Long-Time Evolution of Gas-Free Disc Galaxies in Binary Systems

We present the results of several detailed numerical N-body simulations of the dynamical interactions of two equal mass disc galaxies. Both galaxies are embedded in spherical halos of dark matter and contain central bulges. Our analysis of the dynamical evolution of the binary system focuses on the morphological evolution of the stellar distribution of the discs. The satellite galaxy has coplanar or polar disc orientation in relation to the disc of the primary galaxy and their initial orbits are prograde eccentric ($e=0.1$, $e=0.4$ or $e=0.7$). Both galaxies have mass and size comparable to the Milky Way. We show that the merger of the two disc galaxies, depending on the relative orientation of the discs, can yield either a disc or lenticular remnant, instead of an elliptical one. These are the first simulations in the literature to show the formation of S0-like galaxies from protracted binary galaxy interactions. Additionally, we demonstrate that the time to merger increases linearly with the initial apocentric distance between the galaxies, and decreases with the initial orbital eccentricity. We also show that the tidal forces of the discs excite transient $m=1$ and $m=2$ wave modes, i.e., lopsidedness, spiral arms, and bars. However, after the merging of the discs, such instabilities fade completely, and the remnant is thicker and bigger than the original discs. The maximum relative amplitude of these waves is at most about 15 times greater compared to the control case. of these two wave modes. Finally, the disc settles down quickly, after the merger, in less than one outer disc rotation period.Comment: 23 pages, 3 tables and 16 figures. Accepted for publication in A&

Financial constraints, migration and inequality

Although the self-selection of emigrants is determined by di¤erences in the returns to education, according to the celebrated Roy model, empirical evidence suggests that migrants tend to be favorably selected. This paper argues that financial con- straints might be useful to explain this controversy. These constraints might impose positive correlations between (i) wealth and education, and (ii) wealth and migra- tion, implying a positive bias in the empirical results. We also show that high levels of migration premium and return to education in the source country explain the migration of middle-class individuals, a situation in which migration increases in- equality in the home country.migration, financial constraints, self-selection, human capital

A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy

We propose a new, more realistic, description of the perturbed gravitational potential of spiral galaxies, with spiral arms having Gaussian-shaped groove profiles. We investigate the stable stellar orbits in galactic disks, using the new perturbed potential. The influence of the bulge mass on the stellar orbits in the inner regions of a disk is also investigated. The new description offers the advantage of easy control of the parameters of the Gaussian profile of its potential. We find a range of values for the perturbation amplitude from 400 to 800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force to the axisymmetric force between 3% and 6%, approximately. Good self-consistency of arm shapes is obtained between the Inner Lindblad resonance (ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts to deviate from the imposed logarithmic spiral form. This creates bifurcations that appear as short arms. Therefore the deviation from a perfect logarithmic spiral in galaxies can be understood as a natural effect of the 4:1 resonance. Beyond the 4:1 resonance we find closed orbits which have similarities with the arms observed in our Galaxy. In regions near the center, in the presence of a massive bulge, elongated stellar orbits appear naturally, without imposing any bar-shaped potential, but only extending the spiral perturbation a little inward of the ILR. This suggests that a bar is formed with a half-size around 3 kpc by a mechanism similar to that of the spiral arms. The potential energy perturbation that we adopted represents an important step in the direction of self-consistency, compared to previous sine function descriptions of the potential. Our model produces a realistic description of the spiral structure, able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1

Screening forCronobacterSpecies in Powdered and Reconstituted Infant Formulas and from Equipment Used in Formula Preparation in Maternity Hospitals

Background/Aims: Cronobacter spp. have been identified as being of considerable risk to neonates. The occurrence of organism in infant formulas is therefore of considerable interest. Methods: The occurrence of Cronobacter spp. in infant feeds (formulas and fortified cow’s milk) was determined using most probable number (MPN) analysis, and from formula preparation utensils. Ninety nine samples were analyzed, of which 42 were unopened cans of powdered infant formula (PIF), 25 reconstituted infant formulas in feeding bottles, 27 utensils used from the preparation of infant formula, and 5 samples of fortified cow’s milk. Presumptive Cronobacter spp. isolates were identified using the 7 allele multilocus sequence typing (MLST) scheme. Results: C. sakazakii, C. malonaticus and C. muytjensii were recovered from PIF. Although the incidence of Cronobacter in PIF was 29% (12/42), the level was low with an average of 0.54 MPN/100g. According to MLST profiling, C. sakazakii was the most frequently isolated Cronobacter species, and C. sakazakii ST4 (associated with neonatal meningitis) was recovered from 2/42 PIF samples at 0.51 and 0.92 MPN/100g. Conclusions: Cronobacter spp. can be isolated from PIF and therefore strict hygienic practices during PIF preparation are important to minimize neonate exposure and reduce the risk of severe infections

Comparison of the solophenyl-red polarization method and the immunohistochemical analysis for collagen type III

In the present study, we have compared the staining pattern of the Solophenyl-Red 3 BL-method for the visualization of collagen type III with the immunohistochemical staining in serial sections from 7 skin wounds (wound age 3 days up to 4 weeks) to elucidate the specifity of the histochemical staining method. Large amounts of collagen type III were clearly detectable in the investigated wounds using the immunohistochemical technique. In the sections stained with Solophenyl-Red, however, only 3 out of 7 skin lesions showed a significant positive red staining at the wound margin or in the granulation tissue, while the adjacent normal connective tissue revealed a typical intensive staining. Using polarization microscopy no characteristic bright green fibrils, as reported for collagen type 111, could be seen in the wound areas without positive Solophenyl-Red staining. Since the localization of collagen type III detected by immunohistochemistry and the presumed distribution of this collagen type by the Solophenyl-Red method was not identical, the histochemical polarization method has to be regarded as non-specific for visualization of this collagen type

Equivalence between the Lovelock-Cartan action and a constrained gauge theory

We show that the four-dimensional Lovelock-Cartan action can be derived from a massless gauge theory for the $SO(1,3)$ group with an additional BRST trivial part. The model is originally composed by a topological sector and a BRST exact piece and has no explicit dependence on the metric, the vierbein or a mass parameter. The vierbein is introduced together with a mass parameter through some BRST trivial constraints. The effect of the constraints is to identify the vierbein with some of the additional fields, transforming the original action into the Lovelock-Cartan one. In this scenario, the mass parameter is identified with Newton's constant while the gauge field is identified with the spin-connection. The symmetries of the model are also explored. Moreover, the extension of the model to a quantum version is qualitatively discussed.Comment: 17 pages. No figures. Final version accepted for publication at the EPJ

REFLEXÕES TEÓRICAS E PRÁTICAS SOBRE OS NOVOS LETRAMENTOS E TECNOLOGIAS DIGITAIS: RELATO DE FORMAÇÃO DOCENTE. THEORETICAL REFLECTIONS AND PRACTICES RELATED TO NEW LITERACIES AND DIGITAL TECHNOLOGIES: A TEACHER TRAINING REPORT

O artigo apresenta o relato de experiência de formação, realizada no âmbito do Programa Mais Educação do MEC (Ministério da Educação), Brasil, de um grupo de professores de escolas públicas do estado do Ceará no eixo temático dos novos letramentos e das tecnologias digitais. A formação foi articulada em duas unidades que contemplaram três instâncias da temática trabalhada: a perspectiva sociocultural da cibercultura, a dimensão institucional da escola e a esfera profissional e pessoal do professor. A segunda unidade centrou-se ainda na análise crítica de uma experiência prática de uso de tecnologias digitais com fins educativos em um projeto de aprendizagem desenvolvido em parceria com a Universidade de Michigan, dos Estados Unidos, a partir da experiência contrastante de dois professores. A partir desses elementos a formação estabeleceu um processo dialogado e reflexivo com os professores participantes, contribuindo para sua compreensão sobre os dilemas e possíveis formas de atuação no Programa para uso educativo das tecnologias digitais a partir do paradigma da cibercultura e com fins de melhoria da aprendizagem. The paper presents the experience of teacher training conducted under the Mais Educação (More Education) Program from the Ministry of Education, Brazil, and attended by a group of public school teachers in the state of Ceará in order to learn about digital technologies and new literacies. The course was developed in two units; the first one addressed conceptual elements related to teacher identity in transition and their new professional roles, the dissonance between the paradigm of cyberspace and the space-time of schools. The second unit featured a review of a practical experience in the use of digital technologies for educational purposes on a learning project developed in partnership with the University of Michigan, U.S.A., based on the contrasting experiences of two teachers. The course established reflexive dialogues with participating teachers, contributing to their understanding of the dilemmas and possible ways of acting in the Program to promote improved educational use of digital technologies

Automated analysis of histological images by computational algorithms

The study of cellular tissues provides an incontestable source of information and comprehension about thehuman body and the surrounding environment. Accessing this information is, therefore, crucial to determineand diagnose a wide variety of pathologies detectable only at a microscopic scale. Hence, histology plays animportant role in the clinical diagnosis of pathologies involving abnormal cellular conformation. Inhistological images, semi- or automated segmentation algorithms are able to separate and identify cellularstructures according to morphological differences. The segmentation is usually the first task incomputational vision systems and, concerning histopathology, for the automated analysis of histologicalimages. Since the histological samples are thin, the volumetric features are almost unnoticeable,corresponding to losses of valuable information, mainly topographical and volumetric data, critical for acorrect analysis. Hence, the combination of segmentation and 3D reconstruction algorithms applied tohistological image datasets provides more information about the analyzed pathology and microscopicstructures, highlighting abnormal areas [1].In order to provide insights on pathological volumetric data, the present work focused on developing anautomatic computational solution for performing the 3D surface reconstruction of relevant tissue structurespresented in 2D histological slices. A state of the art technique, called stain deconvolution, was implementedto achieve color image segmentation providing an accurate segmentation of two different stains present inthe histological data: Hematoxylin and Eosin tissues. To register, i.e. align, the image slices presented in theinput datasets, an intensity based registration method was implemented, being the alignment performedbetween each slice in the input dataset and the reference slice (middle slice of the dataset). The datasetchosen for the previous alignment operation was the set of images obtained through the stain deconvolutionmethod for the hematoxylin stain. The transformation matrix obtained for each slice was then applied to theeosin stained images. The 3D reconstruction was implemented based on the Marching Cubes algorithm.Thus, combining algorithms of image segmentation and registration with of 3D surface reconstruction, itwas possible to obtain a volumetric representation of the pertinent tissue structures from the input imagedatasets. The experiments conducted revealed accurate and fast surface reconstructions of the differentstained tissues under study, highlighting the interesting structures and their volumetric interactions with thesurrounding healthy tissue