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Dissertations / Theses on the topic 'Invariants and covariants'

Author: Grafiati

Published: 26 July 2024

Last updated: 31 July 2025

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1

Olive, Marc. "Géométrie des espaces de tenseurs : une approche effective appliquée à la mécanique des milieux continus." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4745/document.

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Plusieurs lois de comportement mécaniques possèdent une formulation tensorielle, comme c'est le cas pour l'élasticité où intervient un espace de tenseurs d'ordre 4, noté Ela. La classification des matériaux élastiques passent par la nécessité de décrire l'espace des orbites ELA/SO(3). Plus généralement, on étudie la géométrie d'un espace de tenseurs sur $mathbb{R}^{3}$, via l'action du groupe O(3). Cette géométrie est caractérisée par ses classes d'isotropies, ou encore classes de symétries. Tout espace de tenseurs possède en effet un nombre fini de classes d'isotropies. Nous proposons alors u

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2

Bruni, Marco. "Covariant and Gauge-Invariant Cosmological Perturbations." Doctoral thesis, SISSA, 1991. http://hdl.handle.net/20.500.11767/4306.

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3

Pissondes, Jean-Claude. "Des invariants quadratiques aux invariants projectifs, covariance d'echelle en theorie de la relativite d'echelle." Paris 6, 1998. http://www.theses.fr/1998PA066292.

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Les resultats presentes dans cette these ont pour point de depart la theorie de la relativite d'echelle, pour finalement concerner les transformations projectives complexes, ainsi que la geometrie non-commutative par certains aspects. En premier lieu, j'analyse la prescription formelle selon laquelle il serait possible de deduire des equations de la mecanique classique, des equations qui soient covariantes d'echelle, et par suite, les equations de mecanique quantique. Cette prescription consiste a remplacer dans les equations classiques, les derivees totales par une derivee covariante d'echell

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4

Fehlberg, Júnior Renato. "Teoria de invariantes de formas binárias." Universidade Federal de São Carlos, 2010. https://repositorio.ufscar.br/handle/ufscar/5865.

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Made available in DSpace on 2016-06-02T20:28:24Z (GMT). No. of bitstreams: 1 2978.pdf: 738093 bytes, checksum: cdf53ae3eecedf2adf9b402da2a3499d (MD5) Previous issue date: 2010-03-26<br>Universidade Federal de Sao Carlos<br>In this work, we studied article [6], that answers the following questions:how are all covariants of binary forms? What are and how to find the canonicalforms of the binary forms of degree n? Is there a finite generating set for theconvariants of binary forms of degree n? The first question will be answered bythe First Fundamental Theorem. The second question will be answe

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5

Guan, Yu. "Covariate-invariant gait recognition using random subspace method and its extensions." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/67147/.

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Compared with other biometric traits like fingerprint or iris, the most significant advantage of gait is that it can be used for remote human identification without cooperation from the subjects. The technology of gait recognition may play an important role in crime prevention, law enforcement, etc. Yet the performance of automatic gait recognition may be affected by covariate factors such as speed, carrying condition, elapsed time, shoe, walking surface, clothing, camera viewpoint, video quality, etc. In this thesis, we propose a random subspace method (RSM) based classifier ensemble framewor

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6

Liang, Yigao. "Fermions in Yang-Mills gauge theories: invariance, covariance and topology." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77824.

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I present a study on the invariance and covariance properties of the Dirac operator describing fermions in Yang-Mills fields. This includes the study of anomalies of the gauge currents. We are particularly interested in the geometric and topological features in the problem. The complicated topological structures and properties present in these theories are made clear by elementary calculations in several simple models. We show explicitly how non-trivial phase and sign ambiguities arise to give the so-called anomalies. The Atiyah-Singer index theorem is seen to be a very powerful tool to calcul

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7

Sharma, Poonam. "Gauge invariant constructions in Yang-Mills theories." Thesis, University of Plymouth, 2012. http://hdl.handle.net/10026.1/1092.

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Understanding physical configurations and how these can emerge from the underlying gauge theory is a fundamental problem in modern particle physics. This thesis investigates the study of these configurations primarily focussing on the need for gauge invariance in constructing the gauge invariant fields for any physical theory. We consider Wu’s approach to gauge invariance by identifying the gauge symmetry preserving conditions in quantum electrodynamics and demonstrate how Wu’s conditions for one-loop order calculations (under various regularisation schemes) leads to the maintenance of gauge i

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8

Wang, Yan. "Covariates in Factor Mixture Modeling: Investigating Measurement Invariance across Unobserved Groups." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7715.

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Factor mixture modeling (FMM) has been increasingly used to investigate unobserved population heterogeneity. This Monte Carlo simulation study examined the issue of measurement invariance testing with FMM when there are covariate effects. Specifically, this study investigated the impact of excluding and misspecifying covariate effects on the class enumeration and measurement invariance testing with FMM. Data were generated based on three FMM models where the covariate had impact on the latent class membership only (population model 1), both the latent class membership and the factor (populatio

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9

Bianchini, Filippo. "Invarianza relativistica delle equazioni di Maxwell." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13558/.

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In questa tesi si dimostra l'invarianza relativistica delle equazioni di Maxwell, partendo da un esempio che illustra la relatività della simultaneità. Si giunge quindi, a partire da alcune ipotesi e tramite alcuni passaggi algebrici, alle trasformazioni di Lorentz, che sono le equazioni che permettono il cambio di coordinate passando da un sistema di riferimento ad un altro sistema di riferimento in moto relativo, e grazie a queste si ricava il teorema di Einstein o di addizione relativistica delle velocità. Le trasformazioni di Lorentz e tale teorema consentono di ricavare, al cambiare del s

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10

Tsagas, Christos G. "Covariant and gauge-invariant analysis of cosmological perturbations in the presence of a primordial magnetic field." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263210.

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11

Ulpat, Rovetta Florent. "Etude arithmétique et algorithmique de courbes de petit genre." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4088/document.

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Cette thèse traite de plusieurs aspects algorithmiques des courbes algébriques. La première partie décrit et implémente en Magma un algorithme de calcul des tordues pour les courbes sur les corps finis et en étudie la complexité. Dans le cas hyperellitptique, il s’agit du premier algorithme complet pour faire cela en tout genre. La deuxième partie construit des familles représentatives pour les courbes non hyperelliptiques de genre 3 afin de permettre leur énumération efficace en lien avec le problème de l’obstruction de Serre. Cette partie a fait l’objet d’une publication dans ANTS et une ann

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12

Liu, Jin. "ESTIMATING KNOTS IN BILINEAR SPLINE GROWTH MODELS WITH TIME-INVARIANT COVARIATES IN THE FRAMEWORK OF INDIVIDUAL MEASUREMENT OCCASIONS." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6044.

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Longitudinal studies of change abound in the fields of epidemiology and public health to evaluate individual growth over time. Analyzing this type of data poses various interesting statistical challenges. Our motivating dataset in this project arises from an osteoarthritis study, where the change patterns of the metrics of interested are theorized to be in two phases. The aim is to identify an individual inflection point (i.e., knot) for each patient's trajectory corresponding to their short-term and long-term recovery periods from treatment. In addition, since we cannot directly observe which

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13

Cheng, Sibo. "Error covariance specification and localization in data assimilation with industrial application Background error covariance iterative updating with invariant observation measures for data assimilation A graph clustering approach to localization for adaptive covariance tuning in data assimilation based on state-observation mapping Error covariance tuning in variational data assimilation: application to an operating hydrological model." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST067.

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Les méthodes d’assimilation de données et plus particulièrement les méthodes variationnelles sont mises à profit dans le domaine industriel pour deux grands types d’applications que sont la reconstruction de champ physique et le recalage de paramètres. Une des difficultés de mise en œuvre des algorithmes d’assimilation est que la structure de matrices de covariance d’erreurs, surtout celle d’ébauche, n’est souvent pas ou mal connue. Dans cette thèse, on s’intéresse à la spécification et la localisation de matrices de covariance dans des systèmes multivariés et multidimensionels, et dans un cad

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14

Haddouche, Mohamed Anis. "Estimation d'une matrice d'échelle." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR058/document.

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Beaucoup de résultats sur l’estimation d’une matrice d’échelle en analyse multidimensionnelle sont obtenus sous l’hypothèse de normalité (condition sous laquelle il s’agit de la matrice de covariance). Or il s’avère que, dans des domaines tels que la gestion de portefeuille en finance, cette hypothèse n’est pas très appropriée. Dans ce cas, la famille des distributions à symétrie elliptique, qui contient la distribution gaussienne, est une alternative intéressante. Nous considérons dans cette thèse le problème d’estimation de la matrice d’échelle Σ du modèle additif Yp_m = M + E, d’un point de

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15

Sardelli, Francesco. "Aspects de la gravitation quantique à boucles : la représentation polymère, la jauge temporelle et lien entre approches covariante et canonique." Thesis, Tours, 2011. http://www.theses.fr/2011TOUR4050/document.

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Dans cette thèse, nous avons étudié quelques aspects fondamentaux de la gravitation quantique à boucles (Loop Quantum Gravity ou LQG). Tout d'abord, nous avons discuté le choix de la représentation polymère dans ce programme de quantification de la relativité générale. Pour cela, nous avons considéré la corde bosonique comme modèle-jouet sur lequel on peut tester les méthodes de quantification de la LQG. Dans cette optique, nous avons introduit et étudié une formulation originale de la corde bosonique, dite corde algébrique. Ensuite, nous nous sommes intéressé au problème important du choix de

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16

Alonzo, Julie. "An examination of early reading skill covariance structure invariance across Spanish-speaking English language learners in grades 3 and 4 and their native English-speaking peers /." view abstract or download file of text, 2007. http://proquest.umi.com/pqdweb?did=1331398351&sid=1&Fmt=2&clientId=11238&RQT=309&VName=PQD.

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Thesis (Ph. D.)--University of Oregon, 2007.<br>Typescript. Includes vita and abstract. Includes bibliographical references (leaves 120-125). Also available for download via the World Wide Web; free to University of Oregon users.

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17

Villaron, Emilie. "Modèles aléatoires harmoniques pour les signaux électroencéphalographiques." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4815.

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Cette thèse s'inscrit dans le contexte de l'analyse des signaux biomédicaux multicapteurs par des méthodes stochastiques. Les signaux auxquels nous nous intéressons présentent un caractère oscillant transitoire bien représenté par les décompositions dans le plan temps-fréquence c'est pourquoi nous avons choisi de considérer non plus les décours temporels de ces signaux mais les coefficients issus de la décomposition de ces derniers dans le plan temps-fréquence. Dans une première partie, nous décomposons les signaux multicapteurs sur une base de cosinus locaux (appelée base MDCT) et nous modéli

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18

Allez, Romain. "Chaos multiplicatif Gaussien, matrices aléatoires et applications." Phd thesis, Université Paris Dauphine - Paris IX, 2012. http://tel.archives-ouvertes.fr/tel-00780270.

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Dans ce travail, nous nous sommes intéressés d'une part à la théorie du chaos multiplicatif Gaussien introduite par Kahane en 1985 et d'autre part à la théorie des matrices aléatoires dont les pionniers sont Wigner, Wishart et Dyson. La première partie de ce manuscrit contient une brève introduction à ces deux théories ainsi que les contributions personnelles de ce manuscrit expliquées rapidement. Les parties suivantes contiennent les textes des articles publiés [1], [2], [3], [4], [5] et pré-publiés [6], [7], [8] sur ces résultats dans lesquels le lecteur pourra trouver des développements plu

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19

Li, Zhonggai. "Objective Bayesian Analysis of Kullback-Liebler Divergence of two Multivariate Normal Distributions with Common Covariance Matrix and Star-shape Gaussian Graphical Model." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28121.

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This dissertation consists of four independent but related parts, each in a Chapter. The first part is an introductory. It serves as the background introduction and offer preparations for later parts. The second part discusses two population multivariate normal distributions with common covariance matrix. The goal for this part is to derive objective/non-informative priors for the parameterizations and use these priors to build up constructive random posteriors of the Kullback-Liebler (KL) divergence of the two multivariate normal populations, which is proportional to the distance between the

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20

Stevens, Syman. "The dynamical approach to relativity as a form of regularity relationalism." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:430d0b64-f54d-45b4-ac10-c8f4f4e53748.

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This thesis investigates the interplay between explanatory issues in special relativity and the theory's metaphysical foundations. Special attention is given to the 'dynamical approach' to relativity, promoted primarily by Harvey Brown and collaborators, according to which the symmetries of dynamical laws are explanatory of relativistic effects, inertial motion, and even the Minkowskian geometrical structure of a specially relativistic world. The thesis begins with a review of Einstein's 1905 introduction to special relativity, after which brief historical introductions are given for the stand

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21

Sirois-Miron, Robin. "Quotients d'une variété algébrique par un groupe algébrique linéairement réductif et ses sous-groupes maximaux unipotents." Thèse, 2010. http://hdl.handle.net/1866/3621.

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La construction d'un quotient, en topologie, est relativement simple; si $G$ est un groupe topologique agissant sur un espace topologique $X$, on peut considérer l'application naturelle de $X$ dans $X/G$, l'espace d'orbites muni de la topologie quotient. En géométrie algébrique, malheureusement, il n'est généralement pas possible de munir l'espace d'orbites d'une structure de variété. Dans le cas de l'action d'un groupe linéairement réductif $G$ sur une variété projective $X$, la théorie géométrique des invariants nous permet toutefois de construire un morphisme de variété d'un ouvert $U$ de $

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22

Weng, Hong-Yuan, and 翁宏源. "Using Covariance matrix and Autocorrelation Invariance for 2D-object Recognition." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/5dhd2w.

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碩士<br>國立臺北科技大學<br>工業工程與管理系所<br>93<br>This study proposes an effective recognition system of two-dimensional objects by incorporating the eigenvalues of covariance matrix with invariance of autocorrelation coefficient. The proposed method first uses mean threshold method to derive the image. Then, a morphologic operation is adopted to extract the boundary of a digital object. Two-stage feature extract is designed in this study. First, the boundary of object is represented by calculating the eigenvalues of the covariance matrix according to the region of support. Secondly, the sampled eigenvalue

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23

Wu, Sz-Shyan. "The impact of poorly translated items on measurement invariance a cross-cultural study using mean and covariance structure and differential item functioning /." 2005. http://purl.galileo.usg.edu/uga%5Fetd/wu%5Fsz-shyan%5F200508%5Fphd.

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24

Weinert, Friedel. "Einstein and the Laws of Physics." 2007. http://hdl.handle.net/10454/4066.

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No<br>The purpose of this paper is to highlight the importance of constraints in the theory of relativity and, in particular, what philosophical work they do for Einstein's views on the laws of physics. Einstein presents a view of local ``structure laws'' which he characterizes as the most appropriate form of physical laws. Einstein was committed to a view of science, which presents a synthesis between rational and empirical elements as its hallmark. If scientific constructs are free inventions of the human mind, as Einstein, held, the question arises how such rational constructs, including th

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25

Weinert, Friedel. "EPR and the 'Passage' of Time." 2013. http://hdl.handle.net/10454/11903.

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Yes<br>The essay revisits the puzzle of the ‘passage’ of time in relation to EPR-type measurements and asks what philosophical consequences can be drawn from them. Some argue that the lack of invariance of temporal order in the measurement of a space-like related EPR pair, under relativistic motion, casts serious doubts on the ‘reality’ of the lapse of time. Others argue that certain features of quantum mechanics establish a tensed theory of time – understood here as Possibilism or the growing block universe. The paper analyzes the employment of frame-invariant entropic clocks in a relativist

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