Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217

As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the well studied jets from young stellar objects. A key point of comparison is the relationship between outflow and accretion activity and in particular the ratio between the mass outflow and accretion rates ($\dot{M}_{out}$/$\dot{M}_{acc}$). The brown dwarf candidate ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric study of brown dwarfs, to be driving an asymmetric outflow with the blue-shifted lobe having a position angle of $\sim$ 20$^{\circ}$. The aim here is to further investigate the properties of ISO-ChaI 217, the morphology and kinematics of its outflow, and to better constrain ($\dot{M}_{out}$/$\dot{M}_{acc}$). The outflow is spatially resolved in the $[SII]\lambda \lambda 6716,6731$ lines and is detected out to $\sim$ 1\farcs6 in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry between the two lobes is confirmed although the velocity asymmetry is less pronounced with respect to our previous study. Using thirteen different accretion tracers we measure log($\dot{M}_{acc}$) [M$_{sun}$/yr]= -10.6 $\pm$ 0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI 217 outflow $\dot{M}_{out}$ was derived for a range of values of A$_{v}$, up to a value of A$_{v}$ = 2.5 mag estimated for the source extinction. The logarithm of the mass outflow ($\dot{M}_{out}$) was estimated in the range -11.7 to -11.1 for both jets combined. Thus $\dot{M}_{out}$/$\dot{M}_{acc}$ [\Msun/yr] lies below the maximum value predicted by magneto-centrifugal jet launching models. Finally, both model fitting of the Balmer decrements and spectro-astrometric analysis of the H$\alpha$ line show that the bulk of the H I emission comes from the accretion flow.Comment: accepted by Astronomy & Astrophysic

CARACTERIZAÇÃO GEOLÓGICA E GEOTÉCNICA DE SOLOS RESIDUAIS TROPICAIS DA REGIÃO CENTRAL DE ANGOLA

Poucos são os trabalhos científicos existentes que contemplem a composição química, mineralógica e textural de solos residuais tropicais de Angola, sendo que os mais comuns têm sido focados para a caracterização pedológica, fundamentalmente para fins agrícolas [Castanheira, 1998], ou baseiam-se em classificações cujas realidades não se enquadram com as de Angola, tanto pela ausência de bibliografia, como pela complexidade que os mesmos apresentam. Em resultado disso, a aplicação destes solos para fins de engenharia traz, muitas das vezes, consequências nefastas que podem ser imprevisíveis e irreversíveis, do ponto de vista da funcionalidade e segurança das obras de engenharia. Assim, o presente trabalho tem como objectivo determinar características geológicas e geotécnicas dos solos residuais da Região Central de Angola (Huambo, Kwanza-Sul e Kwanza-Norte), ilustrados na Figura 1, assim como identificar os principais factores que determinam a formação dos mesmos. Dado que a composição mineralógica e textural de um solo residual, é resultado principalmente da história geológica herdada da rocha-mãe, do clima predominante e das condições geomorfológicas, não se pode caracterizar os solos residuais sem antes conhecer a composição química e mineralógica da rocha-mãe em questão [Duarte, 2002]. Sendo assim, a caracterização mineralógica foi efetuada mediante a aplicação das técnicas de análise mineralógica por difracção de raios-X (DRX) e a análise química por espectrometria de fluorescência de raios-X (FRX), a fim de se identificar os principais tipos de minerais, assim como os elementos químicos constituintes tanto da rocha-mãe, como do solo residual resultante. Os resultados de DRX revelam que as de rochas de origem são constituídas por quartzo muito abundante, presença de feldspatos potássicos (microclina e ortose) e plagioclases ricas em sódio (Albite) [Ferreira da Silva, 2009]. As micas estão presentes em todas as rochas, às vezes com a maior preponderância da biotite (amostras A e B), e noutros casos com o maior predomínio da moscovite/ilite (amostras C e F). Noutros casos (e.g. amostra de rocha F), constata-se que os seus minerais constituintes são o quartzo, a albite, a moscovite/ilite, a ortose e a braunite (óxido silicato de manganês). Esta constituição mineralógica é típica de rochas granitóides, precisamente granitos, e é confirmada pelos dados químicos obtidos por FRX que revelam que as rochas são constituídas por SiO2 (71%), Al2O3 (14%), K2O (4%), Fe3O2 (3%), Na2O (3%) e CaO (2%) [Duarte et al, 2013]. Com a atuação dos mecanismos de alteração, os minerais que se cristalizam em primeiro lugar, formados a temperaturas mais altas (e.g. as biotites) são menos estáveis quando submetidos as condições atmosféricas mais rigorosas (e.g. os solos do Huambo) dando lugar aos óxidos de ferro e de alumínio (hematite, goethite e a gibsite). Ao passo que os minerais que se cristalizam em último lugar, formados em temperaturas mais baixas e mais próximas às das condições superficiais (e.g. o quartzo), são mais estáveis. Os resultados da caracterização mineralógica são confirmados pela FRX que nos revelam que as perdas são muito acentuadas em regiões com taxas altas de precipitação, onde os elementos mais móveis (Na, K, Ca, Mg, etc.) quase desapareceram na totalidade, obtendo-se a composição de um solo rico em alumínio e ferro, com algum titânio. Noutras regiões (e.g. Cassenda, com menor taxa de precipitação), os elementos móveis mantém-se parcialmente nas amostras, o que denota menor disponibilidade de água para lixiviar tais elementos. Os dados obtidos a partir das análises mineralógicas e químicas efetuadas, permitem identificar os processos de alteração envolvidos nos solos em causa, e compreender os resultados experimentais relativos às propriedades físicas e mecânicas (composição textural, consistência, porosidade, peso volúmico seco máximo, teor em água ótimo, C.B.R., etc.), cuja determinação pode aferir acerca das áreas da engenharia geotécnica onde estes solos poderão ser aplicados [Duarte et al, 2011]

Pathway Weathering in Granitoid Rocks from Central Region of Angola: Geochemical and Mineralogical Data

The Central Region of Angola is characterized by the abundance of granitoid rocks, whose weathering “in situ” originated the so-called residual soils. The textural, geochemical and mineralogical properties of these soils depend not only on the chemical composition of parent rock, but mainly on the local climatic and geomorphological characteristics. In the study area, sampling sites were selected, which extend from the region of Kwanza- Norte (Kassenda, Dondo) through Kwanza-Sul (Cangulo, Quibala and Waco Kungo) until the plateau of Huambo, where samples of fresh rock, weathered rock and its residual soil were collected along each weathering profile. Chemical analytical data were determined using X-ray fluorescence (XRF) analysis of the major and minor elements, whereas mineralogical data were determined using X-ray diffraction (XRD), on the samples of rock and on the respective residual soil. The results obtained and their comparative analysis between the sampling sites, as well as along each weathering profile is presented. This paper allows contributing to the knowledge of the geochemical weathering in tropical areas, as is the case of Angola

Assembly of the Auditory Circuitry by a Hox Genetic Network in the Mouse Brainstem

Rhombomeres (r) contribute to brainstem auditory nuclei during development. Hox genes are determinants of rhombomere-derived fate and neuronal connectivity. Little is known about the contribution of individual rhombomeres and their associated Hox codes to auditory sensorimotor circuitry. Here, we show that r4 contributes to functionally linked sensory and motor components, including the ventral nucleus of lateral lemniscus, posterior ventral cochlear nuclei (VCN), and motor olivocochlear neurons. Assembly of the r4-derived auditory components is involved in sound perception and depends on regulatory interactions between Hoxb1 and Hoxb2. Indeed, in Hoxb1 and Hoxb2 mutant mice the transmission of low-level auditory stimuli is lost, resulting in hearing impairments. On the other hand, Hoxa2 regulates the Rig1 axon guidance receptor and controls contralateral projections from the anterior VCN to the medial nucleus of the trapezoid body, a circuit involved in sound localization. Thus, individual rhombomeres and their associated Hox codes control the assembly of distinct functionally segregated sub-circuits in the developing auditory brainstem

EVALUATION OF SOME GEOTECHNICAL PROPERTIES OF GRANITOID RESIDUAL SOILS FROM THE CENTRAL REGION OF ANGOLA

Para avaliar as caracteristicas geotécnicas de um solo é necessário realizar um conjunto de ensaios para obter as respectivas propriedades básicas e permitir a sua classificação geotécnica (USCS, AASHTO e SATCC). Contudo, quando se trata de solos residuais tropicais, esta tarefa é dificultada por causa das suas especificidades químicas e mineralógicas. Neste trabalho apresentam-se algumas propriedades geotécnicas de solos residuais tropicais da Região Central de Angola, relacionando-as com as suas características mineralógicas previamente determinadas em Duarte et al. (2013). A caracterização geotécnica foi efetuada a partir dos parâmetros obtidos nos seguintes ensaios: índices físicos “in situ”, análise granulométrica, limites de consistência, equivalente de areia, expansibilidade, compactação e CBR, com o objetivo de aferir a aptidão destes solos residuais param fins de Engenharia (rodovias, ferrovias, aeródromos, aeroportos, barragens de terra, etc.). Os resultados obtidos permitem relacionar as propriedades geotécnicas destes solos residuais tropicais com as suas características mineralógicas, assim como, indicar a sua aplicação mais adequada em obras geotécnicas

The X-ray emission from Z CMa during an FUor-like outburst and the detection of its X-ray jet

Accretion shocks have been recognized as important X-ray emission mechanism for pre-main sequence stars. Yet the X-ray properties of FUor outbursts, events that are caused by violent accretion, have been given little attention. We have observed the FUor object Z CMa during optical outburst and quiescence with Chandra. No significant changes in X-ray brightness and spectral shape are found, suggesting that the X-ray emission is of coronal nature. Due to the binary nature of Z CMa the origin of the X-ray source is ambiguous. However, the moderate hydrogen column density derived from our data makes it unlikely that the embedded primary star is the X-ray source. The secondary star, which is the FUor object, is thus responsible for both the X-ray emission and the presently ongoing accretion outburst, which seem however to be unrelated phenomena. The secondary is also known to drive a large outflow and jet, that we detect here for the first time in X-rays. The distance of the X-ray emitting outflow source to the central star is higher than in jets of low-mass stars.Comment: 5 pages, accepted for publication in Astronomy & Astrophysic

Positive approximations of the inverse of fractional powers of SPD M-matrices

This study is motivated by the recent development in the fractional calculus and its applications. During last few years, several different techniques are proposed to localize the nonlocal fractional diffusion operator. They are based on transformation of the original problem to a local elliptic or pseudoparabolic problem, or to an integral representation of the solution, thus increasing the dimension of the computational domain. More recently, an alternative approach aimed at reducing the computational complexity was developed. The linear algebraic system $\cal A^\alpha \bf u=\bf f$, $0< \alpha <1$ is considered, where $\cal A$ is a properly normalized (scalded) symmetric and positive definite matrix obtained from finite element or finite difference approximation of second order elliptic problems in $\Omega\subset\mathbb{R}^d$, $d=1,2,3$. The method is based on best uniform rational approximations (BURA) of the function $t^{\beta-\alpha}$ for $0 < t \le 1$ and natural $\beta$. The maximum principles are among the major qualitative properties of linear elliptic operators/PDEs. In many studies and applications, it is important that such properties are preserved by the selected numerical solution method. In this paper we present and analyze the properties of positive approximations of $\cal A^{-\alpha}$ obtained by the BURA technique. Sufficient conditions for positiveness are proven, complemented by sharp error estimates. The theoretical results are supported by representative numerical tests

Alteração de Rochas Granitóides em Angola.

A Região Central de Angola caracteriza-se pela abundância de rochas granitóides, cuja alteração “in-situ” originou os denominados solos residuais. As propriedades texturais, geoquímicas e mineralógicas destes solos dependem não só da composição química da rocha mãe, mas principalmente das características geomorfológicas e climatéricas locais. Na região em estudo, seleccionaram-se locais de amostragem, que se estendem desde a província do Kwanza-Norte (Kassenda, no Alto Dondo), passando pela província do Kwanza-Sul (Cangulo, Quibala e Waco Kungo), até ao Planalto do Huambo, onde se colheram amostras de rocha sã, rocha alterada e respectivo solo residual, ao longo de cada perfil de alteração. Realizaram-se análises de caracterização geoquímica por Fluorescência de Raios-X dos elementos maiores e menores, e de caracterização mineralógica por Difracção de Raios–X, tanto nas amostras de rocha sã, como no respectivo solo residual. Apresentam-se os resultados obtidos e a sua análise comparativa entre os diferentes locais de amostragem, assim como ao longo de cada perfil de alteração. Os resultados obtidos permitem contribuir para o conhecimento dos fenómenos de alteração geoquímica em zonas tropicais, como é o caso de Angola

Multilevel analysis in CSCL Research

Janssen, J., Erkens, G., Kirschner, P. A., & Kanselaar, G. (2011). Multilevel analysis in CSCL research. In S. Puntambekar, G. Erkens, & C. Hmelo-Silver (Eds.), Analyzing interactions in CSCL: Methods, approaches and issues (pp. 187-205). New York: Springer. doi:10.1007/978-1-4419-7710-6_9CSCL researchers are often interested in the processes that unfold between learners in online learning environments and the outcomes that stem from these interactions. However, studying collaborative learning processes is not an easy task. Researchers have to make quite a few methodological decisions such as how to study the collaborative process itself (e.g., develop a coding scheme or a questionnaire), on the appropriate unit of analysis (e.g., the individual or the group), and which statistical technique to use (e.g., descriptive statistics, analysis of variance, correlation analysis). Recently, several researchers have turned to multilevel analysis (MLA) to answer their research questions (e.g., Cress, 2008; De Wever, Van Keer, Schellens, & Valcke, 2007; Dewiyanti, Brand-Gruwel, Jochems, & Broers, 2007; Schellens, Van Keer, & Valcke, 2005; Strijbos, Martens, Jochems, & Broers, 2004; Stylianou-Georgiou, Papanastasiou, & Puntambekar, chapter #). However, CSCL studies that apply MLA analysis still remain relatively scarce. Instead, many CSCL researchers continue to use ‘traditional’ statistical techniques (e.g., analysis of variance, regression analysis), although these techniques may not be appropriate for what is being studied. An important aim of this chapter is therefore to explain why MLA is often necessary to correctly answer the questions CSCL researchers address. Furthermore, we wish to highlight the consequences of failing to use MLA when this is called for, using data from our own studies

The Gaia-ESO Survey: Chromospheric Emission, Accretion Properties, and Rotation in γ\gamma Velorum and Chamaeleon I

We use the fundamental parameters delivered by the GES consortium in the first internal data release to select the members of $\gamma$ Vel and Cha I among the UVES and GIRAFFE spectroscopic observations. A total of 140 $\gamma$ Vel members and 74 Cha I members were studied. We calculated stellar luminosities through spectral energy distributions, while stellar masses were derived by comparison with evolutionary tracks. The spectral subtraction of low-activity and slowly rotating templates, which are rotationally broadened to match the $v\sin i$ of the targets, enabled us to measure the equivalent widths (EWs) and the fluxes in the H$\alpha$ and H$\beta$ lines. The H$\alpha$ line was also used for identifying accreting objects and for evaluating the mass accretion rate ($\dot M_{\rm acc}$). The distribution of $v\sin i$ for the members of $\gamma$ Vel displays a peak at about 10 km s$^{-1}$ with a tail toward faster rotators. There is also some indication of a different $v\sin i$ distribution for the members of its two kinematical populations. Only a handful of stars in $\gamma$ Vel display signatures of accretion, while many more accretors were detected in the younger Cha~I. Accreting and active stars occupy two different regions in a $T_{\rm eff}$-flux diagram and we propose a criterion for distinguishing them. We derive $\dot M_{\rm acc}$ in the ranges $10^{-11}$-$10^{-9} M_\odot$yr$^{-1}$ and $10^{-10}$-$10^{-7} M_\odot$yr$^{-1}$ for $\gamma$ Vel and Cha I accretors, respectively. We find less scatter in the $\dot M_{\rm acc}-M_\star$ relation derived through the H$\alpha$ EWs, when compared to the H$\alpha$ $10\%W$ diagnostics, in agreement with other authors