Tesis sobre el tema "Spectral Stabilization"
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Marras, Simone. "Variational multiscale stabilization of finite and spectral elements for dry and moist atmospheric problems". Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/112755.
Texto completoEn esta tesis los métodos de elementos finitos y espectrales (FEM - finite element method y SEM- spectral element method, respectivamente), aplicados a los problemas de simulaciones atmosféricas, se exploran a través del método de estabilización conocidocomo Variational Multiscale Stabilization (VMS). Tres razones fundamentales justifican este esfuerzo: (i) la necesidad de tener nuevos métodos de solución de las ecuaciones diferenciales a las derivadas parciales usando máquinas paralelas de gran escala –un entorno en expansión en muchos campos de la mecánica computacional, dentro de la cual la predicción numérica de la dinámica atmosférica (NWP-numerical weather prediction)representa una aplicación importante. Métodos del tipo basado en elementos(por ejemplo, FEM, SEM, Galerkin discontinuo) presentan grandes ventajas en el desarrollo de códigos paralelos; (ii) la flexibilidad intrínseca de tales métodos respecto a lageometría de la malla computacional hace que esos métodos sean los candidatos ideales para códigos atmosféricos con mallas adaptativas; y (iii) la difusión localizada que VMSintroduce representa una mejora en las soluciones de problemas con física compleja en los cuales la difusión artificial clásica no funcionaría. La aplicación de FEM o SEM con VMS a problemas de simulaciones atmosféricas es una estrategia innovadora en un campo de investigación abierto. En primera instancia, FEM y VMS vienen descritos y derivados para la solución de flujos estratificados a bajo número de Mach en el contexto de la dinámica atmosférica. La validez del método para simular flujos estratificados es verificada por medio de test estándar aceptado por la comunidad dentro del campo deNWP. Los test incluyen simulaciones de flujos térmicos con efectos de gravedad. Se demostrará que la estabilidad del método numérico se preserva dentro de los regímenesde interés y se discutirá una comparación numérica de los resultados frente a aquellos hallados en la literatura. En segunda instancia, la capacidad de VMS para estabilizarmétodos FEM en problemas de advección dominante (i.e. ecuaciones de Euler y ecuaciones de transporte) se implementa además en la solución a elementos espectrales de alto orden en problemas de advección-difusión. Hasta donde el autor sabe, esta es una contribución original a la literatura de métodos basados en elementos espectrales en problemas de transporte atmosférico. El problema de monotonicidad con métodos de alto orden es tratado mediante la combinación de SEM+VMS con una técnica de shockcapturing para un mejor tratamiento de las discontinuidades. Esta es una alternativa a los filtros que normalmente se aplican a SEM para eilminar las oscilaciones de Gibbsque caracterizan las soluciones de alto orden. Como último punto, se implementa un esquema de humedad acoplado con el núcleo en elementos finitos; este es un primer paso hacia simulaciones atmosféricas más realistas. La microfísica de Kessler se emplea para simular la formación de nubes y tormentas cálidas (warm clouds: no permite la formación de hielo). Esta última parte combina la solución de las ecuaciones de Eulerpara atmósferas estratificadas con la solución de un sistema de ecuaciones de transporte de tres estados de agua: vapor, nubes y lluvia. La calidad del método es verificadautilizando simulaciones de tormenta en dos y tres dimensiones.
Padgett, Miles John. "Techniques for ultra-high resolution saturation spectroscopy and laser stabilization in the 10#mu#m spectral region". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305843.
Texto completoMIRIGALDI, ALESSANDRO. "Power scaling of high power lasersystems". Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2966325.
Texto completoVenet, Caroline. "Développement d’un filtre spectral ultra résolu pour l’imagerie acousto-optique". Thesis, Paris Sciences et Lettres (ComUE), 2019. https://pastel.archives-ouvertes.fr/tel-02929318.
Texto completoOptical imaging for Medicine is limited by the spatial resolution loss due to light scattering in turbid media. A hybrid imaging method called ultrasound optical tomography can overcome this botteneck. Indeed the simultaneous use of light and ultrasound gives access to optical contrast in depth within scattering medium with the ultrasounds resolution. Several interferometric methods have been developed in order to detect an acousto-optic signal. However, none of them is adapted to in vivo imaging. For this reason a filter created with spectral hole burning is of special interest. This thesis presents the development of an ultra-narrow filter based on spectral hole burning in a thulium doped yttrium aluminum garnet crystal (Tm:YAG) under magnetic field. The first part of the manuscript describes the characterization of the filter in the imaging setup. Next, the actual imaging of a scattering gel is described. The following part presents the change of the main laser and its frequency stabilization for technological maturation. The last part of the manuscript details how the experiment have been compacted to be bring in a pharmacetical laboratory in order to launch in vivo imaging trials
Issa, Ibtissam. "Some results on the stabilization of elastic/viscoelastic transmission problems with Kelvin-Voigt or fractional Kelvin-Voigt damping". Thesis, Aix-Marseille, 2021. http://theses.univ-amu.fr.lama.univ-amu.fr/211207_ISSA_690cu840ucxbzr880kpmyt859oe_TH.pdf.
Texto completoThis thesis is devoted to study the stabilization of some locally coupled systems. First, we study the stability of a one-dimensional coupled wave equations with two interior non smooth viscous dampings where we establish exponential stability. Second, we study the stabilization of a locally coupled wave equations with only one internal viscoelastic damping of Kelvin-Voigt type. Both the damping and the coupling coefficients are non smooth. Using a spectrum approach, we prove the non-uniform stability of the system. Next, using a frequency domain approach, combined with a piecewise multiplier technique and the construction of a new multiplier satisfying some ordinary differential equations, we show that the energy of the smooth solution of the system decays polynomially. Third, we investigate the energy decay of hyperbolic systems of wave-wave, wave-Euler Bernoulli beam and beam-beam types. Indeed, the two equations are coupled through boundary connection with only one localized non smooth fractional Kelvin Voigt damping. We establish a polynomial energy decay rate. Finally, we study the stability of a multidimensional system of two wave equations coupled by velocities with only one localized non-smooth Kelvin-Voigt damping. By using a spectral analysis, we prove the non uniform stability of the system. Further, using a frequency domain approach combined with a multiplier technique, we establish some polynomial stability results by considering different geometric conditions on the coupling and the damping domains. In addition, in the absence of any geometric condition, we establish two polynomial energy decay rates of the system on a square domain
Golinelli, Anna. "Development of an original 10 kHz Ti : Sa regenerative cavity allowing 17 fs CEP stable 1 kHz TW-class amplification or wavelength tunability". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS018.
Texto completoThe last decade has seen a lot of progress in attosecond science or in strong field physics. Generating energetic, few-cycle laser pulses with stabilized Carrier-Envelope Phase at high repetition rate constitutes the first step to access the ultra-fast dynamics underlying the interaction of matter with intense, ultrashort coherent light source. The work of this thesis consists in globally improving the performances of a high repetition rate Ti:Sa laser system optimized for attosecond science. We present an original 10 kHz Ti:Sa CPA laser based on an newlydesigneddouble-crystal cavity for thermal lensing management. The amplifier delivers up to 5 W in narrow band mode (35 fs pulses), or 2.7 W in broad band mode, supporting 17 fs pulses after temporal compression. We demonstrate shot-to-shot CEP stabilization with a remaining noise of 210 mrad over three hours at the front-end output. In parallel to the short pulse duration operation mode, it is possible to use the front end in a wavelength tunability mode within a 80 nm range around 800 nm, with a resolution of 1 nm and 30 to 40 nm of bandwidth. We designed and demonstrated a complete water-cooled lens-less multipass amplifier using thermal lensing for modeadaptation boosting the pulse energy up to 10mJ at 1 kHz repetition rate (up to 10 W). The saturation regime of the amplifier ensures negligible variation (±3% peak to peak) of the output power for significant variation of the input power (±25% peak to peak) over the tunability range. The energy scalability of the front-end is demonstrated by coupling its output to cryogenically cooled amplifier, delivering 1 kHz, TW-class pulses at 17.5 fs and CEP stabilized with a residual noise of 350 mrad. A study of CEP noise sources in high dispersive module is also addressed, proposing a numerical approach based on a commercial ray-tracing software (Zemax) for predicting CEP fluctuation in grating based modules
Schmidt, Florian. "Laser-based Absorption Spectrometry : Development of NICE-OHMS Towards Ultra-sensitive Trace Species Detection". Doctoral thesis, Umeå : Department of Physics, Umeå Univ, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1414.
Texto completoSahni, Mohamed Omar. "Contribution à l'étude de techniques pour l'affinement spectral de lasers : application aux diodes à blocage de modes destinées aux télécommunications optiques cohérentes". Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S121/document.
Texto completoOptical frequency combs obtained from mode-locked laser diodes are potential candidates for WDM networks. However, their lines exhibit usually a broad optical linewidth ( 1-100 MHz). Thus their use is incompatible for high order modulation formats WDM based systems. This thesis investigates one solution to overcome this limitation. It consists of using a feed-forward heterodyne technique to reduce the frequency noise of each comb-line and consequently their optical linewidths. In a first approach, the technique is applied to a single-mode laser. This allowed us to validate its proper working and to identify the intrinsic limits of the experimental device set up. The latter analysis enabled us to reveal that the minimum achievable frequency noise level by our system, corresponds to a 50 Hz intrinsic optical linewidth spectrum and a 1,6 kHz optical linewidth based on 10 ms observation time. This technique is then applied to an actively mode-locked laser diode demonstrating, at our system output, a 21-line optical frequency comb with intrinsic optical linewidths reduced to below 7 kHz. It is worth noting that 9 among them, exhibit sub-kHz linewidths. For an observation time of 10 ms, all lines share the same optical linewidth, almost equal to 37 kHz. We thus show that the timing jitter impacts the technique performances. We also highlight the relevance of such coherence level for coherent optical communication. Lastly, we study a laser frequency pre-stabilization technique based on a locking to an unbalanced fiber interferometer. When applied to a single-mode laser, the technique showed a reduction of its technical frequency noise, thus leading to a clear improvement of its integrated optical linewidth from 224 kHz to 37 kHz for 3 ms observation time. This first result provides a good support towards the exploration of mode-locked laser diodes potential for metrological applications
Klein, Guillaume. "Stabilisation et asymptotique spectrale de l’équation des ondes amorties vectorielle". Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD050/document.
Texto completoIn this thesis we are considering the vectorial damped wave equation on a compact and smooth Riemannian manifold without boundary. The damping term is a smooth function from the manifold to the space of Hermitian matrices of size n. The solutions of this équation are thus vectorial. We start by computing the best exponential energy decay rate of the solutions in terms of the damping term. This allows us to deduce a sufficient and necessary condition for strong stabilization of the vectorial damped wave equation. We also show the appearance of a new phenomenon of high-frequency overdamping that did not exists in the scalar case. In the second half of the thesis we look at the asymptotic distribution of eigenfrequencies of the vectorial damped wave equation. Were show that, up to a null density subset, all the eigenfrequencies are in a strip parallel to the imaginary axis. The width of this strip is determined by the Lyapunov exponents of a dynamical system defined from the damping term
Leeman, Aaron 1974. "Stabilization of chromatic functors". Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10227.
Texto completoWe study the Bousfield localization functors known as [Special characters omitted], as described in [MahS]. In particular we would like to understand how they interact with suspension and how they stabilize. We prove that suitably connected [Special characters omitted]-acyclic spaces have suspensions which are built out of a particular type n space, which is an unstable analog of the fact that [Special characters omitted]-acyclic spectra are built out of a particular type n spectrum. This theorem follows Dror-Farjoun's proof in the case n = 1 with suitable alterations. We also show that [Special characters omitted] applied to a space stabilizes in a suitable way to [Special characters omitted] applied to the corresponding suspension spectrum.
Committee in charge: Hal Sadofsky, Chairperson, Mathematics; Arkady Berenstein, Member, Mathematics; Daniel Dugger, Member, Mathematics; Dev Sinha, Member, Mathematics; William Rossi, Outside Member, English
Lu, Jiang-hong. "An algorithm for intrinsic gain and offset stabilization of pulse height spectra". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/47311.
Texto completoBuffe, Rémi. "Inégalités de Carleman près du bord, d’une interface et pour des problèmes singuliers". Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2059/document.
Texto completoIn the first part of this thesis, we derive elliptic Carleman estimates for second-order operators with Ventcel boundary conditions. In the second part, we prove a proper estimate near multi-interfaces for elliptic operatorsof any order, under the classical sub-ellipticity condition of Hörmander and under a compatibility condition between the operators in the interior and at the multi-interface, called the covering condition. This condition is a generalization of the well-known Lopatinskii condition. Finally, in the third part, we focus on controllability properties of the heat equation, and stabilization properties of the wave equation for polygonal domains, with mixed boundary conditions
Chaudhry, Humayun Iqbal. "An evaluation of the performance and mechanistic action of the costabiliser N-phenyl-3-acetyl pyrrolidine-2,4-dione and its derivatives in poly(vinyl chloride)". Thesis, Manchester Metropolitan University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311051.
Texto completoBréant, Christian. "Développement de lasers infrarouges accordables de haute pureté spectrale : application à la spectroscopie hyperfine des molécules HF et SF(6)". Paris 13, 1985. http://www.theses.fr/1985PA132010.
Texto completoSaveleva, Viktoriia. "Investigation of the anodes of PEM water electrolyzers by operando synchrotron-based photoemission spectroscopy". Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF002/document.
Texto completoDevelopment of oxygen evolution reaction (OER) catalysts for proton exchange membrane water electrolysis technology depends on the understanding of the OER mechanism. This thesis is devoted to the application of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and near edge X-ray absorption fine structure (NEXAFS) techniques for operando investigation of the Ir, Ru - based anodes. For Ru-based systems, we observe the potential-induced irreversible transition of Ru (IV) from an anhydrous to a hydrated form, while the former is stabilized in the presence of Ir. Regarding single Ir-based anodes, the analysis of O K edge spectra reveals formation of electrophilic oxygen OI- as an OER intermediate. Higher stability of Ir catalysts supported on antimony-doped tin oxide (ATO) is related to their lower oxidation. This work demonstrates different OER mechanisms on Ir, Ru-based anodes involving anion and cation red-ox chemistry, correspondingly, regardless the oxide nature
Veselý, Jiří. "Elektronicky přeladitelný harmonický oscilátor". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218599.
Texto completoDavis, Kenneth Edward. "Three-Dimensional, Time-Dependent Spectral Element Simulations of a Thermocapillary Liquid Bridge with Magnetic Stabilization". Thesis, 2011. http://hdl.handle.net/1911/64417.
Texto completoChou, Hung-yu y 周虹宇. "Modeling and Stabilization on Emission Spectra of Light-Emitting Diodes". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/95578990987492573753.
Texto completo國立中央大學
光電科學研究所
100
Because of the rapid development in solid-state light technology, the luminescence efficiency of LEDs has been grown up from 50 lm/W in 2009 to 250 lm/W in 2008. LEDs have an extreme potential for future lighting. Besides, combining with the second optics component designed by the light distribution of LEDs, there are all kinds of LEDs products, such as car headlamp, light module for medical treatment, streetlight, and bike lamp etc. However, light emission properties of LEDs, for example light power and chromaticity, would be changed as the operation time goes by. The major factor caused this phenomenon is heat arisen from LEDs under electric current driving. Thus, how to effectively evaluate and manage the thermal effect to achieve an expected luminescence efficiency, is one of most important topics in LED lighting technology. In this dissertation, an accurate model for LEDs’ emission spectra dependent on electric driving current and junction temperature is developed. Based on this emission-spectra model, light-emission characteristics of LEDs could be clearly described under different electric driving conditions, such as light power, light chromaticity and color temperature. And, in this dissertation, an effective method for stabilization on emission spectra of LEDs is proposed. Under this controlled method, light-emission characteristics could be stabilized on a steady state, and are independent on the thermal effect. First we propose a model for precisely describing the emission-spectra distributions of various colored LED through an aid of the experimental data measured by an integrating sphere system. In addition, we developed a system for measuring the junction temperature of LEDs and made this junction temperature to be an influenced factor in this emission-spectra model. Thus, this emission-spectra model could be utilized to predict LED’s emission spectra under different electric driving current and junction temperature, and fit in with the practical situations. Furthermore, we develop a controlled method for stabilization LEDs’ emission spectra. This method is implemented by an active-controlled heat sink and a proper electric current. As results shown, this method could not only modulate, but also stabilize LEDs’ emission spectra. Thus, the light emission characteristics of LEDs could be modulated and stabilized under this method, including light power and light chromaticity of LEDs.
Papasakellariou, Aristides. "Stabilization and throughput of spread spectrum multiple access systems with multiple reception capability". Thesis, 1992. http://hdl.handle.net/1911/13622.
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