An experimental device to elicit social networks

This paper proposes an original mechanism to elicit latent social networks. Subjects are invited to reveal their friends’ name and surname, together with a score measuring the strength of relationship. According to the mechanism, subjects are rewarded of a fixed price either a) when they do not name anybody or b) when the scores of a randomly selected (bidirectional) link are sufficiently close. We test the mechanism’s performance in the field. Our main results are: i) a very large percentage of links (75%) were corresponded. ii) the mechanism largely captures strong friendship relations and practically ignores weak relations. A simple model of friend—regarding preferences is developed to explain this evidence.friendship, networks, experiments, other—regarding preferences.

Modulated equations of Hamiltonian PDEs and dispersive shocks

Motivated by the ongoing study of dispersive shock waves in non integrable systems , we propose and analyze a set of wave parameters for periodic waves of a large class of Hamiltonian partial differential systems-including the generalized Korteweg-de Vries equations and the Euler-Korteweg systems-that are well-behaved in both the small amplitude and small wavelength limits. We use this parametrization to determine fine asymptotic properties of the associated modulation systems, including detailed descriptions of eigenmodes. As a consequence, in the solitary wave limit we prove that modulational instability is decided by the sign of the second derivative-with respect to speed, fixing the endstate-of the Boussinesq moment of instability; and, in the harmonic limit, we identify an explicit modulational instability index, of Benjamin-Feir type

The Collapse of Interwar Vienna: Oskar Morgenstern’s Community, 1925 - 1950

From the perspective of science, art and intellectual life in general, Interwar Vienna was one of the most vibrant communities in modern European history. Within the field of economics, it was home to, amongst others, Ludwig von Mises, Friedrich von Hayek, Hans Mayer, Gottfried Haberler, Fritz Machlup, Oskar Morgenstern, Karl Menger and Abraham Wald. The community flourished after the end of World War I, and then began to suffer in the early 1930’s as a result of growing political instability and rising anti-semitism. With the Anschluss of Austria by the Third Reich in March 1938, it collapsed completely, never to recover. Drawing on the personal papers of two key participants, Oskar Morgenstern and Karl Menger, and also on the archives of the Rockefeller Foundation, this paper provides a portrait of that community, chronicling its evolution and dramatic collapse. Particular attention is paid to the milieu surrounding Morgenstern, both as director of the Rockefeller-funded Austrian Institute for Business Cycle Research and as philosophical “dissident”. In collaborating with mathematicians Menger, Wald and, later, John von Neumann, he gradually forsook his Austrian theoretical legacy. The account detailed here shows conflict and tension to have been central to both the life and death of this fabled community.

Density-Dependence as a Size-Independent Regulatory Mechanism

The growth function of populations is central in biomathematics. The main dogma is the existence of density dependence mechanisms, which can be modelled with distinct functional forms that depend on the size of the population. One important class of regulatory functions is the $\theta$-logistic, which generalises the logistic equation. Using this model as a motivation, this paper introduces a simple dynamical reformulation that generalises many growth functions. The reformulation consists of two equations, one for population size, and one for the growth rate. Furthermore, the model shows that although population is density-dependent, the dynamics of the growth rate does not depend either on population size, nor on the carrying capacity. Actually, the growth equation is uncoupled from the population size equation, and the model has only two parameters, a Malthusian parameter $\rho$ and a competition coefficient $\theta$. Distinct sign combinations of these parameters reproduce not only the family of $\theta$-logistics, but also the van Bertalanffy, Gompertz and Potential Growth equations, among other possibilities. It is also shown that, except for two critical points, there is a general size-scaling relation that includes those appearing in the most important allometric theories, including the recently proposed Metabolic Theory of Ecology. With this model, several issues of general interest are discussed such as the growth of animal population, extinctions, cell growth and allometry, and the effect of environment over a population.Comment: 41 Pages, 5 figures Submitted to JT

An experimental device to elicit social networks

This paper proposes an original mechanism to elicit latent social networks. Subjects are invited to reveal their friends’ name and surname, together with a score measuring the strength of relationship. According to the mechanism, subjects are rewarded of a fixed price either a) when they do not name anybody or b) when the scores of a randomly selected (bidirectional) link are sufficiently close. We test the mechanism’s performance in the field. Our main results are: i) a very large percentage of links (75%) were corresponded. ii) the mechanism largely captures strong friendship relations and practically ignores weak relations. A simple model of friend—regarding preferences is developed to explain this evidence.This paper proposes an original mechanism to elicit latent social networks. Subjects are invited to reveal their friends’ name and surname, together with a score measuring the strength of relationship. According to the mechanism, subjects are rewarded of a fixed price either a) when they do not name anybody or b) when the scores of a randomly selected (bidirectional) link are sufficiently close. We test the mechanism’s performance in the field. Our main results are: i) a very large percentage of links (75%) were corresponded. ii) the mechanism largely captures strong friendship relations and practically ignores weak relations. A simple model of friend—regarding preferences is developed to explain this evidence.Non-Refereed Working Papers / of national relevance onl

An experimental device to elicit soical networks

This paper proposes an original mechanism to elicit latent social net- works. Subjects are invited to reve al their friends’ name and surname, together with a score measuring the strength of relationship. According to the mechanism, subjects are rewarded of a fi xed price either a) when they do not name anybody or b) when the scores of a randomly selected (bidirectional) link are su ffi ciently close. We test the mechanism’s perfor- mance in the fi eld. Our main results are: i) a very large percentage of links (75%) were corresponded. ii) the mechanism largely captures strong friendship relations and practically ignores weak relations. A simple model of friend—regarding preferences is developed to explain this evidence.Pablo Brañas-Garza acknowledges financial support from CICYT-SEJ 2004-07554/ECON and Fundación Ramón Areces. Natalia Jiménez acknowledges financial support by the Generalitat Valenciana under the project CTBPRB/2003/71. Pablo Brañas-Garza, Ramón Cobo-Reyes and Natalia Jiménez acknowledge financial support by Centro de Estudios Andaluces I+D 2006

Random telegraph signals in charge coupled devices

An investigation of fluctuating pixels resulting from proton irradiation of an E2V Technologies CCD47-20 device is presented. The device structure,experimental set up and irradiation methodology are described, followed by a detailed analysis of radiation induced random telegraph signals,RTS. The characteristics of the observed flickering pixels are discussed in detail and the proposed models explaining the mechanism behind the phenomena are viewed in light of the collected data