Establishment of a knee-joint coordinate system from helical axes analysis--a kinematic approach without anatomical referencing

This study establishes a functional knee-joint coordinate system (FCS) derived from active motion. The scale invariant properties of helical axes were used in order to avoid inter-observer errors associated with the traditional anatomical referencing techniques. The algorithm was tested with six cadaveric specimens in a knee-joint motion and loading apparatus. To determine the FCS sensitivity to variable loading, rotational moments were applied to the tibia while extending and flexing the knee. Each derived FCS was compared with the clinically derived anatomical coordinate system (ACS). The FCS was reproducible when the loading condition was the same. Changing the rotational moments from internal to external affected the orientations and the positions of the FCS. The largest displacement of 20.8 mm in average occurred in the medio/lateral direction. The FCS corresponded with the ACS for all specimens and loading conditions. The origin was always located within the femur along the transepicondylar line. The orientations differed less than 16.6 degrees in average, thus allowing the use of clinical terminology. These findings suggest that the FCS might improve the ability to clinically assess kinematic alterations provided that the reference motion is reproducible.     

State estimation on flexible robots using accelerometers and angular rate sensors

Fast moving robots with elastic joints and/or elastic links require vibration suppression to achieve accuracy. We introduce a two-degrees-of-freedom control scheme (2DoF) consisting of a feedforward component based on the flatness approach and a classic feedback component, such as a PD motor joint control with additional link position error or joint torque error feedback. Such a control scheme requires knowledge of the full system state. We present an approach for state estimation using angular rate-and acceleration-sensors-mounted on each robot link-that can be used for any kind of elastic robot manipulator. We validate our theory by measuring a very fast trajectory and the influence of an external disturbance on an articulated robot with two flexible links and three joints.     

A scalable sensor network using a polar coordinate system

Due to the quick development of chip design and antenna manufacturing techniques, wireless facilities, such as wireless sensors, have become significantly smaller and cheaper than before. Their usage has also consequently been widely enriched, such as in the areas of healthcare and forest monitoring. A wireless sensor network (WSN) is often used to monitor a specific environment for a specific purpose. However, how to effectively utilize the limited resources in a sensor, also in a WSN, is crucial. In a WSN, geographical information is usually employed to locate a node and its surroundings. In this article, we propose a system, named relative position for sensor routing using polar-coordinates (RP²), that deploys a polar coordinate system to identify sensor positions and route network packets. A sensor ID that carries geographical metadata can be helpful in positioning a sensor.     

使用混合坐标系统改进椭圆曲线上的运算速度

椭圆曲线密码体制有着巨大的发展前景，然而其运算速度限制了它在实际应用中的发展。本文综合分析了仿射坐标系统、影射坐标系统、雅可比坐标系统、五元素雅可比坐标系统在加法和倍点运算上的优缺点，提出了一个改进的雅可比坐标系统，并且建议使用混合的坐标系统来改进椭圆曲线上的加法和倍点运算的速度。     

Adaptive channel estimation using cyclic prefix in multicarriermodulation system

Multicarrier modulation (MCM) is a promising technique for high rate data transmission and the channel estimation is very important for the implementation of MCM. We found that the cyclic prefix, originally used solely to reduce the intersymbol interference (ISI), can be viewed as a source of channel information. Based on this observation, we propose an adaptive channel estimation algorithm using the cyclic prefix. This algorithm can adaptively track the channel variation without additional training sequences     

Determination of electrical and mechanical parameters in capacitive MEMS accelerometers using electrical measurements

This paper describes a simple technique for characterization of capacitive MEMS accelerometers. The method is based on electrical impedance (admittance) measurements of capacitive MEMS accelerometers treated as electrostatically-driven microelectromechanical resonators. By using this method, it is possible to determine some electrical and mechanical parameters including the shunt capacitance, the mechanical resonance frequency and quality factor. These parameters may serve as measures of structural integrity of the tested structures and their packages during reliability testing, for instance.     

Exact maximum likelihood estimation using masked system data

This work estimates component reliability from masked series-system life data, viz, data where the exact component causing system failure might be unknown. The authors extend the results of Usher and Hodgson (1988) by deriving exact maximum likelihood estimators (MLE) for the general case of a series system of three exponential components with independent masking. Their previous work shows that closed-form MLE are intractable, and they propose an iterative method for the solution of a system of three nonlinear likelihood equations     

利用训练序列进行无线局域网信道估计

研究了基于训练序列的无线局域网信道估计的几种方法，通过Matlab算法仿真分析，总结出适用IEEE802．1la的信道估计方法。并指出了各种算法的优缺点及适用条件，有利于无线局域网信道估计与均衡的硬件实现。     

红外热像仪的作用距离估算

热像仪的作用距离是评价热成像系统性能的一个重要参数。视距是热成像系统的主要战术指标,对系统的设计具有决定性作用。利用作用距离估算模型和插值法分别对某一型号热像仪的作用距离进行估算,结果表明利用插值法估算作用距离是可行的。     

A simple estimation of transverse response of high-g accelerometers by a free-drop-bar method

In this research, a simple free-drop-bar method was proposed to evaluate the transient transverse response (or the transverse sensitivity) of a high-g accelerometer with full-scale of 50,000g. Four different metal bars with different lengths and diameters were used in the dynamical impact experiments. It shows that the transverse response depends on the dimension (aspect ratio) of the round metal bar used. The bar with small diameter is favored due to its low distortion and attenuation of wave. For the same device, the bar with small diameter less than 16 mm gives the very low transverse response about 3%, which approaches the results measured by the sinusoidal vibration method. While the thick bar with 20 mm in diameter gives high transverse response about 10%. When performed in the usual drop-hammer equipment, the transverse response even reaches 24%. Stress analysis shows that the transverse response is proportional to the diameter squared of round metal bar used. It is demonstrated that this method is easy to implement with higher repeatability and reliability. In addition to the transverse response, the parameter such as the sensitivity can also be evaluated using the free-drop-bar method.     

Nonlinear inversion in electrode logging in a highly deviatedformation with invasion using an oblique coordinate system

Electrode logging as known in the oil industry is a method for determining the electrical conductivity distribution around a borehole or between two boreholes from the static-field (dc) measurements in the borehole. The authors discuss the reconstruction of the three-dimensional (3D) conductivity around a borehole in a highly deviated formation with invasion. At this moment, they have not included the borehole effect. To solve this problem, the full vector analysis is required. In most available algorithms, for the forward and inverse modeling of the resistivity data, the dipping bed environment is approximated using the staircase-discretization grid. In contrast, they have modeled the dipping-bed environment by introducing an oblique (nonorthogonal) coordinate system. By using the oblique coordinate system, they have gained some advantages over the usual approach. First, the use of the staircasing approximation for the dipping-bed environment can be avoided. This means that they reduce the discretization error, and they can suffice with less discretization points to obtain the results with the same degree of accuracy as the problem formulated in the Cartesian coordinate system. Secondly, the horizontally-symmetry constraints of the conductivity distribution can be included easily in the inversion procedure. Several numerical results are presented to demonstrate the performance of the inversion method using the synthetic “measured” data, which are generated by solving a forward-scattering problem numerically with the help of the conjugate gradient fast Fourier transform (CGFFT) method     

针对静态感知系统的坐标系改进设计

由于四个菲涅尔透镜和四个热释电传感器组成的四元十字阵列静态感知系统探测视场角度大,相邻感知区域有重叠,导致传统的感知系统坐标系的探测精度降低。为了提高探测目标的可靠性,提出一种改进的二维坐标系。该坐标系根据相邻感知区域的重叠区,重新建立十字坐标系统。文中建立了新坐标系的理论模型,经过实验验证,该改进坐标系设计切实可行,使感知系统探测目标精度有所提高,具有一定的实际应用价值。     

OFDM系统的导频信道估计方法的设计与性能分析

OFDM作为一种多载波的调制方式,在新一代移动通信中得到了非常广泛的应用。信道估计作为其中一种关键技术对系统性能有着十分重要的影响,因此设计一种具有可靠的性能同时又具有比较低的复杂度的估计方法就显得非常重要。本文基于这一目的采用了基于导频的信道估计方法,将LS算法,LMMSE算法,SVD-LMMSE算法应用于信道估计中,在具体的信道模型下对几种算法的性能进行了仿真实验,得到了在不同信噪比的情况下的误比特率变化曲线,并比较了3种算法的性能。     

Torque calculations of current-source induction machines using the1-2-0 coordinate system

The authors extend the use of the classical induction motor equations obtained through the 1-2-0 coordinate system to cover situations with nonsinusoidal, chopped current sources. Detailed analysis is demonstrated through the widely used six-pulse, current-source-inverter-fed induction machines. The derivations of two different types of analytical torque equation (time-domain and frequency-domain series equations) are given. Their results are compared with each other and with results obtained from extensive air-gap and shaft torque measurements. The only difference in results between the frequency- and time-domain methods is that the voltage pulse corresponding to the switching is not included in the time-domain method; however, a voltage spike, as indicated by the frequency-domain-series method, would be expected at each switching point because of the rapid change of flux linkage. Test results agree with calculated results     

Joint estimation of TOA and DOA in IR-UWB system using a successive propagator method

Impulse radio ultra-wideband (IR-UWB) ranging and positioning require accurate estimation of time-of-arrival (TOA) and direction-of-arrival (DOA). With receiver of two antennas, both of the TOA and DOA parameters can be estimated via two-dimensional (2D) propagator method (PM), in which the 2D spectral peak searching, however, renders much higher computational complexity. This paper proposes a successive PM algorithm for joint TOA and DOA estimation in IR-UWB system to avoid 2D spectral peak searching. The proposed algorithm firstly gets the initial TOA estimates in the two antennas from the propagation matrix, then utilises successively one-dimensional (1D) local searches to achieve the estimation of TOAs in the two antennas, and finally obtains the DOA estimates via the difference in the TOAs between the two antennas. The proposed algorithm, which only requires 1D local searches, can avoid the high computational cost in 2D-PM algorithm. Furthermore, the proposed algorithm can obtain automatically paired parameters and has better joint TOA and DOA estimation performance than conventional PM algorithm, estimation of signal parameters via rotational invariance techniques algorithm and matrix pencil algorithm. Meanwhile, it has very close parameter estimation to that of 2D-PM algorithm. We have also derived the mean square error of TOA and DOA estimation of the proposed algorithm and the Cramer-Rao bound of TOA and DOA estimation in this paper. The simulation results verify the usefulness of the proposed algorithm.     

Comparing the efficiency of artificial neural networks in sEMG-based simultaneous and continuous estimation of hand kinematics

Surface Electromyography (sEMG) plays a key role in many applications such as control of Human-Machine Interfaces (HMI) and neuromusculoskeletal modeling. It has strongly nonlinear relations to joint kinematics and reflects the subjects’ intention in moving their limbs. Such relations have been traditionally examined by either integrated biomechanics and multi-body dynamics or gesture-based classification approaches. However, these methods have drawbacks that limit their usability. Different from them, joint kinematics can be continuously reconstructed from sEMG via estimation approaches, for instance, the Artificial Neural Networks (ANNs). The Comparison of different ANNs used in different studies is difficult, and in many cases, impossible. The current study focuses on fairly evaluating four types of ANN over the same dataset and conditions in proportional and simultaneous estimation of 15 hand joint angles from 10 sEMG signals. The presented ANNs are Feedforward, Cascade-Forward, Radial Basis Function (RBFNN), and Generalized Regression (GRNN). Each ANN is applied to its special parametric study. All the methods efficiently solved the regression problem of the complex multi-input multi-output bio-system. The RBFNN has the best performance over the others with a 79.80% mean correlation coefficient over all joints, and its accuracy reaches as high as 92.67% in some joints. Interestingly, the highest accuracy over individual joints is 93.46%, which is achieved via the GRNN. The good accuracy suggests that the proposed approaches can be used as alternatives to the previously adopted ones and can be employed effectively to synchronously control multi-degrees of freedom HMI and for general multi-joint kinematics estimation purposes.     

激光光幕靶坐标测量系统的设计和实现

为了测量大靶面立靶坐标,提出了一种激光光幕靶的坐标测量方法,该方法采用4个90°扇形激光器作为发射光源,高灵敏度的光电二极管阵列作为接收装置。4个激光器发出的光相互交叉形成一个矩形激光光幕,当子弹穿过激光光幕时,会分别在x方向和y方向挡住一部分激光,促使相应的光电二极管产生信号;经过信号的采集和分析得到弹着点坐标,最后经过实弹试验得到子弹的坐标。结果表明,该立靶系统具有高精度和高灵敏度的特点。     

在OFDM系统中用循环前缀对时变色散信道进行估计

目前，正交频分复用（OFDM）技术困能在无线时变信道中进行高速数据传输而受到广泛的关注。在相干的OFDM系统中，接收机能否获得准确的信道状态信息（CSI）是系统性能提高的关键。为了能在接收端获得准确的CSI和提高系统的传输速率，文中将文献[3]的算法由单路发射推广为I/Q两路发射，采用复抽头系数的FIR滤波器对多径衰落信道进行建模，并用通常被丢弃的循环前缀作为训练序列对信道进行估计和均衡，仿真结果表明改进的算法在相同的子数和子载波和比文献[3]传输效率提高一倍的情况下能有效地自动跟踪信道的变化。     

Ambulatory system for human motion analysis using a kinematic sensor: monitoring of daily physical activity in the elderly

A new method of physical activity monitoring is presented, which is able to detect body postures (sitting, standing, and lying) and periods of walking in elderly persons using only one kinematic sensor attached to the chest. The wavelet transform, in conjunction with a simple kinematics model, was used to detect different postural transitions (PTs) and walking periods during daily physical activity. To evaluate the system, three studies were performed. The method was first tested on 11 community-dwelling elderly subjects in a gait laboratory where an optical motion system (Vicon) was used as a reference system. In the second study, the system was tested for classifying PTs (i.e., lying-to-sitting, sitting-to-lying, and turning the body in bed) in 24 hospitalized elderly persons. Finally, in a third study monitoring was performed on nine elderly persons for 45-60 min during their daily physical activity. Moreover, the possibility-to-perform long-term monitoring over 12 h has been shown. The first study revealed a close concordance between the ambulatory and reference systems. Overall, subjects performed 349 PTs during this study. Compared with the reference system, the ambulatory system had an overall sensitivity of 99% for detection of the different PTs. Sensitivities and specificities were 93% and 82% in sit-to-stand, and 82% and 94% in stand-to-sit, respectively. In both first and second studies, the ambulatory system also showed a very high accuracy (> 99%) in identifying the 62 transfers or rolling out of bed, as well as 144 different posture changes to the back, ventral, right and left sides. Relatively high sensitivity (> 90%) was obtained for the classification of usual physical activities in the third study in comparison with visual observation. Sensitivities and specificities were, respectively, 90.2% and 93.4% in sitting, 92.2% and 92.1% in "standing + walking," and, finally, 98.4% and 99.7% in lying. Overall detection errors (as percent of range) were 3.9% for "standing + walking," 4.1% for sitting, and 0.3% for lying. Finally, overall symmetric mean average errors were 12% for "standing + walking," 8.2% for sitting, and 1.3% for lying.     

铷原子磁力仪最佳抽运光强的研究

为了得到铷原子磁力仪的最佳抽运光强,进而优化原子磁力仪的灵敏度,理论分析了抽运光强与磁力仪的极化率、信噪比以及灵敏度之间的关系,设计了实验装置。采用自由感应衰减法对直径20mm的铷原子球形气室在不同抽运光强下对应的横向弛豫时间进行测量,并对相应的纵向弛豫时间进行测量,计算出了不同光强下的极化率,通过拟合得到了光强与极化率、信噪比以及灵敏度之间的关系曲线。结果表明,可在10mW/cm2附近得到系统最佳抽运光强。此研究结果为提高光强利用率并进一步优化铷原子磁力仪的灵敏度提供了指导。