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

Server selection on the internet using passive probing

This paper describes a server selection mechanism for connection oriented services based on passive probing. The criterion of selection is the quality of service expected from each server, expressed as a function of availability and response time. Measures from previous connections to servers made by local clients are used to continuously update a QoS database which the prediction algorithm uses to compute the response time expected in subsequent connections. The forecasting approach is mainly based on prior measurements of TCP connection establishment time. The maximum segment size in a connection is also considered. The proposed metric is compared with other ones normally used to measure network proximity. Results show that the proposed server selection mechanism achieves a reduction of response time of over 50 percent compared with a random selection mechanism

Wireless body area network for cycling posture monitoring

This work presents the design and implementation of a wireless body area network based on Bluetooth Low Energy (BLE) which enables the integration of multiple sensor nodes into a smartphone-based system in order to monitor the posture of cyclists. The wireless posture monitoring system presented in this chapter obtains the orientation in space of each body segment in which the sensor nodes are placed and calculates the trunk angle, the knee angle and the angle of inclination of the road. This system collects raw sensor data from accelerometers, magnetometers and gyroscopes and sends the data via BLE to an Android smartphone, which plays the role of central station and performs the data processing concerning the posture calculation. This chapter describes the development of the hardware and software of the sensor nodes, which are based on the CC2540 BLE system-on-chip, as well as the development of the Android application. Experimental results concerning the measurement of the posture of a cyclist are provided in order to validate the implementation.This work has been supported by FCT (Fundação para a Ciência e Tecnologia) in the scope of the project: UID/EEA/04436/2013.info:eu-repo/semantics/publishedVersio

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

O experimento didático formativo na perspectiva da teoria do ensino desenvolvimental

This text discusses the formative didactic experiment as a modality of didactic research from the perspective of developmental teaching, according to theoretical-methodological principles formulated by Vygotsky, Davydov and Hedegaard within the historical-cultural theory. The premise is that didactic knowledge needs to be incorporated into pedagogical practices to tackle social and school inequalities, which requires research that deepens the didactic analysis of the teaching-learning process. The present study resulted from a bibliographic research of the production of the mentioned authors, with the following objectives: to describe the results of the study, highlighting the contributions of each theorist in the characterization of the formative didactic experiment and its procedures; to argue for the relevance of the formative didactic experiment approach as a microcycle of investigation. In addition, we present one of the modalities of formative didactic experiment developed in the Research Group coordinated by the authors, which integrated the principles of Vygotsky, Davydov and Hedegaard. It is concluded that the formative didactic experiment as a microcycle of investigation gives rise to didactic knowledge capable of sustaining and strengthening the developmental didactics oriented towards educational purposes in order to overcome the social and school inequalities existing in the country.O texto discute o experimento didático formativo como modalidade de pesquisa em didática na perspectiva do ensino desenvolvimental, conforme princípios teórico-metodológicos formulados por Vygotsky, Davydov e Hedegaard a partir da teoria histórico-cultural. Tem-se como premissa que o conhecimento didático necessita avançar na direção de práticas pedagógicas para o enfrentamento das desigualdades sociais e escolares, o que requer pesquisas que aprofundem a análise didática do processo ensino-aprendizagem. O presente estudo decorreu de pesquisa bibliográfica da produção dos autores mencionados, tendo como objetivos: descrever os resultados do estudo, destacando as contribuições de cada teórico na caracterização do experimento didático formativo e seus procedimentos; argumentar pela relevância da abordagem do experimento didático formativo como microciclo de investigação. Adicionalmente, é apresentada uma das modalidades de experimento didático formativo desenvolvida no Grupo de Pesquisa coordenado pelos autores, integrando princípios de Vygotsky, Davydov e Hedegaard. Conclui-se que o experimento didático formativo como microciclo de investigação origina um conhecimento didático capaz de sustentar e fortalecer a didática desenvolvimental orientada para finalidades educativas de superação das desigualdades sociais e escolares existentes no país

Stereoselective cycloaddition of 1-glucosyl-1,3-butadienes with tert-butyl 2H-azirine-3-carboxylate, glyoxylates and imines

Glucosyl dienes 1 have been reacted with the achiral 2H-azirine 4 and with glyoxylates, forming fused structures of type 5 and disaccharide-like compounds 7 with good to excellent selectivity. Glucosyl dienes 1 participated as dienophiles in reactions with Schiff bases derived from anilines forming isoquinolines 10 and 11. The diastereoselectivity of this reaction is poor.Fundação para a Ciência e Tecnologia - POCTI/32723/QUI/2000. FEDER

Long term betaine supplementation regulates genes involved in lipid and cholesterol metabolism of two muscles from an obese pig breed

This study evaluates the effects of betaine supplementation (1 g kg−1 for 20 weeks) on the regulation of genes involved in lipid and cholesterol metabolism of Longissimus lumborum and Biceps femoris from obese Alentejano pigs. Betaine supplementation led to an increase in total cholesterol in both muscles, complementing results previously published indicating a significant increase on the intramuscular lipid content. The expression of twelve genes involved in lipogenesis, lipolysis/FA oxidation, FA transport, and cholesterol metabolism, as well as two transcription factors were also evaluated. Genes related to lipid and cholesterol synthesis plus FA transport were consistently up-regulated in both muscles of betaine fed pigs. On the other hand, genes related to lipolysis/FA oxidation were not affected or down-regulated by betaine supplementation. Our data suggest that the underlying mechanism regulating IMF and cholesterol accumulation in Alentejano pigs supplemented with betaine is associated with the up-regulation of genes involved in lipid synthesis, FA transport, and cholesterol synthesis

A review on the bond behavior of FRP NSM systems in concrete

This paper presents a review of current knowledge on the bond behavior of fiber reinforced polymer (FRP) systems inserted in the cover of concrete elements, commonly known as the near-surface mounted technique (NSM). In the first part, by studying the physics of the phenomenon, the typical failure modes, the most common bond tests and two of the most important design guidelines for FRP NSM systems are introduced. In the second part, a database of bond tests composed by 431 records is presented and the accuracy of existing design guidelines is assessed with this data. Lastly, the formulations proposed by these design guidelines are recalibrated based on the experimental results in the database.This work was supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT (Portuguese Foundation for Science and Technology) under the project CutInDur PTDC/ECM/11 2396/2009. The first author wishes also to acknowledge the Grant No. SFRH/BD/87443/2012 provided by FCT

Comportamento de laminados multi-direccionais de CFRP para aplicações em engenharia civil

No âmbito do presente artigo são apresentados os resultados do desenvolvimento de laminados multi-direccionais de polímeros reforçados com fibras de carbono (MDL-CFRP) na reabilitação e reforço de estruturas de betão armado. A utilização de MDL-CFRP tem como objectivo fundamental permitir a introdução de ancoragens, de modo a aumentar a eficiência da ligação entre este material e os elementos a reforçar de acordo com a técnica AEBR (anchored and externally bonded reinforcement). Segundo esta nova técnica, os MDLCFRP são aplicados nas faces dos elementos a reforçar com recurso à colagem com adesivo e ao uso de ancoragens. Neste trabalho faz-se a descrição do processo de fabrico do MDLCFRP, e apresentam-se os resultados da caracterização geométrica e mecânica dos mesmos

Estudo comparativo entre modelos de previsão de resistência: leis analíticas versus data mining

Neste trabalho apresenta-se um estudo comparativo entre modelos de previsão da resistência de sistemas de polímeros reforçados com fibras (Fiber Reinforced Polymers – FRP) inseridos no betão de recobrimento de elementos de betão. Esta técnica é conhecida por Near-Surface Mounted (NSM). São analisados dois dos mais importantes códigos de projeto existentes e ainda modelos obtidos com recurso a algoritmos de data mining (DM). Os resultados obtidos demonstram que o recurso ao DM pode ser uma alternativa viável aos códigos existentes na previsão da resistência da ligação de sistemas FRP NSM