Function of identified interneurons in the leech elucidated using neural networks trained by back-propagation

Mechanical stimulation of the body surface of the leech causes a localized withdrawal from dorsal, ventral and lateral stimuli. The pathways from sensory to motor neurons in the reflex include at least one interneuron. We have identified a subset of interneurons contributing to the reflex by intracellular recording, and our analysis of interneuron input and output connections suggests a network in which most interneurons respond to more than one sensory input, most have effects on all motor neurons and in which each form of the behaviour is produced by appropriate and inappropriate effects of many interneurons. To determine whether interneurons of this type can account for the behaviour, or whether additional types are required, model networks were trained by back-propagation to reproduce the physiologically determined input-output function of the reflex. Quantitative comparisons of model and actual connection strengths show that model interneurons are similar to real ones. Consequently, the identified subset of interneurons could control local bending as part of a distributed processing network in which each form of the behaviour is produced by the appropriate and inappropriate effects of many interneurons.     

内外啮合齿轮马达的理论分析

从双定子思想出发,力图打破原有齿轮马达的结构,实现在不改变输入流量的情况下,对齿轮马达的转速调节,从而探讨出一种新型结构的内外啮合齿轮马达. 该新型结构的齿轮马达与传统的齿轮马达的区别是:该齿轮马达在一个壳体中,有内啮合齿轮马达和外啮合齿轮马达两个马达. 该马达仅通过切换不同的连接方式就可以实现多级转速和多级转矩的输出,省去了节流阀、减压阀等耗能元件,减少了能源的浪费,提高了效率.      

高强钢平齐式端板连接节点火灾后力学性能试验研究

火灾后,钢构件残余应力和变形的重新分布,导致钢结构整体在火灾后可能比火灾高温作用下更加危险.节点对钢结构整体安全性至关重要,为研究高强钢平齐式端板连接节点火灾后的力学性能,采用稳态试验方法对经历550℃的火灾高温并冷却至常温的7个端板连接节点进行试验,得到节点火灾后的变形状态、弯矩-转角关系曲线以及失效模式等.同时,将试验结果与普通钢端板连接节点过火后的力学性能进行对比分析.此外,将试验结果同现行欧洲钢结构设计规范Eurocode3中相应条文进行比较.研究表明:通过合理的节点设计,与采用较厚普通钢端板的节点相比,采用较薄高强钢端板的节点可实现相同的节点失效模式、相近的剩余承载力以及更高的(至少是相当的)节点转动能力;同时,欧洲钢结构规范Eurocode3中有关节点塑性抗弯承载力的条文适用于高强钢平齐式端板连接节点火灾后塑性抗弯承载力的预测.     

Functional specificity of local synaptic connections in neocortical networks

Neuronal connectivity is fundamental to information processing in the brain. Therefore, understanding the mechanisms of sensory processing requires uncovering how connection patterns between neurons relate to their function. On a coarse scale, long-range projections can preferentially link cortical regions with similar responses to sensory stimuli. But on the local scale, where dendrites and axons overlap substantially, the functional specificity of connections remains unknown. Here we determine synaptic connectivity between nearby layer 2/3 pyramidal neurons in vitro, the response properties of which were first characterized in mouse visual cortex in vivo. We found that connection probability was related to the similarity of visually driven neuronal activity. Neurons with the same preference for oriented stimuli connected at twice the rate of neurons with orthogonal orientation preferences. Neurons responding similarly to naturalistic stimuli formed connections at much higher rates than those with uncorrelated responses. Bidirectional synaptic connections were found more frequently between neuronal pairs with strongly correlated visual responses. Our results reveal the degree of functional specificity of local synaptic connections in the visual cortex, and point to the existence of fine-scale subnetworks dedicated to processing related sensory information.     

门式刚架Г型节点有限元分析

利用ANSYS软件对三种节点进行了低周往复加载和单调加载的对比分析,三种节点包括梁柱常规螺栓端板竖放节点圆弧形整体式节点和圆弧形加腋螺栓端板竖放节点。其结果表明圆弧形整体式节点和加腋改造后的节点要比常规螺栓端板连接节点刚度大,极限承载力高。加腋可缓解节点域应力的过分集中,避免了节点域的脆性破坏。圆弧形整体式节点域为圆弧形,使得该节点受力流畅,加载到破坏阶段,节点域变形较小。圆弧形加腋节点具有便于螺栓安装,节点为栓焊连接,刚度大延性也较好。同时加腋构成了第二道防线,进一步防止了偶然荷载作用下试件脆性破坏的发生。圆弧形整体式节点和圆弧形加腋节点均以梁端位移过大作为破坏准则,这三种节点的对比研究对工程设计有较好的指导意义。对于常规螺栓端板连接节点其节点域剪切变形较大,易引起节点的脆性破坏。剪切变形加大了梁端位移,且由于节点刚度相对较小,节点域应力较为集中,发生了荷载作用下柱翼缘的屈服破坏。     

用COM+实现高效连接池

为解决在大型管理信息系统中存在的数据库连接影响系统性能的问题,运用连接池技术给出了一种有效的解决方案.在描述连接池的一般原理和当前的实现技术基础上,给出应用COM (Component 0bject Model )的对象池机制和运用VC 提供的ATL(Active Template Library),建立了一个高效的连接池.通过连接池可以避免数据库连接对象频繁的创建和销毁带来的系统开销,有效地提高了系统性能,充分体现了多层结构的优点.实际测试结果表明,当活动连接超过200时,通过连接池可以很大程度上提高数据库的响应效率,尤其对于涉及多个连接的分布式事务,提交的准确性和效率都能提高1倍以上.连接池还可以通过限制活动连接的数量,避免因为连接数量过多而造成系统崩溃现象.     

内嵌钢板销式连接胶合木梁短期受力性能

内嵌多块钢板销式连接是重型木结构最有效的连接方式之一,已越来越广泛地应用于木结构节点连接中.采用四点弯曲加载试验方法,对两根内嵌三块钢板销式连接胶合木梁短期受力性能进行了试验研究,其中一根梁的连接节点位于纯弯段,另一根梁的连接节点位于弯剪段.研究采用此类连接胶合木梁的力学性能、破坏模式以及连接位置对胶合木梁力学性能的影响等,并基于试验结果推导采用此类连接胶合木梁的极限承载力和挠度计算公式.试验结果表明:构件的极限承载力和跨中挠度与连接节点的位置有关,连接节点位于弯剪段胶合木梁的承载力大于连接节点位于纯弯段胶合木梁的承载力;理论计算结果与试验数据符合较好,可为木结构的设计和应用提供参考.     

基于ABAQUS分析的顶底角钢连接节点的初始刚度研究

顶底角钢连接是工程中常用的一种梁柱节点连接方式.为深入了解这种节点的力学性能,利用有限元软件Abaqus模拟顶底角钢连接节点,分析顶底角钢连接节点的弯矩转角性能,研究连接节点的初始刚度,提出了顶底角钢连接节点的初始刚度计算公式.将通过计算公式获得的数据与现有的实验数据进行对比,结果表明所提的顶底角钢连接节点初始刚度计算公式具有较好的计算精度.该研究为实际工程应用和设计提供了一定的参考.     

人工神经网络学习的代数方法

介绍了具有自环和无自环的神经网络利用 Ｍｏｏｒｓ－Ｐｅｎｒｏｓｅ伪逆的学习方法，分析 了这种方法获得的权重所具有的优点，如权重方均根值最小等．使得网络具有较好与较 均匀的鲁捧性。找到了具有自环和无自环网络在权重方均根最小条件下权重之间的关 系，从而使无自环网络的学习过程与有自环的网络同样简单。通过伪逆方法找到了确定 阈值的优化办法，使网络鲁棒性有不同程度的提高。     

Channel noise-induced phase transition of spiral wave in networks of Hodgkin-Huxley neurons

The phase transition of spiral waves in networks of Hodgkin-Huxley neurons induced by channel noise is investigated in detail.All neurons in the networks are coupled with small-world connections,and the results are compared with the case for regular networks,in which all neurons are completely coupled with nearest-neighbor connections.A statistical variable is defined to study the collective behavior and phase transition of the spiral wave due to the channel noise and topology of the network.The effect of small-world connection networks is described by local regular networks and long-range connection with certain probability p.The numerical results confirm that (1) a stable rotating spiral wave can be developed and maintain robust with low p,where the breakup of the spiral wave and turbulence result from increasing the probability p to a certain threshold;(2) appropriate intensity of the optimized channel noise can develop a spiral wave among turbulent states in small-world connection networks of H-H neurons;and (3) regular connection networks are more robust to channel noise than small-world connection networks.A spiral wave in a small-world network encounters instability more easily as the membrane temperature is increased to a certain high threshold.     

弧焊逆变器输出整流电路的并联问题及分析

根据逆变电路所用开关元件的工作原理,分析了多个单端式弧焊逆变器输出整流电路中同相位并联电路和不同相位并联电路各自的特点.结果表明,双单端正激逆变电路的两路逆变器发生的可调宽度的脉冲相位相差180°,输出电路并联可共用一个输出电抗器,但不利于并联更多的输出电路;弧焊逆变器输出整流电路同相位并联更有利于弧焊逆变器功率的进一步扩大,理论上其并联数量没有限制,但由于输出整流二极管的反向恢复特性的限制,每一回路必须有输出电感以保证电路的可靠性.     

Early motor activity drives spindle bursts in the developing somatosensory cortex

Sensorimotor coordination emerges early in development. The maturation period is characterized by the establishment of somatotopic cortical maps, the emergence of long-range cortical connections, heightened experience-dependent plasticity and spontaneous uncoordinated skeletal movement. How these various processes cooperate to allow the somatosensory system to form a three-dimensional representation of the body is not known. In the visual system, interactions between spontaneous network patterns and afferent activity have been suggested to be vital for normal development. Although several intrinsic cortical patterns of correlated neuronal activity have been described in developing somatosensory cortex in vitro, the in vivo patterns in the critical developmental period and the influence of physiological sensory inputs on these patterns remain unknown. We report here that in the intact somatosensory cortex of the newborn rat in vivo, spatially confined spindle bursts represent the first and only organized network pattern. The localized spindles are selectively triggered in a somatotopic manner by spontaneous muscle twitches, motor patterns analogous to human fetal movements. We suggest that the interaction between movement-triggered sensory feedback signals and self-organized spindle oscillations shapes the formation of cortical connections required for sensorimotor coordination.     

基于图论算法的脊髓损伤后大脑皮层运动区神经元网络分析

 脊髓损伤(SCI)后大脑皮层运动区神经元的功能重组对机体功能康复的影响仍然不为人知。脊髓损伤前后,对一只在跑步机上直立行走的恒河猴的大脑皮层运动区神经元信号进行记录,利用不同神经元动作电位序列间的相关系数建立神经元网络图。为了研究神经元活动模式的变化与功能康复之间的联系,利用图论算法计算了神经元网络图的全局效能指标和神经元脆弱性指标。结果显示,不同时期神经元活动模式的显著变化意味着运动区神经元的功能重组(神经可塑性)与脊髓损伤后猴子的功能康复状态紧密相关,且这种神经功能重组对于猴子步行功能的康复起了非常重要的积极作用。     

基于互信息的帕金森病脑皮层功能连接

帕金森病的早期症状是很难察觉的,目前还没有一个明确的生物标志物可以准确地检测出早期的帕金森病。本文为了探究帕金森病的潜在生物标志物,分析15名帕金森病患者和15名健康对照者闭眼状态下的溯源后的脑电信号。首先,使用互信息测量两组受试者的大脑各个区域之间的功能连接。之后,对两组受试者之间的每个连接对的互信息值进行独立样本t检验,检测两组受试者之间显著差异的连接边。最后,将具有显著差异的连接边作为特征进行分类。结果表明,帕金森病患者的大脑各个区域之间的互信息值整体小于健康对照组,并发现在额顶叶和顶枕叶之间的功能连接差异十分显著（p<0.01）。利用互信息功能连接指标对帕金森病患者和健康对照组分类时,测试准确率为76.7%,验证了基于互信息的脑功能连接对帕金森病研究的有效性。这些发现表明额顶叶和顶枕叶之间功能连接性的降低可能是帕金森病的一个潜在生物标志物。本文系首次使用互信息这一功能连接指标对帕金森病进行研究,这为帕金森病的神经机制研究提供了一个新的途径。     

Transmitter release from frog motor nerve terminals depends on motor unit size

It has been postulated that the success with which a motor nerve terminal competes for synaptic connections or the ability of an axon to maintain sprouts may depend on the support each terminal receives from its coma, presumably in the form of some substance(s) synthesized there. The support received by each terminal may in turn depend on the total number of terminals maintained by that soma, namely, motor unit size. We show here that when motor unit size is experimentally decreased, transmitter release from the terminals is markedly enhanced. This is consistent with the view that the extent of support from the soma may also influence the effectiveness of synaptic transmission.     

基于有限元的新型高延性角钢连接节点抗震性能评估

探讨了一种新型高延性角钢连接节点的抗震性能.在普通双腹板顶底角钢连接节点的基础上,提出了一种新型高延性角钢连接节点,该新型节点将与梁相连的角钢分肢上的螺栓圆孔扩大成长圆孔.通过有限元分析,对采用常规圆孔的普通角钢节点和采用不同扩孔尺寸的一系列新型角钢节点在转动能力、延性、滞回曲线、耗能能力等方面的差异进行了比较.结果表明,扩孔后的新型节点具有更好的抗震性能.     

半刚性端板连接多层钢框架的Push-over分析

由于缺乏计算理论和方法,大多数半刚性节点按刚性节点进行设计,对结构的静力分析、抗震性能等各方面的设计计算的影响很大.本文采用有限元分析方法,将半刚性连接节点视为弹簧单元,通过通用有限元软件Sap2000对一个半刚性端板连接的多层钢框架建立有限元模型并进行了模态分析、反应谱分析和Push-over(静力弹塑性)分析.结果表明,采用了半刚性端板连接的钢框架结构,相对于理想刚接的情况,结构在多遇和罕遇地震作用下结构的抗震性能明显变化.     

拓扑空间中的连通性

介绍了拓扑空间中的局部连通和道路连通,获得了以下结果:实数空间是道路连通的,欧氏平面中的单位圆周是连通的,欧氏平面中所有至少有一个坐标为有理数的点构成的集合是一个连通子集.证明了几个局部道路连通空间的定理和与拓扑空间中的连通性有关的几个定理.     

装配式大板结构竖缝抗剪承载力与接合筋的关系

旨在对装配式大板结构竖缝在反复荷载作用下的抗剪承载力与接合筋的关系进行研究 ,以使装配式结构最终成为一种完善的抗震体系。本文设计、试验了 3榀试件 ,分析了竖缝的抗剪承载力与接缝宽度的关系及其抗震性能。