Method of Weak Signals Detection Based on Chaos Suppression in the Nonresonant Parametric Drive

The evolution of chaotic state of Iarenz system on the fa- miliar parameter space cabit is analyzed. Based on the principle of chaos suppression with ntmrestmaat parametric drive, the trodel of detecting weak periodic signals in strong noise is Imilt. According to the parametric equivalent relationship obtained using averaging method and rmtmmlization method, the critical values of detection parameters are determined, which lead to a sudden change of system dynamical behavior from periodic orbit to stable equilibritma point. Sinmlation results show that weak periodic signals in strong noise can be detected acomately with the proposed system. The method can obtain aoawate rane of parameter threshold through tlxxtetical analysis, and the detection criterion is rather simple, which is more convenieat for automatic detection.

Transverse myelitis after infection with varicella zoster virus in patient with normal immunity: A case report

BACKGROUND Varicella zoster virus(VZV)is a human neurotropic and double-stranded DNA alpha-herpes virus.Primary infection with VZV usually occurs during childhood,manifesting as chickenpox.Reactivation of latent VZV can lead to various neurological complications,including transverse myelitis(TM);although cases of the latter are very rare,particularly in newly active VZV infection.CASE SUMMARY We report here an unusual case of TM in a middle-aged adult immunocompetent patient that developed concomitant to an active VZV infection.The 46-year-old male presented with painful vesicular eruption on his left chest that had steadily progressed to involvement of his back over a 3-d period.Cerebrospinal fluid testing was denied,but findings from magnetic resonance imaging and collective symptomology indicated TM.He was administered antiviral drugs and corticosteroids immediately but his symptom improvement waxed and waned,necessitating multiple hospital admissions.After about a month of repeated treatments,he was deemed sufficiently improved for hospital discharge to home.CONCLUSION VZV myelitis should be suspected when a patient visits the outpatient pain clinic with herpes zoster showing neurological symptoms.

Finite element analysis for inclined wellbore stability of transversely iso-tropic rock with HMCD coupling based on weak plane strength criterion

The finite element analysis(FEA) technology by hydraulic-mechanical-chemical-damage(HMCD) coupling is proposed in this paper for inclined wellbore stability analysis of water-sensitive and laminated rock, developed basing on the recently established FEA technology for transversely isotropic rock with hydraulic-mechanical-damage(HMD) coupling. The chemical activity of the drilling fluid is considered as phenomenological hydration behavior, the moisture content and parameters of rock considering hydration could be determined with time. The finite element(FE) solutions of numerical wellbore model considering the chemical activity of drilling fluid, damage tensor calculation and weak plane strength criterion for transversely isotropic rock are developed for researching the wellbore failure characteristics and computing the time-dependent collapse and fracture pressure of laminated rock as shale reservoirs. A three-dimensional FE model and elastic solid deformation and seepage flow coupled equations are developed, and the damage tensor calculation technology for transversely isotropic rock are realized by introducing effect of the hydration and the stress state under the current load. The proposed method utilizing weak plane strength criterion fully reflects the strength parameters in rock matrix and weak plane. To the end, an effective and reliable numerically three-step FEA strategy is well established for wellbore stability analysis. Numerical examples are given to show that the proposed method can establish efficient and applicable FE model and be suitable for analyzing the timedependsolutions of pore pressure and stresses, and the evolution region considering the hydration surrounding wellbore,furthermore to compute the collapse cycling time and the safe mud weight for collapse and fracture pressure of transversely isotropic rock.

Bifurcation and Chaos in a Weakly Nonlinear System Subjected to Combined Parametric and External Excitation

In this paper the dynamics of a weakly nonlinear system subjected to combined parametric and external excitation are discussed. The existence of transversal homoclinic orbits resulting in chaotic dynamics and bifurcation are established by using the averaging method and Melnikov method. Numerical simulations are also provided to demonstrate the theoretical analysis.

Recent Development of Chaos Theory in Topological Dynamics

We give a summary on the recent development of chaos theory in topological dynamics, focusing on Li-Yorke chaos, Devaney chaos, distributional chaos, positive topological entropy, weakly mixing sets and so on, and their relationships.

CHAOS IN PERTURBED PLANAR NON-HAMILTONIAN INTEGRABLE SYSTEMS WITH SLOWLY-VARYINGANGLE PARAMETERS

The Melnikov method was extended to perturbed planar non-Hamiltonian integrable systems with slowly-varying angle parameters. Based on the analysis of the geometric structure of unperturbed systems, the condition of transversely homoclinic intersection was established. The generalized Melnikov function of the perturbed system was presented by applying the theorem on the differentiability of ordinary differential equation solutions with respect to parameters. Chaos may occur in the system if the generalized Melnikov function has simple zeros.

Transverse coupling and dynamics of patterns in a photorefractive oscillator

The effect of transverse coupling in a photorefractive oscillator is studied. From the study the condition for stable optical patterns of multimode oscillation is given analytically and verified by numerical simulation. Under the stable condition, the period-doubling route to spatiotemporal chaos is observed.

Several Transitive Properties and Devaney's Chaos

The relation among transitivity, indecomposability and Z-transitivity is discussed. It is shown that for a non-wandering system （each point is non-wandering）, indecomposability is equivalent to transitivity, and for the dynamical systems without isolated points, Z-transitivity and transitivity are equivalent. Besides, a new transitive level as weak transitivity is introduced and some equivalent conditions of Devaney＇s chaos are given by weak transitivity. Moreover, it is proved that both d- shadowing property and d-shadowing property imply weak transitivity.

Transitivity, mixing and chaos for a class of set-valued mappings

Consider the continuous map f : x → X and the continuous map f of K,(X) into itself induced by f, where X is a metric space and K(X) the space of all non-empty compact subsets of x endowed with the Hausdorff metric. According to the questions whether the chaoticity of f implies the chaoticity of f posed by Roman-Flores and when the chaoticity of f implies the chaoticity of f posed by Fedeli, we investigate the relations between f and f in the related dynamical properties such as transitivity, weakly mixing and mixing, etc. And by using the obtained results, we give the satisfied answers to Roman-Flores's question and Fedeli's question.

改进型类Lorenz系统在弱信号检测中的应用

混沌系统具有一定的抑制噪声能力,且对初始条件敏感。因此在弱信号检测方面,相比于传统检测方法混沌系统具有很大的优势。对一种新型的类Lorenz混沌系统进行了改进,通过加入周期扰动的方法,使得改进后的系统对正弦信号幅值变化更加敏感,以满足检测微弱周期信号的条件。同时,引入了0-1测试算法来进一步确认系统混沌状态的阈值,使得改进后的系统对弱信号振幅检测精度达到10^(-4)V。通过计算状态变量方差,实现了对未知频率信号的检测。仿真结果表明,该混沌系统可检测最低信噪比为-63.01 dB。

Imprints of a gravitational wave through the weak field deflection of photons

In this study,we investigate the novel phenomenon of gravitational lensing experienced by gravitational waves traveling past a Schwarzschild black hole perturbed by a specific,first-order,polar gravitational wave.We apply the Gauss-Bonnet theorem,finding a topological contribution to the deflection of light rays passing near the black hole.We demonstrate that the deflection angle can be determined by analyzing a region entirely outside the path of the light ray,leading to a calculation based solely on the parameters of the perturbing wave(Legendre polynomial order,l;frequency,σ).This approach offers a unique perspective on gravitational lensing and expands our understanding of black hole interactions with gravitational waves.

油气测井微弱信号检测方法分析

文章分析研究了油气测井中微弱信号识别检测方法,首先回顾了微弱信号检测的传统方法,指出传统方法在处理高噪声环境下的微弱信号时的局限性;其次,详细介绍了非线性系统理论中的混沌理论和随机共振理论;最后,探讨了这些先进理论在油气测井微弱信号检测中的具体应用。该研究对提升油气资源勘探和开发的效率和准确性具有重要的实践意义,为油气测井领域提供了一种新的微弱信号检测策略。

高比例新能源电力系统可靠性高效评估和薄弱环节辨识方法

新能源渗透率的提高可能诱发供电中断的风险,使电力系统的运行可靠性降低,传统的中长期可靠性评估方法难以满足运行可靠性评估的时间需求。本文提出了一种电力系统运行可靠性高效评估算法,揭示了电力系统运行可靠性指标与风电出力不确定性因素的解析函数关系,避免不确定性因素变化时可靠性的重复计算。首先,基于隐马尔可夫模型对风电出力的分布特性进行建模;然后,通过状态枚举-混沌多项式展开方法建立可靠性指标与风电出力间的解析函数;最后,基于解析函数实现对实时风电出力下的新能源电力系统运行可靠性的高效评估及薄弱环节辨识。以修改的IEEE-RTS79系统为例进行分析计算,验证了所提方法的有效性。

基于混沌理论的电力系统微弱谐波检测方法研究

针对微弱谐波信号时频域分析检测方法在宽谱环境噪声较强场景中无法识别目标信号的缺陷,首先引入混沌系统的随机共振原理,在信号成分完全未知的情况下,利用随机噪声增强微弱目标信号进行频率盲检。进一步引入Duffing混沌系统,利用其对特定频率周期信号幅值的极高敏感性和噪声抵抗力,对检出的各谐波频率分量进行幅值精准检测。在经典随机共振模型的基础上,通过归一化改进了系统参数。结合Duffing混沌系统模型,设计了实时检测控制策略。通过粒子群寻优算法,以系统输入输出信号的互相关系数为适应度函数,寻找最优系统参数。对强随机噪声背景下的多整次谐波与间谐波混叠的谐波信号进行了仿真实验。结果表明,所提方法能在恶劣的噪声环境中,实现各谐波分量的无差频率检测与高精度幅值检测。

具有横向效应的半导体激光器的同步传输技术

通过修正描述半导体激光器的动力学模型,给出了具有横向效应的半导体激光器的动力学方程,并分析了横向效应对半导体激光器输出特性的影响。在此基础上,进一步研究了具有横向效应的半导体激光器输出信号的同步传输技术。结果表明,考虑横向效应后,半导体激光器的输出呈现新的时空混沌态,且对初始值非常敏感。同时,无论是利用半导体激光器进行单通道信号的同步传输还是多通道信号的同步传输,其传输性能均十分稳定。该项同步技术十分简单,非常易于实际应用。

基于改进型Genesio-Tesi混沌系统的弱周期信号检测

利用混沌弱信号检测相对于传统弱信号检测来说具备抗噪声能力强和对微小扰动敏感的优势,通过周期函数策动的方法改进了Genesio-Tesi方程。分析了新方程的策动力的变化范围,数值计算和仿真表明改进型Genesio-Tesi方程随策动力变化从而发生相变的特点适合用于连续白噪声背景下的弱周期信号的检测,选取合适的混沌态过渡到周期态的检测区间,在白噪声背景下信号的最低可检测信噪比达到了-46 dB。在不同色噪声背景下也有良好的检测效果,在紫噪声背景下效果最佳,最低可检测信噪比达到-52 dB。

超再生接收机在ISM频段下的混沌现象

针对超再生振荡器的传统动力学模型的工作频率过低而不具备实际参考意义的问题,本文将超再生接收机模型提升至ISM频段下的433 MHz。使用软件的数值仿真方法对改进后的模型进行混沌态动力学特性研究,采用李雅普诺夫指数法对模型混沌状态进行定量检测,并研究该频率下不同状态的接收机对弱信号的检测能力。仿真结果表明433 MHz超再生接收机在受较低频率熄灭信号控制时能够产生混沌现象,该频段下的混沌态超再生接收机灵敏度要高于周期态约3 dB,证明了混沌能够产生并被应用于实际ISM频段下的超再生接收机,为提高超再生接收机的弱信号检测能力提供了一种可行的方案。

页岩气储层井壁坍塌压力研究

页岩气储层各向异性强,易发生井壁失稳。利用四川盆地所取页岩气储层岩芯测试钻井液对页岩基体及层理面强度的影响规律,结合单一弱面准则,建立页岩气井井壁稳定预测模型,分析层理面倾角、钻井方位、钻井时间及钻井液类型等因素对页岩储层水平井坍塌压力的影响规律。研究结果表明:层理面倾角小于45°时,井壁岩石发生层理面破坏,倾角大于45°时,在某些井眼方位井壁会发生本体破坏;沿最小水平地应力方位附近钻进水平井最容易发生井壁坍塌;随钻井时间的增加,坍塌压力逐渐升高,井壁破坏形式可能会由初始的页岩基体破坏变为层理面破坏;使用油基钻井液比使用水基钻井液更容易保持井壁的长期稳定。研究结果可以为页岩气井钻井设计提供参考依据。

基于Duffing振子的弱正弦信号检测方法研究

数值仿真发现,通过设置Duffing振子初值和参考信号初相使其满足一定关系,Duffing振子从大周期态向混沌态的转变(正向相变),比较其从混沌态向大周期态的转变(逆向相变),对周期策动力的幅值体现出了更稳健的敏感性.据此,提出了一种利用Duffing振子逆向相变实现弱正弦信号检测的方法,分析了其可行性,并通过仿真与传统的检测方法进行了对比.数据表明,相同条件下,所提检测方法具有更高的检测精度.此外,根据相空间分布特点,提出了一种相轨迹运动状态的判别方法.该判别方法计算量小,并具有较好的实时性,通过仿真验证了该方法的正确性.

基于混沌理论和小波变换的微弱周期信号检测方法

根据小波变换具有多分辨率,混沌系统对噪声的强免疫力和对周期微弱信号的敏感性等特性,通过对小波阈值去噪方法和混沌Duffing振子方程的改进,提出小波阈值去噪和混沌系统相结合的微弱周期信号检测新方法。该方法利用小波变换的平滑作用对包含噪声的信号进行有限离散处理,并根据小波分解尺度确定阈值去噪深度,然后把重构的信号作为周期策动力的摄动并入混沌系统,采用混沌振子阵列实现在噪声背景下微弱信号的检测,并采用梅尔尼科夫方法作为混沌判据。该检测方法克服了以往小波分解对尺度确定的盲目性和阈值选择的不合理性以及对混沌临界状态与周期态区别的模糊性;同时能检测多种频率的信号。仿真测试表明:该方法直观、高效,检测精度高,检测的最低信噪比达到-100 dB,频率误差为0.04%左右,改善了湮没在强噪声下的微弱信号检测技术。