Dirac quasinormal modes for a 4-dimensional Lifshitz Black Hole

We study the quasinormal modes of fermionic perturbations for an asymptotically Lifshitz black hole in 4-dimensions with dynamical exponent z=2 and plane topology for the transverse section, and we find analytically and numerically the quasinormal modes for massless fermionic fields by using the improved asymptotic iteration method and the Horowitz-Hubeny method. The quasinormal frequencies are purely imaginary and negative, which guarantees the stability of these black holes under massless fermionic field perturbations. Remarkably, both numerical methods yield consistent results; i.e., both methods converge to the exact quasinormal frequencies; however, the improved asymptotic iteration method converges in a fewer number of iterations. Also, we find analytically the quasinormal modes for massive fermionic fields for the mode with lowest angular momentum. In this case, the quasinormal frequencies are purely imaginary and negative, which guarantees the stability of these black holes under fermionic field perturbations. Moreover, we show that the lowest quasinormal frequencies have real and imaginary parts for the mode with higher angular momentum by using the improved asymptotic iteration method.Comment: Version accepted for publication in EPJC. arXiv admin note: text overlap with arXiv:1306.597

Moir\'e patterns on STM images of graphite from surface and subsurface rotated layer

We have observed with STM moir\'e patterns corresponding to the rotation of one graphene layer on HOPG surface. The moir\'e patterns were characterized by rotation angle and extension in the plane. Additionally, by identifying border domains and defects we can discriminate between moir\'e patterns due to rotation on the surface or subsurface layer. For a better understanding of moir\'e patterns formation we have studied by first principles an array of three graphene layers where the top or the middle layer appears rotated around the stacking axis. We compare the experimental and theoretical results and we show the strong influence of rotations both in surface and subsurface layers for moir\'e patterns formation in corresponding STM images.Comment: 5 pages, 6 figure

Reconstructing paleoseismic deformation, 2: 1000 years of great earthquakes at Chucalén, south central Chile

In this paper we adopt a quantitative biostratigraphic approach to establish a 1000-year-long coastal record of megathrust earthquake and tsunami occurrence in south central Chile. Our investigations focus on a site in the centre of the rupture segment of the largest instrumentally recorded earthquake, the AD 1960 magnitude 9.5 Chile earthquake. At Chucalén coseismic subsidence in 1960 is recorded in the lithostratigraphy and biostratigraphy of coastal marshes, with peat overlain by minerogenic sediment and changes in the assemblages of diatoms (unicellular algae) indicating an abrupt increase in relative sea level. In addition to the 1960 earthquake, the stratigraphy at Chucalén records three earlier earthquakes, the historically documented earthquake of 1575 and two prehistoric earthquakes, radiocarbon dated to AD 1270–1450 and 1070–1220. Laterally extensive sand sheets containing marine or brackish diatom assemblages suggest tsunami deposition associated with at least two of the three pre-1960 earthquakes. The record presented here suggests a longer earthquake recurrence interval, averaging 270 years, than the historical recurrence interval, which averages 128 years. The lack of geologic evidence at Chucalén of two historically documented earthquakes, in 1737 and 1837, supports the previously suggested hypothesis of variability in historical earthquake characteristics. Our estimates of coseismic land-level change for the four earthquakes range from meter-scale subsidence to no subsidence or slight uplift, suggesting earthquakes completing each ∼270 year cycle may not share a common, characteristic slip distribution. The presence of buried soils at elevations below their modern equivalents implies net relative sea-level rise over the course of the Chucalén paleoseismic record, in contrast to relative sea-level fall over preceding millennia inferred from sites on the mainland. Sea-level rise may contribute to the preservation of evidence for multiple earthquakes during the last millennium, while net relative sea-level fall over the last 2000–5000 years may explain the lack of evidence for older earthquakes

On a Conjecture of Goriely for the Speed of Fronts of the Reaction--Diffusion Equation

In a recent paper Goriely considers the one--dimensional scalar reaction--diffusion equation $u_t = u_{xx} + f(u)$ with a polynomial reaction term $f(u)$ and conjectures the existence of a relation between a global resonance of the hamiltonian system $u_{xx} + f(u) = 0$ and the asymptotic speed of propagation of fronts of the reaction diffusion equation. Based on this conjecture an explicit expression for the speed of the front is given. We give a counterexample to this conjecture and conclude that additional restrictions should be placed on the reaction terms for which it may hold.Comment: 9 pages Revtex plus 4 postcript figure

Contribution of Collaborative Work to Teacher Reflection and the Transformation of Pedagogical Practices of School and University Science Teachers // Contribución del trabajo colaborativo en la reflexión docente y en la transformación de las prácticas pedagógicas de profesores de ciencia escolares y universitarios

Poor results of science learning, both at school and university, have led us to acknowledge the need to transform our teaching. Currently, reflection and collaborative work with colleagues are conceived as being key factors in the process of the transformation of practices. Based on the experiences of a group of school and university science teachers working on action-research, we describe the contribution that collaborative work has on reflection for the transformation of practices. The main aspects are the recognition of strengths and weaknesses, listening to and learning from the experience of others, and the discussion of specific classroom practices. On the other hand, these reflections contribute to the transformation at different levels: the teacher, classroom teaching practices, and the school community. The fact that it is a diverse group that includes both school and university teachers generate enriching reflections that help to transform practices in both areas. These reflections not only benefit the school system, but also science teachers education, and provide insights on a new University-School relationship // Los deficientes resultados de aprendizaje en el área de las ciencias, tanto en el ámbito escolar como universitario, nos han llevado a la necesidad de transformar nuestra enseñanza. En la actualidad, la reflexión y el trabajo colaborativo con colegas se conciben como claves en el proceso de transformación de las prácticas. A partir de la experiencia de un grupo de docentes escolares y universitarios de ciencia que realiza una investigación-acción, describimos la contribución que tiene el trabajo colaborativo sobre la reflexión para la transformación de las prácticas. Destacan aspectos como el reconocimiento de debilidades y fortalezas, el escuchar y aprender de la experiencia de otros y la discusión de prácticas concretas de aula. Por otra parte, estas reflexiones contribuyen a la transformación en diferentes niveles: del profesor, de las prácticas del docente en el aula y de la comunidad escolar. El hecho de que sea un grupo diverso, que incluye a profesores tanto del sistema escolar como universitario, genera reflexiones enriquecedoras, que ayudan a transformar las prácticas en estos dos ámbitos, beneficiando no solo al sistema escolar, sino también a la formación de profesores de ciencia, y dando luces acerca de una nueva relación universidad-escuela

(Correcting) misdiagnoses of asthma: A cost effectiveness analysis

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: The prevalence of physician-diagnosed-asthma has risen over the past three decades and misdiagnosis of asthma is potentially common. Objective: to determine whether a secondary-screening-program to establish a correct diagnosis of asthma in those who report a physician diagnosis of asthma is cost effective.Method: Randomly selected physician-diagnosed-asthmatic subjects from 8 Canadian cities were studied with an extensive diagnostic algorithm to rule-in, or rule-out, a correct diagnosis of asthma. Subjects in whom the diagnosis of asthma was excluded were followed up for 6-months and data on asthma medications and heath care utilization was obtained. Economic analysis was performed to estimate the incremental lifetime costs associated with secondary screening of previously diagnosed asthmatic subjects. Analysis was from the perspective of the Canadian healthcare system and is reported in Canadian dollars.Results: Of 540 randomly selected patients with physician diagnosed asthma 150 (28%; 95%CI 19-37%) did not have asthma when objectively studied. 71% of these misdiagnosed patients were on some asthma medications. Incorporating the incremental cost of secondary-screening for the diagnosis of asthma, we found that the average cost savings per 100 individuals screened was $35,141 (95$4,588-$69,278).Conclusion: Cost savings primarily resulted from lifetime costs of medication use averted in those who had been misdiagnosed.This work was funded by the Canadian Institute of Health Research, Canada and the University Of Ottawa Division Of Respiratory Medicine

Analysis of symmetries in models of multi-strain infections

In mathematical studies of the dynamics of multi-strain diseases caused by antigenically diverse pathogens, there is a substantial interest in analytical insights. Using the example of a generic model of multi-strain diseases with cross-immunity between strains, we show that a significant understanding of the stability of steady states and possible dynamical behaviours can be achieved when the symmetry of interactions between strains is taken into account. Techniques of equivariant bifurcation theory allow one to identify the type of possible symmetry-breaking Hopf bifurcation, as well as to classify different periodic solutions in terms of their spatial and temporal symmetries. The approach is also illustrated on other models of multi-strain diseases, where the same methodology provides a systematic understanding of bifurcation scenarios and periodic behaviours. The results of the analysis are quite generic, and have wider implications for understanding the dynamics of a large class of models of multi-strain diseases

The effect of bars on the M*- e relation: offset, scatter and residuals correlations

We analyse a set of collisionless disc galaxy simulations to study the consequences of bar formation and evolution on the M•-σe relation of supermassive black holes (SMBHs). The redistribution of angular momentum driven by bars leads to a mass increase within the central region, raising the velocity dispersion of the bulge, σe, on average by ˜12 per cent and as much as ˜20 per cent. If a disc galaxy with an SMBH satisfying the M•-σe relation forms a bar, and the SMBH does not grow in the process, then the increase in σe moves the galaxy off the M•-σe relation. We explore various effects that can affect this result including contamination from the disc and anisotropy. The displacement from the M•-σe relation for individual model barred galaxies correlates with both the bulge-to-total stellar mass ratio, M(B)/M(B + D), and the 2D anisotropy, βφ(B + D), both measured within the effective radius of the bulge. Overall, this process leads to an M•-σe for barred galaxies offset from that of unbarred galaxies, as well as an increase in its scatter. We assemble samples of observed unbarred and barred galaxies with classical bulges and find tentative hints of an offset between the two consistent with the predicted. Including all barred galaxies, rather than just those with a classical bulge, leads to a significantly larger offset, which is mostly driven by the significantly larger offset of pseudo bulge

The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.9 deg^2 of the COSMOS field down to limiting depths of 1.9 10^-16 erg cm^-2 s-1 in the 0.5-2 keV band, 7.3 10^-16 erg cm^-2 s^-1 in the 2-10 keV band, and 5.7 10^-16 erg cm^-2 s-1 in the 0.5-10 keV band. In this paper we report the i, K and 3.6micron identifications of the 1761 X-ray point sources. We use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources we were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only 2 sources are truly empty fields. Making use of the large number of X-ray sources, we update the "classic locus" of AGN and define a new locus containing 90% of the AGN in the survey with full band luminosity >10^42 erg/s. We present the linear fit between the total i band magnitude and the X-ray flux in the soft and hard band, drawn over 2 orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we test its known correlation with redshift and luminosity, and a recently introduced anti-correlation with the concentration index (C). We find a strong anti-correlation (though the dispersion is of the order of 0.5 dex) between C and X/O, computed in the hard band, and that 90% of the obscured AGN in the sample with morphological information live in galaxies with regular morphology (bulgy and disky/spiral), suggesting that secular processes govern a significant fraction of the BH growth at X-ray luminosities of 10^43- 10^44.5 erg/s.Comment: 21 pages, 17 figures, 4 tables; accepted for publication in ApJS. The catalog is available at the urls listed in the pape