Predicting topology propagation messages in mobile ad hoc networks: The value of history

This research was funded by the Spanish Government under contracts TIN2016-77836-C2-1-R,TIN2016-77836-C2-2-R, and DPI2016-77415-R, and by the Generalitat de Catalunya as Consolidated ResearchGroups 2017-SGR-688 and 2017-SGR-990.The mobile ad hoc communication in highly dynamic scenarios, like urban evacuations or search-and-rescue processes, plays a key role in coordinating the activities performed by the participants. Particularly, counting on message routing enhances the communication capability among these actors. Given the high dynamism of these networks and their low bandwidth, having mechanisms to predict the network topology offers several potential advantages; e.g., to reduce the number of topology propagation messages delivered through the network, the consumption of resources in the nodes and the amount of redundant retransmissions. Most strategies reported in the literature to perform these predictions are limited to support high mobility, consume a large amount of resources or require training. In order to contribute towards addressing that challenge, this paper presents a history-based predictor (HBP), which is a prediction strategy based on the assumption that some topological changes in these networks have happened before in the past, therefore, the predictor can take advantage of these patterns following a simple and low-cost approach. The article extends a previous proposal of the authors and evaluates its impact in highly mobile scenarios through the implementation of a real predictor for the optimized link state routing (OLSR) protocol. The use of this predictor, named OLSR-HBP, shows a reduction of 40–55% of topology propagation messages compared to the regular OLSR protocol. Moreover, the use of this predictor has a low cost in terms of CPU and memory consumption, and it can also be used with other routing protocols.Peer ReviewedPostprint (published version

Minimulticomputador de bajo coste

En la mayoría de los estudios de Grado en Ingeniería Informática hay asignaturas que abordan el tema de la supercomputación. Uno de sus objetivos es adquirir competencias en programación paralela. Para realizar ejercicios y prácticas se suelen usar estándares como OpenMP, MPI y CUDA. Para programar con dichos estándares se usan sistemas de elevado precio, lo que hace que el presupuesto disponible limite el número de procesadores. Por lo tanto, el acceso a un supercomputador con cientos de procesadores (que supone centenares de miles de euros) no parece estar justificado para realizar prácticas con los estudiantes. Sin embargo, y siguiendo la tendencia de usar muchos procesadores pero poco potentes basados en ARM, se puede construir un minimulticomputador de bajo coste por un precio equivalente a un servidor de memoria compartida. Este trabajo presenta un recurso docente basado en placas de HardKernel, que integran 64 placas Odroid y que mediante Gigabit-Ethernet permiten montar un servidor de programación MPI con 256 procesadores. Si bien se trata de un recurso de bajas prestaciones, es interesante el hecho de tener acceso a centenares de procesadores para poder hacer estudios de escalabilidad, manteniendo un buen compromiso entre prestaciones, precio y consumo.In most of Computer Science Degrees, there are subjects that address the topic of supercomputing. One of the objectives of these subjects is to acquire competences in parallel programming. To carry out exercises and practices, standards such as OpenMP, MPI and CUDA are often used. Unfortunately, the most suitable systems to deal with those standards are very expensive and most of the times the available budget limits the number of processors. Owning a supercomputer with hundreds of processors (that means hundreds of thousands of euros) does not seem to be justified in a teaching environment. However, assuming the trend of dealing with many low-power processors (based on ARM architectures), a low-cost minimulticomputer can be built for a price equivalent to a shared memory server. In this work, we present a teaching resource based on HardKernel boards, with 64 Odroid boards connected through Gigabit-Ethernet, to build a MPI server with 256 processors. Although it is a resource with a relatively low performance, the aim is to have access to hundreds of processors to be able to carry out scalability analysis and, above all, maintaining a good trade-off between performance, price and energy consumption.Este trabajo ha contado con la financiación del Gobierno de España bajo los contratos TIN2016-77836-C2-1-R, TIN2016-77836-C2-2-R, TIN2016-75344-R y DPI2016-77415-R, y también de la Generalitat de Catalunya como Grupos de Investigación Consolidados 2017-SGR-688 y 2017-SGR-990

Predicting topology propagation messages in mobile ad hoc networks: The value of history

The mobile ad hoc communication in highly dynamic scenarios, like urban evacuations or search-and-rescue processes, plays a key role in coordinating the activities performed by the participants. Particularly, counting on message routing enhances the communication capability among these actors. Given the high dynamism of these networks and their low bandwidth, having mechanisms to predict the network topology offers several potential advantages; e.g., to reduce the number of topology propagation messages delivered through the network, the consumption of resources in the nodes and the amount of redundant retransmissions. Most strategies reported in the literature to perform these predictions are limited to support high mobility, consume a large amount of resources or require training. In order to contribute towards addressing that challenge, this paper presents a history-based predictor (HBP), which is a prediction strategy based on the assumption that some topological changes in these networks have happened before in the past, therefore, the predictor can take advantage of these patterns following a simple and low-cost approach. The article extends a previous proposal of the authors and evaluates its impact in highly mobile scenarios through the implementation of a real predictor for the optimized link state routing (OLSR) protocol. The use of this predictor, named OLSR-HBP, shows a reduction of 40–55% of topology propagation messages compared to the regular OLSR protocol. Moreover, the use of this predictor has a low cost in terms of CPU and memory consumption, and it can also be used with other routing protocols.Fil: Millán, Pere. Universitat Rovira I Virgili; EspañaFil: Aliagas, Carles. Universitat Rovira I Virgili; EspañaFil: Molina, Carlos. Universitat Rovira I Virgili; EspañaFil: Meseguer, Roc. Universidad Politécnica de Catalunya; EspañaFil: Ochoa, Sergio F.. Universidad de Chile; ChileFil: Santos, Rodrigo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Ciencias e Ingeniería de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e Ingeniería de la Computación. Instituto de Ciencias e Ingeniería de la Computación; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras; Argentin

A low-cost and do-it-yourself device for pumping monitoring in deep aquifers

Water crises due to climate change, high population growth and increasing demands from industry and agriculture claim for increasing efficiency and universalizing water resources management strategies and techniques. Water monitoring helps providing necessary evidences for making sound decisions about managing water resources both now and in the future. In this work, a low cost and “do it yourself” communication device is proposed to record water production and energy consumption of electric pumpings from deep boreholes/wells, and to predict the impact of the ongoing and previous pumpings in the evolution of the water level in the aquifer. The proposal incorporates an edge-computing approach for the simulation of the aquifer response in real-time. Computation of results of interest is performed at the sensor, minimizing communication requirements and ensuring almost immediate results. An approximated solution to physically based modeling of aquifer response is computed thanks to the a priori expression of the water level time evolution in a reduced basis. The accuracy is enough to detect deviations from expected behaviour. The energy consumption of the device is very much reduced with respect to that of a full modelling, which can be computed off-line for calibrating reduced model parameters and perform detailed analyses. The device is tested in a real scenario, in a mountain subbasin of the Ebro river in Spain, obtaining a good trade-off between performance, price, and energy consumption.This research has been partly supported by EU under grant agreement N. 825184 and funded by the Government of Spain under contracts PID2019-106774RB-C21, PID2019-106774RB-C22, and PID2020-113172RB-I00 and by the Government of Catalonia as Consolidated Research Groups 2017-SGR-688 and 2017-SGR-990, and Pre-consolidated Research Group 2017-SGR-1496. The APC was funded by the Open program from Universitat Rovira i Virgili.Peer ReviewedPostprint (published version

Density and Refractive Index of Carbon Monoxide Ice at Different Temperatures

[EN] This paper is intended to study the density and the refractive index of the solid carbon monoxide in the interval 13-28 K to improve our understanding of the dynamics in the astrophysical environments where they are present. A series of deposition experiments have been performed under high vacuum conditions to study the properties of this ice under astrophysical conditions. Ice density has been experimentally calculated at different deposition temperatures of astrophysical interest, which complement the scarce values present in the literature. The refractive index has also been experimentally determined. The data have been used to obtain an experimental relationship between refractive index and density. Values of density are necessary to interpret observations of astrophysical objects or to design irradiation experiments to understand how irradiation affects ices present in these objects. The experimental relationship found between density and refractive index allows us to estimate density from a known refractive index, even for temperatures not reached using our experimental setup.Funds have been provided for this research by the Spanish MINECO, Project PID2020-118974GB-C22.Luna Molina, R.; Millán, C.; Domingo Beltran, M.; Santonja Moltó, MDC.; Satorre, MÁ. (2022). Density and Refractive Index of Carbon Monoxide Ice at Different Temperatures. The Astrophysical Journal. 935(2):1-6. https://doi.org/10.3847/1538-4357/ac800116935

Study of the frequency factor in the thermal desorption of astrophysical ice analogs: CH4, C2H4, C2H6, CH3OH, CO, CO2, H2O and N2

[EN] In this work the frequency factor and the influence of the temperature on this parameter, for zeroth order desorption processes, has been experimentally determined for eight molecules of astrophysical interest. In the literature, this parameter has been estimated indirectly, obtaining values that differ by as much as three orders of magnitude from different authors. As a consequence, there are very different desorption rates reported for the same molecule and additionally its temperature dependence has been systematically neglected. The frequency factor is widely used to model the dynamics of these species under low temperature conditions present in some astrophysical environments. The method reported in this work is based on the analysis of the signal of a quartz crystal microbalance acting as a sample-holder, which is able to directly detect molecules desorbing from it. Two different types of desorption experiments were necessary for this study. In a first set of experiments, carried out at a constant rate of warming up, the desorption energy is obtained. The second set of experiments were performed at several constant temperatures to calculate the frequency factor and its relationship with temperature. The reasons for some anomalous behaviour have been analyzed. The dependence of the frequency factor on temperature should be taken into account when the Polanyi-Wigner equation is used for desorption processes. Every molecule has to be independently studied as no global tendency is found for the variation of the frequency factor with temperature. (C) 2018 Elsevier Ltd. All rights reserved.This work was supported by the Plan Nacional FIS2013-48087-C2-2-P and FIS2016-77726-C3-3-P of the Ministerio de Economia y Competitividad (co-financed by FEDER funds).Luna Molina, R.; Domingo Beltran, M.; Millán Verdú, C.; Santonja Moltó, MDC.; Satorre, MÁ. (2018). Study of the frequency factor in the thermal desorption of astrophysical ice analogs: CH4, C2H4, C2H6, CH3OH, CO, CO2, H2O and N2. Vacuum. 152:278-284. https://doi.org/10.1016/j.vacuum.2018.03.022S27828415

An experimental test for effective medium approximations (EMAs) Porosity determination for ices of astrophysical interest

[EN] Aims. The effective medium approximations (EMAs), or the Lorentz-Lorenz, Maxwell-Garnett, and Bruggeman models, largely used to obtain optical properties and porosities of pure and ice mixtures, have been experimentally tested in this work. The efficiency of these approximations has been studied by obtaining the porosity value for carbon dioxide ice grown at low temperatures. An explanation of the behaviour of the experimental results for all temperatures is given. The analysis carried out for CO2 can be applied to other molecules. Methods. An optical laser interference technique was carried out using two laser beams falling on a growing film of ice at different incident angles which allowed us to determine the refractive index and the thickness of the film. The mass deposited is recorded by means of a quartz crystal microbalance. Porosity is determined from its equational definition by using the experimental density previously obtained. Results. From the experimental results of the refractive index and density, porosity values for carbon dioxide ice films grown on a cold surface at different temperatures of deposition have been calculated and compared with the results obtained from the EMA equations, and with recent experimental results. Conclusion. The values of porosity obtained with the EMA models and experimentally, show similar trends. However, theoretical values overestimate the experimental results. We can conclude that using the EMAs to obtain this parameter from an ice mixture must be carefully considered and, if possible, an alternative experimental procedure that allows comparisons to be made should be used.Funds have been provided for this research by the Spanish MINECO, Project FIS2016-77726-C3-3-P.Millán Verdú, C.; Santonja Moltó, MDC.; Domingo Beltran, M.; Luna Molina, R.; Satorre, MÁ. (2019). An experimental test for effective medium approximations (EMAs) Porosity determination for ices of astrophysical interest. Astronomy and Astrophysics. 628(A63):1-5. https://doi.org/10.1051/0004-6361/201935153S15628A63Aikawa, Y., Wakelam, V., Garrod, R. T., & Herbst, E. (2008). Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores. The Astrophysical Journal, 674(2), 984-996. doi:10.1086/524096Bartels-Rausch, T., Bergeron, V., Cartwright, J. H. E., Escribano, R., Finney, J. L., Grothe, H., … Uras-Aytemiz, N. (2012). Ice structures, patterns, and processes: A view across the icefields. Reviews of Modern Physics, 84(2), 885-944. doi:10.1103/revmodphys.84.885Born M., & Wolf E. 1999, Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light (Cambridge: Cambridge University Press)Bossa, J.-B., Isokoski, K., Paardekooper, D. M., Bonnin, M., van der Linden, E. P., Triemstra, T., … Linnartz, H. (2014). Porosity measurements of interstellar ice mixtures using optical laser interference and extended effective medium approximations. Astronomy & Astrophysics, 561, A136. doi:10.1051/0004-6361/201322549Brovchenko, I., & Oleinikova, A. (2006). Four phases of amorphous water: Simulations versus experiment. The Journal of Chemical Physics, 124(16), 164505. doi:10.1063/1.2194906Cazaux, S., Bossa, J.-B., Linnartz, H., & Tielens, A. G. G. M. (2014). Pore evolution in interstellar ice analogues. Astronomy & Astrophysics, 573, A16. doi:10.1051/0004-6361/201424466Isokoski, K., Bossa, J.-B., Triemstra, T., & Linnartz, H. (2014). Porosity and thermal collapse measurements of H2O, CH3OH, CO2, and H2O:CO2 ices. Physical Chemistry Chemical Physics, 16(8), 3456. doi:10.1039/c3cp54481hKeane, J. V., Boogert, A. C. A., Tielens, A. G. G. M., Ehrenfreund, P., & Schutte, W. A. (2001). Bands of solid CO$_\mathsf{2}$ in the 2-3μm spectrum of S 140:IRS1. Astronomy & Astrophysics, 375(3), L43-L46. doi:10.1051/0004-6361:20010977Loeffler, M. J., Moore, M. H., & Gerakines, P. A. (2016). THE EFFECTS OF EXPERIMENTAL CONDITIONS ON THE REFRACTIVE INDEX AND DENSITY OF LOW-TEMPERATURE ICES: SOLID CARBON DIOXIDE. The Astrophysical Journal, 827(2), 98. doi:10.3847/0004-637x/827/2/98Lorentz, H. A. (1880). Ueber die Beziehung zwischen der Fortpflanzungsgeschwindigkeit des Lichtes und der Körperdichte. Annalen der Physik und Chemie, 245(4), 641-665. doi:10.1002/andp.18802450406Lorenz, L. (1880). Ueber die Refractionsconstante. Annalen der Physik und Chemie, 247(9), 70-103. doi:10.1002/andp.18802470905Luna, R., Millán, C., Domingo, M., & Satorre, M. Á. (2008). Thermal desorption of CH4 retained in CO2 ice. Astrophysics and Space Science, 314(1-3), 113-119. doi:10.1007/s10509-008-9746-2Markel, V. A. (2016). Introduction to the Maxwell Garnett approximation: tutorial. Journal of the Optical Society of America A, 33(7), 1244. doi:10.1364/josaa.33.001244Markel, V. A. (2016). Maxwell Garnett approximation (advanced topics): tutorial. Journal of the Optical Society of America A, 33(11), 2237. doi:10.1364/josaa.33.002237XII. Colours in metal glasses and in metallic films. (1904). Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, 203(359-371), 385-420. doi:10.1098/rsta.1904.0024VII. Colours in metal glasses, in metallic films, and in metallic solutions.—II. (1906). Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, 205(387-401), 237-288. doi:10.1098/rsta.1906.0007Palumbo, M. E., Baratta, G. A., Leto, G., & Strazzulla, G. (2010). H bonds in astrophysical ices. Journal of Molecular Structure, 972(1-3), 64-67. doi:10.1016/j.molstruc.2009.12.017Rodgers, S. D., & Charnley, S. B. (2003). Chemical Evolution in Protostellar Envelopes: Cocoon Chemistry. The Astrophysical Journal, 585(1), 355-371. doi:10.1086/345497Rowland, B., Fisher, M., & Devlin, J. P. (1991). Probing icy surfaces with the dangling‐OH‐mode absorption: Large ice clusters and microporous amorphous ice. The Journal of Chemical Physics, 95(2), 1378-1384. doi:10.1063/1.461119Satorre, M. Á., Domingo, M., Millán, C., Luna, R., Vilaplana, R., & Santonja, C. (2008). Density of , and ices at different temperatures of deposition. Planetary and Space Science, 56(13), 1748-1752. doi:10.1016/j.pss.2008.07.015Satorre M., Luna R., Millán C., Domingo M., & Santonja C. 2018, in Astrophys. Space Sci. Lib., eds. Muñoz Caro G. M., & Escribano R., 451, 51Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur W�gung d�nner Schichten und zur Mikrow�gung. Zeitschrift f�r Physik, 155(2), 206-222. doi:10.1007/bf01337937Schulze, W., & Abe, H. (1980). Density, refractive index and sorption capacity of solid CO2 layers. Chemical Physics, 52(3), 381-388. doi:10.1016/0301-0104(80)85240-2Stroud, D. (1998). The effective medium approximations: Some recent developments. Superlattices and Microstructures, 23(3-4), 567-573. doi:10.1006/spmi.1997.0524Viti, S., Collings, M. P., Dever, J. W., McCoustra, M. R. S., & Williams, D. A. (2004). Evaporation of ices near massive stars: models based on laboratory temperature programmed desorption data. Monthly Notices of the Royal Astronomical Society, 354(4), 1141-1145. doi:10.1111/j.1365-2966.2004.08273.xWarren, S. G. (1986). Optical constants of carbon dioxide ice. Applied Optics, 25(16), 2650. doi:10.1364/ao.25.002650Westley, M. S., Baratta, G. A., & Baragiola, R. A. (1998). Density and index of refraction of water ice films vapor deposited at low temperatures. The Journal of Chemical Physics, 108(8), 3321-3326. doi:10.1063/1.47573

Experimental Measurement of Carbon Dioxide Polarizability in the Solid State

[EN] We have experimentally determined the polarizability of using the Lorentz-Lorenz equation by simultaneously measuring the density and the refractive index. The conditions were solid phase, mbar pressure, and temperature range 10-86 K. The polarizability value compares well with previous gas-phase experimental results and the results from simulations, and does not depend on the temperature of ice formation. This value is constant in the temperature range studied, despite a structural change from amorphous to crystalline.This work was supported by the Spanish Ministerio de Economia y Competitividad (FIS2013-48087-C2-2-P).Domingo Beltran, M.; Luna Molina, R.; Satorre, MÁ.; Santonja Moltó, MDC.; Millán Verdú, C. (2015). Experimental Measurement of Carbon Dioxide Polarizability in the Solid State. Journal of Low Temperature Physics. 181(1):1-9. https://doi.org/10.1007/s10909-015-1326-6S191811K.J. Miller, J. Am. Chem. Soc. 112, 8543 (1990)P. Phillips, Proc. R. Soc. Lond. A 97, 225 (1920)A.C. Newell, R.C. Baird, J. Appl. Phys. 36, 3751 (1965)D.R. Johnston, G.J. Oudemanns, R.H. Cole, J. Chem. Phys. 33, 1310 (1960)D.R. Johnston, R.H. Cole, J. Chem. Phys. 36, 318 (1962)R.H. Orcutt, R.H. Cole, Physica 31, 1779 (1965)R.H. Orcutt, R.H. Cole, J. Chem. Phys. 46, 697 (1967)M. Domingo, C. Millán, M.A. Satorre, J. Cantó, in Proceedings of SPIE, Optical Measurements Systems for Industrial Inspection V, Munich, 2007, ed. by W. Osten, C. Goreki and E.L. Novak, Vol. 6616 (SPIE, EEUU, 2007), p. 6616 4AL. Silberstein, Philos. Mag. 33, 92, 215, 521 (1917)J. Applequist, J.R. Carl, K.K. Fung, J. Am. Chem. Soc. 94, 2952 (1972)G. Maroulis, A.J. Thakkar, J. Chem. Phys. 93, 4164 (1990)M. Lewis, Z. Wu, R. Glaser, J. Phys. Chem. A. 104, 11355 (2000)A. Szabo, N.S. Ostlund, Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory (MacMillan Publishing Co., Inc., New York, 1982)W.L. Hehre, L. Radom, PvR Schleyer, J.A. Pople, Ab Initio Molecular Orbital Theory (Wiley, New York, 1986)N.J. Bridge, A.D. Buckingham, Proc. R. Soc. Lond. A 295, 334 (1966)G.R. Alms, A.K. Burnham, W.H. Flygare, J. Chem. Phys. 63, 3321 (1975)I.R. Gentle, D.R. Laver, G.L. Ritchie, J. Phys. Chem. 93, 3035 (1989)H.A. Stuart, Sv Schieszl, Ann. Phys. 2, 321 (1948)A.D. Buckingham, R.L. Dish, Proc. R. Soc. Lond. A 273, 275 (1963)A.H. England, A.M. Duffin, C.P. Schwartz, J.S. Uejio, D. Prendergast, R.J. Saykally, Chem. Phys. Lett. 514, 187 (2011)T. Takahashi, Encycl. Ocean Sci. 1, 400 (2001)R.M. Haberle, B. Mattingly, T.N. Titus, Geophys. Res. Lett. 31, L05702 (2004)M. Aresta, I. Tommasi, Energy Convers. Manag. 38, S373 (1997)M.A. Satorre, M. Domingo, C. Millán, R. Luna, R. Vilaplana, C. Santonja, Planet. Space Sci. 56, 1748 (2008)S.G. Warren, Appl. Opt. 25, 2650 (1986)J.R. Reitz, F.J. Mildford, R.W. Christy, Foundations of Electromagnetic Theory (Addison Wesley, Boston, 2008)T.K. Bose, R.H. Cole, J. Chem. Phys. 52, 140 (1970)P. Lorrain, D.R. Corson, Campos y ondas electromagnéticos (Selecciones Científicas, Madrid, 1972)I. Thormählen, J. Straub, U. Grigull, J. Phys. Chem. Ref. Data 14, 4, 933 (1985)M. Born, E. Wolf, Principles of Optics (Cambridge University Press, Cambridge, 1999)W. Schulze, H. Abe, Chem. Phys. 52, 381 (1980)E. Hecht, Optics (Addison Wesley, San Francisco, 2002)W.A. Schutte, Molecules in astrophysics: probes & processes:abstract book, 1996, Leiden, 1996, edited by Ewine Fleur vanDishoeck (The Netherlands, 1996), IAU symposium 178, p. 331T. Guella, Thomas M. Miller, J.A.D. Stockdale, B. Bederson, L. Vušković, J. Chem. Phys 94, 6857 (1991)T.M. Miller, in CRC Handbook of Chemistry and Physics, ed. by D. R. Lide , 89th Edn. (CRC Press/Taylor and Francis, Boca Raton, FL, 2009)K.E. Tempelmeyer, D.W. Mills Jr, J. Appl. Phys. 39, 2968 (1968)G. Cardini, P. Procacci, R. Righini, J. Chem. Phys. 117, 355 (1987)M. Falk, J. Chem. Phys. 86, 560 (1987)S.A. Sandford, L.J. Allamandola, Astrophys. J. 355, 357 (1990)R. M. Escribano, G. M. Muñoz Caro, G. A. Cruz-Díaz, Y. Rodríguez-Lezcano et B. Maté, PNAS, 110, 32, 12899 (2013)R. Luna, C. Millan, M. Domingo, M.A. Satorre, Planet. Space Sci. 314, 113 (2008

Experimental study of the frequency factor in the Polanyi-Wigner equation: the case of C2H6

NOTICE: this is the author’s version of a work that was accepted for publication in Vacuum. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in VACUUM [122 (2015) 154-160] DOI 10.1016/j.vacuum.2015.09.021The C2H6 molecule has been used to determine experimentally, for the first time, the frequency factor present in the Polanyi-Wigner equation and to study how temperature influences this magnitude for a zeroth order desorption. This parameter is necessary to calculate the desorption rates for environments in which this process occurs. The method presented is based on the analysis of a quartz crystal microbalance signal. In the literature the frequency factor is not experimentally obtained but is rather assumed to be K-6.T/h (at 50 K), as proposed by the activated state theory for first order desorption processes, or it is estimated by other methods. Additionally, the factor's variation with temperature has not been experimentally explored to date. Two different types of zeroth order desorption experiments have been designed for this study. The purpose of the first experiment, carried out at a constant rate of warming, is to obtain the desorption energy, which is compared with previous values reported in the literature. The second group of desorption experiments is performed at constant temperatures and is used to calculate and study the frequency factor. Several temperatures have been specifically selected, enabling us to determine the influence of the temperature on this parameter. We have calculated a relationship for the frequency factor and temperature, obtaining an increase of approximately 50% for the frequency factor for an increase of only 6 K. This result must be taken into account when the Polanyi-Wigner equation is used for desorption rate calculations. (C) 2015 Elsevier Ltd. All rights reserved.This work was supported by the Plan Nacional FIS2013-48087-C2-2-P of the Ministerio de Economia y Competitividad.Luna Molina, R.; Millán Verdú, C.; Domingo Beltran, M.; Santonja Moltó, MDC.; Satorre, MÁ. (2015). Experimental study of the frequency factor in the Polanyi-Wigner equation: the case of C2H6. Vacuum. 122:154-160. https://doi.org/10.1016/j.vacuum.2015.09.021S15416012

Minimulticomputador de bajo coste

En la mayoría de los estudios de Grado en Ingeniería Informática hay asignaturas que abordan el tema de la supercomputación. Uno de sus objetivos es adquirir competencias en programación paralela. Para realizar ejercicios y prácticas se suelen usar estándares como OpenMP, MPI y CUDA. Para programar con dichos estándares se usan sistemas de elevado precio, lo que hace que el presupuesto disponible limite el número de procesadores. Por lo tanto, el acceso a un supercomputador con cientos de procesadores (que supone centenares de miles de euros) no parece estar justificado para realizar prácticas con los estudiantes. Sin embargo, y siguiendo la tendencia de usar muchos procesadores pero poco potentes basados en ARM, se puede construir un minimulticomputador de bajo coste por un precio equivalente a un servidor de memoria compartida. Este trabajo presenta un recurso docente basado en placas de HardKernel, que integran 64 placas Odroid y que mediante Gigabit-Ethernet permiten montar un servidor de programación MPI con 256 procesadores. Si bien se trata de un recurso de bajas prestaciones, es interesante el hecho de tener acceso a centenares de procesadores para poder hacer estudios de escalabilidad, manteniendo un buen compromiso entre prestaciones, precio y consumo.Este trabajo ha contado con la financiación del Gobierno de España bajo los contratos TIN2016-77836-C2-1-R, TIN2016-77836-C2-2-R, TIN2016-75344-R y DPI2016-77415-R, y también de la Generalitat de Catalunya como Grupos de Investigación Consolidados 2017-SGR-688 y 2017-SGR-990Peer ReviewedPostprint (published version