Power spectra in extended tachyon cosmologies

In the present work the power spectrum of a particular class of tachyon fields is compared with the one corresponding to a cosmological constant model. This is done for different barotropic indexes $\gamma_0$ and the background space time is assumed to be of the spatially flat Friedmann-Robertson-Walker type. The differential equation describing the perturbations is solved numerically and the power spectrum at the scale factor value $a=1$ is plotted for each case. The result is that the power spectrum of the standard tachyon field differs in many magnitude orders from the $\Lambda$CDM. However, the one with $\gamma_0=1.91$, which corresponds to a complementary tachyon field, coincides fairly well with the concordance model. Therefore, we conclude that the perturbed solutions constitute an effective method to distinguish between the different $\gamma_0$ values for the tachionization $\Lambda$CDM model and the fiducial model. The Statefinder parameters $\{r, s\}$, measuring the deviations of the analysed model from the concordance model, are also explicitly calculated. Our result suggest that, depending on the value of $\gamma_0$, these models can explain the observed expansion history or the perturbation power spectrum of the universe, but they may have problems in describing both features simultaneously.Comment: 7 pages, 7 figures, accepted for publication in General Relativity and Gravitatio

Probing global aspects of a geometry by the self-force on a charge: Spherical thin-shell wormholes

The self-interaction for a static point charge in the space-time of a thin-shell wormhole constructed connecting two identical Schwarzschild geometries is calculated in a series expansion. The electrostatic self-force is evaluated numerically. It is found to be attractive towards the throat except for some values of the throat radius proximate to the value of the Schwarzschild horizon for which the force is repulsive or attractive depending on the position of the charge. The result differs from the self-force in the space-time of the Schwarzschild black hole, where it is always repulsive from the center. Although these wormhole and black hole geometries are locally indistinguishable, the different topologies of both backgrounds are manifested in the electrostatic field of a point charge.Comment: 17 pages, 4 figue

Emergent Universe as an interaction in the dark sector

A cosmological scenario where dark matter interacts with a variable vacuum energy for a spatially flat Friedmann-Robertson-Walker space-time is proposed and analysed to show that with a linear equation of state and a particular interaction in the dark sector it is possible to get a model of an Emergent Universe. In addition, the viability of two particular models is studied by taking into account recent observations. The updated observational Hubble data and the JLA supernovae data are used in order to constraint the cosmological parameters of the models and estimate the amount of dark energy in the radiation era. It is shown that the two models fulfil the severe bounds of $\Omega_{x}(z\simeq 1100)<0.009$ at the $2\sigma$ level of Planck.Comment: 15 pages, 8 figure

Exact quantum revivals for the Dirac equation

In the present work, the results obtained in [25] about the revivals of a relativistic fermion wave function on a torus are considerably enlarged. In fact, all the possible quantum states exhibiting revivals are fully characterized. The revivals are exact, that is, are true revivals without taking any particular limit such as the non relativistic one. The present results are of interest since they generalize the Talbot effect and the revivals already found by studying the Schr\"odinger equation to a relativistic situation with nonzero mass. This makes the problem nontrivial, as the dispersion relation is modified and is not linear. The results are obtained by the use of arithmetic tools which are described in certain detail along the text.Comment: 18 pages, 9 figure

Current induction and macroscopic forces for superconducting strings

Superconducting strings are topological defects appearing in cosmological early stage models, in tentative explanations of the high energy cosmic rays, galaxy formation and even in condensed matter to deal with some kind of superconductors. The main topic studied in this paper is the inverse photoelectric effect for superconducting lines namely, it is estimated the cross section corresponding to the adsorption of a fermion with the consequent emission of a photon. This issue is of importance, as some of these fermions can become a zero mode inside the core of the object, thus traveling at the speed of light and generating a possibly large current, whose cosmological implications has been discussed in a variety of works. A discussion is introduced comparing it to the Aharonov-Bohm cross section and relating them to the associated (Magnus) forces. It is also obtained a quite explicit description of the bound states and a version of Weyl's law for the energiesThe present work is supported by CONICET, Argentina and by the Grant PICT 2020-02181. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant agreement No. 777822. F. C. is partially supported by the PID2020–113350 GB-I00 grant of the MICINN (Spain) and by “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2019-000904-S

CONDUCTA DE CABRAS (Capra aegagrus hircus) ESTABULADAS EN CORRALETAS ALIMENTADAS CON BLOQUES NUTRICIONALES ELABORADOS CON PULPA DE MANGO

The production of goats in the tropics requires nutritional supplementation and the use of nutritional blocks (NB) made with local raw materials, such as mango. The objectives of the present study were to determine the NB consumption and to evaluate the consumption behavior of goats by replacing sugarcane molasses with mango pulp. The cane molasses were replaced at 0, 10, 20 and 30% by mango pulp in the elaboration of NB. NB consumption and hay of pangola grass were measured in four goats of the Bóer race and four creoles. The goats were fed with 1 kg of pangola grass and 1 kg of a NB each day. The variables were analyzed with a 4x4 Latin square repeat design. Behavior of the goats was obtained using a sweep sampling for 96 consecutive hours recording the behavior every 15 min. The frequencies of behaviors were analyzed using the Friedman test and behavior by type of NB with the Kruskal-Wallis test. Goats did not present differences (p&gt;0.05) in hay consumption of pangola grass and NB. NB consumption averaged 689 g d-1. Goats were observed mainly defecating, paws, urinating and balding, but without differences between behaviors (p&gt;0.05). Goats presented higher behavior using NB than forage (p?0.05). Goats showed no difference (p&gt;0.05) in their behavior by type of NB offered. Under these conditions. It is concluded that the partial or total substitution of sugarcane molasses for mango pulp does not affect the palatability of the block or the food consumption of the goats. Likewise, it does not modify the activities of the goats and their frequency.La producción de cabras (Capra aegagrus hircus) en el trópico requiere de suplementación nutricional y el uso de bloques nutrimentales (BN) elaborados con materias primas locales, tales como el mango (Mangifera indica L.). Se determinó el consumo de BN y evaluó el comportamiento de consumo de las cabras al sustituir la melaza de caña de azúcar (Saccharum spp.) por pulpa de mango. La melaza de caña se sustituyó en 0, 10, 20 y 30% por pulpa de mango en la elaboración de BN. El consumo de BN y heno de pasto pangola (Digitaria eriantha Steud) se midió en cuatro cabras de la raza Bóer y cuatro criollas. Las cabras se alimentaron con 1 Kg de pasto pangola y 1 Kg de un BN cada día. Las variables se analizaron con un diseño cuadrado latino 4x4 repetido. El comportamiento de las cabras se obtuvo usando un muestreo de barrido durante 96 h consecutivas registrando cada 15 min el comportamiento. La frecuencia conductual se analizó con la prueba Friedman y el comportamiento por tipo de BN con la prueba Kruskal-Wallis. Las cabras no presentaron diferencias (p&gt;0.05) en el consumo de heno de pasto pangola y BN. El consumo del BN fue en promedio 689 g d-1. Las cabras se observaron principalmente defecando, paradas, orinando y balando, pero sin diferencia entre conductas (p&gt;0.05). Las cabras presentaron mayor conducta consumiendo BN que forraje (p&gt;0.05), y no mostraron diferencias (p?0.05) en su conducta por tipo de BN ofrecido. Bajo estas condiciones, se concluye que la sustitución parcial o total de melaza de caña de azúcar por pulpa de mango no afecta la palatabilidad del bloque ni el consumo de alimento de las cabras, y no modifica las actividades de las cabras y su frecuencia

Bending behavior analysis of geogrid reinforced adobe walls

La tierra cruda constituye el material de construcción más importante en muchas regiones del planeta. Dado el riesgo sísmico existente en la mayor parte de estas regiones, es necesario el desarrollo de técnicas de refuerzo eficaces y adecuadas desde un punto de vista tecnológico y socioeconómico. Este artículo analiza desde un punto experimental y analítico el comportamiento a flexión de muros de adobe reforzados con geomallas. Las leyes momento-curvatura de los muros ensayados son aproximadas mediante una serie de modelos analíticos que permiten analizar el comportamiento del material compuesto adobe-geomalla. Los resultados obtenidos muestran como la geomalla mejora el comportamiento de la mampostería de adobe en términos de resistencia y ductilidad, mejorando así su comportamiento en caso de movimiento sísmico.Rammed earth is a widely used building material in many regions of the world. Due to the high seismic risk in those areas, earthen constructions require suitable and efficient reinforcement techniques from a technological and socioeconomic point of view. This paper analyzes the bending behavior of geogrid reinforced adobe walls from an experimental and analytical point of view. The experimental bending moment-curvature relationships are analytically approached. The results show how geogrid reinforcement improves the performance of adobe masonry in terms of strength and ductility. Thus, a better seismic performance is achieve

Bending behavior analysis of geogrid reinforced adobe walls

La tierra cruda constituye el material de construcción más importante en muchas regiones del planeta. Dado el riesgo sísmico existente en la mayor parte de estas regiones, es necesario el desarrollo de técnicas de refuerzo eficaces y adecuadas desde un punto de vista tecnológico y socioeconómico. Este artículo analiza desde un punto experimental y analítico el comportamiento a flexión de muros de adobe reforzados con geomallas. Las leyes momento-curvatura de los muros ensayados son aproximadas mediante una serie de modelos analíticos que permiten analizar el comportamiento del material compuesto adobe-geomalla. Los resultados obtenidos muestran como la geomalla mejora el comportamiento de la mampostería de adobe en términos de resistencia y ductilidad, mejorando así su comportamiento en caso de movimiento sísmico.Rammed earth is a widely used building material in many regions of the world. Due to the high seismic risk in those areas, earthen constructions require suitable and efficient reinforcement techniques from a technological and socioeconomic point of view. This paper analyzes the bending behavior of geogrid reinforced adobe walls from an experimental and analytical point of view. The experimental bending moment-curvature relationships are analytically approached. The results show how geogrid reinforcement improves the performance of adobe masonry in terms of strength and ductility. Thus, a better seismic performance is achieve