Core-periphery organization of complex networks

Networks may, or may not, be wired to have a core that is both itself densely connected and central in terms of graph distance. In this study we propose a coefficient to measure if the network has such a clear-cut core-periphery dichotomy. We measure this coefficient for a number of real-world and model networks and find that different classes of networks have their characteristic values. For example do geographical networks have a strong core-periphery structure, while the core-periphery structure of social networks (despite their positive degree-degree correlations) is rather weak. We proceed to study radial statistics of the core, i.e. properties of the n-neighborhoods of the core vertices for increasing n. We find that almost all networks have unexpectedly many edges within n-neighborhoods at a certain distance from the core suggesting an effective radius for non-trivial network processes

Relativistic Images in Randall-Sundrum II Braneworld Lensing

In this paper, we explore the properties of gravitational lensing by black holes in the Randall-Sundrum II braneworld. We use numerical techniques to calculate lensing observables using the Tidal Reissner-Nordstrom (TRN) and Garriga-Tanaka metrics to examine supermassive black holes and primordial black holes. We introduce a new way tp parameterize tidal charge in the TRN metric which results in a large increase in image magnifications for braneworld primordial black holes compared to their 4 dimensional analogues. Finally, we offer a mathematical analysis that allows us to analyze the validity of the logarithmic approximation of the bending angle for any static, spherically symmetric metric. We apply this to the TRN metric and show that it is valid for any amount of tidal charge.Comment: 13 pages, 3 figures; Accepted for Publication in Physical Review

The Past, Present, and Future of “IS Success”

Since the introduction of information systems more than 60 years ago, organizations want to ensure that their systems are effective or “successful”. Much has changed in the evaluation of information systems success during this period. The role of information systems in organizations has changed dramatically, as have the key stakeholders and the expected benefits of the investments in IS. During this period, IS research has evolved to keep pace with the changing expectations regarding the success of information systems, yet practice tends to lag behind. In this commentary, we discuss five eras of information systems evolution and explain how the perceptions and measures of successful information systems have changed across these eras. By looking at the past and present, we are able to comment on how our understanding of success has evolved over time in research and practice. We discuss the inadequacy of IS success evaluation in practice. Finally, we offer four themes as calls for future action related to the research of information systems success

Monotone Decision Trees

EUR-FEW-CS-97-07 Title Monotone decision trees Author(s) R. Potharst J.C. Bioch T. Petter Abstract In many classification problems the domains of the attributes and the classes are linearly ordered. Often, classification must preserve this ordering: this is called monotone classification. Since the known decision tree methods generate non-monotone trees, these methods are not suitable for monotone classification problems. In this report we provide a number of order-preserving tree-generation algorithms for multi-attribute classification problems with k linearly ordered classes

Power and the Production of Science. Assessing Cod Stocks as the Mechanistic Fishery Collapses

This paper discusses power relations in the production of knowledge claims and the validation of management strategies. The experience of doing stock assessment science and creating management plans for Canada’s east coast cod fishery illustrates this general process. We demonstrate that the cyborgization of fisheries-management is limited by its inability to produce power for stabilizing the relations between managers, fishers, technology and fish. Lack of stability forces scientists and managers either to ignore a threat or to intervene by changing their strategy. Consensus is unlikely. Scientists and managers must reconsider reasons for action or lack of it, thus producing a new rationality. Managers attempt to control that reconstruction process in the interests of resolving shortterm challenges. Some scientists resist change and protect their earlier positions against new evidence or re-interpretations. The winning rationality has more to do with the power of the claimant than with the quality of reasoning

The networked seceder model: Group formation in social and economic systems

The seceder model illustrates how the desire to be different than the average can lead to formation of groups in a population. We turn the original, agent based, seceder model into a model of network evolution. We find that the structural characteristics our model closely matches empirical social networks. Statistics for the dynamics of group formation are also given. Extensions of the model to networks of companies are also discussed

Direct Evidence of the Discontinuous Character of the Kosterlitz-Thouless Jump

It is numerically shown that the discontinuous character of the helicity modulus of the two-dimensional XY model at the Kosterlitz-Thouless (KT) transition can be directly related to a higher order derivative of the free energy without presuming any {\it a priori} knowledge of the nature of the transition. It is also suggested that this higher order derivative is of intrinsic interest in that it gives an additional characteristics of the KT transition which might be associated with a universal number akin to the universal value of the helicity modulus at the critical temperature.Comment: 4 pages, to appear in PR