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This page lists the abstracts for the talks part of the ECCS08 conference and the public events
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Robert J. Aumann Hebrew University |
Rule Rationality vs. Act Rationality abstract |
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Jasmina Arifovic Simon Fraser University |
title abstract |
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Andrea Cavagna CNR - Rome |
Starling Flocks : An empirical study of the interaction ruling collective animal behavior Numerical models indicate that collective animal behaviour may emerge from simple local rules of interaction among the individuals. However, very little is known about the nature of such interaction, so that models and theories mostly rely on aprioristic assumptions. By reconstructing the three-dimensional position of individual birds in airborne flocks of few thousands members, we prove that the interaction does not depend on the metric distance, as most current models and theories assume, but rather on the topological distance. In fact, we discover that each bird interacts on average with a fixed number of neighbours (six-seven), rather than with all neighbours within a fixed metric distance. We argue that a topological interaction, based on the number of birds, rather than their distance, is indispensable to maintain flock's cohesion against the strong perturbations caused by predation. |
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Anna Carbone Politecnico of Torino |
Detrending Moving Average Algorithm (DMA) We discuss properties and applications of a recently proposed method, the Detrending Moving Average (DMA), to investigate long-range correlated signals at varying scales. The extension of the DMA algorithm to higher dimensional fractals will be also presented. The DMA algorithm extracts information and statistical properties from long-range correlated signals related to general aspects of complex systems. In this talk, we will in particular address the problem to quantify some well-known "stylized facts" observed in financial series as the leverage effect, the volatility clustering and asymmetry by showing results obtained from 4 years of tick-by-tick data of the European Market (DAX, EuroStoxx, FIB30). [1] E. Alessio, A. Carbone, G. Castelli, V.Frappietro Eur. J. Phys. B (2002) |
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Gregory John Chaitin IBM Watson Research Center |
A Century of Controversy over the Foundations of Mathematics I'll tell the dramatic story of the recent disputes over the foundations of mathematics. I'll start with the problems in Cantor's theory of infinite sets and then discuss the work of Bertrand Russell, David Hilbert, Kurt Godel and Alan Turing, and finally my own work using complexity. This complexity-based analysis of the foundations of mathematics suggests to me that perhaps mathematics is more similar to physics and to biology than is commonly believed, and should sometimes be carried out quasi-empirically, that is, more in the spirit of an experimental science. |
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Jennifer Dunne Santa Fe Institute |
The Architecture of Ecological Interactions: Patterns and Principles Descriptions of complex feeding relationships among species in ecosystems first appeared more than a century ago, and the quantitative analysis of the network structure of “food webs” dates back several decades. Improvements in food-web data collection, analysis, and modeling, coupled with a resurgence of interdisciplinary research on the topology of many kinds of “real-world” networks, have resulted in renewed interest in ecological network structure. Recent research suggests that food webs display universal scale-dependent patterns in how trophic links and roles are distributed among species in ecological communities. The fundamental ways in which feeding interactions are organized appears to have become established very early in the history of multicellular life on earth. Understanding the principles that underlie robust food-web patterns represents an important frontier of ecological research. |
| John-Dylan Haynes Bernstein Center for Computational Neuroscience Berlin |
Decoding mental states from human brain activity Is it possible to predict what a person is thinking of - or even what they are planning to do - based alone on their current brain activity? Recent advances have made it possible to decode and predict a person's thoughts from functional magnetic resonance imaging (fMRI) data. The key is that each thought is associated with a unique brain activation pattern that can be used as a signature or for that specific thought. It is possible to train pattern classifiers to recognize these characteristic signatures and thus read out a person's thoughts from their brain activity alone. This research can reveal how neural representations of mental contents are stored and transformed in the brain. It also gives rise to many potential applications, as for example in the control of computers and artificial prostheses by brain activity or in the detection of concealed mental states. |
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Mogens Høgh Jensen Niels Bohr Institute - Denmark |
Modelling Ultradian Oscillations and Segmentation: The p53, NF-kB and Wnt-Notch Systems Abstract |
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François Képès CNRS |
Epigenomics and Morphodynamics The substrate for heredity, DNA, is chemically rather inert. However, it bears one of the elements of information that specify the form of the organism. How can a form be specified, starting from DNA ? Recent observations indicate that the dynamics of transcription — the process that decodes the hereditary information — can imprint forms of a certain topological class onto DNA. This topology allows both to optimize transcription and to facilitate the concerted change of the transcriptional status in response to environmental modifications. To the best of our knowledge, this morphogenetic event is first on the path from DNA to organism. |
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David Lane University of Modena and Reggio Emilia |
Artifacts and Organization: A Complexity Perspective on Innovation and Social Change Human sociocultural life is impossible to conceive without two fundamental ingredients: artifacts and organizations. Just about everything we do involves interactions with artifacts, from the clothes we wear and the buildings we inhabit, to the devices through which we communicate with one another and the tools and technologies we use to make ever more artifacts. And almost all of our interactions depend for their setting, purpose and rules on organizations, whether they be churches, businesses, government agencies, political parties, law courts, police forces, armies, social clubs – or even friendship networks on internet. We human beings didn’t invent either artifacts or organizations: biological evolution did. Both fashioning artifacts and deploying collective action are evolutionary strategies that have been around a long time. But even if we didn’t invent them, nothing in biology remotely compares with the use that we human beings have made of these two strategies. The number and complexity of the artifacts we have developed over the millennia, and in particular over the past few centuries, and the variety of activities we have organized around these artifacts, has no counterpart in the pre-human world. If three million years ago, our ancestors had essentially one kind of artifact, and fifty thousand years ago, maybe several hundred, today’s inhabitant of New York City can choose among 1010 different bar-coded items, not to mention a host of other material, informational or performative artifacts currently produced by human beings for the use of human beings! Even more unprecedented are the diversity of forms and the scale of the organizations we have created, through which we collectively carry out political, economic, social and cultural functions that seem far removed from the overriding biological functional imperatives of survival and reproduction. Over the past several years, my colleagues and I have been working out a complexity-based theory of innovation that is intended to explain how human beings have managed to generate the explosion of artifacts and the new functionalities they make possible. The theory starts from the premise that all artifacts have a history, as do the modes of interaction among people in which artifacts figure. The aim of the theory is to describe and analyze the processes through which artifact histories are realized: The main conclusion of the talk is that our species has developed a new modality of innovation, in which artifacts and organization are inextricably linked: human beings generate new artifacts that they embed in new collective activities, which are in turn supported by new organizations and sustained by new values. Over time, this new innovation modality gave rise to a positive feedback dynamic, which we call exaptive bootstrapping. Exaptive bootstrapping explains how we have generated so many transformations in our selves, our societies, our culture and our environment. |
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Ramit Mehr Bar Ilan University |
The Immune System - A Theoretician's View The immune response involves cells of various types, including B, T and Natural Killer (NK) lymphocytes expressing a large diversity of receptors which recognize foreign antigens and self-molecules. The various cell types interact through a complicated network of communication, regulation and control mechanisms. This is what enables the immune system to perform the functions of danger recognition, decision, action, memory and learning. As a result, the dynamics of immune cell repertoires, in particular their development, are highly complex and non-linear. Understanding the dynamics of lymphocyte populations, immuno-receptor repertoire development and evolution, is essential for elucidating the causes of various immune dysfunctions and cancers. We have addressed this issue by combining mathematical modeling of cell population dynamics with experimental data, including BrdU labeling. These studies revealed unexpected feedback mechanisms in T cell development (Reviewed in Immunol. Today 1997, 18:581-585), phenotypic reflux in B cell development (Mehr et al, Int’l Immunol. 2003, 15:301-312; Gorfine et al, Bull. Math. Biol. 2003, 65:1131-1139), selection checkpoints in transitional B cells (Shahaf et al, Int’l Immunol. 2004, 16:1081-1090) and the reasons for age-related decreased production of T cells (Mehr et al, Mech. Age. Develop., 1993, 67:159-172; AGING: Immunology and Infectious Disease, 1996, 6:133-140) and B cells (Shahaf et al, Int’l Immunol. 2006, 18:31-39). Furthermore, we have studied the development of B and T lymphocyte repertoires (Mehr et al., J. Immunol., 1999, 163:1793-1798 and 1799-1808; Kalmanovich & Mehr, 2003, J. Immunol., 170:182-193), Natural Killer cell repertoire education (Reviewed in Salmon-Divon et al., Mol. Immunol. 2004, 42:397-403), and the within-host evolution of immunoglobulin genes during an immune response (e.g., Shannon and Mehr, J. Immunol., 1999, 162:3950-3956; Yaish & Mehr, Bull. Math. Biol., 67:15-32). We combined modeling with novel immuno-informatical methods such as quantification of lineage trees from B cell clones undergoing somatic hypermutation (e.g., Dunn-Walters et al., Dev. Immunol. 2002, 9:233-245 and BioSystems 2004, 76:141-155; Mehr et al., J. Immunol. 2004, 172:4790-4796; Horesh et al., J. Comp. Biol. 2006, 13:1165-1176), and applied these new analyses to the study of humoral response changes in aging (Banerjee et al., Eur. J. Immunol. 2002, 32:1947-1957), autoimmune diseases (Steiman-Shimony et al., Autoimmun. Rev. 2006, 5:242-251) and B cell malignancies (Manske et al., Clin Immunol. 2006, 120(1):106-120 ; Abraham et al., J. Clin. Immunol., in press). My talk will include a very brief introduction to the immune system and its complexity, and then focus on two samples of computational immunology research – simulating the immunological synapse, and analyzing immunoglobulin gene mutational lineage trees. |
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Jean-Pierre Nadal Laboratoire de Physique Statistique de l'École Normale Supérieure |
Pricing of Goods with Bandwagon Properties: Entanglement between Demand and Supply There is a growing economic literature that recognizes the influence of social interactions on consumers. In market situations like the subscription to a telephone network or the choice of a computer operating system, the willingness to pay generally depends not only on the individual preferences but also on the choice made by others. When the utility of a good has a part which increases proportionally to the number of buyers, there may exist multiple equilibria for some range of prices. The Pareto-optimal equilibrium corresponds to the high demand solution, but this equilibrium may be not achieved due to a lack of coordination. In contrast, the analysis of the supply has deserved much less attention. The discussion of price dynamics with positive externalities by Granovetter and Soong (1986) remains qualitative and does not contemplate the possibility of multiple supply strategies. A particular insightful paper is the 1991 Becker's note attributing to social interactions the fact that restaurants do not increase their prices despite a persistent excess demand. In this paper we go one step further, and analyze the profit optimization program of the monopoly for goods with bandwagon effects in its generality. Our introduction of an explicit mathematical model of demand and supply allows us to uncover market characteristics that are specific consequences of the social interactions. Surprisingly, we find that there is a range of parameters where the profit presents two relative maxima (corresponding to different prices) in a region where the demand is a standard monotonic function of the price. Moreover, when the demand is multivalued, not only there exist two possible prices (an optimal and a suboptimal one) as pointed out by Becker, but under certain conditions it may be more profitable to charge high prices and meet the lowest demand. We show that there is a very large range of parameters where increasing the supply to meet the large demand equilibrium, although optimal, may not give the expected payoff unless the customers coordinate themselves. The model suggests possible strategies that might be worth to implement in that case. Mirta B. Gordon, Jean-Pierre Nadal, Denis Phan and Viktoriya Semeshenko Mirta B. Gordon, Jean-Pierre Nadal, Denis Phan and Viktoriya Semeshenko, |
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Andrzej Nowak University of Warsaw |
Dynamics of Information and Evaluation on Social Networks The lecture will concern dynamics of two different processes occurring in social networks: the flow of information and the process of evaluation. Similarities and differences in how networks structure shapes the spread of information and governs social influence in the process of evaluation will be discussed. Research in social psychology suggests that information is not only acquired but also evaluated and interpreted in the process of interaction, as individuals construct common social representation. Both simulation and empirical data show that transmission of information and evaluations operate in a very different ways. Empirical data concerning the structure of selected social networks and dynamics of information on the networks will be presented. |
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Nathalie Questembert-Balaban Hebrew University |
Non-Genetic Individuality in a Predator-Prey system Isogenic bacteria can exhibit a range of phenotypes, even in homogeneous environmental conditions. Such non-genetic individuality has been observed in a wide range of biological processes, including differentiation and stress response(1). A striking example is the heterogeneous response of bacteria to antibiotics, whereby a small fraction of drug-sensitive bacteria can persist under extensive antibiotic treatments. Recently, a renewed interest in the persistence phenomenon has revealed that non-genetic heterogeneity might be one of the main reasons for the failure of antibiotic treatment in infections such as tuberculosis, where a single persistent bacterium can re-start an infection(2). Persistence is typically observed through the monitoring of the survival fraction of a bacterial population exposed to antibiotics. The initially rapid killing of the bacteria is followed by a significantly reduced killing rate which indicates the presence of a persistent sub-population. When cells grown from this persistent sub-population are subjected again to antibiotics, the same bi-phasic killing curve is obtained, suggesting that the persistent sub-population is not genetically different from the original population. We have previously shown that persistent bacteria enter a phenotypic state, identified by slow growth or dormancy, which protects them from the lethal action of antibiotics(3). Here we studied the effect of persistence on the interaction between Escherichia coli and phage lambda. We focused on two different variations of this well-studied predator-prey system: (a) a phage that is present in the genome of each bacterium and can cause bacterial death by a process called "prophage induction" and (b) a lytic phage that attacks bacteria from the outside, infects them and them kills them. The effect of the persistent phenotype was studied in those systems and the experimental results obtained were then implemented in a mathematical description of these interactions(4). We used long-term time-lapse microscopy to follow the expression of GFP under the phage lytic promoter, as well as cellular fate, in single infected bacteria. We found that dormancy that protects bacteria under antibiotic treatments also protects them against prophage induction. A competition experiment run between a low persistence population and a high persistence one demonstrated a clear advantage to the latter. This suggests that persistence might have evolved under the evolutionary pressure of prophage stress. Intriguingly, we found that, while persistent bacteria are protected from prophage induction, they are not protected from lytic infection. Quantitative analysis of gene expression revealed that the expression of lytic genes is suppressed in persistent bacteria. However, when persistent bacteria switch to normal growth, the infecting phage resumes the process of gene expression, ultimately causing cell lysis. Despite its mild effect on the short-term survival of the population, the delayed cell lysis of persistent bacteria needs to be taken in account. Using a mathematical model for this predator-prey interaction, we found that the bacteria's non-genetic individuality can significantly affect the population dynamics, and might be relevant for understanding the co-evolution of bacterial hosts and phages. References |
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Nir Shaviv Hebrew University, Jerusalem |
Predicting Climate Change? I will review the different components of the climate system and try to demonstrate why its behavior is very hard to predict. I will then continue discussing the relative roles of anthropogenic and solar climate driving, and its implications to future climate change (which is not as bleak as most often promoted!) |
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Haim Taitelbaum Bar Ilan University |
Complex Patterns in Reactive-Wetting Interface Dynamics Reactive-wetting interface dynamics exhibits complex spatio-temporal patterns during the kinetic roughening process of the triple line. This could seemingly be described by scaling (growth and roughness) exponents. However, we show that the non-linear interface dynamics is much more complex. Using extreme value statistics, in particular the persistence measure, we demonstrate the difficulties to associate a given universality class to this complex system. Our reactive-wetting system, which is the only known system in room temperature, consists of small mercury droplets (150m in diameter) spreading on thin silver films (2000 – 4000 A). The process is monitored using an optical microscope. In this talk we discuss the growth and roughness exponents of the propagating interface, the temporal interface width fluctuations during a single growth process, and the lateral correlation length along the triple line – all as a function of the silver substrate roughness and the temperature of the system. We then introduce the persistence measure in order to demonstrate the complexity of the system, and suggest several numerical models to obtain better insights regarding the microscopic physical mechanisms that play a role in the process. |
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Naftali Tishby Hebrew University, Jerusalem |
Information theory, predictive information, and the perception-action-cycle Arguably, living organisms can be characterized by their abilities to exchange information with their environment through sensing and acting. When the environment is (asymptotically mean) stationary, the equilibrium interaction of an organism with its environment is determined by the information it can efficiently extract and store from the past of the environment, that is valuable to the organism in the future, on multiple time scales. It's optimal achievable information theoretic performance is thus limited by the “predictive-information” of the environment, which is a function that characterizes its intrinsic complexity. This is somewhat analogous to the roles of the rate-distortion and the cost-capacity functions in Shannon's theory of communication. In that sense, life can be characterized by its ability to utilize the predictability of its environment and modify it in order to increase its predictive capacity. This suggests a new conceptual and quantitative framework that enables design and analysis of biological and cognitive experiments in a new way. I will discuss some recent applications of this framework to auditory and motor physiology. |
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Misha Tsodyks Weizmann Institute of Science |
Information processing in cortical neural networks with dynamic synaptic connections Synaptic transmission in the cortex is characterized by the activity-dependent short-term plasticity (STP), which can be broadly classified as synaptic depression and synaptic facilitation. As recent experiments indicate, different cortical areas exhibit variable mixes of facilitation and depression, which are also specific for connections between different types of neurons. In the first half of my presentation, I will describe the basics of dynamic synaptic transmission, its biophysical underpinnings and the ways it can be captured in biophysically motivated phenomenological models. I will also discuss some immediate implications of STP on information transmission between ensembles of neocortical neurons. In the second half of the presentation, I will focus on the effects of STP on the dynamics of recurrent networks and resulting neural computation. I will introduce the 'population spikes' (PSs), which are brief epochs of highly ynchronized activity that emerge in recurrent networks with dominating synaptic depression between excitatory neurons. PSs can underlie some of the response properties of neurons in the auditory cortex. I will then describe the recently introduced idea that synaptic facilitation could be utilized in order to maintain information about the incoming stimuli in the facilitation level of recurrent connections between the targeted neurons, thus providing an effective mechanism for short-term memory for a period of several seconds after the termination of the stimulus. |
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Leanne J. Ussher Queens College, City University of New York |
Marked to Market Leverage with Zero-Intelligent Agents In liquid markets real-time mark-to-market portfolio valuations may not be expected to impact prices. However during illiquid periods with leveraged trading such settlement can have a significant impact on price volatility and trading-choices. While the assumption of efficient markets confers speculative traders with stabilizing attributes, liquidity or settlement trades can have destabilizing properties in the short run: traders buy when prices rise, and sell when prices fall, to meet collateral requirements. If there are a lot of traders in the market, this situation can become cumulative, producing positive autocorrelation in returns and volatility clustering. Such price dynamics, and a corresponding drying up of market liquidity, can occur even when traders are zero-intelligent, that is, their price expectations or risk aversion does not change in response to price changes. |
| Amotz Zahavi Tel Aviv University |
The use of the Handicap Principle to understand the messages encoded in hormones. The Handicap Principle is now accepted as the mechanism that elects for reliability in the evolution of signals. In the present talk I shall explain why it applies also to the evolution of hormones and suggest how the principle may be used to interpret the message encoded in some hormones. Hormones serve their function because they bring to the receiver real and reliable information about the happenings (the chemical environment) in the signaling cell. The receiving cells react to the information according to their phenotypic destiny. According to the Handicap Principle information by chemical signals is reliable when the signaling cell is able to produce the signal while other cell phenotypes are not able to produce it equally well. The selection for reliability creates a logical relationship between the chemical properties of the hormone and the message encoded in it. This talk will suggest an interdisciplinary approach as the way to decipher the qualitative information encoded in hormones, using, evolutionary principles, anatomy, physiology, chemistry, and the mechanism of the handicap principle. Understanding the chemical properties of signals within the biological environment in which hey are produced may explain why a particular molecule has been selected to convey a particular message. |
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