On Linear Congestion Games with Altruistic Social Context

We study the issues of existence and inefficiency of pure Nash equilibria in linear congestion games with altruistic social context, in the spirit of the model recently proposed by de Keijzer {\em et al.} \cite{DSAB13}. In such a framework, given a real matrix $\Gamma=(\gamma_{ij})$ specifying a particular social context, each player $i$ aims at optimizing a linear combination of the payoffs of all the players in the game, where, for each player $j$, the multiplicative coefficient is given by the value $\gamma_{ij}$. We give a broad characterization of the social contexts for which pure Nash equilibria are always guaranteed to exist and provide tight or almost tight bounds on their prices of anarchy and stability. In some of the considered cases, our achievements either improve or extend results previously known in the literature

Network Creation Games: Think Global - Act Local

We investigate a non-cooperative game-theoretic model for the formation of communication networks by selfish agents. Each agent aims for a central position at minimum cost for creating edges. In particular, the general model (Fabrikant et al., PODC'03) became popular for studying the structure of the Internet or social networks. Despite its significance, locality in this game was first studied only recently (Bil\`o et al., SPAA'14), where a worst case locality model was presented, which came with a high efficiency loss in terms of quality of equilibria. Our main contribution is a new and more optimistic view on locality: agents are limited in their knowledge and actions to their local view ranges, but can probe different strategies and finally choose the best. We study the influence of our locality notion on the hardness of computing best responses, convergence to equilibria, and quality of equilibria. Moreover, we compare the strength of local versus non-local strategy-changes. Our results address the gap between the original model and the worst case locality variant. On the bright side, our efficiency results are in line with observations from the original model, yet we have a non-constant lower bound on the price of anarchy.Comment: An extended abstract of this paper has been accepted for publication in the proceedings of the 40th International Conference on Mathematical Foundations on Computer Scienc

Size reduction of complex networks preserving modularity

The ubiquity of modular structure in real-world complex networks is being the focus of attention in many trials to understand the interplay between network topology and functionality. The best approaches to the identification of modular structure are based on the optimization of a quality function known as modularity. However this optimization is a hard task provided that the computational complexity of the problem is in the NP-hard class. Here we propose an exact method for reducing the size of weighted (directed and undirected) complex networks while maintaining invariant its modularity. This size reduction allows the heuristic algorithms that optimize modularity for a better exploration of the modularity landscape. We compare the modularity obtained in several real complex-networks by using the Extremal Optimization algorithm, before and after the size reduction, showing the improvement obtained. We speculate that the proposed analytical size reduction could be extended to an exact coarse graining of the network in the scope of real-space renormalization.Comment: 14 pages, 2 figure

On Dispersive and Classical Shock Waves in Bose-Einstein Condensates and Gas Dynamics

A Bose-Einstein condensate (BEC) is a quantum fluid that gives rise to interesting shock wave nonlinear dynamics. Experiments depict a BEC that exhibits behavior similar to that of a shock wave in a compressible gas, eg. traveling fronts with steep gradients. However, the governing Gross-Pitaevskii (GP) equation that describes the mean field of a BEC admits no dissipation hence classical dissipative shock solutions do not explain the phenomena. Instead, wave dynamics with small dispersion is considered and it is shown that this provides a mechanism for the generation of a dispersive shock wave (DSW). Computations with the GP equation are compared to experiment with excellent agreement. A comparison between a canonical 1D dissipative and dispersive shock problem shows significant differences in shock structure and shock front speed. Numerical results associated with the three dimensional experiment show that three and two dimensional approximations are in excellent agreement and one dimensional approximations are in good qualitative agreement. Using one dimensional DSW theory it is argued that the experimentally observed blast waves may be viewed as dispersive shock waves.Comment: 24 pages, 28 figures, submitted to Phys Rev

Spin transfer torque generated magnetic droplet solitons (invited)

We present recent experimental and numerical advancements in the understanding of spin transfer torque generated magnetic droplet solitons. The experimental work focuses on nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has an easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The NC-STO resistance and microwave signal generation are measured simultaneously as a function of drive current and applied perpendicular magnetic field. Both exhibit dramatic transitions at a certain current dependent critical field value, where the microwave frequency drops 10 GHz, modulation sidebands appear, and the resistance exhibits a jump, while the magnetoresistance changes sign. We interpret these observations as the nucleation of a magnetic droplet soliton with a large fraction of its magnetization processing with an angle greater than 90°, i.e., around a direction opposite that of the applied field. This interpretation is corroborated by numerical simulations. When the field is further increased, we find that the droplet eventually collapses under the pressure from the Zeeman energy

Принципы организации объектно-ориентированных систем обработки неформализованной информации

Рассматривается класс логико-аналитических систем, использующих специальные лингвистические процессоры и базы знаний (БЗ) для обработки потоков неформализованных документов с целью решения пользовательских задач. На первом этапе формализации текста документа извлекаются информационные объекты и связи, которые образуют структуры знаний и запоминаются в БЗ. На уровне БЗ организуются различные виды анализа и объектных поисков: поиск похожих объектов и ситуаций, поиск по связям и другие. Рассматриваются основные компоненты подобных систем, называемых объектно-ориентированными, их особенности при использовании в различных приложениях: при обработке криминальной информации, при автоматической формализации резюме (заявок на работу), в системах обработки СМИ с выделением террористических групп и их деяний.A class of the logical-analytical systems using special linguistic processors and knowledge bases is considered. Such systems are called object-oriented. These systems are employed for processing of the unstructured documents flow for the user problems decision. At the first stage the document text is formalized: information objects and links are extracted and transferred into the knowledge structures which are stored in the knowledge base (KB). At the level of KB various kinds of analysis and object search are organized: the search for similar objects and situations, the search on the basis of links and other types of search. The basic components of these systems, their main features and the particular use in different applications are considered.The system operation in the subject areas of criminal information processing, automatic formalization of summary texts (applications for work), mass media analysis for extracting information about terrorist formations and their activities are presented

Hierarchies of Pain

Trauma has become a pervasive cultural model for representing individual and collective injuries and suffering. This process has produced what may be called a trauma aesthetic, a set of recognizable tropes in widespread use in trauma narratives. This chapter examines the adoption of this aesthetic in graphic narratives, focusing on the special capacities of the form. Familiar tropes, such as dissociation and the somatic trace, are presented in complex combinations of visual and textual components, often exploiting the differential appearance of text and image to introduce a dynamic of belatedness or disarticulation. This chapter analyses five works ordered according to their diminishing reliance on ‘trauma’. The trauma aesthetic is used, though not explicitly, in Catherine Meurisse’s La Légèreté (2016) about the Charlie Hebdo attack, Jean-Philip Stassen’s Déogratias (2000/2006) about the genocide in Rwanda, and Emmanuel Lepage’s Un printemps à Tchernobyl (2012) about the aftermath of the Chernobyl nuclear disaster. By contrast, it is absent from Mazen Kerbaj’s Beirut Won’t Cry (2007/2017) about the Israel-Hezbollah conflict and Josh Neufeld’s A.D. about Hurricane Katrina (2009). These works’ reliance on formalized and sanctioned trauma tropes not only is influenced by narrative characteristics, such as temporal distance from the event or the presence of a single narrator-protagonist but may also be motivated by the prestige conferred by trauma as recognized suffering, affecting the canonization and translatability of the graphic narratives in question

The Dipion Mass Spectrum In e+e- Annihilation and tau Decay: A Dynamical (rho0, omega, phi) Mixing Approach

We readdress the problem of finding a simultaneous description of the pion form factor data in e+e- annihilations and in tau decays. For this purpose, we work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify the vector meson mass term by including the pion and kaon loop contributions. This leads us to define the physical rho, omega and phi fields as linear combinations of their ideal partners, with coefficients being meromorphic functions of s, the square of the 4--momentum flowing into the vector meson lines. This allows us to define a dynamical, i.e. s-dependent, vector meson mixing scheme. The model is overconstrained by extending the framework in order to include the description of all meson radiative (V P gamma and P gamma gamma couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking (omega/ phi --> pi+ pi-) decay modes. The model provides a simultaneous, consistent and good description of the e+e- and tau dipion spectra. The expression for pion form factor in the latter case is derived from those in the former case by switching off the isospin breaking effects specific to e+e- and switching on those for tau decays. Besides, the model also provides a good account of all decay modes of the form V P gamma, Pgamma gamma as well as the isospin breaking decay modes. It leads us to propose new reference values for the rho^0 --> e+ e- and omega --> pi+ pi- partial widths which are part of our description of the pion form factor. Other topics (phi --> K anti K, the rho meson mass and width parameters) are briefly discussed. Therefore, we confirm the 3.3 sigma discrepancy between the theoretical estimate of a_mu based on e+e- and its direct BNL measurement.Comment: 71 pages, 8 figures. Accepted by EPJ C. Version 3: correct minor typos, minor changes spread out into the text. Extension of Sections 12.2 and 12.3.5 and introduction of the new Appendix

Heavy Majorana neutrinos in e+e- colliders

We investigate possibilities for detecting heavy Majorana neutrinos ($N$'s) in $e^+e^-$ at LEP200 and future Linear Colliders. We concentrate on the processes where the pairs of intermediate heavy $N$'s produce a clear signal of total lepton number violation ($e^+e^- \to NN \to W^+l^-W^+l^{\prime -}$). Such a signal is not possible if the heavy neutrinos are of Dirac nature. Our approach is general in the sense that the intermediate $N$'s can be either on shell or off shell. Discussion of the relative numerical importance of the $s$ and the $t+u$ channels of the $NN$ production is also included.Comment: 11 pages, latex (revtex), 4 eps-figures, text slightly modified, appears in Physical Review Letters (June 7, 1999, issue