Grazing bifurcation and mode-locking in reconstructing chaotic dynamics with a leaky integrate-and-fire model

We examined the firing patterns of a chaotically forced leaky integrate-and-fire (LIF) model, and the validity of reconstructing input chaotic dynamics from an observed spike sequence. We generated inputs to the model from the Rössler system at various values of the bifurcation parameter, and carried out numerical simulations of the LIF model forced by each input. For both chaotic and periodic inputs, therotation numbers and the Lyapunov exponents were calculated to investigate the mode-locked behavior of the system. Similar behaviors as in the periodically forced LIF model were also observed in the chaotically forced LIF model. We observed (i)grazing bifurcation with the emergence of qualitatively distinct behaviors separated by a certain border in the parameter space, and (ii) modelocked regions where the output spike sequences are modelocked to the chaotic inputs. We found that thegrazing bifurcation is related to the reconstruction of chaotic dynamics with the LIF. Our results can explain why the shape of the partially reconstructed ISI attractor, which was observed in previous studies.     

外电场作用下神经元网络同步特性

研究了外部电场对神经元网络同步活动的潜在作用机制。基于HH神经元模型, 通过改进的欧拉法对描述神经元模型的微分方程进行数值求解, 分别研究了直流和交流电场作用下兴奋—抑制性神经元网络的同步行为。结果表明, 直流电场可以有效地削弱引入适应性电流及解除抑制性突触连接所引起的网络同步性减弱的趋势; 对于交流电场同样可以削弱适应性电流所引起的负面影响, 且网络的同步活动对交流电场的幅值和频率都存在一定的选择性。研究结论有助于推动以电刺激作为治疗某些神经系统疾病的有效手段的进一步发展。     

USB技术在飞机外场设备测试中的应用

通用串行总线（USB）是近年来流行的一种新的微机总线接口标准，它可以实现较传统方式更有效、更经济、更多点的数据采集，详细介绍了利用USB技术实现飞机外场快速测试的方法。     

箭载双臂式电场仪前置放大电路设计

设计出性能优异的前置放大电路对空间电场测量是至关重要的。本文在介绍了箭载电场仪探测原理的基础上,给出了电场仪中所用的低噪声、宽频带前置放大电路的设计方法,并通过对前放电路的噪声分析,提出了进一步降低噪声的方法。所设计的前置放大电路带宽0～5MHz,需要重点关注的100Hz～10KHz频段的总输入噪声仅0.4μV。     

Stochastic Resonance and Coincidence Detection in Single Neurons

We demonstrate that a realistic neuron model expressed by the Hodgkin-Huxley equations shows a stochastic resonance phenomenon, by computing cross-correlation between input and output spike timing when the neuron receives both aperiodic signal input of spike packets and background random noise of both excitatory and inhibitory spikes. We consider that such a signal detection is realized because the neuron with active properties is sensitive to fluctuation caused by a sharp increase just after a sudden dip of excitatory noise spikes and a gradual decrease of inhibitory noise spikes. We also show that the model generates highly irregular firing of output spikes on the basis of the modulation detecting property.     

多场耦合下PLZT陶瓷光致电场效应及其应用

针对现有数学模型对高能紫外光束照射下PLZT陶瓷光生电压实验变化规律无法进行合理解释的问题,基于多物理场耦合机制分析构建了PLZT陶瓷多场耦合下的光致电场数学模型,并对光致电场实验曲线进行了理论分析,然后针对光生电压控制提出了单片PLZT陶瓷ON-OFF闭环控制和双片PLZT陶瓷双光源协调激励控制策略,取得了较好的控制效果,探讨了PLZT陶瓷作为光控非接触式电动势源的可行性以及在微机电系统供能器件的应用前景,在此基础上,提出了光电-静电复合驱动微镜和PLZT陶瓷-介电弹性薄膜复合驱动的光控微泵装置.     

载流导线在磁场中混沌运动区域分析

在考虑电磁场对结构变形影响基础上,假设导线变形为小变形,采用弦的模型建立了载流导线在磁场中的周期激励作用下的横向振动控制方程.利用伽辽金原理及Melnikov方法推导出了载流导线发生混沌运动的临界条件,并讨论了导线张力、导线距离、电流等因素对载流导线混沌运动区域的影响.得到了如下的结论:载流导线的混沌运动区域随导线张力、导线距离的增大而变大;电流小于某一值时,载流导线混沌运动区域随电流增大而减小.     

载流梁在磁场中的横向固有振动分析

在考虑结构变形对电磁场的影响基础上，假设载流梁的变形为小变形，把变形后载流梁中的电流方向改变看成是电流矢量的刚性旋转．建立了载流梁在磁场中的横向固有振动控制方程．方程表明载流梁在磁场中的横向固有振动是一个典型的非线性问题．采用摄动法求得了其近似解，得到了载流梁在磁场中的横向固有振动频率及位移解析表达式．并通过实例计算讨论分析了导线与载流梁间距、载流梁的电流与导线电流的方向及大小、载流梁梁长及其半径等因素对载流梁横向固有振动的影响，得到了一些有价值的结论．     

基于有限元法的高压直流输电线路电场强度值模拟研究

为了解决现有的高压直流输电线路电场强度值模拟方法存在模拟完整度较低、误差较大的弊端,提出一种基于有限元法的高压直流输电线路电场强度值模拟方法。该方法引入有限元法并优化,以此为理论基础,根据高压直流输电线路电场强度值模拟的需求对有限元软件ANSYS进行设计,以实际高压直流输电线路为基础构建高压直流输电线路模型,基于此,采用有限元软件ANSYS实现高压直流输电线路电场强度值的模拟计算。实验结果表明,与现有的高压直流输电线路电场强度值模拟方法相比,所提方法能够提高模拟完整度、降低模拟误差,充分说明所提出的高压直流输电线路电场强度值模拟方法具备更好的模拟性能。     

An external field prior for the hidden Potts model with application to cone-beam computed tomography

In images with low contrast-to-noise ratio (CNR), the information gain from the observed pixel values can be insufficient to distinguish foreground objects. A Bayesian approach to this problem is to incorporate prior information about the objects into a statistical model. A method for representing spatial prior information as an external field in a hidden Potts model is introduced. This prior distribution over the latent pixel labels is a mixture of Gaussian fields, centred on the positions of the objects at a previous point in time. It is particularly applicable in longitudinal imaging studies, where the manual segmentation of one image can be used as a prior for automatic segmentation of subsequent images. The method is demonstrated by application to cone-beam computed tomography (CT), an imaging modality that exhibits distortions in pixel values due to X-ray scatter. The external field prior results in a substantial improvement in segmentation accuracy, reducing the mean pixel misclassification rate for an electron density phantom from 87% to 6%. The method is also applied to radiotherapy patient data, demonstrating how to derive the external field prior in a clinical context.