共查询到19条相似文献,搜索用时 78 毫秒
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神经群模型是典型的非线性系统,具有丰富而复杂的动力学行为模式.神经群兴奋性和抑制性突触具有可塑性,并对神经群动力学特性具有重要调控作用,研究突触可塑性对神经群动力学特性的调控规律具有重要意义.本文基于分岔理论,通过神经群模型兴奋性和抑制性突触增益的余维一分岔分析,分别给出了神经群运行于单稳、双稳、正常和异常极限环振荡状态的兴奋性和抑制性突触增益的单参数区间;进而通过兴奋性和抑制性突触增益的余维二分岔分析给出了神经群运行于上述多种状态的双参数区域.上述结果定量剖析了兴奋性与抑制性突触可塑性及二者的相互作用对神经群动力学特性的调控规律,揭示了兴奋性与抑制性的动态平衡在神经电活动调控中所扮演的关键角色,仿真结果验证了分岔分析的正确性.本文的研究对理解突触可塑性在脑功能的维持及各种神经疾病的诱发机制中所扮演的角色具有重要参考价值. 相似文献
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针对深度神经网络训练过程中残差随着其传播深度越来越小而使底层网络无法得到有效训练的问题,通过分析传统sigmoid激活函数应用于深度神经网络的局限性,提出双参数sigmoid激活函数。一个参数保证激活函数的输入集中坐标原点两侧,避免了激活函数进入饱和区,一个参数抑制残差衰减的速度,双参数结合有效的增强了深度神经网络的训练。结合DBN对MNIST数据集进行数字分类实验,实验表明双参数 sigmoid激活函数能够直接应用于无预训练深度神经网络,而且提高了sigmoid激活函数在有预训练深度神经网络中的训练效果。 相似文献
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本文对签字的基本模型进行了总结,并提出一种有足够建模能力、便于用户理解与计算机实现的签字过程定义方法:带条件的链表描述法。 相似文献
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对超声速冷流条件下用于超燃冲压发动机的凹腔火焰稳定器的自激振荡特性进行研究.采用混合RANS/LES方法对非定常流场进行数值模拟,考虑了凹腔的长深比和后缘角度两个关键参数.混合RANS/LES方法很好的捕捉到流场非定常大尺度结构并揭示了凹腔自由剪切层的演化过程.对凹腔压力振荡历程进行幅频分析,所得到的频率和理论分析结果与文献计算结果符合的很好.结果表明,凹腔的长深比和后缘角度对凹腔自激振荡特性都有很大的影响.随着凹腔长深比的减小,振荡能量趋于集中到某些频率对应的振荡模式上.随着凹腔后缘倾角的减小,大部分频率对应的振荡很快的被削弱;相对于陡后缘凹腔,小角度后缘凹腔只有较高频率对应的振荡模式存在. 相似文献
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神经群模型可模拟产生癫痫发作间歇期、发作前期和发作期的脑电信号.本文基于代数估计法,给出一种新型的闭环反馈控制策略以消除神经群模型中的癫痫状棘波.代数估计法用以观测模型中的状态以进一步构造控制器.在多个神经群耦合的模型中,通过数值仿真研究了与所给的闭环反馈控制策略相关的一些特性,包括受控神经群的类型与消除棘波的能力之间的关系、受控神经群的数目与控制能量之间的关系、模型的参量和控制能量之间的关系,以期建立合适的控制规则实现利用尽可能小的控制能量消除癫痫状棘波.此外,通过数值仿真对基于代数估计法的闭环反馈控制策略和直接比例反馈控制策略进行比较,结果表明,利用代数估计法进行滤波能减少消除癫痫状棘波所需的控制能量. 相似文献
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对于采用离轴多程放大技术的高功率激光装置,抑制其自激振荡的技术具有重大研究价值。针对工程中发现的主放大系统小孔板附近结构表面比较光亮,当腔内放大器工作时,在增益足够条件下,光亮结构面和腔镜间形成谐振腔而产生自激振荡,烧蚀腔内器件的问题,基于蒙特卡洛方法模拟结构表面,依据几何光学原理推导了激光光束在结构表面反射模型,采用该模型代入工程中光路部分参数计算了主放大系统结构表面粗糙处理工艺和反射进入放大器内份额的关系,并将该表面处理工艺应用于工程中,通过增大结构表面粗糙度,使形成的谐振腔损耗大于增益,为抑制高功率激光装置主放大系统自激振荡提供了依据。 相似文献
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Analytically determining frequency and amplitude of spontaneous alpha oscillation in Jansen's neural mass model using the describing function method 下载免费PDF全文
Spontaneous alpha oscillations are a ubiquitous phenomenon in the brain and play a key role in neural information processing and various cognitive functions.Jansen's neural mass model(NMM) was initially proposed to study the origin of alpha oscillations.Most of previous studies of the spontaneous alpha oscillations in the NMM were conducted using numerical methods.In this study,we aim to propose an analytical approach using the describing function method to elucidate the spontaneous alpha oscillation mechanism in the NMM.First,the sigmoid nonlinear function in the NMM is approximated by its describing function,allowing us to reformulate the NMM and derive its standard form composed of one nonlinear part and one linear part.Second,by conducting a theoretical analysis,we can assess whether or not the spontaneous alpha oscillation would occur in the NMM and,furthermore,accurately determine its amplitude and frequency.The results reveal analytically that the interaction between linearity and nonlinearity of the NMM plays a key role in generating the spontaneous alpha oscillations.Furthermore,strong nonlinearity and large linear strength are required to generate the spontaneous alpha oscillations. 相似文献
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Perturbation method of studying the EI Nifio oscillation with two parameters by using the delay sea-air oscillator model 下载免费PDF全文
The EI Nio-southern oscillation (ENSO) is an interannual phenomenon involved in tropical Pacific oceanatmosphere interactions. In this paper, we develop an asymptotic method of solving the nonlinear equation using the ENSO model. Based on a class of the oscillator of the ENSO model, a approximate solution of the corresponding problem is studied employing the perturbation method. 相似文献
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The ability of the radial basis function(RBF) approach to extrapolate the masses of nuclei in neutron-rich and superheavy regions is investigated in combination with the Duflo-Zuker(DZ31), Hartree–Fock-Bogoliubov(HFB27), finite-range droplet model(FRDM12) and Weizs?cker-Skyrme(WS4) mass models. It is found that when the RBF approach is employed with a simple linear basis function, different mass models have different performances in extrapolating nuclear masses in the same region, and a single mass model may have different performances when it is used to extrapolate nuclear masses in different regions. The WS4 and FRDM12 models(two macroscopic–microscopic mass models), combined with the RBF approach, may perform better when extrapolating the nuclear mass in the neutron-rich and superheavy regions. 相似文献
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Perturbation method of studying the EI Niño oscillation with two parameters using delay sea—air oscillator model 下载免费PDF全文
The EI Niño-southern oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific ocean-atmosphere interactions. In this paper, we develop an asymptotic method of solving the nonlinear equation using the ENSO model. Based on a class of oscillator of the ENSO model, a approximate solution of the corresponding problem is studied employing the perturbation method. 相似文献
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Jitendra C Parikh 《Pramana》1978,10(1):47-61
A nuclear mass formula is derived using a few extremely reasonable assumptions within an independent particle model with residual
interactions. The parameters in the mass formula are determined by a least square fit to the experimental energies. The mass
formula is further used to study Garvey-Kelson and Franzini-Radicati mass relationships. 相似文献
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A class of delayed oscillators of El Ni?o-southern oscillation (ENSO) models is considered. Using the delayed theory, the perturbed theory and other methods, the asymptotic expansions of the solutions for ENSO models are obtained and the asymptotic behaviour of solution of corresponding problem is studied. 相似文献
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