Detection of delta Scuti-like pulsation in H254, a pre-main sequence F-type star in IC 348

We present time series observations of intermediate mass PMS stars belonging to the young star cluster IC 348. The new data reveal that a young member of the cluster, H254, undergoes periodic light variations with delta Scuti-like characteristics. This occurrence provides an unambiguous evidence confirming the prediction that intermediate-mass pre-main sequence (PMS) stars should experience this transient instability during their approach to the main-sequence. On the basis of the measured frequency f=7.406 c/d, we are able to constrain the intrinsic stellar parameters of H254 by means of linear, non adiabatic, radial pulsation models. The range of the resulting luminosity and effective temperature permitted by the models is narrower than the observational values. In particular, the pulsation analysis allows to derive an independent estimate of the distance to IC 348 of about 320 pc. Further observations could either confirm the monoperiodic nature of H254 or reveal the presence of other frequencies.Comment: 7 pages, including 7 postscript figures, accepted for publication on A&

Amplituhedron meets Jeffrey-Kirwan Residue

The tree amplituhedra A^(m)_n,k are mathematical objects generalising the notion of polytopes into the Grassmannian. Proposed for m=4 as a geometric construction encoding tree-level scattering amplitudes in planar N=4 super Yang-Mills theory, they are mathematically interesting for any m. In this paper we strengthen the relation between scattering amplitudes and geometry by linking the amplituhedron to the Jeffrey-Kirwan residue, a powerful concept in symplectic and algebraic geometry. We focus on a particular class of amplituhedra in any dimension, namely cyclic polytopes, and their even-dimensional conjugates. We show how the Jeffrey-Kirwan residue prescription allows to extract the correct amplituhedron volume functions in all these cases. Notably, this also naturally exposes the rich combinatorial and geometric structures of amplituhedra, such as their regular triangulations.Peer reviewedFinal Accepted Versio

Collisional cross sections and momentum distributions in astrophysical plasmas: dynamics and statistical mechanics link

We show that, in stellar core plasmas, the one-body momentum distribution function is strongly dependent, at least in the high velocity regime, on the microscopic dynamics of ion elastic collisions and therefore on the effective collisional cross sections, if a random force field is present. We take into account two cross sections describing ion-dipole and ion-ion screened interactions. Furthermore we introduce a third unusual cross section, to link statistical distributions and a quantum effect originated by the energy-momentum uncertainty owing to many-body collisions, and propose a possible physical interpretation in terms of a tidal-like force. We show that each collisional cross section gives rise to a slight peculiar correction on the Maxwellian momentum distribution function in a well defined velocity interval. We also find a possible link between microscopical dynamics of ions and statistical mechanics interpreting our results in the framework of non-extensive statistical mechanics.Comment: 8 page

Crisis global de cuidados, migraciones transnacionales y remesas: impactos en y desde América Latina

Este artículo se propone en primer lugar, demostrar las relaciones significativas que tienen especificas condiciones demográficas y sociales con la reorganización global y reorientación regional de los flujos migratorios del cuidado, tanto en países con perfil tradicional de demanda de trabajo de cuidados remunerados como en aquellos más caracterizados por la oferta. En segundo lugar, se realiza una caracterización de la participación de países sudamericanos desde el último cuarto del siglo XX hasta la actualidad, en las dinámicas de las cadenas globales del cuidado. Finalmente, ante una nueva etapa de contracción económica en sentido regresivo que se reinició en 2015 en la región, en conjunción con el cierre de fronteras de los tradicionales países receptores de este tipo específico de migraciones feminizadas de cuidados, se ofrece un análisis sobre los desafíos que tales coyunturas acarrean en el presente y futuro inmediato en países del cono sur latino-americano. La metodología de este trabajo se asienta en el análisis e interpretación de bases de datos e información estadística publicada por fuentes oficiales, tanto de organismos internacionales como de sistemas estadísticos públicos nacionales en diálogo epistemológico con aportes teóricos provenientes de la literatura internacional de referencia en la temática

A game-based learning experience for improving cybersecurity awareness

The use of videogames is an established tool to train a systematic way of thinking that allows users to learn by gaming. In this paper, to address the increasing need of awareness in cybersecurity related issues, we present the realization of a Virtual Reality (VR) videogame targeted towards educating users in the context of cybersecurity

Excess centrosomes perturb dynamic endothelial cell repolarization during blood vessel formation

Blood vessel formation requires dynamic movements of endothelial cells (ECs) within sprouts. The cytoskeleton regulates migratory polarity, and centrosomes organize the microtubule cytoskeleton. However, it is not well understood how excess centrosomes, commonly found in tumor stromal cells, affect microtubule dynamics and interphase cell polarity. Here we find that ECs dynamically repolarize during sprouting angiogenesis, and excess centrosomes block repolarization and reduce migration and sprouting. ECs with excess centrosomes initially had more centrosome-derived microtubules but, paradoxically, fewer steady-state microtubules. ECs with excess centrosomes had elevated Rac1 activity, and repolarization was rescued by blockade of Rac1 or actomyosin blockers, consistent with Rac1 activity promoting cortical retrograde actin flow and actomyosin contractility, which precludes cortical microtubule engagement necessary for dynamic repolarization. Thus normal centrosome numbers are required for dynamic repolarization and migration of sprouting ECs that contribute to blood vessel formation