On the rise and fall of networked societies

We review recent results on the dynamics of social networks which suggest that the interplay between the network formation process and volatility may lead to the occurrence of discontinuous phase transitions and phase coexistence in a large class of models. We then investigate the effects of negative links -- links inhibiting local growth of the network -- and of a geographical distribution of the agents in such models. We show, by extensive numerical simulations, that both effects enhance this phenomenology, i.e. it increases the size of the coexistence region.Comment: 6 pages, 4 figures, Proceedings of Granada Workshop 200

Visual analysis of document triage data

As part of the information seeking process, a large amount of effort is invested in order to study and understand how information seekers search through documents such that they can assess their relevance. This search and assessment of document relevance, known as document triage, is an important information seeking process, but is not yet well understood. Human-computer interaction (HCI) and digital library scientists have undertaken a series of user studies involving information seeking, collected a large amount of data describing information seekers' behavior during document search. Next to this, we have witnessed a rapid increase in the number of off-the-shelf visualization tools which can benefit document triage study. Here we set out to utilize existing information visualization techniques and tools in order to gain a better understanding of the large amount of user-study data collected by HCI and digital library researchers. We describe the range of available tools and visualizations we use in order to increase our knowledge of document triage. Treemap, parallel coordinates, stack graph, matrix chart, as well as other visualization methods, prove to be insightful in exploring, analyzing and presenting user behavior during document triage. Our findings and visualizations are evaluated by HCI and digital library researchers studying this proble

Parallel structurally-symmetric sparse matrix-vector products on multi-core processors

We consider the problem of developing an efficient multi-threaded implementation of the matrix-vector multiplication algorithm for sparse matrices with structural symmetry. Matrices are stored using the compressed sparse row-column format (CSRC), designed for profiting from the symmetric non-zero pattern observed in global finite element matrices. Unlike classical compressed storage formats, performing the sparse matrix-vector product using the CSRC requires thread-safe access to the destination vector. To avoid race conditions, we have implemented two partitioning strategies. In the first one, each thread allocates an array for storing its contributions, which are later combined in an accumulation step. We analyze how to perform this accumulation in four different ways. The second strategy employs a coloring algorithm for grouping rows that can be concurrently processed by threads. Our results indicate that, although incurring an increase in the working set size, the former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo

Structural vulnerability to narcotics-driven firearm violence: An ethnographic and epidemiological study of Philadelphia's Puerto Rican inner-city.

BackgroundThe United States is experiencing a continuing crisis of gun violence, and economically marginalized and racially segregated inner-city areas are among the most affected. To decrease this violence, public health interventions must engage with the complex social factors and structural drivers-especially with regard to the clandestine sale of narcotics-that have turned the neighborhood streets of specific vulnerable subgroups into concrete killing fields. Here we present a mixed-methods ethnographic and epidemiological assessment of narcotics-driven firearm violence in Philadelphia's impoverished, majority Puerto Rican neighborhoods.MethodsUsing an exploratory sequential study design, we formulated hypotheses about ethnic/racial vulnerability to violence, based on half a dozen years of intensive participant-observation ethnographic fieldwork. We subsequently tested them statistically, by combining geo-referenced incidents of narcotics- and firearm-related crime from the Philadelphia police department with census information representing race and poverty levels. We explored the racialized relationships between poverty, narcotics, and violence, melding ethnography, graphing, and Poisson regression.FindingsEven controlling for poverty levels, impoverished majority-Puerto Rican areas in Philadelphia are exposed to significantly higher levels of gun violence than majority-white or black neighborhoods. Our mixed methods data suggest that this reflects the unique social position of these neighborhoods as a racial meeting ground in deeply segregated Philadelphia, which has converted them into a retail endpoint for the sale of astronomical levels of narcotics.ImplicationsWe document racial/ethnic and economic disparities in exposure to firearm violence and contextualize them ethnographically in the lived experience of community members. The exceptionally concentrated and high-volume retail narcotics trade, and the violence it generates in Philadelphia's poor Puerto Rican neighborhoods, reflect unique structural vulnerability and cultural factors. For most young people in these areas, the narcotics economy is the most readily accessible form of employment and social mobility. The performance of violence is an implicit part of survival in these lucrative, illegal narcotics markets, as well as in the overcrowded jails and prisons through which entry-level sellers cycle chronically. To address the structural drivers of violence, an inner-city Marshall Plan is needed that should include well-funded formal employment programs, gun control, re-training police officers to curb the routinization of brutality, reform of criminal justice to prioritize rehabilitation over punishment, and decriminalization of narcotics possession and low-level sales

K-theory of derivators revisited

We define a K-theory for pointed right derivators and show that it agrees with Waldhausen K-theory in the case where the derivator arises from a good Waldhausen category. This K-theory is not invariant under general equivalences of derivators, but only under a stronger notion of equivalence that is defined by considering a simplicial enrichment of the category of derivators. We show that derivator K-theory, as originally defined, is the best approximation to Waldhausen K-theory by a functor that is invariant under equivalences of derivators.Junta de Andalucía (Consejería de Innovación, Ciencia y Empresa)Ministerio de Educación y CienciaGeneralitat de Cataluny

Digital Ricœur

As Ricœur scholars know, the literature by and on Ricœur is vast. Material written by Ricœur that is not collected in published volumes is often difficult to locate, and even in the published volumes it is frequently a challenge to locate where Ricœur discusses a particular topic. Given the amount of his work it can be a challenge too to determine changes in his analyses over the life of his corpus. And locating secondary literature on Ricœur can be equally problematic. In response, we have been working to establish a model for how Ricœur’s corpus might be digitized so that the issues of access, keyword location, and pattern might all be addressed. To develop the model, we are starting with Ricœur’s primary texts in English and plan to expand over time to other languages and to the secondary literature on Ricœur. In the present article we discuss our model and its five steps: digital access; copyright; text preparation for digital searches and analysis; examples of digital searches and analyses; and an archive portal interface that allows users to query based on an extensible set of search variables without needing to know or access the underlying search logic. We also invite interested researchers to help assist the development of this digitization project.Comme le savent les spécialistes de Ricœur, l’œuvre de Ricœur comme la littérature secondaire qui lui est consacrée sont vastes. Les écrits de Ricœur qui ne sont pas réunis dans des volumes publiés sont souvent difficiles à localiser, et même dans les volumes publiés, c’est fréquemment un défi que de localiser dans quels écrits il aborde tel ou tel thème. Étant donné l’ampleur de son œuvre, determiner quels ont été les changement de ses analyses tout au long de son corpus peut aussi constituer un défi. De même, localiser la littérature secondaire sur Ricœur peut s’avérer problématique. En réponse à cela, nous avons travaillé à établir un modèle de numérisation du corpus de Ricœur, de façon à ce que les questions d’accès à l’œuvre, de localisation par mots-clés et de modélisation puissent être toutes solutionnées. Pour developper ce modèle, nous commençons avec les écrits de Ricœur en anglais et nous prévoyons avec le temps d’étendre cette demarche aux écrits du philosophe dans d’autres langues ainsi qu’à la littérature secondaire le concernant. Dans cet article, nous présentons notre modèle dans ses cinq étapes: accès numérique; droits d’auteurs; préparation de textes pour des recherches et des analyses numériques; exemples de recherches et d’analyses numériques; interface de portail destiné aux archives et basée sur un ensemble extensible de variables permettant aux utilisateurs de faire leur recherche sans avoir besoin de connaître ou d’avoir accès à la logique de recherche sous-jacente. Nous invitons également les chercheurs intéressés à contribuer à ce projet de numérisation

Model reduction for analysis of cascading failures in power systems

In this paper, we apply a principal-orthogonal decomposition based method to the model reduction of a hybrid, nonlinear model of a power network. The results demonstrate that the sequence of fault events can be evaluated and predicted without necessarily simulating the whole system