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The effects of the spatial influence function on orthotropic femur remodelling

PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE 2008年第H5期222卷 601-609页

作者： Shang, Y. Bai, I. Peng, L. Tsinghua Univ Dept Biomed Engn Beijing 100084 Peoples R China

The morphology and internal structure of bone are modulated by the mechanical stimulus. The osteocytes can sense the stimulus signals from the adjacent regions and respond to them through bone growth or bone absorption. This mechanism can be modelled as the spatial influence function (SIF) in bone adaptation algorithm. In this paper, the remodelling process was simulated in human femurs using an adaptation algorithm with and without SIF, and the trabecular bone was assumed to be orthotropic. A different influence radius and weighting factor were adopted to study the effects of the SIF on the bone density distribution and trabecular alignment. The results have shown that the mean density and L-T ratio (the ratio of longitudinal modulus to transverse modulus) had an excellent linear relationship with the weighting factor when the influence radius was small. The characteristics of density distribution and L-T ratio accorded with the actual observation or measurement when a small weighting factor was used. The large influence radius and weighting factor led to unrealistic results. In contrast, the SIF hardly affected the trabecular alignment, as the mean variation angles of principal axes were less than 1.0 degree for any influence radius and weighting factor.

关键词： spatial influence function bone remodelling trabecular orthotropic adaptation algorithm

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FORWARD-ERROR-CONTROL (FEC) ASSISTED ADAPTIVE EQUALIZATION FOR DIGITAL CELLULAR MOBILE RADIO

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 1993年第1期42卷 94-102页

作者： SHARMA, R GROVER, WD KRZYMIEN, WA NATL RES COUNCIL CANADA SOLID STATE OPTOELECTR CONSORTIUMOTTAWA K1A 0R6ONTARIOCANADA UNIV ALBERTA DEPT ELECT ENGNEDMONTON T6G 2E1ALBERTACANADA

An adaptive equalization technique using forward error control (FEC) coding is described and evaluated. Computer simulation is used to compare the FEC-assisted adaptive equalization to conventional adaptive equalization. The system model employed is based on the proposed digital cellular communication standard for North America. The FEC-assisted adaptive equalization technique performs better than the conventional equalization method at low and moderate Doppler frequencies with the same level of redundancy in the transmitted data. For systems employing both FEC coding and adaptive equalization, the FEC-assisted adaptive equalization method successfully combines these two functions while using the redundancy required for only one of them. In other words, training required for adaptive equalization can be provided at no extra cost in terms of data redundancy in a system using FEC coding and vice versa.

关键词： .decision feedback equalizers FEC coding data redundancy adaptation algorithm intersymbol interference Doppler frequencies Mobile Radio Adaptive Equalization adaptive equalizer conventional adaptive radio applications equalization technique

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Comparison of methods for determining orthotropic axes in 3D femur remodeling

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Progress in Natural Science:Materials International 2007年第12期17卷 1405-1411页

作者： Lau Jaclyn Beijing 100084 China Department of Biomedical Engineering Tsinghua University

The density distribution and internal structure of trabecular bone are modulated by local mechanical environment. In this study, an orthotropic adaptation algorithm was applied to the 3D femur model to simulate the variations of stiffness and orientation of trabecular bone under multi-loading conditions. This algorithm includes the determination of orthotropic axes and the stiffness modification of trabecular bone. Three methods were used to determine the orthotropic axes, i.e. the maximal cycle method, the stress maximum method, and the composite method. We found that the composite method was better than the other two. Firstly, the characteristics of density distribution obtained by using the composite method agreed better with those in real proximal femur. Secondly, the material orientation aligned with the known trabeculaer pattern. Finally, the ratios of the longitudinal modulus to the transverse modulus were also shown to be realistic in three local regions of the proximal femur.

关键词： orthotropic axes trabecular bone adaptation algorithm stiffness variation.

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Steady-state analysis of a simplified lattice-based adaptive IIR notch filter

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IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES 2000年第6期E83A卷 965-972页

作者： Mvuma, A Nishimura, S Shimane Univ Grad Sch Sci Dept Informat Sci Matsue Shimane 6908504 Japan Shimane Univ Dept Elect & Control Syst Engn Matsue Shimane 6908504 Japan

In this paper we propose a new lattice based second-order adaptive infinite impulse response (IIR) notch filter that uses a simplified adaptation algorithm. Steady-state analysis of the proposed structure is then studied based on the mean-squared error analysis of the steady-state variable coefficient fluctuations. The analysis is used to derive simple analytical expressions for steady-state variable coefficient variance and an upper bound for the step size adaptation constant. The results are shown to be useful in designing an FSK demodulator using the proposed structure. Computer simulation results are shown to confirm derived analytical expressions.

关键词： lattice structure IIR adaptive notch filter adaptation algorithm FSK demodulation

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Complexity evaluation for the implementation of a Pre-FFT equalizer in an OFDM receiver

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IEEE TRANSACTIONS ON CONSUMER ELECTRONICS 2000年第3期46卷 428-437页

作者： Armour, S Nix, A Bull, D Univ Bristol Commun Res Ctr Bristol BS8 1UB Avon England

A Pre-FFT Equalizer (PFE) has been shown to offer a significant throughput efficiency improvement when applied to an OFDM receiver. Alternatively, the PFE can be used to increase the maximum delay spread conditions under which the OFDM system can operate effectively. Due to the manner of its operation, the PFE requires the use of modified adaptation algorithms if iterative, decision directed adaptation is required. In this paper, the computational complexity required to implement a PFE and a suitable adaptation strategy is evaluated Initially, an LMS adaptation algorithm is investigated and evaluated in terms of its suitability for application in conjunction with the PFE to standards such as ETSI DVB-T and HIPERLAN/2 and IEEE 802.11a. The complexity requirements are found to be high, particularly in the case of DVB-T. The demand for a lower complexity adaptation algorithm is thus identified. As a result, a CSI-based adaptation method is subsequently considered. The complexity requirement of this algorithm is also analyzed and evaluated and is shown to be much lower than that of the LMS algorithm. Thus, it is shown that if the CSI-based adaptation method is used, the dominant complexity requirement is due to the implementation of the equalizing filter and not the adaptation method. Reduced filter complexity requirement is thus shown to be the kev to enabling effective application of the PFE. The ATSC 8-VSB standard is identified as a possible source of techniques to reduce or facilitate the high complexity demands for implementation of the PFE filter.

关键词： .maximum delay adaptation algorithm EQUALIZER adaptation method PFE Consumer Electronics COMPLEXITY EVALUATION OFDM RECEIVER efficiency improvement

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Variable-Performance Servo System Design Without Actuator Current and Angle Measurement for Rover Vehicles

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2020年第11期69卷 12725-12733页

作者： Kim, Seok-Kyoon Ahn, Choon Ki Hanbat Natl Univ Dept Creat Convergence Engn Daejeon 34158 South Korea Korea Univ Sch Elect Engn Seoul 136701 South Korea

This study devises a variable-performance control law for rover vehicles servoing velocity and pitch angle commands. This considers both vehicle and actuator dynamics as well as load and parameter variations. The main merits are summarized as follows. First, the proposed auto-tuning law magnifies the feedback gain for desired systems to achieve transient performance improvement with the convergence property guarantee. Second, the collaboration of pole-zero cancellation controller and disturbance observers eliminates over/undershoots through closed-loop order reduction by a special form of feedback gain. Beneficial closed-loop properties are also derived from the closed-loop analysis. The prototype rover vehicle built with TETRIX and MyRIO-1900 experimentally validates the closed-loop performance and robustness improvement.

关键词： Vehicle dynamics Actuators Angular velocity Wheels Current measurement Acceleration Real-time systems Rover vehicle-tracking control learning algorithm adaptation algorithm active-damping injection technique

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REDUCED COMPLEXITY DECISION FEEDBACK EQUALIZATION FOR DIGITAL SUBSCRIBER LOOPS

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1991年第6期9卷 810-816页

作者： YOUNG, G British Telecommunications Research Laboratories Ipswich UK

Decision feedback equalizers (DFE's) are widely used in modern local network digital transmission systems to remove the intersymbol interference caused by slowly decaying pulse tails. This paper describes a simple gradient descent algorithm for adapting a coefficient to model the slowly decaying portion of the tail. An equalization strategy is described that exploits a priori knowledge of the nature of the subscriber loop channel, together with the new adaptation algorithm, to result in reduced complexity DFE structures. The use of this new algorithm in both FIR and IIR equalizer structures is described. These structures can be dimensioned to give equivalent performance to a conventional DFE but with a reduced number of coefficients, or to give improved performance for a given complexity. The use of this new algorithm in both FIR and IIR equalizers is quantitively compared to a conventional DFE in terms of performance and implementation complexity. An analysis is presented describing the operation of the adaptation algorithm in the presence of noise. Simulation results are used to illustrate the trainup of the algorithm and its stability in the presence of near-end crosstalk noise.

关键词： .equalizers gradient descent Decision Feedback Digital Subscriber adaptation algorithm tail decaying subscriber loop Reduced Complexity postcursor

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ADAPTIVE-CONTROL OF ROBOT MANIPULATORS BASED ON PASSIVITY

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IEEE TRANSACTIONS ON AUTOMATIC CONTROL 1994年第9期39卷 1871-1875页

作者： TANG, Y ARTEAGA, MA DEPFI-UNAM National University of Mexico Mexicali Mexico

A new adaptation algorithm is presented for adaptive control of robot manipulators. The passivity property of the proposed algorithm is first established, then the stability is proved based on the passivity properties of the plant and those of the proposed algorithm. Because of the use of the past information and averaging effect, this algorithm gives a smoother tracking and parameter error and a parameter convergence under a weaker excitation condition.

关键词： adaptive control closed loop systems robots stability tracking adaptation algorithm averaging effect excitation condition manipulators parameter convergence passivity robot

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Adaptive Gauss-Hermite filter for non-linear systems with unknown measurement noise covariance

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IET SCIENCE MEASUREMENT & TECHNOLOGY 2015年第8期9卷 1007-1015页

作者： Dey, Aritro Sadhu, Smita Ghoshal, Tapan Kumar Jadavpur Univ Dept Elect Engn Kolkata 700032 W Bengal India

A non-linear adaptive state estimator based on the Gauss-Hermite (GH) quadrature rule has been proposed to suit non-linear signal models where the measurement noise covariance remains unknown. The proposed algorithm which may be used for both parameter and state estimation incorporates online adaptation of the measurement noise covariance (R) following maximum-likelihood estimation-based method. The GH quadrature approach has been considered so that the proposed filter may inherit the enhanced estimation accuracy as exhibited by its non-adaptive counterpart. The proposed adaptation algorithm, in contrast to some other reported methods, automatically ensures positive definiteness of the adapted measurement noise covariance. The efficacy of the adaptive algorithm over the non-adaptive GH filter has been demonstrated using Monte Carlo simulation and two case studies. Performance comparison has also been carried out with respect to adaptive unscented Kalman filter with the help of same case studies.

关键词： adaptive filters measurement errors nonlinear filters nonlinear estimation adaptive estimation maximum likelihood estimation Monte Carlo methods nonlinear systems covariance analysis nonlinear adaptive state estimator Gauss-Hermite quadrature rule nonlinear signal model measurement noise covariance parameter estimation maximum likelihood estimation-based method adaptation algorithm adaptive algorithm nonadaptive GH filter Monte Carlo simulation adaptive Gauss-Hermite filter nonlinear system

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Parallel 1D and 2D vector quantizers using a Kohonen neural network

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NEURAL COMPUTING & APPLICATIONS 1996年第2期4卷 64-71页

作者： Mohamed, AS Attia, EN The American University in Cairo

The process of reconstructing an original image from a compressed one is a difficult problem, since a large number of original images lead to the same compressed image and solutions to the inverse problem cannot be uniquely determined. Vector quantization is a compression technique that maps an input set of k-dimensional vectors into an output set of k-dimensional vectors, such that the selected output vector is closest to the input vector according to a selected distortion measure. In this paper, we show that adaptive 2D vector quantization of a fast discrete cosine transform of images using Kohonen neural networks outperforms other Kohonen vector quantizers in terms of quality (i.e. less distortion). A parallel implementation of the quantizer on a network of SUN Sparcstations is also presented.

关键词： neural networks vector quantizers fast discrete cosine transform adaptation algorithm loosely coupled architecture parallel processing

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