Amer Shreim

I am a former PhD Candidate at the Complexity Science Group at the University of Calgary. I was the first student to join the group in Calgary in September 2005 and the first PhD student to graduate from the group in December 2009. I worked on different projects in complex systems with Prof. Maya Paczuski, Prof. Peter Grassberger, and Prof. Jörn Davidsen.  

I have since moved to the world of finance and I am enjoying working in risk management in Toronto.

Statistical Physics, Dynamical Systems, Complex Networks, Mathematical finance, Econophysics, and Biological Evolution.

• Characterizing of the topology of the state space network of discrete dynamical systems (please refer to publications for more information).
• Niche formation and adaptive radiation in microbial colonies. This project is in collaboration with Jacob Foster and Mike Surette.
• Statistical properties of financial markets. This project is in collaboration with Doyne Farmer at SFI.
• Finding martingale like properties in physical systems. This project is in collaboration with Elliot Martin.

arxiv link: http://arxiv.org/a/shreim_a_1

1. cond-mat/0610447 [abs, ps, pdf, other] 
Title: Network Analysis of the State Space of Discrete Dynamical Systems
Journal-ref: Phys. Rev. Lett. 98, 198701 (2007) Authors: Amer Shreim, Peter Grassberger, Walter Nadler, Bjrn Samuelsson, Joshua E.S. Socolar, Maya Paczuski
In this paper we study the dynamics of discrete systems in their state space and explore the relationship between the network topology of the state space and the complexity of dynamics e.g. as classified by Wolfram. The state space of a discrete dynamical system is a directed network where dynamical states are represented as nodes, the nodes are then connected by drawing links (directed) between each node to its image under the dynamical rule. We start our exploration by studying one dimensional cellular automata and found some new and surprising results for the networks of their state spaces. to characterize the networks we looked two measures: (1) the degree of a node (state) which a local measure and (2) a global measure of the heterogeneity of the paths to the attractors -- what we call the "path diversity." For complex dynamics, both exhibit scaling behavior with respect to the system size whereas for simple dynamics one or the other (or both) does not scale. It turns out that a certaincritical exponent (the scaling of the maximal hub with network size) can be calculated exactly for each model, even though it is generally irrational. We are now investigating a number of different extensions of this network analysis to more general dynamical systems (e.g. non-deterministic, disordered, ...).

 

2. arXiv:0710.0611 [ps, pdf, other]
Title: Complex Network Analysis of State Spaces for Random Boolean Networks
Journal-ref: New J. Phys. 10 (2008) 013028 (Selected for NJP Best of 2008)
Authors: Amer Shreim, Andrew Berdahl, Vishal Sood, Peter Grassberger, Maya Paczuski In this paper we apply complex network analysis to the State Space Network of Random Boolean Networks (RBNs). There are two kinds of network in this study so some confusion might arise because of that. This paper is a somehow a continuation of the Cellular Automata paper, where we use very similar network analysis techniques to study this time RBNs. RBNs were studied first by Kauffman in 1969 as simple models of gene regulation. This system has been studied extensively by physicists since then, it was show that there is a phase transition between an ordered phase and chaotic phase depending on the connectivity, K, of the RBNs, with the transition occurring at K=2. In the paper we show that SSN of RBNs with K=2, also referred to as critical, exhibit large fluctuation on three separate levels: 1) local level, measured by the node in-degree, 2) global level, measured by the path diversity, and 3) sample-to-sample level. Therefore, suggesting that the state space network of discrete dynamical systems that exhibit non-trivial dynamics, is itself non-trivial and complex in the sense used in the networks community. We have also shown a number of interesting analytical results pertaining to the SSNs of RBNs with K=1.

3. arXiv:0805.0326 [ps, pdf, other]
Title: Avalanches, branching ratios, and clustering of attractors in Random Boolean Networks and in the segment polarity network of \emph{Drosophila}
Journal-ref: New J. Phys. 10 (2008) 063002
Authors: Andrew Berdahl, Amer Shreim, Vishal Sood, Joern Davidsen, Maya Paczuski

4. arXiv:0904.3948 [ps, pdf, other] Title: Random sampling vs. exact enumeration of attractors in random Boolean networks Journal-ref: New J. Phys. 11 (2009) 043024 Authors: Andrew Berdahl, Amer Shreim, Vishal Sood, Maya Paczuski, Joern Davidsen 5. arXiv:0910.2447 [ps, pdf, other] 
Journal-ref: Physical Review E 81, 016109 (2010)
Title: Activity Dependent Branching Ratios in Stocks, Solar X-ray Flux, and the Bak-Tang-Wiesenfeld Sandpile Model 
Authors: Elliot Martin, Amer Shreim, Maya Paczuski.    6. arXiv:1003.2120 [pdf, ps, other] Journal-ref: Physical Review E 82, 035102 (2010)
Title: Attractor and Basin Entropies of Random Boolean Networks Under Asynchronous Stochastic Update
Authors: Amer Shreim, Andrew Berdahl, Florian Greil, Jörn Davidsen, Maya Paczuski

7. arXiv:1003.5797 [pdf, other]
Journal-ref: Physical Review Letters 105, 178701 (2010)
Title: The Interacting Branching Process as a Simple Model of Innovation
Authors: Vishal Sood, Myléne Mathieu, Amer Shreim, Peter Grassberger, Maya Paczuski

8. arXiv:1103.2551 [pdf, ps, other]
Journal-ref: Physical Review E 81, 066106 (2010)
Title: Self-organization in two-dimensional swarms
Authors: Jihad Touma, Amer Shreim, Leonid Klushin

PhD Student, Physics, Sept 2005 - Dec 2009
University of Calgary, Calgary, Canada

Master of Science, Physics, 2001-2004
American University of Beirut, Beirut, Lebanon 
Thesis: Self-Organization in 2D Swarms

BSc. with Distinction, Major: Physics - Minor: Mathematics, 1998 -2001 
American University of Beirut, Beirut, Lebanon

           2009   Vision 2010 Postdoctoral Fellowship, University of Ottawa, Canada (declined)
           2009   Dean's Doctoral Scholarship, University of Calgary, Canada
2006 - 2009   Graduate Research Scholarship, University of Calgary, Canada
           2001   B.Sc. with Distinction, American University of Beirut, Lebanon
1999 - 2001   Dean’s Honor List, American University of Beirut, Lebanon