Seminars

DateLecturerTitleLocation
2017-10-27
14:00 - 15:30
L.J. Uberti
(University of Oslo)
The Corruption U-Curve
Abstract
We replicate Saha and Gounder (Econ Model 31: 70-79, 2013), who show that the relationship between corruption and economic development exhibits an inverted U-shaped pattern. Pooled OLS estimates, however, should not be interpreted as conclusive evidence in support of a causal relationship. Using a much longer panel of 156 countries during 1900-2010, we show that a U shape shows up even after controlling for country-level heterogeneity, suggesting that the estimated relationship does not result from a version of the classic “Kuznets fallacy”. The curvilinear relationship is also robust to controlling for potential simultaneity using an instrumental variable approach. Still, the parabola implied by a fixed-effects model is considerably less “peaked” than the one implied by the corresponding OLS model.
CSHV, 8., Josefstädter Str. 39, room 201
2017-10-13
14:00 - 15:30
J. Korbel
(Medical University of Vienna)
Information flows between communities in complex fi nancial networks
Abstract
With the help of transfer entropy, we analyze information flows between communities of complex financial networks. We show that the transfer entropy provides a coherent description of interactions between communities, including non-linear interactions. We analyze transfer entropies between communities of five largest financial markets, represented as networks of interacting stocks. Additionally, we discuss information transfer of rare events, which can be analyzed by Rényi transfer entropy.
CSHV, 8., Josefstädter Str. 39, room 201
2017-10-06
14:00 - 15:30
K. Kaski
(Aalto University School of Science, Finland; Wolfson College, Oxford University, UK; Complexity Science Hub Vienna, Austria)
Circadian rhythms of urban people – are we like fruit flies?
Abstract
All living organisms, including humans, have internal biological or circadian clock that helps them anticipate and adapt to the regular rhythm of the day. The timings of human activities are marked by circadian clocks which in turn are entrained to different environmental signals. In an urban environment, the presence of artificial lighting and various social cues tend to disrupt the natural entrainment with the sunlight. However, it is not completely understood to what extent this is the case. Here we exploit the large-scale data analysis techniques to study the mobile phone calling activity of people in large cities to infer the dynamics of urban daily rhythms. From the calling patterns of about 1,000,000 users spread over different cities but lying inside the same time-zone, we show that the onset and termination of the calling activity synchronizes with the east-west progression of the sun. We also find that the onset and termination of the calling activity of users follows yearly dynamics, varying across seasons, and that its timings are entrained to solar midnight. Furthermore, we show that the average mid-sleep time of people living in urban areas depends on the age and gender of each cohort, most likely as a result of biological and social factors.
CSHV, 8., Josefstädter Str. 39, room 201
2017-06-30
14:15 - 15:45
A. Hinteregger
(University of Vienna)
Systemic risk in the Austrian economy
Abstract
Systemic risk is the notion that a shock may not only render directly affected components but (possibly large) parts of the network non-functioning due to cascading effects. In a financial network this systemic risk stems from the exposures of lending institutes to one another. Network measures such as DebtRank were used to estimate the possible impact on the interbank network resulting from a market shock. In this work, I extend the analysis of systemic risk from financial institutes to the whole economy. and find that the DebtRank distribution of companies is qualitatively similar to the distribution of financial institutes. Companies may have exposures to a disadvantageous set of banks, thus enabling the propagation of an impact through large parts of the network. Even though larger companies tend to have a higher DebtRank, there are companies sharing a very similar DebtRank with total assets that span multiple orders of magnitude. The results suggest that from a systemic risk perspective companies and banks have some similarities. It may therefore be beneficial to extend regulations that try to alleviate systemic collapses to the whole economy.
CSHV, 8., Josefstädter Str. 39, room 101
2017-06-23
14:15 - 15:45
S. Poledna
(International Institute for Applied Systems Analysis - IIASA)
Economic forecasting with an agent-based model
Abstract
We develop an agent-based model (ABM) for the Austrian economy using data from national accounts, input-output tables, government statistics, census data and business surveys. The model incorporates all economic activities (producing and distributive transactions) as classified by the European system of accounts (ESA) and all economic entities, i.e. all juridical and natural persons, are represented by agents (at a scale of 1:10). We show that this model is able to compete with vector autoregressive (VAR) and autoregressive–moving-average (ARMA) models in out-of-sample prediction. Potential applications of this ABM include economic forecasting, as well as the prediction of responses of the economy to endogenous shocks, e.g. from the financial system, or exogenous shocks like natural disasters, transformative technological innovations or unintended consequences of political interventions such as subsidies and tax policies.
CSHV, 8., Josefstädter Str. 39, room 101
2017-06-16
14:15 - 15:45
A. Pichler
(Vienna University of Economics and Business)
Minimization Systemic Risk as an Optimal Network Reorganization Problem - The Case of Overlapping Portfolio Networks in the European Government Bond Market
Abstract
Systemic risk arises as a multi-layer network phenomenon, where layers represent direct financial exposures of various types, including interbank liabilities, derivative- or foreign exchange exposures. Another network layer of systemic risk emerges through common asset holdings of financial institutions. Strongly overlapping portfolios lead to similar exposures caused by price movements of financial assets. We use a simple method to quantify systemic risk of overlapping portfolio networks from endogenous asset sales within the network. We then present a general optimization procedure where we minimize the systemic risk in a given financial market by optimally re-ordering overlapping portfolio networks, under the constraint that the expected returns and risks of the individual portfolios is unchanged. We explicitly demonstrate the method on the overlapping portfolio network of sovereign exposure between major European banks by using data from the European Banking Authority stress test 2016. We show that multiple systemic-risk-efficient allocations do exist, which are actually accessible by the optimization and that do not alter the returns and risks of the institutions’ portfolios. In the case of sovereign exposure, systemic risk can be reduced by more than 56%, without any detrimental effects. We confirm these results by a simple simulation of fire-sales in the government bond market.
CSHV, 8., Josefstädter Str. 39, room 101
2017-06-09
14:15 - 15:45
L. Horstmeyer
(Medical University of Vienna)
The Gillespie Algorithm
Abstract
How can one numerically simulate large stochastic networks? Perhaps one would go through each node in the network and update its state with a probability dictated by the de nition of the model. This may not always be very ecient and can also lead to biases. The Gillespie algorithm provides a great alternative. I will present its merits and its implementation. The talk will close with the illustration of the Gillespie algorithm for an adaptive stochastic network dynamics, namely the SIS model with rewiring.
CSHV, 8., Josefstädter Str. 39, room 101
2017-05-26
14:15 - 15:45
C. Tsallis
(Centro Brasileiro de Pesquisas Físicas)
Nonadditive entropy: small price to satisfy thermodynamics -- Theory and experiments
Abstract
The Galilean composition law of velocities within Newtonian mechanics is additive. But, in order to unify mechanics with Maxwell electromagne+sm, Einstein adopted the Lorentz space-time transformation as the primary mathematical-physical goal to be satisfied. It resulted the well known, nonadditive, relativistic composition law of velocities. This surely is a small price to pay in order to unify mechanics and electromagnetism, and explain very many experimental facts. Analogously, there is a plethora of analytical, experimental, observational and computational evidences (see Bibliography in h]p://tsallis.cat.cbpf.br/biblio.htm) which reveals various kinds of violations of Boltzmann-Gibbs statistical mechanics, including thermodynamics. The adoption of nonadditive entropic functionals which generalize the traditional, additive, Boltzmann-Gibbs entropy enables to satisfy classical thermodynamics: as before, a small price to pay!
CSHV, 8., Josefstädter Str. 39, Salon
2017-05-19
14:15 - 15:45
E. Valdano
(Universitat Rovira i Virgili)
The spread of diseases on time-evolving networks: from models to data and back
Abstract
A wide range of physical, social and biological phenomena can be expressed in terms of spreading processes on networked systems. Notable examples include the spread of infectious diseases through direct contacts, the spatial propagation of epidemics driven by mobility networks, the spread of cyber worms along computer connections, or the diffusion of ideas mediated by social interactions. All these phenomena arise from a complex interplay between the spreading process and the network’s underlying topology and dynamics. Understanding how the time-evolving properties of the network impact the spread of the disease is a crucial step to setting up control and prevention strategies. The increasing availability of highly-resolved interaction data has made it possible to target a wide variety of settings and diseases, but at the same time new methodological challenges have arisen. In particular, a fundamental property of such phenomena is the presence of an epidemic threshold, i.e., a critical transmission probability above which large-scale propagation occurs, as opposed to quick extinction of the epidemic-like process. Computing this threshold is of utmost importance for epidemic containment and control of information diffusion. I will present a new analytical framework for the computation of the epidemic threshold for an arbitrary time-varying network. By reinterpreting the tensor formalism of multi-layer networks, this framework allows the analytical calculation of the epidemic threshold, without making any assumption on contact structure and evolution, and can be applied to a wide class of diseases. Along these theoretical developments, challenges related to the analysis and elaboration of the increased amount of data have emerged. I will present the case of diseases affecting farmed cattle. Such diseases compromise both human and animal health and welfare, and represent a major cause of loss in economic revenue. As a result, studying the networks of animal movements is a key step in devising new prevention and containment strategies. Past works have already analyzed cattle networks in several European countries. A comprehensive study, showing the impact of country-specific driving factors on network evolution and topology, is however still missing. I will present a collaborative platform for analyzing and comparing networks from several European countries. Using a bring code to the data approach, our platform overcomes the strict regulations preventing data sharing, and allows an effective comparative analysis. I will describe the framework, and present the result of this analysis, highlighting both properties that are characteristic of livestock markets, and country-specific features.
CSHV, 8., Josefstädter Str. 39, room 101
2017-05-12
14:00 - 15:30
T. Biro
(WIGNER Research Centre for Physics)
Unidirectional and Resetting Stochastic Dynamics
Abstract
A particular class of linear master equation dynamics with unidirectional internal evolution rates and a long-jump resetting to the zero-state will be discussed. This model class is able to describe several distributions observed in complex systems, derived from the particular state dependence of the transition rates. We select out the exponential (geometrical) and the Waring distribution, along with their large system - continuous model counterparts, the Boltzmann-Gibbs and the Pareto distribution, as examples, respectively. A list of suitable properties for defining an entropic distance measure will also be presented.
CSHV, 8., Josefstädter Str. 39, room 101
2017-05-05
14:15 - 15:45
L. Zavojanni
(Medical University of Vienna)
Dynamical Stationarity in Processes with Sustained Random Growth
Abstract
In sustained growth with random dynamics, stationary distributions can exist without detailed balance. This suggests thermodynamical behaviour in fast growing complex systems. In order to model such phenomena, it is possible to use both a discrete and a continuous master equation. The derivation of elementary rates from known stationary distributions is a generalisation of the fluctuation–dissipation theorem. Entropic distance evolution is given for such systems. Depending on the transition and loss rates, the distributions for growing networks, particle production, scientific citations and income distribution can be reconstructed.
CSHV, 8., Josefstädter Str. 39, room 101
2017-04-28
14:15 - 15:45
R. Hanel
(Medical University of Vienna)
Process, history dependence, and entropy
Abstract
In different fields entropy has been conceptualized in different ways resulting in a functional expression equivalent to Shannon-entropy. Therefore entropy often is thought of as a universal concept. This however is true only as long as the underlying processes in question are essenially Bernoulli processes leading to a degeneracy of most commonly used entropy concepts and the ubiquitous emmergence of the particular functional form of Shannon-entropy. If the underlying process class in question becomes history dependent, also the expressions for the entropy functionals change and it becomes important which concepts we are using in order to define a notion of entropy; whether we think of an extensive property of matter, information rates, or maximum configuration principles, for instance, then starts to make a difference. For history dependent processes entropy is no longer uniquely defined and different entropy concepts have to be distinguished, informing us about distinct properties of the process. We discuss the general situation with simple history dependent example processes.
CSHV, 8., Josefstädter Str. 39, room 101
2017-04-07
14:15 - 15:45
J. Kertesz
(Central European University Budapest, external fellow of the Complexity Science Hub Vienna)
Multiplex Modeling of the Society
Abstract
The society has a multi-layered structure, where the layers represent the different contexts resulting in a community structure with strong overlaps. To model this structure we begin with a single-layer weighted social network (WSN) model showing the Granovetterian correlations between link strength and topology. We find that when merging such WSN models, a sufficient amount of inter-layer correlation is needed to maintain these correlations, but they destroy the enhancement in the community overlap due to multiple layers. To resolve this, we devise a geographic multi-layer WSN model, where the indirect inter-layer correlations due to the geographic constraints of individuals enhance the overlaps between the communities and, at the same time, the Granovetterian structure is preserved. The network of social interactions can be considered as a multiplex from another point of view too: each layer corresponds to one communication channel and the aggregate of all them constitutes the entire social network. However, usually one has information only about one of the channels, which should be considered as a sample of the whole. We show by simulations and analytical methods that this sampling may lead to bias. For example, while it is expected that the degree distribution of the whole social network has a maximum at a value larger than one, we get with reasonable assumptions about the sampling process a monotonously decreasing distribution as observed in empirical studies of single channel data. We analyse the far-reaching consequences of our findings.
CSHV, 8., Josefstädter Str. 39, room 101
2017-03-31
14:15 - 15:45
P. Klimek
(Medical University of Vienna)
Economic resilience quantified
Abstract
Economic and financial crises are extremely costly, yet our understanding of the resilience of economies is only in its infancy. Resilience is typically understood as a system’s ability to absorb, withstand, and also recover from adverse events. The characterization of economic resilience is particularly challenging due to strong interdependences between different industries and the way they absorb and recover from production shocks. In this talk we develop for the first time a quantitative, predictive, and data-driven formalism for the resilience of economies based on linear response theory (LRT). Key to this formalism is Leontief’s input-output model that depicts inter-industry relationships within an economy. We show how the impacts of production shocks in specific industries can be analytically derived from small-scale fluctuations observed in the input-output model using LRT. For each industry sector in 43 different countries, we can compute its time-dependent response to different kinds of shocks in any other sector. That is, a central result of this framework is the derivation of resilience curves for each sector with respect to shocks in any other sector. The so-derived resilience curves are shown to be predictive for, both, the average growth of and fluctuations in the output in a given country. Furthermore, we show that the impact of sector-specific demand shocks on the entire economy can also be understood and to some extent predicted from these curves. The predictions are shown to be particularly accurate when the framework is applied to the financial crisis in 2008. Our work establishes a firm and novel link between the out-of-equilibrium behavior of severely disrupted economies and their steady-state fluctuations.
CSHV, 8., Josefstädter Str. 39, room 101
2017-03-24
14:15 - 15:45
B. Corominas-Murtra
(Medical University of Vienna)
Characterization and statistical footprints of Open-Ended Evolution
Abstract
A major problem for evolutionary theory is understanding the so called open-ended nature of evolutionary change, from its definition to its origins and consequences. Open-ended evolution (OEE) refers to the unbounded increase in complexity that seems to characterise evolution on multiple scales. In this talk we will present a fundamental characterisation of OEE. Essentially, it is assumed intrinsic unpredictability and the need for an always increasing amount of information to explain the successive evolutionary steps —the emergence of innovation. Interestingly, such unpredictability defines the boundary conditions for a mathematical problem which ends with a prediction: The statistical counterpart of the OEE ‘postulates’, based on standard Shannon Information theory, have the structure of a variational problem which is shown to lead to Zipf’s law as the expected consequence of an evolutionary processes displaying OEE. Interestingly, many complex systems candidates of displaying OEE, from language to proteins, share this common scaling behaviour. Other information-theoretic phenomena arising from open-ednedness, such as the paradox of information loss, will be also discussed. We will finish discussing the connection of this general framework with existing models for the understanding of the emergence of innovation.
CSHV, 8., Josefstädter Str. 39, room 101
2017-03-17
14:15 - 15:45
V. Servedio
(Complexity Science Hub Vienna)
Evidence of Weber-Fechner law in political opinions
Abstract
The widespread use of internet allows to conduct experiments in the frame of social science with the engagement of a large number of participants. In this presentation I will show the results of a web-experiment intended to uncover voters' perception of the Italian political space in the early 2013, right before last Italian political elections. We find that political opinions follow a sort of Weber-Fechner law, known to occur in the perception of our five senses, i.e., our perceptions depend on the logarithm of stimuli intensity. Such finding can be exploited in the future to devise more realistic agent-based models of opinion dynamics.
CSHV, 8., Josefstädter Str. 39, room 101
2017-01-27
14:15 - 15:45
R. Hanel
(Medical University of Vienna)
Extortion strategies in iterated prisoners dilemma
Abstract
A brief introduction to the concept of extortion strategies in iterated prisoners dilemma games and recent insights into the evolution of extortion and cooperation. Lit: (i) WH Press & FJ Dyson PNAS 109 (2012) and (ii) C Hilbe, MA Nowak & K Sigmund PNAS 110 (2013)
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2017-01-20
14:15 - 15:45
A. Hinteregger
(Medical University of Vienna)
Cancelled! Systemic risk in the Austrian economyMUW, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor, room 513
2016-12-16
14:15 - 15:45
M. Sadilek
(Medical University of Vienna)
Identifying the driving processes of coupled friendship and enmity dynamics in a two-layer network model
Abstract
With the advent of social media it has become possible to study human social relations in a quantitative way. However, in most cases only data on positive relations (like friendship) are available while social balance theory states that in a social network positive and negative relations strongly depend on each other. In the massive multiplayer online game PARDUS players can mark each other not only as friends but also as enemies, leading to a two-layer multiplex network structure. We discuss the dynamics of friendship and enmity relations between thousands of players in PARDUS. We identify and quantify the driving processes of the associated two-layer social network formation. Well known sociological hypotheses like ‘The enemy of my enemy is my friend’ turn out to be important building blocks of understanding the dynamics of the coupled formation of friendly and hostile interactions within a society.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-11-25
14:15 - 15:45
B. Baumann
(Medical University of Vienna)
Optical imaging applications in the eye and brain
Abstract
Optical imaging enables rapid in vivo imaging with micrometer scale resolution. In this seminar, I will present some recent technological advances and optical imaging applications in the eye and brain. In particular, we will focus on functional extensions of a technique called optical coherence tomography (OCT). OCT enables imaging tissue microstructure as well as polarization properties and perfusion in real time. Several applications for quantitative imaging of pathological changes in humans and small animals will be presented.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-11-18
14:15 - 15:45
S. Kitzler
(Vienna University of Technology)
Comparison of methods to calculate diffusion in complex media
Abstract
Content of my project work and the seminar presentation is to ascertain the probability of the presence of particles which move with Brownian motion in a complex, time-varying medium. Such transport processes are denoted as anomalous diffusion and can't be distinguished by the Fick's laws of diffusion. For such problems computer-aided algorithms of Brownian motion often lead to success, implemented as a numerical simulations of discrete random walker processes on networks. We are especially interested in anomalous diffusion on dynamic, complex networks, which alter over time. Propagation on medium can consist of diffusion or of iterative centrality measure such as the Katz prestige, eigenvector centrality or PageRank which all base on random walker processes with distinct behaviors. We try to illustrate the equivalence of (1) the simulation of random walkers, (2) the numerical calculation of the iterative equation and (3) the closed, analytical form of the diffusion processes. As an interdisciplinary background we use networks of clinical history of patients. The nodes of the network stand for the different phenotypes of diseases and the connecting link represents the likelihood that diagnosis appear together. These networks alter in age which is represented in a time-varying, dynamical network. Another main concern is to clarify how far trajectories and probability of presence of random walkers on network correlate with prevalences, evidence and precursor of diseases.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-10-28
14:15 - 15:45
B. Liu
(Medical University of Vienna)
Statistical patterns in decomposed texts
Abstract
Different from traditional quantitative linguistics, we study languages in the following ways: distribution of the appearing frequencies in the text and emerging speed of new words. Usually these properties are studied for a book or a specific language, while seldom looks into the other aspects. Thanks to the Corpus of Historical American English(COHA), we get the full text corpus for about more than 110,000 texts ranging from 1810 to 2009. The texts are analyzed using the above approaches in terms of different sentence length. We observe patterns that stay invariant through history. This may indicate the invariance of the habits of language use. But more important, the invariant pattern indicates that the sentence length of 7 is sitting at a special point from the view of new word introduction rate and information density. This result is somehow linked to the results from the famous paper “The Magical Number Seven, Plus or Minus Two”.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-10-21
14:15 - 15:45
B. Corominas-Murtra
(Medical University of Vienna)
Sample Space Reducing Processes: Theory and extensions
Abstract
The idea of “path” is fundamental to disentangle the complexity of the systems that are the outcome of an evolutionary process. The path described by an evolving system is often constraining the future space of alternatives, a property usually called history or path-dependence. In this talk I will show how history dependence is deeply linked with the scaling patterns observed in many complex systems, thanks to the recently developed theory of Sample Space Reducing (SSR) processes. From complex networks to critical phenomena, scaling laws emerge in somewhat regular way, and the comprehension of the mechanisms behind scaling patterns has become on of the hot topics of modern statistical physics. SSR process are a totally new route to scaling based on the unique assumption that the phase space reduces as long as the process unfolds. Applications of the theory of SSR processes to diffusive phenomena in complex networks, for example, reveal a source of unexpected results. I will finally revise some work-in-progress extensions of the theory which include i) Sample Space Reducing cascades: Multiplicative processes over a shrinking space, with applications from avalanche study to the energy spectrum of cosmic rays. ii) Sample Space Expanding (SSE) processes, a class of processes which can be understood to be the “mirror” of SSR processes. It is worth to mention that classic results of Record Statistics can be mapped into the simplest case of SSE processes.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-10-14
14:15 - 15:45
P. Klimek
(Medical University of Vienna)
Disentangling genetic and environmental risk factors for diseases from multiplex comorbidity networks
Abstract
Most disorders are caused by a combination of multiple genetic and environmental factors. If two diseases are caused by the same mechanism, they often co-occur in patients. Here we disentangle how much genetic or environmental risk factors contribute to the pathogenesis of 358 individual diseases, respectively. We pool data on genetic, pathway-based, and toxicogenomic disease-causing mechanisms with co-occurrences obtained from almost two million patients. From this data we construct a multilayer network where nodes represent disorders that are connected by links that either represent phenotypic comorbidity or the joint involvement of certain mechanisms. We quantify the similarity of phenotypic and mechanism-based links for each disorder. Most diseases are dominated by genetic risk factors, while environmental influences prevail for disorders such as depressions, cancers, or dermatitis. The relevance of environmental risk factors for a given disease is inversely related to its broad-sense heritability and also inversely related to the rate at which new drugs for the disease are approved. This might be indicative of a lack of successful drug development for diseases with high environmental risks. Our approach allows to rule out certain types of disease-causing mechanisms when their implied comorbidities are not observed and might therefore be used to identify promising leverage points for the development of future therapies of multifactorial diseases.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-06-24
14:15 - 15:45
N. Rekabsaz
(Vienna University of Technology)
CancelledMUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-06-17
14:15 - 15:45
A. Hinteregger
(University of Vienna)
Network Centrality and Systemic Risk
Abstract
There are several different measures for the importance of the vertices in a network, often referred to as „Centrality“. I will compare different centrality measures, in particular the Debt-Rank, introduced by Battiston et al. to analyze the systemic risk in a financial network that can lead to a collapse as seen in the financial crises of 2007 - 2008. In our research we try to reconstruct the liabilities between Austrian companies and banks from aggregated data to estimate what companies could lead to a collapse of the economy in the case of a default.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-06-10
14:15 - 15:45
B. Wang
(Medical University of Vienna)
Quantifying systemic risk in a financial and real economy multi-layer network
Abstract
The financial crises of 2007-2008 has led to increased awareness of the importance of systemic risk, which started pertinent contributions to quantifying the impact of inter-connectedness within financial networks and their interconnection to the real economy. Present research on financial networks and bank-firm networks attempts to estimate systemic risk that is generated by credits or other types of financial contracts. In this work we incorporate ownership-ties as an additional type of interconnection between entities. We generate an Austrian financial and real economy multi-layer network with two layers consisting of liabilities and shares held between and within banks and the real economy. We then quantify the contributions to systemic risk from each layer of this multi-layer network. To generate the network structure we use shareholder data from the Austrian commercial register and aggregated exposure data from banks to the real economy in Austria from the years 2006 to 2015.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-06-03
14:15 - 15:45
I. Smirnov
(Institute of Education, Higher School of Economics, Moscow)
Changing friends is easier than changing grades: evolution of friendship networks of students and social selection
Abstract
Homophily, the tendency of individuals to associate with others who share similar traits, has been identified as a major driving force in the formation and evolution of social ties. In many cases it is however not clear if an observed homophily is the result of a socialization process, where individuals change their traits according to the dominance of that trait in their local social networks, or if it results from a selection process, in which individuals re-shape their social networks so that their traits match those in the new environment. Here we demonstrate the existence of strong homophily in academic achievements of high school and university students. We analyze a unique longitudinal dataset that contains information about the detailed evolution of a friendship network of 4.500 students across 42 months. Combining the evolving social network data with the time series of the academic performance (gpa) of the individual students, we show that academic homophily is a result of selection: students gradually reorganize their social networks according to their performance levels, rather than adapt their performance to the level of their local group. We are able to understand the underlying dynamics of grades and networks with a simple agent-based model. The lack of a social pull effect in classical educational settings could have important implications for the understanding of the observed persistence of segregation, inequality and limited social mobility in societies.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-05-13
14:15 - 15:45
H. Fellermann
(School of Computing, Newcastle University)
Harvesting biology for computing and production
Abstract
Molecular biology and microbiology have rendered a picture of living organisms as minutely orchestrated versatile machines and factories that are able to steer flow of matter with unprecedented control and accuracy. In my talk, I will present a portfolio of work that exploits the physical properties of biomolecules and super-molecular biological aggregates for non-biological, technological applications in the areas of molecular computing and material production. In the first part of the talk, I will present recent work on a DNA implementation of a signal recorder based on a stack data structure that is studied in vitro and in simulation. The second part of the talk expands on these principles and uses DNA computing to arrange and control the dynamics of vesicles that are able to carry molecular cargo. By combined molecular and external control mechanisms, we develop a framework to orchestrate bio-chemical synthesis pathways in a manner that mimics the organization of cellular compart-ments such as the Golgi apparatus. Time allowing, I will present some works that integrates the above approaches of refunctionalizing biomolecules to create life-like yet truly non-biological chemical aggregates de novo.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-04-29
14:15 - 15:45
C. Siebenbrunner
(Austrian National Bank, Vienna University of Technology)
Financial Networks and Systemic Risk
Abstract
My work investigates the implications of systemic risk for financial regulation. I show that in the absence of liquidation costs for defaulted firms, there exists a social dilemma in which socially and pareto efficient bailouts are not performed in a Nash equilibrium by rational agents without government intervention. Next, I establish a general framework for measuring systemic risk capable of separating the effects of direct contagion, asset fire sales and mark-to-market effects. Using Austrian interbank data, I show that the importance of fire sale effects eclipses the effects of the other two channels. Banks-specific indicators of systemic importance are then constructed to assess the efficiency of Basel-III systemic risk regulations, which rely on a simple combination of bank-specific indicators and do not account for network effects. The empirical results suggest that the Basel-III indicator set is an efficient choice of bank-specific indicators, but also that such indicator sets generally perform poorly at capturing the importance of network effects for contagion.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-04-22
14:15 - 15:45
P. Klimek
(Medical University of Vienna)
postponedMUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-04-15
14:15 - 15:45
F. Endel
(Vienna University of Technology)
Secondary use of administrative claims data in the Austrian healthcare system: the GAP-DRG database
Abstract
Secondary use of linked administrative claims data in the healthcare and social insurance system unveils various new possibilities for research and decision making. The Main Association of Austrian Social Security Institutions (“Hauptverband der österreichischen Sozialversicherungsträger”, HVB) operates the so called “GAP-DRG” database, including reimbursement and pseudonymized personal data from the Austrian healthcare system as part of the K-Project DEXHELPP* at the TU Vienna. Two main topics concerning this data collection are addressed. First, current developments as well as the renewal of key components of the database infrastructure in the near future are discussed. Comprehensive changes of hardware and software in the last year – a completely new database server has been deployed – and in the following month are summarized. A novel application platform based on software containers, allowing centralized services and new ways to analyze and present data will be introduced besides improvements due to upgrades of the underlying hardware and software. Second, a concrete example of applied data analysis is presented, bringing together various segments of the database and details of the Austrian public health insurance system. Due to missing genealogical information in GAP-DRG, family relations have to be derived from co-insurance of dependents. Co-insured children and spouses can therefore be distinguished based on their age in relation to the insured person’s age. The presented algorithm can be fitted to diverse objectives concerning the age of parents, spouses and children, while quality control and visualization of multivariate coherences are emphasized. *http://dexhelpp.at
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-04-08
14:15 - 15:45
J. Kertesz
(Budapest University of Technology and Economics)
Kinetics of Social Contagion
Abstract
Diffusion of information, behavioral patterns or innovations follows diverse pathways depending on a number of conditions, including the structure of the underlying social network, the sensitivity to peer pressure and the influence of media. We introduce a general model that incorporates threshold mechanism capturing sensitivity to peer pressure, the effect of ‘immune’ nodes who never adopt, and a perpetual flow of external information and study it by analytical methods and simulations. While any constant, non-zero rate of dynamically-introduced spontaneous adopters leads to global spreading, the kinetics by which the asymptotic state is approached shows rich behavior. In particular we find that, as a function of the immune node density, there is a transition from fast to slow spreading governed by entirely different mechanisms. This transition happens below the percolation threshold of network fragmentation, and has its origin in the competition between cascading behavior induced by adopters and blocking due to immune nodes. This change is accompanied by a percolation transition of the induced clusters. We calibrate and validate the model using Big Data.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-03-18
14:15 - 15:45
R. Hanel
(Medical University of Vienna)
Entropy, matrix-multinomials, regular grammars, and processes on multi-graphs - a unifying perspective
Abstract
Many systems of processes can be characterized by sequences of symbol strings where symbols are sampled from an alphabet (or by sentences of words sampled from a lexicon). Moreover, such symbol sequences may be subject to internal constraints which determine which sequences a process can generate and which not. This can be interpreted as a „grammar'' that distinguishes well-formed sequences from ill-formed ones. For simple grammars (typically referred to as regular grammars) symbols in the underlying alphabet can be represented by matrices acting on a finite dimensional state-space. As a consequence it becomes possible to determine the multiplicity of sequences with identical histograms, and hence the maximum configuration entropy, i.e. the Boltzmann entropy, of the processes. We discuss the general situation in the particular example of the Oslo sandpile-model.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-02-19
14:15 - 15:45
P. Jizba
(Czech Technical University in Prague)
On Statistical Origin of Special and Doubly Special Relativity
Abstract
Petr Jizba and Fabio Scardigli In this talk I will show how a Brownian motion on a short scale can originate a relativistic motion on scales that larger than particle's Compton wavelength. I start by discussing complex dynamical systems whose statistical behavior can be explained in terms of a superposition of simpler underlying dynamics — the so-called superstatistics paradigm. Then I go on by showing that the combination of two cornerstones of contemporary physics — namely Einstein’s special relativity and quantum-mechanical dynamics is mathematically identical (when analytically continued to Euclidean regime) to a complex dynamical system described by two interlocked processes operating at different energy scales. The combined dynamic obeys special and doubly special relativity even though neither of the two underlying dynamics does. To model the double-stochastic process in question, I consider quantum mechanical dynamics in a background space consisting of a number of small crystal-like domains varying in size and composition, known as polycrystalline space (or Voronoi tessellation). There, particles exhibit a Brownian motion. The observed relativistic dynamics then comes solely from a particular grain distribution in the polycrystalline space. In the cosmological context such distribution might form during the early universe’s formation. Salient issues such as Hausdorff dimensions of path-integral trajectories, connection with Feynman chessboard model and implications for quantum field theory and cosmology (leptogenesis) will be also briefly discussed. Related articles: [1] P. Jizba and F. Scardigli, Eur. Phys. J. C (2013) 73: 2491 [2] P. Jizba and F. Scardigli, Phys. Rev. D (2012) 86: 025029
MUW, room 513, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2016-02-05
14:15 - 15:45
I. Smirnov
(Institute of Education, Higher School of Economics, Moscow)
Reproduction of Inequality in the Digital Age
Abstract
The internet and social network sites transformed the world. Instant access to the most of human knowledge and to the millions of peers registered in social networks means that people are not limited by their immediate environment anymore. Can this opportunity be used to break the cycle of inequality reproduction or will we observe the Matthew effect: the rich will get richer and the poor will get poorer? To shed light on this question I've collected a data set from the VK ("Russian Facebook") containing information about 1 million users, their social ties and interests along with their educational background. I'm going to use complex networks analysis in order to estimate the effect of segregation in virtual space and the role of peer influence in overcoming social background.
MUW, Spitalgasse 23, 1090 Vienna, BT86, 3rd floor, seminar room
2016-01-22
14:15 - 15:45
B. Fuchs
(Medical University of Vienna)
Towards Understanding Collective Social and Economic Dynamics in a Virtual World
Abstract
Quantitative social science, which strives for a predictive understanding of social facts, has since its origins faced the challenge of limited availability of empirical data. We approach this challenge by turning to a a model-society inside a large-scale virtual world, i.e. an online game, of which we have nearly complete information. Studying the structure of society as a whole, multiple levels of fractally nested groups and subgroups have been found in real-world anthropological data. By quantitatively analyzing detailed grouping data we find a similar structure in the model-society. This finding indicates that the pattern of fractal organization is universal. Humans within such a hierarchically organized society are clearly unequal. We contribute to the study of inequality by analyzing the wealth distribution inside the virtual world and by comparing it to real-world observations. Our data allow us to investigate connections between wealth and the position of individuals within their social networks. We study pairs of interacting individuals and quantify the interplay between physical distance and social interactions. Our findings are compared to previous real-world data.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-12-18
14:15 - 15:45
N. Rekabsaz
(Vienna University of Technology)
The meaning of ‚Meaning‘: Review of the State-of-the-Art in Statistical Word Representation
Abstract
The endeavor to grasp the meaning of text in Artificial Intelligence starts with understanding the natural building block of the language : „words“. Since years, many methods has provided various computer-understandable representations by trying to resemble the human perception of the meaning and relatedness of the words. The methods basically exploit either human-annotated knowledge or statistical approximation and are broadly used in different fields such as Natural Language Processing, Information Retrieval, Text Mining, Sentiment Analysis, Statistical Machine Translation, etc.. As a main direction for representing words, the statistical methods exploit the implicit knowledge within long text corpora to approximate the representation of words in vector spaces (Word Embeddings). These methods mainly rely on the tendency of natural language to use semantically related words in similar contexts. In the text retrieval community, word and text representation started with Latent Semantic Analysis/Indexing (LSA/LSI), the pioneer approach that initiated a new trend in surface text analysis. Explicit Semantic Analysis (ESA) is one of the early alternatives, aimed at reducing the computational load. However, unlike LSA, ESA does rely on a pre-existing set of concepts, which may not always be available. Random Indexing (RI) is another alternative to LSA/LSI that creates context vectors based on the occurrence of words contexts. It has the benefit of being incremental and operating with significantly less resources while producing similar inductive results as LSA/LSI and not relying on any pre-existing knowledge. Word2Vec further expands this approach using neural networks-based language modeling. When trained on large datasets, it is also possible to capture many linguistic subtleties (e.g., similar relation between Italy and Rome in comparison to France and Paris) that allow basic arithmetic operations within the model. In this talk, we first review the main word representation methods with focus on Word2Vec as an effective and state-of-the-art approach. Putting forward the question of the meaningfulness of the statistical word representations, we then shed light on the topology of the distributional space in different dimensions, based on recent studies in the IFS group of TU WIEN. The analysis provides an understanding about the informativeness versus randomness of the words' relations and motivates the effective use of the word embeddings in different areas.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-12-04
14:15 - 15:45
T. Biró
(MTA Wigner Research Center for Physics, Hungarian Academy of Sciences)
Entropy: Generalizations, Axioms, Scaling.
Abstract
We review a particular approach to generalized entropy formulas based on finite reservoir physics. Ideal systems - correlated only due to restrictions of the total phase space - reveal certain leading order corrections to the traditional entropy formula first suggested by Boltzmann and later extended in use and interpretation by Gibbs, Planck and Shannon. We identify which axioms behind the classical formula are violated by this finiteness and how the large dimension scaling may lead to further formulas beyond the well-studied logarithm.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-11-27
14:15 - 15:45
B. Liu
(Section for Science of Complex Systems)
Statistical Properties of English Language
Abstract
Different from traditional quantitative linguistics, we study languages in the following ways: distribution of the appearing frequencies in the text, emerging speed of new words, nested structure of the potential followers and information needed for creating word sequences among other approaches. Each of the above analyses tells us some properties, either from word-word level or the text as a whole. Usually these properties are studied for a book or a specific language, while other detailed aspects remain vacuum. Thanks to the Corpus of Historical American English(COHA), we get the about more than 110,000 texts ranging from 1810 to 2009 with four genres of fictions, magazines, newspaper articles and non-fictions. The texts are analyzed using the above approaches across history. From the results we observe clear trends in these properties, which indicates that the English language is evolving. Also, texts are decomposed in sentences and then sentences of the same length are clustered and then analyzed. We observe patterns that stay invariant through history. This may indicate the invariance of the habits of language use. The part-of-speech analysis for different sentence length are also presented for the possible explanation of this invariance. These findings may lead to a more comprehensive understand of the statistical properties of language.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-11-13
14:15 - 15:45
B. Corominas-Murtra
(Section for Science of Complex Systems)
Sample Space Reducing processes
Abstract
The comprehension of the mechanisms behind scaling patterns has become on of the hot topics of modern statistical physics [1]. From complex networks to critical phenomena, scaling laws emerge in somewhat regular way. In this talk I will link the scaling patterns observed in many complex systems with a crucial property behind them: history-dependence [2]. Classical examples of history dependent processes with extremely interesting properties are Pólya urns, the Chinese restaurant or the recurrent random sequences proposed by Ulam and Kac. The link between history-dependence and scaling comes from the recently defined Sample Space Reducing (SSR) processes [3,4]. SSR processes connect history dependence and scaling in an extremely intuitive way. In addition, SSR process are a totally new route to scaling which can explain a huge range of power-law exponents thanks to the unique assumption that the sampling space is reduced as long as the process unfolds. Simple forms of SSR processes are regular sampling processes where the ‘left-right’ symmetry is broken, leading to a minimal form of history-dependence. In spite of the simplicity of this basic assumption, SSR processes display a wide spectrum of surprising properties. From this zoo of interesting properties, maybe the most remarkable one is the role of the scaling law known as ‘Zipf’s law’ as an attractor, which provides a new, fundamental explanation for the ubiquity of such scaling pattern in real systems. In addition, it provides a new look to diffusive phenomena, since it assumes the presence of a 'target' or 'sink' region, which may model many diffusion-like phenomena, such as urban movement, animal migration or information routing in the internet. The intuitive rationale behind the SSR processes and the surprisingly simple mathematical apparatus needed to understand them makes the SSR process approach a new research area with promising applications. Bibliography: [1] Newman, M E J (2005) “Power laws, Pareto distributions and Zipf's law" Contemporary Physics 46 (5): 323–351. [2] Arthur, B (1994) Increasing Returns and Path Dependence in the Economy. The University of Michigan Press, Ann Arbor. [3] Corominas-Murtra, B, Hanel, R, and Thurner, S (2015) “Understanding scaling through history-dependent processes with collapsing sample space”. Proc Nac Acad Sci USA. 112 (17) 5348–5353. [4] Thurner, S, Hanel, R, Liu, B, and Corominas-Murtra, B (2015) “Understanding Zipf’s law of word frequencies through sample-space collapse in sentence formation”. J R Soc Interface. 12 (108).
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-11-06
14:15 - 15:45
P. Klimek
(Section for Science of Complex Systems)
The forensics of election fraud: statistical detection of voter coercion?
Abstract
The fundament of a health democracy are free and fair elections. Election forensics is an emerging, interdisciplinary field that aims to develop statistical and data-driven methods to verify whether the preferences of the electorate have been correctly translated into the election outcome. One of the most often reported types of election fraud is voter coercion. This is the practice of intimidating, threatening, or coercing any person for voting or for attempting to vote. Here, we develop a novel statistical method to identify polling centers that show substantial deviations in their electoral behavior with respect to other, geographically close polling centers. We analyse a dataset of twenty different elections in ten different countries and show that in the vast majority of cases no such systematic deviations exist, with the exceptions of electoral referendums after 2003 in Russia, after 2006 in Venezuela, and, to a smaller extent, after 2012 in Mexico. In each of these cases we find a substantial number of polling centers with significantly increased results of turnout and votes for the winning party. Polling centers with a comparably small electorate size are particularly susceptible to such deviations that are compatible with the assumption of widespread voter coercion. We discuss these findings in the context of recent elections in Venezuela, where the deviations are strongest in newly created and strategically located polling centers.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-10-30
14:15 - 15:45
M. Sadilek
(Section for Science of Complex Systems)
Modeling of two-layer dynamics in social systems
Abstract
Human societies can be viewed as complex systems comprising individuals that are simultaneously active in various social networks, each of the latter representing a different type of social relation. Examples for such relations are friendship, enmity, communication, or trade. Dynamical changes of a social system's overall structure due to interactions among individuals are accordingly reflected in structural changes of the corresponding social networks. In the past, some of the observed structural properties of single social networks (e.g. friendship network) could be successfully explained by mathematical models, in the sense that those models generate artificial networks with similar properties. But in general, the individual networks of a social system are not independent from each other: According to structural balance theory, certain triangular configurations of positively connoted relations (such as friendship) and negatively connoted relations (such as enmity) are more balanced that others, and thus more likely to occur. Using a multilayer network formalism, we are currently developing a mathematical model for the dynamics of social systems with one friendship and one enmity network layer. The model is based on local dynamical rules that implement the key processes preferential attachment and triadic closure, and especially respect structural balance theory.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-10-23
14:15 - 15:45
R. Hanel
(Section for Science of Complex Systems)
Maximum Configuration - Constructing the Maximum Entropy Principle for Self Reinforcing Processes
Abstract
Self reinforcing processes are ubiquitously at work in complex dynamical systems in terms of feed-back loops. Polya urns provide a general framework to study the statistics of such processes and their distribution functions. Maximizing entropy under particular conditions (the maximum entropy principle) allows to predict how likely particular types of systems (weakly interacting components, equilibrium conditions, Markovian, etc.) can be found in particular states. The classical MaxEnt approach however breaks down for non-equilibrium processes such as Polya urn processes. However, using standard maximum configuration considerations we can derive the adequate MaxEnt principle for multi-state Polya urn processes. The form of entropy and constraints to consider in MaxEnt are direct consequences of the class of processes MaxEnt is supposed to apply. This observation has far reaching consequences for an information theory of self reinforcing processes.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-06-26
14:15 - 15:45
F. Tria
(Institute for Scientific Interchange, ISI Foundation Turin)
Dynamics on expanding spaces: modeling the emergence of novelties
Abstract
Innovation is the driving force in the evolution of human society as well as of biological systems. A general concept that applies to innovation and the emergence of novelties, is what Kauffman called expanding the adjacent possible. The idea is that by creating fresh opportunities, one novelty can pave the way for others, enlarging the space of possibilities in a self-consistent way. I will highlight some statistical features common to many systems where some kind of innovation occurs, and I will shortly review seminal works devoted to their comprehension. I will then present a recent work aimed at grounding the notion of adjacent possible on real data, by the definition of quantitative measures and the development of a suitable mathematical framework.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-06-19
14:15 - 15:45
M. Grün
(Section for Science of Complex Systems)
A sample-space-reducing approach to study scaling of disease frequencies
Abstract
Power laws appear in a wide variety of physical, biological and man-made phenomena. They can also be observed in frequencies of human diseases. Over a wide range of magnitudes, rank ordered disease frequencies follow an approximate power-law. Several mechanisms have been proposed to understand the origin of power-law behavior of complex systems. A recently proposed approach offers an alternative way to understand scaling, based on sample space reducing (SSR) processes. In respect to the topology of directed networks, SSR can be related to diffusion processes. It was shown that progression of human diseases can be explained by diffusion on phenotypic disease networks (PDN). I will talk about our studies of diffusion-processes on PDN's and their relation to SSR. I will also discuss if we are able to understand the emergence of scaling in disease frequencies by using a SSR approach.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-06-12
14:15 - 15:45
C. Flamm
(Institute for Theoretical Chemistry, Vienna University)
Computational design of catalysed reaction networks
Abstract
With the advent of Synthetic Biology, methods for the computational design of catalysed reaction networks became important. I will present a computational framework, which combines a graph-grammar base formalism for describing chemical transformations with optimal flows on hypergraphs to find solutions for the design problem. An optimal network is perceived from a set of initial molecules and the set of allowed enzymatic reactions.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-05-29
14:15 - 15:45
S. Widder
(Department for Computational Systems Biology, Vienna University)
On the structure-function relationship in microbial communities
Abstract
Classical microbiology has focused on single species. Yet in natural environments and in many industrial applications microbes exist in functional consortia or communities (MCs). MCs play crucial roles in processes as divers as global climate regulation, human health or industrial applications such as wastewater treatment. While sequence-based studies in the last decade revealed immense biodiversity and complexity, we are far from understanding the structure and organisation of MCs and how these translate to function and productivity of microorganisms. Co-occurrence networks of microorganisms from environmental samples facilitate understanding and analysis of this structure-function relationship. In my talk I will focus exemplarily on one ecological and one pathological MCs and their organisation. I will show how the analysis of MC network topology allows inference of functional roles in riverine biofilm MCs and demonstrate that environmental perturbation leads to network fragmentation. For the pathologic MC (cystic fibrosis lung microbiota) we could confirm by network analysis that a shift in the severeness of the condition is related to a taxonomic shift in the MC and the related metabolic core processes. Furthermore we propose functional and taxonomical keystones as targets for novel drug development.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-05-22
14:15 - 15:45
M. Sadilek
(Medical University of Vienna)
Models for social networks with negative ties
Abstract
Social balance theory suggests that within a social network, the subnetworks comprising positive ties (friendship network) respectively negative ties (enmity network) are dynamically interrelated. I will present some results from my recent work which concentrates on finding a realistic generative model for such networks based on data from the massive multiplayer online game Pardus.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-04-29
14:00 - 15:00
G.C. Rodi
(Institute for Scientific Interchange - ISI Foundation Turin)
Optimal learning paths in information networks
Abstract
Each sphere of knowledge and information could be depicted as a complex mesh of correlated items. By properly exploiting these connections, innovative and more efficient navigation strategies could be defined, possibly leading to a faster learning process and an enduring retention of information. It has been investigated how the topological structure embedding the items to be learned can affect the efficiency of the learning dynamics. To this end we introduce a general class of algorithms that simulate the exploration of knowledge/information networks standing on well-established findings on educational scheduling, namely the spacing and lag effects. While constructing their learning schedules, individuals move along connections, periodically revisiting some concepts, and sometimes jumping on very distant ones. In order to investigate the effect of networked information structures on the proposed learning dynamics we focused both on synthetic and real-world graphs such as subsections of Wikipedia and word-association graphs. We highlight the existence of optimal topological structures for the simulated learning dynamics whose efficiency is affected by the balance between hubs and the least connected items. Interestingly, the real-world graphs we considered lead naturally to almost optimal learning performances.
Section for Science of Complex Systems
2015-04-24
14:15 - 15:45
G. Tkacik
(Institute of Science and Technology Austria)
Critical behavior in networks of real neurons
Abstract
The patterns of joint activity in a population of retinal ganglion cells encode the complete information about the visual world, and thus place limits on what could be learned about the environment by the brain. We analyze the recorded simultaneous activity of more than a hundred such neurons from an interacting population responding to naturalistic stimuli, at the single spike level, by constructing accurate maximum entropy models for the distribution of network activity states. This – essentially an ”inverse spin glass” – construction reveals strong frustration in the pairwise couplings between the neurons that results in a rugged energy landscape with many local extrema; strong collective interactions in subgroups of neurons despite weak individual pairwise correlations; and a joint distribution of activity that has an extremely wide dynamic range characterized by a zipf-like power law, strong deviations from ”typicality”, and a number of signatures of critical behavior. We hypothesize that this tuning to a critical operating point might be a dynamic property of the system and suggest experiments to test this hypothesis.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-04-16
14:00 - 15:00
J.-P. Onnela
(Harvard University, Boston)
Cell phones, Social Networks, Crowds, and Digital Phenotyping
Abstract
Cell phones are now ubiquitous: it is estimated that the number of phones in use exceeds the size of the global population in 2015. I will talk about two main lines of work in our lab. First, we use call detail records (CDRs) to investigate the structure of large-scale social networks and their relationship to underlying geography. We also use these data to study population dynamics at massive gatherings of people and to inform models of epidemic spread, in particular cluster randomized trials. Second, we have coined the term digital phenotyping to refer to the moment-by-moment quantification of the individual-level human phenotype, in situ, using data from digital devices. Using a dedicated smartphone application, we collect active data (surveys, voice samples, etc.) and passive data (spatial location, social engagement, etc.) from consenting patients and analyze these data using modern statistical learning methods. I will talk about some of our work that utilizes these two approaches, what types of insights they may yield to the study of social networks and human behavior, and how this work interfaces with public health.
MUW, Jugendstil seminar room, Spitalgasse 23, 1090 Vienna, BT88, 2nd floor
2015-04-10
14:15 - 15:45
J. Menche
(Center for Complex Networks Research and Department of Physics, Northeastern University)
Diseases in the human interactome
Abstract
Recent advances in disease gene identification and high-throughput mapping of physical interactions between gene products offer new opportunities to explore the role of molecular networks in human disease. Here we show that proteins associated with the same disease display a statistically significant tendency to agglomerate in the same neighborhood of the interactome, offering quantitative evidence for the existence of well-localized and potentially identifiable disease modules. Most important, we find that the network-based location of each disease module determines its pathobiological relationship to other diseases. For example, disease pairs with overlapping modules show significant co-expression patterns, symptom similarity, and comorbidity; those that reside in separated network neighborhoods are pathobiologically and clinically distinct. The proposed interactome-based framework offers systematic avenues to discover common molecular roots between clinically unrelated disease phenotypes even if they do not share disease genes, and helps identify the biological role of GWAS genes of small effect size and low genome-wide significance.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-03-20
14:15 - 15:45
I. Kondor
(Parmenides Foundation, Pullach b. München and Corvinus University Budapest )
Risk measures, regularization and market impact
Abstract
This talk will briefly review the history of risk measures appearing in the subsequent generations of international banking regulation, their relative merits and shortcomings, with special emphasis on Expected Shortfall (ES) that is on its way to becoming the next global regulatory market risk measure. When these measures are used to predict the out-of-sample risk or to optimize portfolios they all display a weakness due to the relative scarcity of data compared to the size of institutional portfolios. The resulting estimation errors can be very large, in fact, for some critical values of the parameters they can diverge, with the optimization algorithm undergoing a phase transition. The estimation error problem is particularly serious for downside risk measures, such as ES. The standard way to tackle these high dimensional problems is to use regularization, that is to introduce a penalty for excessive positions. It is shown that investors who optimize their portfolios under any of the coherent risk measures are naturally led to regularized portfolio optimization when they take into account the impact their trades make on the market. The impact function determines which regularizer is to be used. It is shown that any regularizer based on the norm Lp with p > 1 makes the sensitivity of coherent risk measures to estimation error disappear, while regularizers with p < 1 do not. The L1 norm represents a border case: its “soft” implementation does not remove the instability, but rather shifts its locus, whereas its “hard” implementation (equivalent to a ban on short selling) eliminates it. We demonstrate these effects on the important special case of Expected Shortfall.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-03-06
14:15 - 15:45
R. Hanel
(Section for Science of Complex Systems)
How to gauge prior probabilities for hypotheses testing and obtain critical threshold landscapes of the correlation coefficient
Abstract
Lindley's paradoxon is an effect that haunts Bayesian Hypotheses testing especially if hypotheses such as H1: A and B are correlated, versus H0: A and B are independent, are tested against each other. There is of course no real paradoxon only prior probabilities that have been chosen badly. We show that by a simple technique, comparing extreme samples which represent the hypotheses in their purest obtainable form, allows to gage the prior probabilities of the hypotheses adequately. We analyze the situation in the context of binary processes and show that in the limit of large numbers of samples the posterior probabilities of the hypotheses H1 and H0 exhibit a first order phase transition at critical values of the correlation coefficient.
MUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2015-02-11
10:00-12:00
J.S. Lansing
(Complexity Institute at Nanyang Technological University in Singapore)
Genetic and Language Trees in IndonesiaSection for Science of Complex Systems
2015-01-23
14:15 - 15:45
M. Sadilek
(Section for Science of Complex Systems, MUW)
Co-evolution of networksMUW, Spitalgasse 23, 1090 Vienna, BT86, seminar room, 3rd floor
2015-01-16
14:15 - 15:45
G. Percino-Figueroa
(Section for Science of Complex Systems, MUW)
Linking dynamics of tensored networks in virtual societyMUW, Spitalgasse 23, 1090 Vienna, BT86, seminar room, 3rd floor
2015-01-09
14:15 - 15:45
S. Aichberger
(Section for Science of Complex Systems)
Medical multiplex networksMUW, Spitalgasse 23, 1090 Vienna, BT86, seminar room, 3rd floor
2014-12-05
14:15 - 15:45
B. Corominas-Murtra
(Section for Science of Complex Systems, MUW)
Sample space reducing processesMUW, Informatics library, Spitalgasse 23, 1090 Vienna, BT88, 3rd floor
2014-11-28
14:15 - 15:45
R. Hanel
(Section for Science of Complex Systems, MUW)
Molecular regulatory networks and constraints from a dynamical systemic perspectiveMUW, Spitalgasse 23, 1090 Vienna, BT86, seminar room, 3rd floor
2014-11-21
14:15 - 15:45
P. Klimek
(Section for Science of Complex Systems, MUW)
Systemic Trade RiskMUW, Informatics library, Spitalgasse 23, 1090 Vienna,BT88, 3rd floor
2014-10-31
14:15 - 15:45
B. Fuchs
(Section for Science of Complex Systems, MUW)
Physical potentials derived from human interactionsMUW, Spitalgasse 23, 1090 Vienna, BT86, seminar room, 3rd floor
2014-10-17
14:15 - 15:45
I. Daruka
(Johannes Kepler University Linz)
A sustainable avalanche? Publication dynamics and the proliferation of research journals
Abstract
The number of research papers published yearly shows a staggering exponential growth. One can in fact witness a century-long publication avalanche. According to the two major databases INSPEC and Thomson Reuters, there is a 300-fold increase in the number of published items since the year 1900. The world of science has recently reached such a level of proliferating complexity that its structural evolution itself poses challenging scientific problems.
Medizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2014-06-27
14:15 - 15:45
K. Dovzhik
(University of Vienna)
Phase transitions in collective intelligence systemsMedical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2014-06-20
NO SEMINAR
2014-06-13
14:15 - 16:15
Lechner; Mitterwallner
(University of Vienna)
Quantum phase transitionsUniversität Wien, Fakultät für Physik, E. Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2014-06-06
NO SEMINAR
2014-05-30
NO SEMINAR
2014-05-23
14:15 - 15:45
M. Formanek
(University of Vienna)
Phase transitions in telechelic star polymers
Abstract
Novel colloidal systems constitute a broad and developing new field of research in soft matter science. Telechelic star polymers (TSPs), which are a hybrid system that combines the flexibility of chains with the sphericity of colloids, are particularly interesting materials because of their high degrees of freedom and the complex structural and dynamical properties that arise from them. This talk will focus on the ability of TSPs to self-assemble, to undergo macroscopic as well as microscopic phase transitions and to form multiply-connected percolating networks, depending on their functionality and the ratio of solvophilic to solvophobic groups.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2014-05-16
14:15 - 15:45
E. Traxler
(University of Vienna)
Phase transitions in large networks
Abstract
The concept of networking is used in many applications: computational processes (e.g., neural networks), transport, ecology, economics, sociology and many others. Therefore, understanding the dynamics of large, complex networks is becoming increasingly important. In these systems, stability is of utmost importance. Instabilities always lead to disaster and can even assume global proportions. Whereas stable systems can regenerate themselves and thus have some degree of fault tolerance, making them partially immune even to attacks. The question of the conditions for stability in networks is a central theme of my lecture.
Medical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2014-05-09
14:15 - 15:45
M. Sadilek
(Section for Science of Complex Systems, CeMSIIS, MUW)
Phase transitions in the Kuramoto modelMedical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2014-04-11
14:15 - 15:45
D. Lin
(University of Vienna)
Phase transition in random catalytic networks
Abstract
Phase transitions are one of the most interesting topics in physics. They occur in various physics-related disciplines from thermodynamics to network theory. In my talk I'd like to present the content of the paper "Phase transition in random catalytic networks" (by Rudof Hanel, Stuart A. Kauffman and Stefan Thurner). I'll start with some usefull definitions for the description of catalytic networks (like the "product rule density", the "support of a process", the "forward difference", etc.). Afterwards I'll derive the growth equation for catalytic sets and an analytical approximation of the forward-closure size. Plotting the "final number of products" against the "pair density" will lead to diagrams equal to PV-diagrams when considering Van der Waals equation and therefore we'll identify phase transition in catalytic networks.
Medical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2014-04-04
14:15 - 15:45
D. Grumiller
(Faculty of Physics, Vienna University of Technology)
Cooking recipe for a Universe
Abstract
Phase transitions are ubiquitous in Nature. Interestingly, even spacetime itself can be subject to such transitions, like in the famous Hawking-Page phase transition between 'hot curved space' and certain black holes. Recently, we found a similar phase transition between 'hot flat space' and an expanding cosmological spacetime in 2+1 dimensions. I review the ingredients contained in our 'cooking recipe' for a Universe.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2014-03-28
NO SEMINAR
2014-03-21
14:15 - 15:45
P. Schuster
(Faculty of Chemistry, University of Vienna)
Phase Transitions in Evolution: When do quasispecies form error thresholds?
Abstract
The notion of phase transitions is frequently used as a metaphor for abrupt changes in evolutionary dynamics. Here it will by understood more rigorously in the context of selection mutation dynamics. Replication and mutation are modeled as parallel chemical reactions, and evolutionary dynamics is seen as an adaptive or a random walk of population in an abstract space of genotypes represented by nucleic acid sequences. Depending on the distribution of fitness values over sequence space, populations can tolerate replication errors only up to a certain maximal mutation rate, which has been characterized as an error threshold. Below threshold and in the long time limit the populations converge to stationary sequence distributions denoted as quasispecies, whereas above threshold the populations are permanently non-stationary and drift randomly through sequence space. Accordingly, error thresholds are transitions from localized quasispecies to migrating populations, and they become sharper and sharper with increasing lengths of sequences. They have much in common with phase transitions. In the seminar we shall explore the conditions for the existence of error thresholds and analyze the nature of the transitions.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2014-03-14
14:15 - 15:45
H. Grosse
(Faculty of Physics, University of Vienna)
From models describing phase transitions to QFT
Abstract
I first describe simple statistical physics models discribing phase transitions in various dimensions. Ferromagnetic ones are related to lattice regularized Euclidean field theory. In dimensions greater than four one obtains triviality. Next I describe renormalization group ideas and mention the Landau ghost problem. An improvement is obtained by deforming space-time. Together with Raimar Wulkenhaar we found a model which is asymptotic safe and which was constructed recently. The connection to matrix models is mentioned.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2014-03-07
14:15 - 15:45
W. Pueschl
(Faculty of Physics, University of Vienna)
Basics of phases and phase transformations: An introductory tour from the viewpoint of a materials physicist
Abstract
In this overview, we start from the notion of a phase and ask ourselves why it is important to understand and distinguish phases, which leads us to the high cultural and technological significance of multi-phase structures. The equilibrium states of phases such as displayed in phase diagrams can be sought by means of thermodynamic potentials. We discuss how to calculate the quantities found therein. Regarding two-component (as the simplest case of multi-component) systems, it is seen how phase diagrams can easily be derived by graphical thermodynamics. Thermodynamics requires that on entering a miscibility gap a new phase be generated. This leads us to precipitation as a particularly interesting case of phase transformation, with nucleation and spinodal decomposition as alternative pathways. Opposed, in a certain sense, to phase separation are ordering transitions. Atomic configuration can be described by various order parameters based on correlation functions. We consider short-range order and long-range order. The Bragg-Williams model of ordering is the simplest ansatz leading to meaningful qualitative behavior. We recognize in it a one-point mean field approximation to the Ising model. In the framework of the Ising model ordering / phase- separating alloys can be seen analogous to magnetic systems. Finally, martensitic phase transformations are a typical solid-state phenomenon. Once initiated, they proceed almost instantaneously, practically at the speed of sound, and allow remarkable applications such as shape-memory alloys.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2014-01-31
14:15 - 15:45
W. Dvorak
(Forschungsgruppe Theory and Applications of Algorithms, University of Vienna)
Uniform Price Strategies to Exploit Positive Network Externalities. Joint work with: Ludek Cigler, Monika Henzinger, Martin Starnberger
Abstract
Assume a seller wants to sell a digital product in a social network where nodes represent clients and edges represent a friend-like relationship between them. Assume further that the value of the item for a buyer has positive network externalities, i.e., it is a monotone function of the set of neighbors that already have the item. The goal of the seller is to maximize his revenue. Previous work on this problem studies the case where clients are offered the item in sequence and have to pay personalized prices. This is highly infeasible in large scale networks such as the Facebook graph: (1) Offering items to the clients one after the other consumes a large amount of time, and (2) price-discrimination of clients could appear unfair to them and result in negative client reaction or could conflict with legal requirements. On the other side, offering the same price to every client significantly reduces the seller’s revenue. Thus, we study settings where we limit the duration of the selling process and the amount of price discrimination. Specifically, the item is offered in parallel to multiple clients at the same time and at the same price. This is called a round. We show that with O(log n) rounds, where n is the number of clients, a constant factor of the revenue with price discrimination can be achieved and that this is not possible with o(log n) rounds. Moreover we show that it is APX-hard to maximize the revenue even if the externalities in the clients’ valuation functions are very restricted, and we give constant factor approximation algorithms for various further settings of limited price discrimination.
Medical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2014-01-24
14:15 - 15:45
P. Klimek
(Section for Science of Complex Systems, CeMSIIS, MUW)
Systems Medicine& Big Data - New Frontiers in MedicineMedical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2013-12-13
14:15 - 15:45
M. Sadilek
(Section for Science of Complex Systems, CeMSIIS, MUW)
Models of Synchronization in NetworksMedical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2013-12-06
14:15 - 15:45
A. Chmiel
(Section for Science of Complex Systems, CeMSIIS, MUW)
Manlio De Domenico et.al: Mathematical formulation of multi-layer networks
Abstract
A network representation is useful for describing the structure of a large variety of complexsystems. However, most real and engineered systems have multiple subsystems and layers of connectivity,and the data produced by such systems is very rich. Achieving a deep understandingof such systems necessitates generalizing \traditional" network theory, and the newfound deluge of data now makes it possible to test increasingly general frameworks for the study of networks.In particular, although adjacency matrices are useful to describe traditional single-layer networks,such a representation is insucient for the analysis and description of multiplex and time-dependent networks. One must therefore develop a more general mathematical framework to cope with the challenges posed by multi-layer complex systems. In this paper, we introduce a tensorial framework to study multi-layer networks, and we discuss the generalization of several important network descriptors and dynamical processes|including degree centrality, clustering coecients, eigenvector centrality, modularity, Von Neumann entropy, and di usion|for this framework.
Medical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2013-11-29
14:15 - 15:45
B. Corominas-Murtra
(Section for Science of Complex Systems, CeMSIIS, MUW)
The core structure of complex networks
Abstract
What is the core of a complex network? In this talk we will discuss this crucial question of modern complex networks theory. To start with, we will briefly revise the underlying theory of network decomposition and nested subgraphs. We will then discuss specific core-finding and network decomposition methods. Special emphasis will be given to the K-core, the paradigmatic method of core decomposition. It is worth to note that the K-core is nowadays a source of both mathematical and physical problems, but that it was proposed more than 30 years ago to disentangle the deep structure of social networks. However, this core decomposition mechanism has several limitations that lead to new, more sophisticated methods, like the GK-core or the M-core, which better agree to the notion of core in specific problems, specially those related to social networks. We will finally revise some applications of this formal/algorithmic machinery to real problems, like the understanding of the network dynamics defined by virtual society of the massive on line game 'Pardus'. [1] Seidman, Stephen B. (1983), "Network structure and minimum degree", Social Networks 5 (3): 269–287 [2] Dorogovtsev, S.N.; Goltsev, J.F.F.; Mendes, JF (2006), "k-core organization of complex networks", Physical Review Letters 96 (4): 040601 [3] B Corominas-Murtra, JFF Mendes, RV Solé (2008) "Nested subgraphs of complex networks", Journal of Physics A: Mathematical and Theoretical 41 (38), 385003 [4] Bernat Corominas-Murtra, Benedikt Fuchs, Stefan thurner "B Corominas-Murtra, B Fuchs, S Thurner" arXiv preprint http://arxiv.org/abs/1309.6740 [5] Pol Colomer-de-Simón, M. Ángeles Serrano, Mariano G. Beiró, J. Ignacio Alvarez-Hamelin, Marián Boguñá "Deciphering the global organization of clustering in real complex networks", Scientific Reports 3, Article number: 2517 doi:10.1038/srep02517
Medical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2013-11-22
14:15 - 15:45
J.D. Whitfield
(Faculty of Physics, University of Vienna)
Quantum to classical transitions: application to continuous time Markov processes
Abstract
I will give an detailed introduction to Markov theory in quantum and classical contexts and its relation to the "measurement problem" in quantum mechanics. This is followed by an introduction to some notions in graph theory and random walks. The talk will then centered on our article "Quantum Stochastic Walks" Phys. Rev. A, vol 81 page 022323 (2010) and the axiomatic introduction of the quantum stochastic walk. We will then discuss related results on thermodynamics, directed quantum transport, and Lieb-Robinson bounds.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2013-11-15
14:15 - 15:45
S. Poledna
(Section for Science of Complex Systems, CeMSIIS, MUW)
Controlling Financial NetworksMedical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2013-11-08
13:00 - 14:00
A. Bazzani
(National Institute of Physics and Astronomy, University of Bologna)
Statistics of human mobility in Italian traffic dataMedical University of Vienna, Complex Systems Group, seminar room, Spitalgasse 23, 1090 Vienna
2013-11-08
14:15 - 15:45
B. Baumgartner
(University of Vienna)
Irreversible Quantum DynamicsUniversität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2013-10-18
R. Hanel
(Section for Science of Complex Systems, CeMSIIS, MUW)
Maximum Entropy for Aging Complex Systems
Abstract
Statistical mechanics of many statistical systems allows to asymptotically replace expectation values by the so called `maximum configuration'. Sampling processes, where the probabilities of observing a system in particular states evolves stationary, can be described by the reduced Boltzmann entropy that in such cases takes the functional form of Shannon entropy. The probability of observing a non Markovian, aging system in a certain state is by definition not a stationary process and Boltzmann entropy of such systems becomes non extensive. The `maximum configuration' argument on the other hand still holds also for sufficiently large aging systems. Using that entropy is a function that only depends on the frequencies of observing the system in a particular state allows to show that the reduced Boltzmann entropy of aging systems takes the functional form of generalized entropies, as for instance Tsallis entropy.
Universität Wien, Fakultät für Physik, Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 1090 Wien
2013-10-04
14:15 - 15:45
K. Hlavackova-Schindler
(Bioinformatcis, Boku University Vienna)
Equivalence of Granger Causality and Transfer: A Generalization
Abstract
Barnett et al. in 2009 proved that Granger causality and transfer entropy causality measure are equivalent for time series which have a Gaussian distribution. Granger causality test is linear, while transfer entropy a non-linear test. Many biological and physical mechanisms show to have non-Gaussian distributions. In this paper we investigate under which conditions on probability density distributions of the data can the equivalence of the two causality measures be extended. In the complexity sense ”cheaper” linear Granger test can be applied for detection of causality in time series satisfying these conditions. These results have an impact on causality detection in common biological and physical time series.
Medical University of Vienna, Informatics Library, Spitalgasse 23, 1090 Vienna, BT88, E03
2013-03-05
13:00 - 14:00
S. Thurner
(Section for Science of Complex Systems)
Preliminary meeting to "Complex Systems II - Applications" lecture & exerciseInformatics Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-07-27
12:15 - 13:45
K. Goh
(Dept. of Physics, Korea University, Seoul)
Processes on Multiplex NetworksSeminar room COSY, 1090 Vienna, Spitalgasse 23, BT86 E03
2012-06-29
14:00-15:30
G. Kelnhofer
(Universität Wien)
Thermal quantum (gauge) field theoryErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität WIen, Boltzmanngasse 5/5.St., 1090 Wien
2012-06-22
14:15 -15:45
C. Tsiapalis
(Section for Science of Comlex Systems, Medical University of Vienna)
Citizen ScienceInformatics Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-06-15
H. Hüffel
(Fakultät für Physik, Universität Wien)
Quantum (gauge) field theory on bipartite latticesErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität WIen, Boltzmanngasse 5/5.St., 1090 Wien
2012-06-01
14:15 -15:45
M. Schoelling
(Section for Science of Comlex Systems, Medical University of Vienna)
How deterministic is gene transcription?Informatics Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-05-11
14:15 -15:45
B. Fuchs
(Section for Science of Comlex Systems, Medical University of Vienna)
Basic Properties of Complex NetworksInformatics Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-05-04
14:00-15:30
L. Hingerl
(Universität Wien)
Unaboidable order in nonequilibrium systemsErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität WIen, Boltzmanngasse 5/5.St., 1090 Wien
2012-04-27
14:15 - 15:45
P. Klimek
(Section for Science of Complex Systems, Medical University of Vienna)
Linear Response TheoryInformatics Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-04-20
14:15 -15:45
S. Poledna
(Section for Science of Comlex Systems, Medical University of Vienna)
What is Fisher Information?Informatics Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-03-30
14:00-15:30
F. Harbich
(Universität Wien)
White noise limits of multiplicative colored noiseErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität WIen, Boltzmanngasse 5/5.St., 1090 Wien
2012-03-23
14:00-15:30
M. Sadilek
(Universität Wien)
Spectral analysis of white noiseErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität WIen, Boltzmanngasse 5/5.St., 1090 Wien
2012-03-16
14:00 - 15:00
E. Feireisl
(Institute of Mathematics, Academy of Sciences of the Czech Republic, Prague; ESI Wien)
Mathematics of complete fluid systemsErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität WIen, Boltzmanngasse 5/5.St., 1090 Wien
2012-03-01
13:00
Vorbesprechung LVs SS 2012
(Institut für Wissenschaft Komplexe Systeme, Medizinische Universität Wien)
Seminarraum Inst. f. Wiss. Kompl. Systeme, 9., Spitalg. 23, BT 86, 3. St.
2012-01-27
14:15 -15:45
B. Fuchs
(Section for Science of Complex Systems, Medical University of Vienna)
Progress Report on Group Formation and Dynamics in the Pardus GameLibrary, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2012-01-20
14:15-15:45
R. Hanel
(Section for Science of Complex Systems, Medical University of Vienna)
Entropy of a Non-Extensive Spin ModelLibrary, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2011-12-16
14:00-15:30
M. Schoelling
(Section for Science of Complex Systems, Medical University of Vienna)
Reasoning about cellular diversity within a sequentially linear regulatory network model Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2011-12-02
14:00-15:30
M. Szell
(Section for Science of Complex Systems, Medical University of Vienna)
Recent Developments in Socio-dynamicsLibrary, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2011-11-25
14:00-15:30
S. Poledna
(Section for Science of Complex Systems, Medical University of Vienna)
The Role of Leverage in a World of Perfect Hedging
Abstract
We use a toy model of the financial market to test the efficiency and dangers of credit regulation schemes. We find that Basle-type regulation works fine in situations of low leverage levels in the financial system, however they become destabilizing in scenarios with realistic leverage level. We further design an ideal world, where all leverage introduced risk is hedged with options. Even by assuming that option writers never default, we see that introducing the heavy requirement of complete hedging does not make the system systemically more secure.
Library, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2011-11-04
14:15 - 15:45
P. Klimek
(Section for Science of Complex Systems, Medical University of Vienna)
Empirical Confirmation of Creative DestructionSeminar room no. 513, CeMSIIS, Medical University of Vienna, building 88, level 3
2011-10-25
14:00-15:30
Vorbesprechung
(Institut für Wissenschaft Komplexe Systeme, Medizinische Universität Wien)
Lehrveranstaltungen WS 2011/12Seminarraum Inst. f. Wiss. Kompl. Systeme, 9., Spitalg. 23, BT 86, 3. St.
2011-07-01
14:30-16:00
R. Sinatra
(Section for Complex Systems, Medical University of Vienna)
Entropy rate of random walks on networks
Abstract
In the last decade increasing attention has been devoted to the study of random walks on complex topologies. Various features of random walks on networks, such as passage times and spectral properties have been investigated, and random walks have also been used to to detect communities, to evaluate centrality of nodes and to coarse-grain graphs. Another quantity recently considered for the study of random walks is the entropy rate, a measure used to characterize the mixing properties of a stochastic process. In this talk we will first discuss some of the properties of random walks which might have many relevant applications. In particular, we will consider biased random walks, i.e. random walks with a jumping probability which depends on some properties of target node. We will then focus on designing biased random walks with maximal entropy rate on a given graph, i.e. choosing the transition probabilities of the random walk in such a way that the random walkers are maximally dispersing in the graph, exploring every possible walk with equal probability. Although in principle the optimization of the entropy rate requires that a walker has, at each time step, a global information on the structure of the entire graph, information which is often unavailable, we will demonstrate that it is always possible to construct maximal-entropy random walks by defining a set of transition probabilities that are markovian and that rely only local information on the graph structure.
Seminar room no. 513, CeMSIIS, Medical University of Vienna, building 88, level 3, Spitalgasse 23, 1090 Vienna
2011-06-17
14:30-16:00
R. Winkler
(Institut für Diskrete Mathematik, Technische Universität Wien)
Mittelwerte sind wahrscheinlich, doch Extrema sind typisch - Bemerkungen zum Antagonismus von Maß und Kategorie
Abstract
Zentrale Teile der Stochastik kreisen um das Gesetz der großen Zahlen, wonach (bereits unter schwachen Voraussetzungen) die Konvergenz von Mittelwerten gegen den Erwartungswert fast sicher ist. Aus topologischer Sicht, d.h. im Sinne Bairescher Kategorien, ist jedoch ein gänzlich konträres Verhalten typisch. Der allgemeine mathematische Hintergrund dieses Phänomens soll ebenso beleuchtet werden wie einige charakteristische Beispiele.
Medizinische Universität, Bauteil 88, Seminarraum 513, Ebene 3, Spitalgasse 23, 1090 Wien
2011-06-10
14:30-16:00
N.N.
(Institut für Wissenschaft Komplexe Systeme, Medizinische Universität Wien)
Studenten-KurzvortragBibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Medizinische Universität Wien, Bauteil 88, Ebene 3
2011-06-03
14:30-16:00
N.N.
(Institut für Wissenschaft Komplexe Systeme, Medizinische Universität Wien)
Studenten-KurzvortragBibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Medizinische Universität Wien, Bauteil 88, Ebene 3
2011-05-27
14:30-16:00
N.N.
(Institut für Wissenschaft Komplexe Systeme, Medizinische Universität Wien)
Studenten-KurzvortragBibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Medizinische Universität Wien, Bauteil 88, Ebene 3
2011-05-20
14:30-16:00
Ch. Likos
(Fakultät für Physik, Universität Wien)
Electrostatics and soft matter: from star-branched polyelectrolytes to patchy colloidsErwin Schrödinger Hörsaal, Fakultät für Physik, 9., Boltzmanngasse 5, 5.Stock
2011-05-13
14:00-15:30
B. Kuzmany
(Doktoratskolleg Galizien, Universität Wien)
Physik und Technologie von GraphenMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2011-05-06
14:30-16:00
C. Dellago
(Fakultät für Physik, Universität Wien)
Studying rare events with transition path samplingErwin Schrödinger Hörsaal, Fakultät f. Physik, Universität Wien, 9., Boltzmanngasse 5, 5. Stock
2011-04-29
14:30-16:00
H. Posch
(Computergestützte Physik, Universität Wien)
Stochastic and dynamical computer thermostatsMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2011-04-15
14:30-16:00
P. Walther
(ÖAW, Inst. f. Quantenoptik u. Quanteninformation)
Photonic quantum simulation of frustration in chemical and physical systemsUniversität Wien, Fakultät für Physik Erwin Schrödinger Hörsaal, Boltzmanngasse 5 / 5. Stock, 1090 Wien
2011-04-01
14:00-15:30
K. Temme
(Universität Wien)
Thermal States on a Quantum ComputerMedizinische Universität, Bauteil 88, Seminarraum 513, Ebene 3
2011-03-18
14:30-16:00
R. Hanel
(Section for Complex Systems)
Generalized Entropy and Extensivity
Abstract
A short introduction to the concept of generalized entropies: The necessity of generalized entropies is not primarily grounded in alternative means to reproduce particular types of observed distribution functions from some modified maximum entropy principle - but by the concept of Extensivity. By relaxing the axioms of Information Theory an axiomatic approach towards generalized entropies can be taken. The generic functional form of generalized entropies can be deduced as well as conditions which allow to determine which entropy will be the extensive entropy of some system - given the knowledge of how phase-space expands as a system is enlarged.
Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Medizinische Universität Wien, Bauteil 88, Ebene 3
2011-03-17
15:00
M. Schoelling
(Section for Complex Systems)
Exact Matrix Completion Using the Singular Value Threshold AlgorithmBibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Medizinische Universität Wien, Bauteil 88, Ebene 3
2011-03-04
11:00
Lehrveranstaltungen SS 2011 Vorbesprechung
(Section for Complex Systems)
Seminar room BT 86, E 03, Spitalgasse 23, 1090 Vienna
2011-02-04
14:00-15:00
A. Lörincz
(Eötvös Loránd Univ., Dept. of Software Technol. a. Methodol.)
Tools for CHI: From face tracking and reinforcement learning to optimization of typing tool DasherSeminarraum BT 86, Ebene 3
2011-01-28
14:30-16:00
S. Poledna
(Medical University of Vienna)
Danger of leverage in a world of perfect hedgingMedizinische Universität, Bauteil 88, Seminarraum 513, Ebene 3
2011-01-14
14:00-15:30
M. Schoelling
(Medical University of Vienna)
Gene Expression Regulation - from DNA to RNA
Abstract
The regulation of gene expression in live-forms is subject to high > dynamics and nonlinearities. > To create a mathematical model of these systems biological processes > must be reflected adequately. > This talk will handle the biological foundations of gene expression from > DNA to RNA including eukaryotic characteristics like RNA splicing with > respect to the influence on the mathematical model.
Medizinische Universität, Bauteil 88, Seminarraum 513, Ebene 3
2011-01-07
14:30-16:00
M. Poechacker
(Medical University of Vienna)
Stability by adapted dimensionality of dynamics in a minimally non-linear model of gene regulationMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2010-12-17
14:30-16:00
M. Szell
(Medical University of Vienna)
Mobility of human-controlled characters on a synthetic network
Abstract
We study long-time mobility of human-controlled characters on a network-shaped universe of a massive multiplayer online game. We take a number of mobility measurements and compare them with measures of simulated random walkers on the same topology. Mobility of players is sub-diffusive - the mean squared displacement follows a power law with exponent 0.4 - and significantly deviates from mobility patterns of random walkers. Mean first passage times and transition counts relate via a power-law with slope -1/3. We compare our results with studies where human mobility was measured via mobile phone data and find striking similarities.
Medizinische Universität, Bauteil 88, Seminarraum 513, Ebene 3
2010-12-03
14:30-16:00
P. Klimek
(Medical University of Vienna)
An Evolutionary Economics Model for Innovation ProcessesMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2010-11-19
11:00-12:00
M. D'Errico
(Medical University of Vienna)
The economy of the game PardusSeminarraum BT 86
2010-11-19
14:30-16:00
H. Rumpf
(Universität Wien)
Is Gravity an Entropic Force?Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 5. Stock
2010-10-29
11:00-12:30
V. Traag
(Universite Catholique de Louvain)
Cooperation, Reputation & Gossiping
Abstract
Explaining the breadth of human cooperation is a prime challenge in both the social sciences and biology. One possible mechanism focuses on the role of reputation in cooperation. Usually it is assumed that such a reputation is objective--that is, the same for all agents. We develop a model where reputations are private and synchronized through the sharing of information, i.e. gossiping. Interpreting cooperation between two agents as a positive link and defection as a negative link, this model shows an interesting connection to social balance theory. Furthermore, we study its evolutionary stability.
Medizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik und Intelligente Systeme', Ebene 3
2010-10-22
14:30-16:00
F. Verstraete
(Universität Wien)
Renyi entropies and Hypothesis testing for quantum systemsErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2010-06-25
14:30-16:00
S. Thurner
(Medical University of Vienna)
Lecture Series Entropy 2010:
Classification of complex statistical systems in terms of stability and a thermodynamical derivation of their entropy and distribution functions
Abstract
Strongly interacting statistical systems – complex systems in particular – can change their macro- scopic properties merely as a function of the number of their constituents. Examples include neurons, state-forming insects, financial markets, etc. where systemic properties of small systems can differ drastically from those of a large system built from the same components. The origin of this property is not understood on fundamental grounds. Here we explore this phenomenon from first principles within a thermodynamical framework, by asking about the consequences of bringing interacting sub- systems in thermal contact, where the first three Kinchin axioms hold but the 4th is violated. We show that all sufficiently interacting statistical systems fall into two categories: systems which are asymptotically stable, and those which are asymptotically unstable, meaning that small changes in system size can lead to a drastic increase in entropy. We argue that complex systems belong to this unstable class which make drastic qualitative changes possible as a function of system size. Under the same conditions we then derive the unique asymptotic entropy, Scd = Gamma (d + 1,1 - c ln pi) (c, d constants) which covers all equivalence classes of asymptotically stable and unstable, i.e. all interacting and non-interacting systems. The corresponding distribution functions are special forms of Lambert-W exponentials. As special cases they contain Boltzmann, stretched exponential and Tsallis distributions (power-laws) – all widely abundant in nature. This is, to our knowledge, the first ab initio justification for the existence of generalized entropies.
Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 5. Stock
2010-06-24
P. Klimek
(Medical University of Vienna)
DefensioErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2010-06-23
16:00-17:30
C. Brukner
(Universität Wien)
Lecture Series Entropy 2010:
Information Complementary Relation in Quantum Mechanics
Josef Stefan Hörsaal, Boltzmanngasse 5, A-1090 Vienna, 3rd floor
2010-06-18
14:30-16:00
C. Tsallis
(CBPF Rio de Janeiro and Santa Fe Institute)
Lecture Series Entropy 2010:
Statistical Mechanics of Systems lying outside the domain of validity of the Boltzmann-Gibbs theory
Abstract
The celebrated statistical mechanics introduced by Boltzmann and Gibbs more than one century ago lie (for classical systems, for instance) on hypotheses such as ergodicity and mixing. Strongly chaotic systems, with positive maximum Lyapunov exponent, satisfy requirements of this sort. Within this realm, relevant random variables are probabilistically independent or nearly so. It is for such situations, and related quantum ones, that the central limit theorem and the standard entropy (Boltzmann, Gibbs, von Neumann, Shannon) exhibit their well known utility and connections with classical thermodynamics. What can be done outside this world? Can we approach such anomalous, and nevertheless ubiquitous, cases on thermostatistical grounds similar to the usual ones? For wide classes of such systems the answer appears to be positive, by appropriately generalizing the entropy and, consistently, the central limit theorem. Some central concepts as well as typical verifications and applications for natural, artificial and social systems will be briefly presented. BIBLIOGRAPHY: (i) C. Tsallis, Entropy, in Encyclopedia of Complexity and Systems Science (Springer, Berlin, 2009); (ii) C. Tsallis, Introduction to Nonextensive Statistical Mechanics - Approaching a Complex World (Springer, New York, 2009); (iii) S. Umarov, C. Tsallis, M. Gell-Mann and S. Steinberg, J. Math. Phys. 51, 033502 (2010); (iv) CMS Collaboration, J. High Energy Phys. 02, 041 (2010); (v) http://tsallis.cat.cbpf.br/biblio.htm
Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 5. Stock
2010-06-11
14:30-16:00
E. Ortega
(Universität Wien)
Lecture Series Entropy 2010:
Entropy in Many Body Quantum Systems
Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 5. Stock
2010-06-09
16:00-17:30
J. Yngvason
(Universität Wien)
Lecture Series Entropy 2010:
The Entropy of Classical Thermodynamics
Josef Stefan Hörsaal, Boltzmanngasse 5, A-1090 Vienna, 3rd floor
2010-05-18
14:30-16:00
R. Hanel
(Medical University of Vienna)
A simple model of Evolutionary dynamics: Minimally nonlinear systems as model of genetic regulatory network dynamics. Medizinische Universität, Bauteil 86, Ebene 3
2010-05-14
14:00-15:30
M. Poechacker
(Medical University of Vienna)
Stability Analysis of Random Catalytic Network Dynamics in a Linear Model of Gene-RegulationMedizinische Universität, Bauteil 86, Ebene 3
2010-05-07
15:15-16:00
M. Szell
(Medical University of Vienna)
A Multiplex View of Organization and Social Balance in Large-scale Social Networks
Abstract
Human societies can be regarded as large numbers of locally interacting agents, connected by a broad range of social and economic relationships. These relational ties represent e.g. the feeling a person has for another (friendship, enmity, love), communication, exchange of goods, or behavioral interactions. Each type of relation spans a social network on its own. A whole society can be understood systemically only by uncovering interactions between different networks. Here we analyze a complete, multi-relational social network of a society consiting of over 300,000 players of a massive multiplayer online game. We extract networks of six different types of one-to-one interactions between the players. Three of them carry a positive connotation (friendship, communication, trade), three a negative (enmity, armed aggression, punishment). We first analyze these types of networks as separate entities and find that negative interactions differ from positive interactions by their lower reciprocity, weaker clustering and fatter-tail degree distribution. We then proceed to explore how the inter-dependence of different network types determines the organization of the social system. In particular we study correlations and overlap between different types of links and demonstrate the tendency of individuals to play different roles in different networks. As a demonstration of the power of the approach we present the first empirical large-scale verification of the long-standing structural balance theory, by focusing on the specific multiplex network of friendship and enmity relations.
Erwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2010-05-07
14:30-15:15
M. Göll
(Universität Wien)
Lattice Models as Algebraic Dynamical systems, part IIErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5. Stock
2010-04-23
14:30-16:00
C. Losert-Valiente Kroon
(Erwin Schrödinger International Institute for Mathematical Physics)
Stochastic Population Dynamics in Astrochemistry and Aerosol ScienceMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik und Intelligente Systeme', Ebene 3
2010-04-16
14:30-16:00
M. Göll
(Universität Wien)
Lattice models as algebraic dynamical systemsErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2010-03-26
14:30-16:00
R. Hanel
(Medical University of Vienna)
Minimally non-linear systems: Toy genetic regulatory network dynamics at the edge of chaosMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2010-03-05
14:30-16:00
P. Schreivogl
(Universität Wien)
Topological Strings and the Melting CrystalErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2010-01-29
14:30-16:00
H. Hüffel
(Universität Wien)
From Classical Statistical Physics to Quantum Mechanics: Dimers and Crystal MeltingMedizinische Universität, Bauteil 88, Bibliothek 'Zentrum für Medizinische Statistik, Informatik, und Intelligente Systeme', Ebene 3
2010-01-15
14:30-16:00
M. Sadilek
(Universität Wien)
Quantenaspekte aktiver Bewegung und anharmonische Effekte in KristallenErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2010-01-08
14:30-16:00
P. Klimek
(Medical University of Vienna)
Evolutionary DynamicsMedizinische Universität, Bauteil 86, Ebene 2
2009-12-11
14:00-15:30
H. Meyer-Ortmanns
(Jacobs University, Bremen)
Stochastic Transport Processes on NetworksMedizinische Universität, Bauteil 86, Ebene 2
2009-12-04
14:30-16:00
A. Glück
(Universität Wien)
Swarms with canonical active Brownian motionErwin Schrödinger Hörsaal, Boltzmanngasse 5, 5.Stock
2009-11-20
14:30-16:00
M. Szell
(Medical University of Vienna)
Measuring social dynamics in a massive multiplayer online game
Abstract
Quantification of human group-behavior has so far defied an empirical, falsifiable approach. This is due to tremendous difficulties in data acquisition of social systems. Massive multiplayer online games (MMOG) provide a fascinating new way of observing hundreds of thousands of simultaneously socially interacting individuals engaged in virtual economic activities. We have compiled a data set consisting of practically all actions of all players over a period of three years from a MMOG played by 300,000 people. This large-scale data set of a socio-economic unit contains all social and economic data from a single and coherent source. Players have to generate a virtual income through economic activities to 'survive' and are typically engaged in a multitude of social activities offered within the game. Our analysis of high-frequency log files focuses on three types of social networks, and tests a series of social-dynamics hypotheses. In particular we study the structure and dynamics of friend-, enemy- and communication networks. We find striking differences in topological structure between positive (friend) and negative (enemy) tie networks. All networks confirm the recently observed phenomenon of network densification. We propose two approximate social laws in communication networks, the first expressing betweenness centrality as the inverse square of the overlap, the second relating communication strength to the cube of the overlap. These empirical laws provide strong quantitative evidence for the Weak ties hypothesis of Granovetter. Further, the analysis of triad significance profiles validates well-established assertions from social balance theory. We find overrepresentation (underrepresentation) of complete (incomplete) triads in networks of positive ties, and vice versa for networks of negative ties. Empirical transition probabilities between triad classes provide evidence for triadic closure with extraordinarily high precision. For the first time we provide empirical results for large-scale networks of negative social ties. Whenever possible we compare our findings with data from non-virtual human groups and provide further evidence that online game communities serve as a valid model for a wide class of human societies. With this setup we demonstrate the feasibility for establishing a 'socio-economic laboratory' which allows to operate at levels of precision approaching those of the natural sciences.
Medizinische Universität, Bauteil 86, Ebene 2
2009-09-10
11:00-12:30
R. Sinatra
(University of Catania)
Networks of recurrent motifs from sequences of symbols
Abstract
We present a general method to convert an ensemble of symbolic sequences into a weighted directed network. The nodes of the network are short motifs of the ensemble, while the directed links and their weights are defined from statistically significant co-occurrences of two motifs in the same sequence. The method is shown to be able in correlating sequences with functions in protein data, and might find useful applications for structure discovery as well as in computational linguistic and in the theory of dynamical systems.
Medizinische Universität, Bauteil 86, Ebene 2



Seminars before 2009-09 are not available.