Análise dinâmica de colisão de comboios para projeto de segurança passiva

Trabalho final de mestrado para obtenção do grau Mestre em Engenharia MecânicaEste trabalho visa a modelação multicorpo da colisão de comboios com o objetivo de permitir efetuar simulações da colisão, de modo a observar os fenómenos de absorção de energia, de modo a permitir uma redução dos custos computacionais, mas também dos custos com testes reais. O modelo desenvolvido replica de forma bastante correta uma colisão, podendo servir para análise da colisão. O modelo desenvolvido tem por base um modelo real, sendo este modelo constituído por carruagens, onde uma das carruagens apresenta uma dada velocidade inicial enquanto as outras se encontram em repouso, e buffers, sendo estes últimos estruturas de absorção de energia, estas estruturas encontram-se acopladas às carruagens por molas não lineares. Uma vez que os resultados dependem da curva de rigidez das molas é relativamente simples alterar as características do modelo de modo a simular diferentes tipo de colisão a diferentes velocidades e com diferentes massas. Uma vez que se verifica que quando existe o impacto entre carruagens, não existe recuo do corpo que se encontra inicialmente em movimento, é necessário garantir que o mesmo se verifica nas simulações, esta situação apresentou um grande desafio de simulação, sendo que foram necessárias várias tentativas e modelos, de modo a conseguir replicar o melhor possível este fenómeno. Este projeto oferece uma ferramenta de análise da colisão de carruagens, sendo que a utilização do modelo desenvolvido pode ser útil no projeto e fabrico de carruagens, bem como em projetos de segurança passiva de passageiros.This paper aims the multibody modeling of railway collisions, with the purpose of allow collision simulations, in order to observe the energy absorption phenomena, in order to allow reducing the computing cost, and real test cost as well. The model was developed to replicate quite accurately a collision and can be used for collision analysis. The developed model was based on a real model, being this model was made by carriages, where one of them has an initial velocity while the others are at rest, the model also have buffers, wich are structures for energy absorption, these structures are coupled to the carriages by nonlinear springs. Since the results depend on the springs stiffness curve it is relatively simple to change the characteristics of the model in order to simulate different types of collision, at different velocities with different masses. Since it is found that when there is an impact between carriages there is no recoil of the body that was initially moving, it is necessary to ensure this is what happens in the simulations, this situation presented a big challenge, and several models and trials was made in order to replicate this phenomenon as best as possible. This project offers a different railway crash analysis tool, and the use of the developed model can be useful in the project and manufacture of rail carriages, as well as passive passenger safety projects.N/

The Casimir force and the quantum theory of lossy optical cavities

We present a new derivation of the Casimir force between two parallel plane mirrors at zero temperature. The two mirrors and the cavity they enclose are treated as quantum optical networks. They are in general lossy and characterized by frequency dependent reflection amplitudes. The additional fluctuations accompanying losses are deduced from expressions of the optical theorem. A general proof is given for the theorem relating the spectral density inside the cavity to the reflection amplitudes seen by the inner fields. This density determines the vacuum radiation pressure and, therefore, the Casimir force. The force is obtained as an integral over the real frequencies, including the contribution of evanescent waves besides that of ordinary waves, and, then, as an integral over imaginary frequencies. The demonstration relies only on general properties obeyed by real mirrors which also enforce general constraints for the variation of the Casimir force.Comment: 18 pages, 6 figures, minor amendment

Biology and technology in the surgical treatment of malignant bone tumours in children and adolescents, with a special note on the very young

Purpose: The main challenge in reconstruction after malignant bone tumour resection in young children remains how and when growth-plates can be preserved and which options remain if impossible.Methods: We describe different strategies to assure best possible long-term function for young children undergoing resection of malignant bone tumours.Results: Different resources are available to treat children with malignant bones tumours: a) preoperative planning simulates scenarios for tumour resection and limb reconstruction, facilitating decision-making for surgical and reconstructive techniques in individual patients; b) allograft reconstruction offers bone-stock preservation for future needs. Most allografts are intact at long-term follow-up, but limb-length inequalities and corrective/revision surgery are common in young patients; c) free vascularized fibula can be used as stand-alone reconstruction, vascularized augmentation of structural allograft or devitalized autograft. Longitudinal growth and joint remodelling potential can be preserved, if transferred with vascularized proximal physis; d) epiphysiolysis before resection with continuous physeal distraction provides safe resection margins and maintains growth-plate and epiphysis; e) 3D printing may facilitate joint salvage by reconstruction with patient-specific instruments. Very short stems can be created for fixation in (epi-)metaphysis, preserving native joints; f) growing endoprosthesis can provide for remaining growth after resection of epi-metaphyseal tumours. At ten-year follow-up, limb survival was 89%, but multiple surgeries are often required; g) rotationplasty and amputation should be considered if limb salvage is impossible and/or would result in decreased function and quality of life.Conclusion: Several biological and technological reconstruction options must be merged and used to yield best outcomes when treating young children with malignant bone tumours.Orthopaedics, Trauma Surgery and Rehabilitatio

A model independent spin analysis of fundamental particles using azimuthal asymmetries

Exploiting the azimuthal angle dependence of the density matrices we construct observables that directly measure the spin of a heavy unstable particle. A novelty of the approach is that the analysis of the azimuthal angle dependence in a frame other than the usual helicity frame offers an independent cross-check on the extraction of the spin. Moreover, in some instances when the transverse polarisation tensor of highest rank is vanishing, for an accidental or dynamical reason, the standard azimuthal asymmetries vanish and would lead to a measurement with a wrong spin assignment. In a frame such as the one we construct, the correct spin assignment would however still be possible. The method gives direct information about the spin of the particle under consideration and the same event sample can be used to identify the spins of each particle in a decay chain. A drawback of the method is that it is instrumental only when the momenta of the test particle can be reconstructed. However we hope that it might still be of use in situations with only partial reconstruction. We also derive the conditions on the production and decay mechanisms for the spins, and hence the polarisations, to be measured at a collider experiment. As an example for the use of the method we consider the simultaneous reconstruction, at the partonic level, of the spin of both the top and the $W$ in top pair production in $e^+ e^-$ in the semi-leptonic channel.Comment: 42 pages, 7 figures, 4 table

Complementarity of the CERN Large Hadron Collider and the e+e−e^+e^- International Linear Collider

The next-generation high-energy facilities, the CERN Large Hadron Collider (LHC) and the prospective $e^+e^-$ International Linear Collider (ILC), are expected to unravel new structures of matter and forces from the electroweak scale to the TeV scale. In this report we review the complementary role of LHC and ILC in drawing a comprehensive and high-precision picture of the mechanism breaking the electroweak symmetries and generating mass, and the unification of forces in the frame of supersymmetry.Comment: 14 pages, 17 figures, to be published in "Supersymmetry on the Eve of the LHC", a special volume of European Physical Journal C, Particles and Fields (EPJC) in memory of Julius Wes

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes