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At least 217 records · Page 12Linked to original sources

arXiv2009

Universal Complex Structures in Written Language

Quantitative linguistics has provided us with a number of empirical laws that characterise the evolution of languages and competition amongst them. In terms of language usage, one of the most influential results is Zipf's law of word frequencies. Zipf's law appears to be universal, and may not even be unique to human language. However, there is ongoing controversy over whether Zipf's law is a good indicator of complexity. Here we present an alternative approach that puts Zipf's law in the context of critical phenomena (the cornerstone of complexity in physics) and establishes the presence of a large scale "attraction" between successive repetitions of words. Moreover, this phenomenon is scale-invariant and universal -- the pattern is independent of word frequency and is observed in texts by different authors and written in different languages. There is evidence, however, that the shape of the scaling relation changes for words that play a key role in the text, implying the existence of different "universality classes" in the repetition of words. These behaviours exhibit striking parallels with complex catastrophic phenomena.

physics.soc-ph↗

arXiv2009

The Energy Problem

A brief general picture of the world, european and italian energy situations is made, analyzing several different energy sources and paying attention to the relations energy-quality of life, energy-environment and energy-health. Then will be discussed fossil fuels, renewable energies, the role of electric energy, nuclear energy, energy savings, the greenhouse effect, a possible sustainable development, the hydrogen economy and the risk and its perception. Then follow the conclusions and perspectives.

physics.soc-ph↗

arXiv2014

Finite-size effects in the dependency networks of free and open-source software

We propose a continuum model for the degree distribution of directed networks in free and open-source software. The degree distributions of links in both the in-directed and out-directed dependency networks follow Zipf's law for the intermediate nodes, but the heavily linked nodes and the poorly linked nodes deviate from this trend and exhibit finite-size effects. The finite-size parameters make a quantitative distinction between the in-directed and out-directed networks. For the out-degree distribution, the initial condition for a dynamic evolution corresponds to the limiting count of the most heavily liked nodes that the out-directed network can finally have. The number of nodes contributing out-directed links grows with every generation of software release, but this growth ultimately saturates towards a terminal value due to the finiteness of semantic possibilities in the network.

cs.OH↗

arXiv2009

Personalised and Dynamic Trust in Social Networks

We propose a novel trust metric for social networks which is suitable for application in recommender systems. It is personalised and dynamic and allows to compute the indirect trust between two agents which are not neighbours based on the direct trust between agents that are neighbours. In analogy to some personalised versions of PageRank, this metric makes use of the concept of feedback centrality and overcomes some of the limitations of other trust metrics.In particular, it does not neglect cycles and other patterns characterising social networks, as some other algorithms do. In order to apply the metric to recommender systems, we propose a way to make trust dynamic over time. We show by means of analytical approximations and computer simulations that the metric has the desired properties. Finally, we carry out an empirical validation on a dataset crawled from an Internet community and compare the performance of a recommender system using our metric to one using collaborative filtering.

cs.CY↗

arXiv2009

A remark on the BA model of scale-free networks

The degree distributions of many real world networks follow power-laws whose exponents tend to fall between two and three. Within the framework of the Barabasi-Albert model (BA model), we explain this empirical observation by a simple fact. To that end we propose a modified BA model with one parameter that serves as a regulatory factor for the growth rate of added links in scale-free networks. The regulatory factor has something to do with the obvious fact that one link has two nodes. The modified model also allows to connect nodes by newly added links that do not necessarily emanate from new nodes. Another related model using the master equation is also given, from which the same power-law degree distribution can be derived.

physics.soc-ph↗

arXiv2009

Communities in Networks

We survey some of the concepts, methods, and applications of community detection, which has become an increasingly important area of network science. To help ease newcomers into the field, we provide a guide to available methodology and open problems, and discuss why scientists from diverse backgrounds are interested in these problems. As a running theme, we emphasize the connections of community detection to problems in statistical physics and computational optimization.

physics.soc-ph↗

arXiv2014

The effects of using Cesium-137 teletherapy sources as a radiological weapon (dirty bomb)

While radioactive sources used in medical diagnosis do not pose a great security risk due to their low level of radioactivity, therapeutic sources are extremely radioactive and can presumably be used as a radiological weapon. Cobalt-60 and Cesium-137 sources are the most common ones used in radiotherapy with over 10,000 of such sources currently in use worldwide, especially in the developing world, which cannot afford modern accelerators. The present study uses computer simulations to investigate the effects of using Cesium-137 sources from teletherapy devices as a radiological weapon. Assuming a worst-case terrorist attack scenario, we estimate the ensuing cancer mortality, land contamination, evacuation area, as well as the relevant evacuation, decontamination, and health costs in the framework of the linear risk model. The results indicate that an attack with a Cesium-137 dirty bomb in a large metropolitan city (especially one that would involve several teletherapy sources) although would not cause any statistically significant cancer mortality current radiation safety standards would impose the evacuation of large areas and the relocation of thousands of people.

physics.med-ph↗

arXiv2009

Social Networking: An astronomer's field guide

We present a brief introduction to the phenomenon of "social networking" and its potentially powerful use as an astronomy outreach and educational tool. We briefly discuss the development of applications for websites and facebook and the use of web trackers e.g. Google Analytics to analyze your audience. Finally we discuss how social bookmarking can be used to promote your work to unexpected audiences.

astro-ph.IM↗

arXiv2009

Matrix plots of reordered bistochastized transaction flow tables: A United States intercounty migration example

We present a number of variously rearranged matrix plots of the $3, 107 \times 3, 107$ 1995-2000 (asymmetric) intercounty migration table for the United States, principally in its bistochasticized form (all 3,107 row and column sums iteratively proportionally fitted to equal 1). In one set of plots, the counties are seriated on the bases of the subdominant (left and right) eigenvectors of the bistochastic matrix. In another set, we use the ordering of counties in the dendrogram generated by the associated strong component hierarchical clustering. Interesting, diverse features of U. S. intercounty migration emerge--such as a contrast in centralized, hub-like (cosmopolitan/provincial) properties between cosmopolitan "Sunbelt" and provincial "Black Belt" counties. The methodologies employed should also be insightful for the many other diverse forms of interesting transaction flow-type data--interjournal citations being an obvious, much-studied example, where one might expect that the journals Science, Nature and PNAS would display "cosmopolitan" characteristics.

physics.soc-ph↗

arXiv2009

Altruism and reputation: cooperation within groups

In our recent model, the cooperation emerges as a positive feedback between a not-too-bad reputation and an altruistic attitude. Here we introduce a bias of altruism as to favorize members of the same group. The matrix F(i,j) of frequency of cooperation between agents i and j reveals the structure of communities. The Newman algorithm reproduces the initial bias. The method based on differential equations detects two groups of agents cooperating within their groups, leaving the uncooperative ones aside.

physics.soc-ph↗

arXiv2009

The Continuous Node Degree: a New Measure for Complex Networks

A key measure that has been used extensively in analyzing complex networks is the degree of a node (the number of the node's neighbors). Because of its discrete nature, when the degree measure was used in analyzing weighted networks, weights were either ignored or thresholded in order to retain or disregard an edge. Therefore, despite its popularity, the degree measure fails to capture the disparity of interaction between a node and its neighbors. We introduce in this paper a generalization of the degree measure that addresses this limitation: the continuous node degree (C-degree). The C-degree of a node reflects how many neighbors are effectively being used, taking interaction disparity into account. More importantly, if a node interacts uniformly with its neighbors (no interaction disparity), we prove that the C-degree of the node becomes identical to the node's (discrete) degree. We analyze four real-world weighted networks using the new measure and show that the C-degree distribution follows the power-law, similar to the traditional degree distribution, but with steeper decline. We also show that the ratio between the C-degree and the (discrete) degree follows a pattern that is common in the four studied networks.

physics.soc-ph↗

arXiv2009

Complex Dependencies in Large Software Systems

Two large, open source software systems are analyzed from the vantage point of complex adaptive systems theory. For both systems, the full dependency graphs are constructed and their properties are shown to be consistent with the assumption of stochastic growth. In particular, the afferent links are distributed according to Zipf's law for both systems. Using the Small-World criterion for directed graphs, it is shown that contrary to claims in the literature, these software systems do not possess Small-World properties. Furthermore, it is argued that the Small-World property is not of any particular advantage in a standard layered architecture. Finally, it is suggested that the eigenvector centrality can play an important role in deciding which open source software packages to use in mission critical applications. This comes about because knowing the absolute number of afferent links alone is insufficient to decide how important a package is to the system as a whole, instead the importance of the linking package plays a major role as well.

nlin.AO↗

arXiv2009

Persistence and Success in the Attention Economy

A hallmark of the attention economy is the competition for the attention of others. Thus people persistently upload content to social media sites, hoping for the highly unlikely outcome of topping the charts and reaching a wide audience. And yet, an analysis of the production histories and success dynamics of 10 million videos from \texttt{YouTube} revealed that the more frequently an individual uploads content the less likely it is that it will reach a success threshold. This paradoxical result is further compounded by the fact that the average quality of submissions does increase with the number of uploads, with the likelihood of success less than that of playing a lottery.

cs.CY↗

arXiv2009

Prisoner's Dilemma: non-trivial results for the lowest temptation level in the Darwinian and Pavlovian evolutionary strategies

The lowest temptation level (T = 1) is considered a trivial case for the Prisoner's Dilemma. Here, we show that this statement is true only for a very particular case, where the players interact with only one player. Otherwise, if the players interact with more than one player, the system presents the same possible behaviors observed for $T > 1$. In the steady state, the system can reach the cooperative, chaotic or defective phases, when adopting the Darwinian Evolutionary Strategy and the cooperative or quasi-regular phases, adopting the Pavlovian Evolutionary Strategy.

physics.soc-ph↗

arXiv2009

A middle option for choices in the Continuous Opinions and Discrete Actions model

Modeling the conditions for the emergence of extremism is a very important problem, with clear applications for describing the interaction among individuals. Traditional models either are not suited for the task, as in the case of discrete models, or, like Bounded Confidence models, are built with rules that make opinions tend to a common ground between agents or not change at all. Continuous Opinions and Discrete Actions (CODA) model allowed us to observe the emergence of extremist agents, even when every agent was initially a moderate, due to local influence effects. In this paper, the problem of emergence of extremism will be addressed by introducing a middle discrete option in the CODA model, making it similar to a Potts model. Different scenarios for the third option will be discussed: when it is equivalent to withholding judgment, when it is a real third option and when it is a real, middle option. The effects on the opinions will be studied and its effects on extremism discussed. Withholding judgment seems to have an unexpected effect, causing the diminishing of moderate opinions in the long run. For a central third opinion, we find that, under specific conditions, this new choice can act as a buffer between the extreme choices.

physics.soc-ph↗

arXiv2010

Citation graph, weighted impact factors and performance indices

A scheme of evaluating an impact of a given scientific paper based on importance of papers quoting it is investigated. Introducing a weight of a given citation, dependent on the previous scientific achievements of the author of the citing paper, we define the weighting factor of a given scientist. Technically the weighting factors are defined by the components of the normalized leading eigenvector of the matrix describing the citation graph. The weighting factor of a given scientist, reflecting the scientific output of other researchers quoting his work, allows us to define weighted number of citation of a given paper, weighted impact factor of a journal and weighted Hirsch index of an individual scientist or of an entire scientific institution.

physics.soc-ph↗

arXiv2009

Boundary effects on energy dissipation in a cellular automaton model

In this paper, we numerically study energy dissipation caused by traffic in the Nagel-Schreckenberg (NaSch) model with open boundary conditions (OBC). Numerical results show that there is a nonvanishing energy dissipation rate Ed, and no true free-flow phase exists in the deterministic and nondeterministic NaSch models with OBC. In the deterministic case, there is a critical value of the extinction rate $β{cd}$ below which Ed increases with increasing $β$, but above which Ed abruptly decreases in the case of the speed limit vmax>2. However, when vmax<3, no discontiguous change in Ed occurs. In the nondeterministic case, the dissipated energy has two different contributions: one coming from the randomization, and one from the interactions, which is the only reason for dissipating energy in the deterministic case. The relative contributions of the two dissipation mechanisms are presented in the stochastic NaSch model with OBC. Energy dissipation rate Ed is directly related to traffic phase. Theoretical analyses give an agreement with numerical results in three phases (low-density, high-density and maximum current phase) for the case vmax=1.

physics.soc-ph↗

arXiv2009

Characterizing Individual Communication Patterns

The increasing availability of electronic communication data, such as that arising from e-mail exchange, presents social and information scientists with new possibilities for characterizing individual behavior and, by extension, identifying latent structure in human populations. Here, we propose a model of individual e-mail communication that is sufficiently rich to capture meaningful variability across individuals, while remaining simple enough to be interpretable. We show that the model, a cascading non-homogeneous Poisson process, can be formulated as a double-chain hidden Markov model, allowing us to use an efficient inference algorithm to estimate the model parameters from observed data. We then apply this model to two e-mail data sets consisting of 404 and 6,164 users, respectively, that were collected from two universities in different countries and years. We find that the resulting best-estimate parameter distributions for both data sets are surprisingly similar, indicating that at least some features of communication dynamics generalize beyond specific contexts. We also find that variability of individual behavior over time is significantly less than variability across the population, suggesting that individuals can be classified into persistent "types". We conclude that communication patterns may prove useful as an additional class of attribute data, complementing demographic and network data, for user classification and outlier detection--a point that we illustrate with an interpretable clustering of users based on their inferred model parameters.

physics.soc-ph↗