Chemical (in)homogeneity and atomic diffusion in the open cluster M67

Context. The benchmark open cluster M67 is known to have solar metallicity and similar age as the Sun. It thus provides us a great opportunity to study the properties of solar twins, as well as the evolution of Sun-like stars. Aims. Previous spectroscopic studies reported to detect possible subtle changes in stellar surface abundances throughout the stellar evolutionary phase, namely the effect of atomic diffusion, in M67. In this study we attempt to confirm and quantify more precisely the effect of atomic diffusion, as well as to explore the level of chemical (in)homogeneity in M67. Methods. We presented a strictly line-by-line differential chemical abundance analysis of two groups of stars in M67: three turn-off stars and three sub-giants. Stellar atmospheric parameters and elemental abundances were obtained with very high precision using the Keck/HIRES spectra. Results. The sub-giants in our sample show negligible abundance variations ($\le$ 0.02 dex), which implies that M67 was born chemically homogeneous. We note there is a significant abundance difference ($\sim$ 0.1 - 0.2 dex) between sub-giants and turn-off stars, which can be interpreted as the signature of atomic diffusion. Qualitatively stellar models with diffusion agree with the observed abundance results. Some turn-off stars do not follow the general pattern, which suggests that in some cases diffusion can be inhibited, or they might suffered some sort of mixing event related to planets. Conclusions. Our results pose additional challenges for chemical tagging when using turn-off stars. In particular, the effects of atomic diffusion, which could be as large as 0.1 - 0.2 dex, must be taken into account in order for chemical tagging to be successfully applied.Comment: 19 pages, 21 figures; submitted to A&A on February, 2019, accepted for publication in A&A on June, 201

Effective Lagrangian description of Higgs mediated flavor violating electromagnetic transitions: implications on lepton flavor violation

Higgs mediated flavor violating electromagnetic interactions, induced at the one--loop level by a nondiagonal $Hf_if_j$ vertex, with $f_i$ and $f_j$ charged leptons or quarks, are studied within the context of a completely general effective Yukawa sector that comprises $SU_L(2)\times U_Y(1)$--invariant operators of up to dimension--six. Exact formulae for the one--loop $\gamma f_if_j$ and $\gamma \gamma f_if_j$ couplings are presented and their related processes used to study the phenomena of Higgs mediated lepton flavor violation. The experimental limit on the $\mu \to e\gamma$ decay is used to derive a bound on the branching ratio of the $\mu \to e\gamma \gamma$ transition, which is 6 orders of magnitude stronger than the current experimental limit. Previous results on the $\tau \to \mu \gamma$ and $\tau \to \mu \gamma \gamma$ decays are reproduced. The possibility of detecting signals of lepton flavor violation at $\gamma \gamma$ colliders is explored through the $\gamma \gamma \to l_il_j$ reaction, putting special emphasis on the $\tau \mu$ final state. Using the bound imposed on the $H\tau \mu$ vertex by the current experimental data on the muon anomalous magnetic moment, it is found that about half a hundred events may be produced in the International Linear Collider.Comment: 18 pages, 12 figure

Sensibilidad a la colocación de los marcadores en el modelo convencional de análisis cinemático de la marcha

La correcta evaluación del movimiento articular a través de sistemas de análisis del movimiento depende, entre otros factores, de la correcta colocación de los marcadores reflectantes sobre los sujetos analizados. En el modelo convencional de marcha, de los 15 marcadores de miembro inferior, la mayoría se localizan en puntos anatómicos fáciles de localizar y que tienen poca posibilidad de error. Sin embargo, hay dificultad en otros, como el de la articulación de la rodilla y, sobre todo, en los del muslo y pierna. En el estudio, se empleó un sistema VICON 460, con el que se analizó la cinemática de miembro inferior de 5 sujetos adultos sanos (2 mujeres, 3 varones). Para evaluar los movimientos articulares se empleó el modelo convencional de marcha. Determinada la posición correcta de los marcadores en cada sujeto, se procedió a la variación por separado de los marcadores de la rodilla, el muslo y la pierna, moviendo cada uno 15 mm anterior y posteriormente con relación a la posición inicial. Estos pequeños desplazamientos producen importantes variaciones en los resultados cinemáticos obtenidos. Entre ellas en el varo-valgo de rodilla, parámetro que es de gran utilidad a la hora de detectar errores en la colocación de los marcadores

Nonlinear Dynamics of Dipoles in Microtubules: Pseudo-Spin Model

We perform a theoretical study of the dynamics of the electric field excitations in a microtubule by taking into consideration the realistic cylindrical geometry, dipole-dipole interactions of the tubulin-based protein heterodimers, the radial electric field produced by the solvent, and a possible degeneracy of energy states of individual heterodimers. The consideration is done in the frames of the classical pseudo-spin model. We derive the system of nonlinear dynamical ordinary differential equations of motion for interacting dipoles, and the continuum version of these equations. We obtain the solutions of these equations in the form of snoidal waves, solitons, kinks, and localized spikes. Our results will help to a better understanding of the functional properties of microtubules including the motor protein dynamics and the information transfer processes. Our considerations are based on classical dynamics. Some speculations on the role of possible quantum effects are also made.Comment: 14 pages, 15 figures. The high resolution figure files are available by reques

The impact of man on the morphodynamics of the Huelva coast (SW Spain)

The Huelva coast is composed by large sandy beaches and spits, only interrupted by the presence of the estuarine mouths of the Guadiana, Piedras, Tinto-Odiel and Guadalquivir which are in an advanced state of sediment infilling. The morphology and processes of the Huelva coast are mainly linked to tidal regime, wave action, coastal-drift currents, fluvial dynamics, climatic change and anthropogenic activity. In the last five decades anthropogenic activity has modified the natural dynamics by the construction of jetties, docks, harbour and coastal developments. The main consequences have been the interruption of the sedimentary bypassing caused by an active west-to-east littoral drift, the modification of the tidal regime, the wave refraction-diffraction scheme and the intensification of the littoral erosive processes. All these effects will increase with the slow sea-level rise, close to 0.6 cm per year, which will induce a higher efficacy of the erosional events. A future retreat of about 10-15 m of the coastline is estimated.La costa de Huelva esta constituida por extensas playas y flechas litorales, interrumpidas por la presencia de grandes estuarios (Guadiana, Piedras, Tinto-Odiel y Guadalquivir) en un estado avanzado de colmatación. La morfología y los procesos de la costa se deben principalmente a una serie de factores: régimen mareal, olas, corrientes de deriva, dinámica fluvial, cambio climático y la actividad antrópica. En las últimas cinco décadas la actividad antrópica ha modificado la dinámica natural debido a la construcción de espigones, escolleras, puertos y urbanizaciones. Las principales consecuencias de esta actividad han sido la interrupción del trasvase de sedimentos del Este hacia el Oeste por la corriente de deriva litoral, la alteración del régimen mareal, la modificación de los procesos de refracción-difracción de olas y la intensificación de los procesos erosivos. Todos estos efectos se verán incrementados con el paulatino ascenso del nivel del mar en el Golfo de Cádiz, del orden de 0,6 cm anuales, repercutiendo en una mayor eficacia de los eventos erosivos. Se estima una pérdida del orden de 10-15 m en el perfil de las playas