Significant Scales in Community Structure

Many complex networks show signs of modular structure, uncovered by community detection. Although many methods succeed in revealing various partitions, it remains difficult to detect at what scale some partition is significant. This problem shows foremost in multi-resolution methods. We here introduce an efficient method for scanning for resolutions in one such method. Additionally, we introduce the notion of "significance" of a partition, based on subgraph probabilities. Significance is independent of the exact method used, so could also be applied in other methods, and can be interpreted as the gain in encoding a graph by making use of a partition. Using significance, we can determine "good" resolution parameters, which we demonstrate on benchmark networks. Moreover, optimizing significance itself also shows excellent performance. We demonstrate our method on voting data from the European Parliament. Our analysis suggests the European Parliament has become increasingly ideologically divided and that nationality plays no role.Comment: To appear in Scientific Report

The gas–liquid phase-transition singularities in the framework of the liquid-state integral equation formalism

6 pages, 4 figures.-- PACS: 64.70.Fx; 65.20.+w; 02.30.Rz; 62.10.+sThe singularities of various liquid-state integral equations derived from the Ornstein–Zernike relation and its temperature derivatives, have been investigated in the liquid–vapor transition region. As a general feature, it has been found that the existence of a nonsolution curve on the vapor side of the phase diagram, on which both the direct and the total correlation functions become complex—with a finite isothermal compressibility—also corresponds to the locus of points where the constant-volume heat capacity diverges, in consonance with a divergence of the temperature derivative of the correlation functions. In contrast, on the liquid side of the phase diagram one finds that a true spinodal (a curve of diverging isothermal compressibilities) is reproduced by the Percus–Yevick and Martynov–Sarkisov integral equations, but now this curve corresponds to states with finite heat capacity. On the other hand, the hypernetted chain approximation exhibits a nonsolution curve with finite compressibilities and heat capacities in which, as temperature is lowered, the former tends to diverge.E.L. acknowledges financial support of the Dirección General de Investigación Científica y Técnica under Grant No. FIS2004-02954-C03-01. This work has been carried out under the auspices of the exchange agreement between the Consejo Superior de Investigaciones Científicas and the Russian Academy of Sciencies, which supported the exchange visits of E.L. and G.S. in the past two years.Peer reviewe

Bursty egocentric network evolution in Skype

In this study we analyze the dynamics of the contact list evolution of millions of users of the Skype communication network. We find that egocentric networks evolve heterogeneously in time as events of edge additions and deletions of individuals are grouped in long bursty clusters, which are separated by long inactive periods. We classify users by their link creation dynamics and show that bursty peaks of contact additions are likely to appear shortly after user account creation. We also study possible relations between bursty contact addition activity and other user-initiated actions like free and paid service adoption events. We show that bursts of contact additions are associated with increases in activity and adoption - an observation that can inform the design of targeted marketing tactics.Comment: 7 pages, 6 figures. Social Network Analysis and Mining (2013

Multiscale Analysis of Spreading in a Large Communication Network

In temporal networks, both the topology of the underlying network and the timings of interaction events can be crucial in determining how some dynamic process mediated by the network unfolds. We have explored the limiting case of the speed of spreading in the SI model, set up such that an event between an infectious and susceptible individual always transmits the infection. The speed of this process sets an upper bound for the speed of any dynamic process that is mediated through the interaction events of the network. With the help of temporal networks derived from large scale time-stamped data on mobile phone calls, we extend earlier results that point out the slowing-down effects of burstiness and temporal inhomogeneities. In such networks, links are not permanently active, but dynamic processes are mediated by recurrent events taking place on the links at specific points in time. We perform a multi-scale analysis and pinpoint the importance of the timings of event sequences on individual links, their correlations with neighboring sequences, and the temporal pathways taken by the network-scale spreading process. This is achieved by studying empirically and analytically different characteristic relay times of links, relevant to the respective scales, and a set of temporal reference models that allow for removing selected time-domain correlations one by one

Information environment of project training accommodation

The article considers the issues of information support for project teaching of students. The configuration and composition of the information environment based on the areas of knowledge of project management

MAMAP – a new spectrometer system for column-averaged methane and carbon dioxide observations from aircraft: instrument description and performance analysis

Abstract. Carbon dioxide (CO2) and Methane (CH4) are the two most important anthropogenic greenhouse gases. CH4 is furthermore one of the most potent present and future contributors to global warming because of its large global warming potential (GWP). Our knowledge of CH4 and CO2 source strengths is based primarily on bottom-up scaling of sparse in-situ local point measurements of emissions and up-scaling of emission factor estimates or top-down modeling incorporating data from surface networks and more recently also by incorporating data from low spatial resolution satellite observations for CH4. There is a need to measure and retrieve the dry columns of CO2 and CH4 having high spatial resolution and spatial coverage. In order to fill this gap a new passive airborne 2-channel grating spectrometer instrument for remote sensing of small scale and mesoscale column-averaged CH4 and CO2 observations has been developed. This Methane Airborne MAPper (MAMAP) instrument measures reflected and scattered solar radiation in the short wave infrared (SWIR) and near-infrared (NIR) parts of the electro-magnetic spectrum at moderate spectral resolution. The SWIR channel yields measurements of atmospheric absorption bands of CH4 and CO2 in the spectral range between 1.59 and 1.69 μm at a spectral resolution of 0.82 nm. The NIR channel around 0.76 μm measures the atmospheric O2-A-band absorption with a resolution of 0.46 nm. MAMAP has been designed for flexible operation aboard a variety of airborne platforms. The instrument design and the performance of the SWIR channel, together with some results from on-ground and in-flight engineering tests are presented. The SWIR channel performance has been analyzed using a retrieval algorithm applied to the nadir measured spectra. Dry air column-averaged mole fractions are obtained from SWIR data only by dividing the retrieved CH4 columns by the simultaneously retrieved CO2 columns for dry air column CH4 (XCH4) and vice versa for dry air column CO2 (XCO2). The signal-to-noise ratio (SNR) of the SWIR channel is approximately 1000 for integration times (tint) in the range of 0.6–0.8 s for scenes with surface spectral reflectances (SSR)/albedo of around 0.18. At these integration times the ground scene size is about 23 × 33 m2 for an aircraft altitude of 1 km and a ground speed of 200 km/h. For these scenes the actual XCH4 or XCO2 dry air column retrieval precisions are typically about 1% (1 σ). Elevated levels of CH4 have been retrieved above a CH4 emitting landfill. Similarly the plume of CO2 from coal-fired power plants can be well detected and tracked. The measurements by the MAMAP sensor could enable estimates of anthropogenic, biogenic and geological emissions of localized intense CH4 and CO2 sources such as anthropogenic fugitive CH4 emissions from oil and gas industry, coal mining, disposal of organic waste, CO2 emissions from coal-fired power plants, steel production or geologic CH4 and CO2 emissions from seepage and volcanoes. Appropriate analysis of the measurements of MAMAP potentially also yields natural CH4 emissions from less intense but extensive sources such as wetlands