Artículos con la etiqueta ‘Física’

Fractal multi-level organisation of human groups in a virtual world

Por • 21 mar, 2014 • Category: sociologia

Humans are fundamentally social. They have progressively dominated their environment by the strength and creativity provided by and within their grouping. It is well recognised that human groups are highly structured, and the anthropological literature has loosely classified them according to their size and function, such as support cliques, sympathy groups, bands, cognitive groups, tribes, linguistic groups and so on. Recently, combining data on human grouping patterns in a comprehensive and systematic study, Zhou et al. identified a quantitative discrete hierarchy of group sizes with a preferred scaling ratio close to 3 , which was later confirmed for hunter-gatherer groups and for other mammalian societies. Using high precision large scale Internet-based social network data, we extend these early findings on a very large data set.

On the History of Geometrization of Space-time: From Minkowski to Finsler Geometry

Por • 18 mar, 2014 • Category: Educacion

e article is a tribute to Hermann Minkowski leading from his geometry of numbers to an attempt at using Finsler geometry for a break of Lorentz invariance.

Fermi and the Theory of Weak Interactions

Por • 15 mar, 2014 • Category: Educacion

The history of weak interactions starting with Fermi’s creation of the beta decay theory and culminating in its modern avatar in the form of the electroweak gauge theory is described. Discoveries of parity violation, matter-antimatter asymmetry, W and Z bosons and neutrino mass are highlighted.

Selection rules in alliance formation: strategic decisions or abundance of choice?

Por • 15 mar, 2014 • Category: Economía

We study how firms select partners using a large database of publicly announced R&D alliances over a period of 25 years. We identify, for the first time, two distinct behavioral strategies of firms in forming these alliances. By reconstructing and analysing the temporal R&D network of 14,000 international firms and 21.000 publicly announced alliances, we find a «universal» behavior in firms changing between these strategies. In the first strategy, newcomers and nodes of low centrality initially establish links to nodes of similar or higher centrality.

The influence of persuasion in opinion formation and polarization

Por • 15 mar, 2014 • Category: Ambiente

We present a model that explores the influence of persuasion in a population of agents with positive and negative opinion orientations. The opinion of each agent is represented by an integer number k that expresses its level of agreement on a given issue, from totally against k=−M to totally in favor k=M . Same-orientation agents persuade each other with probability p , becoming more extreme, while opposite-orientation agents become more moderate as they reach a compromise with probability q .

Frontiers of chaotic advection

Por • 13 mar, 2014 • Category: Leyes

We review the present position of and survey future perspectives in the physics of chaotic advection; the field that emerged three decades ago at the intersection of fluid mechanics and nonlinear dynamics, which encompasses a range of applications with length scales ranging from micrometers to hundreds of kilometers, including systems as diverse as mixing and thermal processing of viscous fluids, micro-fluidics, biological flows, and large-scale dispersion of pollutants in oceanographic and atmospheric flows.

Beyond network structure: How heterogenous susceptibility modulates the spread of epidemics

Por • 12 mar, 2014 • Category: Ciencia y tecnología

The compartmental models used to study epidemic spreading often assume the same susceptibility for all individuals, and are therefore, agnostic about the effects that differences in susceptibility can have on epidemic spreading. Here we show that–for the SIS model–differential susceptibility can make networks more vulnerable to the spread of diseases when the correlation between a node’s degree and susceptibility are positive, and less vulnerable when this correlation is negative. Moreover, we show that networks become more likely to contain a pocket of infection when individuals are more likely to connect with others that have similar susceptibility (the network is segregated).

Reflections on Gibbs: From Statistical Physics to the Amistad

Por • 12 mar, 2014 • Category: Educacion

J. Willard Gibbs, the younger, was the first American physical sciences theorist. He was one of the inventors of statistical physics. He introduced and developed the concepts of phase space, phase transitions, and thermodynamic surfaces in a remarkably correct and elegant manner. These three concepts form the basis of different areas of physics. The connection among these areas has been a subject of deep reflection from Gibbs’ time to our own. This talk therefore tries to celebrate Gibbs by talking about modern ideas about how different parts of physics fit together.

City growth as a resource utilization problem

Por • 12 mar, 2014 • Category: Economía

We study a resource utilization scenario characterized by intrinsic attractiveness. We consider a system of many restaurants where customers compete, as in a game, to get the best services out of many choices using iterative learning. Results for the case with uniform attractiveness are reported. When attractiveness is uniformly distributed, it gives rise to a Zipf-Pareto law for the number of customers. We perform an exact calculation for the utilization fraction for the case when choices are made independent of attractiveness. A variant of the model is also introduced where the attractiveness can be treated as a fitness to stay in the business. When a restaurant loses customers, its fitness is replaced by a random fitness. The steady state fitness distribution is characterized by a power law, but the distribution in number of customers is still given by power law, implying the robustness of the model. Our model serves as a paradigm for city size distribution and the emergence of Zipf law.

International Transmission of Shocks and Fragility of a Bank Network

Por • 9 mar, 2014 • Category: Economía

The weighted and directed network of countries based on the number of overseas banks is analyzed in terms of its fragility to the banking crisis of one country. We use two different models to describe transmission of shocks, one local and the other global. Depending on the original source of the crisis, the overall size of crisis impacts is found to differ country by country. For the two-step local spreading model, it is revealed that the scale of the first impact is determined by the out-strength, the total number of overseas branches of the country at the origin of the crisis, while the second impact becomes more serious if the in-strength at the origin is increased. For the global spreading model, some countries named «triggers» are found to play important roles in shock transmission, and the importance of the feed-forward-loop mechanism is pointed out. We also discuss practical policy implications of the present work.