检索结果-内蒙古大学图书馆

Higher Order Positive Semidefinite Diffusion Tensor Imaging

SIAM JOURNAL ON IMAGING SCIENCES 2010年第3期3卷 416-433页

作者： Qi, Liqun Yu, Gaohang Wu, Ed X. Hong Kong Polytech Univ Dept Appl Math Kowloon Hong Kong Peoples R China GanNan Normal Univ Sch Math & Comp Sci Jiangxi Key Lab Numer Simulat Technol Ganzhou 341000 Peoples R China Univ Hong Kong Dept Elect & Elect Engn Hong Kong Hong Kong Peoples R China

Due to the well-known limitations of diffusion tensor imaging, high angular resolution diffusion imaging (HARDI) is used to characterize non-Gaussian diffusion processes. One approach to analyzing HARDI data is to model the apparent diffusion coefficient (ADC) with higher order diffusion tensors. The diffusivity function is positive semidefinite. In the literature, some methods have been proposed to preserve positive semidefiniteness of second order and fourth order diffusion tensors. None of them can work for arbitrarily high order diffusion tensors. In this paper, we propose a comprehensive model to approximate the ADC profile by a positive semidefinite diffusion tensor of either second or higher order. We call this the positive semidefinite diffusion tensor (PSDT) model. PSDT is a convex optimization problem with a convex quadratic objective function constrained by the nonnegativity requirement on the smallest Z-eigenvalue of the diffusivity function. The smallest Z-eigenvalue is a computable measure of the extent of positive definiteness of the diffusivity function. We also propose some other invariants for the ADC profile analysis. Experiment results show that higher order tensors could improve the estimation of anisotropic diffusion and that the PSDT model can depict the characterization of diffusion anisotropy which is consistent with known neuroanatomy.

关键词： positive semidefinite diffusion tensor apparent diffusion coefficient Z-eigenvalue convex optimization problem invariants

来源：评论

学校读者我要写书评

暂无评论

Weighted Sum Rate Maximization Under the Given PAPR Constraints for a Multi-user OFDM System

引用

WIRELESS PERSONAL COMMUNICATIONS 2019年第1期109卷 127-137页

作者： Falahati, Abolfazl Anarakifirooz, Elhamsadat Univ Sci & Technol Dept Elect Engn Tehran Iran

Orthogonal frequency division multiplexing (OFDM) is proved to be the best candidate to support the colossal increase in mobile users and their required high rate of transmission in frequency selective fading environments, where the inter-symbol interference is at highest. In an OFDM system, when the sinusoidal signals of the subcarriers are added constructively, the peak to average power ratio (PAPR) becomes very large causing major drawbacks for multicarrier signaling. Earlier efforts to address this problem have been mainly concentrated on the reduction of signal PAPR and various methods of achieving linear and efficient power amplification. However, all the deployed techniques suffer from different ambiguities such as high distortion, complexity, computational time, memory requirements, and above all, the data rate loss. This manuscript is mainly aimed at solving a convex optimization problem in which power and radio resources in an OFDM system are allocated among different subcarriers and users in order to, maximize the weighted sum rate for different users considering total power and PAPR limitations.

关键词： Orthogonal frequency division multiplexing (OFDM) Peak to average power ratio (PAPR) convex optimization problem Power and radio resources

来源：评论

学校读者我要写书评

暂无评论

Output Feedback Model Predictive Tracking Control Using a Slope Bounded Nonlinear Model

引用

JOURNAL OF optimization THEORY AND APPLICATIONS 2014年第1期160卷 239-254页

作者： Lee, S. M. Kwon, O. M. Park, Ju H. Daegu Univ Dept Elect Engn Gyongsan 712714 South Korea Chungbuk Natl Univ Sch Elect Engn Cheongju 361763 South Korea Yeungnam Univ Dept Elect Engn Kyongsan 712749 South Korea

In this paper, an output feedback model predictive tracking control method is proposed for constrained nonlinear systems, which are described by a slope bounded model. In order to solve the problem, we consider the finite horizon cost function for an off-set free tracking control of the system. For reference tracking, the steady state is calculated by solving by quadratic programming and a nonlinear estimator is designed to predict the state from output measurements. The optimized control input sequences are obtained by minimizing the upper bound of the cost function with a terminal weighting matrix. The cost monotonicity guarantees that tracking and estimation errors go to zero. The proposed control law can easily be obtained by solving a convex optimization problem satisfying several linear matrix inequalities. In order to show the effectiveness of the proposed method, a novel slope bounded nonlinear model-based predictive control method is applied to the set-point tracking problem of solid oxide fuel cell systems. Simulations are also given to demonstrate the tracking performance of the proposed method.

关键词： Output feedback Model predictive tracking control Slope bounded nonlinear model convex optimization problem Fuel cell

来源：评论

学校读者我要写书评

暂无评论

CONSTRUCTION OF SELECTION INDEXES WITH RESTRICTIONS

引用

BIOMETRICAL JOURNAL 1984年第1期26卷 3-12页

作者： MIELENZ, N POULTRY RES INST MERBITZGER DEM REP

AbstractIn this paper the problem of unistage selection with inequality constraints is formulated. If the predictor and criterion variables are all normally distributed, this problem can be written as a convex programming problem, with a linear objective function and with linear constraints and a quadratic constraint. Using the duality theory, for convex nonlinear programming it is proved, that its dual problem can be transformed into a convex minimization problem with non‐negativity conditions. Good computational methods are known for solving this problem. By the help of the dual problem sufficient conditions for a solution of the original primal problem are derived and illustrated by an example of practical interes

关键词： Selection index inequality constraints convex optimization problem duality theory

来源：评论

学校读者我要写书评

暂无评论

Optimal Error Correction and Methods of Feasible Directions

引用

JOURNAL OF optimization THEORY AND APPLICATIONS 2012年第1期154卷 209-216页

作者： Ketabchi, Saeed Moosaei, Hossein Univ Guilan Fac Math Sci Dept Appl Math Rasht Iran

The main objective of this study is to discuss the optimum correction of linear inequality systems and absolute value equations (AVE). In this work, a simple and efficient feasible direction method will be provided for solving two fractional nonconvex minimization problems that result from the optimal correction of a linear system. We will show that, in some special-but frequently encountered-cases, we can solve convex optimization problems instead of not-necessarily-convex fractional problems. And, by using the method of feasible directions, we solve the optimal correction problem. Some examples are provided to illustrate the efficiency and validity of the proposed method.

关键词： Absolute value equations convex optimization problem Feasible directions Fractional quadratic problem

来源：评论

学校读者我要写书评

暂无评论

A Min-Max selector controller for turbofan engines with improvement of limit management and low computational burden

引用

TRANSACTIONS OF THE INSTITUTE OF MEASUREMENT AND CONTROL 2019年第1期41卷 36-44页

作者： Imani, Amin Montazeri-Gh, Morteza Iran Univ Sci & Technol Sch Mech Engn Syst Simulat & Control Lab Tehran *** Iran

Recent studies show that there is no guarantee for conventional Min-Max structure containing linear compensators to keep engine limitations in transient state, while limit violation can make dangerous events. Careful analysis indicates that despite the design of limitation loops overshoot-free to reduce the possibility of limit violation, exceeding the limits can occur for some variables affected by engine acceleration or deceleration, when other loop controllers are active. In this study, the limit values of these variables are taken into account in controller design of other loops using state feedback techniques and convex optimization problems, and their dynamic compensators are removed from the Min-Max structure. Thus, in addition to improvement of Min-Max limit protection, computational burden also decreases owing to loop reduction. The condition for limit protection in steady state and thrust tracking assurance is also specified. Simulations carried out with linear and nonlinear turbofan engine model show efficient performance of the proposed methodology in comparison with traditional Min-Max and Min-Max/sliding mode control (SMC) approaches.

关键词： Nonlinear turbofan engine model Min-Max structure limit management state feedback convex optimization problem

来源：评论

学校读者我要写书评

暂无评论

Discrete Total Variation-Based Non-Local Means Filter for Denoising Magnetic Resonance Images

引用

JOURNAL OF INFORMATION TECHNOLOGY RESEARCH 2020年第4期13卷 14-31页

作者： Joshi, Nikita Jain, Sarika Agarwal, Amit Amity Univ Uttar Pradesh Amity Sch Engn & Technol Noida India Dr APJ Abdul Kalam Inst Technol Tanakpur Champawat India

Magnetic resonance (MR) images suffer from noise introduced by various sources. Due to this noise, diagnosis remains inaccurate. Thus, removal of noise becomes a very important task when dealing with MR images. In this paper, a denoising method has been discussed that makes use of non-local means filter and discrete total variation method. The proposed approach has been compared with other noise removal techniques like non-local means filter, anisotropic diffusion, total variation, and discrete total variation method, and it proves to be effective in reducing noise. The performance of various denoising methods is compared on basis of metrics such as peak signal-to-noise ratio (PSNR), mean square error (MSE), universal image quality index (UQI), and structure similarity index (SSIM) values. This method has been tested for various noise levels, and it outperformed other existing noise removal techniques, without blurring the image.

关键词： Antoni Buades convex optimization problem Discrete Total Variation Image Denoising Laurent Condat Noise Non-Local Means Regularization Parameter Search Window Similarity Window

来源：评论

学校读者我要写书评

暂无评论

Multi-Agent Coordination with Lagrangian Measurements

Multi-Agent Coordination with Lagrangian Measurements

引用

6th IFAC Workshop on Distributed Estimation and Control in Networked Systems (NECSYS)

作者： Grushkovskaya, Victoria Ebenbauer, Christian Univ Stuttgart Inst Syst Theory & Automat Control D-70569 Stuttgart Germany Natl Acad Sci Ukraine Inst Appl Math & Mechy UA-84100 Sloviansk Ukraine

The paper is devoted to the study of a class of optimization problems with convex objective and constraint functions by using extremum seeking methods. Multi-agent systems with single integrator and unicycle dynamics are considered. The purpose is to develop a control algorithm that steers the agents to the set of saddle points of the associated Lagrangian, assuming that only Lagrangian measurements are available. For solving this problem, extremum seeking loops are introduced both for the states of a system and for Lagrangian multipliers. It is shown that, under certain assumptions, the trajectories of the system obtained approximate the trajectories of an auxiliary system representing a saddle point flow. The main result of the paper states the practical uniform asymptotic stability of the set of saddle points. The algorithm proposed is applied to distributed optimization problems. (C) 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

关键词： multi-agent systems convex optimization problem asymptotic stability extremum seeking distributed control

来源：评论

学校读者我要写书评

暂无评论

Mode Filtering with a Small Horizontal Line Array 10

Mode Filtering with a Small Horizontal Line Array

引用

10th International Conference on Wireless Communications and Signal Processing (WCSP)

作者： Zhang, Yifeng Wang, Jinjin Liang, Guolong Shi, Zhibo Harbin Engn Univ Underwater Acoust Coll Harbin Heilongjiang Peoples R China

ISBN: (纸本)9781538661192

Mode filtering is a key procedure in passive localization or source depth discrimination. Since the horizontal line array (HLA) lacks sampling of modes in depth direction, the orthogonality of modes can't be utilized in mode filtering with a HLA. Thus, the mode filtering with a HLA, especially with a small HLA is generally a difficult problem. In this paper, we focus on the mode filtering with a small HLA, which can be applied to the passive localization or source depth discrimination with a small HLA. Firstly, the pressure received on the HLA is describe by normal mode model, and several classical mode filters are introduced. Then considering the modal amplitudes are corresponding to the wavenumbers, we regard the mode filtering as generalized beamforming, which is performed in the wavenumber domain. Through constraining the maximum side lobe minimum, the modal amplitudes are beamformed. Finally, the performance of the proposed mode filter is evaluated relative to other methods in Monte Carlo simulation.

关键词： Mode filtering Small horizontal line array (HLA) convex optimization problem

来源：评论

学校读者我要写书评

暂无评论

Clothoid-Based Speed Profiler and Control for Autonomous Driving 18

Clothoid-Based Speed Profiler and Control for Autonomous Dri...

引用

18th IEEE International Conference on Intelligent Transportation Systems

作者： Lima, Pedro F. Trincavelli, Marco Martensson, Jonas Wahlberg, Bo KTH Royal Inst Technol ITRL Dept Automat Control SE-10044 Stockholm Sweden Scania CV AB Res & Dev S-15187 Sodertalje Sweden KTH Royal Inst Technol ACCESS Linnaeus Ctr Dept Automat Control SE-10044 Stockholm Sweden

ISBN: (纸本)9781467365963

This paper presents a method for optimal speed profile generation in specified clothoid-based paths with known semantic maximum speed and longitudinal and lateral acceleration and geometric information. A clothoid can be described using only its kink-points information, i.e. the points defining the start and end of a clothoid. Using the clothoid-based path representation, we formulate the speed profile generation as a convex optimization problem where the objective is to produce a smooth speed that is close to the maximum allowed speed. The vehicle and the road profile define the constraints of the problem. Furthermore, we develop a longitudinal controller by using the speed profiler in a receding-horizon fashion. Thus, we only consider a finite horizon when computing the optimal inputs every sampling time and, in addition, the longitudinal controller also takes into account the newest prediction available from measurements and from the lateral controller. We present simulations that demonstrate the ability of the method to generate safe and feasible speed profiles and the tracking of those by the longitudinal controller. We also study the influence of the clothoid-based path representation in the optimality of the speed profile obtained. We show that we can get a very good suboptimal speed profile approximation with few more points than the kink-points. In addition, we analyze the influence of an acceleration penalization factor in the smoothness of the speed profiler. The higher the acceleration penalization the smoother and the further from the maximum allowed speed is the speed profile.

关键词： approximation theory automobiles convex programming mobile robots predictive control suboptimal control acceleration penalization factor automotive autonomous driving clothoid-based path representation clothoid-based speed control clothoid-based speed profiler convex optimization problem finite horizon geometric information kink-points information lateral acceleration lateral controller longitudinal acceleration longitudinal controller optimal speed profile generation receding-horizon road profile suboptimal speed profile approximation Acceleration Brakes Computational modeling optimization Roads Vehicle dynamics Vehicles

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：