Reduced density matrices in molecular systems: Grand-canonical electron states

Grand-canonical like descriptions of many electron atomic and molecular open systems which are characterized by a non-integer number of electrons are presented. Their associated reduced density matrices (RDMs) are obtained by introducing the contracting mapping for this type of distributions. It is shown that there is loss of information when connecting RDMs of different order by partial contractions. The energy convexity property of these systems simplifies the description. Consequently, this formulation opens the possibility to a new look for chemical descriptors such as chemical potential and reactivity among others. Examples are presented to discuss the theoretical aspects of this work.Fil: Bochicchio, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Miranda Quintana, Ramón A.. Universidad de La Habana. Facultad de Química. Laboratorio de Química Computacional y Teórica; CubaFil: Rial, Diego Fernando. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Investigaciones Matematicas

Temperature, flow and eccentricity measurements in a journal bearing with a single axial groove at 90º to the load line

Parametric experiments have been conducted to analyse the influence of some supply conditions on the performance of a steadily loaded journal bearing. Temperature distribution on the internal surface, flowrate and bearing eccentricity were measured for different sets of operating conditions, at variable supply conditions. Quantitative information is provided which shows the effect of both shaft speed and applied load on maximum bush temperature and flowrate. It has been observed that flowrate was modestly affected by load and significantly affected by rotational speed, oil supply temperature and supply pressure. Maximum bush temperature was modestly affected by supply pressure, moderately affected by load and significantly affected by shaft speed. For low applied loads, the attitude angle was markedly affected by supply pressure. The experimental results also showed that for a small groove length there is a variation of bush temperature in axial direction in the groove region.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI Programme/BD/13922/9

Theoretical simulation of different 3D separator geometries for lithium-ion batteries

The battery separator is an essential component of batteries and affects their cycling performance. In this work, the effect of different 3D geometries of the battery separator on battery performance was studied keeping the same volume. It was observed that the different geometries affect the cycling performance, the best geometry being the perforated one that cycled up to 90 C. The cycling performance is affected by parameters such as the separator thickness and the electrolyte volume. Through the control of the battery separator geometry it is possible to obtain high performance lithium-ion batteries.Portuguese Foundation for Science and Technology (FCT): UID/FIS/04650/2019, PTDC/CTMENE/5387/2014, UID/CTM/50025/2013, PTDC/FIS-MAC/28157/2017, grant SFRH/BPD/112547/2015 (C.M.C.) and contract CEECIND/00833/2017 (R.G.), including FEDER funds through the COMPETE 2020 Programme and National Funds through FCT. Financial support from the Basque Government Industry Department under the ELKARTEK and HAZITEK programs is also acknowledged. F. Miranda was also supported by Portuguese funds through the CIDMA - Center for Research and Development in Mathematics and Applications, and the Portuguese Foundation for Science and Technology (“FCT - Fundação para a Ciência e a Tecnologia”), within project UID/MAT/04106/2013

The role of lubricant feed temperature on the performance of twin groove journal bearings : an experimental study

An experimental assessment of the influence of lubricant feed temperature (Tf) on the behaviour of twin groove hydrodynamic journal bearings has been undertaken. Several loads, shaft speeds and bearing geometries were tested under constant lubricant feed pressure (pf), while Tf took four different values between 29ºC and 58ºC. It was found that the increase of Tf has an effect in bearing performance which is analogous in many ways to the effect of the increase in eccentricity: increase in lubricant flow rate (especially in the low eccentricity range), in outlet temperature (Tout) and in maximum bush temperature (Tmax). Nevertheless, the latter increase was lower than the corresponding increase in Tf. Also, in the high eccentricity range the increase in flow rate due to the increase of Tf could be deceiving in the sense that the additional flow was supplied mainly to the inactive region of the bearing (the unloaded land of the bearing).Fundação para a Ciência e a Tecnologia (FCT

Thermohydrodynamic modelling of journal bearings under varying load angle and negative groove flow rate

The performance of hydrodynamic journal bearings is affected by the conditions under which the lubricant is fed to the bearing gap. Axial grooves are often used and, depending on their location relatively to the load line, they might substantially interfere with the hydrodynamic pressure generation and the thermal behaviour of the bearing. However, many of the existing tools for predicting bearing performance are not able to suitably predict bearing behaviour under varying load angle given the oversimplified way under which they treat lubricant feeding conditions. The present work proposes a detailed Thermohydrodynamic approach which realistically incorporates these conditions into the bearing analysis. Special care is put on the mass and energy-conserving models of the ruptured film region and on a detailed treatment of lubricant mixing within the vicinity of grooves. This includes the first full modelling of the effect of negative flow rate in a groove, a phenomenon originally described experimentally in detail by the authors in previous publications, and which happens for a broad range of load/groove angles. An extensive investigation on the influence of loading direction on the performance of twin groove journal bearings has been performed. This parameter is found to affect deeply all major performance parameters due to the interference of groove regions in the hydrodynamic pressure generation and in the flow rates at each groove.Fundação para a Ciência e a Tecnologia (FCT

Influence des conditions d’alimentation sur l’amélioration des performances et la réduction du frottement dans les paliers

The performance of hydrodynamic journal bearings is significantly affected by the conditions under which the lubricant is fed to the bearing. However, many conventional analyses are not prepared to suitably incorporate these parameters and their effect on bearing performance, due to the over-simplified way they treat them. A thermohydrodynamic analysis suitable for conveniently deal with lubricant feeding conditions is now presented. It couples the numerical solution of the generalized Reynolds equation, the energy equations within the lubricant film and the heat transfer within the bush body. Special attention has been given to the treatment of the phenomena taking place within the grooves and in their vicinity, as well as to the ruptured film region. The effect that lubricant feed pressure and temperature, groove length ratio, groove width ratio and groove number (single / twin) have on bearing performance has been analyzed for a broad range of conditions. The results were found to be in good agreement with experimental published results and the robustness of the model to suitably treat these phenomena has been confirmed. It was found that a careful tuning of the feeding conditions may indeed improve bearing performance.Les performances des paliers lisses hydrodynamiques sont significativement affectées par les conditions dans lesquelles le lubrifiant est introduit dans le palier. Cependant, de nombreuses analyses classiques ne sont pas prêtes à intégrer convenablement ces paramètres et leurs effets sur les performances des paliers, en raison de la façon trop simplifiée avec laquelle ils les traitent. Une analyse thermohydrodynamique appropriée pour traiter convenablement les conditions d'alimentation de lubrifiant est maintenant présenté. Elle intègre la solution numérique simultanée des équations de Reynolds généralisée, de l'énergie dans le film lubrifiant et de la de chaleur dans le coussinet. Une attention particulière a été portée pour le traitement des phénomènes se produisant dans les rainures et dans leur voisinage, ainsi que dans la région de rupture du film. L'influence de la pression et de la température d'alimentation en lubrifiant, de la longueur et largeur de la rainure et du nombre de rainures (simple ou double) sur les performances du palier a été analysée pour un large éventail de conditions. Les résultats numériques obtenus sont en bon accord avec ceux issus de la littérature expérimentale et la robustesse du modèle à traiter convenablement ces phénomènes a pu être confirmée. Il a été constaté qu'un réglage minutieux des conditions d'alimentation peut effectivement améliorer les performances.FCT - POCTI/EME/39202/2001 & Postdoctoral grant SFRH/BPD/89553/201

On the occurrence of negative groove flow rate in twin groove hydrodynamic journal bearings

This paper describes the phenomenon of negative flow rate (hot oil reflux) occurring in one of the grooves of twin axial groove hydrodynamic journal bearings. This rarely described phenomenon, which can occur under severe operating conditions, increases the risk of bearing seizure. Existing codes for predicting bearing behaviour do not seem to be suitably incorporating this phenomenon into the analysis. The present work reports some experimental observations of the phenomenon and the way it can be taken into account in theoretical modelling.FCT - POCTI/39202/EME/2001 & PhD grant SFRH/BD/22278/200

Espacio virtual inalámbrico de altas prestaciones para la educación en Ingeniería

Los espacios virtuales inalámbricos en los campus universitarios se desarrollaron rápidamente en los últimos tiempos. La implementación de un espacio virtual académico de conectividad portable/ móvil en base a una red integrada inalámbricapara la enseñanza de la ingeniería redunda en muchos beneficios. Esta red se puede proyectar con una política de funcionamiento y servicio que admita a sus usuarios desplazarse dentro del mismo, con intuitivas herramientas académicas y de gestión vinculados al ámbito universitario. En este trabajo se describe una propuesta basada en los estándares WiMAX/WiFi

La integración Wi-Fi/Celular, evolución y desafíos

La demanda de datos móviles ha disparado en los últimos años muchos avances en las comunicaciones inalámbricas. La red celular con sus sucesivas generaciones tiende indefectiblemente a un servicio de datos, las redes Wi-Fi enfocadas en los dispositivos denominados portátiles es exclusivamente de datos. Pero ninguna por si sola puede asegurar una cobertura inalámbrica de calidad en todos los ámbitos. La interacción de ambas en los dispositivos a mejorado la experiencia del usuario pero lejos está de ser óptima. La integración de estas redes con protocolos y sistemas enfocados en sacar lo mejor de ambas todo el tiempo es lo que se trata en este trabajo. El estado actual del arte y las proyecciones futuras se abordan dando una idea de presente y futuro de la integración