Computer simulations of figure-ground discrimination in the visual system of the fly

Figure-ground discrimination and pattern discrimination represent one of the most important problems in computer vision. Based on computational neuronal network model proposed by Reichardt et al. for figure-ground discrimination in the visual system of the fly, entire systematic computer simulations were carried out under nonstationary conditions. Results show that the model network and simulations have predictive power for behavioural experimental results. This paper proposes that motion perception and elementary pattern discrimination in human visual system may be mediated by some kind of figure-ground system with movement detectors as input layer.     

Neural Network Approaches to Visual Motion Perception

This paper concerns certain difficult problems in image processing and perception: neuro-computation of visual motion information. The first part of this paper deals with the spatial physiological integration by the figure-ground discrimination neural network in the visual system of the fly. We have outlined the fundamental organization and algorithms of this neural network, and mainly concentrated on the results of computer simulations of spatial physiological integration. It has been shown that the gain control mechanism , the nonlinearity of synaptic transmission characteristic , the interaction between the two eyes , and the directional selectivity of the pool cells play decisive roles in the spatial physiological integration. In the second part, we have presented a self-organizing neural network for the perception of visual motion by using a retinotopic array of Reichardt's motion detectors and Kohonen's self-organizing maps. It .has been demonstrated by computer simulations that the network is abl     

NEUROCOMPUTATION OF VISUAL RELATIVE MOTION INFORMATION

In this paper the neurocomputation of figure-ground relative motion information in thevisual system of the fly have been investigated in great detail by a combination of quanti-tative behavioural experiments and computational model simulations. Only torque responsesabout the vertical axis of the tethered flying flies (Musca domestica) were determined inthe behavioural experiment. The main results of behavioural experiments are: (i) The dynam-ics of the torque responses depends not only on the phase relationship between figure andbackground motion but also on the oscillation frequency of the figure and ground. (ii) Inall the phase relations tested, the time courses are a characteristic fingerprint of the partic-ular phase relationship. (iii) The variation of the amplitude of the response peaks is an espe-cially sensitive indicator for the variability of figure--ground discrimination behaviour. The main results of computer simulations are: (i) The "computer fly", the networkmodel of both the SF-system and     

Finite size effects in tightly meshed polymer networks

Molecular dynamics computer simulations on regular, tightly meshed model networks exhibit variations of the network density with system size. We show that these variations are due mainly to network elasticity. A theoretical expression derived on the basis of the self-consistent-field approach yields finite size scaling behavior in good accord with the simulation for a wide range of thermodynamic conditions.     

模型筛选及计算机分峰法在涤纶X衍射图谱分解中的应用

本文引入数学模型筛选的判别准则,从五种竞争模型中确定了涤纶无定形散射峰的表征函数;并且编制了适用于分解X射线衍射图谱的计算机分峰程序。在上述基础上分解了多种涤纶的X衍射图谱,探索了它们的结构参数,取得了较好结果。     

人工神经网络模型在非ABO3型希土复氧化物电阻率特性分析中的应用

目前,人工神经网络在模式识别及其他领域的应用引起了普遍的关注.本文叙述“反向传播”神经网络模型,算法和在非ABO_3型希土复氧化物电阻率分析中的应用,实验结果表明,神经网络的判别正确率为100％,因此,该方法可望成为化合物分析,材料设计的辅助手段.     

ON THE MICRORHEOLOGICAL MODELING OF AGGREGATING COLLOIDS

ABSTRACT

Microrheological modeling of the aggregating colloidal dispersions in frames of the mean-field approach Is used to relate their Theological behavior to the parameters of the aggregates. Three parameters are shown to form a minimum set of values which one should know to elaborate the simplest self-consistent microrheological model of aggregating colloids. They are: the yield strength of the compact structure o, fractal dimension D and the exponent m, which characterizes the dependence of the aggregates radius R vs shear rate S (R ∝ S^?m). Analytic consideration and computer simulations are carried out to determine the exponent m for the aggregates of different type. The behavior of the aggregate depends on the character of the particles Interaction. In general the interaction force can be considered a superposition of central component (equivalent to ordinary spring) and some non-central component. If the non-central Interaction Is relevant, the aggregate internal structure is rigid (I.e. it elastically responds to small deformation), while in the case of purely central Interaction it Is soft (i.e. it Is irreversibly deformed even under the action of lnfinlteslmally small force). The system with purely central particles interaction seems to be a reasonable model for the coagulation in secondary energy minimum, while the system with non-central component represents (at lest qualitatively) the coagulation in primary minimum. The theoretical calculations of the shear viscosity of aggregating     

自组织神经树用于判别氟化物非晶态形成条件

1人工神经网络──自组织神经树模型人工神经网络（ANN）是八十年代中期迅速兴起的一门非线性科学．它力图模拟人脑的一些基本特性，如自适应性、自组织性、容错性等，已在模式识别、数据处理及自动化控制等领域得到了初步应用，取得了相当好的效果［1，2］．1993年，Tao－Li等提出了自组织神经树网络．它是一个多层树状网络（见图1），每个输入节点与所有神经树的节点（神经元）通过权W相联系，实现对输入信号的非线性降维映射．映射中保持拓扑不变性，即把拓扑意义下相似的输入（即在高维空间中距离较近的输入向量）映射到相同子树的节…     

Energetic Tuning by tRNA Modifications Ensures Correct Decoding of Isoleucine and Methionine on the Ribosome

Chemical modifications of tRNAs are critical for accurate translation of the genetic code on the ribosome. The discrimination between isoleucine (AUA) and methionine (AUG) codons depends on such modifications of the wobble position in isoleucine tRNA anticodon loops, in all kingdoms of life. Bacteria and archaea employ functionally similar lysine‐ and agmatine‐conjugated cytidine derivatives to ensure decoding fidelity, but the thermodynamics underlying codon discrimination remains unknown. Here, we report structure‐based computer simulations that quantitatively reveal the energetics of this decoding strategy in archaea. The results further show that the agmatidine modification confers tRNA specificity primarily by desolvation of the incorrect codon in the non‐cognate complex. Tautomerism is found to play no significant role in this decoding system as the usual amino form of the modified tRNA is by far the most stable.     

露点仪镜面过冷水的自动识别

对露点仪镜面过冷水产生的原因及其对露点测量准确度的影响进行分析,采用图像处理方法对露点仪镜面上的过冷水进行自动识别,经过计算机处理,修正了因露霜判别错误引入的误差,提高了露点测量的准确度和自动化程度。     

Conductivity-viscosity-structure: unpicking the relationship in an ionic liquid

The relationships between the ionic mobility, the viscosity, and the atomic-scale structure are investigated in computer simulations of mixtures of LiF and the network glass-forming material BeF(2). The simulations span a wide range of compositions, across which the fluidity of the system changes greatly due to the break-up of the Be-F network by the addition of the LiF. The relationship between the conductivity and viscosity passes from that expected for independently diffusing ions in the dilute mixtures to strongly decoupled Li+ migration through a viscous network at higher concentrations. The transition between these régimes is linked to the changing local and intermediate-scale structure in the melts. The decoupling phenomenon is associated with the appearance of migration channels in the network which leads to cooperative effects in the Li+ migration.     

菌紫质LB膜对闪光的响应

光敏生物大分子菌紫质(bR)是嗜盐菌(H.Halobium)紫膜中的唯一蛋白质,分子量为26,000 Da.视黄醛共价结合在蛋白上,当吸收了光子后它可在瞬间产生光化学反应,并与光电转换相联系.bR分子在结构与功能方面的这些特征,与动物光感受器中的视紫红质构为类似,从而引起了视觉研究者对它的兴趣.     

Tensegrity and motor-driven effective interactions in a model cytoskeleton

Actomyosin networks are major structural components of the cell. They provide mechanical integrity and allow dynamic remodeling of eukaryotic cells, self-organizing into the diverse patterns essential for development. We provide a theoretical framework to investigate the intricate interplay between local force generation, network connectivity, and collective action of molecular motors. This framework is capable of accommodating both regular and heterogeneous pattern formation, arrested coarsening and macroscopic contraction in a unified manner. We model the actomyosin system as a motorized cat's cradle consisting of a crosslinked network of nonlinear elastic filaments subjected to spatially anti-correlated motor kicks acting on motorized (fibril) crosslinks. The phase diagram suggests there can be arrested phase separation which provides a natural explanation for the aggregation and coalescence of actomyosin condensates. Simulation studies confirm the theoretical picture that a nonequilibrium many-body system driven by correlated motor kicks can behave as if it were at an effective equilibrium, but with modified interactions that account for the correlation of the motor driven motions of the actively bonded nodes. Regular aster patterns are observed both in Brownian dynamics simulations at effective equilibrium and in the complete stochastic simulations. The results show that large-scale contraction requires correlated kicking.     

扩散不稳定相中的化学稳定性和时-空有序结构的形成

利用热力学和动力学的分析方法, 研究了化学稳定性和扩散稳定性的依赖关系。发现, 在远离平衡和强烈非理想的体系中, 不管体系是否扩散稳定, 化学反应可以是稳定的, 也可以是不稳定的。通过对Schlögl模型的分析, 表明扩散不稳定性和化学稳定性之间的竞争可以导致一类时空有序结构的形成。这一结果可以看作是耗散结构理论的推广和延伸。     

高磺化度聚苯胺体系中的分形结构研究

通过透射电镜的观察研究发现磺化聚苯胺的胶体聚集体和胶粒内部结构都具有分形体的特征 ,从而将分形的概念及其数学模型引入共轭导电聚合物体系之中 .磺化聚苯胺胶体的聚集体为很不均匀的分支状开放结构 ,其形成过程可用扩散控制集团聚集模型 (DLCA)进行模拟 ,计算机模拟生成的图形及其分形维数都与实验观测结果相当吻合 .胶粒由于是在分散介质所形成的平均化场中生成 ,屏蔽效应减弱 ,是比由它组成的聚集体要致密的球形结构 ,该结构的生成可用随机雨点模型模拟且结果相近 .     

Computer simulation of chiral liquid crystal phases VIII. Blue phases of the chiral Gay-Berne fluid

The phase diagram of chiral calamitic liquid crystals was studied in the temperature-chirality parameter plane by means of computer simulation. Bulk systems composed of N = 2048 uniaxial chiral calamitic Gay-Berne molecules, i.e. with interactions described by the Gay-Berne potential and an additive term for the energy of the chiral interaction, were investigated using Monte Carlo (MC) simulations in the canonical ensemble (NVT). A rich polymorphism of chiral liquid crystal phases was observed along an isotherm with increasing chirality parameter describing the strength of the chiral interaction. In addition to the cholesteric phase (N*), for the first time a blue phase I (BP I) could be proven by computer simulation of a many-particle system based on model intermolecular interactions. Additionally, at high values of the chirality parameter, a phase with randomly oriented squirming double twist tubes was found as characteristic for the so-called spaghetti model for blue phase III (BP III). The structures of all phases were characterized by order parameters, a set of scalar and pseudoscalar orientational correlation functions, and especially by visual representations of selected configurations.     

Computer simulation of chiral liquid crystal phases VIII. Blue phases of the chiral Gay-Berne fluid

The phase diagram of chiral calamitic liquid crystals was studied in the temperature-chirality parameter plane by means of computer simulation. Bulk systems composed of N = 2048 uniaxial chiral calamitic Gay-Berne molecules, i.e. with interactions described by the Gay-Berne potential and an additive term for the energy of the chiral interaction, were investigated using Monte Carlo (MC) simulations in the canonical ensemble (NVT). A rich polymorphism of chiral liquid crystal phases was observed along an isotherm with increasing chirality parameter describing the strength of the chiral interaction. In addition to the cholesteric phase (N*), for the first time a blue phase I (BP I) could be proven by computer simulation of a many-particle system based on model intermolecular interactions. Additionally, at high values of the chirality parameter, a phase with randomly oriented squirming double twist tubes was found as characteristic for the so-called spaghetti model for blue phase III (BP III). The structures of all phases were characterized by order parameters, a set of scalar and pseudoscalar orientational correlation functions, and especially by visual representations of selected configurations.     

On catenate network formation by end-linking reactions

Catenate network formation by end-linking reactions of linear chains with bifunctional regents is studied theoretically and by computer simulations. It is found that the reaction cannot reach its stationary limit, and catenate networks are never formed by this method. An alternative method that will lead to catenate networks nearly in the topological equilibrium state is proposed. It is pointed out that catenate networks are an ideal system for studying the role of entanglement in rubber elasticity. © 1993 John Wiley & Sons, Inc.     

Efficient energy based modeling and experimental validation of liquid filling in planar micro-fluidic components and networks

This paper presents a model that describes how liquid flow fills micro-fluidic components and networks. As an alternative to computational fluid dynamic (CFD) simulations, we use a constrained energy minimization approach. This approach is based on two assumptions that hold in many micro-fluidic devices: (i) The length scales are small, and we consider slow filling rates, hence fluid momentum and viscous terms are small compared to surface tension forces, consequently the liquid/gas interfaces can be viewed as a succession of quasi-steady equilibrium configurations. (ii) Any equilibrium configuration corresponds to a surface tension energy minima which is constrained by the device shape and the volume of liquid in the device. The model is developed for planar micro-fluidic devices, is based on a fundamental physical principle, and shows accurate agreement with experimental data. It takes us only a few minutes to evaluate the model for a planar component of any shape using the Surface Evolver software, and this is significantly less then the computer run time required for CFD simulations. Moreover, once a library of component models has been created (which takes less than an hour of computer time) it then takes only seconds to simulate different network architectures with thousands of components. This fast "reconfigure the network and simulate in seconds" capability is essential for the design of truly complex networks that will enable the next generation of passive, micro-fluidic, lab-on-a-chip systems.     

Self-organization and pattern formation of janus particles in two dimensions by computer simulations

The phase behavior and associated pattern formation of two-dimensional systems of hard disks decorated with amphiphilic coronae (Janus disks) are studied by means of Monte Carlo computer simulations. A primitive interaction potential that captures the essential interparticle interactions is introduced. Despite its simplicity, the system exhibits a very rich phase polymorphism. Apart from the isotropic phase and depending upon the coronal thickness, the simulated systems self-organize in a number of two-dimensional mesophases of various symmetries exhibiting a variety of novel patterns. The results of these simulations suggest that 2D Janus particles are promising candidates for bottom-up design of precise two-dimensional templates.