真实头模型中的多电流偶极子脑磁源定位

给出了真实头模型下多电流偶极子定位的通用公式,并对多种源的情况进行了计算机模拟,逆问题的求解采用全局优化与局域优化相结合的优化方法,在较强的噪声背景下得到了较好的定位结果.其中,在偶极子源较少时,采用了球对称导体模型与真实头模型相结合的混合模型,进一步提高了求解速度 关键词： 脑磁技术 真实头模型 多偶极子脑磁源 优化方法     

一种新的求解脑磁逆问题的搜索方法

给出一种新的求解真实头模型下脑磁逆问题的搜索方法.通过不同位置的源的相互关系，由上一个搜索源的计算结果通过简单计算，直接得到下一个搜索源的结果，避免了繁琐耗时的边界元积分方法，简化了求解过程，提高了求解速度. 关键词： 脑磁图 逆问题 搜索方法     

基于心磁信号的心脏电流偶极子阵列成像及相关性质的研究

超导量子干涉器（SQUID）能探测到微弱的心脏磁场信号. 通过对所得的心磁信号进行分析,可为许多心脏疾病的诊断提供依据. 利用心磁信号,采用极小范数最小二乘法（MNLS）对心脏的电流偶极子阵列进行重建,从而实现了对心脏内部等效电流源的成像. 在使用MNLS进行电流偶极子阵列反演重建的过程中,反演所需的心磁信号,分别由单电流偶极子和电流多极子作为激发源模拟得到,以及由SQUID实际测量得到. 同时,对不同心磁信号反演得到的电流偶极子的分布规律进行了分析. 此外,还给模拟的人体外心磁信号施加了均匀噪声和随机噪声,研究不同信噪比的均匀噪声和随机噪声对电流偶极子阵列重建的影响.     

基于心磁信号的心脏电流偶极子阵列成像及相关性质的研究

超导量子干涉器（SQUID）能探测到微弱的心脏磁场信号. 通过对所得的心磁信号进行分析,可为许多心脏疾病的诊断提供依据. 利用心磁信号,采用极小范数最小二乘法（MNLS）对心脏的电流偶极子阵列进行重建,从而实现了对心脏内部等效电流源的成像. 在使用MNLS进行电流偶极子阵列反演重建的过程中,反演所需的心磁信号,分别由单电流偶极子和电流多极子作为激发源模拟得到,以及由SQUID实际测量得到. 同时,对不同心磁信号反演得到的电流偶极子的分布规律进行了分析. 此外,还给模拟的人体外心磁信号施加了均匀噪声和随机噪声,研究不同信噪比的均匀噪声和随机噪声对电流偶极子阵列重建的影响. 关键词： 心磁信号 超导量子干涉器 电流偶极子阵列重建 极小范数最小二乘法     

非均匀电磁介质中的等效源重构

本文提出了一种用于等效源重构的磁场极值信号法.并通过给定不同的电流偶极子作为信号源,仿真研究了多腔体心脏磁场模型及非均匀介质情况下等效源重构的精度.分析了体电导对心脏磁场的影响,以及磁场极值信号反映的体电导作用.文中将该方法与其他四种源估计方法:磁场梯度极值法、Nelder-Mead单纯形算法、信赖域反射算法和粒子群优化算法作了比较.分析了这些方法的源重构精度和计算所需时间.结果表明,这种针对非均匀介质情况提出的心脏磁场逆问题求解方法有一定的实用价值.     

互补型自适应滤波器在心磁信号处理中的应用

将心磁信号从干扰噪声中加以提取并有效地消除噪声干扰是心磁信号处理中尤为重要的环节 .从改进算法的角度出发，提出互补型自适应滤波器结构以实现心磁信号的消噪处理.该滤波器针对心磁这类非平稳信号进行设计，有效地解决了常规自适应滤波器应用于心磁信号处理时收敛速度和稳态误差的矛盾.通过仿真实验和心磁实验结果表明，该算法能有效地消除心磁信号的背景噪声和工频干扰噪声.同时该算法也可用于其他非平稳信号的消噪处理. 关键词： 自适应滤波 心磁图 最小均方误差     

基于因子分析方法的相位同步脑电源的时-空动力学分析

头皮脑电时间序列的相关性是大脑皮层源的相位同步性的一种体现,因此对相位同步源进行定位,同时找到源对应的时间序列在脑成像研究领域具有重要意义.基于Rössler 模型提出仿真相位同步偶极子源的时间序列的方法,利用时间序列进行同心四层球头模型正演,获得仿真头皮脑电数据.提出了基于最大似然因子分析的相位同步脑电源的时-空动力学分析方法,对仿真和真实头皮脑电数据进行了验证,并与主成分分析法进行对比.仿真实验结果表明:最大似然因子分析法估计的时间序列与仿真源的时间序列具有更高的相关系数,同时估计源与仿真源 关键词： 脑电图 相位同步 因子分析 主成分分析     

基于原子磁力计的穿戴式脑磁图动态测量研究

脑磁图作为一种无创的脑功能成像技术，依靠超高的时间及空间溯源分辨率，在脑科学研究和临床应用领域中有着极其重要的价值.本文介绍了自主搭建的基于原子磁力计的穿戴式脑磁图系统，通过设计匀场补偿线圈组并结合参考传感器阵列，实现被试头部运动区域内剩磁在±1 nT以内，保证动态测量过程中传感器输出维持在动态范围以内；同时提出了一种虚拟合成梯度去噪方法，显著抑制了环境共模噪声；最终在被试者头部自然运动状态下，成功检测到高信噪比的α节律信号与听觉诱发磁场信号，证实了该系统的有效性，为穿戴式脑磁图应用推广提供更多的可能性.     

脑磁图仪的前世今生与未来

脑磁图仪通过记录大脑神经活动在头皮外产生的磁场来进行脑活动的成像,它具备超高的时间分辨率和较高的空间分辨率,是一种重要的无创脑功能成像技术。文章介绍了脑磁信号的神经生理起源、生物物理特征及其与脑电信号的联系和区别,回顾了当前基于超导量子干涉仪的脑磁图设备与相关技术,并针对制约当前超导脑磁图发展的技术瓶颈,介绍了基于原子磁强计的新型脑磁探测技术及国内相关研究的最新进展,指出了脑磁图在脑科学研究及临床应用中不可或缺的地位和其硬件技术未来发展的方向。     

基于三维磁成像的近场磁性体探测

提出一种近场条件下未知磁源的三维磁成像方法.考虑到大多数磁性体不仅受背景磁场磁化，本身也带有较强剩磁，将观测面上的磁场转换为磁场矢量异常模量，并建立目标函数进行最优化求解，以得到符合观测磁场特征的磁性体磁化模型.仿真和实验表明：此方法可有效消除剩磁对反演结果的影响，能够实现对近场多个磁源磁化率分布的成像，验证了所提方法用于探测隐含磁体位置和形状的可行性.     

Characterization of radiated electromagnetic fields using equivalent sources – Application to the EMC of power printed circuit boards

This article presents an original methodology to characterize electromagnetic disturbances radiated from power electronic devices. The method is based on the substitution of the power device by an equivalent set of elemental dipoles (electric and magnetic dipoles). The set of dipoles radiates the same near-field. The dipoles are determined from a near field cartography of the fields obtained with a measurement bench. The dipoles parameters are determined by solving an inverse problem using a genetic algorithm. The efficiency of the approach is demonstrated on an academic DC-DC converter. Finally some results about the chopper are presented. The methodology has two advantages: first it allows one to define some threshold limitations for electromagnetic fields on the surroundings and secondly it gives the location of the real source distribution. To cite this article: L. Beghou et al., C. R. Physique 10 (2009).     

延迟片法测量光学玻璃电流传感头线性双折射

测量光学传感头内线性双折射的大小对于提高光学电流传感器的性能有重要意义.本文报告了一种测量光学玻璃电流传感头线性双折射的新方法,以琼斯矩阵为数学工具给出了对该方法的理论分析及测量不确定度分析,并用实验方法给出了应用实例.此方法的主要优点是弥补了以前报告测量方法的不足,即无法唯一地确定光学玻璃电流传感头线性双折射的大小.本方法采用的光路所用元件容易获得且测量结构简单实用.     

The forward and inverse problem of cardiac magnetic fields based on concentric ellipsoid torso-heart model

<正>This paper constructs a concentric ellipsoid torso-heart model by boundary element method and investigates the impacts of model structures on the cardiac magnetic fields generated by both equivalent primary source—a current dipole and volume currents.Then by using the simulated magnetic fields based on the torso-heart model as input,the cardiac current sources—an array of current dipoles by optimal constrained linear inverse method are constructed.Next, the current dipole array reconstruction considering boundaries are compared with that in an unbounded homogeneous medium.Furthermore,the influence of random noise on reconstruction is also considered and the reconstructing effect is judged by several reconstructing parameters.     

Front-back confusion resolution in three-dimensional sound localization using databases built with a dummy head

Sound localization plays an important role in everyday life. It helps us to separate sounds coming from different sources and thus to acquire acoustic information. This paper describes an algorithm for localizing the position of a sound source, as recorded by dummy head microphones. The recorded signals are considered to be basic, random signals within an imaginary round room. The goal of this research is to localize random signals produced from different positions using information about basic signals. The method used is based on the identification of similarities between basic and random signals. It includes an interaural time difference comparison at the beginning, and continues with further analysis of the differences in signal spectrums. One of the main issues arising in sound localization is the problem of front-back confusion, and this paper shows how it was resolved by the use of reference signals.     

Numeral eddy current sensor modelling based on genetic neural network

This paper presents a method used to the numeral eddy current sensor modelling based on the genetic neural network to settle its nonlinear problem. The principle and algorithms of genetic neural network are introduced. In this method, the nonlinear model parameters of the numeral eddy current sensor are optimized by genetic neural network （GNN） according to measurement data. So the method remains both the global searching ability of genetic algorithm and the good local searching ability of neural network. The nonlinear model has the advantages of strong robustness, on-line modelling and high precision. The maximum nonlinearity error can be reduced to 0.037% by using GNN. However, the maximum nonlinearity error is 0.075% using the least square method.     

Capture of gravel by the head of a dam-break wave in a dry bed

It is experimentally found that a horizontal vortex is formed in the head of a dam-break wave, whose diameter is of the same order of magnitude as the wave amplitude. A close packing of vortex dipoles with a diameter of about the bottom particle size arises near the bottom. The central part of the dipoles lifts with the captured gravel and is twisted with the large vortex to form a wisp. The central part of the wisp lifts to form a wall composed of water and gravel.     

The electrical conduction variation in stained carbon nanotubes

Carbon nanotubes become stained from coupling with foreign molecules, especially from adsorbing gas molecules. The charge exchange, which is due to the orbital hybridization, occurred in the stained carbon nanotube induces electrical dipoles that consequently vary the electrical conduction of the nanotube. We propose a microscopic model to evaluate the electrical current variation produced by the induced electrical dipoles in a stained zigzag carbon nanotube. It is found that stronger orbital hybridization strengths and larger orbital energy differences between the carbon nanotube and the gas molecules help increasing the induced electrical dipole moment. Compared with the stain-free carbon nanotube, the induced electrical dipoles suppress the current in the nanotube. In the carbon nanotubes with induced dipoles the current increases as a result of increasing orbital energy dispersion via stronger hybridization couplings. In particular, at a fixed hybridization coupling, the current increases with the bond length for the donor-carbon nanotube but reversely for the acceptor-carbon nanotube.