Segui questo link per vedere altri tipi di pubblicazioni sul tema: Orbit method.
Tesi sul tema "Orbit method"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Orbit method".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Mohamed, Ben Hadj Rhouma. "On the continuation of periodic orbits /." free to MU campus, to others for purchase, 1999. http://wwwlib.umi.com/cr/mo/fullcit?p9953845.
Testo completo
2
Litsgård, Malte. "The Orbit Method and Geometric Quantisation." Thesis, Uppsala universitet, Analys och sannolikhetsteori, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-351508.
Testo completo
3
Stevens, Robert E. "Design of optimal cyclers using solar sails." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FStevens.pdf.
Testo completoAbstract (sommario):
Thesis (Aeronautical and Astronautical Engineer)--Naval Postgraduate School, December 2002.<br>Thesis advisor(s): I. Michael Ross, Dennis Byrnes. Includes bibliographical references (p. 119-120). Also available online.
4
Koblick, Darin C. "Parallel high-precision orbit propagation using the modified Picard-Chebyshev method." California State University, Long Beach, 2013.
Cerca il testo completo
5
Elvidge, Michael Edward Carleton University Dissertation Engineering Mechanical and Aerospace. "A stochastic method for calculating spacecraft vulnerability to low earth orbit debris." Ottawa, 1994.
Cerca il testo completo
6
Hart, Andrew Markland Stanley. "Application of the homotopy continuation method to low-eccentricity preliminary orbit determination." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/42500.
Testo completo
7
Sheng, Liu Dong. "A New Method for Refinning Orbit of CPS Satellite Using Phase Measurement." International Foundation for Telemetering, 1990. http://hdl.handle.net/10150/613778.
Testo completoAbstract (sommario):
International Telemetering Conference Proceedings / October 29-November 02, 1990 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>This paper developed a new method of refinning GPS satellite orbit using phase measurement without knowing the GPS codes. Because this approach have no connection with any particular physical model, avoiding introducing any dynamic error, this method make it possible to get high precision GPS satellite orbit.
A simulation computation has been conducted and gave an encouraging result.
8
Scott, Karen Patricia 1964. "Radiometric calibration of on-orbit satellite sensors using an improved cross-calibration method." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282831.
Testo completoAbstract (sommario):
As the field of remote sensing continues to grow with the launches of many new and complex satellite sensors in the next year, the ability to provide absolute calibration of these sensors becomes paramount for the many environmental studies proposed. In particular, temporal studies that monitor global changes in atmospheric constituents, ocean and terrestrial temperatures, and vegetation require that changes in the sensor itself, over the period of the study, be understood so that the data may be corrected. Numerous studies have established that satellite sensors change in orbit with respect to preflight calibration, in some cases, up to 20% or more over periods of three years. This research describes the development of an improved cross-calibration method of on-orbit satellite sensor radiometric calibration. The objective of the cross-calibration method is to transfer one sensor's calibration to another sensor which is typically difficult or expensive to calibrate with other methods. The cross-calibration method is relatively inexpensive to apply, and therefore there was a strong incentive to improve the application of the method and the understanding of the uncertainties associated with the method. The primary effort in this work has been the development of a cross-calibration software program which provides the means to easily perform end-to-end cross-calibrations. The program allows for a multiplicity of sites to be run, provides a search mechanism in order to identify calibration sites with particular characteristics, and contains an extensive error analysis capability. As part of this work, a search for acceptable cross-calibration sites was also performed which would allow a reduction in uncertainties of the method. Calibrations of five different sensor band pairs using System Pour l'Observation de la Terre (SPOT) 3, Landsat Thematic Mapper, and Advanced Very High Resolution Radiometer (AVHRR) sensors are performed. Very good results are obtained when the results are compared with other more expensive calibration methods, and the calibrations yielded uncertainties lower than reported in previous work.
9
Van, Beusekom Craig Joseph. "A new guidance method for a DeltaV and re-entry constrained orbit transfer problem." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/46571.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.<br>Includes bibliographical references (p. 153-154).<br>This thesis proposes a spacecraft guidance system designed for a unique class of orbit transfer problems. It considers a vehicle that undertakes a maneuver with the objective of precisely flying through a point in space at a particular time. The spacecraft must automatically determine a transfer orbit that will take it from a circular, low-earth parking orbit to a velocity-unconstrained rendezvous with a Keplerian trajectory. A constraint exists that both the final transfer orbit and the ultimate paths of any additional stages must lead rapidly to atmospheric reentry, typically within one revolution. Constrained to a fixed [delta]V resulting from a two stage thrust profile, the spacecraft must execute a burn maneuver that can effectively dissipate energy to place it on a transfer orbit with previously unknown velocity requirements. Finally, the guidance strategy should be robust to the uncertainties typically encountered in real spacecraft orbit transfer problems. In order to meet these constraints, this thesis first develops new analytic analysis of the relationship between reentry, perigee, and [delta]V. Next, a framework is developed for selecting a favorable transfer orbit while considering the various hard and soft constraints in the problem. Following transfer orbit selection, a plane of maneuver is calculated that maximizes likelihood of first stage reentry. Then traditional guidance strategies are adapted to the problem and hypothetical spacecraft design to produce a closed loop guidance solution. Results are presented that demonstrate the effectiveness of the new method.<br>by Craig Joseph Van Beusekom.<br>S.M.
10
Bengtsson, Bernander Karl. "A Method for Detecting Resident Space Objects and Orbit Determination Based on Star Trackers and Image Analysis." Thesis, Uppsala universitet, Avdelningen för visuell information och interaktion, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-236873.
Testo completoAbstract (sommario):
Satellites commonly use onboard digital cameras, called star trackers. A star tracker determines the satellite's attitude, i.e. its orientation in space, by comparing star positions with databases of star patterns. In this thesis, I investigate the possibility of extending the functionality of star trackers to also detect the presence of resident space objects (RSO) orbiting the earth. RSO consist of both active satellites and orbital debris, such as inactive satellites, spent rocket stages and particles of different sizes. I implement and compare nine detection algorithms based on image analysis. The input is two hundred synthetic images, consisting of a portion of the night sky with added random Gaussian and banding noise. RSO, visible as faint lines in random positions, are added to half of the images. The algorithms are evaluated with respect to sensitivity (the true positive rate) and specificity (the true negative rate). Also, a difficulty metric encompassing execution times and computational complexity is used. The Laplacian of Gaussian algorithm outperforms the rest, with a sensitivity of 0.99, a specificity of 1 and a low difficulty. It is further tested to determine how its performance changes when varying parameters such as line length and noise strength. For high sensitivity, there is a lower limit in how faint the line can appear. Finally, I show that it is possible to use the extracted information to roughly estimate the orbit of the RSO. This can be accomplished using the Gaussian angles-only method. Three angular measurements of the RSO positions are needed, in addition to the times and the positions of the observer satellite. A computer architecture capable of image processing is needed for an onboard implementation of the method.
11
Korogodski, Leonid I. "Representation of quantum algebras arising from non-compact quantum groups : quantum orbit method and super-tensor products." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39076.
Testo completo
12
Dallow, Andrew Thomas. "Investigating the Enigmatic Orbit of the Suspected 2.5 MJ Planet in the Nu Octantis Binary System." Thesis, University of Canterbury. Physics and Astronomy, 2012. http://hdl.handle.net/10092/10364.
Testo completoAbstract (sommario):
ν Octantis is a spectroscopic binary with a semi-major axis and period of 2.55 AU and 2.9 years, respectively. Ramm et al. (2009) discovered a 52 ms^(-1) radial-velocity (RV) perturbation with a period of 417 days in this system. All evidence, both photometric and spectroscopic, suggests the perturbation is the result of a 2.5 MJ planet orbiting the primary star. However, when assuming a “normal” prograde coplanar orbit, celestial mechanics predicts this orbit is unstable, contradicting the observed stability.
Simulations by Eberle and Cuntz (2010) showed a retrograde orbit for the planet to be stable for at least 10^7 years. In this thesis, we performed a 10^8 -yr simulation of the retrograde orbit, and found it remained stable. Simulations over a range of planetary semi-major axes, eccentricities, and primary/secondary masses showed that stable retrograde orbits are not possible past a semi-major axis of 1.315 +/- 0.092 AU . Therefore, planetary retrograde orbits are most likely inherently more stable than prograde orbits owing to the absence of stability at known mean-motion resonances.
Eccentricity simulations showed that the period of the planet's dominant eccentricity variation is related to the planet's semi-major axis by a second order exponential. However, retrograde orbits tend to have longer eccentricity periods than prograde orbits at the same semi-major axis. There is also evidence that this eccentricity period is connected to the orbital stability.
By fitting a keplerian to both Ramm et al. (2009) and current radial velocities, the period of the ν Octantis binary was determined to be 1050.04 +/- 0.02 days with an eccentricity of 0.2359 +/- 0.001 . The planetary orbital solution for just the data reduced in this thesis gave a period of 416.9 +/- 2.1 days and an eccentricity of 0.099 +/- 0.015 , with an RMS scatter of 9.6 ms^(-1). Therefore, the orbital elements are within 1σ of the Ramm et al. (2009) elements. Assuming a retrograde coplanar orbit about the primary star then the planet has a mass of M_pl = 2.3 M_J and a semi-major axis of a_pl = 1.21 +/- 0.09 AU.
13
Campos, Tiago de. "Spin-orbit coupling effects and g-factors in zinc-blende InSb and wurtzite InAs nanowires using realistic multiband k · p method." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-30012018-163011/.
Testo completoAbstract (sommario):
Spin-dependent phenomena in semiconductor nanowires have recently gained a lot of attention, in special because these nanostructures can be a viable setup to study exotic states of matter like the Majorana fermions. One of the key ingredients to accommodate the Majorana zero modes is the spin-orbit coupling in the nanowires, which has been usually treated with two-band Hamiltonians. The spin-orbit coupling in semiconductors arise from two distinct sources being the bulk inversion asymmetry, when the unit cell does not present inversion symmetry, e.g. when the crystal unit cell is composed by two different atoms, and the structural inversion asymmetry, when the whole system does not have a mirror symmetry. To describe the system these effective models take as input, parameters that are dependent on the system configuration and measurement setups. Although these effective models have been successful in determine relevant physical properties, a more realistic description of the interacting energy bands is required, specially in quantum confined systems where the interplay between both sources of spin-orbit coupling can change the systems properties in non-trivial ways. For instance, in quantum wells there is an anisotropy of the g-factor due to the quantum confinement and structural inversion asymmetry. Furthermore, the in-plane g-factor also have an anisotropy which is due to the intrinsic spin-orbit coupling and it is not captured by these effective models. In this study, we use realistic multiband k · p Hamiltonians, including both spin-orbit coupling mechanisms, to determine the band structure of zincblende InSb and wurtzite InAs nanowires under a transverse electric field. We analyze the effects of the lateral quantum confinement for a hexagonal cross-section geometry and of the change in growth directions, extracting the relevant physical parameters for the first conduction subband. We found that the g-factors are heavily dependent on the quantum confinement and nanowire orientation, with in-plane/out-of-plane anisotropies up to 3%. We also found that for zinc-blende nanowires the extrinsic spin-orbit coupling is dominant over the intrinsic one whereas, for wurztize, the opposite behavior holds. In order to assess if the nanowires could host the aforementioned Majorana zero modes we investigate under which circumstances the topological phase transition occurs, using the Bogoliubov-de Gennes formalism to couple the nanowire with a superconductor, and we found that using realistic and experimental feasible parameters, indeed, the phase transition occurs. In conclusion, our systematic investigation of nanowires shows that the spin-orbit coupling energy can be fine tuned by the external electric field in experimentally achievable setups that ultimately could guide the search for the elusive Majorana modes. Moreover, our numerical approach is not restricted to a specific material or dimensionality and can be used to study others systems to provide useful insights into the electronic and spintronic fields.<br>Recentemente, fenômenos dependentes de spin em nanofios semicondutores se tornaram uma área de pesquisa ativa especialmente porque essas nanoestruturas podem ser viáveis para o estudo de estados exóticos da matéria como, por exemplo, os férmions de Majorana. Um dos ingredientes chave para que esses modos de excitação possam existir em nanofios é o acoplamento spin-órbita, o qual tem sido usualmente tratado com modelos de duas bandas. O acoplamento spin-órbita em semicondutores aparece de duas fontes distintas sendo elas a assimetria de inversão no bulk, quando a célula unitária do cristal não possui simetria de inversão, por exemplo, quando é formada por dois átomos diferentes, e a assimetria de inversão estrutural, quando o sistema como um todo não possui simetria de inversão. Para descrever o sistema, os modelos efetivos de duas bandas usam como entrada parâmetros que dependem tanto do sistema específico quanto da configuração do arranjo experimental. Apesar desses modelos terem sucesso em descrever algumas das propriedades físicas relevantes, uma descrição mais realística da interação entre as bandas de energia se faz necessária, especialmente em sistemas com confinamento quântico onde a ação combinada das duas fontes de acoplamento spin-órbita muda as propriedades do sistema de maneira não-trivial. Por exemplo, o fator giromagnético em poços quânticos é anisotrópico devido aos efeitos de ambos, confinamento quântico e a assimetria de inversão estrutural. Ademais, o fator giromagnético ao longo do plano também possui uma anisotropia, a qual tem origem no acoplamento spin-órbita intrínseco do sistema e não é capturada por esses modelos efetivos. Nesse estudo, nós usamos Hamiltonianos k · p multibanda, incluindo ambos os mecanismos de acoplamento spin-órbita, para determinar a estrutura de bandas de nanofios de InSb na fase blenda de zinco e InAs na fase wurtzita sob a ação de um campo elétrico transversal. Nós analisamos os efeitos do confinamento quântico lateral, para fios com seção transversal hexagonal, e diferentes direções de crescimento, extraindo parâmetros físicos relevantes para a primeira sub-banda de condução. Nós encontramos que os fatores giromagnéticos são fortemente influenciados pelo confinamento quântico e orientação dos nanofios, com anisotropias no plano e fora do plano de até 3%. Nós também encontramos que para nanofios de InSb na fase blenda de zinco, o acoplamento spin-órbita extrínseco domina o intrínseco enquanto que, em nanofios de InAs na fase wurtzita, vale o oposto. Para avaliar se os nanofios podem hospedar os modos de Majorana de energia zero nós investigamos sob quais circunstâncias a transição de fase topológica ocorre usando o formalismo de Bogoliubov-de Gennes para acoplar o nanofio a um supercondutor, e encontramos que usando nossos parâmetros e em condições experimentalmente factíveis, de fato, a transição de fase ocorre. Em conclusão, nossa investigação sistemática nos nanofios mostrou que o acoplamento spin-órbita pode ser ajustado por fontes externas, tais como um campo elétrico aplicado, e em configurações experimentais factíveis e que ultimamente pode guiar à busca dos elusivos modos de Majorana. Além do mais, nossa abordagem numérica não é restrita a esses materiais em específico e nem a nanofios, podendo ser usada para estudar outros sistemas provendo intuições úteis nos campos de eletrônica e spintrônica.
14
Zhou, Ying Fu. "A Study For Orbit Representation And Simplified Orbit Determination Methods." Queensland University of Technology, 2003. http://eprints.qut.edu.au/15895/.
Testo completoAbstract (sommario):
This research effort is concerned with the methods of simplified orbit determination and orbit representation and their applications for Low Earth Orbit (LEO) satellite missions, particularly addressing the operational needs of the FedSat mission. FedSat is the first Australian-built satellite in over thirty years. The microsatellite is approximately 50cm cubed with a mass of 58 kg. The satellite was successfully placed into a low-earth near-polar orbit at an altitude of 780km by the Japanese National Space Development Agency (NASDA) H-IIA launch vehicle on 14, December 2002. Since then, it has been streaming scientific data to its ground station in Adelaide almost daily. This information is used by Australian and international researchers to study space weather, to help improve the design of space computers, communication systems and other satellite technology, and for research into navigation and satellite tracking. This research effort addresses four practical issues regarding the FedSat mission and operations. First, unlike most satellite missions, the GPS receiver onboard FedSat operates in a duty-cycle mode due to the limitations of the FedSat power supply. This causes significant difficulties for orbit tracking, Precise Orbit Determination and scientific applications. A covariance analysis was performed before the mission launch to assess the orbit performance under different operational modes. The thesis presents the analysis methods and results. Second, FedSat supports Ka-band tracking experiments that require a pointing accuracy of 0.03 degree. The QUT GPS group is obligated to provide the GPS precise orbit solution to meet this requirement. Ka-band tracking requests satellite orbital position at any instant time with respect to any of the observation stations. Because orbit determination and prediction software only provide satellite orbital data at a discrete time point, it is necessary to find a way to represent the satellite orbit as a continuous trajectory with discrete observation data, able to obtain the position of the satellite at the time of interest. For this purpose, an orbit interpolation algorithm using the Chebyshev polynomial was developed and applied to Ka-band tracking applications. The thesis will describe the software and results. Third, since the launch of FedSat, investigators have received much flight GPS data. Some research was invested in the analysis of FedSat orbit performance, GPS data quality and the quality of the onboard navigation solutions. Studies have revealed that there are many gross errors in the FedSat onboard navigation solution (ONS). Although the 1-sigma accuracy of each component is about 20 m, there are more than 11 %positioning errors that fall outside +/-50m, and 5% of the errors are outside the 100mbound. The 3D RMS values would be 35m, 87m, and 173m for the above three cases respectively. The FedSat ONS uncertainties are believed to be approximately three times greater than those from other satellite missions. Due to the high percentage of outlier solutions, it would be dangerous to use these without first applying data detection and exclusion procedures. Therefore, this thesis presents two simplified orbit determination methods that can improve the ONS. One is the "geometric method", which makes use of delta-position solutions derived from carrier phase differences between two epochs to smooth the code-based navigation solutions. The algorithms were tested using SAC-C GPS data and showing some improvement. The second method is the "dynamic method", which uses orbit dynamics information for orbit improvements. Fourth, the FedSat ground tracking team at Adelaide use the NORAD TLE orbit for daily FedSat tracking. Research was undertaken to convert an orbit trajectory into these Two Line Elements (TLE). Algorithms for the estimation of TLE solutions from the FedSat onboard GPS navigation solutions are outlined. Numerical results have shown the effects of the unmodelled forces/perturbations in the SPG4 models for the FedSat orbit determination would reach a level of ±1000m. This only includes the orbit representation errors with TLE data sets. The total FedSat orbit propagation should include both the orbit propagation and orbit representation terms. The analysis also demonstrates that the orbit presentation error can be reduced to ±200m and ±100mlevels with the EGM4x4 and EGM10x10 gravity field models respectively. This can meet the requirements for Ka-band tracking. However, a simplified tracking program based on numerical integration has to be developed to replace the SPG4 models.
15
Taylor, Andrew D. "A meteor orbit radar." Thesis, University of Canterbury. Physics, 1991. http://hdl.handle.net/10092/8111.
Testo completoAbstract (sommario):
A Meteor Orbit Radar, AMOR, has been built near Christchurch, New Zealand. It uses a narrow beam pulsed radar to detect meteors down to a + 12.5 radio-meteor magnitude limit. AMOR measures the relative timelags between the onset of meteor echoes at each of three spaced receiver stations to calculate the meteoroid velocity with an accuracy of ±2.5 km.s-¹ . A 'Luggable' MAC AT is used to run the radar, identify meteor echoes and record raw observation records.
A total of 1.3 X 10⁵ meteor velocities have been determined using the new timelag method. For 1.6 X 10⁴ of these observations velocity measurements could be made using Fresnel diffraction patterns and these were in complete agreement with those from the new timelag velocity technique. The diffraction patterns recorded by AMOR allow atmospheric decelerations to be determined by calculating the velocity for overlapping subsections of the patterns. Typically, the atmospheric decelerations found lay between 0 and 40 km.s-².
Observed meteor velocities need to be corrected for the presence of the Earth before a heliocentric meteoroid orbit can be calculated. AMOR uses a new vector scheme to make corrections for atmospheric deceleration, the rotation and gravitational acceleration of the Earth, conversion to a heliocentric frame using rotation matrices and a correction for the orbital velocity of the Earth. This new derivation greatly simplifies the theoretical framework for computer based calculation of meteor orbits.
The 1990 apparition of the ŋ; Aquarid meteor shower was used as a calibration test for the complete AMOR system. 270 shower meteors were detected giving a mean stream orbit with elements of q = 0.57AU, e = 0.98, i = 165.5°, w = 97°, Ω = 46°. This agrees closely with previous orbits given for the r; Aquarid stream and demonstrates the very large improvement in meteor stream characteristics that can be achieved by AMOR. Orbital elements for individual ŋ; Aquarid meteors can be determined within the following measurement limits: 0.33 < q < 0.76 AU, 0.76 < e < 1.45, 163.0° < i < 167.5°,
62° < w < 126°, 35 < Ω < 49°.
Computerised data acquisition, automated reduction to orbital elements and interactive graphical displays were developed and are a significant feature of the system. AMOR is capable of continuous unattended operation producing observation records and reduced orbital elements on site.
16
Sohier, Henri. "Modélisation, analyse et optimisation d’un largage de fusée spatiale depuis un porteur de type avion." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0044/document.
Testo completoAbstract (sommario):
Un système de lancement aéroporté est constitué d'un porteur de type avion larguant un lanceur à une certaine altitude. De tels systèmes sont l'objet d'un intérêt croissant, notamment pour la mise à poste de petits satellites. Les travaux présentés dans cette thèse s'intègrent dans le programme Perseus du CNES qui a déjà donné lieu à la construction d'un modèle réduit appelé EOLE. Il s'agit d'étudier la phase de largage, particulièrement sensible.Les contraintes de similitude pouvant permettre l'étude du largage taille réelle avec EOLE sont d'abord identifiées. Les possibilités d'extrapolation directe et déterministe des mesures réalisées avec EOLE étant limitées par le non respect d'une contrainte de masse, il est choisi d'étudier le largage avec une approche probabiliste en développant un nouveau modèle multi-corps. Une grande variété d'incertitudes est prise en compte, concernant par exemple aussi bien les interactions aérodynamiques que le mécanisme de séparation. Un nouveau critère de performance générique,basé sur des géométries élémentaires, est développé pour évaluer la fiabilité du largage.L'analyse de sensibilité du largage aux facteurs d'incertitude est ensuite réalisée. Compte tenu du nombre élevé de paramètres en jeu et du temps de simulation, il est d'abord recherché une simplification du modèle. La méthode de Morris est utilisée pour identifier des facteurs d'incertitude peu influents pouvant être fixés à une certaine valeur. Cette étape est fréquente, mais il est montré qu'il existe un risque important de fixer des facteurs dont l'influence a en fait été sous-estimée. Une adaptation de la méthode de Morris améliorant l'échantillonnage des facteurs, le calcul de leurs influences et le traitement statistique des résultats permet de réduire considérablement ce risque.Une fois l'impact des différentes incertitudes estimé, il a été possible d'optimiser les conditions de largage afin de réduire la probabilité qu'un problème intervienne<br>In an air launch to orbit, a space rocket is launched from a carrier aircraft. Air launchto orbit appears as particularly interesting for small satellites. This Ph.D. thesis is part of the program Pegasus of the French space agency CNES and it follows the development of a small scale demonstrator called EOLE. It focuses on the very sensitive separation phase.The similitude constraints which have to be respected to study the large scale system with EOLEare first identified. A problem of mass limits the possibilities to directly extrapolate at a larger scale, in a deterministic approach, data obtained with EOLE. It is decided to study the separation in a probabilistic approach by developing a new multi-body model. A great variety of uncertainties are taken into account, from the aerodynamic interactions to the atmospheric turbulences, the separation mechanism, and the launch trajectories. A new performance criterion is developed to quantify the safety of the separation phase. It is based on elementary geometries and it could beused in other contexts.A sensitivity analysis is applied to estimate the influence of the uncertainties on the performance criterion. Given the large number of factors of uncertainty and the non-negligible simulation time,the model is first simplified. The Morris method is applied to identify the factors with a low influence which can be fixed to a given value. It is a frequent step, but it is shown that there isa high risk to fix the wrong factors. Any further study would then be altered. The risk to fix the wrong factors is significantly reduced by improving the factors sampling, the calculation of their influence, and the statistical treatment of the results. This new method is used to estimate the influence of the uncertainties at the separation and the safety is improved by optimizing launch trajectories
17
Forward, Michael. "The complex Lorenz equations and orbit following methods." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47438.
Testo completo
18
Griffith, Daniel Todd. "New methods for estimation, modeling and validation of dynamical systems using automatic differentiation." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1408.
Testo completoAbstract (sommario):
The main objective of this work is to demonstrate some new computational methods
for estimation, optimization and modeling of dynamical systems that use automatic
differentiation. Particular focus will be upon dynamical systems arising in Aerospace
Engineering. Automatic differentiation is a recursive computational algorithm, which
enables computation of analytically rigorous partial derivatives of any user-specified
function. All associated computations occur, in the background without user
intervention, as the name implies. The computational methods of this dissertation are
enabled by a new automatic differentiation tool, OCEA (Object oriented Coordinate
Embedding Method). OCEA has been recently developed and makes possible efficient
computation and evaluation of partial derivatives with minimal user coding. The key
results in this dissertation details the use of OCEA through a number of computational
studies in estimation and dynamical modeling.
Several prototype problems are studied in order to evaluate judicious ways to use
OCEA. Additionally, new solution methods are introduced in order to ascertain the
extended capability of this new computational tool. Computational tradeoffs are studied
in detail by looking at a number of different applications in the areas of estimation,
dynamical system modeling, and validation of solution accuracy for complex dynamical
systems. The results of these computational studies provide new insights and indicate
the future potential of OCEA in its further development.
19
Farhat, Ayman. "Calculs théoriques avec le couplage spin orbitales pour les molécules diatomiques YS, YN, ZrS, et ZrN." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10078/document.
Testo completoAbstract (sommario):
Cette thèse est consacrée à l'étude ab initio des structures électroniques des molécules diatomiques polaires YN, YS, ZrN, et ZrS. Cette étude est motivé par le manque d’informations dans la littérature sur la structure électronique de ces molécules, alors qu’elles ont clairement été identifiées dans le spectre de certaines étoiles. Des calculs théoriques sont ainsi nécessaire puisqu’ils peuvent fournir d'importantes informations quant aux propriétés des états électroniques fondamentaux et excités qui ne sont pas accessibles expérimentalement. Dans ce travail les calculs ab initio ont été effectués par la méthode du champ auto-cohérent de l'espace actif complet (CASSCF), suivie par l'interaction de configuration multiréférence (MRSDCI). La correction de Davidson, notée (MRSDCI+ Q), a ensuite été appliquée pour rendre compte de clusters ou agrégats quadruples non liés. Les calculs ont été effectués selon deux schémas. Dans le premier les effets spin-orbite ont été négligés alors que dans le second les effets spin orbite ont été inclus par la méthode des potentiels de noyau efficaces. Tous les calculs ont été effectués en utilisant le programme de calcul de chimie physique MOLPRO et en tirant parti de l’interface graphique Gabedit. Les courbes d'énergie potentielle ont été construites et des constantes spectroscopiques calculées, ainsi que les moments dipolaires électriques permanent, les champs électriques moléculaires intenses et les structures énergétiques de vibration-rotation. Nous avons détecté dans la molécule ZrS plusieurs niveaux vibrationnels dégénérés ceux-ci peuvent être utilisés pour rechercher les variantes possibles de la constante de structure fine α etdu rapport de masse μ de l’electron par rapport au proton dans trois étoiles de type S, du nomde Rand, les RCas, et χCyg. La comparaison des données expérimentales et théoriques pour la plupart des constantes calculées a montré une bonne précision pour nos prédictions avec une différence relative (en pourcentage) qui varie entre 0,1% et 10%. Ces résultats devraient ainsi mener à des études expérimentales plus poussées pour ces molécules<br>This dissertation is dedicated to the ab initio study of the electronic structures of the polardiatomic molecules YN, YS, ZrN, and ZrS. The identification of these molecules in the spectraof stars as well as the lack in literature on the electronic structures of these molecules motivatedthe present study. Theoretical calculations are useful in this respect since they can provideimportant data for the properties of the ground and excited electronic states that are not availablefrom experimental means. In the present work the ab initio calculations were performed at thecomplete active space self-consistent field method (CASSCF) followed by multireference singleand double configuration interaction method (MRSDCI). The Davidson correction noted as(MRSDCI+Q) was then invoked in order to account for unlinked quadruple clusters. Thecalculations were performed on two stages in the first spin orbit effects were neglected while inthe second type of calculations spin orbit effects were included by the method of effective corepotentials. All of the calculations were done by using the computational physical chemistryprogram MOLPRO and by taking advantage of the graphical user interface Gabedit. In thepresent work potential energy curves were constructed and spectroscopic constants computed,along with permanent electric dipole moments, internal molecular electric fields, and vibrationalrotationalenergy structures. We detected in the ZrS molecule several degenerate vibrationalenergy levels which can be used to search for possible variations of the fine structure constant αand the electron to proton mass ratio μ in three S-type stars, named Rand, RCas, and χCyg. Acomparison with experimental and theoretical data for most of the calculated constantsdemonstrated a good accuracy for our predictions giving a percentage relative difference thatranged between 0.1% and 10%. Finally, we expect that the results of the present work shouldinvoke further experimental investigations for these molecules
20
García, Taberner Laura. "Proximity maneuvering of libration point orbit formations using adapted finite element methods." Doctoral thesis, Universitat Politècnica de Catalunya, 2010. http://hdl.handle.net/10803/78047.
Testo completoAbstract (sommario):
This doctoral dissertation is structured in four chapters as follows. The first chapter contains a summary of formation flying projects that have been taken into consideration since few years ago. We specially focus on the missions that have been planned to be located in a libration point regime. For completeness, this chapter also contains a general state of the art about the main reconfiguration techniques for satellite formations.
The main new contributions of the thesis are contained in chapters 2, 3 and 4. Chapter 2 introduces the general methodology that will be considered in all the dissertation. It is based on a discretization in time by means of a finite element approximation, and at the same time, is suitable to incorporate optimal control problems. In this chapter we study the reconfigurations using linearized equations about a nominal Halo orbit minimizing the functional given by the sum of the square of the magnitude of the maneuvers. This functional is not directly related to the fuel consumption, but has good properties concerning minimization and regularity.
In chapter 3 we are still working with the linearized model about the nonlinear orbit, but the functional that we optimize, given by the sum of the modulus of the maneuvers, is directly related to fuel consumption. As a consequence, the methodology can be tuned in such a way that, if possible, the user can choose to converge to bang-bang optimal controls (when possible) or to low thrust trajectories in general situations.
In this chapter, our objective is not only to study how the reconfigurations can be accomplished. We also consider the problem of obtaining good meshes for our finite element discretization, and up to a certain extent, to decide which is the best mesh for each kind of problem.
Finally, in chapter 4, we deal with non-linear and perturbed problems. In a first step we consider reconfigurations in the Restricted Three Body Problem and in a second one with JPL ephemeris. This fact slightly changes the trajectories of the spacecraft with respect to the ones obtained in the previous chapters. To correct for such deviations we design and implement a methodology based on adding small corrective maneuvers on top of the
nominal ones. We also study the magnitude of corrective maneuvers that will need to be applied in case of errors in the execution of the nominal ones. Finally, this chapter ends with some other applications that can be performed using the methodology we have developed.<br>Aquesta tesi doctoral està estructurada en quatre capítols. El primer capítol comprèn un resum dels projectes de vol en formació que s'han tingut en consideració els últims anys, especialment els que estan planejats de situar-se al voltant dels punts de libració. En aquest capítol també fem un estat de l'art de les principals tècniques de reconfiguració de formacions de satèl•lits.
Les principals contribucions noves d'aquesta tesi es troben als capítols 2, 3 i 4. En el capítol 2 introduïm la metodologia general que s'utilitzarà en tota la dissertació. Aquesta metodologia està basada en una discretització del temps usant una aproximació en elements finits, que al mateix temps la fa factible d'incorporar en problemes d'optimització. En aquest capítol es consideren les equacions linealitzades al voltant d'una òrbita Halo. El problema d'optimització minimitza el funcional obtingut per la suma dels quadrats de les maniobres. Encara que aquest funcional no estigui directament relacionat amb el consum de combustible, es comporta bé a l'hora de minimitzar.
En el capítol 3 es segueixen utilitzant les equacions linealitzades al voltant de l'òrbita Halo, però ara el funcional que es minimitza és la suma dels mòduls de les maniobres, que està directament relacionat amb el consum de combustible. Com a conseqüència, la metodologia permet que es pugui convergir a controls bang-bang en el cas que sigui possible, o a avanç continu en les altres situacions.
En aquest capítol, el nostre objectiu no consisteix només en estudiar com fer les reconfiguracions, sinó que també considerem el problema d'obtenir una bona discretització per al nostre problema d'elements finits, i decidir quina és la millor malla per cada tipus de problema.
Finalment, al capítol 4 considerem problemes no lineals i incloem perturbacions. Comencem considerant les reconfiguracions en el problema restringit de tres cossos, per després veure com es comporta usant les efemèrides JPL. Aquests nous models canvien una mica les trajectòries dels satèl•lits respecte les que havíem obtingut en els capítols anteriors. Per corregir aquestes desviacions implementem una metodologia basada en afegir petites
correccions a les maniobres que estan donades. També estudiem la magnitud de les maniobres que cal aplicar quan es produeixen errors d'execució en les maniobres nominals. Finalment, aquest capítol acaba amb altres aplicacions que es poden dur a terme usant la metodologia que hem desenvolupat.<br>Esta tesis doctoral está estructurada en cuatro capítulos. El primer capítulo contiene un resumen de los proyectos de vuelo en formación que se han tenido en consideración en los últimos años, especialmente aquellos que están planeados de situarse alrededor de los puntos de libración. En este capítulo también se hace un estado del arte de las principales técnicas de reconfiguración de formaciones de satélites.Las principales contribuciones nuevas de esta tesis se encuentran en los capítulos 2, 3 y 4. En el capítulo 2 introducimos la metodología general que se usará en toda la disertación. Esta metodología está basada en una discretización del tiempo usando una aproximación en elementos finitos, que al mismo tiempo la hace factible de incorporar en problemas de optimización. En este capítulo, se consideran las ecuaciones linealizadas alrededor de una órbita Halo. El problema de optimización minimiza el funcional obtenido como la suma de los cuadrados de las maniobras. Aunque este funcional no está directamente relacionado con el consumo de combustible, tiene un buen comportamiento en la minimización.En el capítulo 3 se siguen usando las ecuaciones linealizadas alrededor de la órbita Halo, pero ahora el funcional al minimizar es la suma de los módulos de las maniobras, que está directamente relacionado con el consumo de combustible. Como consecuencia, la metodología permite que se pueda convergir a controles bang-bang en el caso de que sea posible, o a avance continuo en las otras situaciones.En este capítulo, nuestro objetivo no consiste únicamente en estudiar cómo hacer las reconfiguraciones, sino que consideramos el problema de obtener una buena malla para el problema de los elementos finitos, y decidir cuál es la mejor malla para cada tipo de problema.Finalmente, en el capítulo 4 se consideran problemas no lineales y se incluyen perturbaciones. Empezamos considerando las reconfiguraciones en el problema restringido de 3 cuerpos, y luego observamos qué pasa cuando usamos las efemérides JPL. Estos nuevos modelos cambian un poco las trayectorias de los satélites respecto las obtenidas en los capítulos anteriores. Para corregir estas desviaciones, se implementa una metodología basada en añadir pequeñas correcciones a las maniobras dadas. También estudiamos la magnitud de las maniobras que hace falta aplicar cuando se producen errores de ejecución en las maniobras nominales. Para finalizar, este capítulo acaba con otras aplicaciones que se pueden llevar a término con la metodología desarrollada.
21
Chung, Lauren Rose. "Orbit determination methods for deep space drag-free controlled laser interferometry missions." College Park, Md.: University of Maryland, 2006. http://hdl.handle.net/1903/3572.
Testo completoAbstract (sommario):
Thesis (M.S.) -- University of Maryland, College Park, 2006.<br>Thesis research directed by: Dept. of Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
22
Mohan, Swati. "Reconfiguration methods for on-orbit servicing, assembly, and operations with application to space telescopes." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39706.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.<br>Includes bibliographical references (p. 115-118).<br>Reconfiguration is an important characteristic in furthering on-orbit servicing, assembly, and operations. Previous work has focused on large assemblers manipulating small payloads, where the dynamics of the assembler is not significantly changed. This work seeks to identify the impact of reconfiguration on maneuver performance. Reconfiguration is considered in two categories: implementation and application. Implementation of reconfiguration consisted of developing a method for defining and updating a configuration, implementation on the SPHERES testbed, and execution of tests (in simulation and on the International Space Station) to assess the control performance improvement after reconfiguration. Four applications were considered in this work, two hardware applications and two systems applications modeled through simulation. The objective of the SWARM application was to demonstrate autonomous assembly capability through docking and undocking maneuvers. The objective of the SIFFT application was to demonstrate formation reconfiguration capability, through the expansion and rotation of an equilateral triangle of three satellites. The objective of the systems applications was to determine the impact of re-configuration in a larger mission context.<br>(cont.) One application, Mass Property Update, considered how the choice of method for obtaining the mass property information impacts operations. The other application, Modularity Analysis, considered how the implementation of modularity is driven by the mission objectives. Overall, this work has served to demonstrate the control impact of reconfiguration though implementation on the SPHERES testbed. This implementation was used on two hardware applications to determine the performance of reconfiguration for assembly and formation reconfiguration missions. Also, the impact of reconfiguration has been studied in the broader systems context. The choice of method of mass property update was demonstrated to have an impact on operations, in terms of reliability and mass. Finally, the method incorporation of modularity for purposes of on-orbit servicing and assembly was demonstrated to be driven by mission design parameters.<br>by Swati Mohan.<br>S.M.
23
Crofts, Jonathan J. "Efficient method for detection of periodic orbits in chaotic maps and flows." Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/30535.
Testo completoAbstract (sommario):
An algorithm for detecting unstable periodic orbits in chaotic systems [Phys. Rev. E, 60 (1999), pp. 6172-6175] which combines the set of stabilising transformations proposed by Schmelcher and Diakonos [Phys. Rev. Lett., 78 (1997), pp. 4733-4736] with a modified semi-implicit Euler iterative scheme and seeding with periodic orbits of neighbouring periods, has been shown to be highly efficient when applied to low-dimensional system. The difficulty in applying the algorithm to higher dimensional systems is mainly due to the fact that the number of stabilising transformations grows extremely fast with increasing system dimension. in this thesis, we propose to construct stabilising transformations based on the knowledge of the stability matrices of already detected periodic orbits (used as seeds). The advantage of our approach is in a substantial reduction of the number of transformations, which increases the efficiency of the detection algorithm, especially in the case of high-dimensional systems. The dependence of the number of transformations on the dimensionality of the unstable manifold rather than on system size enables us to apply, for the first time, the method of stabilising transformations to high-dimensional systems. Another important aspect of our treatment of high-dimensional flows is that we do not restrict to a Poincare surface of section. This is a particularly nice feature, since the correct placement of such a section in a high-dimensional phase space is a challenging problem in itself. The performance of the new approach is illustrated by its application to the four-dimensional kicked double rotor map, a six-dimensional system of three coupled Henon maps and to the Kuramoto-Sivashinsky system in the weakly turbulent regime.
24
Angstmann, Christopher N. Physics Faculty of Science UNSW. "Deterministic and associated stochastic methods for dynamical systems." Publisher:University of New South Wales. Physics, 2009. http://handle.unsw.edu.au/1959.4/44401.
Testo completoAbstract (sommario):
An introduction to periodic orbit techniques for deterministic dynamical systems is presented. The Farey map is considered as examples of intermittency in one-dimensional maps. The effect of intermittency on the Markov partition is considered. The Gauss map is shown to be related to the farey map by a simple transformation of trajectories. A method of calculating periodic orbits in the thermostated Lorentz gas is derived. This method relies on minimising the action from the Hamiltonian description of the Lorentz gas, as well as the construction of a generating partition of the phase space. This method is employed to examine a range of bifurcation processes in the Lorentz gas. A novel construction of the Sinai billiard is performed by using symmetry arguments to reduce two particles in a hard walled box to the square Sinai billiard. Infinite families of periodic orbits are found, even at the lowest order, due to the intermittency of the system. The contribution of these orbits is examined and found to be tractable at the lowest order. The number of orbits grows too quickly for consideration of any other terms in the periodic orbit expansion. A simple stochastic model for the diffusion in the Lorentz gas was constructed. The model produced a diffusion coefficient that was a remarkably good fit to more precise numerical calculations. This is a significant improvement to the Machta-Zwanzig approximation for the diffusion coefficient. We outline a general approach to constructing stochastic models of deterministic dynamical systems. This method should allow for calculations to be performed in more complicated systems.
25
Li, Yanlin. "A STUDY ON METEOR ECHOES USING THE ARECIBO AND JICAMARCA HIGH POWER LARGE APERTURE RADARS." Miami University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=miami1547218801600341.
Testo completo
26
Miller, Grant Robert MacKinnon. "In the shadows of giants : a tomographic method for analysing the orbits of transiting exoplanets." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3735.
Testo completoAbstract (sommario):
The radial velocity anomaly which affects spectroscopic observations of stars undergoing transit by a companion body is known as the Rossiter-McLaughlin effect. This effect can be used to measure the obliquities of the orbits of transiting planets. In this thesis I present a tomographic method for analysing the effect, which manifests itself in stellar spectral line-profiles. I implement this method on seven systems known to host transiting planets, and some systems with early-type host stars, for which the transit events have not yet been shown to be the result of planetary companions. Despite being well-suited to examining systems with early-type, rapidly-rotating host stars which have a more pronounced Rossiter-McLaughlin effect, I find the tomographic method is able to produce reasonable results for the system parameters of planets orbiting relatively slowly-rotating stars. I show that the method provides a significant increase in the accuracy of determinations of the stellar rotation rate and is able to better constrain values for the transit impact parameter. Though I do not confirm the existence of any new planets around early-type stars, I do use the tomographic method to reject one candidate as a stellar eclipsing binary system, and also reveal that one of the candidate host stars is a non-radial pulsator. I show that the method is able to examine systems involving stars with a range of spectral types and rotation rates.
27
Alinder, Simon. "Space Situational Awareness with the Swedish Allsky Meteor Network." Thesis, Uppsala universitet, Observationell astrofysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-390397.
Testo completoAbstract (sommario):
This thesis investigates the use of the Swedish Allsky Meteor Network (SAMN) for observing, identifying, and determining the orbits of satellites. The overall goal of this project is to determine the feasibility of using such a network for Space Situational Awareness (SSA) purposes, which requires identification and monitoring of objects in orbit. This thesis is a collaboration with the Swedish Defense Research Agency (FOI) to support their efforts in SSA. Within the frame of this project, the author developed software that can take data of observations of an object collected from the all-sky cameras of SAMN and do an Initial Orbit Determination (IOD) of the object. An algorithm that improves the results of the IOD was developed and integrated into the software. The software can also identify the object if it is in a database that the program has access to or, if it could not be identified, make an approximate prediction of when and where the object will be visible again the next time it flies over. A program that analyses the stability of the results of the IOD was also developed. This measures the spread in results of the IOD when a small amount of artificial noise is added to one or more of the observed coordinates in the sky. It was found that using multiple cameras at different locations greatly improves the stability of the solutions. Gauss' method was used for doing the IODs. The advantages and disadvantages of using this method are discussed, and ultimately other methods, such as the Gooding method or Double R iteration, are recommended for future works. This is mostly because Gauss' method has a singularity when all three lines of sight from observer to object lie in the same plane, which makes the results unreliable. The software was tested on a number of observations, both synthetic and real, and the results were compared against known data from public databases. It was found that these techniques can, with some changes, be used for doing IOD and satellite identification, but that doing very accurate position determination required for full orbit determination is not feasible.<br>Detta examensarbete undersöker möjligheterna att använda ett svenskt nätverk av allskykameror kallat SAMN (Swedish Allsky Meteor Network) för att observera, identifiera och banbestämma satelliter. Det övergripande målet med detta projekt är att bestämma hur användbart ett sådant nätverk skulle vara för att skapa en rymdlägesbild, vilken i sin tur kräver bevakning och identifikation av objekt som ligger i omloppsbana. Detta examensarbete är ett samarbete mellan Uppsala Universitet och FOI (Totalförsvarets Forskningsinstitut). Inom ramen för detta projekt har författaren utvecklat mjukvara som kan ta data från observationer av objekt utförda av SAMN och göra initiala banbestämningar av objekten. En algoritm som förbättrar resultaten av den initiala banbestämningen utvecklades och integrerades i programmen. Programmen kan också identifiera satelliter om de finns med i en databas som programmet har tillgång till eller förutsäga objektets nästa passage över observatören om det inte kunde identifieras. Ett annat program som analyserar känsligheten av resultaten av den initiala banbestämningen utvecklades också. Detta program mäter spridningen i resultat som orsakas av små störningar i de observerade koordinaterna på himlen. Det framkom att stabiliteten av resultaten kan förbättras avsevärt genom att använda flera observatörer på olika orter. I detta projekt användes Gauss metod för att göra banbestämningarna. Metodens för- och nackdelar diskuteras och i slutänden rekommenderas istället andra metoder, som Goodings metod eller Dubbel R-iteration, för framtida arbeten. Detta beror mest på att Gauss metod innehåller en singularitet när alla siktlinjer från observatören till objektet ligger i samma plan som varandra vilket gör resultaten opålitliga i de fallen. Programmen testkördes på ett antal olika observationer, både artificiella och verkliga, och resultaten jämfördes med kända positioner. Slutsatsen av arbetet är att de undersökta teknikerna kan, med vissa modifikationer, användas för att göra initiala banbestämningar och satellitidentifikationer, men att göra de väldigt precisa positionsbestämningarna som krävs för fullständig banbestämning är inte genomförbart.
28
Robertson, Erika Marie. "Experimental methods to examine the role of vibrational excitation in the singlet-triplet spin-orbit coupling in acetylene." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57774.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 46-49).<br>Despite being a seemingly simple molecule, acetylene has a complicated electronic structure that has been studied extensively both experimentally and theoretically. Acetylene has been observed to have a complex spin-orbit coupling mechanism where the first excited singlet state S couples to the triplet state T3 which is then coupled to the dense manifold of vibrational states in the T, 2 electronic states. A description of theories imperative to this study is provided and each is related to its application in experiment. A description of how to obtain important parameters in the coupling, such as the coupling strength, the singlet-triplet mixing fraction, the radiative lifetime, and the relative energy ordering and separation between the singlet and coupled triplet, is given. Finally, key vibrational levels of interest that should be investigated are described.<br>by Erika Marie Robertson.<br>S.M.
29
Soja, Rachel Halina. "Dynamics of the Solar System Meteoroid Population." Thesis, University of Canterbury. Department of Physics and Astronomy, 2010. http://hdl.handle.net/10092/4305.
Testo completoAbstract (sommario):
The purpose of this study is to develop an understanding of the observability of small-scale dynamical Solar System features in meteor orbit radar data, particularly with reference to mean motion resonance effects. Particular focus is placed on the presence of `resonant swarms' in meteoroid streams: the resonant swarm at the 7:2 Jovian mean-motion resonance is used as an example, as it best satisfies radar observability criterion. Furthermore, evidence for this structure exists in visual meteor data. The radar dataset used for this study is that of the Canadian Meteor Orbit Radar (CMOR) as this dataset contains the largest number of meteoroid stream particles. The aim here is to determine whether the Taurid resonant swarm is observable in datasets produced by radars such as CMOR, or what improvements in individual orbital uncertainties are necessary for positive detection to be possible.
The observability of the Taurid swarm in radar data depends on the limitations of the radar data (in terms of the individual measurement uncertainties); and on the properties of the resonance itself. Both aspects are investigated in this thesis. A statistical study is first conducted to assess whether evidence for the swarm exists in a dataset containing CMOR Northern and Southern Taurids from the years 2002 to 2007. It is found that the level of variations present is consistent with that expected due to random fluctuations: there is no evidence for a statistically significant resonant feature at the location of the 7:2 Jovian resonance. Additionally, the observability of various sizes of resonant peak for different sizes of dataset and for different levels of measurement uncertainties is investigated by addition of a modelled resonant feature to the data, followed by replacement of individual meteors by Gaussian profiles to simulate the effect of orbital uncertainties. It is clear that the level of broadening resulting from the uncertainties of the CMOR data used will not allow the observation of a resonant peak of the expected size. Detection is expected to be more likely in a `swarm encounter year' (a year in which the geometry between the resonant swarm and Earth is favourable to detection). The velocity uncertainties of a meteor orbit radar (similar to CMOR) need to be improved by a factor of 5 to 10 (relative to the CMOR uncertainties) in order to detect a resonant swarm that is composed of ~30% to ~5% (respectively) of the total number of observed Taurids in a swarm encounter year. An improvement significantly greater than a factor of ~10 is unlikely to result in a significant improvement in the ability to detect the resonant swarm. It is expected that a factor of 10 improvement in radar measurement uncertainties is achievable with the current techniques of radar systems and signal processing.
These statistical tests require knowledge of the resonant width of the 7:2 Jovian resonance in semi-major axis, as this provides the size of the resonant feature of interest. Such resonant or libration widths can be determined analytically for orbits with low eccentricities. As Taurid orbits have high eccentricities (e~0.83), a hierarchical N-body integrator is used to examine the dynamics in the region of the 7:2 resonance, and determine a resonant width of (0.047±0.005) AU. To verify this method the standard analytic equations and a semi-analytic method are compared (at low eccentricities) with the numerical resonant width values: the agreement is within 10% for eccentricities below 0.4.
It is important to know what proportion of radar Taurids are expected to be resonant in a swarm year in order to evaluate the observability of the swarm in radar data. One important factor that may affect this is the mass distribution of particles in the swarm. This is investigated by ejecting particles in multiple directions from three model comets: the first with a mass and orbit in agreement with those of the current 2P/Encke; the second with 2P/Encke mass and an orbit matching that of the proposed proto-Encke object; and a third with the mass and orbit of proto-Encke. The resulting orbits are examined to determine what proportion will land within the 7:2 resonance, for a range of particle masses and densities. The instantaneous effect of radiation pressure on the orbits of ejected particles is also considered. However, it is difficult to determine accurate capture percentage values due to the uncertainty surrounding cometary ejection mechanisms. Nevertheless, it is found that capture of Taurids into the 7:2 resonance by all comets is possible. Using comparisons between the percentages of visual-sized and radar-sized particles captured, it is determined that in weak swarm years (in which only 20% of visual meteoroids detected are resonant) only 4% to 5% of observed visual Taurids are expected to be resonant. Such a swarm would be on the edge of observability. However, in stronger swarm years (such as 2005), the resonant proportion will exceed that required for detection with a reduction in CMOR measurement uncertainties of a factor of ten.
30
Heinze, Martin. "Spectrum and quantum symmetries of the AdS5 × S5 superstring." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17257.
Testo completoAbstract (sommario):
Die AdS/CFT-Dualität zwischen N=4 SYM und dem AdS_5 × S^5 Superstring zeigt Quanten-Integrabilität im planaren Limes und erlaubte die Konstruktion mächtiger Methoden, welche das Spektrale Problem zu lösen scheinen. Unser Verständnis der direkten Quantisierung des AdS_5 × S^5 Superstrings ist jedoch weiterhin unbefriedigend und besonders das Spektrum kurzer Stringzustände war bisher nur in führender Ordnung in starker ''t Hooft-Kopplung bekannt. In dieser Arbeit untersuchen wir verschiedene Methoden der perturbativen Quantisierung kurzer Strings über die führende Ordnung hinaus, wodurch wir uns auch einen besseres Verständnis der vorhandenen Quanten-Symmetrien erhoffen. Wir fokusieren auf die niedrigst angeregten Stringzustände, dual zum Konishi-Supermultiplet, und begutachten kritisch eine angeblichen Berechnung der Konishi anomalen Skalendimension im Pure-Spinor-Superstring-Formalismus. Als nächstes betrachten wir den bosonischen AdS_5 × S^5 String in statischer Eichung und konstruieren eine sog. Einzelmoden-Stringlösung, eine Veralgemeinerung des pulsierenden Strings durch unbeschränkte Nullmoden. Diese ist klassisch integrabel und quanteninvariant unter den Isometrien SO(2,4) × SO(6). Mögliche Korrekturen der vernachlässigten Supersymmetrie werden heuristisch berücksichtigt, wodurch die ersten Quantenkorrekturen der Konishi anomale Skalendimension reproduzieren werden. Wir implementieren statische Eichung für den AdS_5 × S^5 Superstring und finden elegante Ausdrücke für die Lagrangedichte und Superladungen. Unter Beschränkung auf das Superteilchen finden wir auf zwei unterschiedliche Arten kanonische Koordinaten in quadratischer Ordnung in Fermionen. Schließlich betrachten wir eine weitere Quantisierungsmethode: Da der Einzelmoden-String die SO(2,4) × SO(6)-Bahn des pulsierenden Strings ist, wenden wir Bahn-Methoden-Quantisierung auf das Teilchen und Spinning Strings in bosonischem AdS_3 × S^3 an und erhalten konsistente Ergebnisse für die Spektra.<br>The initial AdS/CFT duality pair, the duality between N=4 SYM and the AdS_5 × S^5 superstring, appears to enjoy quantum integrability in the planar limit, which allowed to devise powerful methods ostensibly solving the spectral problem. However, quantization of the AdS_5 × S^5 superstring from first principles is still an open question and especially the spectrum of short string states has previously been derived only at leading order in large ''t Hooft coupling. In this thesis we investigate possible routes to quantize short string states perturbatively beyond the leading order, where equally our aim is to gain better appreciation of the quantum symmetries at play. A prominent role is played by the lowest excited string states, dual to the Konishi supermultiplet, and we start by reviewing critically an asserted derivation of the Konishi anomalous dimension in the setup of pure spinor string theory. Next, we constrain ourselves to bosonic AdS_5 × S^5 String in static gauge, where we construct a so-called single-mode string solution, a generalization of the pulsating string allowing for unconstrained zero-modes. This solution shows classical integrability and invariance under the isometries SO(2,4) × SO(6) at the quantum level. Arguing heuristically about the effects of supersymmetry, we indeed recover the first non-trivial quantum correction to the Konishi anomalous dimension. We continue by implementing static gauge for the full AdS_5 × S^5 superstring and find elegant expressions for the Lagrangian density and the supercharges. We then constrain our interest to the superparticle and, using two different methods, find canonical coordinates at quadratic order in fermions. We conclude by exploring another quantization scheme: As the single-mode string is nothing but the SO(2,4) × SO(6) orbit of the pulsating string, we apply orbit method quantization to the particle and spinning string solutions in bosonic AdS_3 × S^3 yielding consistent results for the spectra.
31
Dias, Mariama Rebello de Sousa. "Transport phenomena in quasi-one-dimensional heterostructures." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/4973.
Testo completoAbstract (sommario):
Made available in DSpace on 2016-06-02T20:15:31Z (GMT). No. of bitstreams: 1
5844.pdf: 11430873 bytes, checksum: b80a5790a9ebf6ae63ff48e52968ae60 (MD5)
Previous issue date: 2014-02-21<br>Universidade Federal de Sao Carlos<br>O crescimento e caracterização de sistemas de heteroestruturas semicondutoras quasi-unidimensionais têm atraído grande interesse devido à sua potencial de aplicação tecnológica, como foto-detectores, dispositivos opto-eletrônicos assim como seu para o processamento de informação quântica e aplicações em fotônica. O objetivo desta tese é o estudo das propriedades de transporte eletrônico e de spin em sistemas semicondutores quasi-unidimensionais, especificamente trataremos de nanofios (NWs) homogêneos, NWs acoplados, NWs do tipo plano-geminado (TP), diodos de tunelamento ressonante (ETD) e cadeias de pontos quânticos (QDCS). Escolhemos o método k-p, particularmente o Hamiltoniano de Luttinger, para descrever os efeitos de confinamento e tensão biaxial. Este sugeriu uma modulação do caráter do estado fundamental que, complementada com a dinâmica fônons fornecidas pelas simulações da Dinâmica Molecular (MD), permitiu a descrição da modulação da mobilidade de buracos por emissão ou absorção de fônons. Em relação ao sistema de NWs acoplado,estudamos, através do método da matriz de transferência (TMM), as propriedades de transporte de elétrons e spin sob a interação de spin-órbita (SOI) de Eashba, localizada na região de acoplamento entre fios. Foram consideradas várias configurações de tensões de gate (Vg) aplicadas nos fios. Desse modo, compreendemos a modulação do transporte de spin quando esse é projetado no direção-z através da combinação do SOI e das dimensionalidades do sistema. Da mesma forma, a combinação de SOI e da Vg aplicada deu origem a modulação da polarização, quando o spin medido é projetado na mesma direção em que o SOI de Eashba atua, a direção y. Usando o TMM, exploramos as propriedades de transporte de um DBS e o efeito de uma resistência em série com o intuito de provar a natureza da biestabilidade das curvas características I V bem como o aumento de sua área com temperatura, resultados fornecidos por experimentos. O modelo indicou que aumentando da resistência pela diminuição sa temperatura aumenta a área biestável. A presença de uma hetero-junção adicional ao sistema induz uma densidade de carga nas suas interfaces. De acordo com esta configuração, a queda de tensão total do ETDS muda, podendo ser confirmada experimentalmente. A formação dos peculiares campos de deformação e sua influência sobre a estrutura eletrônicas e propriedades de transporte em superredes de TP foi estudada sistematicamente. Assim, as propriedades de transporte, de ambos os elétrons e buracos, pode ser sintonizada eficientemente, mesmo no caso de elétrons r em sistemas de blenda de zinco, contrastando com a prevista transparência de elétrons r em superredes de semicondutores III-V heteroestruturados. Além disso, constatamos que a probabilidade de transmissão para buracos da banda de valência também poderia ser efetivamente modificada através de uma tensão externa.Por fim, colaboradores sintetizaram com sucesso sistemas de QDCs de InGaAs através da epitaxia de feixe molecular e engenharia de tensão. Um comportamento anisotrópico da condutância com a temperatura foi observado em QDCs com diferentes concentrações de dopagem, medida realizada ao longo e entre os QDCs. O modelo teórico 1D de hoppíng desenvolvido mostrou que a presença de estados OD modela a resposta anisotrópica da condutância neste sistemas.<br>The growth and characterization of semiconductor quasi-one-dimensional heterostructure systems have attracted increasing interest due to their potential technological application, like photo-detectors, optoelectronic devices and their promising features for quantum information processing and photonic applications. The goal of this thesis is the study of electronic and spin transport properties on quasi-one-dimensional semiconductor systems; specifically, homogenous nanowires (NWs), coupled NW s, twin-plane (TP) NWs, resonant tunneling diodes (RTDs), and quantum dot chains (QDCs). The k-p method, in particular the Luttinger Hamiltonian, was chosen to describe the effects of biaxial confinement and strain. This suggested a modulation of the ground state character that, complemented with the phonon dynamics provided by Molecular Dynamics (MD) simulations, allowed the description of the hole mobility modulation by either phonon emission or absorption. Regarding the coupled NW s system, the electron and spin transport properties affected by a Rashba spin-orbit interaction (SOI) at the joined region were unveiled through the Transfer Matrix Method (TMM). Various configurations of gate voltages (Vg), applied on the wire structure, were considered. We were able to understand the modulation of the spin transport projected in the z-direction trough the combination of the SOI and the system dimensionalities. Likewise, the combination of SOI and applied Vg gave rise to a modulation of the polarization, when the measured spin is projected in the same direction where the Rashba SOI acts, the y-direction. The transport properties of a DBS and the effect of a resistance in series was explored within the TMM to prove the nature of a bistability of the I V characteristics and its enhanced area with temperature provided by the experiment. The model indicates that increasing the resistente by decreasing the temperature, the bistable area enhances. The presence of an additional heterojunction induces a sheet charge at its interfaces. Under this configuration, the total voltage drop of the RTD changes and can be confirmed experimentally.The formation of the peculiar strain fields and their influence on the electronic structure and transport properties of a TP superlattice was systematically studied. Hence, the transport properties of both electrons and holes could be effectively tuned even in the case of T-electrons of zincblende systems, contrasting to the predicted transparency of T-electrons in heterolayered III-V semiconductor superlattices. Also, the transmission probability for holes at valence band could also be effectively modified by applying an external stress. Finally, using molecular-beam-epitaxy and skillful strain engineering, systems of In-GaAs QDCs were successfully synthesized by collaborators. The QDCs with different doping concentrations showed an anisotropic behavior of the conductance, measured along and across the QDCs, with temperature. The theoretical ID hopping model developed found that the presence of OD states shapes the anisotropic response of the conductance in this system.
32
Rebaza-Vasquez, Jorge. "Computation and continuation of equilibrium-to-periodic and periodic-to-periodic connections." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/28991.
Testo completo
33
Mück, Leonie Anna [Verfasser]. "Highly accurate quantum chemistry : spin-orbit splittings via multireference coupled-cluster methods and applications in heavy-atom main-group chemistry / Leonie Anna Mück." Mainz : Universitätsbibliothek Mainz, 2013. http://d-nb.info/1033731374/34.
Testo completo
34
McBeth, Rafe A. "Active Radiation Detectors for Use in Space Beyond Low Earth Orbit| Spatial and Energy Resolution Requirements and Methods for Heavy Ion Charge Classification." Thesis, Colorado State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10604769.
Testo completoAbstract (sommario):
<p> Space radiation exposure to astronauts will need to be carefully monitored on future missions beyond low earth orbit. NASA has proposed an updated radiation risk framework that takes into account a significant amount of radiobiological and heavy ion track structure information. These models require active radiation detection systems to measure the energy and ion charge Z. </p><p> However, current radiation detection systems cannot meet these demands. The aim of this study was to investigate several topics that will help next generation detection systems meet the NASA objectives. Specifically, this work investigates the required spatial resolution to avoid coincident events in a detector, the effects of energy straggling and conversion of dose from silicon to water, and methods for ion identification (Z) using machine learning. </p><p> The main results of this dissertation are as follows: 1. Spatial resolution on the order of 0.1 cm is required for active space radiation detectors to have high confidence in identifying individual particles, i.e., to eliminate coincident events. 2. Energy resolution of a detector system will be limited by energy straggling effects and the conversion of dose in silicon to dose in biological tissue (water). 3. Machine learning methods show strong promise for identification of ion charge (Z) with simple detector designs.</p><p>
35
Fleischer, Stefan [Verfasser], and Andreas [Gutachter] Knauf. "Improbability Results on Collision and Non-Collision Orbits in Multibody Systems via the Poincaré Surface Method / Stefan Fleischer ; Gutachter: Andreas Knauf." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/1154308715/34.
Testo completo
36
Michaud, Yonnel. "Etude phénoménologique de la réaction d'échange de charge (pi)-p -> (pi)[n à haute énergie]." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10097.
Testo completoAbstract (sommario):
La presente these est consacree a l'etude de la reaction d'echange de charge pion negatif proton donne pion nul neutron. Cette reaction fait partie des processus quasi-elastiques, caracterises par de petits moments transferes, et donc non interpretables par la chromodynamique quantique. Le modele de glauber, utilise avec succes dans le cadre de la diffusion elastique, est exploite ici pour l'etude de la reaction d'echange de charge. Une interaction effective entre quarks, incluant un terme central et un terme spinorbite, est employee afin de rendre compte de l'echange du meson rho. Les resultats obtenus permettent de conclure a la nature diffractive de la reaction etudiee, mais ne permettent pas de determiner avec precision les rayons moyens des densites de quarks interagissants
37
Szasz, Csilla. "Radio meteors above the Arctic Circle : radiants, orbits and estimated magnitudes." Doctoral thesis, Umeå universitet, Fysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1603.
Testo completoAbstract (sommario):
This thesis presents results based on data collected with the 930 MHz EISCAT UHF radar system and three SKiYMet specular meteor radars. It describes in detail a method for meteoroid orbit calculation. The EISCAT UHF system comprises three identical 32 m parabolic antennae: one high-power transmitter/receiver and two remote receivers. Precise meteoroid deceleration and radar cross section are determined from 410 meteor head echoes simultaneously observed with all three receivers between 2002 and 2005, during four 24h runs at the summer/winter solstice and the vernal/autumnal equinox. The observations are used to calculate meteoroid orbits and estimate meteor visual magnitudes. None of the observed meteors appear to be of extrasolar or asteroidal origin; comets, particularly short period (<200 years) ones, may be the dominant source for the particles observed. About 40% of the radiants are associated with the north apex sporadic meteor source and 58% of the orbits are retrograde. The geocentric velocity distribution is bimodal with a prograde population centred around 38 km/s and a retrograde population peaking at 59 km/s. The absolute visual magnitudes of meteors are estimated to be in the range of +9 to +5 using a single-object numerical ablation model. They are thus observable using intensified CCD cameras with telephoto lenses. The thesis also investigates diurnal meteor rate differences and sporadic meteor radiant distributions at different latitudes using specular meteor trail radar measurements from 68°N, from 55°N and from 8°S. The largest difference in amplitude of the diurnal flux variation is at equatorial latitudes, the lowest variation is found at high latitudes. The largest seasonal variation of the diurnal flux is observed with the high-latitude meteor radar. The investigations show a variation in the sources with both latitude and time of day. The EISCAT UHF system and the high-latitude meteor radar are located close to the Arctic Circle. Such a geographical position means that zenith points towards the North Ecliptic Pole (NEP) once every day all year round. This particular geometry allows the meteoroid influx from the north ecliptic hemisphere to be compared throughout the year as the ecliptic plane coincides with the local horizon. Considering only the hour when NEP is closest to zenith, the EISCAT UHF head echo rate is about a factor of three higher at summer solstice than during the other seasons, a finding which is consistent with the high-latitude meteor radar measurements.<br>Avhandlingens resultat är baserade på mätningar med den trestatiska EISCAT UHF-radarn och tre SKiYMet meteorradarsystem. En metod för meteoroidbanberäkning presenteras i detalj. EISCAT UHF-systemet består av tre identiska, 32 m stora parabolantenner: en högeffektssändare/mottagare och två fjärrstyrda mottagare. Under fyra 24-timmarsmätningar vid vår-/höstdagjämning och sommar-/vintersolstånd mellan 2002 och 2005 detekterades 410 meteoriska huvudekon simultant med alla tre mottagare. Dessa trestatiska meteorers atmosfärsinbromsning och radartvärsnitt har fastställts mycket noggrant och använts till att beräkna meteoroidernas banor samt uppskatta meteorernas luminositeter. Ingen av de observerade meteoroiderna verkar vara av interstellärt eller asteroidursprung. Deras troligaste ursprung är kometer, framför allt kortperiodskometer (<200 år). Ungefär 40% av meteorradianterna kan associeras till norra apex, ett källområde för sporadiska meteorer, och totalt är 58% av partiklarnas banor retrograda. Meteoroidernas geocentriska hastighetsfördelning har två lokala maxima: ett för den prograda populationen vid 38 km/s och ett för den retrograda vid 59 km/s. Genom att anpassa datat till en numerisk ablationsmodell som simulerar meteoroidernas färd genom atmosfären har de detekterade meteorernas absoluta visuella magnituder uppskattats till mellan +9 och +5. Detta innebär att de är observerbara med bildförstärkta, teleskopiska CCD-kameror. Avhandlingen diskuterar även hur sporadiska meteorers dygns- och säsongsinflöde beror på geografisk latitud och meteorradianternas distribution på himmelssfären. Detta utreds med hjälp av spårekon detekterade under perioden 1999-2004 med tre meteorradarsystem på latituderna 68°N, 55°N och 8°S. Dygnsinflödet varierar mest på låga latituder och minst på höga. Ju högre latitud, desto mer förändras däremot dygnsinflödet över året. Avhandlingen visar att de dominerande källområdena varierar med säsong, över dygnet och med latitud. Både EISCAT UHF-systemet och meteorradarn på 68°N är belägna nära polcirkeln. Detta innebär att norra ekliptiska polen (NEP) är i zenit en gång per dygn, året om. Vid just denna tidpunkt sammanfaller ekliptikan med den lokala horisonten, vilket möjliggör att det observerade meteorinflödet från norra ekliptiska hemisfären kan jämföras över året. Under timmen då NEP är närmast zenit har EISCAT UHF uppmätt ett ungefär tre gånger högre meteorinflöde vid sommarsolståndet än under de andra säsongerna, vilket överensstämmer med resultaten från meteorradarn på 68°N.
38
Pedone, M. (Matteo). "Algebraic methods for constructing blur-invariant operators and their applications." Doctoral thesis, Oulun yliopisto, 2015. http://urn.fi/urn:isbn:9789526208770.
Testo completoAbstract (sommario):
Abstract Image acquisition devices are always subject to physical limitations that often manifest as distortions in the appearance of the captured image. The most common types of distortions can be divided into two categories: geometric and radiometric distortions. Examples of the latter ones are: changes in brightness, contrast, or illumination, sensor noise and blur. Since image blur can have many different causes, it is usually not convenient and also computationally expensive to develop ad hoc algorithms to correct each specific type of blur. Instead, it is often possible to extract a blur-invariant representation of the image, and utilize such information to make algorithms that are insensitive to blur. The work presented here mainly focuses on developing techniques for the extraction and the application of blur-invariant operators. This thesis contains several contributions. First, we propose a generalized framework based on group theory to constructively generate complete blur-invariants. We construct novel operators that are invariant to a large family of blurs occurring in real scenarios: namely, those blurs that can be modeled by a convolution with a point-spread function having rotational symmetry, or combined rotational and axial symmetry. A second important contribution is represented by the utilization of such operators to develop an algorithm for blur-invariant translational image registration. This algorithm is experimentally demonstrated to be more robust than other state-of-the-art registration techniques. The blur-invariant registration algorithm is then used as pre-processing steps to several restoration methods based on image fusion, like depth-of-field extension, and multi-channel blind deconvolution. All the described techniques are then re-interpreted as a particular instance of Wiener deconvolution filtering. Thus, the third main contribution is the generalization of the blur-invariants and the registration techniques to color images, by using respectively a representation of color images based on quaternions, and the quaternion Wiener filter. This leads to the development of a blur-and-noise-robust registration algorithm for color images. We observe experimentally a significant increase in performance in both color texture recognition, and in blurred color image registration<br>Tiivistelmä Kuvauslaitteet ovat aina fyysisten olosuhteiden rajoittamia, mikä usein ilmenee tallennetun kuvan ilmiasun vääristyminä. Yleisimmät vääristymätyypit voidaan jakaa kahteen kategoriaan: geometrisiin ja radiometrisiin distortioihin. Jälkimmäisestä esimerkkejä ovat kirkkauden, kontrastin ja valon laadun muutokset sekä sensorin kohina ja kuvan sumeus. Koska kuvan sumeus voi johtua monista tekijöistä, yleensä ei ole tarkoitukseen sopivaa eikä laskennallisesti kannattavaa kehittää ad hoc algoritmeja erityyppisten sumeuksien korjaamiseen. Sitä vastoin on mahdollista erottaa kuvasta sumeuden invariantin edustuma ja käyttää tätä tietoa sumeudelle epäherkkien algoritmien tuottamiseen. Tässä väitöskirjassa keskitytään esittämään, millaisia eri tekniikoita voidaan käyttää sumeuden invarianttien operaattoreiden muodostamiseen ja sovellusten kehittämiseen. Tämä opinnäyte sisältää useammanlaista tieteellistä vaikuttavuutta. Ensiksi, väitöskirjassa esitellään ryhmäteoriaan perustuva yleinen viitekehys, jolla voidaan generoida sumeuden invariantteja. Konstruoimme uudentyyppisiä operaattoreita, jotka ovat monenlaiselle kuvaustilanteessa ilmenevälle sumeudelle invariantteja. Kyseessä ovat ne rotationaalisesti (ja/tai aksiaalisesti) symmetrisen sumeuden lajit, jotka voidaan mallintaa pistelähteen hajaantumisen funktion (PSF) konvoluutiolla. Toinen tämän väitöskirjan tärkeä tutkimuksellinen anti on esitettyjen sumeuden invarianttien operaattoreiden hyödyntäminen algoritmin kehittelyssä, joka on käytössä translatorisen kuvan rekisteröinnissä. Tällainen algoritmi on tässä tutkimuksessa osoitettu kokeellisesti johtavia kuvien rekisteröintitekniikoita robustimmaksi. Sumeuden invariantin rekisteröinnin algoritmia on käytetty esiprosessointina tässä tutkimuksessa useissa kuvien restaurointimenetelmissä, jotka perustuvat kuvan fuusioon, kuten syväterävyysaluelaajennus ja monikanavainen dekonvoluutio. Kaikki kuvatut tekniikat ovat lopulta uudelleen tulkittu erityistapauksena Wienerin dekonvoluution suodattimesta. Näin ollen tutkimuksen kolmas saavutus on sumeuden invarianttien ja rekisteröintiteknikoiden yleistäminen värikuviin käyttämällä värikuvien kvaternion edustumaa sekä Wienerin kvaternion suodatinta. Havaitsemme kokeellisesti merkittävän parannuksen sekä väritekstuurin tunnistuksessa että sumean kuvan rekisteröinnissä
39
Lippolis, Domenico. "How well can one resolve the state space of a chaotic map?" Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33841.
Testo completoAbstract (sommario):
All physical systems are affected by some noise that limits the resolution that can be attained in partitioning their state space. For chaotic, locally hyperbolic flows, this resolution depends on the interplay of the local stretching/contraction and the smearing due to noise. My goal is to determine the `finest attainable' partition for a given hyperbolic dynamical system and a given weak additive
white noise. That is achieved by computing the local eigenfunctions of the Fokker-Planck evolution operator in linearized neighborhoods of the periodic orbits of the corresponding deterministic system, and using overlaps of
their widths as the criterion for an optimal partition. The Fokker-Planck evolution is then represented by a finite transition graph, whose spectral determinant yields time averages of dynamical observables. The method applies in
principle to both continuous- and discrete-time dynamical systems. Numerical tests of such optimal partitions on unimodal maps support my hypothesis.
40
Mate, Sujay. "Développement d'un simulateur du ciel pour les instruments à grand champ de vue X-gamma en orbite terrestre basse : application à l'évaluation des performances du spectro-imageur SVOM-ECLAIRs." Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30031.
Testo completoAbstract (sommario):
Les sursauts gamma (Gamma-Ray Bursts ou GRBs) sont les explosions les plus lumineuses de l'univers. On les observe sous la forme de bouffées de rayons X/ƴ (d'une durée de quelques millisecondes à quelques dizaines de secondes) suivies d'une émission rémanente (généralement à de plus grandes longueurs d'onde). Ils résultent soit de la fusion de deux objets compacts (une paire d'étoiles à neutrons ou une étoile à neutrons et un trou noir), soit de l'effondrement du noyau d'une étoile massive (>15 masse solaire). Les GRBs sont d'excellents candidats pour étudier la physique aux énergies et densités extrêmes et un outil astrophysique pour sonder l'histoire de l'univers car ils sont observés à tous les âges de celui-ci. La mission spatiale Sino-Française SVOM (lancement prévu en juin 2022) a pour objectif la détection et l'étude des GRBs à l'aide d'instruments spatiaux et terrestres dédiés afin d'obtenir une couverture multi-longueurs d'onde. Le principal instrument à bord du satellite SVOM est ECLAIRs, un imageur à masque codé à grand champ de vue (~2 sr) fonctionnant dans la bande d'énergie de 4 à 150 keV. ECLAIRs détectera et localisera les GRBs (ainsi que d'autres sources transitoires à hautes énergies) en temps quasi réel grâce à son " trigger " embarqué. Le bruit de fond d'ECLAIRs est élevé et variable en raison du grand champ de vue et de la stratégie de pointage de SVOM qui amène la Terre à transiter dans le champ de vue. Une nouvelle méthode (appelée "Particle Interaction Recycling Approach" ou PIRA en anglais), basée sur des simulations de Monte-Carlo (GEANT4), a été développée pour estimer précisément et rapidement le bruit de fond variable. Les simulations du bruit de fond sont complétées avec des sources X et des sursauts gamma afin de générer des scénarios d'observation complets. Le bruit de fond variable d'ECLAIRs pose des problèmes pour la détection des GRBs et affecte la sensibilité de l'instrument. Nous avons évalué les performances du "trigger" embarqué, notamment l'impact du bruit de fond sur la détection des sources transitoires et sa sensibilité aux caractéristiques des GRBs (durée, profil temporel, forme spectrale, position dans le champ de vue). ECLAIRs enverra au sol tous les photons détectés. De plus, la disponibilité d'une plus grande puissance de calcul et une meilleure connaissance du contexte (par exemple, les variations du bruit de fond, les sources dans le champ de vue, etc.) au sol, nous ont conduits à développer un "trigger" sol pour surmonter les difficultés rencontrées par le "trigger" embarqué. Ainsi, nous proposons un algorithme basé sur des transformées en ondelettes pour détecter les GRBs dans le cadre du "trigger" sol. Les travaux de cette thèse, à savoir le développement de PIRA, l'évaluation des performances et le développement d'un nouvel algorithme de détection de sursauts, fournissent une base solide pour construire un "trigger" sol efficace, qui complétera le "trigger" embarqué et améliorera les performances globales de la mission SVOM<br>Gamma-Ray Bursts (GRBs) are the most luminous explosions in the universe. They are observed as bright flashes of gamma/X-rays (lasting a few milliseconds to a few tens of seconds) followed by an "afterglow" emission (usually at longer wavelengths). They are produced either due to the merger of two compact objects (a pair of neutron stars or a neutron star and a black hole) or due to the core collapse of a massive star (> 15 solar mass). GRBs are excellent candidates to study physics at extreme energies and densities. They also constitute important astrophysical tools to probe the history of the universe as they are observed at all epochs. The upcoming (June 2022) Sino-French mission SVOM (Space-based multi-band astronomical Variable Objects Monitor) aims to detect and study GRBs using dedicated space and ground based instruments to obtain multi-wavelength coverage. The primary instrument onboard SVOM spacecraft is ECLAIRs, a wide-field (~ 2 sr) coded-mask imager sensitive in the 4 - 150 keV energy range. ECLAIRs will detect and localise GRBs (and other high energy transients) in near real time using an onboard trigger. ECLAIRs will encounter a high and variable background due to the wide field-of-view (FoV) and the pointing strategy of SVOM which makes the Earth transit through the FoV. A new method (called Particle Interaction Recycling Approach or PIRA), based on Monte-Carlo simulations (GEANT4), was developed to estimate the variable background accurately and rapidly. The simulations of the background are complemented with simulations of X-ray sources and gamma-ray bursts to generate complete observation scenarios. The variable background of ECLAIRs poses challenges to detect GRBs and affects the sensitivity of the instrument. We use the simulated data to evaluate the performance of the onboard trigger, in particular, the impact of the variable background and its sensitivity to the GRB characteristics (duration, temporal profile, spectral shape,position in the FoV). ECLAIRs will send all detected photons to the ground. In addition, the availability of a larger computational power and the better knowledge of the context (e.g. background variations, sources in the FoV, etc.) on the ground motivates us to develop an "offline trigger" to overcome the challenges faced by the onboard trigger. An algorithm based on wavelet transforms is proposed to detect GRBs as part of the offline trigger. The work in this thesis, i.e. the development of PIRA, instrument's performance evaluation and development of a trigger method, provides a sound basis to build an effective offline trigger that will complement the onboard trigger and improve the overall performance of the SVOM mission
41
Prado, Mário César Monteiro do. "Demonstrações assistidas por computador para equações diferenciais ordinárias." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/55/55135/tde-03072015-104300/.
Testo completoAbstract (sommario):
Neste trabalho, apresentamos um método computacional rigoroso para a demonstração de existência de órbitas periódicas de alguns sistemas de equações diferenciais ordinárias com campo autônomo do tipo polinomial. Mostraremos que o problema de encontrar órbitas periódicas para esses sistemas de equações é equivalente a buscar por raízes de certas funções definidas no espaço de Banach das sequências com decaimento algébrico. O método pode ser dividido em duas etapas. Na primeira, buscamos numericamente por soluções periódicas aproximadas. Na segunda, mostraremos a existência de uma órbita periódica numa vizinhança da curva encontrada numericamente. O rigor das verificações computacionais é garantido pelo uso de aritimética intervalar.<br>In this work, we present a rigorous computational method for proving the existence of periodic orbits of some systems of ordinary differential equations with autonomous vector field of polynomial type. We show that the problem of finding periodic orbits for these systems is equivalent to check for roots of certain functions defined in the Banach space of sequences with algebraic decay. The method can be divided into two steps. First, we seek, numerically, to approximated periodic solutions. Then, we show the existence of a periodic orbit in a neighborhood of the curve numerically found in the previous stage. The accuracy of the computational verifications is guaranteed by the use of interval arithmetic.
42
Moussi, El hadi. "Analyse de structures vibrantes dotées de non-linéarités localisées à jeu à l'aide des modes non-linéaires." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4792/document.
Testo completoAbstract (sommario):
Le travail de cette thèse a été réalisé dans le cadre d'une collaboration entre EDF R&D et le LMA de Marseille (CNRS). Le but était de développer des outils théoriques et numériques pour le calcul de modes non-linéaires de structures industrielles possédant des non-linéarités localisées à jeu. La méthode de calcul utilisée est une combinaison de la méthode d'équilibrage harmonique (EH) et de la méthode asymptotique numérique (MAN), appelée EHMAN. Elle est réputée pour sa robustesse sur les problèmes réguliers. L'enjeu de ce travail de thèse est de l'appliquer sur des problèmes non-réguliers régularisés de type butée à jeu pour lequel un grand nombre d'harmonique est nécessaire. Des améliorations ont été apportées à la méthode de base pour rendre effectif le traitement de modèles à "grand" nombre de degrés de liberté (DDL). Les développements réalisés pendant la thèse ont été capitalisés par la création de nouveaux opérateurs dans Code_Aster.Une étude approfondie d'un système à 2 degrés de liberté a permis de faire émerger quelques caractéristiques des systèmes non-linéaires à jeu. Celles-ci ont servi entre autre à établir une méthodologie pour l'étude de systèmes à grand nombre de DDL. Pour finir, la potentialité des modes non-linéaires comme outil de diagnostic vibratoire est démontrée avec l'étude d'un tube cintré de générateur de vapeur. Le calcul des modes non-linéaires a monté l'existence d'une interaction entre un mode hors-plan (basse fréquence) et un mode plan (haute fréquence) expliquant des régimes vibratoires non-standards. Ce résultat, impossible à obtenir avec les outils de l'analyse modale linéaire, est confirmé expérimentalement<br>This work is a collaboration between EDF R&D and the Laboratory of Mechanics and Acoustics. The objective is to develop theoretical and numerical tools to compute nonlinear normal modes (NNMs) of structures with localized nonlinearities.We use an approach combining the harmonic balance and the asymptotic numerical methods, known for its robustness principally for smooth systems. Regularization techniques are used to apply this approach for the study of nonsmooth problems. Moreover, several aspects of the method are improved to allow the computation of NNMs for systems with a high number of degrees of freedom (DOF). Finally, the method is implemented in Code_Aster, an open-source finite element solver developed by EDF R&D.The nonlinear normal modes of a two degrees-of-freedom system are studied and some original characteristics are observed. These observations are then used to develop a methodology for the study of systems with a high number of DOFs. The developed method is finally used to compute the NNMs for a model U-tube of a nuclear plant steam generator. The analysis of the NNMs reveals the presence of an interaction between an out-of-plane (low frequency) and an in-plane (high frequency) modes, a result also confirmed by the experiment. This modal interaction is not possible using linear modal analysis and confirms the interest of NNMs as a diagnostic tool in structural dynamics
43
Antunes, Rodrigo Badotti. "Avaliação do volume orbitário nos avanços frontofaciais." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/5/5132/tde-27022015-095543/.
Testo completoAbstract (sommario):
Craniofaciossinostose sindrômica (CS) é uma desordem congênita associada às mutações dos genes FGFR1, FGFR2 e FGFR3. Ocasiona uma fusão prematura das suturas craniofaciais, levando à deficiência no crescimento do crânio e terço médio da face. A severidade dos sintomas relacionados à hipertensão intracraniana, aparelho respiratório (síndrome da hipopneia-apneia do sono) e ocular (órbitas rasas, proptose ocular, exorbitismo e falta de proteção do globo ocular), são parâmetros para indicar o procedimento cirúrgico. A tomografia-3D é uma opção atual e pouco utilizada para avaliar os volumes orbitais e a magnitude dos avanços craniofaciais e seus vetores; esse método permite melhor definição das estruturas anatômicas sem distorção das imagens, promovendo uma avaliação adequada dos resultados. Os objetivos do presente estudo foram avaliar os volumes orbitais, os avanços craniofaciais e seus vetores nas osteotomias Le Fort III e Monobloco com uso de aparelhos distratores, a correlação entre os avanços craniofaciais e a variação dos volumes orbitais e determinar a eficácia dos avanços craniofaciais por meio da comparação com índices normais de volumes orbitais. No período de janeiro de 2001 a dezembro de 2012, foram selecionados 20 pacientes submetidos ao alongamento ósseo gradual do terço médio da face, divididos em dois grupos. Grupo LF (n = 9), submetidos à osteotomia Le Fort III e Grupo MB (n = 11), submetidos à osteotomia frontofacial monobloco. A avaliação constou da revisão de prontuários e exames tomográficos, em que foram mensurados o volume orbital pela segmentação de imagens no programa InVesalius e modelagem 3D no programa Magics, e a magnitude dos avanços craniofaciais, e seus vetores, foram medidos no programa Rhinoceros. Os resultados foram submetidos à análise estatística: teste t- Student e ANOVA. No Grupo MB, houve aumento de 8,94 mm3 e 9,84 mm3 para a variação do volume orbital, nas órbitas direita e esquerda, respectivamente; no Grupo LF: 5,70 mm3 e 5,77 mm3, respectivamente, para esses parâmetros. A resultante do avanço médio, para a órbita direita e esquerda no Grupo LF foi 11,36 ± 3,80 mm e 11,11 ± 3,45 mm, respectivamente; já no Grupo MB, foi 14,22 ± 4,12 mm e 14,48 ± 4,49 mm, respectivamente. A correlação entre a resultante do avanço e a variação dos volumes orbitais foi significante no Grupo LF e para a órbita esquerda no Grupo MB. Em conclusão, o procedimento cirúrgico foi eficaz, tanto para o Grupo LF como para o Grupo MB, pois, houve aumento estatisticamente significativo do volume orbital no período pós-operatório; não houve diferença estatisticamente significativa, na avaliação da simetria, entre os volumes orbitais pós-operatórios, direito e esquerdo. Ainda, não houve diferença estatisticamente significante entre os volumes orbitais pósoperatórios quando comparados aos índices de normalidade<br>Syndromic craniofacial synostosis (CS) is a congenital disorder, which is most often, an autosomal dominant mutation associated to FGFR1, FGFR2 and FGFR3 genes. It causes a premature fusion of craniofacial sutures, leading to deficiency in skull growth and middle-third of the face. The severity of the intracranial hypertension related, respiratory syndrome (hypopneaapnea) and eye (shallow orbits, ocular proptosis, exorbitism and lack of protection of the eyeball) symptoms, are parameters that indicate the surgical procedure. Distraction osteogenesis of the middle-third of the face is currently the chosen technique for the treatment of patients with Craniofacial Synostosis syndrome candidates for the advancement of the middle-third of the face. The 3D-tomography is a current option and seldom used for this purpose; this method allows better definition of anatomical structures without image distortion, providing a more accurate assessment of the results. The objectives of the present study, were to assess quantitatively the craniofacial advancement and its vectors through 3D tomographic images, the osteotomy Le Fort III and Monobloc with use of distractor devices; Also, to evaluate the correlation between the craniofacial advances and the variation of orbital volumes and determine the effectiveness of craniofacial advances through the comparison with normal levels of orbital volumes. From January 2001 to December 2012, 20 patients underwent distraction osteogenesis of the middle-third of the face, divided into two groups. LF group (n = 9) underwent a Le Fort III osteotomy and MB group (n = 11) underwent a monobloc frontalfacial osteotomy. The evaluation consisted of the reviewing of the records and tomographic exams; measured is the orbital volume by image segmentation on the InVesalius software and 3D modeling on Magics software and the magnitude of facial advances, and their vectors, were measured on Rhinoceros software. The results were subject to statistical analysis: t-Student test and ANOVA. In the MB group, there was an increase of 8.94 mm3 and 9.84 mm3 for the variation of the orbital volume, the right and left orbits, respectively; in Group LF: 5.70 mm3 and 5.77 mm3 for these parameters. The resulting of average advance, for right and left orbit in Group LF was of 11.36 ± 3.80 mm, 11.11 ± 3.45mm, respectively; as for group MB it was 14.22 ± 4.12 mm and 14.48 ± 4.49 mm, respectively. Correlation between the results from the progress and the variation of orbital volume was significant in Group LF and left orbit in MB Group. In conclusion, the surgical procedure was effective for both the LF group as for the MB Group because: there was a statistically significant increase in orbital volume on the postoperative period; there was no statistically significant difference in the evaluation of symmetry between the postoperative period left and right orbital volumes. Still, there was no statistically significant difference between the postoperative orbital volumes when compared to normal ranges
44
Castro, Gian Machado de. "Soluções exatas de equações de Einstein para buracos negros e anéis de matéria." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278547.
Testo completoAbstract (sommario):
Orientadores: Patricio A. Letelier Sotomayor e Marcelo Moraes Guzzo<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin<br>Made available in DSpace on 2018-08-13T19:55:09Z (GMT). No. of bitstreams: 1
Castro_GianMachadode_D.pdf: 3217878 bytes, checksum: 48c026fc06d4c9e5db03014506ffc609 (MD5)
Previous issue date: 2009<br>Resumo: Nesta tese, estudamos o problema de um anel delgado de matéria de densidade constante com um buraco negro de Kerr em seu centro. Nosso objetivo foi resolver as equações de Einstein no vácuo com simetria axial para esse sistema gravitacional. Para fazer a sobreposição não-linear do anel com o buraco negro (BN), utilizamos o método de Belinsky e Zakharov (MBZ). Este método necessita de uma solução conhecida (solução semente) para gerar uma nova solução. Tomamos a aproximação da solução do anel em multipolos como solução semente. Como resultado, obtivemos a solução de um anel com o BN central.
A expansão do anel em multipolos exige o truncamento da série. Esta aproximação introduz um erro em nossa solução. Realizamos o estudo do mesmo devido ao truncamento da série. Também estudamos a estabilidade de órbitas circulares equatoriais de partículas movendo-se ao redor do sistema anel-BN quanto a perturbações epicíclicas e verticais. Analisamos essas perturbações para os modelos de gravitação relativística e newtoniana. Como resultado, encon- tramos o efeito inesperado da duplicação das órbitas circulares de flotons para alguns valores de parâmetros relacionados com o anel e o BN, bem como zonas de estabilidade na região interna do anel.<br>Abstract: In this thesis, we will study the problem of a thin ring of matter of constant density with a central Kerr black hole. The aim of this work is to solve the Einstein equations in the vacuum with axial symmetry for that gravitational system. To do the nonlinear superposition of the ring with the black hole (BH), we used the Belinsky and Zakharov method (BZM). This method needs a known solution (called seed solution) to generate a new one. We took the Newtonian ring potential approximated by a multipolar expansion as seed solution. As result, we obtained the solution of a ring with a central BH.
The ring multipolar expansion demands the truncation of the series. This approach introduces an error in our solution. Estimations of errors due to the truncation of the multipolar expansions are performed. We also studied the stability of equatorial circular orbits of particles moving around the system ring plus BH due to epicycle and vertical perturbations. We analyzed those perturbations for relativistic and Newtonian gravitational models. As result, we found the unexpected effect of the duplication of the photons circular orbits for certain values of parameters related with the ring and BH, as well as zones of stability in the inner area of the matter ring.<br>Doutorado<br>Relatividade e Gravitação<br>Doutor em Ciências
45
Stellin, Filippo. "Anderson localization in interacting quantum systems." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7004.
Testo completoAbstract (sommario):
Dans cette thèse nous étudions au niveau théorique le comportement des particules quantiques (électrons, atomes, photons, etc.) se mouvant dans un milieu désordonné et sujets à la localisation d’Anderson. Pour des particules non interagissantes, le spectre de l’énergie peut posséder un ou plus points critiques, où les fonctions d’onde étendues deviennent localisées, en donnant lieu à une transition de phase métal-isolant connue comme Transition d’Anderson.Une question fondamentale est si et comment les transitions d’Anderson survivent dans des systèmesquantiques interagissants. Dans cet ouvrage, nous étudions un modèle simple décrivant le cas de deux particules dans un réseau désordonné et sujettes à des interactions mutuelles à courte portée. En combinant des simulations numériques sur une grande échelle avec des techniques à la fonction de Green, nous montrons que les transitions d’Anderson à deux particules se produisent en trois dimensions et explorons le diagramme de phase dans l’espace de l’énergie, du désordre et de l’interaction.Cette dernière présente une structure riche, caractérisée par un double renfoncement de la limite de phase, engendrée par la compétition entre les états de diffusion et les états liés de la paire. Nous prouvons aussi que les annonces précédentes concernant l’apparition de transitions d’Anderson en deux dimensions étaient essentiellement dues à des effets de taille finie.Un deuxième problème que nous abordons dans cette thèse est celui de l’occurrence de transitions métal-isolant en deux dimensions pour une particule en la présence d’un potentiel spatialement corrélé et sujette à des interactions spin-orbite, modélisées par les couplages Rashba-Dresselhaus. On éclaire que, indépendamment des propriétés du désordre, il y a un régime où l’énergie critique dépend linéairement du paramètre de désordre. La pente et l’intercepte sont étudiées en voisinage du point de symétrie spin-hélice persistant, dans lequel la symétrie SU(2) est restaurée et la transition métal-isolant disparaît<br>In this thesis we theoretically investigate the behaviour of quantum particles (electrons, atoms, photons, etc.) moving in a random medium and undergoing Anderson localization. For noninteractingparticles, the energy spectrum can possess one or more critical points, where the nature of the single-particle wavefunctions changes from extended to localized leading to a undergoes a metal-insulator phase transition, also known as Anderson transition.A fundamental question is whether and how Anderson transitions survive in interacting quantum systems. Here we study a minimal model of two particles moving in a disordered lattice and subject to short-range mutual interactions. By combining large-scale numerics with Green’s functions techniques, we show that two-particle Anderson transitions do occur in three dimensions and explore the phase diagram in the space of energy, disorder and interaction strength. The latter presents a rich structure, characterized by a doubly reentrant behavior, caused by the competition between scattering and bound states of the pair. We also show that previous claims of 2D Anderson transitions of the pair are essentially due to finite-size effects.A second problem that we address in this thesis is the occurrence of 2D metal-insulator transitions for a single particle in the presence of a spatially correlated potential and subject to spin-orbit interactions, described by Rashba-Dresselhaus couplings. We illustrate that, irrespective of the properties of the disorder, there is a regime where the critical energy depends linearly on the disorder strength. The slope and the intercept are studied in the vicinity of the spin-helix point, where the SU(2) symmetry is restored and the 2D metal-insulator transition disappears
46
Sendrowski, Janek. "Feigenbaum Scaling." Thesis, Linnéuniversitetet, Institutionen för matematik (MA), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-96635.
Testo completoAbstract (sommario):
In this thesis I hope to provide a clear and concise introduction to Feigenbaum scaling accessible to undergraduate students. This is accompanied by a description of how to obtain numerical results by various means. A more intricate approach drawing from renormalization theory as well as a short consideration of some of the topological properties will also be presented. I was furthermore trying to put great emphasis on diagrams throughout the text to make the contents more comprehensible and intuitive.
47
Cardoso, dos Santos Josué. "Study of the dynamics around celestial bodies using analytical and semi-analytical techniques." Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/155950.
Testo completoAbstract (sommario):
Submitted by Josué Cardoso dos Santos (josuesantosunesp@gmail.com) on 2018-09-10T18:36:37Z
No. of bitstreams: 1
Tese_Final_Josue_Cardoso_Santos.pdf: 78449557 bytes, checksum: 4515b9cb7cc346753f7e9682b8e037de (MD5)<br>Approved for entry into archive by Pamella Benevides Gonçalves null (pamella@feg.unesp.br) on 2018-09-10T18:47:05Z (GMT) No. of bitstreams: 1
santos_jc_dr_guara.pdf: 78449557 bytes, checksum: 4515b9cb7cc346753f7e9682b8e037de (MD5)<br>Made available in DSpace on 2018-09-10T18:47:05Z (GMT). No. of bitstreams: 1
santos_jc_dr_guara.pdf: 78449557 bytes, checksum: 4515b9cb7cc346753f7e9682b8e037de (MD5)
Previous issue date: 2018-07-04<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Nowadays, despite the technological development experienced by science in general, a fact especially evident by the available powerful computer machines, the analytical and semi-analytical methods to study different space problems are still of great importance in the fields of astrodynamics and celestial mechanics. From the physical understanding of the motion of celestial bodies to the planing and designing of space missions, the use of mathematical models to deal with a very large number of contemporary problems plays a fundamental role in the progress of human knowledge. In this context, the present thesis presents the use of different mathematical techniques to deal with different various and current problems in astrodynamics and celestial mechanics. The studies developed throughout this work are applicable to both areas. The topics studied are the following ones: (1) The development of disturbing potentials using the double-averaging process, in order to be included in the Lagrange planetary which are numerically integrated to study features of orbits around Mercury and the Galilean moon Callisto; (2) The use of different perturbation integrals, techniques to identify and map different perturbations present in a planetary system, with focus on the analysis of systems of Giant planets with their massive moons; (3) The use of the concept of intermediary Hamiltonian and the use of a canonical transformation called elimination of the parallax, both to deal with binary systems in the context of the roto-orbital dynamics, this one as an approach of the fulltwo body problem; (4) An updated analysis of Gauss variational equations to study quasisatellite orbits around the Martian moon Phobos and with analytical predictions made after obtaining linear and averaged equations of motions. Therefore, this thesis intend not only to provide important analysis and results for each specific problem which it deals with along its pages, but also seeks to highlighting the merit and current relevance of different analytical and semi-analytical methods to be used in the fields of astrodynamics and celestial mechanics. Additionally, the author also hopes to offer an outcome of diverse interesting ideas and methods to be explored in future investigations in these research fields<br>Na atualidade, a despeito do desenvolvimento tecnológico experimentado pela ciência em geral, algo especialmente evidenciado por poderosas máquinas computacionais disponíveis, os métodos analíticos e semianalíticos para o estudo de diferentes problemas espaciais ainda são de grande importância nos campos de astrodinâmica e mecânica celeste. Desde a compreensão física do movimento de corpos celestes até ao planejamento e projeto de missões espaciais, o uso de modelos matemáticos para lidar com um grande número de problemas contemporâneos desempenha um papel fundamental no progresso do conhecimento humano. Neste contexto, a presente tese apresenta o uso de diferentes técnicas matemáticas para lidar com diversos e atuais problemas em astrodinâmica e mecânica celeste. Os estudos desenvolvidos ao longo deste trabalho são aplicáveis à ambas as áreas. Os tópicos estudados são os seguintes: (1) O desenvolvimento de potenciais perturbadores usando o processo de dupla média, de forma a serem incluídos nas equações planetárias de Lagrange que são integradas numericamente para estudar características de órbitas ao redor de Mercúrio e da lua galileana Calisto; (2) A utilização de diferentes integrais de perturbação, técnicas para identificar e mapear diferentes perturbações presentes em um sistema planetário, com foco na análise de sistemas de planetas gigantes com suas luas massivas; (3) A utilização do conceito de hamiltoniana intermediária e o uso de uma transformação canônica chamada eliminação da paralaxe, ambos para lidar com sistemas binários no contexto da dinâmica roto-orbital, essa sendo uma aproximação do problema completo de dois corpos; (3) Uma análise atualizada de equações variacionais de Gauss para o estudo de órbitas quasi-satélite ao redor da lua marciana Fobos e com predições analíticas realizadas após serem obtidas equações de movimento linearizadas e com média. Portanto, esta tese pretende não somente prover importantes análises e resultados para cada problema específico com os quais a mesma lida ao longo de suas páginas, mas também procura destacar o mérito e relevância atual de diferentes métodos analíticos e semianalíticos a serem utilizados nos campos de astrodinâmica e mecânica celeste. Adicionalmente, o autor também espera oferecer um produto de variadas ideias e métodos a serem explorados em futuras investigações nesses campos de pesquisa<br>2013/26652-4<br>2015/18881-9
48
Neubeck, Wolfgang. "Etude des propriétés magnétiques et électroniques des oxydes de métaux de transition MnO, CoO, NiO et CuO par diffraction magnétique de rayons X." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10216.
Testo completoAbstract (sommario):
Ce travail de these presente les resultats d'experiences de diffraction magnetique obtenus sur des oxydes de metaux de transition : mno, coo, nio et cuo. La diffraction magnetique de rayons x non-resonante est une sonde experimentale unique, qui permet la separation des contributions du spin et du moment orbital a la densite totale d'aimantation. Nos resultats experimentaux montrent des moments orbitaux non-nuls dans coo (l/s=0. 95), nio (l/s=0. 34) et cuo (l/s=0. 18). Uniquement dans le cas de mno le moment orbital est nul. En fait, les interactions spin-orbite peuvent retablir partiellement le moment orbital ; nos resultats montrent qu'elles devraient etre considerees quand on discute les proprietes electroniques ainsi que magnetiques. La diffraction magnetique de rayons x resonante est observee quand l'energie des photons est proche des seuils d'absorptions. Elle est interpretee par des transitions electroniques multipolaires entre les etats du coeur et des etats libre au-dessus du niveau de fermi. Des resonances importantes indiquent que les etats intermediaires presentent un fort couplage spin-orbite et qu'il existe un moment orbital. Au seuil k des metaux 3d deux canaux resonants existent : la resonance dipolaire (e1) qui sonde les etats 4p, peu polarises, et la resonance quadrupolaire (e2) qui sonde les etats 3d, fortement polarises. Des resonances e2 sont observees dans nio, coo et cuo, qui ont tous un moment orbital. Par contre dans mno, ou les ions mn 2 + sont dans un etat s, de faibles anomalies sont observees, provenant du couplage spin-orbite dans la couche 3d. En plus de la resonance e2 tous les systemes presentent une resonance supplementaire de type e1. Alors que le processus e2, qui sonde les etats 3d fortement
49
Hsu, Ting-Wei, and 許庭瑋. "GLONASS Orbit Determination and Positioning Method." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/32189896705589068627.
Testo completoAbstract (sommario):
碩士<br>國立臺灣大學<br>電機工程學研究所<br>101<br>In general, GNSS (Global Navigation Satellites System) is described as the satellites-based navigation system. Presently, the available systems include GPS (Global
Positioning system) of United States and GLONASS (Global Navigation Satellites System) of Russia.
With more available satellites, the accuracy of positioning could become more precise, and the combination of GPS and GLONASS could easily reach it. Although GPS and GLONASS are similar to each other, the both systems are not entirely compatible. Before combining these two systems, it is important to be familiar with each system in great details. Therefore, we made a study of GLONASS and attempted to specify the position by means of only GLONASS.
In this paper, we determine the satellite position through GLONASS ephemeris by using Runge-Kutta Method, and then obtain the receiver position with pseudorange measurement. To correct ionosphere delays on GLONASS satellites, we applied Klobuchar Model with little modification. Afterward, we also applied altitude-hold
constraint to positioning equations, and consequently, the results of positioning point have become more precise and stable.
It shall be noted that we not only demonstrated the results but also elaborated on the whole process of positioning. This will benefit the future studies and some relative applications.
50
Ho, Ka-Fai, and 何家輝. "CHAMP Satellite Short-arc Orbit Determination using Kinematic Method." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/25218458994323990843.
Testo completoAbstract (sommario):
碩士<br>國立成功大學<br>測量工程學系碩博士班<br>91<br>In recently years, there is a tendency to develop low-earth orbit（LEO）satellites, as the CAHMP lunched at 2000 and ROCSAT-3 will lunch at 2005, to process many earth sciences researches. The science projects of the LEO include earth gravity recovery, earth atmosphere temperature and pressure retrieval, weather prediction and space/time variability of the magnetic field of the earth. Determine the LEO position is one of the important and necessary task in order to carry out those researches above.
This research process the ionosphere-free triple-differenced carrier phase observation which consist of double frequency GPS observations from the GPS receiver carried on the CHAMP and 40 IGS tracking stations. Besides, the tropospheric correction model, solid earth tide correction, mass center correction of the satellite, earth rotation correction and antenna phase center correction are incorporated. Finally, determine the satellite short-arc orbit with the pure geometry, kinematic, method. The results show that the average RMS of the short-arc orbit at radial、along-track、cross-track components are 20、20 and 15 cm, and the average 3D RMS is 32 cm. The average RMS of the overlap orbit at three components are 25、17 and 13 cm and the average 3D RMS is 32 cm.