基于元胞自动机和SIS传染算法的恐慌状态下行人疏散模型

为了研究人群在恐慌状态下的疏散行为特征,基于元胞自动机和SIS传染算法提出了一种用于恐慌状态下的行人疏散模型.通过场域模型给出了行人的移动收益公式,并利用SIS传染算法来研究恐慌情绪在人群中的传播规律及对疏散行为造成的影响,同时,给出了恐慌情绪量化公式.然后,通过仿真实验对疏散时间、行人密度、恐慌情绪比值和平均速度等参数进行了分析和讨论.仿真实验结果表明:行人密度与恐慌人数之间为正相关,人群到出口的距离与恐慌人数比例、恐慌因子W_p之间为正相关;恐慌情绪比值与疏散时间、恐慌因子Wp之间为负相关,人群平均速度与行人密度之间为负相关.     

Mexican waves in an excitable medium

The Mexican wave, or La Ola, which rose to fame during the 1986 World Cup in Mexico, surges through the rows of spectators in a stadium as those in one section leap to their feet with their arms up, and then sit down again as the next section rises to repeat the motion. To interpret and quantify this collective human behaviour, we have used a variant of models that were originally developed to describe excitable media such as cardiac tissue. Modelling the reaction of the crowd to attempts to trigger the wave reveals how this phenomenon is stimulated, and may prove useful in controlling events that involve groups of excited people.     

面向密集人群的运动分类与跟踪算法

密集场景下的人群分析是当前智能监控技术研究的热点。人群分析首要解决的是对人群运动的模式分类与跟踪。通过对密集人群运动模式的深入研究,提出了一种新的群体分类和跟踪算法。算法通过计算个体之间的相关性,进行群体运动的分类;利用轨迹的一致性进行运动模式匹配,实现了视频序列的群体运动跟踪。实验表明,该算法能准确的进行密集人群运动模式分类,并取得良好的跟踪效果。     

Weak pairwise correlations imply strongly correlated network states in a neural population

Biological networks have so many possible states that exhaustive sampling is impossible. Successful analysis thus depends on simplifying hypotheses, but experiments on many systems hint that complicated, higher-order interactions among large groups of elements have an important role. Here we show, in the vertebrate retina, that weak correlations between pairs of neurons coexist with strongly collective behaviour in the responses of ten or more neurons. We find that this collective behaviour is described quantitatively by models that capture the observed pairwise correlations but assume no higher-order interactions. These maximum entropy models are equivalent to Ising models, and predict that larger networks are completely dominated by correlation effects. This suggests that the neural code has associative or error-correcting properties, and we provide preliminary evidence for such behaviour. As a first test for the generality of these ideas, we show that similar results are obtained from networks of cultured cortical neurons.     

Unconventional critical behaviour in a quasi-two-dimensional organic conductor

Changing the interactions between particles in an ensemble--by varying the temperature or pressure, for example--can lead to phase transitions whose critical behaviour depends on the collective nature of the many-body system. Despite the diversity of ingredients, which include atoms, molecules, electrons and their spins, the collective behaviour can be grouped into several families (called 'universality classes') represented by canonical spin models. One kind of transition, the Mott transition, occurs when the repulsive Coulomb interaction between electrons is increased, causing wave-like electrons to behave as particles. In two dimensions, the attractive behaviour responsible for the superconductivity in high-transition temperature copper oxide and organic compounds appears near the Mott transition, but the universality class to which two-dimensional, repulsive electronic systems belongs remains unknown. Here we present an observation of the critical phenomena at the pressure-induced Mott transition in a quasi-two-dimensional organic conductor using conductance measurements as a probe. We find that the Mott transition in two dimensions is not consistent with known universality classes, as the observed collective behaviour has previously not been seen. This peculiarity must be involved in any emergent behaviour near the Mott transition in two dimensions.     

Theoretical mechanics: crowd synchrony on the Millennium Bridge

Soon after the crowd streamed on to London's Millennium Bridge on the day it opened, the bridge started to sway from side to side: many pedestrians fell spontaneously into step with the bridge's vibrations, inadvertently amplifying them. Here we model this unexpected and now notorious phenomenon--which was not due to the bridge's innovative design as was first thought--by adapting ideas originally developed to describe the collective synchronization of biological oscillators such as neurons and fireflies. Our approach should help engineers to estimate the damping needed to stabilize other exceptionally crowded footbridges against synchronous lateral excitation by pedestrians.     

Indirect reciprocity can stabilize cooperation without the second-order free rider problem

Models of large-scale human cooperation take two forms. 'Indirect reciprocity' occurs when individuals help others in order to uphold a reputation and so be included in future cooperation. In 'collective action', individuals engage in costly behaviour that benefits the group as a whole. Although the evolution of indirect reciprocity is theoretically plausible, there is no consensus about how collective action evolves. Evidence suggests that punishing free riders can maintain cooperation, but why individuals should engage in costly punishment is unclear. Solutions to this 'second-order free rider problem' include meta-punishment, mutation, conformism, signalling and group-selection. The threat of exclusion from indirect reciprocity can sustain collective action in the laboratory. Here, we show that such exclusion is evolutionarily stable, providing an incentive to engage in costly cooperation, while avoiding the second-order free rider problem because punishers can withhold help from free riders without damaging their reputations. However, we also show that such a strategy cannot invade a population in which indirect reciprocity is not linked to collective action, thus leaving unexplained how collective action arises.     

Large-scale vortex lattice emerging from collectively moving microtubules

Spontaneous collective motion, as in some flocks of bird and schools of fish, is an example of an emergent phenomenon. Such phenomena are at present of great interest and physicists have put forward a number of theoretical results that so far lack experimental verification. In animal behaviour studies, large-scale data collection is now technologically possible, but data are still scarce and arise from observations rather than controlled experiments. Multicellular biological systems, such as bacterial colonies or tissues, allow more control, but may have many hidden variables and interactions, hindering proper tests of theoretical ideas. However, in systems on the subcellular scale such tests may be possible, particularly in in vitro experiments with only few purified components. Motility assays, in which protein filaments are driven by molecular motors grafted to a substrate in the presence of ATP, can show collective motion for high densities of motors and attached filaments. This was demonstrated recently for the actomyosin system, but a complete understanding of the mechanisms at work is still lacking. Here we report experiments in which microtubules are propelled by surface-bound dyneins. In this system it is possible to study the local interaction: we find that colliding microtubules align with each other with high probability. At high densities, this alignment results in self-organization of the microtubules, which are on average 15?μm long, into vortices with diameters of around 400?μm. Inside the vortices, the microtubules circulate both clockwise and anticlockwise. On longer timescales, the vortices form a lattice structure. The emergence of these structures, as verified by a mathematical model, is the result of the smooth, reptation-like motion of single microtubules in combination with local interactions (the nematic alignment due to collisions)--there is no need for long-range interactions. Apart from its potential relevance to cortical arrays in plant cells and other biological situations, our study provides evidence for the existence of previously unsuspected universality classes of collective motion phenomena.     

How many-particle interactions develop after ultrafast excitation of an electron-hole plasma.

Electrostatic coupling between particles is important in many microscopic phenomena found in nature. The interaction between two isolated point charges is described by the bare Coulomb potential, but in many-body systems this interaction is modified as a result of the collective response of the screening cloud surrounding each charge carrier. One such system involves ultrafast interactions between quasi-free electrons in semiconductors-which are central to high-speed and future quantum electronic devices. The femtosecond kinetics of nonequilibrium Coulomb systems has been calculated using static and dynamical screening models that assume the instantaneous formation of interparticle correlations. However, some quantum kinetic theories suggest that a regime of unscreened bare Coulomb collisions might exist on ultrashort timescales. Here we monitor directly the temporal evolution of the charge-charge interactions after ultrafast excitation of an electron-hole plasma in GaAs. We show that the onset of collective behaviour such as Coulomb screening and plasmon scattering exhibits a distinct time delay of the order of the inverse plasma frequency, that is, several 10(-14) seconds.     

行人流综述

近十年以来,人们对行人流给予了越来越多的关注.这并不仅仅是这一理论对自身不断完善的要求,更是人们对公共安全有着要求,并希望行人流理论能揭示人群运动的普遍规律.本文回顾了在行人流领域中的一些经典模型及其基本结论.叙述了来源于麦加朝圣的行人流实测结果.鉴于行人在逃生时,具有类似于动物的集体行为,因此,介绍了描述集群运动的Vicsek模型,并将此模型中的视野半径引入行人流模型.重点讨论了行人数量、视野半径和逃生时间三者之间的相互关系.利用元胞自动机模型较简要地论述了行人在逃生时,门前障碍物对行人的影响.     

Crystalline ribonuclease A loses function below the dynamical transition at 220 K.

When the dynamic properties of many different proteins are plotted as a function of temperature, biphasic behaviour is observed, with a broad transition centred around 220 K. Atomic mean-square displacements from X-ray crystallography and M?ssbauer scattering show this behaviour, as do electron transfer rates and dynamic information from inelastic neutron scattering. Molecular dynamics simulations over a range of temperatures also exhibit a transition at about 220 K: high-temperature atomic fluctuations are dominated by anharmonic collective motions of bonded and nonbonded groups of atoms, but below 220 K the predominant dynamic behaviour is harmonic vibration of individual atoms. Here we show by high-resolution X-ray diffraction that crystalline ribonuclease A does not bind substrate or inhibitor at 212 K but will bind either rapidly at 228 K. Once bound at the higher temperature, inhibitor cannot be washed off after the enzyme is cooled to below the transition temperature. These results suggest that enzyme flexibility is required for catalytic function.     

拥挤系统阻碍物位置的遗传算法优化

首先对Helbing等人建立的社会力模型进行了适当修正,建立了人群运动仿真模型;然后采用实数编码遗传算法并设计了自适应的交叉及变异策略,建立了优化阻碍物位置的数学模型;最后通过高性能计算平台进行仿真计算,得到了最有利于提高拥挤人群疏散速度的阻碍物设置.通过优化房间和人群所形成的拥挤系统中阻碍物的大小、数量和位置,有效提高了恐慌发生时房间内人群的逃生效率,该结果对建筑设计具有重要参考价值.     

局部二值平均熵模式与深度残差网络的人群密度估计

针对人群密度估计算法中场景的人群遮挡、尺度光照变化、噪声和低分辨率等问题,提出了一种结合局部二值熵值纹理特征(ELBP)与深度残差网络的人群密度估计算法。该算法首先在原始RGB人群图像上提取LBP特征;然后通过计算邻域像素点的平均信息熵模式构建ELBP纹理特征;随后基于ELBP纹理特征构建了一个深度为18层的深度残差网络;最后形成了对人群密度估计的end-to-end模式。为验证算法的可行性和有效性,在开源的人群密度估计数据集上进行实验。首先邀请10位专家对开源的数据集进行有效的人群聚集标注作为真实输出标签;随后采用研究提出的算法对人群密度完成估计,并与真实结果进行比较。另外,在三种不同的特征和三种不同的机器学习模型上进行了横向比较。实验结果表明,提出的ELBP纹理特征能够很好地应对噪声和低分辨率问题;深度残差网络则能够解决人群遮挡、尺度光照变化的问题。与传统算法相比,提出的算法能够提升人群密度估计的性能。     

Two distinct modes of guidance signalling during collective migration of border cells

Although directed migration is a feature of both individual cells and cell groups, guided migration has been studied most extensively for single cells in simple environments. Collective guidance of cell groups remains poorly understood, despite its relevance for development and metastasis. Neural crest cells and neuronal precursors migrate as loosely organized streams of individual cells, whereas cells of the fish lateral line, Drosophila tracheal tubes and border-cell clusters migrate as more coherent groups. Here we use Drosophila border cells to examine how collective guidance is performed. We report that border cells migrate in two phases using distinct mechanisms. Genetic analysis combined with live imaging shows that polarized cell behaviour is critical for the initial phase of migration, whereas dynamic collective behaviour dominates later. PDGF- and VEGF-related receptor and epidermal growth factor receptor act in both phases, but use different effector pathways in each. The myoblast city (Mbc, also known as DOCK180) and engulfment and cell motility (ELMO, also known as Ced-12) pathway is required for the early phase, in which guidance depends on subcellular localization of signalling within a leading cell. During the later phase, mitogen-activated protein kinase and phospholipase Cgamma are used redundantly, and we find that the cluster makes use of the difference in signal levels between cells to guide migration. Thus, information processing at the multicellular level is used to guide collective behaviour of a cell group.     

Observation of a roton collective mode in a two-dimensional Fermi liquid

Understanding the dynamics of correlated many-body quantum systems is a challenge for modern physics. Owing to the simplicity of their Hamiltonians, (4)He (bosons) and (3)He (fermions) have served as model systems for strongly interacting quantum fluids, with substantial efforts devoted to their understanding. An important milestone was the direct observation of the collective phonon-roton mode in liquid (4)He by neutron scattering, verifying Landau's prediction and his fruitful concept of elementary excitations. In a Fermi system, collective density fluctuations (known as 'zero-sound' in (3)He, and 'plasmons' in charged systems) and incoherent particle-hole excitations are observed. At small wavevectors and energies, both types of excitation are described by Landau's theory of Fermi liquids. At higher wavevectors, the collective mode enters the particle-hole band, where it is strongly damped. The dynamics of Fermi liquids at high wavevectors was thus believed to be essentially incoherent. Here we report inelastic neutron scattering measurements of a monolayer of liquid (3)He, observing a roton-like excitation. We find that the collective density mode reappears as a well defined excitation at momentum transfers larger than twice the Fermi momentum. We thus observe unexpected collective behaviour of a Fermi many-body system in the regime beyond the scope of Landau's theory. A satisfactory interpretation of the measured spectra is obtained using a dynamic many-body theory.     

基于行人运动模型的人群疏散三维仿真

以人群运动过程中人与人和人与建筑之间的相互作用为出发点,探讨了行人群集行为疏散模型及三维仿真问题.建立了一种基于人员行为细节的微观离散仿真模型,采用蒙皮动画和有限状态机技术实现对人物行为和人物模型细节状态的控制,可以实现人群疏散过程的动态三维可视化仿真.     

思维视角下的壮族典籍英译探讨——以布洛陀史诗为例

语言是表现思维的符号,翻译是一种跨文化的双语语码转换和思维方式转换的交际活动。壮语重具象思维和集体本位思维、英语重抽象思维和个体本位思维的差异是进行壮族典籍英译中需要处理的最突出的矛盾。在壮语和英语两种思维之间进行适当转换,能有效避免硬译、误译或错译,提高英语译文的可读性。     

基于Agent的群体性暴力事件的建模与仿真

对群体环境下个体的犯罪行为选择进行了研究。提出了一种新的犯罪风险评估模型,通过对个体的不满度、冒险等级等因素的简化提取,再现了暴乱发展扩散的情形。仿真实验表明,警察的出现能够有效抑制暴乱时"破窗效应"的扩散,而人群中核心分子和易转化分子对暴乱的规模增长和扩散起到了重要作用。研究结果可以为公安机关处置群体性暴力事件提供重要理论依据。     

Cranial design and function in a large theropod dinosaur

Finite element analysis (FEA) is used by industrial designers and biomechanicists to estimate the performance of engineered structures or human skeletal and soft tissues subjected to varying regimes of stress and strain. FEA is rarely applied to problems of biomechanical design in animals, despite its potential to inform structure-function analysis. Non-invasive techniques such as computed tomography scans can be used to generate accurate three-dimensional images of structures, such as skulls, which can form the basis of an accurate finite element model. Here we have applied this technique to the long skull of the large carnivorous theropod dinosaur Allosaurus fragilis. We have generated the most geometrically complete and complex FEA model of the skull of any extinct or extant organism and used this to test its mechanical properties and examine, in a quantitative way, long-held hypotheses concerning overall shape and function. The combination of a weak muscle-driven bite force, a very 'light' and 'open' skull architecture and unusually high cranial strength, suggests a very specific feeding behaviour for this animal. These results demonstrate simply the inherent potential of FEA for testing mechanical behaviour in fossils in ways that, until now, have been impossible.     

Glyoxalase 1 and glutathione reductase 1 regulate anxiety in mice

Anxiety and fear are normal emotional responses to threatening situations. In human anxiety disorders--such as panic disorder, obsessive-compulsive disorder, post-traumatic stress disorder, social phobia, specific phobias and generalized anxiety disorder--these responses are exaggerated. The molecular mechanisms involved in the regulation of normal and pathological anxiety are mostly unknown. However, the availability of different inbred strains of mice offers an excellent model system in which to study the genetics of certain behavioural phenotypes. Here we report, using a combination of behavioural analysis of six inbred mouse strains with quantitative gene expression profiling of several brain regions, the identification of 17 genes with expression patterns that correlate with anxiety-like behavioural phenotypes. To determine if two of the genes, glyoxalase 1 and glutathione reductase 1, have a causal role in the genesis of anxiety, we performed genetic manipulation using lentivirus-mediated gene transfer. Local overexpression of these genes in the mouse brain resulted in increased anxiety-like behaviour, while local inhibition of glyoxalase 1 expression by RNA interference decreased the anxiety-like behaviour. Both of these genes are involved in oxidative stress metabolism, linking this pathway with anxiety-related behaviour.