Friction in wheel-rail contacts

In the autumn, railroad traffic is often interrupted due to the occurrence of slippery tracks. The Dutch main operator (NS) and the infrastructure manager (ProRail) struggle with repeated delays. The layer between wheel and rail causing this phenomenon has not yet been identified, but can be quantified by rheological properties determined by correlating the measured friction between wheel and rail and the developed friction model.\ud To this end, the research described in this thesis is twofold: theoretical; in which the wheel - rail contact is modelled in terms of contact and friction, and experimental; in which the friction between wheel and rail is measured to validate the developed model.\ud The contact model between wheel and rail is approximated to be elliptical, which is shown to be accurate for the described purpose. The low friction situation is assumed to be caused by an interfacial layer, which is acting like a lubricant. Combining these two assumptions, a mixed lubrication friction model is developed for the Hertzian elliptical contact situation in which the interfacial layer is acting as a lubricant governed by the Eyring model. The mixed lubrication friction model results in the so-called Stribeck curve and/or the traction curve, which both take frictional heating and starved conditions into consideration. In addition, the changes in attack angle are also taken into account and a general viscoelastic model is proposed for both interfacial and boundary layers.\ud For the experiments, two devices were developed to be mounted on a train and successfully used on the real track. One is a sliding sensor which measures the coefficient of friction between a curved shaped specimen pressed against and sliding along the rail, i.e. simple sliding conditions. A second device measures traction curves between a measuring wheel and the head (top) of the rail, i.e. rolling/sliding conditions, at velocities of up to 100 km/h.\ud Based on the results from the measuring campaign combined with the modelled wheel - rail friction model, conclusions were drawn and important recommendations made to both the Dutch train operator (NS) and the rail infra manager (ProRail) from theoretical and practical points of view

Design et développement d’un quadrirotor joueur de tennis de table avec des hélices inclinables

RÉSUMÉ Les bras manipulateurs joueurs de tennis de table les plus avancés sont chers et leur configuration requière beaucoup d’espace. On pourrait considérer l’utilisation de robots aériens pour exécuter cette tâche, mais la plupart des avions à décollage et atterrissage verticales (ADAV) ne sont pas suffisamment rapides pour reproduire des mouvements de frappes. L’objectif de la recherche présentée dans ce mémoire est de développer un nouveau type de robot aérien joueur de tennis de table. Un prototype de quadrirotor ayant des hélices inclinables est d’abord considéré pour permettre de suivre des trajectoires agressives. Le robot a besoin d’atteindre des vitesses de 3.5 m/s au point d’impact et de rester suffisamment léger pour être agile. Ensuite, pour obtenir de hautes performances sur ce requis, un contrôleur Itérative Linéaire Quadratique Régulateur (iLQR) qui suit des trajectoires ayant un snap minimum est implémenté. Le contrôle de la boucle interne est délégué à un microcontrôleur PX4 pour le tangage, le lacet et le roulis pour assurer une bonne robustesse et une haute fréquence. Cette approche est testée dans une simulation réaliste et ensuite le framework complet pour cette application est développer sur un ordinateur embarqué. Des résultats expérimentaux ont été obtenus avec des caméras de capture de mouvements donnant la position et le temps d’impact. Cette information est envoyée au quadrirotor par communication sans-fil et la trajectoire est exécutée immédiatement. Au meilleur de nos connaissances, il s’agit du premier robot aérien étant capable de retourner des balles de tennis de table lancées par un humain. Un taux de succès de 40% est obtenu sur les frappes avec le modèle réel du quadrirotor, significativement supérieur à ce qui était possible d’atteindre auparavant avec un quadrirotor.----------ABSTRACT State-of-art table tennis robot manipulators are expensive and their setup require a lot of space. One could consider using aerial robots for this task, but most vertical takeoff and landing (VTOL) vehicles are not fast enough to reproduce hitting motions. The objective of the research presented in this thesis is to develop a novel type of aerial robot tennis table player. A prototype of a quadrotor that uses tilting propellers is first considered to enable the possibility of aggressive trajectory tracking. The system needs to reach speeds up to 3.5 m/s at the position of impact and to remain light enough to be agile. Next, to obtain high performances for this requirement, an Iterative Quadratic Linear Controller (iLQR) method that follows minimum snap planned trajectories is implemented. Inner-loop control is delegated to a PX4 microcontroller for roll, pitch and yaw to ensure good robustness and high frequency. This approach is tested in a realistic simulation and then the complete software for this task is developed on an onboard computer. Experimental results have been conducted with a motion capture system to have the full state estimate of the system. The trajectory of the ball is also estimated by the motion capture system, giving the position and time of impact. This information is then sent to quadrotor wirelessly and the trajectory is executed immediately. To the best of our knowledge, this is the first aerial robot capable to return tennis table balls thrown by a human. Hitting rates of 40% are achieved with the real quadrotor, significantly better than what was possible before for a quadrotor

Hard iron distortion compensation for 3 axis magnetometer

This paper presents the way how the hard iron effect could be compensated and a way to implement it on a small power device such as a microcontroller. Because of the magnetized materials that can stay near a magnetometer sensor and because of the very small magnetic field of the Earth, before the use of the measured values from a magnetometer to determine the heading (angle with the N direction) of the sensor a compensation is needed

Technical Efficiency of the Subsurface Drainage on Agricultural Lands in the Moldova River Meadow

This study aims to investigate the technical efficiency of different subsurface drainage variants, in terms of the depth of the tile drains, spacing between the drain lines, type and thickness of the drain + filter complex, and the improvement procedures. Within the four variants, the discharge rate of the soil moisture excess was studied. In variants A and D, the spacing between drains is 20 m, and in the variants B and E, the spacing is 15 m. The depth of the tile drains is 0.8 m in variants D and E and 1.0 m in variants A and B. In variant A, tile drainage was combined with land shaping in the bedding system with top of ridges and furrows. Soil moisture was determined on checkpoints placed on drain cross section, at 2 m from drain lines, and of the middle of the drain spacing. In the version with land shaping, the drain lines located under the furrows favor the excess moisture removal. A similar technical efficiency was recorded in unimproved variant but with spacing between drains of 15 m. Best efficiency at removing excess water was registered in variant of the filtering material from ballast associated with flax strains

How to Improve Student Education in Cardiology? 13 Essential Answers Through Medical Simulation

DergiPark: 379021tmsjAims: Is there a difference, from a clinical point of view, between a first year resident and a 4th year one, in the branch of Cardiology? If so, do we need to diminish it? And more importantly, do we have the tools? In this study it is aimed to evaluate medical simulation and its applicability in cardiology as an education method contributing to make students and residents more experienced and sufficient. Methods: The descriptive, cross-sectional study based on a survey which was applied to the groups of students in Carol Davila’ University of Medicine and Pharmacy (146) and residents (33 out of which 18 in the first two years and 15 in the last 3 years) was conducted between November 2014 and January 2015. Responses regarding evaluation of medical simulation as an education method were analyzed by using descriptive statistics including frequencies and percentages.Results: The results showed that with the usage of medical simulation as an education method 128 (87.6 %) students would have felt more confident and learnt faster, while 113 (77.5%) students would have found studying more appealing. Furthermore 10 (68%) of residents in the 3rd, 4th, 5th year would have felt more experienced, if they actually encountered rare simulated pathologies; thus 16 (91%) of the residents in the 1st, 2nd year thought the risks would have decreased for patients.Conclusion: Medical Simulation remains a necessity as an education method to improve practical skills of both students and residents in branch of cardiolog

Povezanost polimorfizma rs1437396 gena CCDC88A s poremećajem zloporabe alkohola

Girdin is a protein involved in neuronal migration and hippocampal development. It is encoded by the coiled-coil domain-containing 88A (CCDC88A) gene, located on the short arm of chromosome 2 (2p). The CCDC88A gene is modulated by the intergenic single-nucleotide polymorphism (SNP) of the rs1437396, situated 9.5 kb downstream from its transcription stop site. As recent genome-wide research has associated the T allele of the SNP with increased risk of alcohol use disorder (AUD), we wanted to validate this finding in an independent cohort and to test further for an association with comorbid major depressive disorder (MDD). The study included 226 AUD patients (AUD group), 53 patients with comorbid MDD, and 391 controls selected randomly. The participants were genotyped for the rs1437396 polymorphism using the real-time polymerase chain reaction. The association between the rs1437396 polymorphism and increased risk of AUD and AUD+MDD was tested with logistic regression. Our results show significantly higher frequency of the T risk allele in the AUD group (p=0.027) and even higher in the AUD+MDD group (p=0.016). In conclusion, this is the first study that has validated the association between the rs1437396 polymorphism of the CCDC88A gene and AUD with or without MDD. Studies on larger samples of patients are needed to further investigate the mechanism of this association.Girdin je protein koji sudjeluje u neuronskoj migraciji i razvoju hipokampusa, a kodira ga gen 88A koji sadržava domenu sa smotanom zavojnicom (eng. coiled-coil domain-containing 88A gene, krat. CCDC88A) koja se nalazi na kraćem kraku kromosoma 2 (2p). Gen CCDC88A mijenja se s međugenskim jednonukleotidnim polimorfizmom (eng. single-nucleotide polymorphism, krat. SNP) na mjestu rs1437396, 9,5 kb nizvodno od svojega transkripcijskog završetka. Budući da je u nedavnom istraživanju na razini genoma zamijećena povezanost alela T ovoga polimorfizma s povećanim rizikom od poremećaja zloporabe alkohola (eng. alcohol use disorder), htjeli smo provjeriti tu povezanost u neovisnoj kohorti randomiziranih ispitanika i dodatno ispitati je li polimorfizam povezan i s popratnim povratnim depresivnim poremećajem (eng. major depressive disorder). Ispitivanje je obuhvatilo 226 bolesnika s poremećajem zloporabe alkohola, 51 bolesnika s popratnim povratnim depresivnim poremećajem i 391 kontrolnog ispitanika. Ispitanici su genotipizirani radi utvrđivanja onih koji imaju polimorfizam rs1437396 pomoću polimerazne lančane reakcije u stvarnom vremenu (eng. real-time polymerase chain reaction) te je logaritamskom regresijskom analizom utvrđena povezanost polimorfizma rs1437396 s rizikom od poremećaja zloporabe alkohola s popratnim povratnim depresivnim poremećajem ili bez njega. Naši podatci upućuju na značajno veću učestalost alela T u bolesnika s poremećajem zloporabe alkohola (p=0,027) te na još značajniju učestalost u bolesnika s obama poremećajima (p=0,016). Ovo je prvo istraživanje koje je potvrdilo povezanost između polimorfizma rs1437396 gena CCDC88A i poremećaja zloporabe alkohola s popratnim povratnim depresivnim poremećajem ili bez njega. Daljnja istraživanja mehanizama ove povezanosti potrebno je provesti na većim uzorcima