Discontinuous and continuous transitions of collective behaviors in living systems

Living systems are full of astonishing diversity and complexity of life. Despite differences in the length scales and cognitive abilities of these systems, collective motion of large groups of individuals can emerge. It is of great importance to seek for the fundamental principles of collective motion, such as phase transitions and their natures. Via an eigen microstate approach, we have found a discontinuous transition of density and a continuous transition of velocity in the Vicsek models of collective motion, which are identified by the finite-size scaling form of order-parameter. At strong noise, living systems behave like gas. With the decrease of noise, the interactions between the particles of a living system become stronger and make them come closer. The living system experiences then a discontinuous gas-liquid like transition of density. The even stronger interactions at smaller noise make the velocity directions of the particles become ordered and there is a continuous phase transition of collective motion in addition.     

Critical behavior of higher cumulants of order parameter in the 3D-Ising universality class

QCD deconfinement phase transition is supposed to be the same universality class as the 3D-Ising model. According to the universality of critical behavior, the Binder-like ratios and ratios of higher cumulants of order parameter near the critical temperature in the 3D-Ising model are studied. The Binder-like ratio is shown to be a step function of temperature. The critical point is the intersection of the ratios of different system sizes between two platforms. The normalized cumulant ratios, like the Skewness and Kurtosis, do not diverge with correlation length, contrary to the corresponding cumulants. Possible applications of these characters in locating critical point in relativistic heavy ion collisions are discussed.     

羧酸稀土配合物共聚反应的研究

通过沉淀法和直接法制备羧酸稀土配合物，与丙烯酸等单体共聚反应制备不同稀土含量的稀土有机高分子离聚物。用微量热天平(TG)、差热分析仪(DTA)等分析它的热稳定性以及玻璃化转变温度，用红外光谱分析其结构。讨论了用不同方法合成的稀土配合物对共聚反应和聚合物性能的影响。结果显示直接合成羧酸稀土配合物有利于共聚物性能的稳定和稀土含量的调节。     

聚氯乙烯接枝丙烯酸稀土的研究

将无机稀土有机化后与聚氯乙烯(PVC)进行接枝共聚。探讨了氧化稀土与丙烯酸反应、PVC接枝丙烯酸稀土的原理和方法，并通过红外光谱、扫描电镜对接枝共聚物进行定性表征，用微量热天平对接枝共聚物的热性能进行测定。实验结果表明，经丙烯酸稀土接枝共聚后的PVC，其耐热分解性能和韧性有了明显的提高。     

稀土改性PVC膜的制备及性能研究

利用硝酸稀土作为改性剂，加入到聚氯乙烯（PVC）的四氢呋喃（THF）溶液中，用流延法制得表观透明均匀的PVC膜，经紫外辐射交联后，测试其力学和物理性能，发现经稀土改性后的PVC薄膜的力学和物理性能均有了较大的提高。     

Casimir Force of Piston Systems with Arbitrary Cross Sections under Different Boundary Conditions

We study the Casimir force between two pistons under different boundary conditions inside an infinite cylinder with arbitrary cross section. It is found that the attractive or repulsive character of the Casimir force for a scalar field is determined only by the boundary condition along the longitudinal direction and is independent of the cross section, transverse boundary conditions and the mass of the field. Under symmetric Dirichlet-Dirichlet, Neumann-Neumann and periodic longitudinal boundary conditions the Casimir force is always attractive, but is repulsive under non-symmetric Dirichlet-Neumann and anti-periodic longitudinal boundary conditions. The Casimir force of the electromagnetic field in an ideal conductive piston is also investigated. This force is always attractive regardless of the shape of the cross section and the transverse boundary conditions.     

复杂性科学的机遇：2021年诺贝尔物理学奖解读

2021年诺贝尔物理学奖授予三位科学家(图1),以表彰他们"对我们理解复杂物理系统的开创性贡献"。美籍日裔科学家真锅淑郎(Syukuro Manabe)、德国科学家克劳斯·哈塞尔曼(Klaus Hasselmann)因为"地球气候的物理建模,量化可变性并可靠地预测全球变暖"的研究共享了诺贝尔物理学奖的一半奖金;意大利科学家乔治·帕里西(Giorgio Parisi)因为"发现了从原子尺度到行星尺度物理系统中的无序和涨落的相互作用"而获得了诺贝尔物理学奖的另一半奖金。今年诺贝尔物理学奖授予复杂性科学领域,既说明该领域的研究已经获得学术界的重视,同时也为复杂系统研究的发展带来了新机遇。     

聚氨基硅氧烷-稀土复合物的制备及其性能研究

利用稀土离子与活性硅醇交联聚氨基硅氧烷，得到了聚氨基硅氧烷-稀土复合物；用热重分析仪(TG)分析了其热稳定性，测试了其在电场中的受力状况，推导其相对极化率，发现含不同稀土样品的极化率有较大差异，说明可以用这种方法获得不同电学性能的有机硅材料。同时研究了它们的吸收、发射光谱，并与稀土氯化物溶液的吸收光谱进行了比较，指出了它们的不同并讨论了其原因。     

Cumulants in the 3-dimensional Ising,O（2） and O（4） spin models

Based on the universal properties of a critical point in different systems and that the QCD phase transitions fall into the same universality classes as the 3-dimensional Ising, O（2） or O（4） spin models, the critical behavior of cumulants and higher cumulant ratios of the order parameter from the three kinds of spin models is studied. We found that all higher cumulant ratios change dramatically the sign near the critical temperature. The qualitative critical behavior of the same order cumulant ratio is consistent in these three models.     

自我质疑机制下公共物品博弈模型的相变特性

公共物品博弈是研究群体相互作用的经典模型,广泛用于解释自私个体间合作的涌现和保持.本文从理论分析和蒙特卡罗模拟两个方面研究了二维正方格子上一个有偿惩罚机制下随自我质疑更新规则演化的公共物品博弈模型的相变特性.理论分析方面,将公共物品博弈模型转化为一个外场不为零的铁磁Ising模型.通过有效能量发现:不存在惩罚时,个体间的耦合强度为零,体系只有外场作用;存在惩罚时,个体间包含最近邻、次近邻和第三近邻相互作用且外场不为零.蒙特卡罗模拟方面,首先验证了理论分析的正确性,然后对公共物品博弈模型相关的一级相变和二级相变进行了有限尺度标度分析.研究发现:1)蒙特卡罗模拟所得结果与类Ising模型分析结果完全吻合;2)相比二维Ising模型,公共物品博弈的二级相变临界指数发生了变化;3)公共物品博弈的一级相变与二维Ising模型相同.