About the Aerothermoelastic Stability of Panels in Supersonic Flows

This article provides new insights into the aerothermoelastic stability of thin plates. Particularly, the issue of loss of stability of an isotropic plate-strip of constant thickness immersed in a supersonic flow field and subjected to a variable temperature field through the thickness is examined. Using the basic principles of the theory of aerothermoelasticity of isotropic bodies, the theories of flexible panels, and the linear law of temperature field through the thickness of the panel, the stability equations and associated boundary conditions are obtained. As expected, the coefficients of the aerothermoelastic governing equations depend on the thermal load, and consequently the panel-flutter critical speed depends on temperature. The model takes into account quadratic and cubic aerodynamic non-linearities as well as cubic geometric non-linearities. Due to the inhomogeneity of the temperature field distribution across the thickness plate buckling instability occurs. This instability accounts for the deformed shape of the plate and the stability boundary depends on the variables characterizing the flow speed, the temperature of the middle plane and the temperature gradient in the direction normal to the plane. It is shown that the combined effect of the temperature field and free-stream regulates the process of stability and the temperature field can significantly change the flutter critical speed and flutter behavior. The problem of stability is also considered in the non-linear framework. The existence and behavior of flutter-type vibrations is investigated at pre- and post-critical speeds. The influence of the temperature field on the dependency of the limit cycle amplitude as a function of speed is studied. Results and discussions are presented along with pertinent concluding remarks.     

Diagnosis of plant-wide oscillation through data-driven analysis and process understanding

Disturbances that propagate throughout a plant due to recycle streams, heat integration or other means can have an especially large impact on product quality and running costs. There is thus a motivation for automated detection of a plant-wide disturbance and for determination of the root cause so that the disturbance may be removed. In this article, data-driven techniques are used to diagnose a plant-wide oscillation in an Eastman Chemical Company plant. A numerical non-linearity index derived from routine measurements was able to suggest the root cause. Process understanding possessed by the plant control engineers then enhanced the data-driven analysis, for instance by identifying a proxy measurement for an unmeasured flow through the valve suspected of being the root cause. In situ tests of just one valve confirmed the suspected root cause and the plant-wide oscillation disappeared after repairing the valve. The diagnosis was right first time and the maintenance effort was thus minimized. The success of the study suggests there exists a fruitful direction for future research in the automated linkage of data-driven analysis with information about the structure and connectivity of the process.     

Linearity Testing of A/D Converters Using Selective Code Measurement

Measurement of integral non-linearity (INL) and differential non-linearity (DNL) of an A/D converter using the histogram method incurs large test time. This test time can be a significant percentage of the total test time, especially for high resolution and low sampling-speed A/D converters. This paper describes a test methodology for measuring the INL and DNL specifications of A/D converters by measuring a subset of the total set of code widths. This methodology is based on the fact that manufacturing variations in the electronic components of an A/D converter affect specific sets of codes in a similar manner. The proposed methodology measures code width parameters across such different sets of codes and estimates the A/D converter transfer function from the resulting information. A novel test generation methodology is presented for measuring the relevant code widths using a piecewise linear ramp that is designed to extract test information accurately from test data in minimal test time. The test procedure has been applied to different A/D converters and test time reduction of more than 75% has been achieved.

Harmonic distortion analysis of double gate graded-channel MOSFETs operating in saturation

In this work we present an analysis of harmonic distortion (HD) in graded-channel (GC) gate-all-around (GAA) devices operating in saturation region for analog applications. The study has been performed through device characterization and two-dimensional process and device simulations. The overall study has been done on the total and third order HDs. When applied in the saturation regime as an amplifier, the GC outperforms conventional GAA transistors presenting simultaneously higher transconductance, lower drain output conductance and more than 15 dB improved linearity. The influence of channel length reduction on the HD is also analyzed. Although slight linearity degradation is observed in both the conventional and the GC devices when reducing the channel length, the HD presented by the GC transistor is significantly lower than the one showed by conventional device for any studied channel length. This allows AC input signal amplitude up to 20 times higher than the conventional GAA for a same specified distortion level.     

混合光缆线路与色散分布光缆(上)

介绍了为扩大波分复用光缆系统的传输容量而采用的、由2种不同类型光纤组成的各种混合光缆线路，描述了一些制造商开发出来的沿长度具有不同色散值和不同有效面积的光纤和光缆及其试验结果，最后展望了这种光缆的未来发展。     

Detecting non-linearity induced oscillations via the dyadic filter bank property of multivariate empirical mode decomposition

Non-linearity induced oscillations in control loops are characterized by the presence of higher order harmonics. In this paper the dyadic filter bank property of the multivariate empirical mode decomposition (MEMD) is exploited to reveal the harmonic content of the oscillatory signal to indicate the presence of non-linearity. Once the harmonics are identified the extent of non-linearity is evaluated automatically using degree of non-linearity measure (DNL) introduced in our previous work [11]. Although detection of non-linearity via harmonics is an old concept; any automatic method has still not been reported. Moreover, the existing methods suffer from the restrictive assumption of signal stationarity. The proposed method is more robust in identifying the non-linearity induced oscillations and is adaptive and data driven in nature and thus requires no a priori assumption about the underlying process dynamics. The proposed method can also differentiate among the different sources of multiple oscillations, for example combinations of nonlinearity and linear sources or two nonlinear sources. Apart from detecting the non-linearities the proposed method can also contribute in locating the source of non-linearity, thereby reducing the maintenance time to a considerable extent. The robustness and effectiveness of the proposed method is established using industrial case studies and results are compared with existing methods based on higher order statistics [7] and surrogate based methods [8].     

基于非线性时序信号神经网络预测模型讨论

本文从神经网络理论及实践两个方面，探讨了目前非线性时序信号预测神经网络模型存在的几个问题：网络输入节点数的确定，隐层节点数及隐层数目，节点单元作用函数的确定，三层前向神经网络的逼近能力，神经网络的外延性。本文提出了这些问题，以期加快时序信号预测研究的发展。     

An in situ digital background calibration algorithm for multi-channel R-βR ladder DACs

The R-2R resistor ladder is one of the best topologies for implementing compact-sized digital-to-analog converter (DAC) arrays in implantable neuro-stimulators. However, it has a limited resolution and considerable inter-channel variation due to component mismatches. To avoid losing analog information, we present sub-radix-2 DAC implemented by the R-βR resistor ladder in this paper. The digital successive approximation register (DSAR) algorithm corrects the transfer function of DACs based on their actual bit weights. Furthermore, a low-cost in situ adaptive bit-weight calibration (ABC) algorithm drives the analog output error between two DACs to zero by adjusting their bit weights automatically. The simulation results show that the proposed algorithm can calibrate the non-linear transfer function of each DAC and the gain error among multiple channels in the background.     

线性霍尔传感器在直线位移中的应用

为了实现实时的无接触直线位移测量,通过线性霍尔传感器获取磁场强度信号,采用定时中断方式完成数据采集,并以MSP430F169单片机作为运算及控制单元。考虑到普通的永磁无法形成梯度、线性的磁场分布,因此,在改进磁铁结构的基础上,提出了线性霍尔传感器非线性方法的测量方案,实现了对位置信号的无接触实时精确测量。实验结果表明,该霍尔变送器系统能实现对位置值的准确测量。     

GA-BASED PID NEURAL NETWORK CONTROL FOR MAGNETIC BEARING SYSTEMS

In order to overcome the system non-linearity and uncertainty inherent in magnetic bearing systems, a GA(genetic algorithm)-based PID neural network controller is designed and trained to emulate the operation of a complete system (magnetic beating, controller, and power amplifiers).The feasibility of using a neural network to control nonlinear magnetic beating systems with unknown dynamics is demonstrated. The key concept of the control scheme is to use GA to evaluate the candidate solutions (chromosomes), increase the generalization ability of PID neural network and avoid suffering from the local minima problem in network learning due to the use of gradient descent learning method. The simulation results show that the proposed architecture provides well robust performance and better reinforcement learning capability in controlling magnetic bearing systems.