机抖激光陀螺随机噪声注入方法研究

机抖激光陀螺通过在抖动驱动信号中注入一定强度的随机噪声来消除动态闭锁误差.为了适应机抖激光陀螺小型化和其控制电路数字化的发展,设计了在以抖动驱动信号采用方波形式的基础上,其随机噪声的注入采取了应用寄存器产生的伪随机噪声-m序列按照对方波占空比进行调制的方式,并建立了抖动机构的数学模型,应用所建立的模型通过Matlab中的Simulink进行了仿真.依照随机噪声注入效率的计算方法,文中采用的方式其噪声注入效率要高于以往采用的应用高斯白噪声对交变正弦波驱动信号进行幅值调制的方式,对此进行了实验验证,证明这种随机噪声注入方式效果良好.     

Identification of stiffness, dissipation and input parameters of randomly excited non-linear systems: Capability of restricted potential models (RPM)

A dynamic identification technique in the time domain for time invariant systems under random external forces is presented. This technique is based on the use of the class of restricted potential models (RPM), which are characterized by a non-linear stiffness and a special form of damping, that is a product of the input power spectral density (PSD) matrix and the velocity gradient of a non-linear function of the total mechanical energy. By applying stochastic differential calculus and by specific analytical manipulations, some algebraic equations, depending on the response statistics and on the mechanic parameters that characterize RPM, are obtained. These equations can be used for the dynamic identification of the above mechanic parameters once the response statistics of the system to be identified are evaluated. The proposed technique allows one to identify single-degree-of-freedom or multi-degrees-of-freedom systems in the case of unmeasurable input. Further, the probabilistic characteristics of the external forces can be completely estimated in terms of PSD matrix.     

Toward automatic evaluation of defect detectability in infrared images of composites and honeycomb structures

Non-destructive testing (NDT) refers to inspection methods employed to assess a material specimen without impairing its future usefulness. An important type of these methods is infrared (IR) for NDT (IRNDT), which employs the heat emitted by bodies/objects to rapidly and noninvasively inspect wide surfaces and to find specific defects such as delaminations, cracks, voids, and discontinuities in materials. Current advancements in sensor technology for IRNDT generate great amounts of image sequences. These data require further processing to determine the integrity of objects. Processing techniques for IRNDT data implicitly looks for defect visibility enhancement. Commonly, IRNDT community employs signal to noise ratio (SNR) to measure defect visibility. Nonetheless, current applications of SNR are local, thereby overseeing spatial information, and depend on a-priori knowledge of defect’s location. In this paper, we present a general framework to assess defect detectability based on SNR maps derived from processed IR images. The joint use of image segmentation procedures along with algorithms for filling regions of interest (ROI) estimates a reference background to compute SNR maps. Our main contributions are: (i) a method to compute SNR maps that takes into account spatial variation and are independent of a-priori knowledge of defect location in the sample, (ii) spatial background analysis in processed images, and (iii) semi-automatic calculation of segmentation algorithm parameters. We test our approach in carbon fiber and honeycomb samples with complex geometries and defects with different sizes and depths.     

光学频率梳非线性传输及其在相位噪声探测中的应用

光纤传递链路中相位噪声探测是基于光纤的精确射频标准传递系统中重要组成部分。为解决光纤链路相位噪声探测中节点反射干扰的问题, 本文基于广义非线性薛定谔方程, 理论上研究了窄带光学频率梳在色散位移光纤中的非线性光学传播特性。在理论分析的基础上, 结合密集波分复用架构, 提出了一种基于锁模光学频率梳进行光纤传递射频信号的相位噪声探测新技术, 克服了节点反射干扰, 给出了初步实验验证。     

Viewing the noise propagation mechanism in a unidirectional transition cascade from the perspective of stability

Noise and noise propagation are inevitable and play a constructive role in various biological processes. The stability of cell homeostasis is also a critical issue. In the unidirectional transition cascade of colon cells, stem cells (SCs) are the source. They differentiate into transit-amplifying cells (TACs), and TACs differentiate into fully differentiated cells (FDCs). Two differentiation processes are irreversible. The stability factor is introduced so that the noise propagation mechanism from the perspective of stability is studied according to the noise propagation formulas. It is found that the value of the stability factor corresponding to the minimum noise in FDCs may be the best choice to enable colon cells to maintain high stability and low noise of the cascade. Moreover, for the source cell, the total noise only includes intrinsic noise; for the downstream cell with self-proliferation capability, the total noise mainly depends on its intrinsic noise and transmitted noise from upstream cells, and its intrinsic noise is dominant. For the downstream cell without self-proliferation capability, the total noise is mainly determined by transmitted noises from upstream cells, and there is a minimum value. This work provides a new approach for studying the mechanism of noise propagation while considering the stability of cell homeostasis in biological systems.     

数控裁剪机切割刀壳体振动噪声预测分析*

高频往复式切割刀是柔性材料数控裁剪机的核心部件。该文对切割刀壳体的振动噪声改进措施进行研究。首先对切割刀进行刚体动力学分析,获取其所受动载荷情况,并通过数值计算验证了切割刀刚体动力学模型的可靠性。其次,基于有限元法获取切割刀壳体模态特性,并通过锤击激振实验验证了有限元模型的准确性。然后基于模态仿真结果进行谐响应分析,将计算得到的频域动载荷施加至切割刀壳体各螺栓固定处,获取结构加速度响应频谱,结合振动响应结果,对壳体进行声固耦合分析,并进行实验对比,验证了分析方法的准确性。最后,计算不同的阻尼措施对壳体噪声辐射的影响,为切割刀的减振降噪提供参考。     

Multiple resonances with time delays in scale-free networks of Hodgkin-Huxley neurons subjected to non-Gaussian noise

The spiking behavior with varying time delay in scale-free networks of Hodgkin-Huxley neurons with non-Gaussian noise has been studied,and the effect of non-Gaussian noise on the delay-induced spiking behavior is discussed. It was found that multiple spatio-temporal resonances occur when the delay lengths are integer multiples of the spiking periods,and the resonances may be strengthened when the non-Gaussian noise is appropriate. This result shows that time delays can optimize the spiking temporal regulari...     

Gas damping force noise on a macroscopic test body in an infinite gas reservoir

We analyze here the force noise associated with the mechanical damping of a test body surrounded by a large volume of rarefied gas, considering the statistics of momentum exchange in inelastic molecular collisions. In addition to calculating the force noise on a cube, sphere, and cylinder, we discuss the limits in applying this analysis to experimental configurations in which the test body is surrounded by an enclosure that is only slightly larger than the test body itself.     

Relative intensity noise induced by four-wave mixing in the case of two-wave transmission in an optical fiber

Four-wave mixing (FWM) is a significant nonlinear effect in wavelength division multiplexing (WDM) fiber-optic systems. For two-wave transmission, it is easily found that the FWM noise power decreases with frequency spacing and increases with signal power. However, the variation of relative intensity noise (RIN) with frequency spacing and signal power is only 2 dB at most. The intensity fluctuations induced by the energy exchange between the FWM generated new waves and the original ones are trivial and the influence of FWM on RIN can be neglected. It is also found that the increase of RIN with signal power is mainly attributed to stimulated Brillouin scattering (SBS) rather than FWM.