Expérience de Michelson et Morley

Résumé

L'expérience de Michelson et Morley est une expérience d'optique qui a tenté de démontrer l'existence de l'éther luminifère. Pour y parvenir, Albert Abraham Michelson et Edward Morley ont cherché à mettre en évidence la différence de vitesse de la lumière entre deux directions perpendiculaires et à deux périodes espacées de , et concluent que cette différence était inférieure à ce que le dispositif permettait de mesurer (l'effet attendu étant environ 4 fois supérieur à la précision du dispositif). En fait, il s'agit de toute une série d'expériences entre 1881 (Michelson seul) et 1887 (ensemble), date à laquelle le résultat est définitivement admis (bien que cette expérience soit régulièrement refaite à chaque fois qu'un progrès technique permet de gagner en précision, avec toujours le même résultat) que la vitesse de la lumière est constante. L'interprétation de ce résultat a conduit les physiciens à mettre en doute l'existence de l'éther (qui était supposé être le support matér

Source officielle

https://fr.wikipedia.org/wiki/Exp%C3%A9rience_de_Michelson_et_Morley

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Micro-tubular Solid Oxide Fuel Cells with Nickelate Cathode-support

Henning Lübbe

The shortage of natural resources, rising energy demands and global warming have created an urgent need for more efficient energy conversion devices and different energy resources to achieve a more sustainable and efficient economy. Solid Oxide Fuel Cells (SOFC) are one of the most promising devices for the direct conversion from chemical to electrical energy in conjunction with high system efficiencies. Micro-tubular SOFC have been investigated since roughly 15 years. In contrast to planar systems, which produce electricity in the kW to MW range and target utilisation in stationary applications such as CHP plants, micro-tubular SOFC systems can be envisaged for mobile application due to quick start-up/shutdown operation. While most micro-tubular cells are mechanically supported by the electrolyte or anode, only few researches have investigated cathode-supported cells due to challenging fabrication. In this work, the new cathode material neodymium nickelate (NNO), Nd1.95NiO4+δ, was used as mechanical support, which is a novelty of this work, for micro-tubular SOFC. Different fabrication routes were used to create small tubes of 2-6 mm diameter. These tubes were evaluated with respect to their gas-diffusion properties by a new, self-manufactured diffusion setup and a complementary permeation setup. In order to achieve an economical fabrication process, the low-cost dip-coating method was investigated for the deposition of thin films from wet-chemical suspensions to create entire SOFC single cells. As SOFCs require gas-tight electrolyte layers, cofiring of tubular substrates and thin films must be executed to allow sufficient shrinkage of the deposited electrolyte thin layers to full density. Various electrolyte and electrode powders were characterised in different solvents, dispersants and binders with respect to low-temperature sintering feasibility. The shrinkage of scandia-stabilised zirconia (ScSZ) powder was decreased to 18% to still deliver sufficient sintered density by optimisation of the green density (usually zirconia requires shrinkage of 25% and more for densification). The cofiring temperature depends on the densification behaviour of powders but also on reactivity between adjacent layers. The reactivity between gadolinia-doped ceria (GDC)-interlayers and different zirconia materials was tested and showed lower compatibility of yttria-stabilised zirconia (YSZ) with GDC than for ScSZ/GDC reaction couples, which has not been reported so far. The interface of NNO cathodes and GDC interlayers was analysed by reactivity mapping and quantitative phase analysis. The performance optimisation of NNO/GDC interfaces by exchange current density measurement of NNO-cathodes sintered at different temperatures on GDC pellets is a further contribution of this work. The reactivity and performance investigations provide clear guidelines for maximum allowable cosintering temperature. Some electrochemical single cell tests showed competitive area-specific resistances (ASR) of ca. 1 Ωcm2 but were limited unfortunately by the counterelectrode microstructure and current collection methods, which were not the focus of this work. Open-circuit voltages (OCV) were 0.6-1.1 V at 700 °C in dry hydrogen atmosphere for tubes prepared by extrusion but only 0.3 V for tubes prepared by slip-casting. The electrochemical performances were modest with only 0.035 W/cm2 power density at 700 °C for tubes prepared by extrusion due to the elevated resistances of the counterelectrode and current collection.

EPFL2012

Chargement

Why are classical theories often sufficient to describe the physics of our world even though everything around us is entirely composed of microscopic quantum systems? The boundary between these two fundamentally dissimilar theories remains an unsolved problem in modern physics. Position measurements of small objects allow us to probe the area where the classical approximation breaks down. In quantum mechanics, Heisenbergâs uncertainty principle dictates that any measurement of the position must be accompanied by measurement induced back-action---in this case manifested as an uncertainty in the momentum. In recent years, cavity optomechanics has become a powerful tool to perform precise position measurements and investigate their fundamental limitations. The utilization of optical micro-cavities greatly enhances the interaction between light and state-of-the-art nanomechanical oscillators. Therefore, quantum mechanical phenomena have been successfully observed in systems far beyond the microscopic world. In such a cavity optomechanical system, the fluctuations in the position of the oscillator are transduced onto the phase of the light, while fluctuations in the amplitude of the light disturb the momentum of the oscillator during the measurement. As a consequence, correlations are established between the amplitude and phase quadrature of the probe light. However, so far, observation of quantum effects has been limited exclusively to cryogenic experiments, and access to the quantum regime at room temperature has remained an elusive goal because the overwhelming amount of thermal motion masks the weak quantum effects. This thesis describes the engineering of a high-performance cavity optomechanical device and presents experimental results showing, for the first time, the broadband effects of quantum back-action at room temperature. The device strongly couples mechanical and optical modes of exceptionally high quality factors to provide a measurement sensitivity

\sim\!10^4

times below the requirement to resolve the zero-point fluctuations of the mechanical oscillator. The quantum back-action is then observed through the correlations created between the probe light and the motion of the nanomechanical oscillator. A so-called âvariational measurementâ, which detects the transmitted light in a homodyne detector tuned close to the amplitude quadrature, resolves the quantum noise due to these correlations at the level of 10% of the thermal noise over more than an octave of Fourier frequencies around mechanical resonance. Moreover, building on this result, an additional experiment demonstrates the ability to achieve quantum enhanced metrology. In this case, the generated quantum correlations are used to cancel quantum noise in the measurement record, which then leads to an improved relative signal-to-noise ratio in measurements of an external force. In conclusion, the successful observation of broadband quantum behavior on a macroscopic object at room temperature is an important milestone in the field of cavity optomechanics. Specifically, this result heralds the rise of optomechanical systems as a platform for quantum physics at room temperature and shows promise for generation of ponderomotive squeezing in room-temperature interferometers.

EPFL2017

Chargement

Improved pivot-slide model of the motion of a curling rock

Laurent De Schoulepnikoff

The pivot-slide model (Shegelski and Lozowski) successfully predicts the slide and curl distances of a curling rock. However, in this model, there is no dependence of the curl distance on the initial velocity, because the ratio between the pivot to sliding times is constant. A refined model is presented, in which the ratio of the pivot to sliding times depends on the stone velocity via two parameters. Confidence limits for these parameters are deduced from experimental data, which show that the pivot-slide ratio depends on the stone velocity. However, precise values of these parameters could not be obtained with this study, as more precise experiment data are needed. The refined model allows one to qualitatively explain two characteristics of the stone trajectory observed in a curling game, namely the bigger final curl with lower initial velocity and the lower curl with the effect of sweeping the ice.

CANADIAN SCIENCE PUBLISHING2019

Chargement

Micro-tubular Solid Oxide Fuel Cells with Nickelate Cathode-support

Henning Lübbe

EPFL2012

\sim\!10^4

EPFL2017