Constraining a possible time variation of the gravitational constant G with terrestrial nuclear laboratory data

Testing the constancy of the gravitational constant G has been a longstanding fundamental question in natural science. As first suggested by Jofr\'{e}, Reisenegger and Fern\'{a}ndez [1], Dirac's hypothesis of a decreasing gravitational constant $G$ with time due to the expansion of the Universe would induce changes in the composition of neutron stars, causing dissipation and internal heating. Eventually, neutron stars reach their quasi-stationary states where cooling due to neutrino and photon emissions balances the internal heating. The correlation of surface temperatures and radii of some old neutron stars may thus carry useful information about the changing rate of G. Using the density dependence of the nuclear symmetry energy constrained by recent terrestrial laboratory data on isospin diffusion in heavy-ion reactions at intermediate energies and the size of neutron skin in $^{208}Pb$ within the gravitochemical heating formalism, we obtain an upper limit of the relative changing rate of $|\dot{G}/G|\le4\times 10^{-12}yr^{-1}$ consistent with the best available estimates in the literature.Comment: 27 pages, 11 figures, and 2 tables. Accepted version to appear in PRC (2007

Optimal income tax enforcement in the presence of tax avoidance

This collection provides a comprehensive guide to students and academics on the subjects of tax avoidance from an interdisciplinary perspective

The role of eggs in the diet: nutraceutical and epigenetic aspects

The use of eggs in human diet has been object of many prejudices which are not yet completely disappeared The evolution of knowledge in the field of nutrition has, partially, countered these prejudices by highlighting the biological importance of several compounds present in the eggs. The nutritional and commercial revaluation of the eggs are passed through the enrichment of the lipid fraction in ω3 polyunsaturated fatty acids (PUFA ω3) which, have shown positive effects against cardiovascular diseases and development of the central nervous system and retina. The enrichment of eggs lipid with ω3 fatty acids is carried out by the integration of feeding hens with oils rich in ω3 fatty acids such as plant or marine oils. The results showed that the accumulation of ω3 in the egg yolk lipids is strongly affected by the type of oil used as supplement and by the amounts of oils administrated to the hens

Model selection for spectro-polarimetric inversions

Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios favor models without gradients along the line-of-sight. If the observations shows clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large signal-to-noise ratios favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future.Comment: 16 pages, 2 figures, 8 tables, accepted for publication in Ap

Sistema experto en análisis de fallas en líneas eléctricas de transmisión

Los Sistemas eléctricos de Transmisión están sometidos a distintos tipos de fallas, que degradan la capacidad de transporte de energía, y provocan como consecuencia un elevado costo en penalidades a la empresa responsable del transporte. Frente a las dificultades que plantea la obtención rápida de un diagnóstico, se estableció como objetivo el desarrollo de un Sistema Experto que procese en tiempo real la información adquirida y que frente a un suceso característico de una falla, emita un diagnóstico y asista a los especialistas y los operadores a identificar rápidamente el origen del problema y efectuar las operaciones que correspondan.Eje: Sistemas de información y MetaheurísticaRed de Universidades con Carreras en Informática (RedUNCI

Milne-Eddington inversion of the Fe I line pair at 630~nm

The iron lines at 630.15 and 630.25 nm are often used to determine the physical conditions of the solar photosphere. A common approach is to invert them simultaneously under the Milne-Eddington approximation. The same thermodynamic parameters are employed for the two lines, except for their opacities, which are assumed to have a constant ratio. We aim at investigating the validity of this assumption, since the two lines are not exactly the same. We use magnetohydrodynamic simulations of the quiet Sun to examine the behavior of the ME thermodynamic parameters and their influence on the retrieval of vector magnetic fields and flow velocities. Our analysis shows that the two lines can be coupled and inverted simultaneously using the same thermodynamic parameters and a constant opacity ratio. The inversion of two lines is significantly more accurate than single-line inversions because of the larger number of observables.Comment: Accepted for publication in Astronomy and Astrophysics (Research Note