Effective dynamics of scalar perturbations in a flat Friedmann-Robertson-Walker spacetime in Loop Quantum Cosmology

We study the evolution of a homogeneous and isotropic spacetime whose spatial sections have three-torus topology, coupled to a massless scalar field with small scalar perturbations within loop quantum cosmology. We consider a proposal for the effective dynamics based on a previous hybrid quantization completed by us. Consequently, we introduce a convenient gauge fixing and adopt reduced canonical variables adapted to that hybrid quantum description. Besides, we keep backreaction contributions on the background coming from terms quadratic in the perturbations in the action of the system. We carry out a numerical analysis assuming that the inhomogeneities were in a massless vacuum state at distant past (where the initial data are set). At distant future, we observe a statistical amplification of the modes amplitude in the infrared region, as well as a phase synchronization arising from quantum gravity phenomena. A description of the perturbations in terms of the Mukhanov-Sasaki gauge invariants provides the same qualitative results. Finally, we analyze some consequences of the backreaction in our effective description.Comment: 15 pages, 9 figures. Accepted for publication in Phys. Rev.

Hybrid quantization of an inflationary model: The flat case

We present a complete quantization of an approximately homogeneous and isotropic universe with small scalar perturbations. We consider the case in which the matter content is a minimally coupled scalar field and the spatial sections are flat and compact, with the topology of a three-torus. The quantization is carried out along the lines that were put forward by the authors in a previous work for spherical topology. The action of the system is truncated at second order in perturbations. The local gauge freedom is fixed at the classical level, although different gauges are discussed and shown to lead to equivalent conclusions. Moreover, descriptions in terms of gauge-invariant quantities are considered. The reduced system is proven to admit a symplectic structure, and its dynamical evolution is dictated by a Hamiltonian constraint. Then, the background geometry is polymerically quantized, while a Fock representation is adopted for the inhomogeneities. The latter is selected by uniqueness criteria adapted from quantum field theory in curved spacetimes, which determine a specific scaling of the perturbations. In our hybrid quantization, we promote the Hamiltonian constraint to an operator on the kinematical Hilbert space. If the zero mode of the scalar field is interpreted as a relational time, a suitable ansatz for the dependence of the physical states on the polymeric degrees of freedom leads to a quantum wave equation for the evolution of the perturbations. Alternatively, the solutions to the quantum constraint can be characterized by their initial data on the minimum-volume section of each superselection sector. The physical implications of this model will be addressed in a future work, in order to check whether they are compatible with observations.Comment: 20 pages, no figures. v2: minor changes, in particular, abstract shortened, final discussion improve

A complete hybrid quantization in inhomogeneous cosmology

A complete quantization of a homogeneous and isotropic spacetime with closed spatial sections coupled to a massive scalar field is provided, within the framework of Loop Quantum Cosmology. We identify solutions with their initial data on the minimum volume section, and from this we construct the physical Hilbert space. Moreover, a perturbative study allows us to introduce small inhomogeneities. After gauge fixing, the inhomogeneous part of the system is reduced to a linear field theory. We then adopt a standard Fock representation to quantize these degrees of freedom. For the considered case of compact spatial topology, the requirements of: i) invariance under the spatial isometries, and ii) unitary implementation of the quantum dynamics, pick up a unique Fock representation and a particular set of canonical fields (up to unitary equivalence).Comment: 6 page

Evaluation of water quality through the Biological Monitoring Working Party method in the Santa Maria del Lago wetland of Bogotá city – Colombia

Se presenta el siguiente documento con el fin de mostrar a la comunidad en general la investigación realizada sobre la evaluación de la calidad del agua del humedal Santa María del Lago de la ciudad de Bogotá a través de la implementación del método BMWP con un índice de identificación adaptado para Colombia, basándose en la utilización de macroinvertebrados acuáticos como bioindicadores. Además de la identificación taxonómica, para validación de la información obtenida, se efectúa la evaluación de parámetros fisicoquímicos en puntos aleatoriamente seleccionados dentro del área del humedal y su respectiva relación con lo identificado a través de macroinvertebrados acuáticos. Adicionalmente, se proponen acciones correctivas y/o nuevas prácticas para su conservación.The following document is presented with the purpose to show the community in general the research carried out on the evaluation of the water quality of the Santa María del Lago wetland in the city of Bogotá through the implementation of the BMWP method with an identification index Adapted for Colombia, based on the use of aquatic macroinvertebrates as bioindicators. In addition to the taxonomic identification, to validate the information obtained, the evaluation of physicochemical parameters in randomly selected points within the area of the wetland and its respective relation with the identified through aquatic macroinvertebrates is carried out. In addition, corrective actions and / or new practices are proposed for their conservation

A uniqueness criterion for the Fock quantization of scalar fields with time dependent mass

A major problem in the quantization of fields in curved spacetimes is the ambiguity in the choice of a Fock representation for the canonical commutation relations. There exists an infinite number of choices leading to different physical predictions. In stationary scenarios, a common strategy is to select a vacuum (or a family of unitarily equivalent vacua) by requiring invariance under the spacetime symmetries. When stationarity is lost, a natural generalization consists in replacing time invariance by unitarity in the evolution. We prove that, when the spatial sections are compact, the criterion of a unitary dynamics, together with the invariance under the spatial isometries, suffices to select a unique family of Fock quantizations for a scalar field with time dependent mass.Comment: 11 pages, version accepted for publication in Classical and Quantum Gravit

Criteria for the determination of time dependent scalings in the Fock quantization of scalar fields with a time dependent mass in ultrastatic spacetimes

For Klein-Gordon fields, it is well known that there exist an infinite number of nonequivalent Fock representations of the canonical commutation relations and, therefore, of inequivalent quantum theories. A context in which this kind of ambiguities arises and prevents the derivation of robust results is, e.g., in the quantum analysis of cosmological perturbations. In these situations, typically, a suitable scaling of the field by a time dependent function leads to a description in an auxiliary static background, though the nonstationarity still shows up in a time dependent mass. For such a field description, and assuming the compactness of the spatial sections, we recently proved in three or less spatial dimensions that the criteria of a natural implementation of the spatial symmetries and of a unitary time evolution are able to select a unique class of unitarily equivalent vacua, and hence of Fock representations. In this work, we succeed to extend our uniqueness result to the consideration of all possible field descriptions that can be reached by a time dependent canonical transformation which, in particular, involves a scaling of the field by a function of time. This kind of canonical transformations modify the dynamics of the system and introduce a further ambiguity in its quantum description, exceeding the choice of a Fock representation. Remarkably, for any compact spatial manifold in less than four dimensions, we show that our criteria eliminate any possible nontrivial scaling of the field other than that leading to the description in an auxiliary static background. Besides, we show that either no time dependent redefinition of the field momentum is allowed or, if this may happen, the redefinition does not introduce any Fock representation that cannot be obtained by a unitary transformation.Comment: 37 pages. Modified title. Improved discussion concerning the spatial symmetry group. New section (section VI

Evaluation of Factors Present During Labor Stress

Se define el estrés como un constructo interactivo, que constituye una reacción de la persona tanto en el ámbito fisiológico como psicológico, ante un estímulo configurado por la interacción de factores individuales, ambientales y sociales, y que conlleva a un proceso de adaptación o desequilibrio del organismo.A partir de esta definición, este estudio constituye una evaluación del estrés en la empresa, mediante la medición de cinco variables: a) Estrés Percibido; b) Percepción de Apoyo Social Familiar; c) Percepción de Apoyo Social de las Amistades; d) Nivel de Sintomatología y e) Nivel de Estrés generado por la Preocupación u Ocurrencia de Sucesos de Vida.Estas variables se estudian en una muestra de 107 trabajadores que presentan elevados índices de accidentalidad y que forman parte de una importante empresa minera del país.El análisis de los resultados fue realizado a través de un procedimiento descriptivo y correlacional. El primero de ellos orientado a determinar los niveles de estrés y sus variables asociadas en la muestra en estudio. El análisis correlacional tuvo como objetivo determinar el grado de relación existente entre las variables evaluadas y como éstas se encuentran relacionadas con el nivel de estrés.Como principales conclusiones del estudio pueden establecerse; a) la calidad psicométrica de una batería de escalas sometidas a exhaustivo tratamiento estadístico, b) la presencia de niveles significativos de estrés y de sus variables asociadas en la muestra evaluada, lo que vincularía potencialmente la accidentabilidad y el estrés, y c) la presencia de correlaciones estadísticamente significativas entre las variables evaluadas.Del análisis de variables se extraen factores claves a ser considerados como puntos de partida en futuros programas de intervención para el manejo del estrés en los trabajadores.Stress has been defined as an interactive construct. It constitutes the reaction of a person both at a physiological and psychological level, when confronting a stimulus configured by the interaction of individual, environmental and social factors, leading to an adaptation or an imbalance of the organism.Departing from this definition which globalizes the theoretical perspective on thematter, this study constitutes an analysis of stress mechanisms through the evaluation of five variables: a) perceived stress; b) perception of family social support; c) perception of friends’ social support; d) the level of stress generated by worries or life events.These variables were studied in a group of 107 workers presenting a high index of accidents, belonging to an important mining company of Chile.Analysis of results was done through descriptive and correlated procedures. Thefirst was oriented at determining stress levels and its associated variables in the sample studied. The correlational analysis has as its objective to determine the degree of existing relationship among the variables and how these are associated with stress.The main conclusions are: a) the quality of a battery of scales undergoing an exhaustive statistical analysis; b) the presence of significant levels of stress and the associated variables in the sample being evaluated and c) the presence of statistically significant correlations among the evaluated variables.From the analysis of variables, key factors are extracted to be considered as points of departure for future programs of intervention in stress management of workers

Development of a Prototype for the Quality Control of Bovine Meat Determined by its Organoleptic Characteristics, based on an Automatic Inspection System for Artificial Vision

The world beef market is in full growth and with unsatisfied demands and prices up and these depend very much on their quality when arriving at the final consumer, while the national market, our country also has a future potential in the meat industry. In the present investigation is to evaluate the sensory characteristics of color and texture by means of the presence of a bovine meat sample in the system whose final result will be the acceptance or negation of its organoleptic quality. The system is constituted by a transport band in charge of taking the sample to a capsule where both the Lighting System (LS) and the Computer Vision System (CVS) are located, and when leaving there it will be automatically classified by an actuator, guaranteeing less manipulation and estimation of time by human intervention throughout the process while providing greater security to the final consumer about the meat that is entering their home. &nbsp