The fast development of wireless networks, which are intrinsically exposed to eavesdropping, has created a growing concern for confidentiality. While classical cryptographic schemes require a key provided by the end-user, physical-layer security leverages the randomness of the physical communication medium as a source of secrecy. The main benefit of physical-layer security techniques is their relatively low cost and their ability to combine with any existing security mechanisms. This dissertation provides an analysis including the theoretical study of the two-way wiretap channel to obtain a better insight into how to design coding mechanisms, practical tests with experimental systems, and the design of actual codes. From a theoretical standpoint, the study confirms the benefits of combining several multi-user coding techniques including cooperative jamming, coded cooperative jamming and secret key generation. For these different mechanisms, the trade-off between reliability, secrecy and communication rate is clarified under a stringent strong secrecy metric. Regarding the design of practical codes, spatially coupled LDPC codes, which were originally designed for reliability, are modified to develop a coded cooperative jamming code. Finally, a proof-of-principle practical wireless system is provided to show how to implement a secret key generation system on experimental programmable radios. This testbed is then used to assess the realistic performance of such systems in terms of reliability, secrecy and rate.

Although companies and organisations worldwide publish in-house journals, there is no comprehensive theory (including technical and normative dimensions) available on this important public relations instrument. In particular, no research is available on what the characteristics of excellent South African in-house journals are or ought to be. In this study a number of dimensions are thus introduced in order to help create a comprehensive framework for analysing in-house journals, in particular South Africa’s leading in-house journals. Firstly, James Grunig’s excellence in public relations theory (published in 1992), which incorporates the concept of two-way symmetrical communication (which in turn is informed by a “symmetric” world view), is put forward as basic point of departure. Secondly, a set of technical criteria for excellent in-house journals gleaned from a wide range of sources, is compiled. Furthermore, the internal and external environments in which South African in-house journals function are identified. The role of other new media (such as e-mail, intranet, television and radio) is also taken into account. Five leading South African in-house journals are then analysed and the views of editors reflected. It was found that Abacus (Absa Bank), Harmonise (Harmony Gold Mining Company), Hello the future (MTN), Pick ’n Patter (Pick ’n Pay) and Sandaba (Sanlam) all measured up well against the theoretical statements flowing from the said theoretical points of departure. However, the analysis did also bring to the fore deviations from the said statements which give new insight into what is required to publish an excellent in-house journal. In conclusion, the criteria are evaluated against some of the more detailed findings of the analysis and adapted to create a set of theoretically based guidelines that can be used by South African companies, focusing inter alia on how the unique character and environment of a company influence its internal communication, to create excellent in-house journals. In final analysis, it is argued that all factors, starting with the philosophical points of departure informing communication strategies, management’s attitude toward internal communication, organisation culture, the socio-political environment in which in-house journals function as well as the technical aspects of these publications, need to be considered when formulating criteria for “excellent” in-house journalism. This study thus endeavours to contribute to the professional integrity of public relations in a sea of asymmetric, marketing-driven internal communication. / Thesis (Ph.D. (Communication Studies))--North-West University, Potchefstroom Campus, 2006.

In this research, Communicative Accommodation Theory (CAT) is investigated while native speakers address nonnative peers. For the intentions of this research, three native speakers of Canadian English were asked to have conversations with native and nonnative peers. The conversations were in the form of giving directions on the map. Later on, the participants’ formants and vowel durations were measured and used for comparing native-nonnative peer effect(s) on the speakers’ vowel formants and duration. Based on the analyses, it is suggested that accommodation may take place based on providing stereotypical vowel durations and formants, as well as reducing inter-token variations in the nonnative peer context.

In this research, Communicative Accommodation Theory (CAT) is investigated while native speakers address nonnative peers. For the intentions of this research, three native speakers of Canadian English were asked to have conversations with native and nonnative peers. The conversations were in the form of giving directions on the map. Later on, the participants’ formants and vowel durations were measured and used for comparing native-nonnative peer effect(s) on the speakers’ vowel formants and duration. Based on the analyses, it is suggested that accommodation may take place based on providing stereotypical vowel durations and formants, as well as reducing inter-token variations in the nonnative peer context.

Although companies and organisations worldwide publish in-house journals, there is no comprehensive theory (including technical and normative dimensions) available on this important public relations instrument. In particular, no research is available on what the characteristics of excellent South African in-house journals are or ought to be. In this study a number of dimensions are thus introduced in order to help create a comprehensive framework for analysing in-house journals, in particular South Africa’s leading in-house journals. Firstly, James Grunig’s excellence in public relations theory (published in 1992), which incorporates the concept of two-way symmetrical communication (which in turn is informed by a “symmetric” world view), is put forward as basic point of departure. Secondly, a set of technical criteria for excellent in-house journals gleaned from a wide range of sources, is compiled. Furthermore, the internal and external environments in which South African in-house journals function are identified. The role of other new media (such as e-mail, intranet, television and radio) is also taken into account. Five leading South African in-house journals are then analysed and the views of editors reflected. It was found that Abacus (Absa Bank), Harmonise (Harmony Gold Mining Company), Hello the future (MTN), Pick ’n Patter (Pick ’n Pay) and Sandaba (Sanlam) all measured up well against the theoretical statements flowing from the said theoretical points of departure. However, the analysis did also bring to the fore deviations from the said statements which give new insight into what is required to publish an excellent in-house journal. In conclusion, the criteria are evaluated against some of the more detailed findings of the analysis and adapted to create a set of theoretically based guidelines that can be used by South African companies, focusing inter alia on how the unique character and environment of a company influence its internal communication, to create excellent in-house journals. In final analysis, it is argued that all factors, starting with the philosophical points of departure informing communication strategies, management’s attitude toward internal communication, organisation culture, the socio-political environment in which in-house journals function as well as the technical aspects of these publications, need to be considered when formulating criteria for “excellent” in-house journalism. This study thus endeavours to contribute to the professional integrity of public relations in a sea of asymmetric, marketing-driven internal communication. / Thesis (Ph.D. (Communication Studies))--North-West University, Potchefstroom Campus, 2006.

loveLife, the South African national HIV/AIDS prevention programme for youth, is known for its brand-oriented billboards and mass media campaign that ranges over various print-, broadcast- and alternative media. However, the organisation also implements a national grass-roots peer motivation programme where various activities are co-ordinated by youths (GroundBREAKERS and Mpintshis) from the community. The organisation has been criticised for its communication approach, with many researchers primarily focusing on the organisation's mass media and billboards. This study investigates the communicative approach(es) in loveLife's programme implementation in the light of the normative theory of participatory communication. The focus of this study is to identify how loveLife describes its communication approach, what communication approach the organisation employs and how the organisation's communication approach is perceived by a sample of its target audience. The research was conducted by means of a literature review, qualitative content analysis of loveLife's policy documentation and a selection of the organisation's media. Semi-structured interviews were also conducted at head office, which are contrasted with focus groups with the participants at an implementation site. Broadly, it was found that loveLife's programme is more participatory than most critics would expect and that the organisation attempts to put its primary focus on face-to-face communication. But, there is also tension in what loveLife communicates on a national level and how it relates to grass-roots activities as the national / media-driven communication is more modernistic in its approach, whereas the grass-roots communication is more participatory. / Thesis (M.A. (Communication Studies))--North-West University, Potchefstroom Campus, 2010.

loveLife, the South African national HIV/AIDS prevention programme for youth, is known for its brand-oriented billboards and mass media campaign that ranges over various print-, broadcast- and alternative media. However, the organisation also implements a national grass-roots peer motivation programme where various activities are co-ordinated by youths (GroundBREAKERS and Mpintshis) from the community. The organisation has been criticised for its communication approach, with many researchers primarily focusing on the organisation's mass media and billboards. This study investigates the communicative approach(es) in loveLife's programme implementation in the light of the normative theory of participatory communication. The focus of this study is to identify how loveLife describes its communication approach, what communication approach the organisation employs and how the organisation's communication approach is perceived by a sample of its target audience. The research was conducted by means of a literature review, qualitative content analysis of loveLife's policy documentation and a selection of the organisation's media. Semi-structured interviews were also conducted at head office, which are contrasted with focus groups with the participants at an implementation site. Broadly, it was found that loveLife's programme is more participatory than most critics would expect and that the organisation attempts to put its primary focus on face-to-face communication. But, there is also tension in what loveLife communicates on a national level and how it relates to grass-roots activities as the national / media-driven communication is more modernistic in its approach, whereas the grass-roots communication is more participatory. / Thesis (M.A. (Communication Studies))--North-West University, Potchefstroom Campus, 2010.

TiNiPd high-temperature shape memory alloys (HTSMAs) have attracted considerable attention as potential solid-state actuators capable of operating at temperatures up to 500 °C, exhibiting excellent corrosion resistance, adequate ductility levels and significant strain recovery under both constrained and unconstrained thermomechanical conditions. During operation, these actuators may be subjected to multiple cycles and from an application point of view, the functional stability, i.e. conservation of original actuator dimensions and transformation temperatures during repeated employment, is of considerable importance. This study addresses the issue of functional stability in a model HTSMA, Ti50.5Ni24.5Pd25, for its use as a compact solid-state actuator. Since the primary reason for functional instability is the creation of lattice defects (dislocations, vacancies, etc.) during repeated transformation cycles, several methods were successfully undertaken to improve the functional stability through inhibiting the generation of these defects. Solid-solution strengthening through Sc microalloying and thermomechanical treatments via severe plastic deformation were the two approaches used to strengthen the HTSMA against defect generation. Thermal cycling the HTSMA under stress was the third method to voluntarily introduce defects into the microstructure such that further defect generation during application would be impeded. Overall, severe plastic deformation was found to be more efficient than other strengthening methods in improving the functional stability of TiNiPd HTSMA, yet it brought about disadvantages such as reduction in transformation strain and transformation temperatures. While functional instability is due to the creation of lattice defects, the generation of these defects is mainly controlled by the crystallographic incompatibility between martensitically transforming phases and the strength levels for plastic deformation. It was shown that TiNiPd HTSMAs, which exhibited martensitic transformation from a cubic (B2) to orthorhombic (B19) symmetry, illustrated better compatibility and thus better functional stability levels compared to TiNi SMAs, which had a B2 to monoclinic (B19’) transition. Although crystallographic incompatibility seems to be the governing factor for the functional stability of the TiNiPd HTSMA, the strength differential between the onset of plastic deformation and local constraint due to the martensitic transformation was also found to be an influential factor determining the overall stable behavior. Functional stability was also investigated for the two-way shape memory effect (TWSME) in TiNiPd HTSMAs. Better strength and compatibility levels compared to TiNi SMAs were also reflected in the TWSME characteristics in the form of enhanced stability under stress-free thermal cycling. The stability during constrained thermal cycling was not as good and TWSME degraded rapidly while doing work against an opposing stress. Nevertheless, work output levels were much higher as compared to those obtained from conventional TiNi and Cu-based SMAs.

abstract: There are many wireless communication and networking applications that require high transmission rates and reliability with only limited resources in terms of bandwidth, power, hardware complexity etc.. Real-time video streaming, gaming and social networking are a few such examples. Over the years many problems have been addressed towards the goal of enabling such applications; however, significant challenges still remain, particularly, in the context of multi-user communications. With the motivation of addressing some of these challenges, the main focus of this dissertation is the design and analysis of capacity approaching coding schemes for several (wireless) multi-user communication scenarios. Specifically, three main themes are studied: superposition coding over broadcast channels, practical coding for binary-input binary-output broadcast channels, and signalling schemes for two-way relay channels. As the first contribution, we propose an analytical tool that allows for reliable comparison of different practical codes and decoding strategies over degraded broadcast channels, even for very low error rates for which simulations are impractical. The second contribution deals with binary-input binary-output degraded broadcast channels, for which an optimal encoding scheme that achieves the capacity boundary is found, and a practical coding scheme is given by concatenation of an outer low density parity check code and an inner (non-linear) mapper that induces desired distribution of "one" in a codeword. The third contribution considers two-way relay channels where the information exchange between two nodes takes place in two transmission phases using a coding scheme called physical-layer network coding. At the relay, a near optimal decoding strategy is derived using a list decoding algorithm, and an approximation is obtained by a joint decoding approach. For the latter scheme, an analytical approximation of the word error rate based on a union bounding technique is computed under the assumption that linear codes are employed at the two nodes exchanging data. Further, when the wireless channel is frequency selective, two decoding strategies at the relay are developed, namely, a near optimal decoding scheme implemented using list decoding, and a reduced complexity detection/decoding scheme utilizing a linear minimum mean squared error based detector followed by a network coded sequence decoder. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Ce manuscrit de thèse rapporte quelques études méthodologiques sur la régionalisation du climat par l’approche dynamique. Le domaine géographique couvre une large zone allant du milieu de l’Atlantique Nord à l’Europe de l’Est, et du Sahel à l’Arctique. La quête à tout prix d’une amélioration du climat régional n’est pas au cœur du manuscrit. Pourtant, l’accent est mis sur trois points clefs, généralement rencontrés par toutes tentatives de régionalisation du climat. Le premier point concerne le schéma d’imbrication : imbrication du sens unidirectionnel du GCM vers le RCM (one-way nesting, OWN) ou bidirectionnelle entre le GCM et le RCM (two-way nesting, TWN). Le deuxième point examine la réalisation technique d’imbrication, qui est généralement une opération de relaxation newtonienne ajoutée aux équations pronostiques du modèle. Le troisième point est sur l’effet du raffinement de maille dans le RCM. L’esprit général du manuscrit consiste à conceptualiser et réaliser des simulations numériques pour traiter ces trois points avec astuces afin de les isoler et quantifier. Le modèle de circulation générale LMDZ est utilisé pour l’ensemble des expériences. Il joue à la fois le rôle du GCM et celui du RCM. Dans les deux cas, il conserve strictement ses paramétrisations physique et sa configuration dynamique, ainsi que tous les forçages ou paramètres externes. La stratégie d’expérimentation, qualifiée comme Master versus Slave, consiste à réaliser des simulations sous deux protocoles reliés l’un et l’autre : « DS-300-to-300 » désigne Downscaling du GCM à 300 km de résolution horizontale au RCM qui est identique au GCM, aussi à 300 km de résolution spatiale ; « DS-300-to-100 » désigne Downscaling de 300 km (GCM) à 100 km (RCM). Il est clair que « DS-300-to-300 » est un cadre idéalisé, particulièrement approprié pour évaluer l’effet de l’opération de relaxation. Le protocole « DS-300-to-100 », soustrait du « DS-300-to-300 », permet d’évaluer très précisément l’effet de la résolution du RCM augmentée. Dans chaque protocole, deux schémas de communication entre le RCM et le GCM ont été implémentés, l’un (OWN) est la méthodologie classique du sens unique qui consiste à piloter le RCM par les sorties du GCM, l’autre (TWN) est d’établir un échange mutuel entre les deux modèles. Le climat régional est sensible au choix des schémas de communication entre le RCM et le GCM, surtout aux moyennes latitudes. TWN apporte une nette amélioration sur la représentation des informations frontalières. Au niveau des modes régionaux de circulation atmosphérique, exprimés en structures d’EOF, OWN et TWN sont tous deux capables de les reproduire, mais avec de légères déformations dans l’espace. La relaxation newtonienne, largement utilisée dans la régionalisation du climat, permet au RCM de bien suivre la trajectoire synoptique du GCM. Pourtant, la concomitance temporelle et la ressemblance spatiale sont dépendantes des variables considérées, des saisons, des régimes de temps, et des échelles spatio-temporelles de circulations atmosphériques. Des cas de dé-corrélation sont remarquables quand la circulation dominante de la région est de petites échelles. Le raffinement de maille augmente la liberté du RCM à développer sa dynamique interne, surtout aux petites échelles, mais aussi à l’ensemble du spectre de la circulation à travers l’interaction des échelles. Ainsi le RCM devient plus indépendant et s’écarte davantage du GCM. Cette thèse, autour des aspects méthodologiques de la régionalisation du climat, aide à avoir une meilleure compréhension sur la pratique. Elle adresse aussi un message de précaution à la communauté RCM et l’invite à bien vérifier leur méthodologie de régionalisation. / The work developed in this thesis explores through methodological modelling studies the current techniques of climate regionalization. In this case, the regionalization focuses on a geographical domain covering from the North Atlantic to Eastern Europe longitudinal wise, and from the Sahel to the Arctic as a latitudinal interval. The aim of this thesis is not the improvement of regional climate modelling per se, but tackling three key questions that are commonly met by all attempts when trying to improve climate regionalization. Firstly, the choice and advantages of the nesting scheme: one-way nesting (OWN) versus two-way nesting (TWN). Secondly, the evaluation of the nesting method, which is generally a Newtonian relaxation operation added to the prognostic equations of the model. And finally, the consequences of the mesh refinement in Regional Circulation Models (RCM). The objective of this manuscript consists in conceptualizing and carrying out numerical simulations to answer these three questions by isolating each individual effect and quantifying the consequences of each of the effects. The general circulation model LMDZ is used for all experiments. It is able to play the role of the General Circulation Model (GCM) and the RCM, keeping the same physical parameterizations and the same dynamical configuration, as well as the same external forcings and model parameters. Our experimental set-up, referred as “Master versus Slave”, consists on two related protocols: “DS-300-to-300” and “DS-300-to-100”. The former implies the downscaling of the GCM at 300 km of horizontal resolution while the RCM has the identical resolution of 300 km. The latter implies the downscaling from 300 km (GCM) to 100 km (RCM). We have assumed the “DS-300-to-300” as an idealized framework, particularly appropriate to evaluate the relaxation operation effect. In parallel, the “DS-300-to-100” protocol, subtracted from the “DS-300-to-300”, allows assessing the effect of the increased resolution for the RCM. In each protocol, two communication schemes between the RCM and the GCM have been implemented. The first one -OWN- is the classic one-way methodology to control the RCM by the outputs of the GCM. The second one -TWN- is used to establish a mutual exchange between the two models (RCM and GCM). This thesis has found that climate regionalization is highly sensitive to the choice of the communication scheme between the RCM and the GCM, especially at mid-latitudes. TWN clearly improves the representation at the boundaries. For the regional atmospheric circulation modes, expressed in EOF structures, both OWN and TWN are able to reproduce them, but with a slight deformation in space. Newtonian relaxation, widely used in climate regionalization, allows the RCM to follow the GCM’s synoptic trajectory. However, temporal concomitance and spatial resemblance of the two depend on the variables considered, on the particular seasons selected, on the weather regimes, and on the spatiotemporal scales of atmospheric circulation. De-correlation cases are remarkable when the dominant circulation on a regional scale is small. Moreover, mesh refinement increases the freedom of the RCM to develop its internal dynamic circulation, especially at small scales, and also across the whole spectrum of circulation regimes through the scales in which the RCM operates. Thus, when resolution increases, the RCM becomes more independent from the GCM behavior and the model results deviate significantly from the GCM. Focused on the methodological aspects of climate regionalization, this thesis helps to gain a better understanding on the regionalization practice. Il also sends a precautionary message to the RCM community, kindly inviting to verify their regionalization strategy.