Industry concentration and market volatility

In this paper our aim is to gain a better understanding of the relationship between market volatility and industrial structure. As conflicting results have been documented regarding the relationship between market industry concentration and market volatility, this study investigates this relationship in the time series. We have found that this relationship is only significant and positive for Spain. Our results suggest that we cannot generalize across different countries that market industrial structure (concentration) is a significant factor in explaining market volatility

Transmisión de información y carteras óptimas en el mercado bursátil español

ResumenEn este trabajo se analiza la transmisión de información y la formación de carteras de mínimo riesgo óptimas entre las empresas de mayor, mediano y pequeño tamaño del mercado de valores español representadas, respectivamente, por los índices bursátiles IBEX 35, IBEX MEDIUM CAP e IBEX SMALL CAP. La comparación de dos modelos de volatilidad, uno multivariante simétrico y otro asimétrico con cambios estructurales, muestra que existen diferencias en la transmisión de volatilidad. Las carteras de mínimo riesgo, por su parte, están formadas en todos los escenarios posibles analizados por la combinación de las empresas de mediano y pequeño tamaño (con una mayor ponderación de las empresas medianas) siendo, incluso, menor el riesgo cuando se consideran los efectos asimétricos y los cambios estructurales en la volatilidad. Estos resultados, pues, refuerzan el interés por conocer las características de este tipo de empresas frente a las que componen el IBEX 35.AbstractThis article examines the transmission of volatility and the creation of optimal risk minimizing portfolios among large-, medium- and small-capitalization companies of the Spanish stock market, which are represented by the IBEX 35, IBEX MEDIUM CAP and IBEX SMALL CAP indexes respectively. A comparison of two volatility models, a symmetric and an asymmetric multivariate GARCH model with structural changes, shows that there are differences in the transmission of volatility. We demonstrate that, in all the possible scenarios analyzed, the risk minimizing portfolio is composed of medium and small indexes with a higher weight of medium firms. The risk is even lower when asymmetric effects and structural changes are taken into account. These results therefore illustrate the importance of knowing the main characteristics of these firms with respect to those than compose the IBEX 35 index

Intraday linkages between the Spanish and the US stock markets: evidence of an overreaction effect

This paper focuses on short-term information transmission between the US stock market, properly the DOW index, and the main Spanish stock index, IBEX-35, in its early and final hours. We follow the approaches of Lin, Engle and Ito (1994), Susmel and Engle (1994) and Baur and Jung (2005) who use a GARCH model to analyze the influence of the previous daytime and overnight returns and volatility of the DOW upon the overnight returns and daytime returns of the IBEX from Open-to-3:30 and from 3:30-to-Close. The results suggest that the Spanish stock market usually has a low price movement till Wall Street opens. Additionally, they indicate that the Spanish market reacts quickly to the news, basically in the first four minutes following the opening of the US market. Furthermore, we find the existence of an overreaction effect during the two hours before the closing of the Spanish market

La enseñanza de la física en el siglo XVIII: La física moderna, racional y experimental (1745) de Andrés Piquer Arrufat (primer libro de física escrito en español)

En este trabajo pretendemos llegar al conocimiento de la situación, influencia y nivel de la Ciencia Física en el siglo XVIII

On the magnetic field evolution timescale in superconducting neutron star cores

We revisit the various approximations employed to study the long-term evolution of the magnetic field in neutron star cores and discuss their limitations and possible improvements. A recent controversy on the correct form of the induction equation and the relevant evolution timescale in superconducting neutron star cores is addressed and clarified. We show that this ambiguity in the estimation of timescales arises as a consequence of nominally large terms that appear in the induction equation, but which are, in fact, mostly irrotational. This subtlety leads to a discrepancy by many orders of magnitude when velocity fields are absent or ignored. Even when internal velocity fields are accounted for, only the solenoidal part of the electric field contributes to the induction equation, which can be substantially smaller than the irrotational part. We also argue that stationary velocity fields must be incorporated in the slow evolution of the magnetic field as the next level of approximation.Comment: 6 pages, version accepted by MNRA

The relevance of ambipolar diffusion for neutron star evolution

We study ambipolar diffusion in strongly magnetised neutron stars, with special focus on the effects of neutrino reaction rates and the impact of a superfluid/superconducting transition in the neutron star core. For axisymmetric magnetic field configurations, we determine the deviation from $\beta-$equilibrium induced by the magnetic force and calculate the velocity of the slow, quasi-stationary, ambipolar drift. We study the temperature dependence of the velocity pattern and clearly identify the transition to a predominantly solenoidal flow. For stars without superconducting/superfluid constituents and with a mixed poloidal-toroidal magnetic field of typical magnetar strength, we find that ambipolar diffusion proceeds fast enough to have a significant impact on the magnetic field evolution only at low core temperatures, $T \lesssim 1-2\times10^8$ K. The ambipolar diffusion timescale becomes appreciably shorter when fast neutrino reactions are present, because the possibility to balance part of the magnetic force with pressure gradients is reduced. We also find short ambipolar diffusion timescales in the case of superconducting cores for $T \lesssim 10^9$ K, due to the reduced interaction between protons and neutrons. In the most favourable scenario, with fast neutrino reactions and superconducting cores, ambipolar diffusion results in advection velocities of several km/kyr. This velocity can substantially reorganize magnetic fields in magnetar cores, in a way that can only be confirmed by dynamical simulations.Comment: 14 pages, 11 figures, version accepted for publication in MNRA

Population synthesis of isolated Neutron Stars with magneto--rotational evolution

We revisit the population synthesis of isolated radio-pulsars incorporating recent advances on the evolution of the magnetic field and the angle between the magnetic and rotational axes from new simulations of the magneto-thermal evolution and magnetosphere models, respectively. An interesting novelty in our approach is that we do not assume the existence of a death line. We discuss regions in parameter space that are more consistent with the observational data. In particular, we find that any broad distribution of birth spin periods with $P_0\lesssim 0.5$ s can fit the data, and that if the alignment angle is allowed to vary consistently with the torque model, realistic magnetospheric models are favoured compared to models with classical magneto-dipolar radiation losses. Assuming that the initial magnetic field is given by a lognormal distribution, our optimal model has mean strength $\langle\log B_0{\rm [G]}\rangle \approx 13.0-13.2$ with width $\sigma (\log B_0) = 0.6-0.7$. However, there are strong correlations between parameters. This degeneracy in the parameter space can be broken by an independent estimate of the pulsar birth rate or by future studies correlating this information with the population in other observational bands (X-rays and $\gamma$-rays).Comment: 10 pages, 9 figures, submitted and accepted to MNRAS, comments welcom

El uso del correo electrónico en el trabajo

Treball final de Grau en Relacions Laborals i Recursos Humans. Codi: RL0947. Curs academic 2015-201

Guidoblogs: dinamizando la blogosfera de Conservatorios y Escuelas de Música

El blog, como medio digital de comunicación en la sociedad de la información sirve principalmente como nexo de unión entre los diferentes miembros de la Comunidad Educativa, propiciando el flujo de información y conocimiento en diversas direcciones: profesor ↔ alumno, alumno ↔ familia, familia ↔ profesor, profesor ↔ profesor, alumno ↔ alumno,... GuidoBlogs.org es un planeta de blogs.Blogs, as digital communication environments in the information society, stand as links mainly between the different members of the educational community, thus fostering the flux of information and knowledge in a plethora of directions: teacher ↔ student, student ↔ family, family ↔ teacher, teacher ↔ teacher, student ↔ student, etc. GuidoBlogs.org represents that world of blogs