用MTF确定三维面形测量系统的投影光栅频率

在基于光栅投影的三维物体面形测量技术中,投影光栅的频率将直接影响着最终的测量精度,在系统参数允许的情况下,尽可能大地光栅频率将带来高的系统测量精度,因此,光栅频率选择是一个关键问题.提出了一种确定投影系统物面光栅频率上限的方法,采用基于图像分析的调制度传递函数测量原理,首先测得系统的调制度传递函数曲线,再由此确定满足系...     

概率初步

随机事件频率与概率 中考要求 理解和概率相关的概念:频数、频率、必然事件、不可能事件、随机事件、概率等,并会计算简单事件的概率. 在具体情境中理解概率的意义,会利用列表法、画树状图法计算简单事件的概率,并能运用计算的结果作出估计、判断、决策,以解决一些实际问题.     

关于薛定谔方程的一个注记

使用振幅-频率公式和残量可求解线性和非线性薛定谔方程,该方法在得到精确解的同时,求解过程相对其它方法比较简洁,但需对所得解进行检验,以避出现增解.     

Study on the mean trabecular bone spacing based on fundamental frequency estimation method

Ultrasonic backscatter signals from the cancellous bone can be used to diagnose osteoporosis effectively due to its ability to provide the information of bone microstructure. Mean trabecular bone spacing(MTBS)is one of the important parameters for characterization of bone microstructure.This paper proposed a MTBS estimating method based on the fundamental frequency estimation,which was applied to backscatter signals from simulations, and in vitro bovine trabeculae.The estimated MTBS were compared with those of simplified inverse filter tracking(SIFT)algorithm and autoregressive(AR)cepstrum method.The results demonstrated that the proposed method is very robust for the MTBS estimation with more precise estimates and smaller estimated variance in the presence of a small signal-to-noise ratio (SNR),and a large scattering strength ratio of diffuse scatterers to regular ones.     

A detecting method for line-spectrum target based on variance-of-frequency weight

There are highly intensive and stable line-spectrums in the radiated noise of passive target,and different targets have line-spectrums with different frequencies.This paper puts forward Conventional BeamForming(CBF) variance-of-frequency detector,which weights bearing spectrum using the variance of frequency of line spectrum with maximum amplitude in each azimuth. It is able to suppress multi-target interferences effectively,and detect faint signal in the background of strong interferences.What’s more,CBF variance-of-frequency detector needs only three-dimension display,while other line-spectrum detectors require for four-dimension display.The simulation and trial data analysis show that the CBF variance-of-frequency detector is able to detect faint line-spectrum target in the background of the continuous spectrum strong interferences.     

Frequency driven scanning characteristic of a pinna model inspired from the Brown Big-eared bat（Plecotus auritus）

According to the parameters of a Brown Big-eared bat’s pinna,a simple obliquely truncated bat ear model that made by line and plane was designed,which was numerically simulated with finite element method.The change of far-field directivity was analyzed in elevation and azimuth as the frequency increased.The results show that,compared with the pinna of the Brown big-eared bat,the present model has the advantages in wider bandwidth of frequency driven scanning,better directivity in azimuth and larger angle scales in elevation. In addition,a wireless positioning method based on single base station could be achieved by using a frequency driven scanning antenna.     

微晶玻璃腔体一体化兰姆凹陷稳频He-Ne激光器(Ⅰ):结构与工艺

介绍了利用兰姆凹陷稳频He-Ne激光器的基本结构与腔长调节工作方式,从激光器结构方面对影响其预热时间、频率稳定度和频率重复性的主要因素进行了深入探讨。介绍改进设计的新型微晶玻璃腔体一体化兰姆凹陷稳频He-Ne激光器的基本结构、制作工艺与优势。该激光器腔体采用极低膨胀系数的微晶玻璃材料,反射镜采用石英镜片光胶连接,无应力超高真空铟封形式,谐振腔稳定性好。利用该激光器进行了实验,实验结果表明,该激光器工作中不需要预热,环境适应能力极强,在高低温与冲击振动条件下均能稳定工作,频率稳定度可以达到10-10量级。     

采用正交光功率比值的光子型微波频率测量方案设计

通过构建两个正交的光功率比值,以光子技术实施微波频率测量.首先,待测微波信号经外调制器加载到连续光源上,在单边带载波抑制调制下仅得到单个光边带;以光学梳状滤波器对其进行滤波处理,在输出端检测得到随微波频率增大而呈现余弦函数和正弦函数变化趋势的两个光功率;将这两个光功率与参考光功率进行比较后,进而得到余弦函数型和正弦函数...     

神经系统疾病与认知动力学(II): 神经振荡与认知动力学

大脑神经系统具有从慢到快多种不同的振荡节律, 这些节律振荡被认为参与了大脑多种功能的实现, 其中高频的伽马同步振荡被认为与大脑的认知功能最为相关. 本文阐述了生物学实验方面关于伽马振荡及其功能的研究进展, 并针对实验中伽马振荡的频率敏感依赖于外部刺激特征的现象, 综述了基于神经网络模型进行变频伽马振荡及其认知功能的动力学建模研究工作, 解释了视觉刺激调控的变频率伽马振荡动力学产生机理, 提出了基于同步抑制增强全局放电率对比度的神经认知机制. 研究成果有助于理解神经系统同步振荡的产生机理及其认知作用, 为大脑认知原理以及类脑智能的研究奠定基础.