Tidal Disruption Flares: The Accretion Disk Phase

The evolution of an accretion disk, formed as a consequence of the disruption of a star by a black hole, is followed by solving numerically the hydrodynamic equations. The present investigation aims to study the dependence of resulting light curves on dynamical and physical properties of such a transient disk during its existence. One of main results derived from our simulations is that black body fits of X-ray data tend to overestimate the true mean disk temperature. The temperature derived from black body fits should be identified with the color X-ray temperature rather than the average value derived from the true temperature distribution along the disk. The time interval between the beginning of the circularization of the bound debris and the beginning of the accretion process by the black hole is determined by the viscous timescale, which fixes also the raising part of the resulting light curve. The luminosity peak coincides with the beginning of matter accretion by the black hole and the late evolution of the light curve depends on the evolution of the debris fallback rate. Peak bolometric luminosities are in the range 10^45-10^46 erg s^-1 whereas peak luminosities in soft X-rays (0.2-2.0 keV) are typically one order of magnitude lower. The timescale derived from our preferred models for the flare luminosity to decay by two orders of magnitude is about 3-4 years. Predicted soft X-ray light curves were fitted to data on galaxies in which a variable X-ray emission, related to tidal events, was detected.Comment: 14 pages, 11 figures, Accepted for publication in Ap

Policies of accountability in Portugal

This communication stems from the global/local method proposed by Pinar (2006) for analysing changes that have affected curricular development in Portugal in the globalised context. It is argued that the most evident effects of globalisation on current curricular changes relate to homogenisation and standardisation (Anderson-Levitt, 2008), intersected by key concepts, such as accountability, good practices, quality, efficiency, evaluation and testing, amongst others, even though heterogeneity of practices persists. In Portugal, the political agenda has suffered a two-fold pressure – on one side, from globalisation and transnationalisation and, on the other, the trend to Europeanise educational policies – leading to processes of curricular re-centralisation and a performance-oriented culture in schools (Ball, 2004). The concept of accountability is seen as one of the central aspects for understanding this, so this text uses a series of reflective questions, organised in three regulatory dimensions - political, institutional and pedagogical - to analyse the concept of accountability

A New Understanding and Modelling of TSP and BP Indices Compared to Safety IMO Ship Requirements

[Abstract] Due to the lack of information about the concept of Tons of Steering Pull (TSP) of many escort tugs, and the lack of research works relating the TSP demanded by a tethered vessel with respect to the TSP provided by tugs, the present paper shows an original study with mathematical models on how to solve these problems. What is more, an important percentage of the towing sector always employs Bollard Pull (BP), which is considered the only parameter capable of defining performance, so this paper aims to relate BP with TSP. The present research was carried out based on more than 25 escort tugs of different towing companies. Furthermore, a real case study of different tanker vessels was used for modelling purposes of tethered vessels’ TSP. Finally, once the proposed models were obtained, they were compared with International Maritime Organization (IMO) guidelines. The results showed charts with the main independent variables of tugs and vessels in order to be as useful and practical as possible to the shipping industry, mainly to ship owners and tug operators, from a safety point of view.This research was funded by the Spanish Ministry of Education and the University of A Coruña (Spain) in their research project to reduce energy consumption in ships (Grant No. 64900

Evolution of the phase-space density and the Jeans scale for dark matter derived from the Vlasov-Einstein equation

We discuss solutions of Vlasov-Einstein equation for collisionless dark matter particles in the context of a flat Friedmann universe. We show that, after decoupling from the primordial plasma, the dark matter phase-space density indicator Q remains constant during the expansion of the universe, prior to structure formation. This well known result is valid for non-relativistic particles and is not "observer dependent" as in solutions derived from the Vlasov-Poisson system. In the linear regime, the inclusion of velocity dispersion effects permits to define a physical Jeans length for collisionless matter as function of the primordial phase-space density indicator: \lambda_J = (5\pi/G)^(1/2)Q^(-1/3)\rho_dm^(-1/6). The comoving Jeans wavenumber at matter-radiation equality is smaller by a factor of 2-3 than the comoving wavenumber due to free-streaming, contributing to the cut-off of the density fluctuation power spectrum at the lowest scales. We discuss the physical differences between these two scales. For dark matter particles of mass equal to 200 GeV, the derived Jeans mass is 4.3 x 10^(-6) solar masses.Comment: 18 pages, 2 figures. Accepted for publication in JCA

A bending cell for small batches

This article presents the study that is done for the conception of an automated bending cell devoted to the processing of parts in small batches, gathering the real necessities of potential customers. Joining the maximum of possible information, on the present cells, is has been able to conceive an automated bending cell devoted to the bending of parts, with dif-ferent form, weight, thickness, etc., in small batches. To be able to reach the proposed objec-tives, the cell is equipped with auxiliary systems, such as ATC (Automatic Tool Change) allied to a tool warehouse, AGC (Automatic Gripper Change) with three different grippers, a repo-sition station, and a dedicated 7th axis in the press brake designed to dock a standard 6 axes robot, that provide to cell a sufficient grade of autonomy. Allied with the idea of creating a cell for small batches, is introduced the target of getting this cell at lower price as possible. Thus the cell acquires an extended application range very important for potential customers. To get real perception of the money saving when working with this automated bending cell comparisons between Man work times vs. machine work times in production of small batches have been made

Experimental studies on structural timber glass adhesive bonding

The utilization of timber in building structures has been increasing in the last years, partly due to technological developments in this field. New tectonic concepts such as prefabricated and industrialised systems arose, though very different from the ones presented by traditional solutions. Hence, the combination of timber with other constructive materials is emerging. Steel, composites materials or glass can be combined with timber, in order to obtain resistant products, highly typified, standardised and with low behavioural variation. The structural utilization of timber glass composite solutions is a daring construtive system, which although still in a very early stage, already presents an important potential of applicability in architecture. In order to fully benefit from composite timber glass cross sections, an adequate bonding between these two elements is essential. With the purpose of achieving the ideal balance between strength and flexibility, an extensive set of experimental tests is being carried out at the University of Minho. This presentation focus on the analysis of results regarding shear stress tests with timber glass bondings, using adhesive as structural bonding system. In these tests, various adhesives were applied, including different trades and adhesive types such as silicone, methacrylate, polyurethane, acrylics and superflex polymers.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BDE/15538/200

Impacto e efeitos da avaliação externa das escolas nas práticas curriculares das lideranças intermédias

O reconhecimento da avaliação externa como um elemento - chave na mudança dos sistemas educativos trouxe para o centro do debate a importância das lideranças intermédias na melhoria das práticas curriculares e o aumento da qualidade do ensinoaprendizagem. Esta comunicação apresenta os resultados parciais de um projeto de investigação, em que se objetivou compreender de que modo o primeiro ciclo da avaliação externa das escolas, em Portugal, influenciou as dinâmicas curriculares e eficácia das lideranças intermédias. A análise dos dados quantitativos, recolhidos junto de uma amostra nacional de professores, através de um questionário on line (n=1102), remete para uma dicotomia entre, por um lado, o reconhecimento de que a Avaliação Externa tem um impacto mais positivo que negativo nas escolas, criando patamares de exigência mais elevados e abertura à mudança; por outro, a constatação de que ainda não produziu efeitos/resultados substanciais, no trabalho colaborativo de planificação, articulação, gestão e avaliação do currículo

Teaching students with learning difficulties or disabilities: regular education teachers’ professional development and practices

This article focuses on how curricular and pedagogical differentiation for students of special education is perceived by teachers of the second cycle of basic education in Portugal. The objectives of this research were (i) to inquire about the teachers’ perceptions regarding their training path and their training needs; (ii) to characterize the teaching practices of teachers, aimed at students of special education; and (iii) to learn the perceptions of these teachers regarding their curricular and pedagogical practices directed at students of special education—this called for an interpretative methodology. The data were collected through semi-structured interviews and subjected to content analysis. The results indicate a widespread concern with teachers’ current professional development and the management of diversity. The respondents’ perceptions, shown as favorable to change, are in line with personalized work, enhancing visible contributions to students’ personal and social development.This research was funded by Fundação para a Ciência e a Tecnologia S.A. (FCT), grant number SFRH/BD/136655/2018, and projects UIDB/04372/2020 and UIDP/04372/2020info:eu-repo/semantics/publishedVersio