实减去“杂质”光谱的拉曼光谱确实是非晶拉曼光谱,从而表明新采用的扣除加权“杂质”光谱的方法是正确和具有广泛应用价值的。     

一种估算热导率的方法

径向热导率是金刚石膜应用中的一项主要技术指标.本文介绍了一种通过热导率和X衍射晶面图间相关性估算直流电弧等离子体喷射化学气相沉积金刚石膜径向热导率的方法.该方法需满足的条件为(111)为主的三向系中(220)和(311)的CPS值分别是23～33;和8～15;,或者是在四取向膜中要求(400)的CPS值低于5;.估算值的最大偏差为-9.5;和3.5;.当(220)的CPS值高时或(311)的CPS值低时,估算值比测量值高,反之亦然.     

薄型超声电机与定子振动模态的激发

论述了薄型超声电机的工作机理。分析了电机压电片的布置与激励信号的关系，探讨了定子弯曲模态的激发问题。设计并制作了一种新的薄型超声电机。电机转子安装在圆环定子内，能够显著减小电机厚度，电机定子采用双压电片结构，可以避免激发出定子的非轴称模态。完成了电机运转实验，电机运转平稳。     

依托学科优势建设有特色的流体力学教学实验体系

介绍北京航空航天大学流体力学教学实验体系及其课程建设，包括：从基础演示实验、流体 力学基本方程实验到综合、扩展、学生自主的设计创新实验的3个层次的教学实验体系，理 论学习、计算机虚拟实验、实际动手操作实验有机结合的教学方式，与国内外高校的切磋交 流以及在中央电视台、北京电视台相关栏目演播等内容.     

Scale effect and geometric shapes of grains

The rule-of-mixture approach has become one of the widely spread ways to investigate the mechanical properties of nano-materials and nano-structures,and it is very important for the simulation results to exactly compute phase volume fractions.The nanocrystalline(NC)materials are treated as three-phase composites consisting of grain core phase,grain boundary(GB)phase and triple junction phase,and a two-dimensional three-phase mixture regular polygon model is established to investigate the scale effect of mechanical properties of NC materials due to the geometrical polyhedron characteristics of crystal grain.For different multi-sided geometrical shapes of grains,the corresponding regular polygon model is adopted to obtain more precise phase volume fractions and exactly predict the mechanical properties of NC materials.     

积分中值定理逆问题及其渐近性

本文讨论积分中值定理的逆问题及逆问题的渐近性     

Landau定理中上界的一个改进

通过相关文献给出的穿孔平面C\{0,1}的双曲度量的密度函数的新的下界估计,借助广义Schwarz引理我们对Landau定理中关于上界做了进一步改进并得到了一个带参数的上界表达式.并且当参数取到0时,此结论正好为相关文献得到的结果.     

纳米棒组装的WO3·0.33H2O及其光催化性能改善

以十二烷基苯磺酸(DBSA)和钨酸钠为原料,在无其它辅助剂条件下,通过水热方法制备了由纳米棒组装成的三维多级微结构WO₃·0.33H₂O。 结果表明,反应原料DBSA不仅在反应中提供氢离子,而且还具备表面活性剂调控产物形貌的作用。 在可见光照射下,由于其特殊的多级结构,WO₃·0.33H₂O展现出较强的光催化降解罗丹明B活性,降解率达100%,重复使用5次后,降解率仍保持较高水平。