共查询到20条相似文献,搜索用时 78 毫秒
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众所周知,脑与心脏都能产生一个弱磁场,它与脑电场不同的是利用它可以显示出某些疾病,如癫痫、心律不齐等的精细差异.以超导量子干涉装置(简称为SQUID)为核心的灵敏磁力计常用来作详细的脑磁扫描图(简称为MEGs).但这个装置的缺点是使用时要求液态氦以及与其配套的深冷致冷设备. 相似文献
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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。 相似文献
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为了提高块匹配运动估计快速算法的搜索速度、精度和鲁棒性,提出了一种多起点并发式快速运动估计搜索方法。根据匹配块搜索的特性,提出了均匀选取多个起始点的方法,同时根据搜索区域的大小制定了自适应的限制条件和进度表,使得算法的收敛速度有了很大的提高。该算法在迭代过程中不但能够接受使目标向好的方向前进的解,而且能够在一定限度内接受使目标恶化的解,这使得算法能够有效地跳出局部极小的陷阱。使用基于TMS320C6415芯片的DSP图像处理系统对抖动视频图像序列进行实验。实验结果表明,当视频图像为PAL制,分辨率为720×576个像素,并且相邻图像间的抖动范围为±40个像素时,使用新提出的方法,匹配参数的计算量不大于使用全域匹配方法计算量的1/8,并且搜索精度远高于其他传统的快速搜索方法。 相似文献
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本文针对一个金属凝固过程的逆热传导问题,即由金属表面温度求其表面热流的问题,提出了一种基于边界元法的求解算法;并且利用离散化后的数值计算验证了该算法的有效性。 相似文献
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李源 《工程物理研究院科技年报》2004,(1):238-238
逆合成孔径雷达(ISAR)是一种高分辨率的二维成像雷达,必须经过运动补偿才能实现目标的二维成像。运动补偿实质是补偿由目标运动引起的相邻距离像之间的相位。如果通过无源或有源的方法对雷达回波的相位进行调制,必然会干扰ISAR的二维成像。在ISAR的无源干扰方面:有关文献分析了目标的时变抖动运动、随机运动对ISAR成像的影响。有源干扰可以采用噪声干扰和欺骗干扰。本文将脉冲压缩失配法的概念引申到ISAR的有源对抗中,提出了基于正弦调相的ISAR干扰方法。 相似文献
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应用电子与光子非弹性碰撞模型,分析、计算了磁逆多光子非线性Compton微分散射截面的特性。结果表明:该微分散射截面随与电子同时作用光子数及电子与光子碰撞非弹性成分的增大而减小,散射光子的频率逐渐趋于共振频率,但不具有共振性;当电子被光场俘获时,磁逆多光子非线性Compton微分散射截面为一恒定值。 相似文献
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本文介绍了多路逆磁测量方法及利用这一方法在HER装置上测量热电子环沿轴向的长度与晃荡电子密度的轴向分布的实验结果。 相似文献
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《Waves in Random and Complex Media》2013,23(4):433-455
A time-harmonic acoustic inverse scattering problem involving smart obstacles is formulated and a method to solve it is proposed. A smart obstacle is an obstacle that, when hit by an incoming acoustic wave, tries to pursue a given goal circulating a suitable pressure current on its boundary. A pressure current is a quantity whose physical dimension is pressure divided by time. The goals pursued by the smart obstacles that we have considered are the following ones: to be undetectable or to appear with a shape and/or acoustic boundary impedance different from its actual ones eventually in a location in space different from the actual location. The following time-harmonic inverse scattering problem is considered: from the knowledge of several far fields generated by the smart obstacle when hit by known time-harmonic waves, the knowledge of the goal pursued by the smart obstacle and of its acoustic boundary impedance reconstruct the boundary of the obstacle. A method to solve this inverse problem that generalizes the so-called Herglotz function method is proposed. Some numerical experiments that validate the method proposed are presented. The website http://www.econ.univpm.it/recchioni/w13 contains some auxiliary material that helps the understanding of the current paper. 相似文献
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This paper presents an inverse problem in analytical dynamics. The
inverse problem is to construct the Lagrangian when the integrals of
a system are given. Firstly, the differential equations are obtained
by using the time derivative of the integrals. Secondly, the
differential equations can be written in the Lagrange equations
under certain conditions and the Lagrangian can be obtained.
Finally, two examples are given to illustrate the application of the
result. 相似文献
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A novel method based on the relevance vector machine(RVM) for the inverse scattering problem is presented in this paper.The nonlinearity and the ill-posedness inherent in this problem are simultaneously considered.The nonlinearity is embodied in the relation between the scattered field and the target property,which can be obtained through the RVM training process.Besides,rather than utilizing regularization,the ill-posed nature of the inversion is naturally accounted for because the RVM can produce a probabilistic output.Simulation results reveal that the proposed RVM-based approach can provide comparative performances in terms of accuracy,convergence,robustness,generalization,and improved performance in terms of sparse property in comparison with the support vector machine(SVM) based approach. 相似文献
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D. V. Glamazda 《Physics of Particles and Nuclei Letters》2009,6(4):325-333
A new relativistic method of one-component wave functions applicable for describing fields with arbitrary spins is suggested. This method is used to solve the problem of energy states of hydrogen-like atoms with different required accuracies and under differing conditions (rough estimate, relativistic correction, fine structure, Zeeman effect in a magnetic field, or hyperfine splitting with account of nucleus spin) 相似文献
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An inverse problem of inhomogeneity identification inside a nonlinear magnetic material from the local measurements of the magnetic induction is investigated. The representation of the shape of the inhomogeneity and its evolution during an iterative reconstruction process is achieved by the level set method. The reconstruction is realized by the minimization of a cost function using the steepest descent method. The gradient directions are evaluated using the sensitivity equation and the adjoint variable method. Simulations has been performed showing the robustness of the algorithm and its ability to reconstruct single inhomogeneities, convex and non-convex, as well as multiple inhomogeneities. 相似文献
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针对广义Birkhoff系统动力学,提出广义Birkhoff系统动力学的一类逆问题,研究由已知积分流形来建立广义Birkhoff方程. 这类逆问题的解通常不是唯一的,需给出必要的补充要求. 最后举例说明结果的应用.
关键词:
广义Birkhoff系统
动力学逆问题
积分流形 相似文献