Galvanic vestibular stimulation elicits consistent head-neck motion in seated subjects

Humans actively stabilize the head-neck system based on vestibular, proprioceptive and visual information. Galvanic vestibular stimulation (GVS) has been used previously to demonstrate the role of vestibular feedback in standing balance. This study explores the effect of GVS on head-neck kinematics and evaluates the approach to investigate the vestibular contribution to head-neck stabilization. GVS was applied to 11 seated subjects using seven different stimuli (single sinusoids and multisines) at amplitudes of 0.5-2 mA and frequencies of 0.4-5.2 Hz using a bilateral bipolar configuration while 3-D head and torso kinematics were recorded using motion capture. System identification techniques were used evaluating coherence and frequency response functions (FRFs). GVS resulted in significant coherence in roll, yaw and lateral translation, consistent with effects of GVS while standing as reported in the literature. The gain of the FRFs varied with frequency and no modulation was observed across the stimulus amplitudes, indicating a linear system response for the stimulations considered. Compared to single sine stimulation, equivalent FRFs were observed during unpredictable multisine stimulation, suggesting the responses during both stimuli to be of a reflexive nature. These results demonstrate the potential of GVS to investigate the vestibular contribution to head-neck stabilization.     

Postural control adaptation during galvanic vestibular and vibratory proprioceptive stimulation

The objective for this study was to investigate whether the adaptation of postural control was similar during galvanic vestibular stimulation and during vibratory proprioceptive stimulation of the calf muscles. Healthy subjects were tested during erect stance with eyes open or closed. An analysis method designed to consider the adaptive adjustments was used to evaluate the motion dynamics and the evoked changes of posture and stimulation response. Galvanic vestibular stimulation induced primarily lateral body movements and vibratory proprioceptive stimulation induced anteroposterior movements. The lateral body sway generated by the galvanic stimulation was proportionally smaller and contained more high-frequency movements (> 0.1 Hz) than the anteroposterior body sway induced by the vibratory stimulation. The adaptive adjustments of the body sway to the stimulation had similar time course and magnitude during galvanic and vibratory stimulation. The perturbations induced by stimulation were gradually reduced within the same time range (15-20 s) and both kinds of stimulation induced a body leaning whose direction was dependent on stimulus. The similarities in the adjustment patterns suggest that postural control operates in the same way independent of the receptor systems affected by the disturbance and irrespective of whether the motion responses were induced in a lateral or anteroposterior direction.     

Acclimation to chronic constant-rate peripheral stimulation provided by a vestibular prosthesis

We are developing two types of vestibular prosthetics that electrically stimulate afferent neurons. One type replaces absent sensory function by providing stimulation that modulates above and below a baseline established with the head stationary. The other type provides constant stimulation and is turned on only when necessary, for example, to override unnatural variations like those experienced by patients suffering from Ménère's syndrome; this prosthesis does not provide motion information. Both prostheses require neural plasticity, which we investigated by providing chronic constant-rate stimulation to semicircular canal neurons in three guinea pigs. The stimulation was alternately switched on or off for eight consecutive weeks before being switched daily. A brisk horizontal nystagmus was measured when the stimulation was first turned on and then dissipated over the course of a day. The nystagmus demonstrated an after-effect in the opposite direction when the stimulation was turned off. The nystagmus that we measured after just a few (2 to 5) off-to-on transitions returned to baseline more rapidly than when first turned on. In fact, after many such off-to-on or on-to-off transitions, little nystagmus was evoked by turning the stimulation on or off. These findings show that the brain acclimates to constant-rate stimulation.     

Robust stability analysis for current-programmed regulators

Uncertainty models for the three basic switch-mode converters: buck, boost, and buck-boost are given in this paper. The resulting models are represented by linear fractional transformations with structured dynamic uncertainties. Uncertainties are assumed for the load resistance R=R/sub O/(1+/spl delta//sub R/), inductance L=L/sub O/(1+/spl delta//sub L/), and capacitance C=C/sub O/(1+/spl delta//sub C/). The interest in these models is clearly motivated by the need to have models for switch-mode DC-DC converters that are compatible with robust control analysis, which require a model structure consisting of a nominal model and a norm-bounded modeling uncertainty. Therefore, robust stability analysis can be realized using standard /spl mu/-tools. At the end of the paper, an illustrative example is given which shows the simplicity of the procedure.     

NIR laser stimulation for dynamic timing analysis

Dynamic Laser Stimulation (DLS) is an important technique for IC analysis and timing characterization. Implementations and practical considerations are presented for SDL, RIL and LADA techniques as well as the latest methodology know as Delay Variation Mapping (DVM). Downside of dynamic laser techniques is higher complexity of IC setup and results interpretation. Understanding these aspects is necessary to benefit from DLS for the IC analysis and timing characterization.     

Special stability analysis for the Shichman formula

The Shichman formula for numerical integration is shown to be A stable for all step ratios a. However, for a > 1+?2 with a negative real eigenvalue K, there is an initial instability phenomenon whose presence precludes the use of this a range. The phenomenon is absent when a <1+?2.     

芯片制造过程中的电化学侵蚀控制

芯片金属键合孔上的电化学侵蚀会引起封装时键合接触不好等问题,因此在芯片加工时消除电化学侵蚀非常重要。文章通过一个解决侵蚀斑问题的案例,找到了引起侵蚀斑的根本原因和有效的解决方法,阐述了电化学侵蚀反应的理论模型。通过严控冲水后和甩干工艺间的间隔时间可以彻底解决由于湿法清洗工艺引起的电化学腐蚀。     

选择性化学镍金板贾凡尼效应改善

贾凡尼效应在PCB业界已讨论过很多,本文从实际生产选择性化金板工艺流程出发,应用原电池理论,总结出一套解决因为贾凡尼效应而产生BGA焊盘缩小、孔口无铜等缺陷的方法。     

Invariant density analysis: modeling and analysis of the postural control system using Markov chains

In this paper, a novel analysis technique, invariant density analysis (IDA), is introduced. IDA quantifies steady-state behavior of the postural control system using center of pressure (COP) data collected during quiet standing. IDA relies on the analysis of a reduced-order finite Markov model to characterize stochastic behavior observed during postural sway. Five IDA parameters characterize the model and offer physiological insight into the long-term dynamical behavior of the postural control system. Two studies were performed to demonstrate the efficacy of IDA. Study 1 showed that multiple short trials can be concatenated to create a dataset suitable for IDA. Study 2 demonstrated that IDA was effective at distinguishing age-related differences in postural control behavior between young, middle-aged, and older adults. These results suggest that the postural control system of young adults converges more quickly to their steady-state behavior while maintaining COP nearer an overall centroid than either the middle-aged or older adults. Additionally, larger entropy values for older adults indicate that their COP follows a more stochastic path, while smaller entropy values for young adults indicate a more deterministic path. These results illustrate the potential of IDA as a quantitative tool for the assessment of the quiet-standing postural control system.     

Robust stability analysis for two-dimensional systems via eigenvalue sensitivity

This paper presents a robust stability analysis tool for the two-dimensional (2-D) discrete system by using eigenvalue sensitivity. It includes the 2-D system stability test via one-dimensional (1-D) system robust stability analysis. The merits of this method are fewer computations and good programmability. How to estimate the stability margin, on which the degree of stability and the spatial performance of the system depend, is also an important issue in this paper.Parts of this work have been presented at the IEEE International Conference On Acoustic, Speech, and Signal Processing, 1993 in Minnesota, USA. This work was supported by the National Science Council of the Republic of China under Grant NSC 81-E036-514.     

The dynamic properties and stability analysis for vertical-cavitysurface-emitting lasers

In this paper, a phenomenal analysis on the wavelength dependence of the gain temperature coefficient is presented. Based on this model, the relation between the dynamic properties and the lasing wavelength within the gain regime are investigated using the rate equations, including the wavelength dependence of both the differential gain and linewidth enhancement factor. Our calculation shows that when the lasing mode occurs in the negative damping rate regime, the relative intensity noise (RIN) is more than 43 dB higher, and the linewidth is broadened out more than 30 dB, which indicates laser being in a chaotic state. The stability of the vertical-cavity surface-emitting lasers with distant external optical feedback is analyzed numerically. The results for different cavity designs are compared. The effects of the nonlinear gain coefficient on RIN and spectral linewidth of the VCSEL's with external optical feedback is investigated     

A statistical mechanical analysis of postural sway using non-Gaussian FARIMA stochastic models

In this paper, postural sway is modeled using a fractional autoregressive integrated moving average (FARIMA) family of models: the center-of-pressure (COP) motion is viewed in terms of a self-similar, anti-persistent random-walk process, obtained by fractionally summating non-Gaussian random variables, whose correlation structure for small time lags is shaped by a linear time-invariant low-pass filter. The model parameters are: the strength of the stochastic driving, e.g., the root mean square (rms) value of the time-difference COP motion; the DC gain, damping ratio and natural frequency of the filter; the Hurst exponent, which measures the random-walk antipersistence magnitude. In the proposed modeling procedure, a graphical estimator for determining the Hurst exponent is cascaded to a method for matching autoregressive (AR) models to fractionally difference COP motion via higher order cumulants. The effect of the presence or absence of vision on the model parameter values is discussed with regard to data from experiments on healthy young adults.     

光电检测前置放大电路设计及稳定性分析

光电检测前置放大电路的设计直接影响整个检测电路的性能。选择光电二极管在光伏模式下工作,使用低输入偏置电流和低噪声放大器,设计了光电检测前置放大电路,重点分析了转换电路的稳定性,给出了转换电路元器件参数选择的依据。电路在实际应用中取得了良好的效果。     

Closed-loop stability analysis of microwave amplifiers

A stability analysis technique of microwave amplifiers, valid for large- or small-signal regimes, is presented. The technique calculates the system poles and zeroes from a closed-loop frequency response of the circuit linearised around its steady state. The method has been applied to an S-band monolithic amplifier, detecting spurious oscillations for certain specific bias conditions and input power levels, in good agreement with measurements     

基于图像分析的体操落地稳定性分析

针对体操落地稳定性控制和定量分析难度较大的问题,提出基于图像区域特征同态分割的体操落地图像视觉评估和稳定性分析方法。首先构建Pairwise MRF模型提取体操落地视觉特征,并划分图像区域;然后对采集的体操落地视觉图像在MRF框架下构建视觉观察分布模型,采用图像区域特征同态分割方法设计体操落地稳定性的视觉判别模型,实现体操落地稳定性视觉定量分析;最后仿真结果表明,该方法的体操落地稳定性控制和评价置信度较高,可靠性好,具有一定的实际应用价值。     

Averaging analysis approach for stability analysis of speed-sensorless induction motor drives with stator resistance estimation

In this paper, the stability property of speed-sensorless induction motor drives with stator resistance estimation is analyzed using the averaging analysis technique. Explicit stability conditions are then derived to clarify analytically when the instability may occur and how the regressor vectors used in the estimation and the integral adaptation gains should be designed to assure stability. The derived stability conditions also reveal that the coupling between the speed and the stator resistance estimation loops is the main cause of instability and that stabilization of each individual estimation loop is necessary but insufficient to guarantee stability. Instead of the conventional regressor vectors that are shown to make the estimation unstable in some regenerative regions, two new regressor vectors are introduced to achieve stability for the whole operating conditions. Moreover, investigation of the persistently exciting (PE) conditions points out theoretically the loss of identifiability of the rotor speed and the stator resistance at no loads and at zero frequency operations. Validity of all the analytical results is verified by simulation and experiment.     

复合表面处理贾凡尼效应的研究

文章针对复合表面处理组合（碳墨-沉锡、碳墨-沉银、碳墨-OSP、沉金-OSP）在生产中存在的贾凡尼效应,从设计上试验抓取不同焊盘面积比的贾凡尼效应的规律,为改善贾凡尼缺陷提供指导。     

Large-signal stability analysis of spacecraft power processingsystems

The authors present a comprehensive large-signal stability analysis of a solar-array power system. The stability of the equilibrium points of a system with a typical nonlinear load characteristic is analyzed. Employing state-plane analysis techniques, the dynamic behavior of the system from an arbitrary initial condition is characterized, and the region of the desired stable operation is identified. The stability and transient response of the system operation near the solar array's maximum power point are evaluated. The dynamic response of the spacecraft power system operating in the shunt mode and battery-discharge mode is analyzed     

Early recognition of postural disorders in multiple sclerosisthrough movement analysis: a modeling study

In the present study, spontaneous postural behavior has been analyzed in freely standing multiple sclerosis (MS) patients, exhibiting no clinically assessable abnormalities of postural control. This population has been compared with two other groups, healthy people and hemiparetic patients. This latter group represents a situation where the central nervous system (CNS) lesion is precisely localized in one anatomical site and no signal-conduction disorders are present; i.e., it has an opposite anatomical character with respect to the MS at a preclinical stage. The hypothesis underlying the modeling study is the presence of a controller block working in a feedback posture control system. This controller block receives the body sway as input, and produces the corresponding ankle torque stabilizing the body, the latter being modeled as an inverted pendulum. The CNS damage, caused by MS, is supposed to be reflected in some detectable change in the structure of the controller of the posture control system. The identification of the controller has been performed by means of a parametric estimation procedure which employed as input sequences, data recorded by means of a movement-analysis (MA) system. Reported findings show a structural change of the model of the controller block in the posture control system. This result may suggest the presence of an MS-specific reorganization of the posture control system. Some speculation is finally made on the black-box approach in comparison with traditional posturography, to arrive at hypothesizing a progression path for postural disorders     

Direct methods for transient stability analysis of power systems: Recent results

Transient stability analysis of a power system is concerned with the system's ability to remain in synchronism following a disturbance. In utility planning, transient stability is studied by numerical simulation. The long CPU run times for simulation preclude their use for on-line security analysis. Interest has therefore shifted toward the Lyapunov direct method of stability analysis. This paper provides a critical review of research on direct methods since 1970. Considerable progress has been made on both theoretical properties of energy functions and on criteria suitable for on-line implementation. Current theory provides a satisfactory treatment of voltage-dependent reactive power demand, transfer conductances, and flux decay. However, it cannot incorporate the exciter control Proposed on-line criteria appear to work very well on sample examples; but, they still lack rigorous justification. Finally, recent work has shown that power systems can exhibit chaotic behavior. This surprising fact demonstrates that our understanding of the dynamics of power systems remains incomplete.