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Search Results: 1 - 10 of 297 matches for " Manel. "
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El contingut i la metodologia de l'Educació Ambiental. Continuem pensant-hi
Manel Cervera
Temps d'Educació , 1995,
L'ensenyament modern de la música a Catalunya
Manel Camp
Temps d'Educació , 2001,
Postmodernism and Consumer Psychology: Transformation or Break?
Manel Hamouda
International Journal of Academic Research in Business and Social Sciences , 2012,
Abstract: The research’s aim is to identify the postmodern consumer characteristics. Studied through its main conditions (Hyperreality, Fragmentation, Decentered subject, Reversal of production and consumption and Paradoxical juxtaposition of opposites), postmodernism seems to affect some psychological traits of the consumer (Materialism, social desirability, locus of control and social identity). We tried to generate a number of assumptions. The check of these assumptions could answer us whether these psychological characteristics have been radically influenced by postmodernism and in this case, the consumer would have undergone a break or the effect is partial and it is only a simple transformation within the consumer.
Prediction of Financial Distress for Tunisian Firms: A Comparative Study Between Financial Analysis and Neuronal Analysis
Manel Hamdi
Business Intelligence Journal , 2012,
Abstract: This paper presents a prognosis of financial distress of Tunisian firms. For the purpose, we empirically compared the financial analysis to artificial neural network analysis. Five multilayer perceptron are applied to improve banking-decision. Based on the results of correct classification rate, artificial neural network proved an intact predictive ability. As well, the findings of generalization test confirmed the conclusion of the classical financial analysis of a company not included in our base sample. The artificial neural network can effectively automate the granting credit decision then performed better than traditional financial analysis.
Jet stability, dynamics and energy transport
Manel Perucho
Physics , 2011, DOI: 10.1142/S2010194512004667
Abstract: Relativistic jets carry energy and particles from compact to very large scales compared with their initial radius. This is possible due to their remarkable collimation despite their intrinsic unstable nature. In this contribution, I review the state-of-the-art of our knowledge on instabilities growing in those jets and several stabilising mechanisms that may give an answer to the question of the stability of jets. In particular, during the last years we have learned that the limit imposed by the speed of light sets a maximum amplitude to the instabilities, contrary to the case of classical jets. On top of this stabilising mechanism, the fast growth of unstable modes with small wavelengths prevents the total disruption and entrainment of jets. I also review several non-linear processes that can have an effect on the collimation of extragalactic and microquasar jets. Within those, I remark possible causes for the decollimation and decelleration of FRI jets, as opposed to the collimated FRII's. Finally, I give a summary of the main reasons why jets can propagate through such long distances.
Jet propagation and deceleration
Manel Perucho
Physics , 2013, DOI: 10.1142/S2010194514601653
Abstract: Extragalactic jets in active galactic nuclei (AGN) are divided into two morphological types, namely Fanaroff-Riley I (FRI) and Fanaroff-Riley II (FRII). The former show decollimated structure at the kiloparsec scales and are thought to be decelerated by entrainment within the first kiloparsecs of evolution inside the host galaxy. The entrainment and deceleration can be, at least partly, due to the interaction of jets with stellar winds and gas clouds that enter in the jet as they orbit around the galactic centre. In this contribution, I review recent simulations to study the dynamic effect of entrainment from stellar winds in jets and the direct interaction of jets with gas clouds and stellar winds. I also briefly describe the importance of these interactions as a possible scenario of high-energy emission from extragalactic jets.
Jets in high-mass microquasars
Manel Perucho
Physics , 2011,
Abstract: The morphologies of detected jets in X-ray binaries are almost as diverse as their number. This is due to different jet properties and ambient media that these jets encounter. It is important to understand the physics of these objects and to obtain information about possible sites suitable for particle acceleration in order to explain the observations at very high energies. Here I present the results obtained from the first relativistic hydrodynamical simulations of jets in high-mass microquasars. Our results allow us to make estimates for the emission originated in different sites of the whole structure generated by the jets. These works represent a first step in trying to obtain a deeper understanding of the physics and emission processes related with jets in high-mass microquasars.
The nature of extragalactic radio-jets from high-resolution radio-interferometric observations
Manel Perucho
Physics , 2014,
Abstract: Extragalactic jets are a common feature of radio-loud active galaxies. The nature of the observed jets in relation to the bulk flow is still unclear. In particular it is not clear whether the observations of parsec-scale jets using the very long baseline interferometric technique (VLBI) reveal wave-like structures that develop and propagate along the jet, or trace the jet flow itself. In this contribution I review the evidence collected during the last years showing that the ridge-lines of helical radio-jets do not correspond to observational artifacts. This conclusion was reached by studying a number of VLBI observations of the radio jet in the quasar S5~0836+710 at different frequencies and epochs. The ridge-line of the emission in the jet coincides at all frequencies within the errors. Moreover, small differences between the ridge-lines as observed at different epochs reveal wave-like motion transversal to the jet propagation axis. I also discuss similar results, albeit with different interpretations, obtained by other authors. The current challenge is to measure the propagation velocities of these waves and to try to characterise them in terms of simple perturbations or Kelvin-Helmholtz instability, which would help understanding the physical conditions of the flow where the waves develop. This problem can only be tackled by high-resolution observations such as those that can be achieved by the space radio-antenna Radioastron.
First hints of pressure waves in a helical extragalactic jet: S5~0836+710
Manel Perucho
Physics , 2013, DOI: 10.14311/APP.2014.01.0265
Abstract: One of the open questions in extragalactic jet Astrophysics is related to the nature of the observed radio jet, namely whether it traces a pattern or the flow structure itself. In this paper I summarize the evidence collected for the presence of waves in extragalactic jets. The evidence points towards the peak of emission in helical jets corresponding to pressure-maxima of a wave that is generated within the core region and propagates downstream. Making use of a number of very long baseline interferometry (VLBI) observations of the radio jet in the quasar S5~0836+710 at different frequencies and epochs, Perucho et al. (2012) were able to observe wave-like behavior within the observed radio-jet. The ridge-line of the emission in the jet coincides within the errors at all frequencies. Moreover, small differences between epochs at 15 GHz reveal wave-like motion of the ridge-line transversal to the jet propagation axis. The authors conclude that the helicity is a real, physical structure. I report here on those results and discuss this result in the light of new results recently announced by other authors that confirm the presence of waves in the close-by object BL Lac (Cohen et al., in preparation), and the possible magnetic or hydrodynamic nature.
Radio source evolution
Manel Perucho
Physics , 2015,
Abstract: Baldwin (1982) wrote that \emph{the distribution of sources in the radio luminosity, $P$, overall physical size, $D$, diagram} could be considered as \emph{the radio astronomer's $H-R$ diagram}. However, unlike the case of stars, not only the intrinsic properties of the jets, but also those of the host galaxy and the intergalactic medium are relevant to explain the evolutionary tracks of radio radio sources. In this contribution I review the current status of our understanding of the evolution of radio sources from a theoretical and numerical perspective, using the $P-D$ diagram as a framework. An excess of compact (linear size $\leq 10$~kpc) sources could be explained by low-power jets being decelerated within the host galaxy, as shown by recent numerical simulations. Finally, I discuss the possible tracks that radio sources may follow within this diagram, and the physical processes that can explain the different tracks.
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