X-ray spectral variability of Seyfert 2 galaxies

Variability across the electromagnetic spectrum is a property of AGN that can help constraining the physical properties of these galaxies. This is the third of a serie of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern in a sample of optically selected type 2 Seyfert galaxies. We use the 26 Seyferts in the Veron-Cetty and Veron catalogue with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source are simultaneously fitted and we let different parameters to vary in the model. Whenever possible, short-term variations and/or long-term UV flux variations are studied. We divide the sample in Compton-thick, Compton-thin, and changing-look candidates. Short-term variability at X-rays is not found. From the 25 analyzed sources, 11 show long-term variations; eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related with absorbers at hard X-rays are less common, and in many cases these variations are accompained with variations of the nuclear continuum. At UV frequencies nuclear variations are nor found. We report for the first time two changing-look candidates, MARK273 and NGC7319. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results; the Compton-thick candidates are dominated by reflection, which supresses their continuum making them seem fainter, and not showing variations, while the Compton-thin and changing-look candidates show variations.Comment: Accepted for publication in A&

X-ray spectral variability of seven LINER nuclei with XMM-Newton and Chandra data

One of the most important features in active galactic nuclei (AGN) is the variability of their emission. Variability has been discovered at X-ray, UV, and radio frequencies on time scales from hours to years. Among the AGN family and according to theoretical studies, Low-Ionization Nuclear Emission Line Region (LINER) nuclei would be variable objects on long time scales. Our purpose is to investigate spectral X-ray variability in LINERs and to understand the nature of these kinds of objects, as well as their accretion mechanism. Chandra and XMM-Newton public archives were used to compile X-ray spectra of seven LINER nuclei at different epochs with time scales of years. To search for variability we fit all the spectra from the same object with a set of models, in order to identify the parameters responsible for the variability pattern. We also analyzed the light curves in order to search for short time scale (from hours to days) variability. Whenever possible, UV variability was also studied. We found spectral variability in four objects, with variations mostly related to hard energies (2-10 keV). These variations are due to changes in the soft excess, and/or changes in the absorber, and/or intrinsic variations of the source. Another two galaxies seem not to vary. Short time scale variations during individual observations were not found. Our analysis confirms the previously reported anticorrelation between the X-ray spectral index and the Eddington ratio, and also the correlation between the X-ray to UV flux ratio and the Eddington ratio. These results support an Advection Dominated Accretion Flow (ADAF) as the accretion mechanism in LINERs.Comment: 35 pages, 53 figures, recently accepted pape

X-ray spectral variability of LINERs selected from the Palomar sample

Variability is a general property of active galactic nuclei (AGN). At X-rays, the way in which these changes occur is not yet clear. In the particular case of low ionisation nuclear emission line region (LINER) nuclei, variations on months/years timescales have been found for some objects, but the main driver of these changes is still an open question. The main purpose of this work is to investigate the X-ray variability in LINERs, including the main driver of such variations, and to search for eventual differences between type 1 and 2 objects. We use the 18 LINERs in the Palomar sample with data retrieved from Chandra and/or XMM-Newton archives corresponding to observations gathered at different epochs. All the spectra for the same object are simultaneously fitted in order to study long term variations. The nature of the variability patterns are studied allowing different parameters to vary during the spectral fit. Whenever possible, short term variations from the analysis of the light curves and UV variability are studied.Comment: 49 pages, accepted. arXiv admin note: text overlap with arXiv:1305.222

Psychotria inegi, una especie nueva en Jalisco (México)

Abstract The new Psychotria species belongs to the panamensis-mexiae complex with its large long deciduous ferrugineous terminal stipules, but differs from them by having shorter inflorescence, 2–3 times larger flowers, smaller leaves and less numerous secondary nerves. It is of allopatric distribution being endemic to Jalisco state, while the area of P. mexiae Standl. extends from Veracruz to Costa Rica and the populations of P. panamensis Standl. are found from Veracruz to Colombia

The complexity of a numerical semigroup

Let S and Delta be numerical semigroups. A numerical semigroup S is an I(Delta)-semigroup if S \ {0} is an ideal of Delta. We denote by J (Delta) = {S vertical bar S is an I(Delta)-semigroupg, and we say that Delta is an ideal extension of S if S is an element of J (Delta). In this work, we present an algorithm to build all the ideal extensions of a numerical semigroup. We recursively denote by J(0) (N) = N; J(1)(N) = J (N) and J(k+1) (N) = J (J(k) (N)) for all k is an element of N: The complexity of a numerical semigroup S is the minimum of the set {k is an element of N vertical bar S is an element of J(k) (N)}. In addition, we introduce an algorithm to compute all the numerical semigroups with fixed multiplicity and complexity.Junta de Andalucia MTM2017-84890-

Mechanical modeling of collective cell migration: An agent-based and continuum material approach

We develop a novel modeling approach that combines a discrete agent-based model and a continuum material model to simulate collective cell migration in epithelial layers. In this approach, cells are represented as particles located at their geometrical center, but also as a polygonal body derived from the Voronoi diagram. Furthermore, we model the tissue as a continuum medium with different spatial domains that represent cell and substrate materials. In fact, the mechanical behavior of each domain is affected by the presence of cells from the discrete model. Moreover, we solve this mechanical problem using the finite element method (FEM). The forces generated by cells are projected to the FE mesh, that is created dynamically during the simulation from the discrete cell representation. After the FE resolution, we use the mesh displacements to determine the new cell positions in the agent-based model. Finally, to demonstrate the potential of this approach to model epithelial tissue mechanics, we simulate two well-studied cases of collective cell migration: durotaxis and gap closure. We use the experimental data from the literature to validate our numerical results. Therefore, the modeling strategy here presented offers a new perspective for a deeper understanding of tissue mechanics that emerge from cell dynamics in epithelial layers

Self-Assembly Behavior of Amphiphilic Janus Dendrimers in Water: A Combined Experimental and Coarse-Grained Molecular Dynamics Simulation Approach

Indexación: Scopus.Acknowledgments: M.E.E.G. thank the Ph. D. scholarship (251115) from CONACyT. The authors would like to thank: Luis Elizalde-Herrera (CIQA) for his help running the NMR spectra; Gloria Macedo-Raygoza and Miguel J. Beltrán-García (UAG), for their help in the measuring of MALDI-TOF mass spectra; and Maricela Rodríguez-Nieto and Jorge Luis Menchaca (UANL), for their help with the AFM measurements. FDGN thanks to the USA Air Force Office of Scientific Research Awards.Amphiphilic Janus dendrimers (JDs) are repetitively branched molecules with hydrophilic and hydrophobic components that self-assemble in water to form a variety of morphologies, including vesicles analogous to liposomes with potential pharmaceutical and medical application. To date, the self-assembly of JDs has not been fully investigated thus it is important to gain insight into its mechanism and dependence on JDs’ molecular structure. In this study, the aggregation behavior in water of a second-generation bis-MPA JD was evaluated using experimental and computational methods. Dispersions of JDs in water were carried out using the thin-film hydration and ethanol injection methods. Resulting assemblies were characterized by dynamic light scattering, confocal microscopy, and atomic force microscopy. Furthermore, a coarse-grained molecular dynamics (CG-MD) simulation was performed to study the mechanism of JDs aggregation. The obtaining of assemblies in water with no interdigitated bilayers was confirmed by the experimental characterization and CG-MD simulation. Assemblies with dendrimersome characteristics were obtained using the ethanol injection method. The results of this study establish a relationship between the molecular structure of the JD and the properties of its aggregates in water. Thus, our findings could be relevant for the design of novel JDs with tailored assemblies suitable for drug delivery systems. © 2018 by the authors.https://www.mdpi.com/1420-3049/23/4/96

Activity rhythms and the influence of some environmental variables on summer ungulate behaviour in Ordesa-Monte Perdido National Park

13 pages, 1 figure, 1 table, 2 photographs[EN] We have studied daily activity rhythms and time-budgets of four large herbivores (cattle, sheep, goats and chamois) which form a multi-species grazing system in a summer pastoral unit of the Central Pyrenees. Also, the influence of some environmental variables (altitude, slope and plant cover) on the main activities has been appraised. Grazing is the activity to which most time is dedicated in all the species: cattle 48%, sheep 53%, goats 55% and chamois 68%. Cattle is the species with the highest resting rate (41%) and sheep is the species spends most time walking (35%). Results suggest the existence of an inverse relationship between body size and grazing time. Cattle show two clear grazing peaks during the day at early morning and late evening. Contrary to this, sheep and chamois show a multimodal pattern, with some peaks for this activity throughout the day. Environmental factors clearly influence cattle and chamois activities. Sheep and goats show a less definite pattern in respect to environmental factors, probably because of their herded condition.[ES] Se estudian los ritmos de actividad diarios y la distribución del tiempo entre diferentes actividades, de cuatro grandes herbívoros (vacas, ovejas, cabras y rebecos) que utilizan durante el verano la misma unidad pastoral (Puerto de Góriz, Parque Nacional de Ordesa) en el Pirineo Central. Asimismo, se determina la influencia de diversas variables ambientales (altitud, pendiente y cobertura vegetal) sobre la conducta de dichos rumiantes. El pastoreo es la actividad a la que más tiempo dedican todas las especies: vacas 48%, ovejas 53%, cabras 55% y rebecos 68%. El ganado vacuno es la especie que más tiempo dedica al descanso (41%) y el ovino el que más tiempo emplea en desplazarse (35%). Los resultados sugieren la existencia de una relación inversa entre tamaño corporal y tiempo dedicado al pastoreo, ya apuntada por otros autores. Vacas y cabras presentan dos períodos máximos de pastoreo a primeras horas de la mañana y al atardecer, mientras que ovejas y rebecos presentan varios máximos de pastoreo a lo largo del día. Vacas y rebecos muestran claras relaciones entre varios tipos de actividad y los factores ambientales, mientras que la relación es menos aparente para ovejas y cabras.[FR] Nous avons étudié les rythmes d'activité journaliers ainsi que la distribution temporelle des différents types de comportement de quatre ongulés {vaches, brebis, chèvres et isards); ils utilisent la même unité pastorale (estive de Goriz) dans les Pyrénées Centrales, au Parc National d'Ordesa. Aussi nous avons evalué l'influence de diverses variables environnenmentales (altitude, pente et recouvrement végétal) sur le comportement des rumiants. Le pâturage devient l'activité prépondérante chez toutes les espèces: vaches 58%, brebis 53%, chèvres 55% et isards 68% du temps diurne. Les bovins passent plus de temps que les autres au repos (41%) et les brebis dédient beaucoup de leur temps au déplacement (35%). Ces résultats suggèrent une relation inverse le poids vif et le temps du pâturage, phénomène déjà noté par d'autres. Bovins et caprins montrent deus périodes maximales de pâturage: le matin et la tombée du jour, tandis qu'ovins et isards présentent plusieurs pics du pâturage pendant la journée. Enfin bovins et isards montrent des relations significatives entre chacun des différents types de conduite et certains de l'environnement, tandis que ces rapports s'avèrent moins clairs pour les brebis et les caprins.This study was developed within the frame of a CSICICONA co-operation project entitled «Livestock use of supraforestal pastures of the Ordesa-Monte Perdido National Park». The study was also partly supported by the Basque Government through two PhD grants.Peer reviewe