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关键词： spike-timing   dependent synaptic plasticity   short-term synaptic depression   direction selectivity   simple cell   phase advance  

摘要： In the companion paper we presented extended simulations showing that the recently observed spike-timing dependent synaptic plasticity can explain the development of simple cell direction selectivity (DS) when simultaneously modifying the synaptic strength and the degree of synaptic depression. Here we estimate the spatial shift of the simple cell receptive field (RF) induced by the long-term synaptic plasticity, and the temporal phase advance caused by the short-term synaptic depression in response to drifting grating stimuli. The analytical expressions for this spatial shift and temporal phase advance lead to a qualitative reproduction of the frequency tuning curves of non-directional and directional simple cells. In agreement with in vivo recordings, the acquired DS is strongest for test gratings with a temporal frequency around 1-4 Hz. In our model this best frequency is determined by the width of the learning function and the time course of depression, but not by the temporal frequency of the 'training' stimuli. The analysis further reveals the instability of the initially symmetric RF, and formally explains why direction selectivity develops from a non-directional cell in a natural, directionally unbiased stimulation scenario.

关键词： cell cycle   G1-phase regulation   mathematical model   bifurcation   Rb   cyclin E  

摘要： Mathematical analysis is performed on a 3-variable nonlinear ordinary differential equation system which had been previously introduced to model the regulation of the G1 phase of the cell cycle. The nature and stability of the model's steady states and periodic solutions are described. These results are obtained via linear stability analysis, bifurcation theory and computational techniques using AUTO. The model exhibits different,types of bifurcations. The bifurcation results are further confirmed by numerical simulations. This original model (three variables) and a model for a special biological case (the original reduced to two variables) are compared. Some mathematical properties of the 3-variable model are preserved, while others are lost, when the model is reduced to a 2-variable system. The possible biological relevance of the mathematical results is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： EDCs   ERs   fractal dimensions   heterogeneity   binding and dissociation rate coefficients  

摘要： A fractal analysis which takes into account the affect of surface heterogeneity brought about by ligand immobilization on the reaction kinetics is presented. The binding and dissociation of estrogen receptors ERalpha and ERbeta to different ligands is analyzed within the fractal framework. The heterogeneity on the biosensor surface is made quantitative by using a single number, the fractal dimension, D-f. The analysis provides physical insights into the binding of these receptors to different ligands and compounds, particularly the endocrine disrupting compounds (EDCs), which can have deleterious affects on humans and wildlife. Single- and dual-fractal models were employed to fit the ER binding data obtained from literature. Values of the binding and dissociation rate coefficient and fractal dimensions were obtained from a regression analysis provided by Corel Quattro Pro 8.0 [Corel Corporation Limited, Ottawa, Canada, 1997]. In some cases both a single- and dual-fractal model was required to completely and adequately describe the kinetics involved. For example, the binding of 40 nM ERalpha + 17beta-estradiol in solution to 300 RU of TIF2 immobilized on a SPR biosensor surface [J. Clin. Ligand Assay 18 (4) (1995) 215] requires a dual-fractal model. The dissociation, however, could be satisfactorily described using a single-fractal analysis. Values for the affinity, K-D(=k(d)/k(a)) were also calculated. This provides us with some extra flexibility in designing biomolecular assays. Predictive expressions relating the binding and dissociation rate coefficients and fractal dimensions to the analyte concentration were also developed. The analysis should provide further information on the mode of action and interaction of EDCs with the ERs. This would help in the design of agents and modulators against these EDCs. (C) 2002 Published by Elsevier Science B.V.

关键词： 项目管理知识体系   平面内   项目管理人员   职业道德   PMBOK   项目管理技术   项目组织机构   矩阵   数学分析   生命期   知识领域   项目管理学  

摘要： 国际项目管理的状况和动向:1.发达国家的项目管理已形成了学科和行业2.

关键词： 糖衣片   含量测定   不剥除糖衣测定法   数学分析方法  

摘要： [目的 ]考察剥除与不剥除糖衣进行糖衣片含量测定的差异。 [方法 ]采用数学分析方法 ,证明在包衣物质对含量测定方法无干扰的情况下 ,剥除与不剥除糖衣进行含量测定在理论上存在着差异。 [结果 ]剥除糖衣后 ,片心的损失会造成含量测定结果偏低 ,而糖衣的残留不会影响含量测定结果。 [结论 ]在包衣物质不影响含量测定的条件下 。

关键词： 风窗   曲面导线   包络线   数学分析   曲率半径   客车   包络过渡  

摘要： 本文通过对客车弧形风窗玻璃曲面导线的包络线过渡的分析 ,以得到两侧显得丰满圆滑并有较大的随意性的光滑过渡风窗 。

关键词： 教学内容改革   《数学分析》   高师   高等师范院校   实用性  

摘要： 阐述了现行高等师范院校《数学分析》教学内容改革的必要性以及教学内容改革的方向 ;

关键词： 数学分析   孤立极值   充要条件   动力系统   奇点   微分方程   定性理论  

摘要： 讨论了数学分析中求极值的经典问题,给出了n元函数孤立极值存在的充要条件.作者引入一些方法将极值问题转化为动力系统中奇点的分类问题或稳定性问题,采用自创的关于奇点稳定性的判别方法,给出了函数有孤立极值的充要条件.架起了微分方程定性理论和求极值问题之间的桥梁.方法可用来讨论无约束和有约束的最优化问题,对新算法给出了粗略的流程图.

关键词： 软开关   逆变器   电路   效率   功率损耗   数学分析   电力驱动系统  

摘要： 首先对一种软开关技术三相PWM逆变器电路的工作原理及实验验证结果进行了介绍和分析。然后用对比的方法对文中讨论的软开关逆变器电路的功率损耗及工作效率进行了详细的数学描述 ,给出了开关器件及由其构成的逆变器功率损耗的简化数学模型。最后在一个驱动三相电动机的逆变器实际电路中对相关的数学分析结论进行了实验验证 。

关键词： 创新人才   数学分析   极限理论   教学法  

摘要： “极限理论”这一主线始终贯穿数学分析课程内容的全部。通过阐述极限理论的教学法 ,并结合自身的教学实践 。