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While most micrometeorological measurement techniques are only suitable for windy conditions, the Nocturnal Boundary Layer Technique can be used to measure trace gas flux during calm, clear nights as the nighttime stability enables gas emitted at the ground to accumulate. The difference between two measurements over the whole depth of this layer is believed to integrate emissions from a large area representative of, in this study, an agricultural farm. A tethersonde and infrared gas analyzer attached to a blimp carrying a bag sampling system monitored atmospheric variables for each ascent during two summer field campaigns. A mini-SODAR was installed in the field to obtain the wind flowfield. Strong accumulation was observed under low level jets suggesting that this feature acts as a good lid for trace gases. An average background vertical motion different from zero seemed to have more influence on gas propagation than did intermittent turbulence. On at least one night, a density current created by the nearby St-Lawrence River was observed to influence measurements.

Optimized Schwarz methods are iterative domain decomposition procedures with greatly improved convergence properties, for solving second order elliptic boundary value problems. The enhanced convergence is obtained by replacing the Dirichlet transmission conditions in the classical Schwarz iteration with more general conditions that are optimized for performance. The convergence is optimized through the solution of a min-max problem. The theoretical study of the min-max problems gives explicit formulas or characterizations for the optimized transmission conditions for practical use, and it permits the analysis of the asymptotic behavior of the convergence. / In the first part of this work, we continue the study of optimized transmission conditions for advection-diffusion problems with smooth coefficients. We derive asymptotic formulas for the optimized parameters for small mesh sizes, in the overlapping and non-overlapping cases, and show that these formulas are accurate when the component of the advection tangential to the interface is not too large. / In a second part, we consider a diffusion problem with a discontinuous coefficient and non-overlapping domain decompositions. We derive several choices of optimized transmission conditions by thoroughly solving the associated min-max problems. We show in particular that the convergence of optimized Schwarz methods improves as the jump in the coefficient increases, if an appropriate scaling of the transmission conditions is used. Moreover, we prove that optimized two-sided Robin conditions lead to mesh-independent convergence. Numerical experiments with two subdomains are presented to verify the analysis. We also report the results of experiments using the decomposition of a rectangle into many vertical strips; some additional analysis is carried out to improve the optimized transmission conditions in that case. / On a third topic, we experiment with different coarse space corrections for the Schwarz method in a simple one-dimensional setting, for both overlapping and non-overlapping subdomains. The goal is to obtain a convergence that does not deteriorate as we increase the number of subdomains. We design a coarse space correction for the Schwarz method with Robin transmission conditions by considering an augmented linear system, which avoids merging the local approximations in overlapping regions. With numerical experiments, we demonstrate that the best Robin conditions are very different for the Schwarz iteration with, and without coarse correction.

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Let Ω be a Lipschitz domain in Rᴺ,n ≥ 3, and L = divA∇ - B∇ be a second order elliptic operator in divergence form with real coefficients such that A is a bounded elliptic matrix and the vector field B ɛ L∞loc(Ω) is divergence free and satisfies the growth condition dist(X,∂Ω)|B(X)|≤ ɛ1 for ɛ1 small in a neighbourhood of ∂Ω. For these elliptic operators we will study on the basis of the theory for elliptic operators without drift terms the Dirichlet problem for boundary data in Lp(∂Ω), 1 < p < ∞, and the regularity problem for boundary data in W¹,ᵖ(∂Ω) and HS¹. The main result of this thesis is that the solvability of the regularity problem for boundary data in HS1 implies the solvability of the adjoint Dirichlet problem for boundary data in Lᵖ'(∂Ω) and the solvability of the regularity problem with boundary data in W¹,ᵖ(∂Ω for some 1 < p < ∞. In [KP93] C.E. Kenig and J. Pipher have proven for elliptic operators without drift terms that the solvability of the regularity problem with boundary data in W¹,ᵖ(∂Ω) implies the solvability with boundary data in HS1. Thus the result of C.E. Kenig and J. Pipher and our main result complement a result in [DKP10], where it was shown for elliptic operators without drift terms that the Dirichlet problem with boundary data in BMO is solvable if and only if it is solvable for boundary data in Lᵖ(∂Ω) for some 1 < p < ∞. In order to prove the main result we will prove for the elliptic operators L the existence of a Green's function, the doubling property of the elliptic measure and a comparison principle for weak solutions, which are well known results for elliptic operators without drift terms. Moreover, the solvability of the continuous Dirichlet problem will be established for elliptic operators L = div(A∇+B)+C∇+D with B,C,D ɛ L∞loc(Ω) such that in a small neighbourhood of ∂Ω we have that dist(X,∂Ω)(|B(X)| + |C(X)| + |D(X)|) ≤ ɛ1 for ɛ1 small and that the vector field B satisfies |∫B∇Ø| ≤ C∫|∇Ø| for all Ø ɛ Wₒ¹'¹ of that neighbourhood.

The aim of this work was to develop an envelope function method to calculate the electronic states and optical properties of complex quantum well heterostructures, and to demonstrate its effectiveness by application to some device structures of topical interest. In particular, structures have been considered which might form the basis of intensity modulators and polarization insensitive amplifier devices for light at a wavelength of 1.55 µm. The modulator structures considered all have the general form of two coupled quantum wells of different widths as the active region. The application of an electric field in the growth direction is intended to result in a shift in the energy and spatial localisation of the confined states and produce an increase in the absorption coefficient at longer wavelengths than the zero field absorption edge. The effectiveness of certain structures is examined in terms of field induced absorption increase at 1.55 µm. A system which shows a significant increase in absorption coefficient at this wavelength on application of a practical electric field has been identified as a possible candidate for an intensity modulator. In the case of the amplifier, the active region of the most promising structure considered consists of a stepped well which comprises two layers, one with tensile and one with compressive strain. It is known that the presence of the two oppositely strained layers can result in the TE and TM gain peaks appearing at similar photon energies. Our calculations show that a suitable choice of strain and layer widths can result in a small or zero difference between the TE and TM gains at 1.55 µm, which can be important for the polarization insensitive operation of devices in optical communications applications. In order to predict the optical properties of quantum well devices it is necessary to calculate the electron and hole states for a range of in-plane wavevectors. The calculations developed and carried out in this work are based on a multi-layer (eight band) k.p model including strain effects. The interfacial boundary conditions which result from approximations to Burt's exact envelope function theory are included in the model. The effect of an electric field is modelled by including a potential energy term in each layer Hamiltonian which is equal to the average energy shift across the layer in question due to the presence of the field. The model has been developed with flexibility in mind and has applications beyond the specific devices considered in this thesis.

The north-east Atlantic margin (NEAM) is important for hydrocarbon exploration because of the growing evidence of hydrocarbon reserves in the region. However, seismic exploration of the sub-surface is hampered by large deposits of flood basalts, which cover possible hydrocarbon-bearing reservoirs underneath. There are several hypotheses as to why imaging beneath basalt is a problem. These include: the high impedance contrast between the basalt and the layers above; the thin-layering of the basalt due to the many flows which make up a basalt succession; and the rough interfaces on the top-basalt interface caused by weathering and emplacement mechanisms. I perform forward modelling to assess the relative importance of these factors for imaging of sub-basalt reflections. The boundary element method (BEM) is used for the rough-interface modelling. The method was selected because only the interfaces between layers need to be discretized, in contrast to grid methods such as finite difference for which the whole model needs to be discretized, and so should lead to fast generation of shot gathers for models which have only a few homogeneous layers. I have had to develop criteria for accurate modelling with the boundary element method and have considered the following: source near an interface, two interfaces close together, removal of model edge effects and precise modelling of a transparent interface. I have improved efficiency of my code by: resampling the model so that fewer discretization elements are required at low frequencies, and suppressing wrap-around so that the time window length can be reduced. I introduce a new scheme which combines domain decomposition and a far-field approximation to improve the efficiency of the boundary element code further. I compare performance with a standard finite difference code. I show that the BEM is well suited to seismic modelling in an exploration environment when there are only a few layers in the model and when a seismic profile containing many shot gathers for one model is required. For many other cases the finite difference code is still the best option. The input models for the forward modelling are based on real seismic data which were acquired in the Faeroe-Shetland Channel in 2001. The modelling shows that roughness on the surface of the basalt has little effect on the imaging in this particular area of the NEAM. The thin layers in the basalt act as a low-pass filter to the seismic wave. For the real-data acquisition, even the topbasalt reflection is a low frequency event. This is most likely to be due to high attenuation in the layers above the basalt. I show that sea-surface multiple energy is considerable and that it could mask possible sub-basalt events on a seismic shot gather, but any shallow sub-basalt events should still be visible even with the presence of multiple energy. This leaves the possibility that there is only one major stratigraphic unit between the base of the basalt and the crystalline basement. The implication of the forward modelling and real data analysis for acquisition is that the acquisition parameters must emphasize the low frequencies, since the high frequencies are attenuated before they even reach the top-basalt interface. The implication for processing is that multiple removal is of prime importance.

A map is important for autonomous mobile robots to traverse an environment safely and efficiently through highly competent abilities in path planning, navigation and localization. Maps are generated from sensors data. However, sensor uncertainties affect the mapping process and thus influence the performance of path planning, navigation and localization capabilities. This thesis proposes to incorporate sensor uncertainty information in robot environmental map using Fuzzy Boundary Representation (B-rep). Fuzzy B-rep map is generated by first converting measured range data into scan polygons, then combining scan polygons into resultant robot B-rep map by union operation and finally fuzzifying the B-rep map by sweeping sensor uncertainty membership function along generated B-rep map. A map of the fifth floor of E1 building is generated using the proposed method to demonstrate the alleviation in computational and memory load for robot environment mapping using Fuzzy B-rep, in contrast to the conventional grid based mapping methods.

The volume of poetry Kleur kom nooit alleen nie (Colour never comes on its own) by Antjie Krog, is analysed extensively in this thesis. The main focus of the study is the way in which metaphors associated with boundaries, bordering, transgression and the crossing of boundaries are used to represent the struggle to come to terms with a traumatic past and to rethink new possibilities of co-existence in the future. In the poems the boundaries of the word, the text and the genre of poetry, as well as geographical and political boundaries and the boundaries of gender, especially the boundaries instituted by the patriarchal order, are challenged. The narration of alternative histories to supplement and correct documented history may also be considered as a boundary-crossing activity. Although colour is the most obvious metaphor of the divisions between people and is indeed used as the central metaphor throughout the volume, many other, sometimes more subtle examples of boundaries and bordering are explored and developed. There is for instance a strong focus on the psychological complexity of creativity and of writing poetry. The poet's withdrawal to a liminal zone which incorporates the almost spiritual dimension of her creative activities clearly forms a kind of leitmotiv in the collection. The text clearly suggests that the artist as a liminal figure achieves an enhanced ability to understand the forces at work in a community. Sharing the results of this insight from the liminal zone with the community implies that the artist can stimulate innovative processes which will obliterate boundaries and enable people to co-exist peacefully. Although the crossing of borders in most cases result in being wounded, there are also the possibilities of recovery and healing. The resultant scars are often regarded as strong identity-shaping features in people. Krog argues that language plays a decisive role in processes of reconciliation and that the text itself becomes a threshold area where different discourses interact and cross-fertilise one another. The structure of the thesis reflects the theoretical approach and is an attempt to present a balanced discussion of the aesthetic and the ideological aspects of Kleur kom nooit alleen nie as a poetic text. Appropriate theories are implemented to do justice to both the aesthetic qualities and the ideological undercurrents of single poems as well as the volume as such. Two discourses are therefore superimposed in order to present an adequate reading of this polyphonic and ambivalent text. 'The exploration of the varied manifestations of the boundary forms a continuous thematic line throughout the thesis but related themes such as identity, liminality and hybridity are also incorporated. On account of the postmodernistic nature of the text, the basic theoretical framework is that of literary postmodernism, with narrativity of the text, intertextuality, post-colonialism and feminism as its most significant manifestations. / Thesis (Ph.D. (Afrikaans and Dutch))--North-West University, Potchefstroom Campus, 2007.