排序方式: 共有78条查询结果,搜索用时 15 毫秒
71.
We have investigated the transport and ultraviolet photovoltaic properties
of Fe$_{3}$O$_{4}$ thin films grown on glass substrates by facing-target
sputtering technique. The nonlinear dependence of current-density on voltage
suggests that the transport process is most likely the tunnelling process and
grain boundaries act as barriers. Furthermore, nonequilibrium electron-hole
pairs are excited in the grains and grain boundary regions for
Fe$_{3}$O$_{4}$ film under ultraviolet laser, since the energy gap of
Fe$_{3}$O$_{4}$ is smaller than the ultraviolet photon energy. And then the
built-in electric field near the grain boundaries will separate carriers,
leading to the appearance of an instant photovoltage. 相似文献
72.
Ultrafast photoelectric effects have been observed in p-n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3_/Si for the first time. The rise time was about 1 ns and the full width at half maximum was about 2ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of -25 ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV//mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6 μm CO2 laser. 相似文献
73.
采用基于密度泛函理论的投影缀加波方法研究了Heusler合金Pd2CrAl的四方变形、磁性和弹性常数. 四方变形中,Pd2CrAl在c/a≈1.20处出现总能的局域最小值,对应一个稳定的马氏体. Pd2CrAl的L21结构和四方结构的单胞总磁矩分别为3.825μB和3.512μB. 在这两种结构中Cr原子均是Pd2CrAl总磁矩的主要贡献者,Pd和Cr原子间存在很强的杂化作用,Cr的3d电子的t2g和eg两个亚能带是Pd2CrAl磁性的主要来源. 弹性常数的计算结果显示,Pd2CrAl的L21结构和四方结构的弹性常数均满足相应结构的稳定性判据.
关键词:
Heusler合金
四方变形
磁性
弹性常数 相似文献
74.
75.
Detecting holes in oil–gas reservoirs is vital to the evaluation of reservoir potential. The main objective of this study is to demonstrate the feasibility of identifying general micro-hole shapes, including triangular, circular, and square shapes, in oil–gas reservoirs by adopting terahertz time-domain spectroscopy(THz-TDS). We evaluate the THz absorption responses of punched silicon(Si) wafers having micro-holes with sizes of 20 μm–500 μm. Principal component analysis(PCA) is used to establish a model between THz absorbance and hole shapes. The positions of samples in three-dimensional spaces for three principal components are used to determine the differences among diverse hole shapes and the homogeneity of similar shapes. In addition, a new Si wafer with the unknown hole shapes, including triangular, circular, and square, can be qualitatively identified by combining THz-TDS and PCA. Therefore, the combination of THz-TDS with mathematical statistical methods can serve as an effective approach to the rapid identification of micro-hole shapes in oil–gas reservoirs. 相似文献
76.
应用太赫兹技术对大气中动力学直径小于2.5μm(PM_(2.5))的细颗粒物进行了定量研究。PM_(2.5)质量和太赫兹吸光度之间存在线性关系,相关系数为0.86。应用主成分分析的方法,可证明随着PM_(2.5)质量的增加,与吸收系数存在相似的趋势。为了提高预测精度,采用偏最小二乘,支持向量机和反向传播人工神经网络对PM_(2.5)进行定量研究。与单一的线性模型相比,统计模型具有较大的预测相关性和较小的误差。对于神经网络模型,训练集与预测集的相关系数和均方根误差分别达到0.999和0.016mg,0.912和0.207mg。因此,THz技术和统计学方法的结合可提供较高精度的预测,作为一种监测PM_(2.5)的有效手段。 相似文献
77.
太赫兹时域光谱无损检测核桃品质的研究 总被引:2,自引:0,他引:2
以核桃为研究对象,探讨太赫兹时域光谱技术对其变质情况、壳厚测量的研究。首先对虫蛀、霉变、正常核桃壳、仁标样采集太赫兹时域光谱,比较分析变质与正常核桃谱图及吸收谱差异,为剔除变质核桃打下基础。其次联用透射和反射式太赫兹时域光谱系统,创建核桃壳计算公式,在获取核桃壳理论折射率基础上,换算得到未知核桃壳厚,相对误差为3.7%。分别从物理、化学指标光谱响应特征差异入手,实现太赫兹无损检测核桃品质。 相似文献
78.