排序方式: 共有88条查询结果,搜索用时 15 毫秒
31.
近年来,掺Er3+的CdF2-CdCl2-NaF-BaF2-BaCl2-ZnF2玻璃已成为固体材料激光冷却领域中新的研究材料之一.本文利用激光器输出理论和驻波腔内共振增强原理分析了该材料的两种腔内增强激光的冷却,计算结果表明腔增强可获得几十到几百倍的增强因子.此外,比较了内腔和外腔这两种增强方案,研究结果表明,当材料的吸收比较小时,特别是材料长度小于0.3 mm时,采用内腔增强方案,腔内抽运功率高,冷却材料对激光的吸收大.然而当材料的吸收比较大时,特别是材料长度大于3 mm时,外腔增强方案更具优越性.最后,根据Er3+掺杂材料制冷工作波长和功率的要求,指出腔增强实验可通过半导体激光器来实现. 相似文献
32.
33.
假设问题中所含随机过程为鞅,本文证明了带随机过程的随机规划问题共最优值过程与最优解集过程分别为实值上鞅与集值上鞅,且存在最优鞅通过程。 相似文献
34.
通过分析门极换流晶闸管(GCT)透明阳极的电流输运过程,研究了透明阳极的机理,导出 了透明阳极电子电流密度的表达式.并利用MEDICI软件对GCT的开关特性进行了模拟,验证了 理论分析的正确性.另外,将GCT与具有普通阳极的门极可关断晶闸管(GTO)进行比较,分 析了透明阳极的特性,结果表明将透明阳极与缓冲层结合使用,可以更好地协调GCT的阻断 特性、通态特性及开关特性之间的矛盾,从而有效地改善GCT的综合特性.结论得到了实验结 果的证实.
关键词:
透明阳极
电力半导体器件
门极换流晶闸管
注入效率 相似文献
35.
Thermal concentrators and cloaks with ellipsoidal shapes are designed by utilizing the transformation thermotics method and finite element simulations.The thermal conductivities for the concentrator and cloak are directly derive in Cartesian coordinates.The simulation results show that the ellipsoidal thermal concentrator can focus heat flux into a central region and that the ellipsoidal thermal cloak can guide heat flux around the cloaked region smoothly without disturbing the external temperature distribution and heat flux.The present method can be extended to design arbitrarily shaped thermal metadevices with novel properties. 相似文献
36.
37.
为提高稀土长余辉发光材料SrMgAl4 O8:Eu2+,Dy3+在非极性树脂中的分散性和相容性,用硅烷偶联剂YDH-570在强酸条件下对其进行了表面改性.通过质量变化、比表面积、ATR-FTIR、SEM(能谱分析)和发光性能分别研究了该条件下不同ptH值改性对材料表面组成、形貌和性能的影响.结果发现:强酸条件下改性效果十分显著;当pH值由0.6增加到0.72时,样品增重率达23.3%,33.3%,53.3%,比表面积净增75.6%,215.2%,265.4%;对于改性效果较明显的pH为0.72的样品,能谱分析证实是一种片状有机包覆层结构;余辉衰减曲线表明,表面改性对材料发光性能影响不大. 相似文献
38.
This paper proposes a novel super junction (SJ) SiGe switching power
diode which has a columnar structure of alternating p- and
n- doped pillar substituting conventional n- base region
and has far thinner strained SiGe p+ layer to overcome the
drawbacks of existing Si switching power diode. The SJ SiGe diode
can achieve low specific on-resistance, high breakdown voltages and
fast switching speed. The results indicate that the forward voltage
drop of SJ SiGe diode is much lower than that of conventional Si
power diode when the operating current densities do not exceed
1000 A/cm2, which is very good for getting lower operating
loss. The forward voltage drop of the Si diode is 0.66V whereas that
of the SJ SiGe diode is only 0.52 V at operating current density of
10 A/cm2. The breakdown voltages are 203 V for the former and
235 V for the latter. Compared with the conventional Si power diode,
the reverse recovery time of SJ SiGe diode with 20 per cent Ge
content is shortened by above a half and the peak reverse current is
reduced by over 15%. The SJ SiGe diode can remarkably improve the
characteristics of power diode by combining the merits of both SJ
structure and SiGe material. 相似文献
39.
低温燃烧法制备纳米Ce1-xNdxO2-x/2(0≤x≤0.6) 粉体的研究 总被引:2,自引:0,他引:2
采用低温燃烧合成工艺,在甘氨酸-硝酸盐体系下制备出纳米Ce1-xNdxO2-x/2(0≤x≤0.6)系列粉体(NDC)。X射线衍射(XRD)结果表明。Nd^3 取代Ce^4 进入晶格内部,形成具有单相立方萤石型结构的固溶体,其晶格常数随Nd^3 掺杂浓度的增大而线性增加,晶粒尺寸在17~28nm之间。透射电镜(TEM)结果表明,粉体尺寸在30-40nm之间,具有较高的烧结活性。拉曼光谱(Rman spectrum)表明%宽化峰与掺杂后固溶体中产生的氧空位有关。 相似文献
40.