TQ—Ⅰ型自动周期测量仪

ＴＱ—Ⅰ型自动周期测量仪覃以威，唐汉雄（广西师大物理系桂林）在普通物理力学实验中，周期测量是一项重要内容。例如单摆、三线摆等实验都要测量周期。而一般测量周期的传统方法是通过人工记数和手动计时来实现的，这就难免会带进实验者许多人为的误差。为此，我们研制...     

周期激励微分方程中超次谐周期轨道的不存在性

证明了在一类周期激励微分动力系统中如果存在周期解则只可能是次谐周期解，超次谐周期解不可能存在，并进一步证明了在一类平面问题中所定义的旋转（R）型超次谐周期解同样不可能存在.作为该结论的一个应用，通过考察几个典型的算例，指出平面扰动系统是否存在超次谐周期轨道不能通过现有的二阶Melnikov方法作出判断，并作出了几何上的解释.     

混沌体系中寻找周期轨迹的方法

一个不可积混沌体系，由于扰动而遭到破坏时，存活的周期轨迹体现了体系的本质特征，是 体系的运动骨架.在一定程度上， 可以由周期轨迹来量子化不可积体系，这充分说明了 周期轨迹的重要性.而寻找周期轨迹，也就成为研究混沌体系动力学特性以及对混沌体系进 行量子化的关键问题.结合具体实例，给出了3种常用的寻找周期轨迹方法，并详细探讨了各 种方法的优缺点和适用范围. 关键词： 周期轨迹 数值方法 混沌     

一维准周期结构声子晶体透射性质的研究

提出了一维准周期结构的声子晶体模型.对弹性波通过该一维准周期结构声子晶体的透射系数进行了数值计算，并与周期结构的透射系数进行了比较.计算结果表明，弹性波通过一维准周期结构声子晶体时，同样会有带隙的出现，且带隙所在频率范围与周期结构的情形完全一样，不同的是在准周期结构声子晶体中，带隙内有很强的局域共振模.对此局域模性质的研究有助于声波或弹性波滤波器的制作. 关键词： 准周期结构 声子晶体 局域化     

零功率反应堆周期测量系统研制

反应性是表征反应堆系统临界性的主要参数。在堆运行到临界以上时，测量堆的反应性的一个主要手段就是通过周期测量系统来测量堆功率上升的二倍渐进周期，再通过堆反应性与渐进周期的关系，推算出堆反应性。     

注入半导体激光器混沌相位周期控制方法研究

提出外部光注入半导体激光器混沌相位控制方法，通过周期调制注入光的相位相移将激光器的混沌控制到多种周期状态.数值结果表明：在不同强度光注入下，(1)通过半波长周期相位相移调制控制混沌激光到周期态、双周期态、三周期态、四周期态以及多周期态等；(2)通过四分之一波长周期相位相移调制控制混沌激光到周期态和多周期态，并在高频调制控制时能够产生激光锁模现象，其锁模区域是19—21GHz；(3)波长周期相位相移调制控制也能使混沌激光控制到三周期态和多周期态等. 关键词： 混沌 控制 激光器 周期     

凹形曲面上纯滚刚体的等周期性讨论

质点在竖直面内旋轮线上作摆动时，已经证明周期是与摆幅无关，而匀称刚体在一个旋轮面上作纯滚摆动时，其周期是否也与摆幅无关呢？本文论述其摆动周期与摆幅有关，仅在刚体质心所走过的轨迹为旋轮线时周期与振幅才无关．     

沿摆线振动质点的周期

沿摆线振动质点的周期任常愚蔡吉花（黑龙江矿业学院，鸡西１５８１０５）我们知道单摆在摆动时，当振幅保持足够小时其振动周期才可以认为是一个定值，振幅比较大时周期就不能保持定值．而对于沿摆线振动的质点（摆线摆）其振动周期却不随振幅变化，只与振动轨迹的形状有...     

利用周期信号驱动Chua电路实现相同步

我们在实验上和理论上对周期信号驱动的混沌电路的相同步问题进行了研究。我们选择三类周期信号作为驱动信号，包括Chua电路产生的周期信号，正弦信号和脉冲信号。改变驱动信号的频率、振幅和脉冲信号的占空比，在周期信号和混沌信号存在小的频率失配的条件下，驱动信号的振幅在适当的变化范围内，以及脉冲信号的占空比在适当的变化范围内，都可以获得相同步。甚至当占空比小到3%的情况下，仍然可以得到相同步。特别是这类脉冲信号的控制在实际中是有意义的。     

可兴奋性细胞混沌放电区间的识别机理

在神经起步点记录到加周期分岔过程的生理实验数据，在对此分岔过程中位于周期n爆发 和周期(n+1)爆发之间的混沌的峰峰间期数据检测不稳定的周期轨道时，发现从靠近周期 n爆发的混沌的峰峰间期数据中，可以检测出不稳定的周期n轨道；而从靠近周期(n+1)爆 发的混沌的峰峰间期数据中，不仅可以检测出不稳定的周期(n+1)轨道，还可以检测出不稳 定的周期n轨道.针对该现象，借助于Sherman建议的胰腺β细胞模型，从非线性动力 学角度给出了理论解释.指明了由鞍结分岔和倍周期分岔分别产生第一类阵发和第三类阵发 为出现该 关键词： 峰峰间期 不稳定的周期轨道 鞍结分岔 倍周期分岔     

Real-time analysis of Doppler waveforms

The usefulness of objective analysis of Doppler waveforms is now well established but to date such measures have generally not been available in real-time. This Paper describes a real-time data analysis and collection system in use with a duplex scanner which is capable of producing objective measures of waveform shape during the investigation. It is shown as an example that this information can be used to identify, with high accuracy, babies likely to be classified at birth as distressed as early as the 34th week of pregnancy.     

主动声呐恒包络波形设计及其性能分析

为主动声呐设计恒包络的伪随机编码MSK调制波形。通过分析MSK信号表达式,得到波形的复包络信号。使用遗传算法优化伪随机序列,降低波形的自相关旁瓣,可减小声呐的虚警概率。通过优化复包络信号的自相关函数旁瓣值和互相关函数值,得到自相关性能和正交性能优良的恒包络波形,可以缓解多部声呐间的同频干扰。通过仿真分析波形的模糊度图,波形具有良好的频率分辨率和距离分辨率,可以取代峰均比过高的编码调相信号,满足主动声呐对运动目标的探测需求。     

A Reference Optical System of Laser Doppler Longitudinal Displacement Measurement

In this paper, a new reference optical system is put forward to achieve longitudinal displacement measurement. An optical grating is used for frequency mixing and getting high SNR signals in the measurement. Conditions and methods for getting Doppler beat signals are presented.The experiments indicate that this optical syetem can be used to measure the longitudinal displacement with high accuracy.     

A Reference Optical System of Laser Doppler Longitudinal Displacement Measurement

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改进的经验模态分解法分离超声多普勒血流与管壁信号

超声多普勒血流信号常包含管壁信号的干扰,准确分离二者对提高血流检测的精度具有重要作用。本文提出两种改进的经验模态分解(EMD)方法,先将含管壁信号的超声多普勒信号分解成多层本征模态函数(IMF),然后根据血流信号与管壁信号的不同特性,对既含管壁信号又含血流信号的IMF分量进行分离处理,最后将各层IMF分量中的管壁成分叠加得到管壁信号的估计,而血流信号可通过原信号减去估计的管壁信号而得到。将本方法用于计算机仿真信号和人体实测的超声多普勒信号,并与高通滤波器法、空间选择性降噪法和原EMD法进行比较,结果表明:本文提出的两种方法能在较大的管壁搏动速度范围内准确地分离血流信号和管壁信号,其平均相对误差比高通滤波器的结果降低了约52%和57%。可见,本文提出的两种方法有望用于血流信号与管壁信号的准确分离。      

Detecting Doppler ultrasound embolic signals using the wavelet-based feature extraction algorithm

The non-invasive detection of circulating emboli with the Doppler ultrasound technique is of active significance in clinical applications. In order to eliminate drawbacks of artifacts brought by the movement of probes or patients and detect emboli accurately, relevant feature parameters are extracted from two angles of the wavelet transform of Doppler signals. The singularity of the signal waveform is analyzed based on its wavelet scalogram; then transverse and longitudinal parameters are extracted to represent the scalogram characteristics. A novel method is proposed based on the adaptive wavelet packet basis, from which several parameters such as the energy, the scale, etc. are extracted to represent the optimized signal approximation features. With all feature parameters in two aspects, a classification system is established for Doppler Ultrasound embolic signals by solving the generalized Fisher discriminant plane. From experiments on 300 simulated and 298 clinical Doppler ultrasound signals of cerebral arteries, it is shown that the proposed system can achieve the emboli detection rates of 99.0% and 98.5% for the training set and the testing set respectively. Therefore this method makes an improve- ment of emboli detection compared to traditional in the automatic detection of clinical emboli. methods and has the possibility to be applied     

对超声DOPPLER声谱图进行分类决策的两种方法

本文介绍了两种对超声多普勒血流声谱图进行了波形自动分类法决策的方法，方法一与统计得到的标准波形相比，按适当判据进行自动分类，方法二，送入训练的人工神经网络进行自动分类，待分类波形由计算多普勒信号的最大频率提取声谱包络并经分段，平均和归一化等处理得以，文中给出了计算机模拟的结果。     

Estimation of the blood Doppler frequency shift by a time-varying parametric approach

Doppler ultrasound is widely used in medical applications to extract the blood Doppler flow velocity in the arteries via spectral analysis. The spectral analysis of non-stationary signals and particularly Doppler signals requires adequate tools that should present both good time and frequency resolutions. It is well-known that the most commonly used time-windowed Fourier transform, which provides a time-frequency representation, is limited by the intrinsic trade-off between time and frequency resolutions. Parametric methods have then been introduced as an alternative to overcome this resolution problem. However, the performance of those methods deteriorates when high non-stationarities are present in the Doppler signal. For the purpose of accurately estimating the Doppler frequency shift, even when the temporal flow velocity is rapid (high non-stationarity), we propose to combine the use of the time-varying autoregressive (AR) method and the (dominant) pole frequency. This proposed method performs well in the context where non-stationarities are very high. A comparative evaluation has been made between classical (FFT based) and AR (both block and recursive) algorithms. Among recursive algorithms we test an adaptive recursive method as well as a time-varying recursive method. Finally, the superiority of the time-varying parametric approach in terms of frequency tracking and delay in the frequency estimate is illustrated for both simulated and in vivo Doppler signals.     

Mode separation of Lamb waves based on dispersion compensation method

Ultrasonic Lamb modes typically propagate as a combination of multiple dispersive wave packets. Frequency components of each mode distribute widely in time domain due to dispersion and it is very challenging to separate individual modes by traditional signal processing methods. In the present study, a method of dispersion compensation is proposed for the purpose of mode separation. This numerical method compensates, i.e., compresses, the individual dispersive waveforms into temporal pulses, which thereby become nearly un-overlapped in time and frequency and can thus be extracted individually by rectangular time windows. It was further illustrated that the dispersion compensation also provided a method for predicting the plate thickness. Finally, based on reversibility of the numerical compensation method, an artificial dispersion technique was used to restore the original waveform of each mode from the separated compensated pulse. Performances of the compensation separation techniques were evaluated by processing synthetic and experimental signals which consisted of multiple Lamb modes with high dispersion. Individual modes were extracted with good accordance with the original waveforms and theoretical predictions.     

任意复包络信号的匀速运动目标回波脉间补偿及相干积累

现代声呐、水下制导等水声探测系统常常使用窄带脉冲、调制、编码、伪随机等种类繁多的发射信号波形来满足低信噪比检测、高分辨估计、抗干扰、主动隐蔽探测的应用需求.针对这一情况,本文研究了任意信号的长时间积累问题,给出了一种任意复包络信号的匀速运动目标回波脉间补偿及相干积累检测方法.通过构建任意发射信号波形的广义模糊函数,将匹配滤波器输出表示为所构造的广义模糊函数,使得任意复包络信号的脉压波形不仅能够用统一的数学模型来表述和计算,而且能够提供多脉冲回波的距离走动信息和多普勒频移信息,为多脉冲距离位置对齐和Fourier变换(FFT)积累提供了依据.对于用广义模糊函数表示的匹配滤波器输出,采用Keystone变换将复包络对齐,消除了距离走动,采用FFT补偿多普勒频移项,实现了任意复包络信号的长时间相干积累.对于水下探测中使用的连续波信号、线性调频信号以及复杂的m序列编码信号、Costas跳频编码信号波形进行了信号积累及检测的计算机仿真,验证了任意复包络信号的匀速运动目标回波脉间补偿及相干积累的正确性.消声水池实验验证了该方法的有效性.