Topological analysis of a novel compact omnidirectional three-legged robot with parallel hip structures regarding locomotion capability and load distribution

In this study, a novel design for a compact, lightweight, agile, omnidirectional three-legged robot involving legs with four degrees of freedom, utilizing an spherical parallel mechanism with an additional non-redundant central support joint for the robot hip structure is proposed. The general design and conceptual ideas for the robot are presented, targeting a close match of the well-known SLIP-model. CAD models, 3d-printed prototypes, and proof-of-concept multi-body simulations are shown, investigating the feasibility to employ a geometrically dense spherical parallel manipulator with completely spherically shaped shell-type parts for the highly force-loaded application in the legged robot hip mechanism. Furthermore, in this study, an analytic expression is derived, yielding the calculation of stress forces acting inside the linkage structures, by directly constructing the manipulator hip Jacobian inside the force domain

Mechanical design and analysis of a novel three-legged, compact, lightweight, omnidirectional, serial–parallel robot with compliant agile legs

In this work, the concept and mechanical design of a novel compact, lightweight, omnidirectional three-legged robot, featuring a hybrid serial–parallel topology including leg compliance is proposed. The proposal focusses deeply on the design aspects of the mechanical realisation of the robot based on its 3D-CAD assembly, while also discussing the results of multi-body simulations, exploring the characteristic properties of the mechanical system, regarding the locomotion feasibility of the robot model. Finally, a real-world prototype depicting a single robot leg is presented, which was built by highly leaning into a composite design, combining complex 3D-printed parts with stiff aluminium and polycarbonate parts, allowing for a mechanically dense and slim construction. Eventually, experiments on the prototype leg are demonstrated, showing the mechanical model operating in the real world

Energy efficient parallel configuration based six degree of freedom machining bed

The process of material removal from a workpiece to obtain the desired shape is termed machining. Present-day material removal technologies have high spindle speeds and thus allow quick material removal. These high-speed spindles are highly exposed to vibrations and, as a result, the accuracy of the final workpiece’s dimensions is compromised. To overcome this problem, the motion of the tool is restricted, and multiple degrees of freedom are given through the motion of the workpiece in different axes. A machining bed configured as a parallel manipulator capable of giving six degrees of freedom (DOF) to the workpiece is proposed in this regard. However, the proposed six DOF machining bed should be energy efficient to avoid an increase in machining cost. The benefit of using the proposed configuration is a reduction in dimensional error and computational time which, as a result, reduces the energy utilization, vibrations, and machining time in practice. This paper presents kinematics, dynamics and energy efficiency models, and the development of the proposed configuration of the machining bed. The energy efficiency model is derived from the dynamics model. The models are verified in simulation and experimentally. To minimize error and computation time, a PID controller is also designed and tested in simulation as well as experimentally. The resulting energy efficiency is also analyzed. The results verify the efficacy of the proposed configuration of the machining bed, minimizing position error to 2% and reducing computation time by 27%, hence reducing the energy consumption and enhancing the energy efficiency by 60%

Les extrêmes de l'accrétion : comprendre l'accrétion super-Eddington et les processus de rétroaction dans les sources ultra-lumineuses en X

Les processus d'accrétion de matière permettent au trous noirs supermassifs (TNSMs; 10^6-10M⊙) au centre de la plupart des galaxies massives de convertir une partie de l'énergie potentielle gravitationnelle du gaz accrété sous forme de rayonnements et des vents/jets. L'étude de ce processus fondamental impliqué dans la croissance du trou noir (TN) central et sa rétroaction dans la galaxie est cruciale pour comprendre comment les TNs ont participé à la formation des structures à grande échelle de l'Univers. Observations de l'Univers primordial ont révélé que les TNSM avec des masses de 10^8-9M⊙ existaient déjà lorsque l'Univers n'avait que 5% de son âge actuel, suggérant que les TN ont dû croître extrêmement rapidement. Encore aujourd'hui, les mécanismes de croissance de ces trous noirs, notamment via l'accrétion super-Eddington, reste encore mal compris. S'il est impossible d'étudier en détail ces premiers TNSM avec l'instrumentation actuelle, il existe maintenant des preuves solides que la plupart des sources ultralumineuses en X (ULX), généralement trouvé dans les galaxies externes, sont des systèmes accrétant à des taux super-Eddington de manière stable. Telle une version réduite des TNSM, l'abondance de rayonnements et vents que ces sources produisent peuvent ioniser des nébuleuses de gaz s'étalant sur des centaines de parsecs, offrant une base observationnelle pour étudier la rétroaction et l'efficacité du régime Super-Eddington. Pourtant, la nature de l'accréteur dans la plupart d'entre elles reste inconnue, tandis que quelques unes montrent des pulsations en rayons X indiquant que l'accréteur est une étoile à neutrons (EN). De plus, les géométries des flots d'accrétion et sa dépendance avec la nature de l'accréteur sont encore mal contraintes. Cette thèse a pour ambition d'aider à mieux comprendre les propriétés de l'accrétion super-Eddington dans les ULXs et les phénomènes de rétroaction associés sur de multiples échelles spatiales au moyen d'études multi-longueur d'onde. Cette thèse est divisée en deux volets. Dans le premier, j'ai exploité les grandes quantités de données d'archive offertes par les principaux télescopes à rayons X (XMM-Newton, Chandra et NuSTAR) pour réaliser une étude détaillée des transitions spectrales d'un large échantillon d'ULXs, afin de tester les differents modèles d'émission. Pour la plupart des sources, j'ai montré que leurs transitions spectrales sont mieux décrites par des modèles invoquant une émission anisotrope induite par des vents autour de EN faiblement magnétisées (B < 10^12G) ou de TN accrétants. La richesse des données permet aussi d'examiner les différences/similitudes spectrales entre les ULX à ENs connues et celles dont l'accréteur est inconnu; entraînant la découverte d'un nouveau candidat de ce type. Ce travail est suivi d'une étude approfondie de deux ULX, Holmberg II X-1 & NGC 5204 X-1, pour laquelle j'ai exploité la cadence d'observation élevée du Swift-XRT pour révéler que ces deux sources suivent un cycle évolutif spectral récurrent. Les transitions spectrales et la variabilité associées au cycle sont discutées dans le cadre de l'accrétion super-Eddington, en invoquant des changements de taux d'accrétion et un degré variable d'obscuration par les vents super-Eddington. Le deuxième volet se concentre sur l'exploration des données d'archive du Multi-Unit Spectroscopic Explorer sur le Very Large Telescope en mettant l'accent sur la caractérisation des principales sources d'ionisation du gaz nébulaire en utilisant une série de diagnostics spectraux. Le résultat principal de cette partie est la découverte d'une bulle gonflée par des chocs s'étendant sur des centaines de parsecs autour de l'ULX NGC 1313 X-1. Je montre que la puissance mécanique estimée attribuée à l'éjection de vents par la source centrale est supérieure à la puissance radiative, suggérant que dans le régime super-Eddington, la rétroaction mécanique pourrait être plus importante que la rétroaction radiative.The supermassive black holes (SMBHs; 10^6-10M⊙) sitting at the centre of most massive galaxies act as enormous reservoirs of energy, accreting gas from the galaxy and efficiently converting part of the energy into radiation, outflows and jets. Studying this fundamental process involved in the growth of the central BHs and their feedback into their host galaxies is crucial to understand how BHs shaped the large-scale structures of the Universe as we observe them today. Surprisingly, the deepest infrared surveys have revealed that SMBHs with masses 10^8-9M⊙ were already present when the Universe was only 5% of its current age, suggesting that these BHs must have grown extremely fast, but the extreme accretion regime that would be required to allow these BHs to grow so fast is poorly understood. While studying these early SMBHs in detail is not feasible with current instrumentation, after two decades of studies, there is now firm evidence supporting that most of the Ultraluminous X-ray sources (ULXs) typically found in external galaxies are accreting binary systems undergoing sustained super-Eddington accretion. Much like a scaled-down version of a SMBH, the copious amounts of radiation and outflows these mighty sources produce can ionise large nebulae of gas extending hundreds of parsecs in size, offering an observational template to study the feedback and efficiency of the super-Eddington regime. Yet the nature of the accretor in most of them remains unknown, while a few show X-ray pulsations indicative of a neutron star (NS) accretor. Moreover, the accretion flow geometry allowing them to reach such extreme luminosities and its dependency with the nature of the accretor is still highly debated. This thesis presents a multi-wavelength study in an effort to shed light on the engines behind ULXs, the properties of their inflows and outflows as well the feedback signatures in their surroundings. Two main lines of investigation are presented. In the first one, I exploited the extensive archival data offered by the major X-ray telescopes (XMM-Newton, Chandra and NuSTAR) to present a comprehensive study of the long-term spectral transitions of a broad sample of high-quality data ULXs, including known pulsating NS-ULXs, in order to test which of the current models to explain their extreme luminosities fit the data best. The analysis suggest that for the most part, their spectral transitions are best described by models invoking anisotropic emission induced by super-Eddington winds, with accreting lowly magnetised (B < 10^12G) NSs or BHs as their engines. The wealth of data served also to examine the spectral differences/similarities between the known NS-ULXs and those for which the accretor is unknown, revealing a potential new NS-ULX. This work is followed by an in-depth study of two archetypal ULXs, Holmberg II X-1 and NGC 5204 X-1, where I exploited the high-observing cadence of Swift-XRT to reveal that these two sources follow a spectral recurrent evolutionary cycle. The spectral transitions and variability associated with the cycle is discussed in the framework of super-Eddington accretion, by invoking mass-accretion rate changes and varying degree of obscuration by the super-Eddington winds. The second part of this thesis focuses on exploring the archival data from the Multi-Unit Spectroscopic Explorer at the Very Large Telescope to study the feedback properties of super-Eddington winds at larger scales, with focus on characterising the main sources of ionisation of the nebular gas through state-of-the art spatially-resolved gas diagnostics. The main result of this work is the discovery of a shock-powered bubble nebula extending hundreds of parsecs around the ULX NGC 1313 X-1. The estimated mechanical power attributed to the outflow is in excess of the radiative power, suggesting that in the super-Eddington regime the mechanical feedback by outflows and jets may be more prevalent than the radiative feedback

ɤd→ dπ+π- 反応におけるNΛ共鳴の探索

Tohoku University中村哲課

Design and prototyping of a network-enabled low-cost low-power seismic sensor monitoring system

Esta tese explora recentes desenvolvimentos em tecnologias de informação, comunicações e sensores no campo da sismologia. A tese aborda o potencial das redes de monitorização sísmica de elevada densidade na melhoria da resolução da actividade sísmica observada e, consequentemente, na melhor compreensão dos processos físicos que estão na base da ocorrência de terramotos. A tese argumenta que a tecnologia de sistemas de microelectromecânica (MEMS), usada na produção de acelerómetros de pequena dimensão, tem aplicabilidade e elevado potencial no domínio da sismologia. Acelerómetros MEMS já facilitaram a instalação de redes sísmicas de elevada densidade com superior resolução espacial pela Universidade da Califórnia (Rede Sísmica Comunitária) e pela Universidade de Évora (Rede Sísmica de Sensores do Alentejo), esta última ainda em fase de instalação. Neste contexto, a tese descreve o trabalho conduzido no desenho e desenvolvimento de sistemas de sensores baseados em acelerómetros MEMS. Este trabalho inclui a conceptualização de componentes de arquitectura usados para a implementação de quatro protótipos. Adicionalmente, foram também desenvolvidos os componentes necessários para a operação e gestão da rede de sensores, que inclui servidores dedicados a operar software especificamente desenvolvido neste trabalho. A tese descreve também a instalação e avaliação de protótipos, usando como base de comparação uma estação sísmica de elevado desempenho, recorrendo inclusivamente à actividade sísmica resultante de dois eventos sísmicos. A tese conclui que a arquitectura conceptualizada para o sistema sensor e para a rede de sensores demonstrou ser eficaz. Adicionalmente, embora a tecnologia MEMS seja promissora, ainda exibe limitações que limitam a sua aplicabilidade no domínio da sismologia, especificamente na observação de eventos sísmicos moderados e fortes. Conclui-se também que a instalação de acelerómetros MEMS em conjunto com sismómetros pode trazer benefícios na observação de actividade sísmica. Espera-se também que futuras gerações de acelerómetros MEMS possam ter uma adoção generalizada na sismologia; ABSTRACT: This thesis exploits advances in information technologies, communications and sensor systems to the field of seismology. It addresses the potential for high-density networks for seismic monitoring aiming to improve the resolution of the recorded seismic activity and, consequently, to improve the understanding of the physical processes that cause earthquakes, as well as to gather more detailed seismic characterisation of studied regions. It argues that microelectromechanical systems (MEMS) technology, used to produce small size accelerometers, has a potential application in seismology. Indeed, MEMS accelerometers have enabled the deployment of high-density seismic networks capable of monitoring seismic activity with high spatial resolution, such as CalTech's Community Seismic Network (CSN) and University of Évora’s SSN-Alentejo, currently in the deployment phase. In this context, this thesis describes the work conducted to design and develop low-cost seismic sensor systems, based on low-cost MEMS accelerometers. This work includes the conceptualisation of the architectural components that were implemented in four prototypes. Moreover, server-side components, necessary to operate and manage the sensor network, as well as to provide visualisation tools for users, are also developed and presented. This work also describes the field deployment and evaluation of selected prototypes, using a high-performance seismic station as the reference sensor for comparison, based on generated signals and two recorded seismic events. It is concluded that the herein conceptualised architecture for the high-dense network and sensor prototypes has been demonstrated to be effective. Moreover, albeit promising, MEMS accelerometers still exhibit performance limitations constraining their application in seismology addressing moderate and strong motion. In addition, MEMS accelerometers characteristics complement seismometers, thus installing MEMS accelerometers with seismometers, may provide additional insights concerning seismic activity and seismology in general. It is also expected that next generation MEMS accelerometers will be capable to compete with traditional seismometers, becoming the de facto technology in seismology