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According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod- ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.  相似文献   
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强损耗介质中相干光脉冲的传输效应   总被引:2,自引:0,他引:2       下载免费PDF全文
蒋孟衡  林福成 《物理学报》1990,39(12):1887-1892
本文利用密度矩阵形式的Bloch方程和Maxwell方程耦合,讨论了相干光脉冲在共振强损耗介质中的传输过程,同时考查了脉冲演化和对介质的影响,得到了脉冲面积的阶跃式下降和空间损耗粒子数的周期振荡等强损耗条件下特有的瞬态相干现象。 关键词:  相似文献   
3.
蒋孟衡  林福成 《光学学报》1990,10(12):057-1062
本文由半经典理论推得了原子电离率随脉冲空间传输出现周期性起伏这一新的相干作用结果,这点与速率方程的预计相差甚远.文中定量说明了利用速率方程对同位素分离过程进行分析时产生的系统误差,为实验分析工作提供了依据.  相似文献   
4.
According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod-ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.  相似文献   
5.
 基于密度泛函理论的第一性原理方法,计算了硅铍石型和尖晶石型结构BeP2N4的总能量随体积的变化关系。利用Brich-Murnaghan状态方程,通过能量和体积拟合,得到了2种结构的体变模量及其对压强的一阶导数。在压力作用下,BeP2N4的相变是从硅铍石型结构(空间群R-3,No.148)转变到尖晶石型结构(空间群Fd-3m,No.227),计算出的相变点与其它理论值符合得非常好。同时计算了BeP2N4的相对晶格常数a/a0和相对体积V/V0的压缩率,在低压下发现,尖晶石结构BeP2N4的压缩率接近金刚石,进一步计算了不同压力下的体弹模量BH、剪切模量GH、BH/GH和杨氏模量E。此外,对两种结构的BeP2N4的电子态密度和带隙随压强的变化关系进行了计算和分析。结果表明:在压力作用下,上价带顶向费米能级移动,并有一定的展宽。Be—N、P—N键缩短,电子转移增加,导致电荷发生重新分布。  相似文献   
6.
丁迎春  陈敏  高秀英  蒋孟衡 《中国物理 B》2012,21(6):67101-067101
According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod- ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.  相似文献   
7.
两步共振光电离中的动力学过程分析   总被引:2,自引:1,他引:1  
蒋孟衡  林福成 《光学学报》1991,11(9):69-775
利用密度矩阵方程和麦克斯韦方程耦合,探讨了光学厚样品中两步共振光电离的物理机制,利用数值求解分析了有关原子及脉冲参量对分离效率的影响,给出了优化实验方案的一些限制条件,并对多脉冲相干类孤立子(Simulton)现象进行了初步讨论。  相似文献   
8.
高激发StarK能级寿命的计算   总被引:1,自引:0,他引:1       下载免费PDF全文
蒋孟衡  张森 《物理学报》1995,44(3):357-364
用零场下Rydberg态波函数为基矢,在空间展开求得Stark能态的波函数,进而计算了K原子n=15,|m_1|=1的Stark簇在I混合区各能态自发辐射速率及环境黑体辐射引起的受激跃迁速率,讨论了Stark能级寿命与外电场强度及环境温度的关系. 关键词:  相似文献   
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