Flow patterns and heat transfer in a square cross-section micro condenser working at low mass fluxes

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Flow patterns and heat transfer in an air-cooled square cross-section micro condenser were investigated. The test section consisted of a borosilicate square micro channel, of inner and outer hydraulic diameters of 0.49 mm and 0.6 mm respectively, and a length of 100 mm. The transparent material of the micro channel allowed the visualization of the different condensation flow patterns. The imposed mass velocities were ranging between 1 and 10 kg m-2 s-1. In this range of mass fluxes, three main flow regimes were identified: Annular regime, intermittent regime, and spherical bubbles regime. Then, the isolated bubbles zone (the end of the intermittent zone + the spherical bubbles zone) was particularly studied. A specific experimental procedure was developed, basing on bubble tracking, in order to determine accurately the hydraulic and thermal parameters profiles in this zone according to the axial position in the micro channel, such as the vapour quality profile x(z). Thanks to energy balance, the liquid temperature profile Tl(z) in the isolated bubbles zone was determined for different initial values. A thermal non-equilibrium between the liquid and vapour phases was identified. Therefore, the latent heat flux was then quantified and compared to the total heat flux in this zone.FNRAE (MATRAS) and the Microgravity Application Program of the European Space Agenc

Analytical solution of an irreversible surface reaction model

In this work, we consider a simple model of reaction-limited annihilation A + B → 0 with a random source and desorption in the spirit of the reaction model proposed by Fitchthorn, Ziff, and Gulari, and we solve it exactly using a spin model. We show that the situation is similar to a diffusion-limited kinetic situation (though diffusion was a priori absent from the model). We find the occurrence of a large-scale organization phenomenon at low dimension called segregation, and for a finite size system, a transition to a saturated state at low desorption probability. We show how this transition is affected by the dimensionality of the substrate. We also show how the fluctuation spectrum of two quantities such as the saturation and the reaction rate can be drastically different, the first being universal and the other sensitive to the geometry of the substrate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45164/1/10955_2005_Article_BF01049590.pd

Ferromagnetic semiconductors

The current status and prospects of research on ferromagnetism in semiconductors are reviewed. The question of the origin of ferromagnetism in europium chalcogenides, chromium spinels and, particularly, in diluted magnetic semiconductors is addressed. The nature of electronic states derived from 3d of magnetic impurities is discussed in some details. Results of a quantitative comparison between experimental and theoretical results, notably for Mn-based III-V and II-VI compounds, are presented. This comparison demonstrates that the current theory of the exchange interactions mediated by holes in the valence band describes correctly the values of Curie temperatures T_C magnetic anisotropy, domain structure, and magnetic circular dichroism. On this basis, chemical trends are examined and show to lead to the prediction of semiconductor systems with T_C that may exceed room temperature, an expectation that are being confirmed by recent findings. Results for materials containing magnetic ions other than Mn are also presented emphasizing that the double exchange involving hoping through d states may operate in those systems.Comment: 18 pages, 8 figures; special issue of Semicon. Sci. Technol. on semiconductor spintronic

Measurement of the atmospheric muon depth intensity relation with the NEMO Phase-2 tower

The results of the analysis of the data collected with the NEMO Phase-2 tower, deployed at 3500 m depth about 80 km off-shore Capo Passero (Italy), are presented. Cherenkov photons detected with the photomultipliers tubes were used to reconstruct the tracks of atmospheric muons. Their zenith-angle distribution was measured and the results compared with Monte Carlo simulations. An evaluation of the systematic effects due to uncertainties on environmental and detector parameters is also included. The associated depth intensity relation was evaluated and compared with previous measurements and theoretical predictions. With the present analysis, the muon depth intensity relation has been measured up to 13 km of water equivalent.Comment: submitted to Astroparticle Physic

Communication studies cartography in the Lusophone world

Within the Lusophone community of over 250 million speakers only a minority developed a sense of belonging based on their common language, a phenomenon that is still very real today. According to the Mozambican writer, Mia Couto, Lusophony is not a ‘loud’ reality, rather a “luso-aphonic” one, that is, a place of low voices, no knowledge and no acknowledgement of the commonalities between themselves in this vast geographic and cultural space. Recognizing precisely this gap, Communication research associations in Lusophone countries (Lusocom) have promoted the setting up of a research cooperation network primarily between Portuguese and Brazilian researchers, and then extending it to the Galician community, and subsequently to the entire Lusophone space. This movement is based on the assumption that linguistic diversity enriches science and that science should be globally and contextually relevant. Lusophony can be discussed from various points of view, all related to the cultural identity of the Portuguese-speaking countries. I would like to explain my point of view, focused on the social status of language. Then, I will refer to the English language has a dominant language. Finally, I would like to point out some challenges that, from my perspective, the Lusophone research groups have to face in a global world dominated by English and anglo-saxon paradigms. My approach is in fact focused on the perspective of language, understood as a cultural manifestation, the expression of thought, a relational space, and an instrument of symbolic organization of the world. Such understanding is coincident with the symbolic power of language (Pierre Bourdieu’s theory), and with the post-colonial perspective which questions the domination, submission, subordination and control of peripheries, minorities, diasporas, migrants…(undefined)info:eu-repo/semantics/publishedVersio

The Antares Collaboration : Contributions to the 34th International Cosmic Ray Conference (ICRC 2015, The Hague)

The ANTARES detector, completed in 2008, is the largest neutrino telescope in the Northern hemisphere. Located at a depth of 2.5 km in the Mediterranean Sea, 40 km off the Toulon shore, its main goal is the search for astrophysical high energy neutrinos. In this paper we collect the 21 contributions of the ANTARES collaboration to the 34th International Cosmic Ray Conference (ICRC 2015). The scientific output is very rich and the contributions included in these proceedings cover the main physics results, ranging from steady point sources, diffuse searches, multi-messenger analyses to exotic physics

Search for muon-neutrino emission from GeV and TeV gamma-ray flaring blazars using five years of data of the ANTARES telescope

The ANTARES telescope is well-suited for detecting astrophysical transient neutrino sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. The background due to atmospheric particles can be drastically reduced, and the point-source sensitivity improved, by selecting a narrow time window around possible neutrino production periods. Blazars, being radio-loud active galactic nuclei with their jets pointing almost directly towards the observer, are particularly attractive potential neutrino point sources, since they are among the most likely sources of the very high-energy cosmic rays. Neutrinos and gamma rays may be produced in hadronic interactions with the surrounding medium. Moreover, blazars generally show high time variability in their light curves at different wavelengths and on various time scales. This paper presents a time-dependent analysis applied to a selection of flaring gamma-ray blazars observed by the FERMI/LAT experiment and by TeV Cherenkov telescopes using five years of ANTARES data taken from 2008 to 2012. The results are compatible with fluctuations of the background. Upper limits on the neutrino fluence have been produced and compared to the measured gamma-ray spectral energy distribution.Comment: 27 pages, 16 figure