Exotic Compact Objects and How to Quench their Ergoregion Instability

Gravitational-wave astronomy can give us access to the structure of black holes, potentially probing microscopic or even Planckian corrections at the horizon scale, as those predicted by some quantum-gravity models of exotic compact objects. A generic feature of these models is the replacement of the horizon by a reflective surface. Objects with these properties are prone to the so-called ergoregion instability when they spin sufficiently fast. We investigate in detail a simple model consisting of scalar perturbations of a Kerr geometry with a reflective surface near the horizon. The instability depends on the spin, on the compactness, and on the reflectivity at the surface. The instability time scale increases only logarithmically in the black-hole limit and, for a perfectly reflecting object, this is not enough to prevent the instability from occurring on dynamical time scales. However, we find that an absorption rate at the surface as small as 0.4% (reflectivity coefficient as large as $|{\cal R}|^2=0.996$) is sufficient to quench the instability completely. Our results suggest that exotic compact objects are not necessarily ruled out by the ergoregion instability.Comment: v3: 14 pages, 9 figures; further clarifications added, new appendix on the superspinar case, results unchanged. Accepted in Phys. Rev.

Analysis of the Catecholaminergic Phenotype in Human SH-SY5Y and BE(2)-M17 Neuroblastoma Cell Lines upon Differentiation

Human cell lines are often used to investigate cellular pathways relevant for physiological or pathological processes or to evaluate cell toxicity or protection induced by different compounds, including potential drugs. In this study, we analyzed and compared the differentiating activities of three agents (retinoic acid, staurosporine and 12-O-tetradecanoylphorbol-13-acetate) on the human neuroblastoma SH-SY5Y and BE(2)-M17 cell lines; the first cell line is largely used in the field of neuroscience, while the second is still poorly characterized. After evaluating their effects in terms of cell proliferation and morphology, we investigated their catecholaminergic properties by assessing the expression profiles of the major genes involved in catecholamine synthesis and storage and the cellular concentrations of the neurotransmitters dopamine and noradrenaline. Our results demonstrate that the two cell lines possess similar abilities to differentiate and acquire a neuron-like morphology. The most evident effects in SH-SY5Y cells were observed in the presence of staurosporine, while in BE(2)-M17 cells, retinoic acid induced the strongest effects. Undifferentiated SH-SY5Y and BE(2)-M17 cells are characterized by the production of both NA and DA, but their levels are considerably higher in BE(2)-M17 cells. Moreover, the NAergic phenotype appears to be more pronounced in SH-SY5Y cells, while BE(2)-M17 cells have a more prominent DAergic phenotype. Finally, the catecholamine concentration strongly increases upon differentiation induced by staurosporine in both cell lines. In conclusion, in this work the catecholaminergic phenotype of the human BE(2)-M17 cell line upon differentiation was characterized for the first time. Our data suggest that SH-SY5Y and BE(2)-M17 represent two alternative cell models for the neuroscience field

Grown and artificial mosaic GaAs crystals for hard X-ray astronomy

In order to increase the collection efficiency of a lens for hard X-ray energies, mosaic GaAs crystals to be used as optic elements in Laue diffraction are proposed. In fact, GaAs crystals show a natural degree of mosaicity due to the spontaneous formation during the growth of cellular structures with dislocations at the boundaries. Several GaAs samples grown by LEC method have been characterized by means of high-resolution X-ray diffraction. Mosaicity values ranging from 10 to 25 arcsec have been measured. Since proper growth conditions allow to control and modify both the dislocation density and the cellular structure responsible of the mosaic spread, the possibility of obtaining crystals with a given degree of mosaicity by tuning the LEC growth conditions is proposed. A complementary strategy to increase the Darwin width of the diffraction curve based on curved crystals has also been proposed. The lattice curvature was achieved by introducing a compressive stress on the crystal surface. Curvature radii between 2 and 8m were easily obtained in wafer crystals 500 μm thick

Estudo retrospectivo dos atendimentos a animais silvestres de vida livre (2016-2018) no Núcleo de Conservação e Reabilitação de Animais Silvestres da Universidade Federal do Rio Grande do Sul

O Brasil é considerado o país com a maior biodiversidade do mundo mas apesar disso com o crescimento da população e a exigência de expansão socioeconômica, a cada dia a fauna silvestre perde espaço e aumentam os conflitos entre humanos e animais. Dessa maneira foi realizado um estudo retrospectivo dos atendimentos realizados a animais silvestres de vida livre pelo Núcleo de Conservação e Reabilitação de Animais Silvestres (PRESERVAS) do Hospital de Clínicas Veterinária (HCV) da Universidade Federal do Rio Grande do Sul (UFRGS) entre os anos de 2016 e 2018. Foram analisados os dados referentes ao número de atendimentos, as principais classes, espécies, fase de desenvolvimento, origem, destinação, conflitos, etiologias de atendimento e o tempo de permanência. Durante os três anos foram realizados 955 atendimentos, sendo a classe das aves a mais prevalente (56,44%) seguida pela dos mamíferos (34,97%). As ordens com maior ocorrência foram a Didelphimorphia (19,27%) e os Passeriformes (16,13%), e a espécie mais frequente foi o Gambá-de-orelha-branca (Didelphis albiventris) (19,27%). Os meses de setembro a janeiro foram os com maior número de atendimentos no setor. Foi detectada a ocorrência de seis espécies consideradas invasoras. Foram recebidos animais de 46 diferentes municípios, sendo que 44,4%, dos atendimentos foram da cidade de Porto Alegre e 18,4% de Viamão. A entrega por populares foi a principal forma de chegada dos animais atendidos no núcleo (58,01%). Adultos (37,17%) e animais de sexo indefinido (60%) foram os mais frequentes. Os históricos mais encontrados foram os “órfãos” (45,77%) e “encontrado em área urbana, via pública ou propriedade rural” (22,58%). As etiologias de atendimento de “criação artificial” (30,05%) e do sistema musculoesqueléticos (23,35%) foram as mais registradas. O óbito foi o principal desfecho (48,65%). O tempo médio de permanência em internação foi de 24,64 dias, mas houve grande variação entre atendimentos. Baseado nos achados é possível concluir que o PRESERVAS atende animais silvestres principalmente da região metropolitana de Porto Alegre e originários de conflitos antrópicos. Dessa forma, há necessidade de políticas públicas visando a mitigação de tais problemas, visto que a educação ambiental é um importante aliado para a conscientização da população.Brazil is considered to be the country with the world's largest biodiversity, however with population growth and the socioeconomic expansion every day the wild fauna loses space and the conflicts between humans and animals increase. Thus, a retrospective study was made of the cases of free-living animals received by the Núcleo de Conservação e Reabilitação de Animais Silvestres (PRESERVAS) of the Hospital de Clínicas Veterinária (HCV) of the Universidade Federal do Rio Grande do Sul (UFRGS) between the years 2016 and 2018. The data analyzed was referent of the number of animals received, such as the main classes, species, development phase, origin, destination, conflicts, etiology of attendance and the length of stay. During the three years, 955 cases were received, the bird class being the most prevalent (56.44%) followed by the mammalian group (34.97%). The orders with the highest frequency were Didelphimorphia (19.27%) and Passeriformes (16.13%), and the species with the higher frequency was that of Opossum-White-Eared (Didelphis albiventris) (19.27%). The months of September to january were the ones with the highest number of attendances in the sector. The occurrence of six invasive species was detected. Animals from 46 different cities were received, of which 44.4% were from the city of Porto Alegre and 18.4% from Viamão. Delivery by people was the main form of entry of the animals treated in the nucleus (58.01%). Adults (37.17%) and animals of undefined sex (60%) were more frequent. The two most frequente backgrounds described were “orphans” (45.77%) and “found in urban, public or rural property” (22.58%). As etiology of attendance "artificial creation" (30.05%) and musculoskeletal system (23.35%) were the most recorded. Death remained as the main (48.65%) outcome. The mean length of hospital stay was 24.64 days, but there was a large variation between cases. Based on the findings, it is possible to conclude that the PRESERVAS serves wild animals mainly from the metropolitan region of Porto Alegre and originated from anthropic conflicts. Thus, there is a need for public policies aimed at mitigating such problems, since environmental education is an important ally for raising public awareness

Percepção da imagem corporal e fatores associados em universitários do curso de educação física

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Desportos. Programa de Pós-Graduação em Educação Física.Objetivou-se verificar a prevalência de insatisfação com a imagem corporal e a associação com características sociodemográficas (sexo, idade, escolaridade dos pais, estado civil, curso, trabalho, moradia, turno de estudo e renda); comportamentos relacionados à saúde (hábitos alimentares, uso do tabaco e consumo excessivo de bebidas alcoólicas); estado nutricional. Foram avaliados 36 universitários (40% da população), sendo 124 do curso de licenciatura e 127 homens, selecionados por voluntariedade. A percepção da imagem corporal foi mensurada utilizando a escala de silhuetas corporais e as variáveis sociodemográficas, nível de atividade física, hábitos alimentares e estado nutricional por meio de um questionário em versão web construído a partir de instrumentos validados e empregados em outros estudos no Brasil. Os dados foram tratados utilizando-se a estatística descritiva apropriada e a associação entre as variáveis por meio de qui-quadrado (exato de Fisher) e da regressão multinomial utilizando o pacote estatístico SPSS®, versão 15.0. O nível de significância adotado foi de 5%. A insatisfação com a imagem corporal foi de 69,7% no sexo masculino e 69,3% no feminino. A insatisfação por excesso esta associada ao sexo feminino e ao IMC 25,0 kg/m². Os fatores associados à insatisfação por magreza foram: sexo masculino, prática de <739,61min semanais de atividade física, alimentação inadequada e consumir tabaco. Com relação aos estágios de mudança de comportamento, o mesmo esteve associado à insatisfação com a imagem corporal para o sexo feminino, sendo que as mulheres que apresentaram um comportamento inativo fisicamente demonstraram insatisfação tanto por excesso de peso, quanto por magreza. Estes achados indicam, a necessidade de intervenções voltadas a aceitação corporal no ambiente acadêmico a partir da aquisição de comportamentos saudáveis, como, rática regular de atividade física e alimentação adequada, a fim de gerar maior satisfação com a imagem corporal

Electronic and magnetic states in core multishell nanowires: Edge localization, Landau levels and Aharonov-Bohm oscillations

We study the electronic states of hexagonal core multishell semiconductor nanowires, including the effect of magnetic fields. We find that the two dimensional electron states formed at the interface between different layers are mostly localized at the six edges of the hexagonal prism, and behave as a set of quasi-1D quantum channels. They can be manipulated by magnetic fields either parallel or perpendicular to the wire axis. These results can be rationalized in terms of Aharonov-Bohm oscillations or Landau level formation. We also show that inter-channel coupling and magnetic behavior is influenced by the geometric details of the nanowires. © 2009 IOP Publishing Ltd

Magnetic states in prismatic core multishell nanowires

We study the electronic states of core multi-shell semiconductor nanowires, including the effect of strong magnetic fields. We show that the multi-shell overgrowth of a free-standing nanowire, together with the prismatic symmetry of the substrate, may induce quantum confinement of carriers in a set of quasi-1D quantum channels corresponding to the nanowire edges. Localization and inter-channel tunnel coupling are controlled by the curvature at the edges and the diameter of the underlying nanowire. We also show that a magnetic field may induce either Aharonov-Bohm oscillations of the energy levels in the axial configuration, or a dimensional transition of the quantum states from quasi-1D to Landau levels for fields normal to the axis. Explicit predictions are given for nanostructures based on GaAs, InAs, and InGaN with different symmetries.Comment: 13 pages, 4 figures, To be published in Nano Letter

Análisis de enunciados de problemas matemáticos para la escuela secundaria

La resolución de problemas está ampliamente aceptada por los teóricos para abordar procesos de enseñanza pero, al parecer, se encuentra escasamente implementada en las aulas. Los datos del presente estudio están constituidos por 45 enunciados de problemas matemáticos para la escuela secundaria que fueron propuestos por los 38 asistentes al curso de posgrado y capacitación docente “Enseñar Matemática mediante problemas en la escuela secundaria” desarrollado hacia fines del año 2010. Tales enunciados se analizan mediante las siguientes categorías de análisis: claridad semántica; precisión matemática; cantidad de información; registro de representación; contenido involucrado; vinculación con la realidad; momento de utilización. Se ha podido evidenciar que se requiere trabajo formativo en la redacción y selección de los enunciados de problemas para la clase de Matemática

Directions for Web and E-Commerce Applications Security

This paper provides directions for web and e-commerce applications security. In particular, access control policies, workflow security, XML security and federated database security issues pertaining to the web and ecommerce applications are discussed