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Mathematical models for emerging disease

It has been nearly 25 years since the publication of Infectious Disease of Humans, the “vade mecum” of mathematical modeling of infectious disease; the proliferation of epidemiological careers that it initiated is now in its fourth generation. Epidemiological models have proved very powerful in shaping health policy discussions. The complex interactions that lead to pathogen (and pest) outbreaks make it necessary to use models to provide quantitative insights into the counterintuitive outcomes that are the rule of most nonlinear systems. Thus, epidemic models are most interesting when they suggest unexpected outcomes; they are most powerful when they describe the conditions that delineate the worst-case unexpected scenario, and provide a framework in which to compare alternative control strategies. But what are the limits of mathematical models and what kinds provide insight into emerging disease?


Mathematical models for emerging disease
Andy Dobson

Science 12 December 2014:
Vol. 346 no. 6215 pp. 1294-1295
http://dx.doi.org/10.1126/science.aaa3441

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Towards synthetic biological approaches to resource utilization on space missions

Towards synthetic biological approaches to resource utilization on space missions | Papers | Scoop.it

This paper demonstrates the significant utility of deploying non-traditional biological techniques to harness available volatiles and waste resources on manned missions to explore the Moon and Mars. Compared with anticipated non-biological approaches, it is determined that for 916 day Martian missions: 205 days of high-quality methane and oxygen Mars bioproduction with Methanobacterium thermoautotrophicum can reduce the mass of a Martian fuel-manufacture plant by 56%; 496 days of biomass generation with Arthrospira platensis and Arthrospira maxima on Mars can decrease the shipped wet-food mixed-menu mass for a Mars stay and a one-way voyage by 38%; 202 days of Mars polyhydroxybutyrate synthesis with Cupriavidus necator can lower the shipped mass to three-dimensional print a 120 m3 six-person habitat by 85% and a few days of acetaminophen production with engineered Synechocystis sp. PCC 6803 can completely replenish expired or irradiated stocks of the pharmaceutical, thereby providing independence from unmanned resupply spacecraft that take up to 210 days to arrive. Analogous outcomes are included for lunar missions. Because of the benign assumptions involved, the results provide a glimpse of the intriguing potential of ‘space synthetic biology’, and help focus related efforts for immediate, near-term impact.


Towards synthetic biological approaches to resource utilization on space missions
Amor A. Menezes, John Cumbers, John A. Hogan, Adam P. Arkin
http://dx.doi.org/10.1098/rsif.2014.0715

Journal of the Royal Society Interface, Volume: 12 Issue: 102

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Effects of the gut microbiota on bone mass

•Studies in germ-free (GF) mice demonstrate that the gut microbiota (GM) is a regulator of bone mass.
•The GM affects bone mass via effects on the immune status, which in turn regulates osteoclastogenesis.
•Probiotic and prebiotic treatments may impact GM composition and affect bone metabolism.
•The GM may be a novel therapeutic target for osteoporosis.


Effects of the gut microbiota on bone mass
Claes Ohlsson, Klara Sjögren

Trends in Endocrinology & Metabolism

http://dx.doi.org/10.1016/j.tem.2014.11.004
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Statistical Physics of Adaptation

All living things exhibit adaptations that enable them to survive and reproduce in the natural environment that they inhabit. From a biological standpoint, it has long been understood that adaptation comes from natural selection, whereby maladapted individuals do not pass their traits effectively to future generations. However, we may also consider the phenomenon of adaptation from the standpoint of physics, and ask whether it is possible to delineate what the difference is in terms of physical properties between something that is well-adapted to its surrounding environment, and something that is not. In this work, we undertake to address this question from a theoretical standpoint. Building on past fundamental results in far-from-equilibrium statistical mechanics, we demonstrate a generalization of the Helmholtz free energy for the finite-time stochastic evolution of driven Newtonian matter. By analyzing this expression term by term, we are able to argue for a general tendency in driven many-particle systems towards self-organization into states formed through exceptionally reliable absorption and dissipation of work energy from the surrounding environment. Subsequently, we illustrate the mechanism of this general tendency towards physical adaptation by analyzing the process of random hopping in driven energy landscapes.


Statistical Physics of Adaptation
Nikolai Perunov, Robert Marsland, Jeremy England

http://arxiv.org/abs/1412.1875

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Invasion of cooperation in scale-free networks: Accumulated vs. average payoffs

It is well known that cooperation cannot be an evolutionary stable strategy for a non-iterative game in a well-mixed population. In contrast, structured populations favor cooperation since cooperators can benefit each other by forming local clusters. Previous studies have shown that scale-free networks strongly promote cooperation. However, little is known about the invasion mechanism of cooperation in scale-free networks. To study microscopic and macroscopic behaviors of cooperators' invasion, we conducted computational experiments of the evolution of cooperation in scale-free networks where, starting from all defectors, cooperators can spontaneously emerge by mutation. Since the evolutionary dynamics are influenced by the definition of fitness, we tested two commonly adopted fitness functions: accumulated payoff and average payoff. Simulation results show that cooperation is strongly enhanced with the accumulated payoff fitness compared to the average payoff fitness. However, the difference between the two functions decreases as the average degree increases. Moreover, with the average payoff fitness, low-degree nodes play a more important role in spreading cooperative strategies compared to the case of the accumulated payoff fitness.


Invasion of cooperation in scale-free networks: Accumulated vs. average payoffs
Genki Ichinose, Hiroki Sayama

http://arxiv.org/abs/1412.2311

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Understanding Human Mobility from Twitter

We analyse a large dataset with more than six million get-tagged tweets posted in Australia, and demonstrate that Twitter can be a reliable source for studying human mobility patterns. We find that crucial information of human mobility, such as its multi-scale and multi-modal nature, returning tendency and regularity, as well as the heterogeneous moving scale among individuals, can be extracted from geo-tagged tweets using various statistical indicators. Our analysis of the spatial-temporal patterns for people with different moving scales shows that long-distance travellers have highly concentrated urban movements. Our study not only deepens overall understanding of human mobility but also opens new avenues for tracking human mobility.


Understanding Human Mobility from Twitter
Raja Jurdak, Kun Zhao, Jiajun Liu, Maurice AbouJaoude, Mark Cameron, David Newth

http://arxiv.org/abs/1412.2154

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Economic complexity: A different way to look at the economy

Economic complexity: A different way to look at the economy - Foundations & Frontiers - Medium

By W. Brian Arthur; External Professor, Santa Fe Institute; Visiting Researcher, Palo Alto Research Center. 

Economics is a stately subject, one that has altered little since its modern foundations were laid in Victorian times. Now it is changing radically. Standard economics is suddenly being challenged by a number of new approaches: behavioral economics, neuroeconomics, new institutional economics. One of the new approaches came to life at the Santa Fe Institute: complexity economics.

Complexity economics got its start in 1987 when a now-famous conference of scientists and economists convened by physicist Philip Anderson and economist Kenneth Arrow met to discuss the economy as an evolving complex system. That conference gave birth a year later to the Institute’s first research program – the Economy as an Evolving Complex System – and I was asked to lead this. That program in turn has gone on to lay down a new and different way to look at the economy.


Via Alessandro Cerboni
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Fàtima Galan's curator insight, December 10, 2014 8:43 AM

"Where does complexity economics find itself now? Certainly, many commentators see it as steadily moving toward the center of economics. And there’s a recognition that it is more than a new set of methods or theories: it is a different way to see the economy. It views the economy not as machine-like, perfectly rational, and essentially static, but as organic, always exploring, and always evolving – always constructing itself."

Jason Leong's curator insight, January 2, 2015 11:34 PM

"Where does complexity economics find itself now? Certainly, many commentators see it as steadily moving toward the center of economics. And there’s a recognition that it is more than a new set of methods or theories: it is a different way to see the economy. It views the economy not as machine-like, perfectly rational, and essentially static, but as organic, always exploring, and always evolving – always constructing itself."

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Natural gas: The fracking fallacy

Natural gas: The fracking fallacy | Papers | Scoop.it

The United States is banking on decades of abundant natural gas to power its economic resurgence. That may be wishful thinking.

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A deceleration model for bicycle peloton dynamics and group sorting

Extending earlier computer models of bicycle peloton dynamics, we add a deceleration parameter by which deceleration magnitude varies as a function of cyclist strength. This model is validated by applying speed data from a mass-start race composed of 14 cyclists, and running simulation trials using 14 simulated cyclists that generated positional profiles which compare well with the positional profiles observed in the actual mass-start race data. Keeping constant the speed variation profile from the mass-start race as introduced into the simulation, a set of simulation experiments were run, including: varying the number of cyclists; varying the duration of a single near-threshold output event; and varying the course elevation. The results consistently show sorting of pelotons into smaller groups whose mean fitness corresponds with relative group position, i.e. fitter groups are closer to the front. Sorting of pelotons into fitness-related groups provides insight into the mechanics of similar group divisions within biological collectives in which members present heterogeneous physiological fitness capacities.


Trenchard, H., Ratamero, E., Richardson, A., Perc, M. A deceleration model for peloton dynamics and group sorting,  App. Math. and Computation, Volume 251, 15 January 2015, Pages 24–34 

http://dx.doi.org/10.1016/j.amc.2014.11.031

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The Entropy of Attention and Popularity in YouTube Videos

The vast majority of YouTube videos never become popular, languishing in obscurity with few views, no likes, and no comments. We use information theoretical measures based on entropy to examine how time series distributions of common measures of popularity in videos from YouTube's "Trending videos" and "Most recent" video feeds relate to the theoretical concept of attention. While most of the videos in the "Most recent" feed are never popular, some 20% of them have distributions of attention metrics and measures of entropy that are similar to distributions for "Trending videos". We analyze how the 20% of "Most recent" videos that become somewhat popular differ from the 80% that do not, then compare these popular "Most recent" videos to different subsets of "Trending videos" to try to characterize and compare the attention each receives.


The Entropy of Attention and Popularity in YouTube Videos
Jonathan Scott Morgan, Iman Barjasteh, Cliff Lampe, Hayder Radha

http://arxiv.org/abs/1412.1185

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On the Complexity and Behaviour of Cryptocurrencies Compared to Other Markets

We show that the behaviour of Bitcoin has interesting similarities to stock and precious metal markets, such as gold and silver. We report that whilst Litecoin, the second largest cryptocurrency, closely follows Bitcoin's behaviour, it does not show all the reported properties of Bitcoin. Agreements between apparently disparate complexity measures have been found, and it is shown that statistical, information-theoretic, algorithmic and fractal measures have different but interesting capabilities of clustering families of markets by type. The report is particularly interesting because of the range and novel use of some measures of complexity to characterize price behaviour, because of the IRS designation of Bitcoin as an investment property and not a currency, and the announcement of the Canadian government's own electronic currency MintChip.


On the Complexity and Behaviour of Cryptocurrencies Compared to Other Markets
Daniel Wilson-Nunn, Hector Zenil

http://arxiv.org/abs/1411.1924

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Social and Natural Sciences Differ in Their Research Strategies, Adapted to Work for Different Knowledge Landscapes

Do different fields of knowledge require different research strategies? A numerical model exploring different virtual knowledge landscapes, revealed two diverging optimal search strategies. Trend following is maximized when the popularity of new discoveries determine the number of individuals researching it. This strategy works best when many researchers explore few large areas of knowledge. In contrast, individuals or small groups of researchers are better in discovering small bits of information in dispersed knowledge landscapes. Bibliometric data of scientific publications showed a continuous bipolar distribution of these strategies, ranging from natural sciences, with highly cited publications in journals containing a large number of articles, to the social sciences, with rarely cited publications in many journals containing a small number of articles. The natural sciences seem to adapt their research strategies to landscapes with large concentrated knowledge clusters, whereas social sciences seem to have adapted to search in landscapes with many small isolated knowledge clusters. Similar bipolar distributions were obtained when comparing levels of insularity estimated by indicators of international collaboration and levels of country-self citations: researchers in academic areas with many journals such as social sciences, arts and humanities, were the most isolated, and that was true in different regions of the world. The work shows that quantitative measures estimating differences between academic disciplines improve our understanding of different research strategies, eventually helping interdisciplinary research and may be also help improve science policies worldwide.


Jaffe K (2014) Social and Natural Sciences Differ in Their Research Strategies, Adapted to Work for Different Knowledge Landscapes. PLoS ONE 9(11): e113901. http://dx.doi.org/10.1371/journal.pone.0113901

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tom cockburn's curator insight, December 4, 2014 9:25 AM

Intriguing study worth a second look

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Influence of sociodemographic characteristics on human mobility

Human mobility has been traditionally studied using surveys that deliver snapshots of population displacement patterns. The growing accessibility to ICT information obtained from portable digital media has recently opened the possibility of going beyond such fixed pictures, exploring human behavior at high spatio-temporal resolutions. Mobile phone records, geolocated tweets, check-ins from Foursquare or geotagged photos, have contributed to this purpose at different scales from cities to countries and in different areas of the world. Many of these previous works have lacked, however, details on the attributes of the individuals. In this work, we analyze credit-card transaction records as mobility proxies and assess the influence of sociodemographic characteristics on the way people move and spend their money in cities. In particular, we focus on Barcelona and Madrid, the two most populated cities of Spain, and by examining the geolocated credit-card transactions of individuals living in the two provinces, we find that consumption habits and mobility patterns vary according to gender, age and occupation. Differences in distance traveled and travel purpose are observed between younger and older people, but, curiously, either between males and females of similar age. While mobility displays some generic features, here we show that sociodemographic characteristics play a relevant role and must be taken into account for human mobility modelization.


Influence of sociodemographic characteristics on human mobility
Maxime Lenormand, Thomas Louail, Oliva G. Cantu-Ros, Miguel Picornell, Ricardo Herranz, Juan Murillo Arias, Marc Barthelemy, Maxi San Miguel, Jose J. Ramasco

http://arxiv.org/abs/1411.7895

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The retail market as a complex system

Aim of this paper is to introduce the complex system perspective into retail market analysis. Currently, to understand the retail market means to search for local patterns at the micro level, involving the segmentation, separation and profiling of diverse groups of consumers. In other contexts, however, markets are modelled as complex systems. Such strategy is able to uncover emerging regularities and patterns that make markets more predictable, e.g. enabling to predict how much a country’s GDP will grow. Rather than isolate actors in homogeneous groups, this strategy requires to consider the system as a whole, as the emerging pattern can be detected only as a result of the interaction between its self-organizing parts. This assumption holds also in the retail market: each customer can be seen as an independent unit maximizing its own utility function. As a consequence, the global behaviour of the retail market naturally emerges, enabling a novel description of its properties, complementary to the local pattern approach. Such task demands for a data-driven empirical framework. In this paper, we analyse a unique transaction database, recording the micro-purchases of a million customers observed for several years in the stores of a national supermarket chain. We show the emergence of the fundamental pattern of this complex system, connecting the products’ volumes of sales with the customers’ volumes of purchases. This pattern has a number of applications. We provide three of them. By enabling us to evaluate the sophistication of needs that a customer has and a product satisfies, this pattern has been applied to the task of uncovering the hierarchy of needs of the customers, providing a hint about what is the next product a customer could be interested in buying and predicting in which shop she is likely to go to buy it.


The retail market as a complex system
Pennacchioli D, Coscia M, Rinzivillo S, Giannotti F, Pedreschi D
EPJ Data Science 2014, 3 :33 (11 December 2014)

http://dx.doi.org/10.1140/epjds/s13688-014-0033-x ;

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Eli Levine's curator insight, December 13, 2014 10:43 PM

With this knowledge and insight into the world that's dawning.  One world must be destroyed in order for the new world to come forth; one segment of society must give way to the new in order to facilitate and ease this transition.

 

The top of society is where and what determines the ease or the possibility of this transition.  That is the point that needs to be altered in order to bring about this new dawn.  

 

Unfortunately, it is the point in society that is least willing, although most capable of change.  They'll cling to illusions and delusions of relative power over people and unsustainable material wealth than allow for everyone, including themselves, to realize something that could truly be wonderful for our lives, our well-being, and our health as living organisms.  This is before we talk about the bottom-up resistance that will be experienced as well, especially if the transition is done badly by the people who are at the top of the given social unit.  A shame that something so relatively simple can be so completely complicated and complex to carry out.

 

Silly world.

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Scratching the surface of martian habitability

Earth and Mars, though formed at the same time from the same materials, look very different today. Early in their histories they evolved through some of the same processes, but at some point their evolutionary paths diverged, sending them in perhaps irrevocably different directions. Knowledge of the factors that contributed to such different outcomes will help to determine how planets become habitable and how common habitable planets may be. The Mars surface environment is harsh today, but in situ measurements of ancient sedimentary rock by Mars Science Laboratory reveal chemical and mineralogical evidence of past conditions that might have been more favorable for life to exist. But chemistry is only part of what is required to make an environment habitable. Physical conditions constrain the chemical reactions that underlie life processes; the chemical and physical characteristics that make planets habitable are thus entangled.


Scratching the surface of martian habitability
Pamela G. Conrad

Science 12 December 2014:
Vol. 346 no. 6215 pp. 1288-1289
http://dx.doi.org/10.1126/science.1259943

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The Information Theory of Individuality

We consider biological individuality in terms of information theoretic and graphical principles. Our purpose is to extract through an algorithmic decomposition system-environment boundaries supporting individuality. We infer or detect evolved individuals rather than assume that they exist. Given a set of consistent measurements over time, we discover a coarse-grained or quantized description on a system, inducing partitions (which can be nested). Legitimate individual partitions will propagate information from the past into the future, whereas spurious aggregations will not. Individuals are therefore defined in terms of ongoing, bounded information processing units rather than lists of static features or conventional replication-based definitions which tend to fail in the case of cultural change. One virtue of this approach is that it could expand the scope of what we consider adaptive or biological phenomena, particularly in the microscopic and macroscopic regimes of molecular and social phenomena.


The Information Theory of Individuality
David Krakauer, Nils Bertschinger, Eckehard Olbrich, Nihat Ay, Jessica C. Flack

http://arxiv.org/abs/1412.2447

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Not Just a Theory—The Utility of Mathematical Models in Evolutionary Biology

Progress in science often begins with verbal hypotheses meant to explain why certain biological phenomena exist. An important purpose of mathematical models in evolutionary research, as in many other fields, is to act as “proof-of-concept” tests of the logic in verbal explanations, paralleling the way in which empirical data are used to test hypotheses. Because not all subfields of biology use mathematics for this purpose, misunderstandings of the function of proof-of-concept modeling are common. In the hope of facilitating communication, we discuss the role of proof-of-concept modeling in evolutionary biology.


Servedio MR, Brandvain Y, Dhole S, Fitzpatrick CL, Goldberg EE, et al. (2014) Not Just a Theory—The Utility of Mathematical Models in Evolutionary Biology. PLoS Biol 12(12): e1002017. http://dx.doi.org/10.1371/journal.pbio.1002017

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Concurrent Bursty Behavior of Social Sensors in Sporting Events

The advent of social media expands our ability to transmit information and connect with others instantly, which enables us to behave as "social sensors." Here, we studied concurrent bursty behavior of Twitter users during major sporting events to determine their function as social sensors. We show that the degree of concurrent bursts in tweets (posts) and retweets (re-posts) works as a good indicator of winning or losing a game. More specifically, our tweet analysis of Japanese professional baseball games in 2013 revealed that social sensors can immediately show reactions to positive and negative events through bursts of tweets, but that positive events are more likely to induce a subsequent burst of retweets. These findings were also confirmed in an analysis of the 2014 FIFA World Cup final. We further showed active interactions among social sensors by constructing retweet networks during a baseball game. The resulting networks commonly exhibited user clusters depending on the baseball team, with a scale-free connectedness that is indicative of hub sensors. Contrary to the well-tested analogy that "Twitter is a mirror of reality," the results of this study imply more dynamic aspects to social sensors, offering new insights into human behavior in a highly connected world.


Concurrent Bursty Behavior of Social Sensors in Sporting Events
Yuki Takeichi, Kazutoshi Sasahara, Reji Suzuki, Takaya Arita

http://arxiv.org/abs/1412.2188

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Pattern formation in multiplex networks

The advances in understanding complex networks have generated increasing interest in dynamical processes occurring on them. Pattern formation in activator-inhibitor systems has been studied in networks, revealing differences from the classical continuous media. Here we study pattern formation in a new framework, namely multiplex networks. These are systems where activator and inhibitor species occupy separate nodes in different layers. Species react across layers but diffuse only within their own layer of distinct network topology. This multiplicity generates heterogeneous patterns with significant differences from those observed in single-layer networks. Remarkably, diffusion-induced instability can occur even if the two species have the same mobility rates; condition which can never destabilize single-layer networks. The instability condition is revealed using perturbation theory and expressed by a combination of degrees in the different layers. Our theory demonstrates that the existence of such topology-driven instabilities is generic in multiplex networks, providing a new mechanism of pattern formation.


Pattern formation in multiplex networks
Nikos E. Kouvaris, Shigefumi Hata, Albert Díaz-Guilera

http://arxiv.org/abs/1412.2923

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Universal Power Law Governing Pedestrian Interactions

Universal Power Law Governing Pedestrian Interactions | Papers | Scoop.it

Human crowds often bear a striking resemblance to interacting particle systems, and this has prompted many researchers to describe pedestrian dynamics in terms of interaction forces and potential energies. The correct quantitative form of this interaction, however, has remained an open question. Here, we introduce a novel statistical-mechanical approach to directly measure the interaction energy between pedestrians. This analysis, when applied to a large collection of human motion data, reveals a simple power law interaction that is based not on the physical separation between pedestrians but on their projected time to a potential future collision, and is therefore fundamentally anticipatory in nature. Remarkably, this simple law is able to describe human interactions across a wide variety of situations, speeds and densities. We further show, through simulations, that the interaction law we identify is sufficient to reproduce many known crowd phenomena.


Universal Power Law Governing Pedestrian Interactions
Phys. Rev. Lett. 113, 238701 – Published 2 December 2014
Ioannis Karamouzas, Brian Skinner, and Stephen J. Guy

http://dx.doi.org/10.1103/PhysRevLett.113.238701

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Liz Rykert's curator insight, December 13, 2014 9:19 PM

Love this kind of research describing the actual patterns of interaction, in this case the space between pedestrians described as the time to potential collision!

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Evolution of the Division of Labor between Genes and Enzymes in the RNA World

The RNA world refers to the stage of early evolution when RNA macromolecules were responsible both for storing hereditary information and performing enzymatic activities. Conflict arises between these two functions, however, as enzymatic activities of the ribozymes are in tradeoff with their replication rates. Here we address this problem by investigating the evolutionary emergence of a primordial transcription-like system in model protocells inhabited by unlinked replicators. Our numerical analysis demonstrates that division of labor between genes and enzymes could have emerged, given that there was a moderate to strong tradeoff between the enzymatic and template efficiency of one strand of the ribozymes. This division of labor results in a strong asymmetry in the numbers of the enzymatic and genetic strands of the macromolecules, in favor of the former. We offer insight into the emergence of the first transcription-like system, which is today characteristic of all known life forms.


Boza G, Szilágyi A, Kun Á, Santos M, Szathmáry E (2014) Evolution of the Division of Labor between Genes and Enzymes in the RNA World. PLoS Comput Biol 10(12): e1003936. http://dx.doi.org/10.1371/journal.pcbi.1003936

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Maximum sustainable yield from interacting fish stocks in an uncertain world: two policy decisions and underlying trade-offs

The case of fisheries management illustrates how the inherent structural instability of ecosystems can have deep-running policy implications. We contrast eleven types of management plans to achieve maximum sustainable yields (MSY) from multiple stocks and compare their effectiveness based on management strategy evaluations (MSE) using complex food webs in their operating models. Plans that primarily target specific stock sizes (B_MSY) consistently led to higher yields than plans to target fishing pressures (F_MSY). A new type of self-optimising control rule, introduced here to conquer uncertainty due to structural instability, led to intermediate yields. Plans to "maximise the yield from each stock separately" in the sense of a Nash equilibrium produced total yields comparable to plans to maximise total harvested biomass, but tended to be more robust to structural instability. Most types of plans outperformed single-species management plans that defined pressure targets without explicitly considering ecological interactions. Our analyses highlight trade-offs between yields, amiability to fair negotiations, and continuity with current approaches in the European context. Based on these results, we recommend directions for future developments of EU fisheries policy.


Maximum sustainable yield from interacting fish stocks in an uncertain world: two policy decisions and underlying trade-offs
Adrian Farcas, Axel G. Rossberg

http://arxiv.org/abs/1412.0199

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Degree correlations in signed social networks

We investigate degree correlations in two online social networks where users are connected through different types of links. We find that, while subnetworks in which links have a positive connotation, such as endorsement and trust, are characterized by assortative mixing by degree, networks in which links have a negative connotation, such as disapproval and distrust, are characterized by disassortative patterns. We introduce a class of simple theoretical models to analyze the interplay between network topology and the superimposed structure based on the sign of links. Results uncover the conditions that underpin the emergence of the patterns observed in the data, namely the assortativity of positive subnetworks and the disassortativity of negative ones. We discuss the implications of our study for the analysis of signed complex networks.


Degree correlations in signed social networks
Valerio Ciotti, Ginestra Bianconi, Andrea Capocci, Francesca Colaiori, Pietro Panzarasa

http://arxiv.org/abs/1412.1024

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Structural Properties of Ego Networks

The structure of real-world social networks in large part determines the evolution of social phenomena, including opinion formation, diffusion of information and influence, and the spread of disease. Globally, network structure is characterized by features such as degree distribution, degree assortativity, and clustering coefficient. However, information about global structure is usually not available to each vertex. Instead, each vertex's knowledge is generally limited to the locally observable portion of the network consisting of the subgraph over its immediate neighbors. Such subgraphs, known as ego networks, have properties that can differ substantially from those of the global network. In this paper, we study the structural properties of ego networks and show how they relate to the global properties of networks from which they are derived. Through empirical comparisons and mathematical derivations, we show that structural features, similar to static attributes, suffer from paradoxes. We quantify the differences between global information about network structure and local estimates. This knowledge allows us to better identify and correct the biases arising from incomplete local information.


Structural Properties of Ego Networks
Sidharth Gupta, Xiaoran Yan, Kristina Lerman

http://arxiv.org/abs/1411.6061

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tom cockburn's curator insight, December 4, 2014 9:17 AM

An interesting study of the granular aspects as well as the interfaces in networks

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A Unifying Framework for Measuring Weighted Rich Clubs

Network analysis can help uncover meaningful regularities in the organization of complex systems. Among these, rich clubs are a functionally important property of a variety of social, technological and biological networks. Rich clubs emerge when nodes that are somehow prominent or ‘rich’ (e.g., highly connected) interact preferentially with one another. The identification of rich clubs is non-trivial, especially in weighted networks, and to this end multiple distinct metrics have been proposed. Here we describe a unifying framework for detecting rich clubs which intuitively generalizes various metrics into a single integrated method. This generalization rests upon the explicit incorporation of randomized control networks into the measurement process. We apply this framework to real-life examples, and show that, depending on the selection of randomized controls, different kinds of rich-club structures can be detected, such as topological and weighted rich clubs.


A Unifying Framework for Measuring Weighted Rich Clubs
• Jeff Alstott, Pietro Panzarasa, Mikail Rubinov, Edward T. Bullmore & Petra E. Vértes

Scientific Reports 4, Article number: 7258 http://dx.doi.org/10.1038/srep07258

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tom cockburn's curator insight, December 4, 2014 9:18 AM

More details on nodes