Σκοπός της παρούσας διατριβής είναι η κατασκευή και μελέτη συνολοθεωρητικών λύσεων της κβαντικής εξίσωσης Yang-Baxter (απεικονίσεις Yang-Baxter) και η συσχέτισή τους με την ολοκληρωσιμότητα διακριτών δυναμικών συστημάτων. Οι κατασκευές απεικονίσεων Yang-Baxter που προτείνονται προέρχονται από την αναπαραγοντοποίηση ισχυρών ζευγών Lax εξαρτώμενων από μια φασματική παράμετρο. Οι αντίστοιχοι πίνακες Lax προκύπτουν από την συμπλεκτική εμφύλλωση διωνυμικών πινάκων εφοδιασμένων με μια κατάλληλη δομή Poisson (αγκύλη Sklyanin). Στην περίπτωση των 2x2 πινάκων Lax, οι αντίστοιχες απεικονίσεις είναι συμπλεκτικές, τετράρητες και ταξινομούνται με βάση τον μεγιστοβάθμιο όρο του πίνακα Lax ως προς την ισοδυναμία απεικονίσεων Yang-Baxter. Εκφυλισμένες απεικονίσεις Yang-Baxter, οι οποίες σχετίζονται με γνωστές ολοκληρώσιμες εξισώσεις, προκύπτουν από όρια των τετράρητων (μη-εκφυλισμένων). Η σύνδεση μεταξύ απεικονίσεων Yang-Baxter και ολοκληρωσιμότητας επιτυγχάνεται θεωρώντας περιοδικά προβλήματα αρχικών τιμών σε δισδιάστατα πλέγματα. Σε κάθε απεικόνιση Yang-Baxter αντιστοιχεί μια οικογένεια αντιμεταθετικών απεικονίσεων μεταφοράς στο πλέγμα (transfer maps) που διατηρούν αναλλοίωτο το φάσμα του μονόδρομου πίνακά τους. Η αγκύλη Sklyanin εξασφαλίζει την ενέλιξη των ολοκληρωμάτων που προκύπτουν από το φάσμα του μονόδρομου πίνακα. Κατά αυτόν τον τρόπο από τις συμπλεκτικές απεικονίσεις Yang-Baxter που κατασκευάσαμε παράγονται ολοκληρώσιμες απεικονίσεις μεταφοράς. Τέλος, η μελέτη μας επεκτείνεται σε συστήματα πεπλεγμένων απεικονίσεων Yang-Baxter (entwining Yang-Baxter maps) . / The purpose of this thesis is the construction and the study of set theoretical solutions of the quantum Yang-Baxter equation (Yang-Baxter maps) and the connection with the integrability of discrete integrable systems. The constructions that we present are derived from the re-factorization of strong Lax pairs depending on a spectral parameter. The corresponding Lax matrices are obtained from the symplectic foliation of binomial matrices equipped with an appropriate Poisson bracket (Sklyanin bracket). In the case of 2x2 binomial Lax matrices, the corresponding maps are symplectic, quadrirational and can be classified with respect to the Yang-Baxter equivalence. Degenerate Yang-baxter maps constructed as limits of the quadrirational maps, are connected to known integrable equations. The connection between Yang-Baxter maps and integrability is achieved by considering periodic initial value problems on two dimensional lattices. For any Yang-Baxter map that admits a Lax matrix, there is a family of commuting transfer maps which preserve the spectrum of their monodromy matrix. The Skllyanin bracket ensures that the integrals obtained from the spectrum of the monodromy matrix are in involution. In this way, integrable transfer maps are generated from the symplectic Yang-Baxter maps that we constructed. Finally, our study is extended for systems of entwining Yang-Baxter maps.

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In this thesis we address the analytic and numerical aspects of isospectral flows. Such flows occur in mathematical physics and numerical linear algebra. Their main structural feature is to retain the eigenvalues in the solution space. We explore the solution of Isospectral flows and their stochastic counterpart using explicit generalisation of Magnus expansion. \par In the first part of the thesis we expand the solution of Bloch--Iserles equations, the matrix ordinary differential system of the form $ X'=[N,X^{2}],\ \ t\geq0, \ \ X(0)=X_0\in \textrm{Sym}(n),\ N\in \mathfrak{so}(n), $ where $\textrm{Sym}(n)$ denotes the space of real $n\times n$ symmetric matrices and $\mathfrak{so}(n)$ denotes the Lie algebra of real $n\times n$ skew-symmetric matrices. This system is endowed with Poisson structure and is integrable. Various important properties of the flow are discussed. The flow is solved using explicit Magnus expansion and the terms of expansion are represented as binary rooted trees deducing an explicit formalism to construct the trees recursively. Unlike classical numerical methods, e.g.\ Runge--Kutta and multistep methods, Magnus expansion respects the isospectrality of the system, and the shorthand of binary rooted trees reduces the computational cost of the exponentially growing terms. The desired structure of the solution (also with large time steps) has been displayed. \par Having seen the promising results in the first part of the thesis, the technique has been extended to the generalised double bracket flow $ X^{'}=[[N,X]+M,X], \ \ t\geq0, \ \ X(0)=X_0\in \textrm{Sym}(n),$ where $N\in \textrm{diag}(n)$ and $M\in \mathfrak{so}(n)$, which is also a form of an Isospectral flow. In the second part of the thesis we define the generalised double bracket flow and discuss its dynamics. It is noted that $N=0$ reduces it to an integrable flow, while for $M=0$ it results in a gradient flow. We analyse the flow for various non-zero values of $N$ and $M$ by assigning different weights and observe Hopf bifurcation in the system. The discretisation is done using Magnus series and the expansion terms have been portrayed using binary rooted trees. Although this matrix system appears more complex and leads to the tri-colour leaves; it has been possible to formulate the explicit recursive rule. The desired structure of the solution is obtained that leaves the eigenvalues invariant in the solution space.

Mechanisation of Mathematics refers to use of computers to generate or check proofs in Mathematics. It involves translation of relevant mathematical theories from one system of logic to another, to render these theories implementable in a computer. This process is termed formalisation of mathematics. Two among the many ways of mechanising are: 1 Generating results using automated theorem provers. 2 Interactive theorem proving in a proof assistant which involves a combination of user intervention and automation. In the first part of this thesis, we reformulate the question of equivalence of two Links in first order logic using braid groups. This is achieved by developing a set of axioms whose canonical model is the braid group on infinite strands B∞. This renders the problem of distinguishing knots and links, amenable to implementation in first order logic based automated theorem provers. We further state and prove results pertaining to models of braid axioms. The second part of the thesis deals with formalising knot Theory in Higher Order Logic using the interactive proof assistant -Isabelle. We formulate equivalence of links in higher order logic. We obtain a construction of Kauffman bracket in the interactive proof assistant called Isabelle proof assistant. We further obtain a machine checked proof of invariance of Kauffman bracket.

Ce travail est consacré a l'étude des déformations covariantes des orbites co-adjointes du groupe de Lie SL(2,R).Nous établissons un lien entre des méthodes de quantification basées sur les crochets de Rankin-Cohen et les matrices de fusion pour les modules de Verma. Par ailleurs nous formalisons et étudions la notion associée d'algèbre de Rankin-Cohen qui contrôle l'associativité de ces déformations. / This work is devoted to the study of covariant star-product on coadjointorbits of the Lie group SL(2,R). We establish a correspondence between two quantization methods. The first is based on the Rankin-Cohen brackets and the second is based in the canonical element associate to the Shapovalov form and fusion matrices for Verma modules.Furthermore we formalize and study the associated notion of non-commutative algebra that controls the associativity of these deformations.

Goldman [Gol86] introduced a Lie algebra structure on the free vector space generated by the free homotopy classes of oriented closed curves in any orientable surface F . This Lie bracket is known as the Goldman bracket and the Lie algebra is known as the Goldman Lie algebra. In this dissertation, we compute the center of the Goldman Lie algebra for any hyperbolic surface of finite type. We use hyperbolic geometry and geometric group theory to prove our theorems. We show that for any hyperbolic surface of finite type, the center of the Goldman Lie algebra is generated by closed curves which are either homotopically trivial or homotopic to boundary components or punctures. We use these results to identify the quotient of the Goldman Lie algebra of a non-closed surface by its center as a sub-algebra of the first Hochschild cohomology of the fundamental group. Using hyperbolic geometry, we prove a special case of a theorem of Chas [Cha10], namely, the geometric intersection number between two simple closed geodesics is the same as the number of terms (counted with multiplicity) in the Goldman bracket between them. We also construct infinitely many pairs of length equivalent curves in any hyperbolic surface F of finite type. Our construction shows that given a self- intersecting geodesic x of F and any self-intersection point P of x, we get a sequence of such pairs.

Tato diplomová práce se zabývá popisem kinematického modelu řízení neholonomního mechanismu, konkrétně robotického hada. Model je zkoumán prostředky diferenciální geometrie. Dále je odvozena jeho nilpotentní aproximace. Lokální říditelnost je zjištěna pomocí dimenze Lieovy algebry generované řídícími vektorovými poli a jejich Lieovými závorkami. V závěru jsou navrženy dva jednoduché řídící algoritmy, jeden pro globální a druhý pro lokální řízení, a poté následuje srovnání jednotlivých modelů.

The purpose of this thesis is to overview the basic design solutions of full aluminum radiators. By finite element method to check the first generation of full aluminum low temperature radiator bracket and based on this calculation to modify the design to reduce tension in the critical areas. At the end of this thesis to evaluate the new design.

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In a bus chassis, welded connections are often preferred to other fastening techniques due to low cost and broad competence among suppliers but are usually the weakest parts due to fatigue life. Evaluation of welds is often costly in time and competence. Long iteration times are often leaving welded designs unoptimized and poorly understood by designers and engineers. The goal of this thesis is to gather knowledge about a plug-welded bracket commonly found welded to beams in bus chassis and body, aiding the design and dimensioning of such brackets. A factorial design study was performed using FEM analysis with the “Effective notch method,” revealing the effects of seven different design parameters on the stresses in the weld. A theory to analytically calculate the profile of the bracket is presented. The theory is taking the beam’s second moment of area and the bending moment into consideration, essentially tuning the bracket’s stiffness to the beam and the load situation. An improved bracket is presented, analyzed, and compared to the design study. The results show how stresses in the weld are affected by the stiffness of the bend in the bracket, the location of bolts (or other fastening technique) and the plug weld dimensions. When the weld is made to run longer along the beam, the importance of adjusting the stiffness in the bracket increases in order to balance the load throughout the whole weld. / Svetsade fästelement är ofta att föredra i ett busschassi över andra tekniker av kostnadsskäl och att en bred kompetens finns inom svets hos många underleverantörer. Men på grund av utmattning är ofta svetsade infästningar den svagaste punkten i ett chassi. Utvärdering av svetsar är kostsamt i tid och kompetens. Långa iterationstider i svetsutvärderingar lämnar ofta svetsen ooptimerad och undermåligt förstådd av designers och ingenjörer. Målet med detta arbete är att samla kunskap runt ett pluggsvetsat fästelement som ofta förekommer i busschassier och busskarosser, för att underlätta design och dimensionering av dessa fästelement. En faktoriell designstudie var utförd med FEM analys enligt ”Effective Notch” metoden för att undersöka effekten från sju olika designparametrar på spänningskoncentrationerna i svetsen. En teori för att analytiskt beräkna profilen på fästelementet presenteras. Teorin tar balkens böjtröghetsmoment och böjmoment med i beräkningen för att optimera fästelementets styvhet till balken och lastsituationen. Ett förbättrat fästelement är presenterat, analyserat och jämförd med designstudien. Resultaten visar hur spänningarna i svetsen påverkas av styvheten i den böjda delen av fästelementet, placeringen av bultar (eller annan infästningsteknik) och dimensioner på ”svetspluggen.” När svetsen är går längre längs med balken blir fästelementets styvhet allt viktigare för att kunna balansera lasten igenom det svetsade området.