排序方式: 共有12条查询结果,搜索用时 15 毫秒
1.
讨论了布尔矩阵平方根问题及其与图着色问题的关系.首先得到有平方根的布尔矩阵具有的一些性质;然后给出布尔矩阵存在平方根的一个充要条件;最后证明布尔矩阵的平方根问题可以转化为简单图的着色问题. 相似文献
2.
计算电容是复现电学阻抗单位的基准装置, 利用计算电容值和量子霍尔电阻值可以准确计算出精细结构常数α. 计算电容的本质是通过高准确度地测量屏蔽电极的位移, 实现对电容量值的测量. 因此, 基于Fabry-Perot干涉仪的精密电极位移测量系统是计算电容装置中最为核心和关键的部分. 在Fabry-Perot干涉仪测位移过程中, 由于高斯激光束存在轴向Gouy相位, 该附加相位将会引起相邻干涉条纹对应位移的变化(大于或者小于λ/2), 导致位移的测量值与实际值存在偏差. 本文阐述了高斯激光场的传播特性, 利用高斯激光束在自由空间和透过薄透镜复振幅的变换关系, 建立了计算电容装置中Fabry-Perot干涉仪透射光束的传输模型; 通过对不同腔长的Fabry-Perot干涉仪透射光场相位的分析, 获得了高斯激光束轴向Gouy相位修正与传输距离的关系. 结果表明, 当腔长从111.3 mm移动至316.3 mm时, 在接收距离为560 mm的情况下, 高斯光束轴向Gouy 相位引起的位移修正的绝对值最小为0.7 nm, 其相对相位修正量|δL|/|ΔL| = 3.4×10-9. 相似文献
3.
讨论了布尔矩阵的可实现问题及其与色数问题的关系.首先给出布尔矩阵可实现的一些充要条件,讨论可实现布尔矩阵的性质,其次证明可实现布尔矩阵的容度等于该矩阵所生成的图的色数;简单图的邻接矩阵的对偶阵是可实现的,且其容度就是简单图的色数的一个上界. 相似文献
4.
Fuzzy矩阵Schein秩的计算复杂性 总被引:1,自引:0,他引:1
本文讨论Fuzzy矩阵Schein秩的计算复杂性问题,证明了它是一个"NP-完全问题".首先,刻画了交可分解的Puzzy关系的交分解解集.然后,从Fuzzy关系的交分解与广义分解之间的关系出发,给出了Fuzzy关系广义分解的算法.最后,从Fuzzy关系广义分解的角度来讨论Fuzzy矩阵的Schein秩.指出它与色数问题之间的关系,即Fuzzy矩阵的Schein秩等于由它生成的简单图的色数,从而证明了计算Fuzzy矩阵的Schein秩是一个"NP-完全问题". 相似文献
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6.
采用传统固相反应法制备了CaCu3Ti4O12陶瓷.XRD证实其CaCu3Ti4O12相;SEM观察到明显的晶粒晶界结构,晶界区亦由小晶粒构成;结合EDS结果,判定晶界区小晶粒为CuO.在较宽的温度范围内,CaCu3Ti4O12陶瓷的介电常数保持在105左右;当频率为103 Hz温度小于150 K时,介电常数迅速下降.在173—373 K温度范围内,通过其I-V特性,得到CaCu3Ti4O12陶瓷直流电导随温度的变化:直流电导与温度的关系可分为三部分,对应的活化能分别为0.681 eV,0.155 eV和0.009 eV,这与CuO陶瓷直流电导活化能一致.可以认为晶界区的CuO小晶粒在CaCu3Ti4O12陶瓷的直流电导中占主导,这为解释CaCu3Ti4O12陶瓷反常的介电性能提供了新的思路.
关键词:
3Ti4O12')" href="#">CaCu3Ti4O12
微观结构
直流电导
介电特性 相似文献
7.
在-180?℃—100?℃温度范围内研究了ZnO-Bi2O3二元、ZnO-Bi2O3-MnO三元以及商用ZnO压敏陶瓷的I-V特性.研究发现:二元试样电导由散射电导串联构成;三元试样电导由热电子发射电导混联构成;商用试样电导由热电子发射电导和隧道效应电导并联构成.对整个电流范围内的电导拟合表明:通过同一温度下电导分量同电流的关系,可以计算出该部分电导对应的非线性指数.在商用试样中,隧道电流产生的非线性指数为33,与实测值接近;该隧穿分量在小电流区也存在,且在低温下表现地更为明显.
关键词:
ZnO压敏陶瓷
I-V特性')" href="#">I-V特性
导电机理 相似文献
8.
With the help of broadband dielectric spectroscopy in a wide temperature and frequency range, the conductivity spectra of ZnO polycrystalline ceramics are measured and the direct-current-like (DC-like) conductivity and relaxation polarization conductivity are observed successively along the frequency axis. According to the classical Debye theory and Cole-Cole equation, the physical meanings of the two conductivities are discussed. It is found that the DC-like conductivity corresponds to electron transportation over the Schottky barrier at the grainboundary. The relaxation polarization conductivity corresponds to electronic trap relaxation of intrinsic point defects (zinc interstitial and oxygen vacancy). When in the high frequency region, the relaxation conductivity obeys the universal law with the index n equal to the index α in the Cole-Cole equation as an indictor of disorder degree. 相似文献
9.
Effect of Tunneling Current on Schottky Barrier Height in ZnO Varistors at Low Temperature 下载免费PDF全文
On the basis of the Schottky barrier and thermionic emission models, the temperature dependence of barrier height in ZnO varistors is investigated by the I - V characteristics in a wide temperature range from 93 K to 373 K. The obtained barrier height decreases with reducing temperature, which is ascribed to the contribution of tunneling current in measured current. From the proposed equivalent circuit, it is suggested that two current components coexist. One is thermionic emission current, which reflects the thermionic emission barrier height. The other is tunneling current, which appears even at low voltage, especially in low temperature ranges, and thus makes the barrier height obtained from measured current vary with temperature. 相似文献
10.
This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature,frequency and bias,in addition to the steady state response.It discusses the nature of net current flowing over the barrier affected by interface state,and then obtains temperature-dependent barrier height by approximate calculation from steady I-V (current-voltage) characteristics.Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal.From the resonances due to deep bulk trap relaxation on dielectric spectra,the activation energies are obtained as 0.22 eV and 0.35 eV,which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer.Under moderate bias,another resonance due to interface relaxation is shown on the dielectric spectra.The DC-like conductance is also observed in high temperature region on dielectric spectra,and the activation energy is much smaller than the barrier height in steady state condition,which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors. 相似文献