Énergie du point zéro | EPFL Graph Search

L'énergie du point zéro est la plus faible énergie possible qu'un système physique quantique puisse avoir ; cela correspond à son énergie quand il est dans son état fondamental, c'est-à-dire lorsque toute autre forme d'énergie a été retirée. Tous les systèmes mécaniques quantiques subissent des fluctuations même quand ils sont à leur état fondamental (auquel est associée une énergie du point zéro), une conséquence de leur nature ondulatoire. Le principe d'incertitude implique que chaque système physique possède un point zéro pour son énergie, supérieure au minimum de son puits de potentiel classique. Aux échelles macroscopiques, cette énergie est négligeable car les fluctuations s'annulent sur de grands volumes. Cette énergie possède cependant des effets physiques microscopiques comme l'effet Casimir, l'émission spontanée de photons par des atomes, la création de paires de particules/antiparticules, ou une agitation minimale des molécules. Ceci implique notamment que la températu

Development of a Photo-Fenton Catalyst Supported on Modified Polymer Films

Félicien Mazille

The work presented in this thesis is a part of the European project INNOWATECH. The global objective of this project was to provide effective technological solutions for the treatment of industrial wastewater, to propose new concepts in wastewater treatment with potential benefits for the protection of the environment. In particular photo-assisted Fenton oxidation was investigated. It is a promising technology to decontaminate industrial wastewater as it makes use of the natural energy that provides the sun, abundant chemicals (iron ions and hydrogen peroxide) and does not produce toxic waste. Apart from short detour about homogenous photo-Fenton reaction (chapter 2) where the influence of pollutant physico-chemical properties on reactivity is studied, this thesis focuses on photo-Fenton treatment using a new solid catalysis. The immobilization of iron oxide on a suitable support is a strategy proposed to overcome the practical limitation related to homogeneous photo-Fenton treatment (i.e. the limited operational pH range and the problems caused by the separation of catalyst from the effluent). The preparation and the surface characterization of new photo-Fenton catalysts based on iron oxide supported on modified polymer films is described in chapters 3 and 4. The photocatalytic activities of prepared materials were evaluated mainly toward organic pollutant degradation both at laboratory (chapter 3-5) and at pilot (chapter 6) scales. In detail, chapter 2 focuses on the effect of contaminant physico-chemical properties on the reactivity via photo-assisted Fenton catalysis. Several para-substituted phenols were used in order to cover a wide range of electronics effects. Many physico-chemical descriptors were correlated with the initial Fenton and photo-Fenton degradation rates (r0). Electronic descriptors such as calculated zero point energy (Ezero) and energy of the highest occupied orbital were found to be the most adequate to predict Fenton and photo-assisted Fenton reactivity. The preparation of iron oxide-coated polymer films is described in chapter 3. Polyvinyl fluoride (PVF) film surface was functionalized by different methods, either by Vacuum-UV radiation, radio-frequency plasma, photo-Fenton oxidation or TiO2 photocatalysis. These pre-treatments were performed to increase iron oxide adhesion to polymer surface. Afterward the functionalized polymers films were immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl3. The catalytic activities of resulting materials were compared during hydroquinone degradation in presence of H2O2 and under simulated solar light illumination. The most efficient and stable catalyst obtained was prepared by means of TiO2 photocatalytic functionalization of polymers followed by iron oxide coating (leading to so called Pf-TiO2-Fe oxide), therefore this preparation procedure was selected in chapters 4-6. Chapter 4 focuses on the study of the mechanisms involved during the preparation and use of Pf-TiO2-Fe oxide. In particular, the modifications induced by TiO2 photocatalysis on polymer surface such as oxygen group formation and deposition of TiO2 particles were characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and UV-visible spectrophotometry. The photocatalytic activity of Pf-TiO2-Fe oxide in presence of H2O2 and under simulated solar light radiation was evaluated toward HQ degradation. The occurrence of important synergistic effects between TiO2 and iron oxide was discussed. Finally, the effect of preparation parameters on photocatalytic activity of Pf-TiO2-Fe oxide/H2O2/light system was determined allowing the optimization of preparation procedure. Hence highly efficient photocatalysts for hydroquinone degradation and E. Coli inactivation were obtained. The degradation of hydroquinone and nalidixic acid (NA) mediated the system Pf-TiO2-Fe oxide/H2O2/light was examined (chapter 5). The contribution of homogeneous photo-Fenton oxidation in the degradation process was determined and the mechanisms involved in iron leaching are discussed. Besides, the effect of operational parameters on degradation rates was assessed. The rates are independent on initial pH and NaCl presence but were enhanced by increasing temperature. Long-term stability of Pf-TiO2-Fe oxide was evaluated by repetitive nalidixic acid degradation runs. The adaptation of Pf-TiO2-Fe oxide to pilot scale in a compound parabolic collector (CPC) solar photoreactor is described in chapter 6: solar photocatalytic degradation of phenol, nalidixic acid, mixture of pesticides, and another of emerging contaminants, in water was investigated. The influences of operational pH and pollutant structure on the degradation rates were evaluated. It was found that compounds with chelating moieties (or carboxylic acids) were the most quickly removed by Pf-TiO2-Fe oxide/H2O2/light and allowed the photo-Fenton catalyst to be efficient at higher pH values.

EPFL2010

Development and validation of a double focalizing magnetic spectrometer for beta spectrum measurements

François Bochud, Guido Haefeli

In the framework of the EMPIR project MetroBeta, the development and optimization of a double focalizing magnetic spectrometer have been realized in order to measure the beta spectra shape. The acquisition is designed to perform, after focalization by the magnetic field, an energy selection using a window on the deposited energy in the Si detector. The energy calibration is performed using conversion electrons from Cd-109, Cs-137, Ba-133 and Bi-207 and the measured energy resolution is 1.3% at 1 MeV. The efficiency is measured experimentally using a Tl-204 source and is used to reconstruct the spectrum shape for beta emitters with end-point energy up to 750 keV. Two beta emitters with allowed transitions, Cs-134 and Co-60, are used to validate the measurement and the reconstruction method. Finally the measurement of the beta shape of Cl-36, a non-unique 2nd forbidden transition is presented.

ELSEVIER2019

Quantum optomechanics at room temperature

Hendrik Schütz

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