共查询到20条相似文献,搜索用时 46 毫秒
1.
A study on the influence of the external resistor and the external voltage source during the injection of the electromagnetic pulse(EMP) into the bipolar transistor(BJT) is carried out.Research shows that the increase of the external resistor R_b at base makes the burnout time of the device decrease slightly,the increase of the external voltage source V_(be) at base can aid the damage of the device when the magnitude of the injecting voltage is relatively low and has little influence when the magnitude i... 相似文献
2.
多光子Tavis-Cummings模型中运动原子与二项式光场相互作用的量子纠缠 总被引:2,自引:2,他引:0
利用全量子理论,研究了多光子Tavis-Cummings模型中运动原子与二项式光场相互作用系统的量子纠缠特性,讨论了不同初始状态下的二项式光场系数和原子运动速度对纠缠特性的影响.结果表明:二项式光场系数不影响场熵演化的周期性,但影响场熵峰值大小.随着原子跃迁光子数的增多,场熵演化的周期性和消纠缠现象逐渐消失.原子运动的速度影响场熵的演化周期,且影响场熵峰值的大小,而原子跃迁光子数的增大,会消弱原子运动速度对场熵演化的影响.当光场处于中间态,原子运动速度较低,且原子跃迁光子数较大时,光场与原子可以长久地处于量子纠缠态. 相似文献
3.
对高空气球与机载探测器所处环境特性进行分析,利用MODTRAN大气传输模型计算了相同时刻下不同探测点的背景噪声强度,和不同时刻下目标处的背景光亮度,采用反向蒙特卡罗法计算出空基探测点处接收到的高空气球的散射亮度,计算出探测数据的信噪比,并就目标的光谱可见性进行了分析。计算表明,机载探测时,当目标位置与探测高度固定的情况下,探测夹角越小,目标的太阳天顶角越大,则探测信噪比越高,越容易满足探测仪器的阈值并有利于探测谱段的选择。 相似文献
4.
对0.7mm×1.2mm槽孔分别添加0.4mm、0.55mm导向孔,并分别添加在槽孔中心,距槽孔边1mil及与槽孔边相切,得出添加0.55mm导向孔并其与槽孔边相切时,槽孔孔形最为优良,并且在添加0.55mm导向孔时,其不同添加位置对槽长影响最为显著。 相似文献
5.
本文通过矩量法及其高效数值方法(MLFMA)对近距离目标--单脉冲收发天线的电磁互作用进行一体化数值仿真,定量研究了单脉冲天线的近场角度测量特性.在该近场模型中,目标散射近场的幅、相分布和同轴探针激励的喇叭单脉冲天线的辐射场(对应远场和波束)、接收端响应(对应远场差波束)均采用全波数值模拟获得.首先,计算单脉冲天线的辐射场并将其作为对目标照射的激励条件;接着,计算目标散射近场的空间分布;并计算出单脉冲天线所接收到的目标散射场;最后,使用幅值法和相位法计算出单脉冲天线近场测角角度,并在此基础上对近距离测角误差进行研究.在导弹目标算例中,将天线--目标一体化建模和天线口径面上散射近场的幅、相分布计算结果用于近距离条件下单脉冲天线测角误差的研究,并通过频率、距离的变化对测角精度做了对比分析;发现目标近场散射幅、相分布的非均匀性,是导致单脉冲天线近距离角度测量产生较显著的测角误差的主要原因;而频率较低时,测角误差较小.文中给出了物理解释,并提出近距离测向时借助于较低频信号的校正以降低测角误差的建议. 相似文献
6.
7.
8.
在光缆随路状态监测过程中,为避免因光信号波 长分离难度大而影响状态监测的准确 性,本研究在现场监测站采集光信号的基础上,利用光波分复用过程实现对不同波长光信号 的分离处理。根据分离结果,通过OTDR测试获得监测点到光缆故障点之间的距离,再结合小 波变换过程确定最大故障衰减信息。基于此,利用BP算法实现对超长距离光缆随路中存在的 故障点的定位,实现对光缆随路状态的监测。实验结果表明:该方法的监测过程耗时始终保 持在4min之内,且故障定位准确度在80%左右,证明该方法监测过程 耗时短、效率高,且对故障点的定位准确度较高,大大提升了状态监测结果的准确性。 相似文献
9.
励磁系统的PID参数对发电机组和电网稳定的可靠性和动态品质具有重要的作用。检验励磁系统PID参数准确性的方法主要是进行发电机空载阶跃响应试验。本文采用中国电力科学研究院研制的电力系统综合仿真程序PSASP对沧东电厂4号机励磁系统进行了5%机端电压阶跃仿真试验,然后根据仿真结果进行了现场试验,结果表明仿真结果对现场试验具有重要的指导意义,不仅节省了现场调试的时间,而且进一步提高了现场试验的安全性。 相似文献
10.
11.
12.
陶瓷基板与印制电路板之间的热膨胀系数差异较大导致的热失配,和大尺寸、高质量带来的抗振动性能下降,是这类器件板级装联失效的主要原因。针对铜带缠绕型焊柱CCGA板级装联结构在温度循环和随机振动载荷下焊点的失效模式和失效机理进行研究。结果表明,最大应力应变点出现在铜带与焊柱接触界面铜带边缘处,裂纹沿铜带缠绕方向的焊柱横截面向内扩展最终导致开裂。由于铜带和焊柱材料弹性模量性能差异较大,铜带与柱芯接触界面存在应力突变现象,器件长期使用过程中会出现焊柱与铜带剥离进而导致互连失效。铜带材质的选择、铜带与柱芯缠绕质量是影响铜带缠绕型焊柱高可靠应用的关键,铜带与焊柱间良好的冶金互连、铜带间隙充分的焊料填充是有效提高铜带缠绕型焊柱的抗热/机械性能的主要途径。 相似文献
13.
InSb and GaSb single crystals were grown by the Czochralski method. The impurity concentration distribution in the melt and
crystal was investigated experimentally and computationally as a function of the interface segregation coefficient, the shape
of the solid-liquid interface and the growth rate. It was found that the impurity concentration distribution in the melt was
largely influenced by the interface segregation coefficient; the impurity concentration in the crystal increased as the shape
of the solid-liquid interface became more planar and also as the growth rate increased; the impurity concentration was more
markedly influenced by the growth rate than by the shape of the solid-liquid interface. When the growth rate was large, the
impurity concentration increased and the shape of the solid-liquid interface was concave toward the melt near the crystal
periphery. When the growth rate was small, the impurity concentration decreased and the shape of the solid-liquid interface
was convex toward the melt. 相似文献
14.
15.
16.
Miyoshi S Shimizu S Matsushima J Ifukube T 《IEEE transactions on bio-medical engineering》1999,46(4):451-460
We have proposed the tripolar electrode stimulation method (TESM) for narrowing the stimulation region and continuously moving the stimulation site for cochlear implants. The TESM stimulates the auditory nerve array using three adjacent electrodes which are selected among the electrodes of an electrode array within the lymphatic fluid. Current is emitted from each of the two lateral electrodes and received by the central electrode. The current received by the central electrode is made equal to the sum of the currents emitted from the lateral electrodes. In this paper, we evaluate whether or not TESM works according to a theory which is based on numerical analysis using an electrical equivalent circuit model of the auditory nerve fibers. In this simulation, the sums of the excited model fibers are compared to the compound action potentials (CAP's) which we obtained through animal experiments. To identify the main parameter while maintaining the amplitude of the CAP (the sum of the fired fibers), we assumed the presence of some parameters from the radial current density profile. In the case of the width value among the parameters being kept constant, the amplitude of the CAP was almost constant; thus, the number of the fired fibers was also almost constant. The width value equals the distance between the points at which the profile of the radial current density of the electrode array and the line of the radial threshold current density of the electrode array intersect. It is possible to determine the measure of the stimulation region or site by controlling the width value and the ratios of the currents emitted from the lateral electrodes. As a result, we succeeded in narrowing the stimulation region by controlling the sum of the currents emitted from the two lateral electrodes. Also we succeeded in continuously moving the stimulation site by modifying the currents emitted from the two lateral electrodes. 相似文献
17.
在目标检测领域,分形理论中的盒维数常被用来检测海杂波中的微弱目标,但直接采用盒维数检测目标却得不到的较好检测性能.为提高采用盒维数检测目标方法的检测性能,文章在Hilbert-Huang变换域分析了实测海杂波数据的Hilbert谱脊线盒维数特性以及目标的影响,提出了采用Hilbert谱脊线盒维数检测目标的方法.仿真结果表明,目标出现时海杂波的Hilbert谱脊线盒维数明显减小,采用Hilbert谱脊线盒维数检测海杂波中的微弱目标能够获得较好的检测性能,其性能要优于直接采用盒维数的目标检测方法和多脉冲单元平均恒虚警检测方法的检测性能. 相似文献
18.
基于广义惠更斯-菲涅耳原理、交叉谱密度函数,利用修正Von Karmon谱模型以及ITU-R颁布的大气折射率结构常数模型,推导出部分相干高斯-谢尔光束在大气湍流中传输时的束宽及角扩展表达式,讨论并对比斜程和水平两种传输方式下天顶角、传输距离、湍流强度、相干长度等参数对光束束宽与角扩展的影响,同时分别从相对束宽和相对角扩展的角度分析各种参数对于光束抑制湍流能力的影响,并给予相应的物理解释。结果表明:当天顶角小于 /3时,光束在斜程传输时的光束扩展和角扩展量接近于垂直传输,所受湍流影响很小。传输距离大于1 km时,束宽和相对束宽随传输距离的增加而明显增加。光束相干长度越大,光束所受湍流影响越大,而束宽及角扩展会随之减小。 相似文献
19.
光束横截面内偏振态分布均匀性是影响径向偏振光光束质量及其实际应用的关键因素。通过PBS测量法、狭缝法和S波片法三种方法对径向偏振光偏振纯度进行测量和对比,分析了径向偏振光偏振态在横截面内分布均匀性。在PBS测量法和狭缝法测量径向偏振光过程中,给出了径向偏振光纯度表达式,分别测得径向偏振光纯度为93.4%和84.1%,并引入方差公式评价径向偏振光偏振态分布均匀特性。其中PBS测量法表达径向偏振光纯度更为准确,狭缝法可以通过比较不同区域偏振度更精确地反映径向偏振光偏振态分布特性。S波片法可以使用市场现有偏振分析仪间接测量径向偏振光纯度,更适应于测量径向偏振光在放大过程中偏振态变化情况。 相似文献