Complex Systems Research Lab

The Complex Systems Research Lab is devoted to studying various aspects of complex systems and their many diverse applications, such as physical and social networks, liquid water, financial networks and neuroscience.

Research Publications Database

• Aggregation
• Barkhausen Effect and Microfracture
• DNA
• Econophysics
• Granular Materials
• Neuroscience
• Percolation: Geometric Phase Transitions
• Phase Transitions and Critical Phenomena
• Physical and Social Networks
• Physiology and Medicine
• Surface Physics and Chemistry
• Water

Research projects include:

• Complexity and Coupled Networks. In the past several decades, there has been a radical shift in the way much of science is done, and an emphasis on applying network science and complexity to real-world problems (including cyberinfrastructures and computational and database approaches). In social, political and defense systems, among others, there is growing appreication that what happens in one network significantly affects another network. For example, infrastructures show a large number of interdependencies: physical interdependency when energy, material or people flow from one infrastructure to another; cyber interdependency when information is transmitted or exchanged; geographic interdependency signaling the co-location of infrastructure elements; logical interdependency that signals financial, political coordination, and other interactions. One area of focus is the exploration of the new kinds of vulnerabilities that coupled networks create and the kinds of countermeasures that can be developed against such threats (Buldyrev et al. 2010).

• Physical Mechanisms in Liquid Water. Water is an anomolous liquid. In addition, water is ubiquitous, important for everything from protein folding to quenching thirst. Water has a number of unusual properties that cannot that distinguish if from other liquids. For example: (i) Density Maximum in the liquid state (i.e., ice floats!), (ii) Growth of Isothermal compressability on cooling (cold water is more "squeezeable" than warm water), (iii) Formation of Hydrogen bond networks (see image). The hydrogen bond network is believed to be responsible for the anamolous behaviour of water. In order to explain the strange behavior of water, researchers have started to look in the supercooled (liquid below the freezing point) and stretched (negative pressure) regions for answers. It appears that many of the anomalous properties can be explained by the behavior at supercooled temperatures, including the possiblity of a second low temperature critical point. At temperatures below this possible critical point, there exist TWO liquid phases, one high-density and one low-density (strong bond network). This is analogous to cooling steam below the high temperature critical point where a high density fluid (liquid water) and a low density fluid (water vapor) condense out. For more information, see Simulation of Water.

• Econophysics. Econophysics is an interdisciplinary research field, applying theories and methods originally developed by physicists in order to solve problems in economics, usually those including uncertainty or stochastic processes and nonlinear dynamics. One driving force behind econophysics arising at this time was the availability of huge amounts of financial data, starting in the 1980s. It became apparent that traditional methods of analysis were insufficient—standard economic methods dealt with homogeneous agents and equilibrium, while many of the more interesting phenomena in financial markets fundamentally depended on heterogeneous agents and far-from-equilibrium situations. The term was coined by H. Eugene Stanley and Rosario Mantegna in the mid 1990s, to describe the large number of papers written by physicists in the problems of (stock and other) markets, and first appeared in a conference on statistical physics in Calcutta in 1995 and its following publications. The inaugural meeting on Econophysics was organised 1998 in Budapest. Currently, the almost regular meeting series on the topic include: Econophysics Colloquium, ESHIA/ WEHIA, ECONOPHYS-KOLKATA, APFA. For more information see: Introduction to Econophysics by Mantegna and Stanley (Cambridge University Press, 1999).

• Physiologic Dynamics. We study a broad range of topics at the interface of statistical physics and medicine. Topics include the exploration of fractal characteristics of cardiac dynamics, fluid flow through respiratory systems and branching patterns, circadian rhythm in human gait activity, complexity in scale-invariant neural signals. One of our main contributions is to the NIH sponsored PhysioNet which offers collections of recorded physiologic signals and open-source software to the science research community.

• Statistical Mechanics in Neuroscience. Alzheimer's disease is a progressive neurodegenerative disorder of the central nervous system. The exact causes of the disease are unknown. The symptoms are familiar: loss of memory and other cognitive functions and eventually loss of control of bodily functions. The most obvious change in the brain of Alzheimer's disease patients is the loss of neurons. In addition, Alzheimer's victims have formations of senile plaques and neurofibrilary tangles, neither of which is present in normal brains. In a collaborative research between physicists from the Center for Polymer Studies at Boston University and neurologists from the Massachusetts General Hospital, researchers are studying immunostained pictures of senile plaques, neuronal bodies, dendrites and tangles, taken by confocal microscope. The pictures are then analyzed using methods of statistical physics. The overall purpose of the research is to find out the mechanisms of the growth of senile plaques, to understand how the neuronal architecture is altered in the disease, and to quantify changes in the geometry of dendrites as compared to the dendrites in the cortex of healthy brains. New experimental advances applied to the understanding of the molecular origin of Alzheimer's disease have pointed to important clues that implicate small molecular assemblies of the protein Ab in neuronal impairment and later death. Using tools derived from computational physics, researchers from the Center for Polymer Studies are studying the initial stages of Ab aggregation that may lead to the formation of the toxic oligomers. The endpoint of their research is to investigate the oligomer topology and 3D composition in order to aid in drug development to target oligomer formation. See also the Density Correlation Analysis of the Brain Cortex Architecture Java applet along with a downloadable Java application and associated examples as well as Alzheimer's Disease Research Notes.

Image Notes: The first image shows fracturing in a disordered network. The second image is a close-up of a computer model of liquid water. water.