光辅助瞬时测量多个微波频率的方法研究

提出一种基于布里渊散射的瞬时测量多个微波信号频率的新方法.待测的包含一个或多个频率的微波信号通过载波抑制双边带调制加载在光载波上,经滤波器输出上边带光信号,将上边带光信号同时送入多个色散位移光纤的一端,另有多个频率间隔为0.1GHz的单频激光分别送入多个色散位移光纤的另一端,若两端的光信号频率差为布里渊频移,则两路光在色散位移光纤发生布里渊散射,上边带光信号强度增强.判断色散位移光纤的输出上边带光信号是否增强即可测得相应频率.该方法频率测量分辨率为0.1GHz,最高测量精度为±0.05GHz.     

冲击激励下非线性能量阱振动抑制效果分析

研究当舰船设备受外部冲击激励扰动时非线性能量阱的振动抑制效果.首先,建立单自由度主结构耦合非线性能量阱的系统动力学模型,通过数值计算得到了非线性能量阱振动抑制能力与系统初始输入能量等级之间的规律;然后,通过复变量平均法研究了系统慢变动力流特性,阐述了激发靶能量传递现象的主要原因;最后,比较了非线性能量阱与等效线性动力吸振器的振动抑制效果.研究结果表明:瞬态共振俘获是导致靶能量传递现象的内在原因,只有当外部冲击能量超过一定临界阈值时,系统靶能量传递过程才能被激发,从而使非线性能量阱具备较强的振动抑制能力;与等效线性动力吸振器相比,非线性能量阱具备在宽频范围内吸收和耗散外部冲击能量的优势,鲁棒性更佳,能使受冲击激励扰动的舰船设备快速趋于稳定.     

水下连续爆炸声学特性分析

为了分析水下连续爆炸的水声学特性,采用具有统一时间间隔的多个爆炸单元进行水下连续爆炸试验及测量。根据测试获得的声信号数据,分析了水下连续爆炸冲击波的衰减及传播特性,研究了声信号的声持续时间、声压级和声能量。研究表明,水下连续爆炸会产生很强的声功率,声持续时间为连续爆炸单元的爆炸时间间隔之和。声信号的频率范围宽,其能量主要集中分布在频率24 k Hz以下,在低频段能量更大。说明水下连续爆炸作为功率高、频带宽、声持续时间长的水声声源,在水声干扰方面具有重要作用。     

一种单模垂直腔面发射激光器自混合测距系统研制

研究了一种小调制高精度单模垂直腔面发射激光器(VCSEL)自混合测距系统,根据单模VCSEL的特性曲线可知,其波长Δλ/ΔI非线性失真严重,且与调制电流幅度ΔI大小相关,该特性严重地影响系统的测距精度.通过对单模VCSEL进行小电流幅度调制以及采用专用的光电信号处理技术,明显提高了系统的测距精度.实验结果表明当使用调制电流幅度ΔIp-p=0.28 mA,调制频率fm=500 Hz对单模VCSEL进行频率调制,并且应用差频模拟锁相环(APLL)处理带有相位突变的自混合拍频信号,在采样时间为0.1 s,系统测距动态范围为50～500 mm,测距精度优于2 mm.     

基于Prony算法的暂态电能质量扰动信号分析

针对电能质量扰动信号特性,提出了一种基于Prony方法的信号分解算法.该方法将指数变换的时频特性与暂态信号特性描述相结合,可以提供各种分量的特征指标,如频率、幅值、相位等,利用最小二乘法得到高精度的拟合,并对暂态电能质量扰动的仿真信号和实测信号进行了分析.结果表明,Prony算法在暂态电能质量扰动信号分析中,可提供有效、准确的分析结果.     

基于非线性扰动观测器的四旋翼鲁棒编队控制

为了补偿四旋翼飞行器编队飞行过程中受到的模型不确定性和外部干扰,提出了一种分布式非线性扰动观测器(NDOB).首先,考虑四旋翼模型不确定性和外部干扰,提出了一种新的四旋翼动力学模型.其次,在四旋翼飞行器的内部姿态回路中应用非线性扰动观测器,并且引入低通滤波器以滤除低频干扰.最后,引入风和不规则负载作为线性/非线性外部干扰,将NDOB控制器应用在领导-跟随的四旋翼编队中.仿真结果表明,在该观测器的作用下,扰动观测器能够完全抑制系统外部的线性风扰动,编队队形的整体偏移率在x和y轴上分别下降到0.01%和0.5%.对于非线性不规则负载运输实验,非线性扰动观测器对扰动的补偿率达到99.36%,能够有效地补偿四旋翼飞行器编队飞行过程中受到的模型不确定性和外部干扰.     

调制气流声源流场声场特性的实验研究

已有大功率调制气流声源的实验集中于声场的测量,但对与声场特性密切相关的声源内部流场的演化过程研究较少.本文设计了稳态流场粒子图像测速(PIV)实验系统和流动致声单点测试系统,并分别用于内流场稳态和瞬态流动特性的研究.稳态流场实验结果中,喉道内呈减速增压流动,外壁面流动分离和近壁面高低压区域交替成为高气窒压力下声源稳态流场的重要特征.流场扰动致声过程的测量数据表明,调制频率对内流场分布的变化有显著影响,强声波产生的频率相关性受气室压力、激励信号强度和声源几何参数等多种因素共同作用.气路系统的流动对调制部件的振动过程有一定影响.所测声源频率响应峰值位于0.5～1kHz.激励电流低于10 A时.声压级输出随着气室压力和激励信号强度的增加而增加.喷口出口和喉道入口宽度对于声源性能也有明显的影响.从提高声源输出声压级角度,实际应用中应根据加载激励信号选择合适的喷口参数使声源工作于满调制状态,同时适当减小喉道入口宽度.单频调制的声源产生过程伴有谐波分量,非均匀流动中传递压力扰动的强度随管道截面积的增大而降低.压力扰动量级和成分与所测量声信号间存在密切联系.     

铣削主动减振平台设计及控制

设计了一种用于铣削减振的2自由度主动式工件装夹平台,平台在控制信号作用下使工件产生运动以抵消切削时刀具和工件之间的振动.在控制器设计时以主动平台作为被控对象并将切削时的刀具一工件相对振动视为对系统的扰动,将其转化为鲁棒干扰抑制问题.针对由对象模型和扰动通道传递函数内模构成的增广系统设计了状态反馈的控制器,由于在控制器设计时不需确切的扰动通道的模型而仅需了解扰动频率,设计过程被有效简化.通过比较有无控制作用时的振幅检验了控制效果,结果表明振动明显得到抑制且对对象模型的参数扰动具有一定的鲁棒性.     

单周动态补偿的光通信码间抑制抗干扰新方法

在对光通信码间进行抑制抗干扰的过程中,光信号会受温度、大气流动等不确定性因素的影响,干扰随机性较大,导致传统的调相阵列技术由于不能实时检测,从而无法有效实现光通信码间的干扰抑制。提出一种单周动态补偿的光通信码间抑制抗干扰方法,分析带有干扰的光通信系统,给出外部扰动向量的动态特性,分析无限时域的性能指标,将原系统和干扰系统和期望输出联立,获取光通信增广系统。在调制信号中引入直流偏置信号,将经调制的数据向量划分成不同子序列,赋予各子序列对应的加权系数,依据光通信码间安全工作区域信号范围对光信号进行限幅,通过正信号的切顶信号求出补偿信号。对正信号与翻转负信号进行符号拼接、偏置信号添加等操作,将光信号以光功率的形式传输至光无线信道。将加性高斯白噪声信道作为信道模型,将负信号置零,进而抑制光通信码间的干扰。仿真实验结果表明,所提方法具有很好的抗干扰性能。     

一类中立非线性系统的未知参数谐波扰动补偿

对于一类受到外部未知参数谐波信号干扰下的中立非线性不确定系统,提出了一种基于自适应前馈补偿的控制器设计方法。首先设计非线性观测器将未知扰动估计问题转换为参数辩识问题,并在前馈通道对扰动进行抵消,其次设计具有鲁棒性能的状态反馈控制器来抑制未建模动态,从而在外部扰动和模型参数不确定同时作用下,使系统具有较好的控制性能。对二关节机械臂的仿真证明该方法的有效性。     

Spike-timing-dependent synaptic modification induced by natural spike trains

The strength of the connection between two neurons can be modified by activity, in a way that depends on the timing of neuronal firing on either side of the synapse. This spike-timing-dependent plasticity (STDP) has been studied by systematically varying the intervals between pre- and postsynaptic spikes. Here we studied how STDP operates in the context of more natural spike trains. We found that in visual cortical slices the contribution of each pre-/postsynaptic spike pair to synaptic modification depends not only on the interval between the pair, but also on the timing of preceding spikes. The efficacy of each spike in synaptic modification was suppressed by the preceding spike in the same neuron, occurring within several tens of milliseconds. The direction and magnitude of synaptic modifications induced by spike patterns recorded in vivo in response to natural visual stimuli were well predicted by incorporating the suppressive inter-spike interaction within each neuron. Thus, activity-induced synaptic modification depends not only on the relative spike timing between the neurons, but also on the spiking pattern within each neuron. For natural spike trains, the timing of the first spike in each burst is dominant in synaptic modification.     

Unique features of action potential initiation in cortical neurons

Neurons process and encode information by generating sequences of action potentials. For all spiking neurons, the encoding of single-neuron computations into sequences of spikes is biophysically determined by the cell's action-potential-generating mechanism. It has recently been discovered that apparently minor modifications of this mechanism can qualitatively change the nature of neuronal encoding. Here we quantitatively analyse the dynamics of action potential initiation in cortical neurons in vivo, in vitro and in computational models. Unexpectedly, key features of the initiation dynamics of cortical neuron action potentials--their rapid initiation and variable onset potential--are outside the range of behaviours described by the classical Hodgkin-Huxley theory. We propose a new model based on the cooperative activation of sodium channels that reproduces the observed dynamics of action potential initiation. This new model predicts that Hodgkin-Huxley-type dynamics of action potential initiation can be induced by artificially decreasing the effective density of sodium channels. In vitro experiments confirm this prediction, supporting the hypothesis that cooperative sodium channel activation underlies the dynamics of action potential initiation in cortical neurons.     

Distributed synaptic modification in neural networks induced by patterned stimulation.

Activity-dependent changes in synaptic efficacy or connectivity are critical for the development, signal processing and learning and memory functions of the nervous system. Repetitive correlated spiking of pre- and postsynaptic neurons can induce a persistent increase or decrease in synaptic strength, depending on the timing of the pre- and postsynaptic excitation. Previous studies on such synaptic modifications have focused on synapses made by the stimulated neuron. Here we examine, in networks of cultured hippocampal neurons, whether and how localized stimulation can modify synapses that are remote from the stimulated neuron. We found that repetitive paired-pulse stimulation of a single neuron for brief periods induces persistent strengthening or weakening of specific polysynaptic pathways in a manner that depends on the interpulse interval. These changes can be accounted for by correlated pre- and postsynaptic excitation at distant synaptic sites, resulting from different transmission delays along separate pathways. Thus, through such a 'delay-line' mechanism, temporal information coded in the timing of individual spikes can be converted into and stored as spatially distributed patterns of persistent synaptic modifications in a neural network.     

Purkinje neuron synchrony elicits time-locked spiking in the cerebellar nuclei

An unusual feature of the cerebellar cortex is that its output neurons, Purkinje cells, release GABA (γ-aminobutyric acid). Their high intrinsic firing rates (50?Hz) and extensive convergence predict that their target neurons in the cerebellar nuclei would be largely inhibited unless Purkinje cells pause their spiking, yet Purkinje and nuclear neuron firing rates do not always vary inversely. One indication of how these synapses transmit information is that populations of Purkinje neurons synchronize their spikes during cerebellar behaviours. If nuclear neurons respond to Purkinje synchrony, they may encode signals from subsets of inhibitory inputs. Here we show in weanling and adult mice that nuclear neurons transmit the timing of synchronous Purkinje afferent spikes, owing to modest Purkinje-to-nuclear convergence ratios (～40:1), fast inhibitory postsynaptic current kinetics (τ(decay) = 2.5?ms) and high intrinsic firing rates (～90?Hz). In vitro, dynamically clamped asynchronous inhibitory postsynaptic potentials mimicking Purkinje afferents suppress nuclear cell spiking, whereas synchronous inhibitory postsynaptic potentials entrain nuclear cell spiking. With partial synchrony, nuclear neurons time-lock their spikes to the synchronous subpopulation of inputs, even when only 2 out of 40 afferents synchronize. In vivo, nuclear neurons reliably phase-lock to regular trains of molecular layer stimulation. Thus, cerebellar nuclear neurons can preferentially relay the spike timing of synchronized Purkinje cells to downstream premotor areas.     

神经元簇状放电锋电位数的研究

利用水蛭心脏细胞的神经元膜电位的动力学方程,讨论外界刺激电流对簇状放电中锋电位数目的影响,发现外界刺激电流和非失活钾离子通道激活电位具有相同的作用,神经元的活动状态随着外界刺激电流的变化,可以在簇状放电、持续放电和无放电三种状态之间转换.神经元簇状放电时,刺激电流导致神经元膜电位的去极化程度越高,在一次簇状放电过程中产生的锋电位数也越多.     

Neural encoding of individual words and faces by the human hippocampus and amygdala

Patients with lesions in the medial temporal lobe (MTL) of the brain, which includes the hippocampus, amygdala and parahippocampal gyrus, are severely impaired in their ability to remember and recognize words or faces which they saw only a short time ago. These lesions also prevent the effect of word repetition on cortical event-related potentials that are associated with these tasks. We have been able to study the response of individual neurons in the human medial temporal lobe to such delayed recognition tasks in epileptic patients undergoing neurosurgery. We found that some MTL neurons preferentially fired on sight of one particular word from a set of ten words used in a memory task, and others fired in response to one particular face. This stimulus-specific firing was maximal during the time that the neocortical event potentials are most sensitive to stimulus repetition, suggesting that the MTL contributes specific information to the cortex during the retrieval of recent memories.     

Rulkov神经元的的簇放电类型与分岔条件

讨论了Rulkov神经元产生锥形簇放电、方形簇放电及峰放电的非线性动力学特征,尤其是锥形簇放电的放电规律和动力学特征。指出产生锥形簇放电的关键在于鞍结点分岔和flip分岔,属于fold/flip型簇放电;而锥形簇放电的持续距离随着控制参数的增加而增大。首次给出了单个神经元产生各种簇放电的参数取值范围。     

耦合双量子阱间的隧穿时间

通过研究在外电场驱动下的双量子阱系统中电子的动力学行为，利用微扰理论得到了两个量子阱间的相干隧穿时间及电子局域化条件，并用数值演化方法验证了上述理论结果的正确性．这一方法可以推广到多模电场作用下的系统．     

考虑系统总和扰动的多关节机械臂 反步有限时间滑模控制

针对多关节机械臂轨迹跟踪控制中存在的模型参数摄动和外部有界扰动等不确定性因素影响问题,设计了一种考虑系统总和扰动的反步有限时间滑模控制算法,用于实现多关节机械臂轨迹跟踪控制任务。首先,利用严格反馈形式描述多关节机械臂的动力学模型,并将模型参数摄动和外部有界扰动等不确定性因素看成系统的总和扰动,进而设计非线性扩张状态观测器对系统总和干扰加以估计,以提高系统的鲁棒性能;其次,在传统反步法设计的基础上结合有限时间滑模控制技术,完成系统反步有限时间滑模控制器的设计;最后,应用Lyapunov稳定性理论证明了多关节机械臂的位置矢量能够实现对期望位置矢量的有限时间稳定跟踪。仿真对比结果表明设计反步有限时间滑模控制算法的有效性。     

基于磁光材料的磁可调石墨烯多带吸收特性

为了改善石墨烯的吸收性能,基于石墨烯的磁光效应,提出了一种采用磁性材料构成的光子晶体异质结构。该光学结构可使石墨烯实现多带吸收。吸收带的数目可通过改变光子晶体的周期数来调节。利用4×4传输矩阵法数值研究了该光子晶体异质结构的相关参数对石墨烯吸收率的影响。结果表明:石墨烯的吸收特性表现出一定的磁圆二色性。但通过调节费米能量,在外磁场的作用,左旋圆偏振光和右旋圆偏振光均可具有较高的吸收率。研究结果为偏振光学领域石墨烯基新型光子学器件的设计制作提供了理论依据。