10,463 research outputs found
Centralized vs Decentralized Markets in the Laboratory: The Role of Connectivity
This paper compares the performance of centralized and decentralized markets experimentally. We constrain trading exchanges to happen on an exogenously predetermined network, representing the trading relationships in markets with differing levels of connectivity. Our experimental results show that, despite having lower trading volumes, decentralized markets are generally not less efficient. Although information can propagate quicker through highly connected markets, we show that higher connectivity also induces informed traders to trade faster and exploit further their information advantages before the information becomes fully incorporated into prices. This not only reduces market efficiency, but it increases wealth inequality. We show that, in more connected markets, informed traders trade not only relatively quicker, but also more, in the right direction, despite not doing it at better prices
White dwarfs as test objects of Lorentz violations
In the present work the thermodynamical properties of bosonic and fermionic
gases are analyzed under the condition that a modified dispersion relation is
present. This last condition implies a breakdown of Lorentz symmetry. The
implications upon the condensation temperature will be studied, as well, as
upon other thermodynamical variables such as specific heat, entropy, etc.
Moreover, it will be argued that those cases entailing a violation of time
reversal symmetry of the motion equations could lead to problems with the
concept of entropy. Concerning the fermionic case it will be shown that Fermi
temperature suffers a modification due to the breakdown of Lorentz symmetry.
The results will be applied to white dwarfs and the consequences upon the
Chandrasekhar mass--radius relation will be shown. The possibility of resorting
to white dwarfs for the testing of modified dispersion relations is also
addressed. It will be shown that the comparison of the current observations
against the predictions of our model allows us to discard some values of one of
the parameters appearing in the modifications of the dispersion relation.Comment: Accepted in Classical and Quantum Gravitatio
Ensayo sobre la evaluación de la extinción en hábitats extremos
Inference and estimation are the Achilles heel of many biological disciplines. The validation of results is the first step before taking any further decision. In Biodiversity studies the technical problems in validation are similar to those faced in other disciplines. The main difference with areas like medicine is that a validation error in the latter can easily take you to court, but very few responsibilities apart from moral or ethical ones generally derive from a faulty estimation or validation in Biodiversity. However, many political decisions concerning conservation issues, which in many cases affect powerful economic interests depend on the reliability of those biodiversity studies. Getting good, reliable information is not always easy, and this explains in part, the success of critical voices like Simon (1998) and Lomborg (2001). New methodologies like Population Viability Analysis has been developed to take advantage of the potential information contained in periodical sampling. We apply it to a peculiar and difficult to study fauna: the fauna of the aquatic subterranean environment. Lack of regular information and scarcity of the fauna due to difficulty to reach their proper habitat are the main problems that confront this analysis. However, despite its limitations, the analysis points towards a need to better understand the structure of the subterranean habitat from “an animal point of view” and the need of more regular sampling at the same time that the other environmental parameters are taken.La inferencia y la estima son el talón de Aquiles de muchas disciplinas biológicas. La validación de resultados es el primer paso antes de tomar decisiones ulteriores. En estudios de Biodiversidad los problemas técnicos de validación son semejantes a los que se enfrentan otras disciplinas. La principal diferencia con áreas como Medicina es que un error en validación en ésta última puede terminar fácilmente en el juzgado, pero muy pocas responsabilidades, aparte de la éticas o morales suelen afectar a estimas o validaciones defectuosas de Biodiversidad. Sin embargo, muchas decisiones políticas en relación a la conservación de especies y habitats, que en muchos casos implican poderosos intereses económicos, dependen precisamente de la fiabilidad de los estudios de biodiversidad. Obtener una información buena y fiable no es siempre fácil y explica, en parte, el éxito de voces críticas como Simon (1998) o Lomborg (2001). En este trabajo revisamos uno de los problemas de estimación en un habitat especialmente difícil, el medio subterráneo acuático. La carencia de información periódica y la escasez de esta fauna, debido principalmente a las dificultades de acceso a su habitat, son los principales problemas que hemos encontrado al tratar de aplicar análisis PVA (Populations Viability Analysis). No obstante, a pesar de la escasez de datos consistentes, este análisis pone de manifiesto la necesidad de entender mejor la estructura del habitat subterráneo, en lo que respecta a la distribución de su fauna y la necesidad de realizar más muestreos y de realizarlos con mayor regularidad
Quantum Measurements and the kappa--Poincare Group
The possible description of the vacuum of quantum gravity through the so
called kappa--Poincare group is analyzed considering some of the consequences
of this symmetry in the path integral formulation of nonrelativistic quantum
theory. This study is carried out with two cases, firstly, a free particle, and
finally, the situation of a particle immersed in a homogeneous gravitational
field. It will be shown that the kappa--Poincare group implies the loss of some
of the basic properties associated to Feynman's path integral. For instance,
loss of the group characteristic related to the time dependence of the
evolution operator, or the breakdown of the composition law for amplitudes of
events occurring successively in time. Additionally some similarities between
the present idea and the so called restricted path integral formalism will be
underlined. These analogies advocate the claim that if the kappa--Poincare
group contains some of the physical information of the quantum gravity vacuum,
then this vacuum could entail decoherence. This last result will also allow us
to consider the possibility of analyzing the continuous measurement problem of
quantum theory from a group--theoretical point of view, but now taking into
account the kappa--Poincare symmetries.Comment: Accepted in General Relativity and Gravitation. Dedicated to Alberto
Garcia on the occasion of his 60th. birthda
Alpha Emitter Intrinsic Concentration in Copper required for Nuclear Spectrometry Application
Low-level radioactivity content in copper are employed for bolometric thermal radiation sensors and astro-nuclear spectrometers. The required lowest achievable alpha emitters concentration, for treated and untreated surfaces, are measured by Double Sided Silicon Strip Detectors in a high vacuum chamber and provide information on its intrinsic NORM content. Results shows that copper alpha emitters content can be achieved in the range below 0.01 (counts. keV-¹·kg-¹·y-¹) adequate for specific nuclear spectrometry applications
Fluid--Gravity Correspondence under the presence of viscosity
The present work addresses the analogy between the speed of sound of a
viscous, barotropic, and irrotational fluid and the equation of motion for a
non--massive field in a curved manifold. It will be shown that the presence of
viscosity implies the introduction, into the equation of motion of the
gravitational analogue, of a source term which entails the flow of energy from
the non--massive field to the curvature of the spacetime manifold. The
stress-energy tensor is also computed and it is found not to be constant, which
is consistent with such energy interchange
Critical points in a relativistic bosonic gas induced by the quantum structure of spacetime
It is well known that phase transitions arise if the interaction among
particles embodies an attractive as well as a repulsive contribution. In this
work it will be shown that the breakdown of Lorentz symmetry, characterized
through a deformation in the relation dispersion, plus the bosonic statistics
predict the emergence of critical points. In other words, in some quantum
gravity models the structure of spacetime implies the emergence of critical
points even when no interaction among the particle has been considered.Comment: 5 pages, no figure
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