一类生物细胞系统钙离子振荡行为的同步研究

针对一类描述钙离子振荡行为的生物数学模型,讨论两种类型钙振荡的三耦合生物细胞系统在链式与环式连接情况下的同步问题。通过分析和数值模拟,进一步说明链式耦合所需的临界值要大于环式耦合所需的临界值,即链式耦合往往需要更大的临界值才能达到系统的同步状态。     

近邻耦合极限环振子的集体同步

在不忽略极限环振子振幅变化的情况下，考察了具有自然频率分布的极限环振子的最近邻耦合。观察到一些具体现象．适当选择自然频率的范围和耦合强度，通过序参数随时间的周期、准周期和混沌演化，可以看到耦合极限环的频率锁定，振幅死亡和不连贯等现象．通过增大耦合强度，我们同时可以看到相同步的分岔树系列．同时，还可以观察到振子振幅分布的时间演化．     

分数维环式单向耦合Lorenz系统的同步

主要采用分数维方法,基于Lalace变换,对环式单向耦合的3个Lorenz混沌系统的同步进行了研究,并对取得的结果作了相关数值模拟,模拟结果证实我们取得的成果的正确性和有效性.     

耦合极限环系统同步的振幅效应

研究了耦合极限环系统同步的振幅效应.结果表明,耦合系统中振子的平均频率随耦合强度的变化过程表现为同步分岔树结构,而振子的平均振幅随相同步的进程却是由均匀化逐渐分岔而达到非均匀化的过程.还发现振子振幅的变化范围在临界点处的突然减小.     

非线性系统流的耦合同步

基于一些自然系统混沌同步的考虑,提出了流的耦合同步法。在Ｌｏｒｅｎｚ系统中数值实验验证了我们的方法,实现了人武部分量、部分分量和单个分量上流的对称耦合的混沌同步。     

时空混沌的相互耦合同步

给出利用相互耦合来实现混沌同步的一种方法,计算最大Liapunov指数谱,讨论并给出耦合系数合同步时间之间的关系。     

耦合混沌系统同步问题的研究

数值研究了两个耦合混沌系统的同步问题，结论是只要二系统中对应振子的耦合系数相同就可实现二系统的完全同步，它同文献〔１、２〕要求二系统中所有振子的耦合系数都相同是不一样的，若用本文方法来实现文献〔２〕中所提到的多路保密通信，则本文的同步方法将提高其保密程度。     

耦合混沌系统同步问题的研究

数值研究了两个耦合混沌系统的同步问题，结论是只要二系统中对应振子的砂蛤 系统相同就可实现二系统的完全同步，它同文献（１，２）要求二系统中所有振子的耦合系数都相同是不一样的，若用本文方法来实现文献（２）中所提到的多路保密通信，将会提高其保密程度。     

一类直接耦合系统的混沌同步

将一个完整系统通过分解得到的多个子系统中,有的子系统是稳定的,有的子系统是不稳定的。稳定的子系统和不稳定的子系统之间通过某种耦合后能组成一个复合系统。作者在本文中研究了这个耦合的复合系统中稳定的子系统和不稳定的子系统之间的同步问题,结论是在这个耦合的复合系统中稳定的子系统和不稳定的子系统之间也可能达到混沌或非混沌同步。     

Lorenz系统单一耦合同步研究

针对耦合同步法中如何确定耦合强度的问题,提出了Lorenz系统单一耦合同步定理。在单向耦合同步基础上进行改进,减少状态变量耦合数目,提出了单一耦合同步方法;利用Lyapunov稳定性理论及Routh-Hurwitz判据,通过判定误差系统系数矩阵的特征值符号,推导了同步误差渐进稳定时耦合系数需满足的充分条件;仿真验证了该定理的正确性和有效性,表明了该定理下的单一耦合同步具有良好的抗干扰能力。     

带有变耦合时滞的神经网络的同步性

为了研究了带有变耦合时滞的细胞神经网络的同步问题,运用Lyapunov第二方法,通过构造lyapunov泛函,采用Kroneck积的性质,以及线性矩阵不等式技术,得到一些新的同步性的判据,使此问题得到更好的解决.     

A new cellular mechanism for coupling inputs arriving at different cortical layers

Pyramidal neurons in layer 5 of the neocortex of the brain extend their axons and dendrites into all layers. They are also unusual in having both an axonal and a dendritic zone for the initiation of action potentials. Distal dendritic inputs, which normally appear greatly attenuated at the axon, must cross a high threshold at the dendritic initiation zone to evoke calcium action potentials but can then generate bursts of axonal action potentials. Here we show that a single back-propagating sodium action potential generated in the axon facilitates the initiation of these calcium action potentials when it coincides with distal dendritic input within a time window of several milliseconds. Inhibitory dendritic input can selectively block the initiation of dendritic calcium action potentials, preventing bursts of axonal action potentials. Thus, excitatory and inhibitory postsynaptic potentials arising in the distal dendrites can exert significantly greater control over action potential initiation in the axon than would be expected from their electrotonically isolated locations. The coincidence of a single back-propagating action potential with a subthreshold distal excitatory postsynaptic potential to evoke a burst of axonal action potentials represents a new mechanism by which the main cortical output neurons can associate inputs arriving at different cortical layers.     

Excitation of Earth's continuous free oscillations by atmosphere-ocean-seafloor coupling

The Earth undergoes continuous oscillations, and free oscillation peaks have been consistently identified in seismic records in the frequency range 2-7 mHz (refs 1, 2), on days without significant earthquakes. The level of daily excitation of this 'hum' is equivalent to that of magnitude 5.75 to 6.0 earthquakes, which cannot be explained by summing the contributions of small earthquakes. As slow or silent earthquakes have been ruled out as a source for the hum (except in a few isolated cases), turbulent motions in the atmosphere or processes in the oceans have been invoked as the excitation mechanism. We have developed an array-based method to detect and locate sources of the excitation of the hum. Our results demonstrate that the Earth's hum originates mainly in the northern Pacific Ocean during Northern Hemisphere winter, and in the Southern oceans during Southern Hemisphere winter. We conclude that the Earth's hum is generated by the interaction between atmosphere, ocean and sea floor, probably through the conversion of storm energy to oceanic infragravity waves that interact with seafloor topography.     

不同系统之间的混沌同步

基于稳定性理论,针对SQCF系统和SCCF系统提出了两种不同系统之间的混沌同步控制策略：一是选取一正定的李亚普诺夫函数,基于李亚普诺夫直接法求出混沌同步的控制量,从而使两个不同的系统达到混沌同步;二是运用激活控制法实现两个不同系统的混沌同步．这两种方法均适用于一般的混沌系统,并用Mathematica软件给出了数值模拟．理论分析及仿真结果都表明该方法可以较快地实现不同系统之间的混沌同步．     

Three types of neuronal calcium channel with different calcium agonist sensitivity

How many types of calcium channels exist in neurones? This question is fundamental to understanding how calcium entry contributes to diverse neuronal functions such as transmitter release, neurite extension, spike initiation and rhythmic firing. There is considerable evidence for the presence of more than one type of Ca conductance in neurones and other cells. However, little is known about single-channel properties of diverse neuronal Ca channels, or their responsiveness to dihydropyridines, compounds widely used as labels in Ca channel purification. Here we report evidence for the coexistence of three types of Ca channel in sensory neurones of the chick dorsal root ganglion. In addition to a large conductance channel that contributes long-lasting current at strong depolarizations (L), and a relatively tiny conductance that underlies a transient current activated at weak depolarizations (T), we find a third type of unitary activity (N) that is neither T nor L. N-type Ca channels require strongly negative potentials for complete removal of inactivation (unlike L) and strong depolarizations for activation (unlike T). The dihydropyridine Ca agonist Bay K 8644 strongly increases the opening probability of L-, but not T- or N-type channels.     

不同碳酸钙掺量压实黄土的力学性能试验研究

为探讨碳酸钙改良黄土强度和湿陷性的可行性,针对陕西洛川黄土抗剪强度和湿陷特性,采用0、5%、10%、20%和25%质量比的碳酸钙粉末掺入黄土的方式,进行固结慢剪试验和湿陷性试验。结果表明:改良黄土试样的脆性随碳酸钙掺量增加而增大,当碳酸钙含量较低时,试样剪应力-剪切位移曲线为应变硬化型,碳酸钙掺量达到20%时应力-应变曲线呈软化型;在81%、87%、93%压实度下,不同掺量碳酸钙改良黄土的抗剪强度均显著提高,粘聚力和内摩擦角均随着碳酸钙掺量的增加而增大;而对黄土湿陷性的改良效果与压实程度有关,湿陷系数随压实度的增大显著减小,达93%压实度时碳酸钙改良黄土试样的湿陷性全部消除。因此,使用碳酸钙进行黄土的改良,能够取得填筑黄土抗剪强度增大、湿陷性降低的显著效果,而且绿色环保。     

Houart-Dupont钙振荡模型的复杂动态

运用中心流形定理和分岔理论分析了Houart-Dupont钙振荡模型的非线性动态,包括随参数变化时平衡点的类型及其稳定性的变化,从理论上严格证明了系统振荡现象产生与消失是由于平衡点发生了2次supercritical Hopf分岔导致的。通过运用matlab软件进行数值模拟,验证了理论分析结果的正确性。     

不同内填材料的生态复合墙体破坏模式

为了提高生态复合墙体的抗震性能,对不同内填材料的生态复合墙体进行低周反复荷载模型试验,模型比例为1∶2.与前期试验进行对比分析,探讨了试件的破坏机理及破坏模式.对发生不同破坏模式墙体的各部分钢筋应变进行非线性数值分析,提出并验证了墙体破坏模式的判定标准.试验结果和非线性数值分析表明,边肋柱和边框柱钢筋应变能反映墙体不同的破坏模式.因此,建议将边肋柱和边框柱钢筋应变的变化规律作为墙体破坏模式的判定标准,有利于墙体最优破坏模式的理论研究.     

Modulation of synchronous calcium oscillations in hippocampal neurons by photostimulation of astrocytes with femtosecond laser

A large body of evidence indicates that astrocytes play an important role in a range of brain functions through calcium (Ca²⁺) signaling. Experimentally evoking Ca²⁺ signaling is a useful technique for investigating the functions of astrocytes. However, conventional stimulation methods typically have poor spatio-temporal precision, and some are invasive. Our group has developed a technique to overcome these problems, in which astrocytes are photostimulated with a femtosecond laser. In the current study, we applied this method to a hippocampal neural network to explore astrocytic functions in detail. The results revealed that applying photostimulation to astrocytes in a cultured hippocampal astrocyte-neuron network caused the following changes: (i) Synchronous Ca²⁺ oscillations in neurons were induced; (ii) spontaneous Ca²⁺ synchrony instantaneously emerged; and (iii) high-frequency spontaneous Ca²⁺ synchrony was regulated. Thus, astrocytic Ca²⁺ signaling evoked by photostimulation was found to modulate synchronous Ca²⁺ oscillations in hippocampal neurons. We propose that photostimulation with a femtosecond laser will serve as a powerful tool in investigating astrocytic functions at the network level.