Parameter Estipiates in a Five-Element Respiratory Mechanical Model

Using four sets of forced random noise impedance data from each of five normal subjects and five patients with obstructuve lung disease, we computed parameter estimates for a three-element series model and a five-element parallel compartment model. For normal subjects, the five-element model provided no better fit to the impedance data than did the simple series model. Estimates obtained from normal subjects using this three-element model were reasonable and reproducible within 25 percent. For all subjects with lung disease, the five-element model provided a significantly (p 0.05) better fit than the three-element model. Estimates for parameters representing central inertance and resistance, airway compliance, and peripheral resistance were reasonable and reproducible-within 18 percent. However, estimates for the compliance of the lung and chest wall were more variable since measured impedance appeared to be insensitive to this parameter in the frequency range used.     

A Model for Stability, Noise, and Angle Modulation Analysis of Injection-Locked Oscillators

A model is presented for an injection-locked oscillator. It is derived from a perturbation of the free-running oscillator steady state, which is accurately determined from a harmonic balance (HB) simulation. As a first application, the proposed model is used to trace the existing solutions of the injection-locked system and their stability. It is then extended to include the effect of noise on the stability. Finally, the injection-locked system performance is studied under phase modulation. Sinusoidal phase modulation is considered and the stability of the modulated solutions is examined by Floquet theory. The validity of the model is verified for a 4.422-GHz oscillator, by HB and envelope transient simulations, as well as measurements.     

基于拓扑辨识的光伏暂态故障定位方法

光伏电网暂态故障结构复杂,传统故障定位方法对故障数据之间存在的隐含关联规则辨识能力较弱,导致最终的定位存在偏差。为此,提出基于拓扑辨识的光伏电网暂态故障自动定位方法。以电压相位拓扑结构为依据,利用光伏列阵寻找到功率与电压之间的联系,并对电网暂态进行实时跟踪。当电网中的电压、电流发生畸变时,利用贝叶斯模型分析故障数据之间的依赖关系,实现故障位置的定位。实验结果表明:与传统方法相比,该方法能够准确辨识隐含的关联规则、精准界定故障数据边界、确定电网故障的具体位置,为保障光伏电网的正常运行提供技术支持。     

Pattern Nulling in Coupled Oscillator Antenna Arrays

An optimization method is presented for constrained beam steering with null formation in linear coupled oscillator arrays. The method is based on a perturbation model of the far field of the array that includes both amplitude and phase perturbations, to accommodate prescribed nulls. Moreover, it takes into account the array nonlinear dynamics through a first-order approximation model of the array steady state. The optimization results are verified by harmonic balance simulations. Also, the stability of the optimized solutions is examined by perturbing the steady state solution and is verified with envelope transient. Design examples are used to demonstrate the validity and limitations of the proposed method     

传输线的随机建模及瞬态响应数值实验分析

该文考虑集成电路制造过程中传输线制造工艺参数随机扰动对传输线传输性能的影响,建立了传输线的随机模型,针对该模型提出了基于蒙特卡洛法的传输线瞬态响应统计分析方法。统计分析中采用精细积分算法求解传输线样本瞬态响应,并对模型输出的正态性进行偏度-峰度检验,给出了最差情况估计。试验结果表明该文提出的传输线随机模型及统计分析方法可以对传输线的传输性能进行有效的评估,对于传输线制造过程的控制及优化有着重要意义。     

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.     

Components of disparity vergence eye movements: application of independent component analysis

The "dual mode" theory for the control of disparity vergence eye movements states that two control components, a preprogrammed "transient" component and a feedback-controlled "sustained" component, mediate the motor response. Although prior experimental work has isolated and studied the transient component, little is known of the sustained component's contribution to the dynamic vergence response. The timing between the two components and their relative magnitudes are of interest as they relate to the strategies used by the brain to coordinate and control the two components. Modeling studies provide an estimate of component magnitudes, but cannot uniquely identify component timing nor can the provide detailed information on component dynamics. Here, an eigenvector analysis is applied to a multivariate data set consisting of multiple responses to a step stimulus to confirm the presence of two major components in the vergence response. Next, a new application of independent component analysis is used to estimate the activation patterns of the two components. Results from five subjects show that the sustained component is activated concurrently with the transient component, dominates the later portion of the response, and maintains final position.     

Compressed Speech: Correlates of Listening Ability

To identify sources of individual differences in the ability to comprehend compressed speech, a battery of tests was administered to 52 college students. The criterion variable was performance on four multiple choice tests based on the content of four recorded history passages. Subjects listened to these passages at a normal rate of approximately 175 wpm, and at three compressed rates: 250, 325, and 450 wpm. Compressed versions were prepared using the Tempo-Regulator. Certain ancillary data on intelligibility and comprehension were separately obtained from the same subjects by means of a sentence perception task. The results of a multiple regression analysis of test score data indicated that the best predictor of comprehension at high rates of compression was the Best Trend Name Test, originally developed as a measure of the ability to evaluate semantic relations -one of the components in the Guilford structure-of-intellect model of abilities. The outcome of a factor analysis of the test data supported an interpretation that the ability to rapidly match or compare concepts on the basis of semantic relatedness was a determinant of performance on the Best Trend Name Test. In an attempt to account for the significance of this ability in the comprehension of compressed speech, Guilford's concept was juxtaposed with the test or comparison operation postulated to be one stage in the “analysis-by-synthesis” model of speech perception.     

Estimation of gravity wave momentum flux with spectroscopic imaging

Atmospheric gravity waves play a significant role in the dynamics and thermal balance of the upper atmosphere. In this paper, we present a novel technique for automated and robust calculation of momentum flux of high-frequency quasi-monochromatic wave components from spectroscopic imaging and horizontal radar wind measurements. Our approach uses the two-dimensional (2-D) cross periodogram of two consecutive Doppler-shifted time-differenced (TD) images to identify wave components and estimate intrinsic wave parameters. Besides estimating the average perturbation of dominant waves in the whole field of view, this technique applies 2-D short-space Fourier transform to the TD images to identify localized wave events. With the wave parameters acquired, the momentum flux carried by all vertically propagating wave components is calculated using an analytical model relating the measured intensity perturbation to the wave amplitude. This model is tested by comparing wave perturbation amplitudes inferred from spectroscopic images with those from sodium lidar temperature measurements. The proposed technique enables characterization of the variations in the direction and strength of gravity waves with high temporal resolution for each clear data-taking night. The nightly results provide statistical information for investigating seasonal and geographical variations in momentum flux of gravity waves.     

Assessment of closed-loop ventilatory stability in obstructive sleep apnea

Previous studies on ventilatory control in obstructive sleep apnea (OSA) have generally indicated depressed chemosensitivity, implying greater stability of the chemical control of breathing in these subjects. However, these results were based on tests involving steady-state or quasi-steady measurements obtained in wakefulness. We have developed a method for assessing the dynamic stability characteristics of chemoreflex control in OSA patients during sleep. While continuous positive airway pressure was applied to stabilize the upper airways, acoustically stimulated arousals were used to perturb the respiratory system during sleep. The fluctuations in esophageal pressure that ensued were analyzed, using a closed-loop minimal model, to estimate the chemoreflex loop impulse response (CLIR). Tests using simulated data confirmed the validity of our estimation algorithm. Application of the method to arousal responses measured in six OSA and five normal subjects revealed no statistically significant differences in gain margins and loop gain magnitudes between the two groups. However, the CLIR in the OSA subjects exhibited faster and more oscillatory dynamics. This result implies that, in addition to unstable upper airway mechanics, an underdamped chemoreflex control system may be another important factor that promotes the occurrence of periodic obstructive apneas during sleep.     

Galvanic vestibular stimulation for analysis of postural adaptationand stability

Human postural dynamics was investigated in 12 normal subjects by means of a force platform recording body sway, induced by bipolar transmastoid galvanic stimulation of the vestibular nerve and labyrinth. The model adopted was that of an inverted segmented pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces actuated by the feet as a result of complex muscular activity subject to state feedback of body sway and position. Time-series analysis demonstrates that a transfer function from stimulus to sway-force response with specific parameters can be identified. In addition, adaptation to the vestibular stimulus is demonstrated to exist, and the authors describe this phenomenon using quantification in terms of a postural adaptation time constant in the range of 40-50 s. The results suggest means to evaluate adaptive behavior and postural control in the erect human being which may be useful in the rehabilitation of individuals striving to regain upright stance     

Analysis of the posture control system under fixed andsway-referenced support conditions

To delineate the relative roles of each of the feedback sensors in the posture control system such as the visual, vestibular, and proprioceptive sensors, an identification technique was applied to measurements of antero-posterior sway angles of the body and ankle moments under the following conditions: standing on a fixed support with eyes open (ox), standing on a fixed support with eyes closed (cx), standing on a sway-referenced support with eyes open (os), and standing on a sway-referenced support with eyes closed (cs). Frequency response functions from the sway angle to the ankle moment were calculated. Gain and phase characteristics for conditions (os) and (cs) were similar to those of Nashner's (1972) vestibular model in the high-frequency range, which shows that the vestibular system may be dominant. The gain was higher under condition (cx) than under (ox). Judging from the phase characteristics, this was probably due to increased weighting of the proprioceptive sensor over the vestibular sensor. There was a tendency for gain to increase as balance tasks became more demanding     

Balance prosthesis based on micromechanical sensors using vibrotactile feedback of tilt

A prototype balance prosthesis has been made using miniature, high-performance inertial sensors to measure lateral head tilt and vibrotactile elements mounted on the body to display head tilt to the user. The device has been used to study the feasibility of providing artificial feedback of head tilt to reduce postural sway during quiet standing using six healthy subjects. Two vibrotactile display schemes were used: one in which the individual vibrating elements, called tactors, were placed on the shoulders (shoulder tactors); another in which columns of tactors were placed on the right and left sides of the trunk (side tactors). Root-mean-square head-tilt angle (Tilt) and center of pressure displacement (Sway) were measured for normal subjects standing in a semi-tandem Romberg position with eyes closed, under four conditions: no balance aids; shoulder tactors; side tactors; and light touch. Compared with no balance aids, the side tactors significantly reduced Tilt (35%) and Sway (33%). Shoulder tactors also significantly reduced Tilt (44%) and Sway (17%). Compared with tactors, light touch resulted in less Sway, but more Tilt. The results suggest that healthy normal subjects can reduce their lateral postural sway using head tilt information as provided by a vibrotactile display. Thus, further testing with balance-impaired subjects is now warranted.     

B-Spline Based, Large-Signal DC and Microwave-Model for SOI MOSFETs

We present a large/small-signal, non-quasi-static, charge conserving, SOI MOSFET modeling technique suitable for DC and high frequency circuit design. The device model is extracted from small signal microwave iso-thermal Y-parameter data and DC I–V characteristics. Low frequency dispersions associated with self-heating and floating body effects are verified to not limit the performance of this technique since it relies on both DC and transient I–V characteristics. The technique is applied to the modeling of a short-channel, partially depleted, SOI nMOSFET simulated on PISCES. The model generated is incorporated into a circuit simulator, which is used to perform large-signal transient and harmonic balance simulations. The transient I–V and gate charge extracted from the iso-thermal small-signal microwave Y-parameters, are in excellent agreement with the iso-thermal transient I–V and gate charge obtained from PISCES, respectively. The model topology is extended with a parasitic bipolar sub-circuit which automatically calculates the DC operating point for self-biasing circuits. Transient and non-linear power characterization results predicted with this model agree well with those obtained from PISCES for a wide range of input power drives. A complete electro-thermal model is proposed and verified to be able to predict temperature and transient I–V response.     

Traffic-based performance comparison of mobile support strategies

This paper presents performance comparison among five strategies for mobile support. The major facilities, that are required for a network protocol to support mobile hosts are location management and packet forwarding. Based on this observation, we consider five basic strategies which use distinct methods to achieve these facilities and compare their performance. These five strategies are Broadcast Notification (BN), Broadcast Forwarding (BF), Broadcast Query (BQ), Default Forwarding (DF), and Default Query (DQ). As a result of analytical evaluation and comparison, it is shown that under different network conditions, such as number of routers, network topology, migration/communication ratio, data/control packet size ratio, different strategies produce minimum network traffic. In short, DF and DQ show the best performance in network size scaling, while BF and BQ are efficient for frequent migration. On the other hand, BN is suitable for a small network which has hosts with infrequent migration.     

Comparison of AdaBoost and Support Vector Machines for Detecting Alzheimer's Disease Through Automated Hippocampal Segmentation

We compared four automated methods for hippocampal segmentation using different machine learning algorithms: 1) hierarchical AdaBoost, 2) support vector machines (SVM) with manual feature selection, 3) hierarchical SVM with automated feature selection (Ada-SVM), and 4) a publicly available brain segmentation package (FreeSurfer). We trained our approaches using T1-weighted brain MRIs from 30 subjects [10 normal elderly, 10 mild cognitive impairment (MCI), and 10 Alzheimer's disease (AD)], and tested on an independent set of 40 subjects (20 normal, 20 AD). Manually segmented gold standard hippocampal tracings were available for all subjects (training and testing). We assessed each approach's accuracy relative to manual segmentations, and its power to map AD effects. We then converted the segmentations into parametric surfaces to map disease effects on anatomy. After surface reconstruction, we computed significance maps, and overall corrected $p$-values, for the 3-D profile of shape differences between AD and normal subjects. Our AdaBoost and Ada-SVM segmentations compared favorably with the manual segmentations and detected disease effects as well as FreeSurfer on the data tested. Cumulative $p$-value plots, in conjunction with the false discovery rate method, were used to examine the power of each method to detect correlations with diagnosis and cognitive scores. We also evaluated how segmentation accuracy depended on the size of the training set, providing practical information for future users of this technique.      

A voltage calibration technique of electro-optic probing for characterization internal to IC’s chip

This paper simulates the electric potential distribution and the electro-optic (EO) signal amplitude in a longitudinal poled EO polymer external probe tip on the electric signal transmission lines under test. The influence of the circuit layout on the EO probing is discussed. A novel probing configuration with a poled polymer EO probe tip is built and demonstrated for the first time, by which the signal voltage level corresponding to the EO signal can be calibrated. Using the new probe tip, we examine the influence of the variations of the linewidth and the spacing between neighboring lines on the EO signal. The results indicate that when the vertical distance between the tested point on the lines and the reference electrode is not larger than that between the tested point and its neighboring conductor, the disturbance from circuit layout can be avoided so that the voltage calibration of EO signal can be carried out.     

Measurement of stand-sit and sit-stand transitions using a miniature gyroscope and its application in fall risk evaluation in the elderly

A new method of evaluating the characteristics of postural transition (PT) and their correlation with falling risk in elderly people is described. The time of sit-to-stand and stand-to-sit transitions and their duration were measured using a miniature gyroscope attached to the chest and a portable recorder placed on the waist. Based on a simple model and the discrete wavelet transform, three parameters related to the PT were measured, namely, the average and standard deviation of transition duration and the occurrence of abnormal successive transitions (number of attempts to have a successful transition). The comparison between two groups of elderly subjects (with high and low fall-risk) showed that the computed parameters were significantly correlated with the falling risk as determined by the record of falls during the previous year, balance and gait disorders (Tinetti score), visual disorders, and cognitive and depressive disorders (p < 0.01). In this study, the wavelet transform has provided a powerful technique for enhancing the pattern of PT, which was mainly concentrated into the frequency range of 0.04-0.68 Hz. The system is especially adapted for long-term ambulatory monitoring of elderly people.