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Wang, Peng. "IMPEDANCE-TO-SCATTERING MATRIX METHOD FOR LARGE SILENCER ANALYSIS." UKnowledge, 2017. https://uknowledge.uky.edu/me_etds/102.
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Large silencers used in the power generation industry usually have a very large cross section at the inlet and outlet. Higher-order modes will populate the inlet and outlet even at very low frequencies. Although the silencer itself is often modeled by a three-dimensional analysis tool such as the boundary element method (BEM) or finite element method (FEM), a direct computation of the transmission loss (TL) from the BEM or FEM model can be challenging without incorporating certain forms of modal expansion.
A so-called “impedance-to-scattering matrix method” is proposed to extract the modes at the inlet and outlet from the BEM impedance matrix based on the point collocation method. The BEM impedance matrix relates the sound pressures at the inlet and outlet to the corresponding particle velocities, while the scattering matrix relates the modes at the inlet and outlet. Normally there are more boundary elements than the total number of modes at the inlet and outlet, and a least-squares procedure is used to condense the element-based impedance matrix to the mode-based scattering matrix. The TL computation will follow if a certain form of the incident wave is assumed and the outlet is non-reflective. Several commonly used inlet/outlet configurations are considered in this dissertation, which include axisymmetric, non-axisymmetric circular, and rectangular inlet/outlet shapes. In addition to the single inlet and outlet silencers, large multi-inlet and multi-outlet silencers are also investigated.
Besides the collocation-based impedance-to-scattering matrix method, an integral-based impedance-to-scattering matrix method based on the reciprocal identity is also proposed for large silencer analysis. Although it may be more time-consuming to perform the additional numerical integration, an integral-based method is free of any uncertainties associated with collocation points. The computational efficiency, accuracy and stability are compared between two proposed methods.
One bonus effect of producing the scattering matrix is that it can also be used to combine subsystems in series connection. The Redheffer’s star product is introduced to combine scattering matrices of subsystems.
In the design stage, rapid assessment of the silencer performance is always preferred. However, the existing analytical approaches are only suitable for simple dissipative silencers such as straight lined ducts. A two-dimensional first-mode semi-analytical solution is developed to quickly evaluate the performance of tuned dissipative silencers below the cut-off frequency. The semi-analytical solution can also serve as a validation tool for the BEM.
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Harvey, A. "Electron re-scattering from aligned molecules using the R-matrix method." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1302063/.
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Electron re-scattering in a strong laser field provides an important probe of molecular structure and processes, and can allow for time resolved study of nuclear and electronic dynamics at sub-femtosecond timescales with Angstrom spatial resolution. In such experiments a molecule is ionised in a strong, few cycle, laser field. The changes in sign of the laser field during the cycle can cause the electron to re-collide with its parent molecular ion. Under these circumstances the electron can either recombine leading to high harmonic generation, or it can be re-scattered. This scattering can be thought of as electron self-diffraction and the process has the potential to act as a detailed probe of the target molecule. It is usual for such experiments to be performed on aligned molecules, as the dynamics of the ionisation and re-collision changes with alignment. This introduces extra physics compared to the standard gas-phase, electron-molecule scattering problem. It is important for the understanding and analysis of such experiments to have a physically sound theoretical model of re-scattering which is capable of treating quantum mechanically the complicated scattering dynamics of an electron-molecular ion collision. This thesis explores the use of sophisticated ab initio quantum mechanical techniques to model this part of the re-scattering process. Previous theoretical models of the re-collision problem have thus greatly simplified this aspect of the problem. An introduction to attosecond physics, and a review of the relevant scattering and R-matrix theory is given. A simple preliminary model not including molecular alignment is described for molecules of experimental interest. Then the formalism for scattering from aligned linear molecules is presented. For linear molecules consisting of more than two atoms we use the polyatomic R-matrix codes. However the polyatomic version of the code only uses Abelian point groups which means that calculations on symmetric or asymmetric linear molecules are performed using the D2h or C2v point groups respectively. A further step is required, involving the reconstruction of T-matrices into the linear molecule symmetry groups D1h or C1v. The formalism for this is also presented. Finally differential and integral cross sections are presented for re-scattering for H2 and CO2.
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Weiss, Thomas. "Advanced numerical and semi-analytical scattering matrix calculations for modern nano-optics." Thesis, Clermont-Ferrand 2, 2011. http://www.theses.fr/2011CLF22150.
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Les propriétés optiques des nanomatériaux, tels que les cristaux photoniques ou les métamatériaux, ont reçu beaucoup d’attention dans les dernières années [1–9]. La dérivation numérique de ces propriétés se révèle pourtant très compliquée, en particulier dans le cas des structures métallo-diélectriques, qui comportent des résonances plasmoniques. C’est pourquoi des méthodes numériques avancées et des modèles semi-analytiques sont nécessaires. Dans cette thèse, nous montrerons que le formalisme de la matrice de diffraction peut satisfaire ces deux aspects. La méthode de la matrice de diffraction est un concept très général en physique. Dans le cas des structures périodiques, on peut dériver la matrice de diffraction à l’aide de la méthode modale de Fourier [10]. Pour la description exacte des géométries planes, nous avons développé la méthode des coordonnées adaptées [11], qui nous donne un nouveau système de coordonnées, dans lequel les interfaces des matériaux sont des surfaces de coordonnées constantes. En combinaison avec la méthode de la résolution spatiale adaptative, la méthode des coordonnées adaptées permet d’améliorer considérablement la convergence de la méthode modale de Fourier, de telle sorte qu’on peut calculer des structures métalliques compliquées très efficacement. Si on utilise la matrice de diffraction, il est non seulement possible de dériver les propriétés optiques en illumination de champ lointain, comme la transmission, la réflexion, l’absorption, et le champ proche, mais aussi de décrire l’émission d’un objet à l’intérieur d’une structure et d’obtenir les résonances optiques d’un sytème. Dans cette thèse, nous présenterons une méthode efficace pour la dérivation des résonances optiques tridimensionnelles, utilisant directement la matrice de diffraction [14]. Si on connaît les résonances d’un système isolé, il est aussi possible d’obtenir une approximation des résonances dans le cas d’un système combiné à l’aide de notre méthode du couplage des résonances [15, 16]. Cette méthode permet de décrire le régime de couplage des champs lointain et proche, y compris le couplage fort avec les résonances Fabry-Perot, pour des systèmes qui se composent d’un empilement de deux structures planes et périodiques. Pour cette raison, on peut étudier efficacement le couplage de ces systèmes. Cette thèse est écrite de manière à donner une idée d’ensemble du formalisme de la matrice de diffraction et de la méthode modale de Fourier. En outre, nous décrivons notre généralisation de ces méthodes et nous montrons la validité de nos approches pour différents exemplesThe optical properties of nanostructures such as photonic crystals and metamaterials have drawn a lot of attention in recent years [1–9]. The numerical derivation of these properties, however, turned out to be quite complicated, especially in the case of metallo-dielectric structures with plasmonic resonances. Hence, advanced numerical methods as well as semi-analytical models are required. In this work, we will show that the scattering matrix formalism can provide both. The scattering matrix approach is a very general concept in physics. In the case of periodic grating structures, the scattering matrix can be derived by the Fourier modal method [10]. For an accurate description of non-trivial planar geometries, we have extended the Fourier modal method by the concept of matched coordinates [11], in which we introduce a new coordinate system that contains the material interfaces as surfaces of constant coordinates. In combination with adaptive spatial resolution [12,13], we can achieve a tremendously improved convergence behavior which allows us to calculate complex metallic shapes efficiently. Using the scattering matrix, it is not only possible to obtain the optical properties for far field incidence, such as transmission, reflection, absorption, and near field distributions, but also to solve the emission from objects inside a structure and to calculate the optical resonances of a system. In this work, we provide an efficient method for the ab initio derivation of three-dimensional optical resonances from the scattering matrix [14]. Knowing the resonances in a single system, it is in addition possible to obtain approximated resonance positions for stacked systems using our method of the resonant mode coupling [15, 16]. The method allows describing both near field and far field regime for stacked two-layer systems, including the strong coupling to Fabry-Perot resonances. Thus, we can study the mutual coupling in such systems efficiently. The work will provide the reader with a basic understanding of the scattering matrix formalism and the Fourier modal method. Furthermore, we will describe in detail our extensions to these methods and show their validity for several examples
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Suryadharma, Radius Nagassa Setyo [Verfasser], and C. [Akademischer Betreuer] Rockstuhl. "T-matrix method for the analysis of electromagnetic scattering / Radius Nagassa Setyo Suryadharma ; Betreuer: C. Rockstuhl." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1212512499/34.
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Zhai, Pengwang. "A fourth-order symplectic finite-difference time-domain (FDTD) method for light scattering and a 3D Monte Carlo code for radiative transfer in scattering systems." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1839.
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Alexander, Jennifer Mary. "Optical properties of mineral dust aerosol including analysis of particle size, composition, and shape effects, and the impact of physical and chemical processing." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1819.
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Atmospheric mineral dust has a large impact on the earth’s radiation balance and climate. The radiative effects of mineral dust depend on factors including, particle size, shape, and composition which can all be extremely complex. Mineral dust particles are typically irregular in shape and can include sharp edges, voids, and fine scale surface roughness. Particle shape can also depend on the type of mineral and can vary as a function of particle size. In addition, atmospheric mineral dust is a complex mixture of different minerals as well as other, possibly organic, components that have been mixed in while these particles are suspended in the atmosphere. Aerosol optical properties are investigated in this work, including studies of the effect of particle size, shape, and composition on the infrared (IR) extinction and visible scattering properties in order to achieve more accurate modeling methods.
Studies of particle shape effects on dust optical properties for single component mineral samples of silicate clay and diatomaceous earth are carried out here first. Experimental measurements are modeled using T-matrix theory in a uniform spheroid approximation. Previous efforts to simulate the measured optical properties of silicate clay, using models that assumed particle shape was independent of particle size, have achieved only limited success. However, a model which accounts for a correlation between particle size and shape for the silicate clays offers a large improvement over earlier modeling approaches. Diatomaceous earth is also studied as an example of a single component mineral dust aerosol with extreme particle shapes. A particle shape distribution, determined by fitting the experimental IR extinction data, used as a basis for modeling the visible light scattering properties. While the visible simulations show only modestly good agreement with the scattering data, the fits are generally better than those obtained using more commonly invoked particle shape distributions.
The next goal of this work is to investigate if modeling methods developed in the studies of single mineral components can be generalized to predict the optical properties of more authentic aerosol samples which are complex mixtures of different minerals. Samples of Saharan sand, Iowa loess, and Arizona road dust are used here as test cases. T-matrix based simulations of the authentic samples, using measured particle size distributions, empirical mineralogies, and a priori particle shape models for each mineral component are directly compared with the measured IR extinction spectra and visible scattering profiles. This modeling approach offers a significant improvement over more commonly applied models that ignore variations in particle shape with size or mineralogy and include only a moderate range of shape parameters.
Mineral dust samples processed with organic acids and humic material are also studied in order to explore how the optical properties of dust can change after being aged in the atmosphere. Processed samples include quartz mixed with humic material, and calcite reacted with acetic and oxalic acid. Clear differences in the light scattering properties are observed for all three processed mineral dust samples when compared to the unprocessed mineral dust or organic salt products. These interactions result in both internal and external mixtures depending on the sample. In addition, the presence of these organic materials can alter the mineral dust particle shape. Overall, however, these results demonstrate the need to account for the effects of atmospheric aging of mineral dust on aerosol optical properties.
Particle shape can also affect the aerodynamic properties of mineral dust aerosol. In order to account for these effects, the dynamic shape factor is used to give a measure of particle asphericity. Dynamic shape factors of quartz are measured by mass and mobility selecting particles and measuring their vacuum aerodynamic diameter. From this, dynamic shape factors in both the transition and vacuum regime can be derived. The measured dynamic shape factors of quartz agree quite well with the spheroidal shape distributions derived through studies of the optical properties.
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Tricoli, Ugo [Verfasser], and Klaus [Akademischer Betreuer] Pfeilsticker. "Electromagnetic scattering with the GDT-matrix method: an application to irregular ice particles in cirrus / Ugo Tricoli ; Betreuer: Klaus Pfeilsticker." Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180501780/34.
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Azizoglu, Suha Alp. "Time Domain Scattering From Single And Multiple Objects." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609413/index.pdf.
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The importance of the T-matrix method is well-known when frequency domain scattering problems are of interest. With the relatively recent and wide-spread interest in time domain scattering problems, similar applications of the T-matrix method are expected to be useful in the time domain. In this thesis, the time domain spherical scalar wave functions are introduced, translational addition theorems for the time domain spherical scalar wave functions necessary for the solution of multiple scattering problems are given, and the formulation of time domain scattering of scalar waves by two spheres and by two scatterers of arbitrary shape is presented. The whole analysis is performed in the time domain requiring no inverse Fourier integrals to be evaluated. Scattering examples are studied in order to check the numerical accuracy, and demonstrate the utility of the expressions.
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Li, Ming. "The study of electromagnetic wave propagation in photonic crystals via planewave based transfer (scattering) matrix method with active gain material applications." [Ames, Iowa : Iowa State University], 2007.
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Chobeau, Pierre. "Modeling of sound propagation in forests using the transmission line matrix method : study of multiple scattering and ground effects related to forests." Thesis, Le Mans, 2014. http://www.theses.fr/2014LEMA1016/document.
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Les trois principaux phénomènes acoustiques propres au milieu forestier nécessitant d'être pris en compte sont (1) l'absorption due à la présence d'un sol multi-couche, (2) la diffusion multiple due à la présence d'obstacles tels que les troncs, (3) les effets micro-météorologiques rattachés aux variations des gradients de vitesse de vent et de température. Parmi les méthodes numériques de référence, la méthode des lignes de transmission (TLM), semble particulièrement adaptée pour la modélisation de la propagation acoustique en présence de forêt, à condition de procéder à de nouveaux développements. La première nécessité pour l'adaptation de la méthode TLM aux simulations acoustiques sur de grandes distances est la définition de couches absorbantes, permettant de tronquer efficacement le domaine d'étude, sans introduire de réflexions parasites. La formulation ainsi développée dans le cadre de la thèse est rigoureusement équivalente à l'équation de propagation des ondes amorties, et se traduit dans la méthode TLM par l'introduction et l'optimisation d'un terme de dissipation. L'étape suivante a consisté à vérifier la capacité de la méthode TLM à modéliser les phénomènes de diffusion par des cylindres. L’une des originalités introduites dans cette thèse réside dans le placement des éléments diffuseurs, à partir de lois de distribution aléatoire et de Gibbs, permettant ainsi de définir des répartitions proches de celles rencontrées en forêt. À titre d'application de la méthode développée dans le cadre de la thèse, une étude paramétrique a été réalisée afin de définir les conditions pour lesquelles une forêt peut également être considérée comme un dispositif de protectionThe prediction of sound propagation in presence of forest remains a major challenge for the outdoor sound propagation community. Reference numerical models such as the Transmission Line Matrix (TLM) method can be developed in order to accurately predict each acoustical phenomenon that takes place inside forest. The first need for the TLM method is an efficient theory-based absorbing layer formulation that enables the truncation of the numerical domain. The two proposed absorbing layer formulations are based on the approximation of the perfectly matched layer theory. The most efficient proposed formulation is shown to be equivalent to wave propagation in a lossy media, which, in the TLM method formulation, is introduced using an additional dissipation term. Then, the ability of the TLM method for the simulation of scattering is studied comparing the numerical results to both analytical solutions and measurements on scale models. Lastly, the attenuation of acoustic levels by a simplified forest is numerically studied using several arrangements of cylinders placed normal to either reflecting or absorbing ground. It is observed that randomly spaced arrangements are more inclined to attenuate acoustic waves than periodic arrangements. Moreover, the sensitivity to the density, the length of the array and the ground absorption is tested. The main trend shows that the density and the distribution are two important parameters for the attenuation. In future work, it can be interesting to look at the sensitivity of each parameter. This study could then be used to relate the morphology (i.e. distribution, density, length) of a forest to the acoustical properties of the forest
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Rezaiesarlak, Reza. "Design and Detection Process in Chipless RFID Systems Based on a Space-Time-Frequency Technique." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/73506.
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Recently, Radio Frequency Identification (RFID) technology has become commonplace in many applications. It is based on storing and remotely retrieving the data embedded on the tags. The tag structure can be chipped or chipless. In chipped tags, an integrated IC attached to the antenna is biased by an onboard battery or interrogating signal. Compared to barcodes, the chipped tags are expensive because of the existence of the chip. That was why chipless RFID tags are demanded as a cheap candidate for chipped RFID tags and barcodes. As its name expresses, the geometry of the tag acts as both modulator and scatterer. As a modulator, it incorporates data into the received electric field launched from the reader antenna and reflects it back to the receiving antenna. The scattered signal from the tag is captured by the antenna and transferred to the reader for the detection process.
By employing the singularity expansion method (SEM) and the characteristic mode theory (CMT), a systematic design process is introduced by which the resonant and radiation characteristics of the tag are monitored in the pole diagram versus structural parameters. The antenna is another component of the system. Taking advantage of ultra-wideband (UWB) technology, it is possible to study the time and frequency domain characteristics of the antenna used in chipless RFID system. A new omni-directional antenna element useful in wideband and UWB systems is presented. Then, a new time-frequency technique, called short-time matrix pencil method (STMPM), is introduced as an efficient approach for analyzing various scattering mechanisms in chipless RFID tags. By studying the performance of STMPM in early-time and late-time responses of the scatterers, the detection process is improved in cases of multiple tags located close to each other. A space-time-frequency algorithm is introduced based on STMPM to detect, identify, and localize multiple multi-bit chipless RFID tags in the reader area. The proposed technique has applications in electromagnetic and acoustic-based detection of targets.Ph. D.
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Cotter, Nicholas Paul Kyle. "Scattering matrix modelling of optical gratings." Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300552.
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Fabregas, Flavia Francesc. "A numerical tool for the frequency domain simulation of large clusters of wave energy converters." Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0011.
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Plusieurs convertisseurs d’énergie houlomotrice composés d’un grand réseau compact O(100) de petits flotteurs ont été proposés comme étant des systèmes avantageux pour l’extraction de l’énergie des vagues et représentent une alternative aux technologies basées sur un seul flotteur de plus grande taille. Leur capacité d’extraction d’énergie ayant été prouvé, l’accent est désormais mis sur l’optimisation pour adapter le coût de l’électricité produite aux tarifs du marché. L’un des défis les plus importants auxquels la modélisation numérique de ces systèmes houlomoteurs fait face est le calcul des interactions hydrodynamiques entre le grand nombre de sous-unités de production d’énergie qu’ils contiennent. En effet, les capacités des logiciels standards basés sur l’approche Boundary Element Method pour le calcul de l’interaction houle/structure sont largement dépassées quand un nombre de flotteurs O(100) est atteint. L’implémentation d’une méthode basée sur une théorie d’interaction plus adapté au problème de diffraction multiple s’avère donc indispensable. Cette nouvelle approche, connue sous le nom de Direct Matrix Method, permet de réduire le nombre d’inconnues du problème d’interaction traditionnel en se basant sur la connaissance de la manière dont un convertisseur d’énergie houlomotrice diffracte et génère des vagues. L’accélération apportée par l’outil mis en place a permis de modéliser et optimiser un houlomoteur composé d’une soixantaine d’unités de type flotteur pilonnant. On a montré qu’il existe un nombre optimal de flotteurs pour une empreinte du dispositif donnée. Dépasser l’optimum entraîne une perte de performance nuisible à sa viabilité économiqueCompact arrays of small wave absorbers constitute an example of the multiple existing categories of wave energy converters (WECs) and have been identified as being an advantageous solution for the extraction of wave energy when compared to a big isolated point absorber. Among the numerous challenges associated with the numerical modeling of such devices, one of the most relevant one is the evaluation of the hydrodynamic interactions amid the large number of floats O(100) they are composed of. Direct computations with standard Boundary Element Method (BEM) solvers, used extensively in wave/structure interaction problems, become prohibitive when the number of bodies increases. Thus, there is a need to employ an alternative approach more suitable for the study of the multiple-scattering in large arrays. In this work, the Direct Matrix Method interaction theory has been implemented. Based on characterizing the way a WEC scatters and radiates waves, this methodology enables one to significantly reduce the number of unknowns of the classical boundary value problem dealt with by standard BEM solvers and, therefore, the computational time. The acceleration provided by the numerical tool developed has allowed examining the power capture of a generic bottom-reference heave-buoy array WEC and optimizing its layout. We have shown that there exist an optimum number of floats for a given device footprint. Exceeding this number results in a “saturation” of the power increase which is undesirable for the economic viability of the device
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Barlabé, i. Dalmau Antoni. "Anàlisi de discontinuïtats finline." Doctoral thesis, Universitat Politècnica de Catalunya, 1996. http://hdl.handle.net/10803/6936.
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En esta tesis se han desarrollado los siguientes métodos numéricos para el análisis de estructuras planares, especialmente finline, en la banda de microondas y ondas milimétricas: -el método de las líneas con discretizacion uniforme y no uniforme.
-el método de los elementos finitos aplicado al análisis de guías homogéneas e inhomogeneas.
-el método de la matriz de lineas de transmisión tridimensional.
-el método de la matriz se generalizada para el análisis de estructuras uniformes y discontinuidades planares.
-el método del dominio espectral para el análisis de estructuras planares uniformes.
-el método del circuito planar con corrección de la dispersión.
Se ha elegido el método de la resonancia transversal generalizado como el mas idóneo para el análisis preciso y rápido de discontinuidades finline con un mínimo de recursos informáticos. Se ha desarrollado incluyendo el carácter singular de los campos en las aristas de la estructura, consiguiéndose minimizar el fenómeno de la convergencia relativa y obteniéndose resultados precisos con expansiones reducidas de las funciones modales que representan los campos, validándose los resultados obtenidos al analizar diversas estructuras con medidas experimentales.
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Liu, Hainan. "Theoretical study of electron collisions with NO2 and N2O molecules for control and reduction of atmospheric pollution." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST030.
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Cette thèse présente des recherches théoriques sur la diffusion électronique avec deux molécules polyatomiques d’intérêt pour la pollution atmosphérique, les molécules NO2 et N2O. En ce qui concerne la molécule NO2, nous étudions l’excitation vibrationnelle entre les niveaux les plus bas des états électroniques fondamentaux de cette molécule. Le calcul est effectué par une approche qui combine l’approximation des modes normaux pour les états vibrationnels du NO2, le code de la UK R-matrice pour obtenir la électron-molécule S-matrice pour les géométries fixes de la cible et la « vibrational frame transformation » pour évaluer le matrices de diffusion pour les transitions vibrationnelles. En ce qui nous concerne, la sections efficaces d’excitation vibrationnelle calculée dans cette thèse est rapportée pour la première fois pour la molécule NO2. L’estimation de l’incertitude des résultats est ainsi réalisée pour valider la présente approche théorique. De même, les sections efficaces d’excitation vibrationnelle de la molécule de N2O sont déterminées. Les résultats obtenus sont en accord raisonnable avec les données expérimentales. Les rate coefficient d’excitation vibrationnelle sont obtenus à partir des sections efficaces pour la plage de températures de 10K à 10000 K. La structure rotationnelle des molécules neutres cibles est négligée dans la présente approche, ce qui implique que les sections efficaces et les rate coefficient obtenus doivent être considérés comme une moyenne sur états de rotation initiaux et additionnés sur les états de rotation finaux des niveaux vibrationnels initial et final correspondants. Enfin, l’attachement dissociatif aux électrons (DEA) du NO2 est également étudié dans cette thèse. Ce processus est en concurrence avec l’excitation vibrationnelle dans la plage d’énergie de diffusion en dessous du premier état électronique excité de la cible. La DEA sections efficaces est calculée par la méthode basée sur la théorie de Bardsley-O’Malley développée pour les molécules diatomiques et généralisée aux molécules polyatomiques complexes par Chi Hong Yuen et al. par la suite par rapport aux mesures expérimentales disponibles. Les résultats obtenus pourraient être utilisés dans la modélisation du plasma pour le contrôle et la réduction de la pollution atmosphériqueThis thesis presents theoretical investigations on electron scattering with two polyatomic molecules of atmospheric pollution interest, the NO2 and N2O molecules. Regarding the NO2 molecule, we study the vibrational excitation between the lowest levels within the ground electronic states of this molecule. The calculation is carried out by an approach that combines the normal modes approximation for the vibrational states of the NO2, the UK R-matrix code to obtain electron–molecule S-matrix for fixed geometries of the target and the vibrational frame transformation to evaluate the scattering matrices for vibrational transitions. To our knowledge, the vibrational excitation cross section calculated in this thesis is reported for the first time for NO2 molecule. The uncertainty estimation of the results is thus performed to validate the present theoretical approach. Similarly, the vibrational excitation cross sections of N2O molecule are determined. The obtained results are in reasonable agreement with experimental data. The rate coefficient of vibrational excitation are obtained from the cross-sections for temperatures in the 10–10000 K range. The rotational structure of the target neutral molecules is neglected in the present approach, which implies that the obtained cross-sections and rate coefficients should be viewed as averaged over initial rotational states and summed over final rotational states of the corresponding initial and final vibrational levels. Finally, the dissociative electron attachment (DEA) of NO2 are also studied in this thesis. This process competes with vibrational excitation at the scattering energy range below the first electronic excited state of the target. The DEA cross section is calculated by the method based on the Bardsley-O’Malley theory developed for diatomic molecules and generalized to complex polyatomic molecules by Chi Hong Yuen et al. afterwards compared with available experimental measurements. The obtained results could be used in plasma modeling for control and reduction of atmospheric pollution
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Jiang, Xianwu. "Hydrocarbon molecules databases for waste treatment applications." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST039.
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Dans cette thèse, nous étudions la (dé)excitation vibronique et la recombinaison dissociative du CH+ par impact d'électrons de faible énergie. Nous développons d'abord une approche théorique de l'excitation (dé)vibronique de CH+ par impact d'électrons. Dans cette approche, la méthode de la matrice R à noyaux fixes est utilisée pour calculer les matrices de diffusion des électrons et des ions dans l'approximation de Born-Oppenheimer. Une transformation vibronique du cadre et la procédure d'élimination à canal fermé dans l'esprit de la théorie des défauts quantiques moléculaires sont utilisées pour construire une matrice de diffusion dépendant de l'énergie décrivant les interactions entre les canaux vibroniques de l'ion cible induits par l'électron incident. La matrice de diffusion obtenue tient compte de la série de résonances vibroniques de Rydberg dans le spectre de collision. Les sections transversales de l'excitation vibronique pour différentes combinaisons d'états vibroniques initiaux et finaux sont calculées. Un bon accord entre les sections transversales d'excitation électronique, obtenu en utilisant la théorie des défauts quantiques et dans un calcul direct de matrice R, démontre que l'approche actuelle fournit un outil fiable pour la détermination des sections transversales d'excitation (dé)vibronique pour des cibles avec des résonances électroniques de faible énergie. De telles cibles étaient difficiles à traiter théoriquement avec les méthodes précédentes. Dans le même cadre que celui appliqué aux excitations (dé)vibroniques, nous calculons en outre la section transversale pour la recombinaison dissociative à basse énergie de CH+ couplant la fonction de base de l'onde sortante définie par le potentiel d'absorption complexe. La contribution des trois états ioniques X 1Σ +, a 3Π et A 1Π les plus bas et la série de Rydberg convergeant vers ces états sont pris en compte. Les sections transversales DR obtenues sont quantitativement en bon accord avec les mesures expérimentales et présentent une caractéristique de résonance analogue à la courbe de la section transversale expérimentale. L'origine des résonances proéminentes dans les résultats calculés est analysée par le calcul des probabilités de DR pour les ondes partielles de l'électron incident. On constate que les ondes partielles de type d, notamment dσ, dπ et dδ, contribuent considérablement à la DR du état de terrain CH+. Cela peut expliquer les écarts observés entre la théorie et l'expérience dans les études précédentesIn this thesis, we investigate the vibronic (de-) excitation and dissociative recombination of CH+ by low-energy electron impact. We first develop a theoretical approach for the electron-impact vibronic (de-) excitation of CH+. In this approach, the fixed-nuclear R-matrix method is employed to compute electron-ion scattering matrices in the Born-Oppenheimer approximation. A vibronic frame transformation and the closedchannel elimination procedure in a spirit of molecular quantum defect theory are employed to construct an energy-dependent scattering matrix describing interactions between vibronic channels of the target ion induced by the incident electron. The obtained scattering matrix accounts for Rydberg series of vibronic resonances in the collisional spectrum. Cross sections for vibronic excitation for different combinations of initial and final vibronic states are computed. A good agreement between electronic-excitation cross sections, obtained using the quantum defect theory and in a direct R-matrix calculation, demonstrates that the present approach provides a reliable tool for determination of vibronic (de-) excitation cross sections for targets with low-energy electronic resonances. Such targets were difficult to treat theoretically using earlier methods. Within the same framework applied for the vibronic (de-) excitations, we further compute the cross section for low-energy dissociative recombination of CH+ coupling the outgoing-wave basis function defined by complex absorbing potential. The contribution of the three lowest X 1Σ +, a 3Π and A 1Π ionic states and the Rydberg series converging to those states are taken into account. The obtained DR cross sections are quantitatively in good agreement with the experimental measurements and exhibit a resonanc feature analogous to the experimental cross-section curve. The origination of the prominant resonances in the computed results are analyzed through computing the DR probabilities for the partial waves of the incident electron. The d-type partial waves including dσ, dπ and dδ are found considerably contributing to the DR of the ground-state CH+. This may explain the discrepancies observed between thoery and experiment in the preceeding studies
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Chiniard, Renaud. "Contribution à la modélisation de la surface équivalente radar des grandes antennes réseaux par une approche multi domaine/Floquet." Toulouse 3, 2007. http://www.theses.fr/2007TOU30295.
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Cette étude propose de traiter les grandes antennes réseaux par une approche originale permettant d’atteindre des problèmes dont les grandes dimensions les rendent inaccessibles aux méthodes classiques et rigoureuses. Ainsi, la première partie est consacrée à la description des méthodes employées. La première d’entre elles est la méthode multi domaine qui permet de découper en sous domaines le problème initial. Chaque domaine est alors calculé à l’aide de la méthode numérique (équations intégrales, éléments finis,…) la plus appropriée dans le but d’obtenir un opérateur condensé (matrice S) pour chacun des sous domaines de manière indépendante. La grande force de cette méthode réside dans son approche modulaire qui la rend très efficace dans les études paramétriques par réutilisation des matrices S des volumes inchangés. Nous présentons ensuite le développement en modes de Floquet utilisable dans le cadre de structures planes, infinies et périodiques. Il permet de réduire le problème que nous traitons à la taille de la cellule élémentaire. Dans la deuxième partie, nous présentons l’hybridation des deux méthodes précédemment introduites. Ce couplage de méthode est accompagné d’un cas canonique de validation (réseau de guide rectangulaire) qui, en plus de valider notre approche, a permis la mise en place d’indicateurs physiques. Nous apportons dans le chapitre suivant deux modularités supplémentaires pour traiter des problèmes plus réalistes de réseaux sur structure. Le dernier chapitre confronte notre code à des mesures effectuées sur une maquette d’antenne réseau réelle. Il permet de jauger le potentiel de la méthode présentée. Au terme de cette étude, un outil a été développé et il permet de calculer la Surface Équivalente Radar des grandes antennes réseaux insérées dans leurs supports et pour différentes conditions d’impédances au niveau des accèsThis study proposes to treat large array antennas with an original approach. It makes it possible to reach problems whose great dimensions lead traditional and rigorous methods to be unsuccessful. The first part is devoted to the description of the employed methods. The first one is the multi domain method which makes it possible to split in sub domains the initial problem. Each domain is then calculated using the numerical method (integral equations, finite elements,…) adapted. It allows to obtain a condensed operator (S matrix) for each sub domain in an uncoupled way. Once they have been put together with the feeding, the problem can be solved. The main advantage lies in the modular approach which makes it very efficient in parametric studies by re-use of the matrices S of unchanged volumes. We further present the development in Floquet modes, assuming the planar, infinite and periodic hypothesis. It thus makes it possible to reduce the problem to the size of the elementary cell. In the second part, the hybridization of the two methods previously introduced is shown. It is discussed on a rectangular guide array case which, in addition to validating our approach, allows the installation of physical indicators. To enhance our tool, in the next chapter we couple the array to its mechanical support and propose an efficient modelling of this global realistic antenna. The final chapter makes it possible to confront our code with the measurements of one real array antenna. It allows to estimate all the capabilities of the method developed during this study. At the end of this study, a software tool has been developed and it makes it possible to calculate Radar Cross Section of the large antenna arrays inserted in their supports and for various conditions of feeding impedances
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Ghazel, Ramzi. "Méthodes de caractérisation en bruit des dispositifs radiofréquences multi accès." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0122.
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Dans tout système de télécommunication micro-onde, les performances en bruit représentent un critère très important des dispositifs des chaînes de réception. La connaissance des sources de bruit interne des composants et leur corrélation permet de prédire et optimiser les performances en bruit d’un récepteur. Ce thème fait l’objet de nombreuses études et publications à travers le monde. Le travail proposé dans cette thèse consiste à évaluer les performances en bruit d’un dispositif multiport (N-ports) au sens le plus général et sans aucune approximation, en se basant sur une nouvelle méthode d’extraction de l’intégralité de la matrice de corrélation des ondes de bruit qui contient tous les informations relatives aux performances en bruit. Cette nouvelle méthode est basée sur l’utilisation du formalisme des ondes de bruit et la matrice de répartition [S], les résultats d’extraction sont validés par des calculs et par des mesures sur deux dispositifs deux ports (passif et actif) et sur deux octopôles (4 accès) en mode standard et mixte (passif et actif)In any microwave telecommunication system, noise performance is a very important criterion for receiving chain devices. Knowledge of the internal noise sources of the components and their correlation makes it possible to predict and optimize the noise performance of a receiver. This theme is the subject of numerous studies and publications around the world. The work proposed in this thesis consists in evaluating the noise performance of a multiport device (N-ports) in the most general sense and without any approximation, based on a new method of extracting the entire noise wave correlation matrix that contains all the information relating to noise performance. This new method is based on the use of noise wave formalism and the scattering matrix[S], the extraction results are validated by calculations and measurements on a two-port device (passive and active) and on a 4-port in standard and mixed mode (passive and active)
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Onelli, Olimpia Domitilla. "Complex photonic structures in nature : from order to disorder." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273768.
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Structural colours arise from the interaction of visible light with nano-structured materials. The occurrence of such structures in nature has been known for over a century, but it is only in the last few decades that the study of natural photonic structures has fully matured due to the advances in imagining techniques and computational modelling. Even though a plethora of different colour-producing architectures in a variety of species has been investigated, a few significant questions are still open: how do these structures develop in living organisms? Does disorder play a functional role in biological photonics? If so, is it possible to say that the optical response of natural disordered photonics has been optimised under evolutionary pressure? And, finally, can we exploit the well-adapted photonic design principles that we observe in Nature to fabricate functional materials with optimised scattering response? In my thesis I try to answer the questions above: I microscopically investigate $\textit{in vivo}$ the growth of a cuticular multilayer, one of the most common colour-producing strategies in nature, in the green beetles $\textit{Gastrophysa viridula}$ showing how the interplay between different materials varies during the various life stages of the beetles; I further investigate two types of disordered photonic structures and their biological role, the random array of spherical air inclusions in the eggshells of the honeyguide $\textit{Prodotiscus regulus}$, a species under unique evolutionary pressure to produce blue eggs, and the anisotropic chitinous network of fibres in the white beetle $\textit{Cyphochilus}$, the whitest low-refractive index material; finally, inspired by these natural designs, I fabricate and study light transport in biocompatible highly-scattering materials.
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Hunter, Brandon. "Channel Probing for an Indoor Wireless Communications Channel." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/64.
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The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.
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Silva, Marcello Antônio Ferreira Marques da. "Caracterização óptica e estrutural de materiais isolantes dopados com metais de transição do grupo do ferro." Universidade do Estado do Rio de Janeiro, 2010. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=6727.
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O objetivo deste trabalho foi a investigação das propriedades ópticas e estruturais de materiais isolantes contendo metais de transição do grupo do ferro como impurezas substitucionais.
As técnicas usadas para o estudo de amostras MgGa2O4, MgGa2O4 + B- Ga2O3 e ZnGa2O4 dopadas com Cr3+e Fe3+ foram: fotoluminescência, excitação, difração de raios-X, espalhamento de nêutrons, método de Rietveld para o refinamento da estrutura e espectroscopia fotoacústica.
Estas técnicas permitem a determinação da coordenação
do sítio impureza, a atribuição das transições de energia, o
cálculo dos parâmetros de energia e a determinação de propriedades cristalográficas. As amostras apresentam largas
bandas de energia nas regiões do visível e do infravermelho. Estas transições indicam a relevância deste estudo pelo interesse tecnológico na obtenção de novos materais com
bandas sintonizáveis. No primeiro capítulo apresentamos uma introdução à teoria de campo cristalino. No segundo capítulo apresentamos medidas de fotoluminescência e excitação do MgGa2O4 dopado com 0,1, 0,5, 1,0 e 5,0 % de Cr3+ a 77 K e temperatura ambiente. No terceiro capítulo usamos fotoluminescência, excitação, espalhamento de
nêutrons, difração de raios X, fotoacústica e método de refino de Rietveld para analisar o sistema MgGa2O4 + B-Ga2O3 contendo 0,1, 0,5, 1,0 e 5,0 % de Cr3+. No quarto capítulo mostramos resultados de fotoacústica para o ZnGa2O4 dopado com 5% e 10% de Fe3+.The aim of this work was the investigation of optical and structural properties of insulating materials containing iron group metal transition ions as substitutional impurities. The used techniques for the study of MgGa2O4, MgGa2O4 + B-Ga2O3 and ZnGa2O4 samples doped with Cr3+ and Fe3+ were: photoluminescence, excitation, X-ray diffraction, neutron scattering, Rietveld method for structure refinement and photoacoustic spectroscopy. These techniques allow the determination of impurity site coordination, the assignment of energy transitions, the calculation of energy parameters and the determination of crystallographic properties. The samples present broad energy bands at visible and infrared spectral regions. These transitions point to the relevance of this study for being of technological interest. In the first chapter we present an introduction to crystal field theory. In the second chapter we present the photoluminescence and excitation measurements of MgGa2O4 doped with 0.1, 0.5, 1.0 and 5.0 % of Cr3+ at 77 K and room temperature. In the third chapter we used the photoluminescence, excitation, neutrons scattering, X-ray diffraction, photoacoustic and Rietveld method for analysis of the MgGa2O4, MgGa2O4 + B-Ga2O3 system containing 0.1, 0.5, 1.0 and 5.0 % of Cr3+. In the fourth chapter we show the photoacoustic results for ZnGa2O4 doped with 5% and 10% of Fe3+.
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Moeferdt, Matthias. "Nonlocal and Nonlinear Properties of Plasmonic Nanostructures Within the Hydrodynamic Drude Model." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18129.
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In dieser Arbeit werden die nichtlokalen sowie nichtlinearen Eigenschaften plasmonischer Nanopartikel behandelt, wie sie im hydrodynamischen Modell enthalten sind. Das hydrodynamische Materialmodell stellt eine Erweiterung des Drude Modells dar, in der Korrekturen in der Beschreibung des Elektronenplasmas berücksichtigt werden. Einer ausführlichen Einführung des Materialmodells folgt eine analytische Diskussion der Auswirkungen der Nichtlokalität am Beispiel eines einzelnen Zylinders. Hierbei werden die durch die Nichtlokalität herbeigeführten Frequenzverschiebungen in den Streu- und Absorptionsspektren quantifiziert und asymptotisch behandelt. Des Weiteren wird mit Hilfe einer konformen Abbildung das Problem eines zylindrischen Dimers in der Elektrostatischen Näherung gelöst und die Moden der Struktur bestimmt. Diese Untersuchungen dienen als maßgebliche Grundlage für weiterführende numerische Studien die mit der diskontinuierlichen Galerkin Zeitraummethode durchgeführt werden. Die durch die analytischen Betrachtungen gewonnene Kenntnis der Moden ermöglicht es, im Zusammenhang mit gruppentheoretischen Betrachtungen und numerischen Untersuchungen, rigorose Auswahlregeln für die Anregung der Moden durch lineare und nichtlineare Prozesse aufzustellen. In weiterführenden numerischen Simulationen werden außerdem Strukturen niedrigerer Symmetrie, auf die sich die Auswahlregeln übertragen lassen, untersucht. Zudem werden numerische Studien präsentiert in denen der Einfluss der Nichtlokalität auf Feldüberhöhungen in Dimeren und doppel-resonantes Verhalten (es liegt sowohl bei der Frequenz des eingestrahlten Lichtes als auch bei der zweiten harmonischen eine Resonanz vor) untersucht werden.This thesis deals with the nonlocal and nonlinear properties of plasmonic nanoparticles, as described by the hydrodynamic model. The hydrodynamic material model represents an extension of the Drude model that contains corrections to the descriptions of the electron plasma. After a thorough derivation of the material model, analytical discussions of nonlocality are presented for the example of a single cylinder. The frequency shifts in the scattering and absorption spectra are quantified and treated asymptotically. Furthermore, by applying a conformal map, the problem of a cylindrical dimer is solved in the electrostatic limit and the modes of the structure are determined. These investigations lay the foundations for numerical investigations which are performed employing the discontinuous Galerkin time domain method. The analytical knowledge of the modes, in conjunction with group theoretical considerations and numerical analysis, enables the formulation of rigorous selection rules for the excitation of modes by linear and nonlinear processes. In further numerical studies, the influence of nonlocality on the field enhancement in dimer structures and double-resonant behavior (a resonance is found at the frequency of the incoming light and at the second harmonic) are investigated.
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Cassiani-Ingoni, Lionel. "Etude d'un hydrogel, copolymere (mma-co-vp) utilise comme precurseur de lentilles de contact : caracterisation du gel, diffusion et activite du lysozyme dans la matrice." Paris 6, 1987. http://www.theses.fr/1987PA066299.
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Lian, Chii-Fa, and 連啟發. "A scattering-matrix method to study the conductance propoties of GaAs narrow wire." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/12569495837144781236.
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碩士國立清華大學
電子工程研究所
92
We study two types of different scattering-matrix(constant matrix Scattering, function scattering) to describe the configuration of a single impurity in GaAs narrow wire. We combine the total scattering-matrix and use Landauer formula to get the conductance. Then we discuss some interesting conductance properties in mesoscopic regime.
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Huang, Jun-Xian, and 黃俊憲. "Application of the FDTD Method with the Scattering Matrix in Microwave Circuit Simulation." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/63240379774708142463.
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碩士國立中山大學
電機工程學系研究所
91
The finite-Difference Time Domain method (FDTD) is to derive the discrete form of the Maxwell’s equations by second-order central difference with the electromagnetic distribution of the Yee space lattice, and computes the value of the electric field and magnetic field in the simulation space by using leapfrog for time derivatives. This method is also different with the frequency domain method which needs to analyze its value individually (ex. Finite Element method). The frequency domain method needs to take a long time for analyzing the response on each spectrum point when the bandwidth is very wide. The advantage of time domain analysis is to obtain the complete frequency response from the simulation value through Fourier Transform method. It’s impossible to combine the electromagnetic analysis with the lumped circuit simulation in current simulation CAD. Thereby the performance of the simulation result and the practical implementation always occurs error because of the lake of the consideration. The FDTD method is the full-wave algorithm which can also simulate the lump element, nonlinear element or active element in simulation space by linking to SPICE or S-parameter. The purpose of this thesis is to develop the method for simulating microwave circuit, and to verify the credibility between the equivalent source method and the S-parameter method in FDTD by the simulation of active antenna and low-noise amplifier.
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Xing-Xiang, Liu. "A Study of Surface plasmon Resonance on 3D Metal Spherical Nanoparticles by Multiple Scattering Matrix Method." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1907200615513000.
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Liu, Xing-Xiang, and 劉信翔. "A Study of Surface plasmon Resonance on 3D Metal Spherical Nanoparticles by Multiple Scattering Matrix Method." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/52224490597156082783.
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碩士國立臺灣大學
應用力學研究所
94
In this thesis we theoretically investigate the surface plasmon resonance in metal nanoparticles. We use the multiple scattering method to simulate the electromagnetc propagation and surface plasmon behaviors in particle systems. By this method, the fundamental resonance modes can be clearly resolved. We consider the permittivity functions obtained from the Drude model, experimental results and modification of the size effect. The simulations show that the surface plasmon resonance is greatly influenced by the particle size and arrangement. The enormous field enhancement due to surface plasmon coupling between particles is reported. The interparticle distance and the wave polarization are responsible for the large field magnitude. Finally, we study the plasmon resonance for chains of particles aligned in the polarization and propagating directions. We show the propagation of electromagnetic energy in the chains. These results may improve the development of plasmonic devices.
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Loupas, Alexandra Cristina Rodrigues. "Study of Low-energy Electron Collisions with Molecules of Biological Relevance." Doctoral thesis, 2019. http://hdl.handle.net/10362/93349.
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This thesis is focused on the application of the R-matrix method, as implemented in the
UKRmol and UKRmol+ suites, to study low-energy electron collisions with three medium-sized
molecules of biological relevance: para-benzoquinone, thiophene and alanine. Our goals for
all the targets are mainly three: (i) to identify and characterize respective resonances; (ii) to
calculate elastic and inelastic integral and elastic differential cross sections; and (iii) compare
our results with the literature. To do so, we use several scattering models, choosing the most
suitable on the basis of the characteristics being investigated: Static Exchange, Static Exchange
plus Polarization and/or Close-Coupling approximation.
Specially at higher energies, we find an unexpectedly large number of resonances for the
three targets, most of them of core-excited and core-excited shape character. We compare our
results with other calculations and/or experiments in the literature, but the absence of detailed
experimental results for many targets at these energies precludes a meaningful comparison.
Nonetheless, three scenarios are then obtained: in the first one, for para-benzoquinone, the
agreement with previous results is satisfactory; in the second, for thiophene, is excellent; and
finally, for alanine, there is not much prior information on the literature to make decisive conclusions.
This work was all published in peer-reviewed journals.
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Schlosser, Peter [Verfasser]. "Matrix compression methods for the numerical solution of radiative transfer in scattering media / Peter Schlosser." 2003. http://d-nb.info/967305225/34.
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Heinemeyer, Eric. "Integral Equation Methods for Rough Surface Scattering Problems in three Dimensions." Doctoral thesis, 2008. http://hdl.handle.net/11858/00-1735-0000-000D-F15F-2.
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Tiegel, Alexander Clemens. "Finite-temperature dynamics of low-dimensional quantum systems with DMRG methods." Doctoral thesis, 2016. http://hdl.handle.net/11858/00-1735-0000-0028-8801-A.
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