126,273 research outputs found
Numerical investigation of the influence of leading and sequential bubbles on slug flow boiling within a microchannel
No full textMultiphase CFD simulations are presently employed to investigate the flow boiling of multiple sequential elongated bubbles in a horizontal microchannel. Most of the computational studies published so far explored the features of boiling flows within microchannels by simulating the fluid-dynamics of a single evaporating bubble, but the present work shows that multiple bubble simulations are necessary to capture the essential features of the heat transfer process of a slug flow. In particular, it is shown that leading and sequential bubbles interact thermally and hydrodynamically due to the evaporation process, thus possessing different growth rates, velocities and thicknesses of the thin liquid films trapped between the bubbles interfaces and the channel wall. The evaporation of this thin liquid film is the dominant heat transfer mechanism in the vapor bubble region and the transit of trailing bubbles strongly enhances the time-averaged heat transfer coefficient of the bubble-liquid slug unit, by as much as 60% higher relative to the leading bubble under the operating conditions presently set. Furthermore, the presence of a recirculating vortex just after the tail of the bubble in the liquid slug trapped between the bubbles was found in the simulations, significantly improving the heat transfer between the wall and the bulk liquid, thus maintaining the heat transfer coefficient much higher than otherwise expected in the liquid slug region as well. Finally, a new multiple bubble heat transfer model is proposed to predict the local variation of the heat transfer coefficient, which might prove to be useful to improve the current boiling heat transfer methods, such as the three-zone model of Thome et al. [1,2]. The numerical framework employed to perform this study was the commercial CFD solver ANSYS Fluent 12 with a Volume Of Fluid interface capturing method, which was improved here by implementing external functions, in particular a Height Function method to better estimate the surface tension force and an evaporation model to compute the phase change. (C) 2013 Elsevier Masson SAS. All rights reserved.LTC
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Polyvalence
No full textFor computer, flute, B♭ clarinet, violin and viola, cello, piano, and vibraphone and glockenspiel. Parts for violin/viola and vibraphone/glockenspiel are each performed by one player. This composition and the essay, "Toward structural characterization of the timbral domain", together constitute the composer's Ph. D. dissertation.Contact [email protected] for more informatio
Polyvalence for computer and six players
No full textFor computer, flute, B♭ clarinet, violin and viola, cello, piano, and vibraphone and glockenspiel. Parts for violin/viola and vibraphone/glockenspiel are each performed by one player. This composition and the essay, ""Toward structural characterization of the timbral domain"", together constitute the composer's Ph. D. dissertation
Eastern Europe's experience with banking reform : is there a role for banks in the transition?
No full textAre there lessons to be learned about how Eastern European countries have dealt with problems in their banking systems? What role have these countries assigned to banks during the transition? How have they used banks in dealing with the enterprise problem? The author addresses these questions by analyzing experience in Bulgaria, Hungary, Poland, Romania, and the former Czech and Slovak Federal Republic. Most of these countries have made substantial progress in restructuring their banking systems, but few have used their banking systems to improve the allocation of credit and hence stimulate the supply response. The author finds the following. The problem is not whether banks hold nonperforming loans but how banks can avoid accumulating more nonperforming loans. The underlying problem is how to close loss-making and nonviable enterprises. The countries that have encouraged the establishment of new private banks, that have introduced regulation and supervision, and that have tried to make banks more competitive have been more successful at improving the allocation of credit and achieving more control over loss-making enterprises. Banks must focus on assessing risk - and for this, capital, private ownership, and adequate regulation are crucial. How quickly banks achieve independence in credit decisions depends on how fast new governance structures can be introduced. In this, the five countries have been less successful. The objectives of bank recapitulation should be to prevent banks from accumulating more nonperforming loans (that is, dealing with the enterprise problem) and to give them the governance structure that would prevent them from incurring new nonperforming loans. This requires introducing a system of risk and reward - by making banks comply with capital adequacy requirements, by privatizing a critical number of banks, and by introducing strong regulation and supervision. Government should see that banks provide efficient payment systems, the basis for trust in banking systems. Introducing adequate regulation and supervision has been difficult as it requires knowing what the banks'role should be. Evidence strongly supports the need to recapitalize and privatize a critical number of banks. Authorities cannot rely on banks to exert control on enterprises early in the transition. In the early stages, control over state-owned enterprises should be exercised by a semipublic institution.Banks&Banking Reform,Financial Intermediation,Financial Crisis Management&Restructuring,Municipal Financial Management,Banking Law
Sermones panegíricos predicados en festiuidades de varios santos
No full textSign.: [calderón]-2[calderón], 3[calderón], A, B, A, B, A-Z, 2A-2E, 2F, 2G-2I, 2KTexto a dúas colPort. con grav. xi
Numerical investigation of hydrodynamics and heat transfer of elongated bubbles during flow boiling in a microchannel
No full textFlow boiling within microchannels has been explored intensively in the last decade due to their capability to remove high heat fluxes from microelectronic devices. However, the contribution of experiments to the understanding of the local features of the flow is still severely limited by the small scales involved. Instead, multiphase CFD simulations with appropriate modeling of interfacial effects overcome the current limitations in experimental techniques. Presently, numerical simulations of single elongated bubbles in flow boiling conditions within circular microchannels were performed. The numerical framework is the commercial CFD code ANSYS Fluent 12 with a Volume Of Fluid interface capturing method, which was improved here by implementing, as external functions, a Height Function method to better estimate the local capillary effects and an evaporation model to compute the local rates of mass and energy exchange at the interface. A detailed insight on bubble dynamics and local patterns enhancing the wall heat transfer is achievable utilizing this improved solver. The numerical results show that, under operating conditions typical for flow boiling experiments in microchannels, the bubble accelerates downstream following an exponential time-law, in good agreement with theoretical models. Thin-film evaporation is proved to be the dominant heat transfer mechanism in the liquid film region between the wall and the elongated bubble, while transient heat convection is found to strongly enhance the heat transfer performance in the bubble wake in the liquid slug between two bubbles. A transient-heat-conduction-based boiling heat transfer model for the liquid film region, which is an extension of a widely quoted mechanistic model, is proposed here. It provides estimations of the local heat transfer coefficient that are in excellent agreement with simulations and it might be included in next-generation predictive methods.LTC
New matrix partial order based spectrally orthogonal matrix decomposition
No full text[EN] We investigate partial orders on the set of complex square matrices and introduce a new order relation based on spectrally orthogonal matrix decompositions. We also establish the relation of this concept with the known orders.The research of the first author was supported by the Grants [grant number RFBR-15-01-01132], [grant number MD-962.2014.1]. The second and third authors have been partially supported by Ministerio de Economia y Competitividad from Spain, DGI [grant number MTM2013-43678-P].Guterman, A.; Herrero Debón, A.; Thome, N. (2016). New matrix partial order based spectrally orthogonal matrix decomposition. Linear and Multilinear Algebra. 64(3):362-374. https://doi.org/10.1080/03081087.2015.1041365S362374643Meyer, C. (2000). Matrix Analysis and Applied Linear Algebra. doi:10.1137/1.9780898719512Mitra, S. K., & Bhimasankaram, P. (2010). MATRIX PARTIAL ORDERS, SHORTED OPERATORS AND APPLICATIONS. SERIES IN ALGEBRA. doi:10.1142/9789812838452Baksalary, O. M., & Trenkler, G. (2010). Core inverse of matrices. Linear and Multilinear Algebra, 58(6), 681-697. doi:10.1080/03081080902778222Baksalary, O. M., & Trenkler, G. (2014). On a generalized core inverse. Applied Mathematics and Computation, 236, 450-457. doi:10.1016/j.amc.2014.03.048Hernández, A., Lattanzi, M., Thome, N., & Urquiza, F. (2012). The star partial order and the eigenprojection at 0 on EP matrices. Applied Mathematics and Computation, 218(21), 10669-10678. doi:10.1016/j.amc.2012.04.034Hernández, A., Lattanzi, M., & Thome, N. (2013). On a partial order defined by the weighted Moore–Penrose inverse. Applied Mathematics and Computation, 219(14), 7310-7318. doi:10.1016/j.amc.2013.02.010Hernández, A., Lattanzi, M., & Thome, N. (2015). Weighted binary relations involving the Drazin inverse. Applied Mathematics and Computation, 253, 215-223. doi:10.1016/j.amc.2014.12.102Lebtahi, L., Patrício, P., & Thome, N. (2013). The diamond partial order in rings. Linear and Multilinear Algebra, 62(3), 386-395. doi:10.1080/03081087.2013.779272Malik, S. B., Rueda, L., & Thome, N. (2013). Further properties on the core partial order and other matrix partial orders. Linear and Multilinear Algebra, 62(12), 1629-1648. doi:10.1080/03081087.2013.839676Rakić, D. S., & Djordjević, D. S. (2012). Space pre-order and minus partial order for operators on Banach spaces. Aequationes mathematicae, 85(3), 429-448. doi:10.1007/s00010-012-0133-2Nambooripad, K. S. S. (1980). The natural partial order on a regular semigroup. Proceedings of the Edinburgh Mathematical Society, 23(3), 249-260. doi:10.1017/s0013091500003801Mitra, S. K. (1987). On group inverses and the sharp order. Linear Algebra and its Applications, 92, 17-37. doi:10.1016/0024-3795(87)90248-
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