Another brick in understanding chemical and kinematical properties of BSSs: NGC 6752

We used high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 22 Blue Straggler Stars (BSSs) and 26 red giant branch stars in the nearby globular cluster NGC 6752. We measured radial and rotational velocities and Fe, O and C abundances. According to radial velocities, metallicity and proper motions we identified 18 BSSs as likely cluster members. We found that all the BSSs rotate slowly (less than 40 km/s), similar to the findings in 47 Tucanae, NGC 6397 and M30. The Fe abundance analysis reveals the presence of 3 BSSs affected by radiative levitation (showing [Fe/H] significantly higher than that measured in "normal" cluster stars), confirming that element transport mechanisms occur in the photosphere of BSSs hotter than 8000 K. Finally, BSS C and O abundances are consistent with those measured in dwarf stars. No C and O depletion ascribable to mass transfer processes has been found on the atmospheres of the studied BSSs (at odds with previous results for 47 Tucanae and M30), suggesting the collisional origin for BSSs in NGC 6752 or that the CO-depletion is a transient phenomenon.Comment: ApJ accepte

FLAMES and XSHOOTER spectroscopy along the two BSS sequences of M30

We present spectroscopic observations acquired with FLAMES and XSHOOTER at the Very Large Telescope for a sample of 15 Blue Straggler Stars (BSSs) in the globular cluster (GC) M30. The targets have been selected to sample the two BSS sequences discovered, with 7 BSSs along the blue sequence and 8 along the red one. No difference in the kinematical properties of the two groups of BSSs has been found. In particular, almost all the observed BSSs have projected rotational velocity lower than ~30 km/s, with only one (blue) fast rotating BSS (>90 km/s), identified as a W UMa binary. This rotational velocity distribution is similar to those obtained in 47 Tucanae and NGC 6397, while M4 remains the only GC studied so far harboring a large fraction of fast rotating BSSs. All stars hotter than ~7800 K (regardless of the parent BSS sequence) show iron abundances larger than those measured from normal cluster stars, with a clearcut trend with the effective temperature. This behaviour suggests that particle trasport mechanisms driven by radiative levitation occur in the photosphere of these stars, as already observed for the BSSs in NGC 6397. Finally, 4 BSSs belonging to the red sequence (not affected by radiative levitation) show a strong depletion of [O/Fe], with respect to the abundance measured in Red Giant Branch and Horizontal Branch stars. This O-depletion is compatible with the chemical signature expected in BSSs formed by mass transfer processes in binary systems, in agreement with the mechanism proposed for the formation of BSSs in the red sequence.Comment: Accepted for publication in Ap

Música instrumental, tópicas e identidade cultural: um olhar sobre as produções de Milton Nascimento, Wagner Tiso e Nivaldo Ornelas no cenário da música mineira dos anos 70

Nos anos 70, Wagner Tiso e Nivaldo Ornelas começaram a se projetar na cena da música instrumental brasileira como compositores e instrumentistas. Neste artigo, analiso a primeira fase de suas carreiras procurando, inicialmente, relacionar seus trabalhos à trajetória de Milton Nascimento, cujos sucesso e prestí­gio alcançados na MPB se refletiram nas carreiras dos músicos citados. A partir do marco teórico das tópicas musicais – utilizado em estudos de música popular por autores como Acácio Piedade – procuramos demonstrar como algumas das produções desses artistas evocaram elementos formadores da identidade cultural mineira, contribuindo para forjar a imagem de músicos vinculados à Minas Gerais

Blue straggler masses from pulsation properties. II. Topology of the Instability Strip

We present a new set of nonlinear, convective radial pulsation models for main sequence stars computed assuming three metallicities: Z=0.0001, 0.001 and 0.008. These chemical compositions bracket the metallicity of stellar systems hosting SX Phoenicis stars (SXPs or pulsating Blue Stragglers), namely Galactic globular clusters and nearby dwarf spheroidals. Stellar masses and luminosities of the pulsation models are based on alpha--enhanced evolutionary tracks from the BASTI website. We are able to define the topology of the instability strip (IS), and in turn the pulsation relations for the first four pulsation modes. We found that third overtones approach a stable nonlinear limit cycle. Predicted and empirical IS agree quite well in the case of 49 SXPs belonging to omega Cen. We used theoretical Period-Luminosity relations in B,V bands to identify their pulsation mode. We assumed Z=0.001 and Z=0.008 as mean metallicities of SXPs in omega Cen. We found respectively 13-15 fundamental, 22-6 first and 9-4 second overtone modes. Five are unstable in the third overtone mode only for Z=0.001. Using the above mode identification and applying the proper mass-dependent Period-Luminosity relations we found masses ranging from ~1.0 to 1.2 Mo (=1.12, sigma=0.04 Mo) and from ~1.2 to 1.5 Mo (=1.33, sigma=0.03 Mo) for Z=0.001 and 0.008 respectively. Our investigation supports the use of evolutionary tracks to estimate of SXP masses. We will extend our analysis to higher Helium content that may have an impact in our understanding of the BSS formation scenario.Comment: 14 pages, 5 figures, 7 tables, ApJ accepte

On border traps in back-side-illuminated CMOS image sensor oxides

CMOS image sensors (CISs) in back-side-illuminated configuration consist of photodiode arrays having metal lines and drive electronics beneath the active region with respect to the device/air interface so that the light reaches the photodiode active region directly. This enhances sensor quantum efficiency but reduces the electrical performance and reliability. The back-side configuration is realized by flipping the wafer upside down, bonding it to a handling wafer, mechanically thinning it, and opening a through-silicon via with a long plasma etch. As a result, gate oxides in back-side CISs show an increased density of donor-like border traps with respect to the conventional front-side-illuminated sensors. In this article, we try to add some information toward the comprehension of the origin and the electrical nature of those traps in back-side gate oxides. To this aim, we performed negative bias temperature instability stress on p-channel MOSFETs during which the traps were filled by holes tunneling from the substrate and then studied the relaxation transients of the drain current after the stress was removed. The characteristic emission times of a few specific levels were obtained at different temperatures. This allowed us to extract values of the trap activation energies, which resulted coherent with hole-capturing E′ donor-like centers (trivalent silicon dangling bonds) commonly attributed to ionizing radiation

Application of the Higher-Order Hamilton Approach to the Nonlinear Free Vibrations Analysis of Porous FG Nano-Beams in a Hygrothermal Environment Based on a Local/Nonlocal Stress Gradient Model of Elasticity

Nonlinear transverse free vibrations of porous functionally-graded (FG) Bernoulli–Euler nanobeams in hygrothermal environments through the local/nonlocal stress gradient theory of elasticity were studied. By using the Galerkin method, the governing equations were reduced to a nonlinear ordinary differential equation. The closed form analytical solution of the nonlinear natural flexural frequency was then established using the higher-order Hamiltonian approach to nonlinear oscillators. A numerical investigation was developed to analyze the influence of different parameters both on the thermo-elastic material properties and the structural response, such as material gradient index, porosity volume fraction, nonlocal parameter, gradient length parameter, mixture parameter, and the amplitude of the nonlinear oscillator on the nonlinear flexural vibrations of metal–ceramic FG porous Bernoulli–Euler nano-beams

O devir docente: olhares para a formação dos licenciandos em educação física a partir do estágio curricular supervisionado

We understand becoming a teacher as a process ofcontinuous construction of teacher identities. This concept implies thinking of teacher education as a permanent and unfinished process. Thus, we adopt the conception of professional development for allocating a connotation of evolution and continuity, seeking to overcome the juxtaposition between initial training and teacher improvement. The constitution of teaching identities goes through experiences prior to the choice of the profession, the initial training period, and the professional experiences in different institutional spaces. Undergraduate courses play a relevant role in this process by providing future teachers with the necessary knowledge for professional practice. One of the central axes of initial training is the supervised curricular internship (SCI), whose main characteristic is to insert the students into the real context of their future profession. In this sense, this research aims to understand and analyze the pedagogical relationships built in the supervised curricular internship developed in the Physical Education undergraduate course at Juiz de Fora Federal University. This study was characterized as qualitative interpretive and used the case study method. The participants were eleven undergraduate students, five supervising teachers, and one supervising teacher. The data collection instruments were document analysis, participant observation, and semi-structured interviews. Content analysis was used to interpret the data. Four categories emergedfrom the data analysis: a) the graduation in Physical Education course; b) the SCIin the context of initial formation; c) the pedagogical relationships built during the SCI;d) the contributions of the SCIin the perception of the students. In this analytical path, we came across several actors related to initial training in undergraduate courses that had a negative impact on the construction of pedagogical relationships during the development of the SCI: the fragmentation of the course into undergraduate and bachelor's degrees, the centrality attributed to the bachelor's degree, the secondary training in undergraduate courses, and the anachronism of the curriculum. The time allotted to SCIin this training context is reduced, not meeting the minimum proposed by the national guidelines for teacher training, not providing moments for discussions and reflections on pedagogical practice during the SCI. The main thread of this curricular component is conditioned and restricted to bureaucratic actions, causing a distance between the educational institutions, school and university. The analysis of the pedagogical constructions between the supervising teacher and the supervising teacher pointed out that they happen in a distant way, with rare moments of interaction,and are based on the fulfillment of bureaucratic actions. Regarding the pedagogical constructions between the supervising teacher and the undergraduate students, the research made it possible to understand that, despite the problems present in the development of this curricular component, these constructions prove to be powerful in contributing to the construction of teaching knowledge and professional identities. The instructors make an effort to welcome the trainees, although they have no time, other than during the classes, to analyze and discuss the pedagogical practices with the trainees. The instructors drew on their personal experiences to conduct the internships, imprinting their own characteristics. In the perception of the undergraduates, the SCIis considered fundamental in initial teacher education, proving to be a determining factor, in some cases, in their choice to remain in the profession. The direct contact with the professional field was pointed out as the most relevant component, and the relationship with the students, the teachers, the dynamics of the classes, the development of the activities, among others, were also mentioned as components that contributed to the professional training. Based on the analytical path of the research, itis possible to consider the SCIas primordial for the constitution of the professional identity of future teachers. However, it is necessary to review the curriculum that makes up the initial training of undergraduate students and how the SCIis developed in this training context. The research findings demonstrate the need for greater inter-relation between the training fields and the subjects of the process, so that the pedagogical constructions in this period of training are meaningful.Compreendemos o devir docente como o processo de construção contínua das identidades docentes. Esse conceito acarreta pensar a formação dos professorescomo um processo permanente e inacabado. Adotamos,assim, a concepção de desenvolvimento profissional docente,por alocaruma conotação de evolução e continuidade, buscando superar a justaposição entre formação inicial e aperfeiçoamento dos professores. A constituição das identidades docentesperpassaas experiências anteriores a escolha da profissão, o período da formação inicial e as experiências profissionais nos diferentes espaços institucionais. Os cursos de licenciatura assumem um papel relevante nesse processo,por proporcionarem aos futuros professoreso contato com os saberes necessários para a prática profissional. Um dos eixos centrais da formação inicial é o Estágio Curricular Supervisionado (ECS),que tem como característica principal inserir os licenciandos ao contexto real de sua futura profissão. Nesse sentido, esta pesquisa tem como objetivo compreender e analisar as relações pedagógicas construídas no estágio curricular supervisionado desenvolvido no curso de Licenciatura em Educação Física da Universidade Federal de Juiz de Fora.Este estudo se caracterizou por ser qualitativo interpretativo e foi utilizado o método do estudo de caso. Os participantes foram onze licenciandos, cinco professores orientadores e um professor supervisor. Os instrumentos de coleta de dados foram análise documental, observação sistemáticae entrevistas semiestruturadas. Para interpretação dos dados,foi utilizada a análise de conteúdo. A partir das análises dos dados emergiram quatro categorias: a) a licenciatura no curso de Educação Física; b) o ECS no contexto da formação inicial; c) as relações pedagógicas construídas no decorrer do ECS; d) as contribuições do ECS na percepção dos licenciandos.Nesse percurso analítico,deparamo-noscom vários intervenientes relativos à formação inicial em licenciatura que repercutiram negativamente na construção das relações pedagógicas no desenvolvimento do ECS: a fragmentação do curso em licenciatura e bacharelado, a centralidade atribuída à formação em bacharelado, aformação em licenciatura de maneira secundária e o anacronismo do currículo. O tempo atribuído ao ECS nesse contexto de formação é reduzido, não atendendo o mínimo proposto pelas diretrizes nacionais para formação docente,não proporcionandomomentos de discussões e reflexões sobre a práticapedagógica no decorrer do ECS.Ofio condutor desse componente curricular fica condicionado erestrito às ações burocráticas,provocando um distanciamento entre as instituições formadoras, escola e universidade.As análises sobre as construções pedagógicas entre professor supervisor e professor orientador apontaram que estasacontecem de forma distante, com raros momentos de interação,e se baseiam no cumprimento de ações burocráticas. Relativo às construções pedagógicasentre professor orientador e licenciandos,a pesquisa possibilitou compreender que, apesar dos problemas presentes no desenvolvimento desse componente curricular, essas construções se mostram potentes na contribuição da construção dos saberes docentes e das identidades profissionais. Os professores orientadores empreendem esforços para realizaro acolhimento dos licenciandos,apesar de não terem momentos, além das aulas, para analisar e discutir aspráticas pedagógicas com os estagiários. Os professores orientadores se basearam em suas experiências pessoais para conduzirem os estágios, imprimindo características próprias. Na percepção dos licenciandos, o ECS é considerado fundamental na formação inicial docente, mostrando-sedeterminante, em alguns casos, na escolha por permanecer na profissão. O contato direto com o campo profissional foi apontado como o componente de maior relevância;foram citadostambém, como componentes que contribuíram paraformação profissional,a relação com os alunosecom os professores, a dinâmica das aulas, o desenvolvimento das atividades, entre outros.A partir do percurso analítico da pesquisa,é possível considerar o ECS como primordial para a constituição da identidade profissional dos futuros docentes. Entretanto, faz-se necessário rever o currículo que compõe a formação inicial dos licenciandos e a maneira como o ECS se desenvolve nesse contexto de formação. Os achados da pesquisa demonstram a necessidade de uma maior inter-relação entre os campos de formação e entre os sujeitos do processo, para que as construções pedagógicas nesse período da formação sejam significativas