A frequency domain method for the measurement of nonlinearity in heterodyne interferometry

This paper presents a method for the measurement of nonlinearity in heterodyne interferometry which utilizes the frequency spectrum of the output of the photodetector for the direct measurement of the magnitudes of the first and second harmonic nonlinearities. The underlying theory and the experimental technique are discussed. Results showing the application of this technique for the determination of the influence of the azimuthal alignments of the polarization beamsplitter, the analyzer and measurement retroreflector are presented. The applicability of the technique to the in situ optimization of an interferometer system is demonstrated. It is shown that using this technique an interferometer system can be optimized to reduce the first-harmonic nonlinearity to below 0.5 nm p-p and the second harmonic nonlinearity to 2 nm p-p. This method is contrasted with other methods and the advantages conferred by the elimination of an external reference and the phase measuring electronics are highlighted.     

Absolute angle measurement using a phase-encoded binary graduated disk

A new absolute angle measurement method using a phase-encoded binary graduated disk (PE-BGD) is presented. An absolute position binary code (APBC) is encoded by shifting the positions of binary patterns, and can be sub-divided by detecting their positions with sub-pixel resolution of a multi-element detector. Using an n-bit linear shift feedback register, we expressed a recursive APBC dividing the full circle by 2ⁿ − 1 angular positions. An experimental setup was constructed with a microscopic imaging system, a rotation stage having a precision angle encoder, and two kinds of PE-BGDs which employed 10-bit and 13-bit APBC. The resolution of the APBC, which equals to signal period of the PE-BGD, used in each disk is 0.352° and 0.044°, respectively. We evaluated its performance by comparing the readouts of the proposed system and the angle encoder, throughout the full circle range and for one signal period. In the full circle range, the differences between two measurement systems were less than 1/50 of the resolution of the APBC. We also proved that the absolute angle could be measured with small nonlinearity error, which was less than 1/600 of the signal period.     

Surrogate data test for nonlinearity of EEG signals: A newborn EEG burst suppression case study

This paper applies the surrogate data method to investigate the presence of nonlinearity in neonatal electroencephalogram (EEG) burst suppression (B/S) patterns in order to rationalize the use of nonlinear methods for automated detection of such patterns. To generate surrogate data, the statically transformed autoregressive process (STAP) algorithm is deployed, and, the correlation dimension (CD) and asymmetry due to time reversal (REV) are applied as discriminating statistics. The results of the surrogate data test demonstrate the nonlinearity characteristic of real neonatal EEG signals during both burst and suppression phases at the 0.05 significance level. The evidence of nonlinearity is found in 90% and 87% of bursts and suppressions respectively. Furthermore, the ability of nonlinear tools in detecting B/S patterns in multichannel neonatal EEG signals is investigated using receiver operating characteristic analysis. The experimental results show that the CD outperforms existing methods based on the nonlinear energy operator.     

Nonlinear dynamic of the renewable energy cycle transition in Tunisia: Evidence from smooth transition autoregressive models

In this paper, we focus on the problem of the energy transition in Tunisia were we suggest to study and modeling the nonlinear dynamic of the endogenous renewable energy cycle.As today the socioeconomic development in Tunisia is too complicated and dependent on the adopted energetic strategy. Our contribution consists on recognizing exactly the main bases of this correlative development.In this context, we try to provide some theoretical and empirical studies for renewable energy politics especially under the chaotic transition in the post revolution period in Tunisia.All this work will be based on the application of the univariate STAR (smooth transition autoregressive) method composed by two transition process types the logistic STAR model (LSTAR) and the exponential STAR model (ESTAR). As results we found that the LSTAR process is more adequate for asymmetric data for our case. In this regard, our results indicated that the renewable energy can not only work as a possible factor for energetic strategy transition in Tunisia, but also, is a promising candidate for stability and socioeconomic development.     

预应力管桩桩-土动力p-y曲线研究

通过有限元软件ABAQUS建立以振动台试验为基础的数值模型来研究桩-土水平位移的变化规律。并使用P-Y曲线法分别对预应力管桩在不同加速度峰值、不同桩型以及不同土体类别的条件下桩与土的变形进行了研究。研究表明,随着地震加速度峰值的增大,淤泥质粘土地区的桩侧土体以及桩身都会提前出现破坏。两桩、三桩、四桩桩身水平位移随着水平荷载的增大变化较单桩变化大,在相同水平地震荷载作用下,桩数越多,水平位移变化越大,其中三桩和四桩位移变化规律接近,四桩具有承受较强地震荷载的受力性能,体现了群桩受力的优势。     

Optical nonlinearity of CdSe-PMMA hybrid nanocomposite investigated via Z-scan technique and semi-empirical relations

CdSe-PMMA nanocomposite has been synthesized by ex-situ technique. The effect of different Ag doping concentrations on its structural and optical properties has been studied. X-ray diffraction reveals the hexagonal wurtzite structure of the polymer nanocomposites with preferential growth of the nanocrystals along (1 0 0) direction. Transmission electron micrograph shows the spherical CdSe nanoparticles embedded in polymer matrix. The nonlinear refractive index of the nanocomposites has been calculated using Tichy & Ticha semi-empirical relations and Z-scan technique. Z-scan results disclose the two photon absorption process in the hybrid nanocomposites with self focussing behaviour. With Ag doping, the nonlinearity is found to be increased up to 0.2% Ag doping concentration due to the confined effect of Surface Plasmon, Quantum confinement and thermal lensing. Above 0.2% Ag concentration, its value decreases due to the declined linear refractive index of the nanocomposites. Maximum two photon figure of merit is 76 for 0.2% Ag doped CdSe-PMMA hybrid nanocomposite. The present results accentuate the possibility of tuning the optical non-linearity of CdSe-PMMA hybrid nanocomposite by adjusting the doping concentration.     

车辆悬架K&C特性分析

汽车作为一种交通工具已经融入到了大多数人的生活当中,悬架系统是现代汽车的重要组成部分。一个具有良好综合性能的悬架系统,对提高汽车的平顺性和操纵稳定性有着重要的意义。建立了整车动力学模型,在此基础上对七自由度整车模型进行简化,得到1/4悬架动力学模型。对影响汽车平顺性的主要参数K&C进行了理论分析,并在该理论分析的基础上采用分段方法描述了悬架K&C非线性特性表达式,从而为研究车辆整体性能和进一步了解悬架非线性特性的时域性提供思路。     

金属丝网减振器数学建模与参数识别

金属丝网弹性元件的阻尼具有滞后非线性特性，使得实际系统中阻尼力描述较为因难。在介绍几种非线性模型的基础上，主要分析了兼有干摩擦和线性阻尼特性的混合型阻尼模型，并以此建立了某金属丝网减振器的数学模型。参数辨识的结果表明，该模型能够合理反映兼有不同性质阻尼的滞后非线性特性。     

三相电压型PWM整流器的模糊PI控制策略研究

三相电压型PWM整流器由于开关器件的非线性和对电路参数的依赖性,使得传统的PI双闭环控制无法更好的提高其动态性能,因此限制了其在更宽负载范围内的运用。本文在建立三相PWM整流器数学模型的基础上,针对目前三相PWM整流器动态性能较差的特点,设计了一种模糊PI控制器。仿真实验表明：该控制方法设计简单,提高了PWM整流器的动...     

预应力钢-混凝土连续组合梁的非线性有限元分析

以六根两跨预应力钢-混凝土连续组合梁的系列试验结果为基础,以通用有限元程序MSC.MARC(2005r2)为平台,提出了用于模拟预应力连续组合梁非线性全过程受力行为的精细有限元模型,并给出了单元选取、材料建模以及整体组装的详细过程。有限元分析基于弹塑性本构模型,能充分考虑材料非线性和几何非线性,反映结构受力全过程中预应力筋内力变化、滑移效应、内力重分布、应力分布、曲率分布以及塑性铰形成等复杂特性,深入揭示了预应力连续组合梁的受力机理和特点。模型计算结果和实测结果以及理论分析结果吻合良好,表现出良好的数值特性。文中模型对于预应力连续组合梁的精细化分析具有较高的精度和广泛的适用性,为研究预应力连续组合梁受力性能提供了强有力的工具。