On the weak field approximation of Brans-Dicke theory of gravity

It is shown that in the weak field approximation solutions of Brans-Dicke equations are simply related to the solutions of General Relativity equations for the same matter distribution. A simple method is developed which permits to obtain Brans-Dicke solutions from Einstein solutions when both theories are considered in their linearized forms. To illustrate the method some examples found in the literature are discussed.Comment: 12 pages, latex, no figure

Gravitomagnetic time delay and the Lense-Thirring effect in Brans-Dicke theory of gravity

We discuss the gravitomagnetic time delay and the Lense-Thirring effect in the context of Brans-Dicke theory of gravity. We compare the theoretical results obtained with those predicted by general relativity. We show that within the accuracy of experiments designed to measure these effects both theories predict essentially the same result.Comment: 10 pages Typeset using REVTE

A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy

We propose a new, more realistic, description of the perturbed gravitational potential of spiral galaxies, with spiral arms having Gaussian-shaped groove profiles. We investigate the stable stellar orbits in galactic disks, using the new perturbed potential. The influence of the bulge mass on the stellar orbits in the inner regions of a disk is also investigated. The new description offers the advantage of easy control of the parameters of the Gaussian profile of its potential. We find a range of values for the perturbation amplitude from 400 to 800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force to the axisymmetric force between 3% and 6%, approximately. Good self-consistency of arm shapes is obtained between the Inner Lindblad resonance (ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts to deviate from the imposed logarithmic spiral form. This creates bifurcations that appear as short arms. Therefore the deviation from a perfect logarithmic spiral in galaxies can be understood as a natural effect of the 4:1 resonance. Beyond the 4:1 resonance we find closed orbits which have similarities with the arms observed in our Galaxy. In regions near the center, in the presence of a massive bulge, elongated stellar orbits appear naturally, without imposing any bar-shaped potential, but only extending the spiral perturbation a little inward of the ILR. This suggests that a bar is formed with a half-size around 3 kpc by a mechanism similar to that of the spiral arms. The potential energy perturbation that we adopted represents an important step in the direction of self-consistency, compared to previous sine function descriptions of the potential. Our model produces a realistic description of the spiral structure, able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1

Experience with the Open Source based implementation for ATLAS Conditions Data Management System

Conditions Data in high energy physics experiments is frequently seen as every data needed for reconstruction besides the event data itself. This includes all sorts of slowly evolving data like detector alignment, calibration and robustness, and data from detector control system. Also, every Conditions Data Object is associated with a time interval of validity and a version. Besides that, quite often is useful to tag collections of Conditions Data Objects altogether. These issues have already been investigated and a data model has been proposed and used for different implementations based in commercial DBMSs, both at CERN and for the BaBar experiment. The special case of the ATLAS complex trigger that requires online access to calibration and alignment data poses new challenges that have to be met using a flexible and customizable solution more in the line of Open Source components. Motivated by the ATLAS challenges we have developed an alternative implementation, based in an Open Source RDBMS. Several issues were investigated land will be described in this paper: -The best way to map the conditions data model into the relational database concept considering what are foreseen as the most frequent queries. -The clustering model best suited to address the scalability problem. -Extensive tests were performed and will be described. The very promising results from these tests are attracting the attention from the HEP community and driving further developments.Comment: 8 pages, 4 figures, 3 tables, conferenc

Rendimientos del cultivo de colza en Mendoza con distintos regímenes de riego en períodos no críticos

Actualmente existe interés en el cultivo de colza (Brassica napus) para la obtención de biodiesel porque sus semillas contienen hasta un 50% de su peso en materia grasa. Desde hace un tiempo, debido a la producción de biocombustibles, el cultivo cobró impulso, como bioenergético, dado que cumple con todos los requisitos de calidad, de acuerdo al estándar europeo (Körbitz, 1999). Si bien en Argentina la producción de aceites vegetales se hace exclusivamente basándose en cultivos estivales, la colza se presenta como una interesante alternativa de producción invernal para una amplia zona. En Argentina, a partir del año 2010 debe usarse en el gasoil un mínimo de 5% de biodiesel. Por esa razón consideramos importante realizar esta experiencia en colza. Al ser un cultivo de ciclo inverno-primaveral, el uso del recurso hídrico no compite con los principales cultivos de la región que en su gran mayoría son de ciclo primavero estival. Mendoza es de clima árido, donde los cultivos solo prosperan bajo riego y como es sabido, el agua es un recurso escaso. Esto nos motivó a cuantificar sus necesidades hídricas totales y también a determinar el manejo óptimo del riego en cuanto a láminas y momentos de aplicación, a fin de maximizar la ecuación producción por m 3 de agua aplicada. Encontramos importante determinar y cuantificar esos “ahorros de agua" que se puedan realizar durante la fase o período no crítico al estrés hídrico, sin que esto produzca disminuciones en el rendimiento. Se propuso analizar durante dos años la respuesta del cultivo al riego diferenciado, aplicándo 4 diferentes tratamientos durante el período no sensible, reponiéndose en todos los casos durante el período crítico el 100% de la demanda evapotranspirativa. Los períodos no sensibles son: Fase nº 1: Plántula, Roseta y Elongación y Fase nº 3 de endurecimiento de grano a cosecha. Esta experiencia se llevó a cabo en los dos predios que posee la Facultad de Ciencias Agrarias. (Bermejo y Luján ambos sitios ubicados dentro del oasis norte. Mendoza, Argentina) La variedad utilizada fue: SW 2836, variedad de tipo primaveral, ciclo corto. Los tratamientos fueron los siguientes: T0 en donde se aplicó el 100 % de las necesidades hídricas del cultivo y luego tres tratamientos denominados T1, T2 y T3 en los que se aplicó respectivamente el 125, 75 y 50 % de las mismas. También se cuantificaron los rendimientos en semilla y aceite que se obtuvieron con distintos manejos del riego en cuanto a láminas y momentos de aplicación, para determinar el manejo que maximice la ecuación Kg de semilla y/o aceite por m 3 de agua aplicada. Es importante destacar que en esta experiencia contamos con estudiantes avanzados de la carrera de agronomía, como así también con personal de campo de las fincas de la facultad.Fil: Antonini, C. A. Universidad Nacional de Cuyo. Facultad de Ciencias AgrariasFil: Barros, R. A. Universidad Nacional de Cuyo. Facultad de Ciencias Agraria

Precise masses for the transiting planetary system HD 106315 with HARPS

Context. The multi-planetary system HD 106315 was recently found in K2 data. The planets have periods of P_b ~ 9.55 and P_c ~ 21.06 days, and radii of r_b = 2.44 ± 0.17 R⊕ and r_c = 4.35 ± 0.23 R⊕. The brightness of the host star (V = 9.0 mag) makes it an excellent target for transmission spectroscopy. However, to interpret transmission spectra it is crucial to measure the planetary masses. Aims. We obtained high precision radial velocities for HD 106315 to determine the mass of the two transiting planets discovered with Kepler K2. Our successful observation strategy was carefully tailored to mitigate the effect of stellar variability. Methods. We modelled the new radial velocity data together with the K2 transit photometry and a new ground-based partial transit of HD 106315c to derive system parameters. Results. We estimate the mass of HD 106315b to be 12.6 ± 3.2 M⊕ and the density to be 4.7 ± 1.7 g cm^(-3), while for HD 106315c we estimate a mass of 15.2 ± 3.7 M⊕ and a density of 1.01 ± 0.29 g cm^(-3). Hence, despite planet c having a radius almost twice as large as planet b, their masses are consistent with one another. Conclusions. We conclude that HD 106315c has a thick hydrogen-helium gaseous envelope. A detailed investigation of HD 106315b using a planetary interior model constrains the core mass fraction to be 5–29%, and the water mass fraction to be 10–50%. An alternative, not considered by our model, is that HD 106315b is composed of a large rocky core with a thick H–He envelope. Transmission spectroscopy of these planets will give insight into their atmospheric compositions and also help constrain their core compositions

Circular Cosmic String Loop in Brans-Dicke Theory

The gravitational field of a stationary circular cosmic string loop ,externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding solution in GR when the Brans-Dicke parameter $\omega$ becomes infinitely large

Global aspects of gravitomagnetism

We consider global properties of gravitomagnetism by investigating the gravitomagnetic field of a rotating cosmic string. We show that although the gravitomagnetic field produced by such a configuration of matter vanishes locally, it can be detected globally. In this context we discuss the gravitational analogue of the Aharonov-Bohm effect.Comment: 10 pages - Typeset using REVTE