Disputats, Göteborg : Chalmers Tekniska Högskola ; Göteborgs universitet, 2008. / Findes også på internet. Med litteraturhenvisninger.

In this thesis we collect the study of two problems in the Calculus of Variations and Partial Differential Equations. Our first group of results concern the analysis of minimizers in a variational model describing the shape of liquid drops and crystals under the influence of gravity, resting on a horizontal surface. Making use of anisotropic symmetrization techniques and an analysis of fine properties of minimizers within the class of sets of finite perimeter, we establish existence, convexity and symmetry of minimizers. In the case of smooth surface tensions, we obtain uniqueness of minimizers via an ODE characterization. In the second group of results discussed in this thesis, which is joint work with A. Vasseur, we treat a problem in compressible fluid dynamics, establishing a uniform bound from below on the temperature for a variant of the compressible Navier-Stokes-Fourier system under suitable hypotheses. This system of equations forms a mathematical model of the motion of a compressible fluid subject to heat conduction. Building upon the work of (Mellet, Vasseur 2009), we identify a class of weak solutions satisfying a localized form of the entropy inequality (adapted to measure the set where the temperature becomes small) and use a form of the De Giorgi argument for L[superscript infinity] bounds of solutions to elliptic equations with bounded measurable coefficients. / text

M. Tech. Mathematical Technology. / Discusses the main problems in terms of how to derive mathematical models for a free, a forced and a damped spring pendulum and determining numerical solutions using a computer algebra system (CAS), because exact analytical solutions are not obvious. Hence this mini-dissertation mainly deals with how to derive mathematical models for the spring pendulum using the Euler-Lagrange equations both in the Cartesian and polar coordinate systems and finding solutions numerically. Derivation of the equations of motion are done for the free, forced and damped cases of the spring pendulum. The main objectives of this mini-dissertation are: firstly, to derive the equations of motion governing the oscillatory and rotational components of the spring pendulum for the free, the forced and damped cases of the spring pendulum ; secondly, to solve these equations numerically by writing the equations as initial value problems (IVP); and finally, to introduce a novel way of incorporating nonlinear damping into the Euler-Lagrange equations of motion as introduced by Joubert, Shatalov and Manzhirov (2013, [20]) for the spring pendulum and interpreting the numerical solutions using CAS-generated graphics.

This report provides an introduction to geometric mechanics, which seeks to model the behavior of physical mechanical systems using differential geometric objects. In addition to its elegance as a method of representation, this formulation also admits the application of powerful analytical techniques from geometry as an aid to understanding these systems. In particular, it reveals the fundamental role that symplectic geometry plays in mechanics (something which is not at all obvious from the traditional Newtonian formulation), and in the case of systems exhibiting symmetry, leads to an elucidation of conservation and reduction laws which can be used to simplify the analysis of these systems. The contribution here is primarily one of exposition. Geometric mechanics was developed as an aid to understanding physics, and we have endeavored throughout to highlight the physical principles at work behind the mathematical formalism. In particular, we show quite explicitly the entire development of mechanics from first principles, beginning with Newton's laws of motion and culminating in the geometric reformulation of Lagrangian and Hamiltonian mechanics. Self-contained presentations of this entire range of material do not appear to be common in either the physics or the mathematics literature, but we feel very strongly that this is essential in order to understand how the more abstract mathematical developments that follow actually relate to the real world. We have also attempted to make many of the proofs contained herein more explicit than they appear in the standard references, both as an aid in understanding and simply to make them easier to follow, and several of them are original where we feel that their presentation in the literature was unacceptably opaque (this occurs primarily in the presentation of the geometric formulation of Lagrangian mechanics and the appendix on symplectic geometry). Finally, we point out that the fields of geometric mechanics and symplectic geometry are vast, and one could not hope to get more than a fragmentary glimpse of them in a single work, which necessiates some parsimony in the presentation of material. The subject matter covered herein was chosen because it is of particular interest from an applied or engineering perspective in addition to its mathematical appeal. / text

Parametric equations are used to represent the pathway of an object in terms of time or another changing variable. This allows, for example, for equations that are written using two variables to be examined in terms of the passage of time. In this paper the author examines two traditional application problems whose solutions can be enriched through the use of parametric equations. In the first, the falling ladder problem, a ladder is leaned against a wall then pulled away with a constant velocity. Deriving parametric equations for this scenario permits the pathway of the ladder to be plotted. Parametric equations also make it possible for the horizontal and vertical velocities of the ladder to be examined separately. The second problem is that of maximizing the length of a ladder that can fit around a hallway corner. In this problem an envelope algorithm is first developed, then parametrized to further investigate this scenario. Using these two situations, this report ultimately shows how parametric equations can be used to give a more thorough approach to some of today’s most classic calculus problems. / text

A psi-calculus is an extension of the pi-calculus with nominal data types for data structures, logical assertions, and conditions. These can be transmitted between processes and their names can be statically scoped as in the standard pi-calculus. Expressiveness and therefore modelling convenience significantly exceed those of other formalisms: psi-calculi can capture the same phenomena as other extensions of the pi-calculus, and can be more general, e.g. by allowing structured channels, higher-order formalisms such as the lambda calculus for data structures, and predicate logic for assertions. Ample comparisons to related calculi are provided and a few significant applications are discussed. The labelled operational semantics and definition of bisimulation is straightforward, without a structural congruence. Minimal requirements on the nominal data and logic are established in order to prove general algebraic properties of psi-calculi. The purity of the semantics is on par with the pi-calculus. The theory of weak bisimulation is established, where the tau actions are unobservable. The notion of barb is defined as the output label of a communication action, and weak barbed equivalence is bisimilarity for tau actions and preservation of weak barbs in all static contexts. It is proved that weak barbed equivalence coincides with weak bisimulation equivalence. A symbolic transition system and bisimulation equivalence is presented, and shown fully abstract with respect to bisimulation congruence in the non-symbolic semantics. The symbolic semantics is necessary for an efficient implementation of the calculus in automated tools exploring state spaces, and the full abstraction property means processes are bisimilar in the symbolic setting if they are bisimilar in the original semantics. Psi-calculi remove the necessity of proving general properties every time a new mobile process calculus is defined. By properly instantiating the framework the properties are guaranteed to hold, thus removing the need to do tedious and error-prone proofs.

This was a qualitative study carried out with learners from a grade twelve Standard Grade mathematics class from a South Durban school in the province of KwaZulu-Natal, South Africa. The main purpose of this study was to explore learners‟ understanding of the concept of the derivative. The participants comprised one class of twenty seven learners who were enrolled for Standard Grade mathematics at grade twelve level. Learners‟ responses to May and August examinations were examined. The examination questions that were highlighted were those based on the concept of the derivative. Additionally semi-structured interviews were carried out with a smaller sample of four of the twenty seven learners to gauge their perceptions of the derivative. The learners‟ responses to the examination questions and semi-structured interviews were exhaustively analysed. Themes that ran across the data were identified and further categorised in a bid to provide answers to the main research question. It was found that most learners‟ difficulties with the test items were grounded in their difficulties with algebraic manipulation skills. A further finding was that learners overwhelmingly preferred working out items that involved applying the rules. Although the Higher and Standard grade system of assessing learners‟ mathematical abilities has been phased out, with the advent of the new curriculum, the findings of this study is still important for learners, teachers, curriculum developers and mathematics educators because calculus forms a large component of the new mathematics curriculum. / Thesis (M.Ed.)-University of KwaZulu-Natal, Durban, 2008.

This thesis investigates the mathematical cognitive errors made in elementary calculus concepts by first-year University of Technology students. A sample of 34 first year students, the experimental group, from the Durban University of Technology Faculty of Engineering were invited to participate in project in elementary calculus using computer technology (CT). A second group, the control group, also consisted of 34 first year engineering students from the same University were given a conventional test in elementary calculus concepts. The experimental group was then given the same conventional test as the control group on completion of the project in elementary calculus using computer technology (CT). The purpose of the analysis was to study the effect of technology on the understanding of key concepts in elementary calculus. The major finding was that technology helps students to make connections, analyse ideas and develop conceptual frameworks for thinking and problem solving. The implications include: • Improvement of curriculum in mathematics at tertiary level; • New strategies for lecturers of elementary calculus; • An improved understanding by students taking the course in elementary calculus. • Redesign of software to improve understanding in elementary calculus. / Thesis (M.Ed.)-University of KwaZulu-Natal, Durban, 2007.

The Lie theory of extended groups is a practical tool in the analysis of differential equations, particularly in the construction of solutions. A formalism of the Lie theory is given and contrasted with Noether's theorem which plays a prominent role in the analysis of differential equations derivable from a Lagrangian. The relationship between the Lie and Noether approach to differential equations is investigated. The standard separation of Lie point symmetries into Noetherian and nonNoetherian symmetries is shown to be irrelevant within the context of nonlocality. This also emphasises the role played by nonlocal symmetries in such an approach. / Thesis (M.Sc.)-University of Natal, Durban, 1997.

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