Effect of size and oxidation state of size-controlled rhodium nanoparticles on the aqueous-phase hydrodechlorination of 4-chlorophenol

Unsupported size-controlled Rh nanoparticles of different size and oxidation state were tested as catalysts models in aqueous phase hydrodechlorination (303-318K, 1atm) using 4-chlorophenol (4-CP) as target compound. A chemical reduction method was employed for the synthesis of the nanoparticles using methanol and poly(N-vinyl-2-pyrrolidone) (PVP) as reducing and capping agent, respectively. The size of Rh nanoparticles was in a narrow range (1.9-4.9nm) whereas Rhn+/Rh0 ratio values were found within a wide range (0.56-3.89).High 4-CP conversion values (c.a. 100%) were achieved at low Rh concentration (2.45·10-3gL-1). Phenol, cyclohexanone, cyclohexanol and traces of cyclohexane were identified as reaction products. A wide range of activity values (1.7-29.4mmolg-1min-1) were obtained, being equivalent to the measured in a previous work with unsupported Pd nanoparticles, in spite of the fact that Rh supported catalysts have generally been reported as less active than Pd ones in liquid phase hydrodechlorination. As the size of Rh nanoparticles decreased the activity increased reaching a maximum at 2.8nm, lower size values leading to a significant decrease of activity. A remarkable dependence of activity on the Rhn+/Rh0 ratio was found, thus a higher activity corresponded to a higher relative amount of zero-valent Rh in the nanoparticles samples. Regression models were developed in order to address the significance of nanoparticles size and oxidation state for the prediction of selectivity to cyclohexanone and cyclohexanol at varying reaction times. A crossed effect of particle size and Rhn+/Rh0 ratio was identified as a significant factor influencing the selectivityWe greatly appreciate financial support from the Spanish MCYT (CTQ2009-09983 and CTQ2012-32821) and CAM (REMTAVARES S-2009/AMB-1588). J.A. Baeza thanks to the Spanish MICINN a research grant (BES-2010-030059

Dynamic model of a railway wheelset for corrugation problem analysis

[EN] In the present work a model of flexible shafts is adapted for modelling the railway wheelset. The dynamic properties of the solid are obtained from a solid finite element model of a real wheelset. The model adopts an Eulerian coordinate set for numerical efficiency. Results of the crossed-receptance and mobility functions are presented, where the excitation is the vertical wheel-rail contact force and the displacement (or velocity) is measured in the wheel-rail contact plane. These results let us know that the gyroscopic effect may contribute to define the wavelength-fixing mechanism in some corrugation problems, even if the train speed is low.This work was sponsored by Projects T79/2006 (Ministerio de Fomento - Metro de Madrid- CDM) and TRA2007-67167 (Ministerio de Educación y Ciencia - FEDER).Vila Tortosa, MP.; Rovira, A.; Fayos Sancho, J.; Baeza González, LM. (2009). Dynamic model of a railway wheelset for corrugation problem analysis. Noise & Vibration Worldwide. 40(11):10-18. https://doi.org/10.1260/095745609790251579S1018401

Effect of structural ordering of the carbon support on the behavior of Pd catalysts in aqueous-phase hydrodechlorination

Catalysts consisting of Pd supported on virgin and heat-treated carbon blacks (homemade and commercial), graphites (natural and synthetic) and commercial carbon nanofibers were prepared and tested in the aqueous phase hydrodechlorinaton (HDC) of 4-chlorophenol (4-CP) under near ambient conditions (30 °C, 1 atm) in order to explore the effect of the support on the catalytic behavior. The homemade graphitized supports were prepared from commercial carbon black (CB) and from a carbon black-like material (CBPE) obtained from pyrolysis of low-density polyethylene. All the catalysts prepared yielded complete 4-CP conversion, although a wide range of activity was observed (10.7–173.5 mmol gPd−1 min−1). The graphitized carbon black provided the most active catalysts, showing Pd nanoparticles around 3 nm in size and a well-balanced contribution of Pd species (Pdn+/Pd0 = 0.9). Substantial differences of activity were found between the graphitized and not graphitized supports, even for catalysts with similar Pd nanoparticle size. The higher activity of the catalysts with graphitized supports can be partly associated to a more balanced initial Pdn+ to Pd0 ratio. Moreover, higher selectivity to hydrogenation products (cyclohexanone) was also achieved with those catalysts due to a higher contribution of the Pd0 speciesThe authors greatly appreciate financial support from the Spanish MINECO (CTQ2012-32821

Study of the biomass accumulation from inoculation to clogging in a biofilter treating toluene at high loads

Peer ReviewedPostprint (author's final draft

Study of the Falling Friction Effect on Rolling Contact Parameters

[EN] The existence of a wheel rail friction coefficient that depends on the slip velocity has been associated in the literature with important railway problems like the curving squeal and certain corrugation problems in rails. Rolling contact models that take into account this effect were carried out through the so-called Exact Theories adopting an exact elastic model of the solids in contact, and Simplified Theories which assume simplified elastic models such as Winkler. The former ones, based on Kalker s Variational Theory, give rise to numerical problems; the latter ones need to adopt hypotheses that significantly deviate from actual conditions, leading to unrealistic solutions of the contact problem. In this paper, a methodology based on Kalker s Variational Theory is presented, in which a local slip velocity-dependent friction law is considered. A formulation to get steady-state conditions of rolling contact by means of regularisation of the Coulomb s law is proposed. The model allows establishing relationships in order to estimate the global properties (creepage velocities vs. total longitudinal forces) through local properties (local slip velocity vs. coefficient of friction) or vice versa. The proposed model shows a good agreement with experimental tests while solving the numerical problems previously mentioned.The authors acknowledge the financial contribution of the Spanish Ministry of Economy and Competitiveness through the Project TRA2013-45596-C2-1-R.Giner Navarro, J.; Baeza González, LM.; Vila Tortosa, MP.; Alonso Pazos, A. (2017). Study of the Falling Friction Effect on Rolling Contact Parameters. Tribology Letters. 65(1). https://doi.org/10.1007/s11249-016-0810-8S651Grassie, S.L., Elkins, J.A.: Rail corrugation on North American transit systems. Veh. Syst. Dyn. 28, 5–17 (1998)Hsu, S.S., Huang, Z., Iwnicki, S.D., Thompson, D.J., Jones, C.J.C., Xie, G., Allen, P.D.: Experimental and theoretical investigation of railway wheel squeal. Proc. Inst. Mech. Eng. F J. Rail Rapid Transit 221, 59–73 (2007)Kalker, J.J.: Three-Dimensional Elastic Bodies in Rolling Contact. Kluwer, Dordrecht (1990)Polach, O.: Influence of locomotive tractive effort on the forces between wheel and rail. Veh. Syst. Dyn. 35, 7–22 (2001)Giménez, J.G., Alonso, A., Gómez, E.: Introduction of a friction coefficient dependent on the slip in the FastSim algorithm. Veh. Syst. Dyn. 43, 233–244 (2005)Baeza, L., Vila, P., Roda, A., Fayos, J.: Prediction of corrugation in rails using a non-stationary wheel–rail contact model. Wear 265, 1156–1162 (2008)Vollebregt, E.A.H., Schuttelaars, H.M.: Quasi-static analysis of two-dimensional rolling contact with slip-velocity dependent friction. J. Sound Vib. 331, 2141–2155 (2012)Avlonitis, M., Kalaitzidou, K., Streator, J.: Investigation of friction statics and real contact area by means a modified OFC model. Tribol. Int. 69, 168–175 (2014)Berger, E.J., Mackin, T.J.: On the walking stick–slip problem. Tribol. Int. 75, 51–60 (2014)Alonso, A., Guiral, A., Baeza, B., Iwnicki, S.D.: Wheel–rail contact: experimental study of the creep forces–creepage relationships. Veh. Syst. Dyn. 52(S1), 469–487 (2014)Spiryagin, M., Polach, O., Cole, C.: Creep force modelling for rail traction vehicles based on the Fastsim algorithm. Veh. Syst. Dyn. 51, 1765–1783 (2013)Vollebregt, E.A.H.: Numerical modeling of measured railway creep versus creep-force curves with CONTACT. Wear 314, 87–95 (2014)Kalker, J.J.: On the Rolling Contact of Two Elastic Bodies in the Presence of Dry Friction. PhD Thesis, Technical University of Delft (Holland) (1967)Baeza, L., Fuenmayor, F.J., Carballeira, J., Roda, A.: Influence of the wheel–rail contact instationary process on contact parameters. J. Strain Anal. Eng. 42, 377–387 (2007)Le Rouzic, J., Le Bot, A., Perret-Liaudet, J., Guibert, M., Rusanov, A., Douminge, L., Bretagnol, F., Mazuyer, D.: Friction-induced vibration by Stribeck’s law: application to wiper blade squeal noise. Tribol. Lett. 49, 563–572 (2013)Rabinowicz, E.: The nature of the static and kinetic coefficients of friction. J. Appl. Phys. 22, 1373–1379 (1951)Carter, F.W.: On the action of locomotive driving wheel. Proc. R. Soc. Lon. Ser. A 112, 151–157 (1926)Kalker, J.J.: A fast algorithm for the simplified theory of rolling contact. Veh. Syst. Dyn. 11, 1–13 (1982

Harnessing Supervised Learning for Adaptive Beamforming in Multibeam Satellite Systems

In today's ever-connected world, the demand for fast and widespread connectivity is insatiable, making multibeam satellite systems an indispensable pillar of modern telecommunications infrastructure. However, the evolving communication landscape necessitates a high degree of adaptability. This adaptability is particularly crucial for beamforming, as it enables the adjustment of peak throughput and beamwidth to meet fluctuating traffic demands by varying the beamwidth, side lobe level (SLL), and effective isotropic radiated power (EIRP). This paper introduces an innovative approach rooted in supervised learning to efficiently derive the requisite beamforming matrix, aligning it with system requirements. Significantly reducing computation time, this method is uniquely tailored for real-time adaptation, enhancing the agility and responsiveness of satellite multibeam systems. Exploiting the power of supervised learning, this research enables multibeam satellites to respond quickly and intelligently to changing communication needs, ultimately ensuring uninterrupted and optimized connectivity in a dynamic world.Comment: under review for conferenc

Flexible Payload Configuration for Satellites using Machine Learning

Satellite communications, essential for modern connectivity, extend access to maritime, aeronautical, and remote areas where terrestrial networks are unfeasible. Current GEO systems distribute power and bandwidth uniformly across beams using multi-beam footprints with fractional frequency reuse. However, recent research reveals the limitations of this approach in heterogeneous traffic scenarios, leading to inefficiencies. To address this, this paper presents a machine learning (ML)-based approach to Radio Resource Management (RRM). We treat the RRM task as a regression ML problem, integrating RRM objectives and constraints into the loss function that the ML algorithm aims at minimizing. Moreover, we introduce a context-aware ML metric that evaluates the ML model's performance but also considers the impact of its resource allocation decisions on the overall performance of the communication system.Comment: in review for conferenc

Supervised Learning Based Real-Time Adaptive Beamforming On-board Multibeam Satellites

Satellite communications (SatCom) are crucial for global connectivity, especially in the era of emerging technologies like 6G and narrowing the digital divide. Traditional SatCom systems struggle with efficient resource management due to static multibeam configurations, hindering quality of service (QoS) amidst dynamic traffic demands. This paper introduces an innovative solution - real-time adaptive beamforming on multibeam satellites with software-defined payloads in geostationary orbit (GEO). Utilizing a Direct Radiating Array (DRA) with circular polarization in the 17.7 - 20.2 GHz band, the paper outlines DRA design and a supervised learning-based algorithm for on-board beamforming. This adaptive approach not only meets precise beam projection needs but also dynamically adjusts beamwidth, minimizes sidelobe levels (SLL), and optimizes effective isotropic radiated power (EIRP).Comment: conference pape

Updating models of finite elements by modal operational analysis and genetic algorithms. Application to architectural heritage built

The use of Operational Modal Analysis is establishing as an acceptable tool to estimate the dynamic properties of heritage buildings as a non‐destructive technique. Through its application, mechanical properties of structural elements, as stiffness or mass, can be obtained with great accuracy. The information obtained can be used to update finite element models, however this process is complicated due to presently it is made manually. This work wants to develop a technique which expects improve the effort and the time invert in this process. The genetic algorithms are going to be used to update tow finite element models of tow patrimonial buildings, the Pavilion of Charles V and the San Jeronimo Monastery both located in Seville, in which variables like elasticity module or boundary conditions are going to be updating in order to have a real behaviour model to carry out the structural assessment of the buildings