The Chrono-geometrical Structure of Special and General Relativity: a Re-Visitation of Canonical Geometrodynamics

A modern re-visitation of the consequences of the lack of an intrinsic notion of instantaneous 3-space in relativistic theories leads to a reformulation of their kinematical basis emphasizing the role of non-inertial frames centered on an arbitrary accelerated observer. In special relativity the exigence of predictability implies the adoption of the 3+1 point of view, which leads to a well posed initial value problem for field equations in a framework where the change of the convention of synchronization of distant clocks is realized by means of a gauge transformation. This point of view is also at the heart of the canonical approach to metric and tetrad gravity in globally hyperbolic asymptotically flat space-times, where the use of Shanmugadhasan canonical transformations allows the separation of the physical degrees of freedom of the gravitational field (the tidal effects) from the arbitrary gauge variables. Since a global vision of the equivalence principle implies that only global non-inertial frames can exist in general relativity, the gauge variables are naturally interpreted as generalized relativistic inertial effects, which have to be fixed to get a deterministic evolution in a given non-inertial frame. As a consequence, in each Einstein's space-time in this class the whole chrono-geometrical structure, including also the clock synchronization convention, is dynamically determined and a new approach to the Hole Argument leads to the conclusion that "gravitational field" and "space-time" are two faces of the same entity. This view allows to get a classical scenario for the unification of the four interactions in a scheme suited to the description of the solar system or our galaxy with a deperametrization to special relativity and the subsequent possibility to take the non-relativistic limit.Comment: 33 pages, Lectures given at the 42nd Karpacz Winter School of Theoretical Physics, "Current Mathematical Topics in Gravitation and Cosmology", Ladek, Poland, 6-11 February 200

Discrete breathers for understanding reconstructive mineral processes at low temperatures

Reconstructive transformations in layered silicates need a high tem- perature in order to be observed. However, very recently, some systems have been found where transformation can be studied at temperatures 600 C below the lowest experimental results previously reported, including sol-gel methods. We explore the possible relation with the existence of intrinsic localized modes, known as discrete breathers. We construct a model for nonlinear vibrations within the cation layer, obtain their parameters and calculate them numerically, obtaining their energies. Their statistics shows that although there are far less breathers than phonons, there are much more above the activation energy, being therefore a good candidate to explain the reconstructive transformations at low temperature.Comment: 27 pages, 11 figure

Localizing gravity on exotic thick 3-branes

We consider localization of gravity on thick branes with a non trivial structure. Double walls that generalize the thick Randall-Sundrum solution, and asymmetric walls that arise from a Z_2-symmetric scalar potential, are considered. We present a new asymmetric solution: a thick brane interpolating between two AdS_5 spacetimes with different cosmological constants, which can be derived from a ``fake supergravity'' superpotential, and show that it is possible to confine gravity on such branes.Comment: Final version, minor changes, references adde

Social Preference of Building Materials: Decision-Making towards Low Carbon Housing Constructions

Material considerations are essential while trying to achieve low energy and carbon constructions. According to our preliminary findings, decisions regarding materials in new buildings are mostly done by clients or by self-builders often without the aid of an architect or planner. Therefore, community studies are important to understand today’s building dynamics. In this exploratory study - carried out in USA and Mexico - we analysed the public’s preferences for building materials for the exterior of dwellings and the factors that have more influence over their decisions while choosing the materials. We also studied the update in the subjects’ preference after receiving certain information concerning the materials. We wanted to know if the environmental factors play an important role in today's public preference in the building sector and what type of information could greater affect their beliefs. Preliminary results for Mexico and after a follow up analysis for USA show that acknowledging unfamiliar information (e.g. carbon emissions or price) might have a greater influence on the public’s update of preference of materials. This could have implications for the construction market dynamics in the usage promotion of low carbon building materials. KEYWORDS: Building materials, decision-making, low carbon, social cognitio

A Method to Find Community Structures Based on Information Centrality

Community structures are an important feature of many social, biological and technological networks. Here we study a variation on the method for detecting such communities proposed by Girvan and Newman and based on the idea of using centrality measures to define the community boundaries (M. Girvan and M. E. J. Newman, Community structure in social and biological networks Proc. Natl. Acad. Sci. USA 99, 7821-7826 (2002)). We develop an algorithm of hierarchical clustering that consists in finding and removing iteratively the edge with the highest information centrality. We test the algorithm on computer generated and real-world networks whose community structure is already known or has been studied by means of other methods. We show that our algorithm, although it runs to completion in a time O(n^4), is very effective especially when the communities are very mixed and hardly detectable by the other methods.Comment: 13 pages, 13 figures. Final version accepted for publication in Physical Review

Locally Preferred Structure and Frustration in Glassforming Liquids: A Clue to Polyamorphism?

We propose that the concept of liquids characterized by a given locally preferred structure (LPS) could help in understanding the observed phenomenon of polyamorphism. ``True polyamorphism'' would involve the competition between two (or more) distinct LPS, one favored at low pressure because of its low energy and one favored at high pressure because of its small specific volume, as in tetrahedrally coordinated systems. ``Apparent polyamorphism'' could be associated with the existence of a poorly crystallized defect-ordered phase with a large unit cell and small crystallites, which may be illustrated by the metastable glacial phase of the fragile glassformer triphenylphosphite; the apparent polyamorphism might result from structural frustration, i. e., a competition between the tendency to extend the LPS and a global constraint that prevents tiling of the whole space by the LPS.Comment: 11, 6 figures, Proceedings of the Conference "Horizons in Complex Systems", Messina; in honor of the 60th birthday of H.E. Stanle

The York map as a Shanmugadhasan canonical transformation in tetrad gravity and the role of non-inertial frames in the geometrical view of the gravitational field

A new parametrization of the 3-metric allows to find explicitly a York map in canonical ADM tetrad gravity, the two pairs of physical tidal degrees of freedom and 14 gauge variables. These gauge quantities (generalized inertial effects) are all configurational except the trace ${}^3K(\tau ,\vec \sigma)$ of the extrinsic curvature of the instantaneous 3-spaces $\Sigma_{\tau}$ (clock synchronization convention) of a non-inertial frame. The Dirac hamiltonian is the sum of the weak ADM energy $E_{ADM} = \int d^3\sigma {\cal E}_{ADM}(\tau ,\vec \sigma)$ (whose density is coordinate-dependent due to the inertial potentials) and of the first-class constraints. Then: i) The explicit form of the Hamilton equations for the two tidal degrees of freedom in an arbitrary gauge: a deterministic evolution can be defined only in a completely fixed gauge, i.e. in a non-inertial frame with its pattern of inertial forces. ii) A general solution of the super-momentum constraints, which shows the existence of a generalized Gribov ambiguity associated to the 3-diffeomorphism gauge group. It influences: a) the explicit form of the weak ADM energy and of the super-momentum constraint; b) the determination of the shift functions and then of the lapse one. iii) The dependence of the Hamilton equations for the two pairs of dynamical gravitational degrees of freedom (the generalized tidal effects) and for the matter, written in a completely fixed 3-orthogonal Schwinger time gauge, upon the gauge variable ${}^3K(\tau ,\vec \sigma)$, determining the convention of clock synchronization. Therefore it should be possible (for instance in the weak field limit but with relativistic motion) to try to check whether in Einstein's theory the {\it dark matter} is a gauge relativistic inertial effect induced by ${}^3K(\tau ,\vec \sigma)$.Comment: 90 page

Seawater quality control of microcontaminants in fish farm cage systems: Application of passive sampling devices

Increasingly, developed countries are imposing restrictions on chemicals used in aquaculture, and introducing residue monitoring programmes to ensure the highest possible seafood safety standards. Chemotherapeutants, additives or chemical residues in edible tissues of aquaculture products are now attracting attention, and a major issue is the accumulation of microcontaminants in seafood flesh. Environmental quality control is related to the provision of high-quality, safe products. The present paper evaluates the effectiveness of passive sampling devices as tools in environmental monitoring programmes for fish farm cage systems. Capability to detect trace levels of microcontaminants, sampling rates, and accumulation kinetic is assessed. Devices tested were Polar Organic Chemical Integrative Samplers (POCIS), for detecting pharmaceuticals, pesticides and hormone residues; Semi-Permeable Membrane Devices (SPMD), to detect bioaccumulable pollutants; and Diffusive Gradients in Thin films (DGT), for metals.Las restricciones que imponen los países desarrollados al uso de sustancias químicas en la acuicultura para asegurar la salubridad de sus productos son cada vez mayores. También es creciente la preocupación por el control de los aditivos, residuos químicos o los preparados farmacéuticos que pudieran encontrarse en las partes comestibles de las especies acuícolas, así como la acumulación de micro-contaminantes en las mismas. En este trabajo se presenta un estudio sobre el uso de los sistemas de muestreo pasivo para los programas de control ambiental de las piscifactorías de jaulas flotantes. Se valora su capacidad de detectar niveles traza, la tasa de muestreo y la cinética de acumulación de micro-contaminantes. Se han probado los POCIS (Polar Organic Chemical Integrative Samplers) para detectar productos farmacéuticos, pesticidas y residuos hormonales, los SPMD (Semi-Permeable Membrane Devices) para detectar contaminantes bioacumulables y las membranas DGT (Diffusive Gradients in Thin films) para metales.Instituto Español de Oceanografí