Universality of Complex Systems near Critical Points
Xiaosong Chen
Institute of Theoretical Physics, Chinese Academy of Sciences

The notation of a universality class is a basic tenet in the physics of critical phenomena. It is characterized by the dimensionality d of the system and by the number n of the components of the order parameter. In anisotropic systems of a given (d,n) universality class, two-scale factor universality universality is absent in bulk correlation functions, and finite-size scaling functions are shown to be nonuniversal. In a two-dimensional magnetic lattice gas model, we find that the critical exponents depend on the density of system. These challenge the traditional view of universality in the critical phenomena. 

Bio:
Professor Xiaosong Chen obtained his B.Sc. degree in 1982 and Master's degree in 1984 from the Department of Physics of Central China Normal University, Wuhan. From 1985 to 1987 he worked as assistant in the Department of Physics of Xi'an Jiaotong University. From 1987 he worked in the Department of Physics of Free University Berlin, Federal Republic Germany. In the June of 1992, he obtained his Ph.D. there and afterwards did postdoctoral research until the end of 1992. From 1993 to 1997, he worked as an assistant in the Institute of Theoretical Physics of Aachen Technical University, Germany. From 1996 to 2000, he was a full professor in the Institute of Particle Physics, Central China Normal University. He was a guest professor in the Institute of Theoretical Physics of Aachen Technical University. From 2000, he became a full professor in the Institute of Theoretical Physics, the Chinese Academy of Sciences.

Rank-size Distribution of a Percolation System near its Critical Point
Liangsheng Li
Institute of Theoretical Physics, Chinese Academy of Sciences

The rank-size distribution of the clusters in a system has been investigated widely for social and natural systems. It was believed that the rank-size distribution of many system should follow the Zipf’s law, which is a power law with exponent  = 1. Here we have studied the rank-size distribution of a percolation near its critical point. We find that the rank-size distribution is approximately a power law near the critical point and deviates obviously from a pure power law above and below the critical point. The rank-size distribution follows the finite-size scaling near the critical point.

Hysteresis and Fluctuations of Interfacial Forces near a Moving Contact Line
Yong Jian Wang
Department of Physics, The Hong Kong University of Science and Technology *

Atomic force microscope (AFM) is used as a force sensor to measure the capillary forces on a long vertical glass fiber with one end glued onto a rectangular shaped cantilever beam and the other end immersed through a liquid-air interface. Using a cleaned glass fiber of ~2 m in diameter, we were able to determine the surface tension of a class of liquids with good accuracy. For this class of liquids, no detectable hysteresis is found when the contact line between the liquid and glass fiber moves at a constant speed. The AFM force measurements, however, revealed considerable fluctuations in the force amplitude. The probability density function of the force fluctuations all shows a Gaussian form. Investigations are carried out to find the relationship between the mean squared value of force fluctuations and the chemical properties of the liquid. Water as a polar liquid was also investigated in the experiment. No hysteresis was observed when a freshly-plasma-cleaned glass fiber is used, but hysteresis developed gradually with time. The increase of the hysteresis is found to be proportional to the mean squared value of force fluctuations.

* Work done in collaboration with Shuo Guo, Ping Sheng, and Penger Tong and was supported by the Research Grants Council of Hong Kong SAR