La vida de Aristóteles de Abu Sulayman al-Siyistani.

Sin resume

Global and cocycle attractors for non-autonomous reaction-diffusion equations. The case of null upper Lyapunov exponent

In this paper we obtain a detailed description of the global and cocycle attractors for the skew-product semiflows induced by the mild solutions of a family of scalar linear-dissipative parabolic problems over a minimal and uniquely ergodic flow. We consider the case of null upper Lyapunov exponent for the linear part of the problem. Then, basically two different types of attractors can appear, depending on whether the linear coefficient in the equations determines a bounded or an unbounded associated real cocycle. In the first case (the one for periodic equations), the structure of the attractor is simple, whereas in the second case (which happens in aperiodic equations), the attractor is a pinched set with a complicated structure. We describe situations in which the attractor is chaotic in measure in the sense of Li-Yorke. Besides, we obtain a non-autonomous discontinuous pitchfork bifurcation scenario for concave equations, applicable for instance to a linear-dissipative version of the Chafee-Infante equation.Ministerio de Economía y CompetitividadFondo Europeo de Desarrollo RegionalEuropean CommissionJunta de Andalucí

An Efficient NVoD Scheme Using Implicit Error Correction and Subchannels for Wireless Networks

Implicit Error Correction (IEC) is a near Video-on-Demand (nVoD) scheme that trades bandwidth utilization for initial playback delay to potentially support an infinite number of users. Additionally, it provides error protection without any further bandwidth increase by exploiting the implicit redundancy of nVoD protocols, using linear combinations of the segments transmitted in a given time slot. However, IEC packet loss protection is weaker at the beginning of the playback due to the lack of implicit redundancy and lower decoding efficiency, resulting in worse subjective playback quality. In tackling this issue, this paper contributes with an extension of the original nVoD architecture, enhancing its performance by adding a new element namely, subchannels. These subdivisions of the original channels do not provide further packet loss protection but significantly improve the decoding efficiency, which in turn increases playback quality, especially at the beginning. Even for very high packet loss probabilities, subchannels are designed to obtain higher decoding efficiency which results in greater packet loss protection than that provided by IEC. The proposed scheme is especially useful in wireless cooperative networks using techniques such as network coding, as content transmissions can be split into different subchannels in order to maximize network efficiency.This work was supported by the AEI/FEDER, UE Project AIM under Grant TEC2016-76465-C2-1-R

Efficient spatial-domain implementation of a multiscale image representation based on Gabor functions

Contiene tablas y fórmulasGabor schemes of multiscale image representation are useful in many computer vision applications. However, the classic Gabor expansion is computationally expensive due to the lack of orthogonality of Gabor functions. Some alternative schemes, based on the application of a bank of Gabor filters, have important advantages such as computational efficiency and robustness, at the cost of redundancy and lack of completeness. In a previous work we proposed a quasicomplete Gabor transform, suitable for fast implementations in either space or frequency domains. Reconstruction was achieved by simply adding together the even Gabor channels. In this work, we develop an optimized spatial-domain implementation, using one-dimensional, 11-tap filter masks, that is faster and more flexible than Fourier implementations. The reconstruction method is improved by applying fixed and independent weights to the Gabor channels before adding them. Finally, we analyze and implement, in the spatial domain, two ways to incorporate a high-pass residual, which permits a visually complete representation of the image.Peer reviewe

Hacia un modelo integral para la generación de Mundos Virtuales

Uno de los problemas más importantes en los sistemas de Realidad Virtual es la diversidad de los dispositivos visuales y de interacción que existen en la actualidad. Junto a esto, la heterogeneidad de los motores gráficos, los motores físicos y los módulos de Inteligencia Artificial, propicia que no exista un modelo que aúne todos estos aspectos de una forma integral y coherente. Con el objetivo de unificar toda esta diversidad, presentamos un modelo formal que afronta de forma integral el problema de la diversidad en los sistemas de RV, así como la definición de los módulos principales que los constituyen. El modelo propuesto se basa en la definición de una gramática, que integra la actividad necesaria en un sistema de RV, su visualización y su interacción con el usuario. La descripción de un mundo se presenta como una secuencia ordenada de primitivas, transformaciones que modifican el comportamiento de las primitivas y actores que definen la actividad del sistema. Los conceptos de primitiva, transformación y actor son mucho más amplios de lo que es habitual en estos sistemas: Las primitivas no son simples primitivas de dibujo sino acciones que se deben ejecutar en un determinado sistema de presentación, gráfico o no; las transformaciones modifican las primitivas, dependiendo de su naturaleza; los actores desarrollan una o varias actividades en el mundo virtual, se visualizan mediante primitivas y transformaciones, y usan eventos que también se definen en sentido amplio. El modelo presentado tiene como virtud la separación de la actividad del sistema de los dispositivos visuales y de interacción concretos que lo componen. Esto supone varias ventajas: los dispositivos pueden ser sustituidos por otros dispositivos o por simulaciones de estos, los elementos del sistema pueden ser reutilizados, y la representación gráfica puede ser diferente dependiendo del dispositivo visual. En definitiva, se ha pretendido diseñar un sistema integral, adaptativo, reutilizable y genérico. Por último se presenta un caso práctico que permite concretar cómo se utiliza el modelo propuesto

Fracture test of a Gothic ribbed vault

A Gothic ribbed vault has been built at the School of Architecture of Madrid in order to investigate the construction complexities of this kind of vaults. The ribbed vault is described in the manuscript of Alonso de Vandelvira, and its shape was reconstructed making using the drawings this architect from the 16th century. The fracture test was carried on by loading the central keystone of the vault until its collapse took place. The experiment was filmed and by doing so, it was possible to observe the failure mechanism of the vault. At the same time, it was interesting to compare this collapse experience with the results obtained using two different me-thods. First, a stability calculation was carried out through graphic statics, and secondly a calcu-lation was performed using the rigid-block analysis method. The focus of this paper is to show and analyze the results of both studies

Quality management practices, knowledge management and key business results in SMEs and large organizations: a multi-group analysis

Following the Total Quality Management philosophy and the knowledge management (KM) approach, this contribution aims to study the influence of process management methodology (PMM) and partner management (PM) on KM, and the relationships between this variable and key business results. The conceptual model is tested on a sample of 225 Spanish companies. PLS-SEM approach was used to test the research model. In order to assess the moderating effects of organisational size, a multi-group approach was adopted using two subsamples with large companies and small and medium-sized enterprises (SMEs). The findings indicate that the use of PMM and partner involvement are key factors for KM to have a significant impact on the key business results (KBR). Moreover, the organisational size is determinant when analysing the effect of PMM and PM on K

OMEx-diesel blends as high reactivity fuel for ultra-low NOx and soot emissions in the dual-mode dual-fuel combustion strategy

[EN] Previous works demonstrated that the use of Oxymethylene ether (OMEx) in advanced combustion modes, as the dual-mode dual-fuel combustion, leads to a notable reduction of the lifecycle CO2 emissions while promoting lower NOx and soot emissions than those from conventional diesel combustion. Nonetheless, the low heating value of OMEx results in a fuel consumption increase. A possible solution to avoid this drawback is by blending OMEx with diesel fuel. This will help to introduce the OMEx in the market with minimum changes in the infrastructure. In this context, this work evaluates the impact of using OMEx-diesel blends in different mass percentages (50% and 70% of OMEx in diesel), compared to the reference net fuels (net diesel and OMEx) in a multi-cylinder compression ignition engine operating under dual-mode dual-fuel combustion at different engine loads (25%, 50%, 80% and 100%) and 1800 rpm. At each condition, an air mass sweep was performed to assess the limiting operating conditions with each fuel due to either excessive pressure gradients and soot production, or low combustion efficiency. The results suggested that the OMEx-diesel blends allow to reduce the soot emissions compared to net diesel for all the conditions tested. In addition, blends having an OMEx mass content greater than 70% allowed to fulfill the EUVI limits for NOx with ultra-low soot levels (.Soler A. Role of e-fuels in the European transport system. Literature review. Concawe, Brussels, January 2020.Benajes, J., García, A., Monsalve-Serrano, J., & Martínez-Boggio, S. (2019). Optimization of the parallel and mild hybrid vehicle platforms operating under conventional and advanced combustion modes. Energy Conversion and Management, 190, 73-90. doi:10.1016/j.enconman.2019.04.010Luján, J. M., García, A., Monsalve-Serrano, J., & Martínez-Boggio, S. (2019). Effectiveness of hybrid powertrains to reduce the fuel consumption and NOx emissions of a Euro 6d-temp diesel engine under real-life driving conditions. Energy Conversion and Management, 199, 111987. doi:10.1016/j.enconman.2019.111987Pastor, J. V., García, A., Micó, C., & Lewiski, F. (2020). An optical investigation of Fischer-Tropsch diesel and Oxymethylene dimethyl ether impact on combustion process for CI engines. Applied Energy, 260, 114238. doi:10.1016/j.apenergy.2019.114238Ershov, M., Potanin, D., Gueseva, A., Abdellatief, T. M. M., & Kapustin, V. (2020). Novel strategy to develop the technology of high-octane alternative fuel based on low-octane gasoline Fischer-Tropsch process. Fuel, 261, 116330. doi:10.1016/j.fuel.2019.116330Verhelst, S., Turner, J. W., Sileghem, L., & Vancoillie, J. (2019). Methanol as a fuel for internal combustion engines. Progress in Energy and Combustion Science, 70, 43-88. doi:10.1016/j.pecs.2018.10.001Deutz, S., Bongartz, D., Heuser, B., Kätelhön, A., Schulze Langenhorst, L., Omari, A., … Bardow, A. (2018). Cleaner production of cleaner fuels: wind-to-wheel – environmental assessment of CO2-based oxymethylene ether as a drop-in fuel. Energy & Environmental Science, 11(2), 331-343. doi:10.1039/c7ee01657cOmari A, Heuser B, Pischinger S. Potential of oxymethylenether-diesel blends for ultra-low emission engines, Fuel, 209, 2017, 232–237, ISSN 0016-2361, doi: 10.1016/j.fuel.2017.07.107.Burre, J., Bongartz, D., & Mitsos, A. (2019). Production of Oxymethylene Dimethyl Ethers from Hydrogen and Carbon Dioxide—Part II: Modeling and Analysis for OME3–5. Industrial & Engineering Chemistry Research, 58(14), 5567-5578. doi:10.1021/acs.iecr.8b05577Burre J, Bongartz D, Mitsos A. Production of oxymethylene dimethyl ethers from hydrogen and carbon dioxide—Part II: Modeling and analysis for OME3–5, Ind Eng Chem Res, March 2019, 58, 5567–5578, doi: 10.1021/acs.iecr.8b05577.García, A., Monsalve-Serrano, J., Villalta, D., Lago Sari, R., Gordillo Zavaleta, V., & Gaillard, P. (2019). Potential of e-Fischer Tropsch diesel and oxymethyl-ether (OMEx) as fuels for the dual-mode dual-fuel concept. Applied Energy, 253, 113622. doi:10.1016/j.apenergy.2019.113622Payri, R., De La Morena, J., Monsalve-Serrano, J., Pesce, F. C., & Vassallo, A. (2018). Impact of counter-bore nozzle on the combustion process and exhaust emissions for light-duty diesel engine application. International Journal of Engine Research, 20(1), 46-57. doi:10.1177/1468087418819250Di Sarli, V., Landi, G., Lisi, L., Saliva, A., & Di Benedetto, A. (2016). Catalytic diesel particulate filters with highly dispersed ceria: Effect of the soot-catalyst contact on the regeneration performance. Applied Catalysis B: Environmental, 197, 116-124. doi:10.1016/j.apcatb.2016.01.073Orihuela, M. P., Gómez-Martín, A., Miceli, P., Becerra, J. A., Chacartegui, R., & Fino, D. (2018). Experimental measurement of the filtration efficiency and pressure drop of wall-flow diesel particulate filters (DPF) made of biomorphic Silicon Carbide using laboratory generated particles. Applied Thermal Engineering, 131, 41-53. doi:10.1016/j.applthermaleng.2017.11.149Pachiannan T, Zhong W, Rajkumar S, He Z, Leng X, Wang Q. A literature review of fuel effects on performance and emission characteristics of low-temperature combustion strategies. Appl Energy, 251,2019,113380.Martins M, Fischer I, Gusberti F, Sari R et al., HCCI of wet ethanol on a dedicated cylinder of a diesel engine, SAE Technical Paper 2017-01-0733, 2017, doi: 10.4271/2017-01-0733.Reitz, R. D., & Duraisamy, G. (2015). Review of high efficiency and clean reactivity controlled compression ignition (RCCI) combustion in internal combustion engines. Progress in Energy and Combustion Science, 46, 12-71. doi:10.1016/j.pecs.2014.05.003Olmeda, P., García, A., Monsalve-Serrano, J., & Lago Sari, R. (2018). Experimental investigation on RCCI heat transfer in a light-duty diesel engine with different fuels: Comparison versus conventional diesel combustion. Applied Thermal Engineering, 144, 424-436. doi:10.1016/j.applthermaleng.2018.08.082Benajes, J., García, A., Monsalve-Serrano, J., & Lago Sari, R. (2018). Fuel consumption and engine-out emissions estimations of a light-duty engine running in dual-mode RCCI/CDC with different fuels and driving cycles. Energy, 157, 19-30. doi:10.1016/j.energy.2018.05.144Curran S, Hanson R, Wagner R. Reactivity controlled compression ignition combustion on a multi-cylinder light-duty diesel engine. Int J Engine Res 13 (3), 216–225.Kokjohn SL, Hanson RM, Splitter DA, Reitz RD. Fuel reactivity controlled compression ignition (RCCI): a pathway to controlled high-efficiency clean combustion, Int J Engine Res, 2011. 12, June 2011, 209–226.Benajes, J., Molina, S., García, A., & Monsalve-Serrano, J. (2015). Effects of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions in a heavy-duty diesel engine. Energy, 90, 1261-1271. doi:10.1016/j.energy.2015.06.088Benajes, J., Molina, S., García, A., & Monsalve-Serrano, J. (2015). Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels. Energy Conversion and Management, 99, 193-209. doi:10.1016/j.enconman.2015.04.046Benajes, J., García, A., Monsalve-Serrano, J., & Lago Sari, R. (2018). Experimental investigation on the efficiency of a diesel oxidation catalyst in a medium-duty multi-cylinder RCCI engine. Energy Conversion and Management, 176, 1-10. doi:10.1016/j.enconman.2018.09.016García, A., Piqueras, P., Monsalve-Serrano, J., & Lago Sari, R. (2018). Sizing a conventional diesel oxidation catalyst to be used for RCCI combustion under real driving conditions. Applied Thermal Engineering, 140, 62-72. doi:10.1016/j.applthermaleng.2018.05.043Benajes, J., García, A., Monsalve-Serrano, J., & Villalta, D. (2018). Exploring the limits of the reactivity controlled compression ignition combustion concept in a light-duty diesel engine and the influence of the direct-injected fuel properties. Energy Conversion and Management, 157, 277-287. doi:10.1016/j.enconman.2017.12.028Benajes, J., García, A., Monsalve-Serrano, J., Balloul, I., & Pradel, G. (2017). Evaluating the reactivity controlled compression ignition operating range limits in a high-compression ratio medium-duty diesel engine fueled with biodiesel and ethanol. International Journal of Engine Research, 18(1-2), 66-80. doi:10.1177/1468087416678500Molina, S., García, A., Monsalve-Serrano, J., & Estepa, D. (2018). Miller cycle for improved efficiency, load range and emissions in a heavy-duty engine running under reactivity controlled compression ignition combustion. Applied Thermal Engineering, 136, 161-168. doi:10.1016/j.applthermaleng.2018.02.106Pedrozo V, May W, Guan W, Zhao H. High efficiency ethanol-diesel dual-fuel combustion: a comparison against conventional diesel combustion from low to full engine load. Fuel, 230, 2018, 440–451, ISSN 0016-2361, doi: 10.1016/j.fuel.2018.05.034.Benajes, J., García, A., Monsalve-Serrano, J., & Boronat, V. (2017). Achieving clean and efficient engine operation up to full load by combining optimized RCCI and dual-fuel diesel-gasoline combustion strategies. Energy Conversion and Management, 136, 142-151. doi:10.1016/j.enconman.2017.01.010García, A., Monsalve-Serrano, J., Rückert Roso, V., & Santos Martins, M. E. (2017). Evaluating the emissions and performance of two dual-mode RCCI combustion strategies under the World Harmonized Vehicle Cycle (WHVC). Energy Conversion and Management, 149, 263-274. doi:10.1016/j.enconman.2017.07.034Benajes, J., García, A., Pastor, J. M., & Monsalve-Serrano, J. (2016). Effects of piston bowl geometry on Reactivity Controlled Compression Ignition heat transfer and combustion losses at different engine loads. Energy, 98, 64-77. doi:10.1016/j.energy.2016.01.014Luján, J. M., Dolz, V., Monsalve-Serrano, J., & Bernal Maldonado, M. A. (2019). High-pressure exhaust gas recirculation line condensation model of an internal combustion diesel engine operating at cold conditions. International Journal of Engine Research, 22(2), 407-416. doi:10.1177/1468087419868026AVL manufacturer manual. Smoke value measurement with the filter-papermethod. Application notes. June 2005 AT1007E, Rev. 02. Web:.Payri R, Gimeno J, Mata C, Viera A. Rate of injection measurements of a direct-acting piezoelectric injector for different operating temperatures. Energy Convers Manage, 154, 2017, 387-393, ISSN 0196-8904, doi: 10.1016/j.enconman.2017.11.029.Pedrozo, V. B., May, I., & Zhao, H. (2017). Exploring the mid-load potential of ethanol-diesel dual-fuel combustion with and without EGR. Applied Energy, 193, 263-275. doi:10.1016/j.apenergy.2017.02.04