Measurement of the Effect of Thermal Noise on the Amplitude of Oscillation of a Maser Oscillator

Experimental verification of the effect of thermal noise on the oscillation amplitude of a maser is described. Two different masers are considered, the H maser with an homogeneous atomic line and the Rb maser with an inhomogeneous line. The effect is characterized by the spectral density of the relative amplitude fluctuations and this parameter is measured with a conventional superheterodyne AM receiver for various maser saturation factors. Experimental results show good agreement with theoretical predicted values. At high saturation factors, a peak appears with a maximum at a frequency close to the Rabi frequency. Observed values at high Fourier frequencies allow a measurement of the atomic power by the knowledge of the absolute temperature of the cavity and the prediction of the oscillator short-term frequency stability. Furthermore, the effect on amplitude and on frequency noise of an external feedback loop used to increase the cavity quality factor is discussed.     

Analytical Approach to Mean Field Theory of BSP Transition in Solid Hydrogens Under Pressure

The mean-field analytical equation for the orientational order parameter of the system of quantum rotors as a function of pressure, temperature and crystal field is derived and analyzed.     

单摆大振幅振动的解析逼近解

构造了单摆大振幅振动的高精度解析逼近周期和周期解.首先,利用Maclaurin展开和Chebyshev多项式加速技术将单摆振动方程中的正弦型恢复力用三次多项式近似代替,得到一个Duffing型方程;然后,将牛顿法与谐波平衡法结合起来建立Duffing方程的解析逼近周期及周期解,从而给出单摆振动的解析逼近解.因此,在求解过程中避免了关于参数的非线性代数方程组的出现,只需解线性代数方程组就能建立单摆振动的解析逼近周期及周期解.几乎在振幅(初始摆角)的全部取值范围内,与数值方法给出"精确"周期及周期解比较,得到的解析逼近解都有很高的逼近精度.     

测量系统存在幅值和相位误差时准确测量频率响应函数的方法

给出了一种在测量系统存在幅值和相位误差时准确测量频率响应函数的方法，导出了频率响应函数测量系统的系统函数一般表达式；确定了测量系统误差特征函数，并以此为基础消除了测量系统误差对测量结果的影响。实验结果表明，该方法行之有效，并具有一般性。     

Differences in Estimates of the Amplitude,Phase, and Frequency for Analytical and Complex Representations of a Gaussian Radio Pulse

Exact expressions are obtained for the representation of a Gaussian radio pulse by an analytical signal and quantitative estimates are derived for the difference in the instantaneous values of the amplitude, phase and frequency for complex and analytical representations of this signal. It is shown that for a fairly narrow-band signal both representations are equivalent from the point of view of estimates of the instantaneous values of the amplitude, phase and frequency, while for a broadband signal the differences may amount to tens of percent.     

The Influence of Fin Shape on the Amplitude of Random Telegraph Noise in the Subthreshold Regime of a Junctionless FinFET

Technical Physics Letters - The dependence of random telegraph noise (RTN) amplitude on the gate overdrive in a junctionless field-effect transistor (FinFET) with rectangular and trapezoidal...     

确定斜拉索减振阻尼器优化参数的一种方法

斜拉桥拉索的大幅振动越来越引起人们的关注，目前减振的主要手段是安装阻尼器。本文推导了考虑拉索垂度、弯曲刚度的拉索-阻尼器系统运动方程，根据最优控制原理得到最优控制反映，提出了一种在具有控制结构约束下求解准最优控制力，进而求得优化阻尼系数的方法，并结合实桥拉索进行了仿真计算，所得结果表明该方法是有效可行的。所提方法对斜拉减振阻尼器参数优化设计具有一定的指导意义。     

Determining the Amplitude of a Sound Wave Oscillatory Velocity with a Thermoanemometer in a Flowing Medium

A method is proposed for isolating and estimating the oscillatory and hydrodynamic components of the velocity measured by a constant-temperature thermoanemometer when high-intensity sound propagates in a flowing medium.     

SPWM中载波对电机振动和噪声的影响

阐述了在采用正弦脉宽调制（SPWM）技术变频驱动交流电动机的情况下，载波对于电机振动和噪声的影响，并且分析了及其作用的机理。最后介绍了交流电动机在SPWM变频驱动下减小载波对振动和噪声影响的措施。     

Characterization of Frequency Stability: A Transfer Function Approach and Its Application to Measurements via Filtering of Phase Noise

Frequency stability of high-quality signal sources is characterized in the Fourier frequency domain by the spectral density Sy(f) of the fractional instantaneous frequency deviation y(t), and in the time domain by the Allan variance ?y2(?). Two well-known types of measuring apparatus used to evaluate these parameters are analog spectrum analyzers and digital electronic counters, respectively. A detailed analysis of the structure of the relation between ?y2(?) and Sy(f) shows that it is possible to define a variance, i.e., a time-domain measure, by its transfer function in the Fourier frequency domain, even when no corresponding measurement sequence exists in the time domain. Two different kinds of variance are then defined, which possess different properties for white and flicker phase noises. One of these variances is an estimate of the Allan variance. These variances may be measured by a suitable filtering of phase noise at the output of a phase detector.     

Analytical Representation of the Complex Frequency Response of a Hydrophone

Measurement Techniques - The problem of analytical representation of the experimental complex frequency response of a hydrophone based on a model consisting of a lead line and a minimum-phase...     

非高斯噪声激励下分段非线性系统的平均首次穿越时间

噪声诱导的逃逸问题出现在众多研究领域,平均首次穿越时间作为用来表征粒子逃逸现象的重要特征量,现已被广泛应用于电子器件的开关时间及双稳器件的寿命等问题的研究之中.本文研究了由乘性非高斯噪声和加性高斯白噪声共同驱动下分段非线性系统的平均首次穿越时间问题.运用路径积分法、统一色噪声近似和最速下降法,得到了系统平均首次穿越时间的表达式.通过数值计算发现,在非高斯噪声偏离参数、噪声关联时间和互关联强度的作用下,非高斯噪声强度的增加会导致平均首次穿越时间曲线出现单峰结构,而加性噪声强度的增加会导致平均首次穿越时间的单调减小,这表明在该模型中非高斯噪声和高斯噪声对平均首次穿越时间的影响是不同的.此外还进一步讨论了非高斯噪声偏离参数、噪声关联时间和噪声互关联强度对平均首次穿越时间的影响.     

应用逆子结构方法确定包装耦合体动态特性

应用动态逆子结构分析理论,针对"产品-包装耦合-运载体"系统中的包装耦合体,提出一套基于系统与部件实验测量的耦合动态特性分析计算新方法,包括直接逆子结构法和间接逆子结构法.应用集总参数模型及部分实验结果检验该套技术方法的有效性.这两种方法是为实际包装耦合体的设计及其缓冲防震性能的评价而提出的.     

Microprocessor Implementation of a Fast and Simultaneous Amplitude and Frequency Detector for Sinusoidal Signals

A microprocessor-controlled implementation of a fast and simultaneous amplitude and frequency detector for sinusoidal signals is introduced. The method computes the amplitude and frequency from three successive samples of the input signal. A special feature is that the samples are taken within a fraction of the period of the signal being measured, thereby minimizing the measurement time. Automatic selection of the sampling interval is based on the input frequency range.     

An Approximate Method to Obtain the Amplitude Distribution on the Exit Reference Sphere Due to a Non-uniform Transmission Filter

Abstract

A method is proposed to calculate the amplitude on the reference sphere due to a non-uniform transmission filter. The method may be divided into two stages: imaging of the filter plane, and projection of the filter image plane on the reference sphere. In this way we deduce some expressions which relate the coordinates on the filter plane to those on the reference sphere. Although the method is approximate, it has the advantage of saving computing time, since it is only necessary to trace two rays for each considered field. The accuracy of the method is studied by applying it to different real systems.     

An Analytical Study on a Model Describing Heat Conduction in Rectangular Radial Fin with Temperature-Dependent Thermal Conductivity

The coupling of the homotopy perturbation method (HPM) and the variational iteration method (VIM) is a strong technique for solving higher dimensional initial boundary value problems. In this article, after a brief explanation of the mentioned method, the coupled techniques are applied to one-dimensional heat transfer in a rectangular radial fin with a temperature-dependent thermal conductivity to show the effectiveness and accuracy of the method in comparison with other methods. The graphical results show the best agreement of the three methods; however, the amount of calculations of each iteration for the combination of HPM and VIM was reduced markedly for multiple iterations. It was found that the variation of the dimensionless temperature strongly depends on the dimensionless small parameter ${\varepsilon_1}$ . Moreover, as the dimensionless length increases, the thermal conductivity of the fin decreases along the fin.     

正交异性环板-刚性质量系统的大幅振动和热屈曲

采用数值计算方法分析了具有中心刚性质量的极正交各向异性环形薄板在均匀升温下的大振幅振动和热过屈曲,基于von Karman薄板理论给出了问题轴对称位移形式的动力学控制方程,分析了系统的自由横向谐振动,借助了Kantorovich平均法消去时间变量,将偏微分控制方程转化为非线性常微分方程边值问题,采用打靶法获得了周边固定夹紧环板－刚性质量系统非线性振动幅－频响应以及热过屈曲响应,给出了不同材料刚度参数和中心质量参数下的幅－频响应曲线及过屈曲平衡路径。     

Oscillators with Frequency and Amplitude Outputs for the Measurement of Two Parameters

A class of harmonic oscillators is described which has the frequency of oscillation determined by one parameter of an RC or RL circuit and the amplitude of oscillation by the other parameter. These oscillators are useful in the impedance measurement of physical or biological objects when two attributes of the object are related to two electrical parameters of the equivalent circuit. A pole or zero is derived from the measured object by isolating it from the oscillator. The remainder of the oscillator contains linear elements and a single memoryless nonlinearity. Second-order oscillators containing a hard nonlinearity and third-order oscillators containing a soft nonlinearity are presented. The frequency and amplitude relationships are derived using linear theory and the describing function method. The theoretical results are verified by analog computer simulations. The oscillators are described in general terms by means of flow graphs.