A Thesis presented to the Department of Geophysics of the University of the Witwatersrand, Johannesburg / Violent failure of the rock surrounding under ground excavations forms a major hazard and obstacle in deep-level mining. (Abbreviation abstract) / AC 2018

Friction stir welding (FSW) is a relatively new solid-state welding technology invented at The Welding Institute of UK in 1991. It is versatile and has been widely adopted to join various materials. There has been strong research activity on revealing the details of the material flow pattern in the nugget zone induced by the conventional shoulder tool. However, there is insufficient understanding on the aspects of the scroll shoulder tool design and the shoulder flow zone formation utilizing this type of tool. The major objective of this study was to conduct experiments, analyse results and then reveal the shoulder flow zone forming mechanism for the scroll shoulder tool. The method used was to identify the flow pattern in the shoulder flow zone using a ‘marker insert’ technique, and then to suggest the forming mechanism of the shoulder flow zone based on the obtained flow pattern; although the ‘marker insert’ technique has never been used to study the shoulder flow zone flow pattern induced by the scroll shoulder tool. Experiments were conducted to examine the thick sections 6061 aluminium ‘marker insert’ welds, which were welded using a scroll shoulder tool at a range of welding parameters. These were followed by quantifying the mass of the accumulated work piece material within the scroll groove (pick up material-PUM), evaluating the effect of welding parameters on the shoulder flow zone formation, and documenting the shoulder flow zone flow pattern. The major finding was that there is a simple banded structure which forms in a layer to layer manner in the bottom portion of the shoulder flow zone, but it disappears in the top portion of the shoulder flow zone. Accordingly, the forming mechanism of the shoulder flow zone for the scroll shoulder tool was suggested as follows. Firstly, the tool pin is plunged into the work piece; the work piece material is extruded by the pin and pushed up into the scroll groove forming the PUM. Secondly, after the tool shoulder is plunged into the work piece to a certain depth, the scroll groove is fully filled up with the PUM. Finally, during the forward movement of the tool, the central portion of PUM is driven downward by the root portion of the pin and then detaches from the pin (tip portion) in a layer to layer manner. It has also found that the thickness of the shoulder flow zone varies with a thicker on the advancing side than on the retreating side, and there is a positive linear relationship between the mass of PUM and the weld quality. This study has revealed for the first time the forming mechanism of the shoulder flow zone, and has improved the understanding of the shoulder flow zone formation using a scroll shoulder tool. It is recommended that a ‘shoulder-breaking’ technique is developed to break the rotating shoulder suddenly and hence embed it into the work piece during FSW, in which a real-time shoulder-work piece couple could be produced for a better three-dimensional examination of the shoulder flow zone.

Friction stir welding (FSW) is a relatively new solid-state welding technology invented at The Welding Institute of UK in 1991. It is versatile and has been widely adopted to join various materials. There has been strong research activity on revealing the details of the material flow pattern in the nugget zone induced by the conventional shoulder tool. However, there is insufficient understanding on the aspects of the scroll shoulder tool design and the shoulder flow zone formation utilizing this type of tool. The major objective of this study was to conduct experiments, analyse results and then reveal the shoulder flow zone forming mechanism for the scroll shoulder tool. The method used was to identify the flow pattern in the shoulder flow zone using a ‘marker insert’ technique, and then to suggest the forming mechanism of the shoulder flow zone based on the obtained flow pattern; although the ‘marker insert’ technique has never been used to study the shoulder flow zone flow pattern induced by the scroll shoulder tool. Experiments were conducted to examine the thick sections 6061 aluminium ‘marker insert’ welds, which were welded using a scroll shoulder tool at a range of welding parameters. These were followed by quantifying the mass of the accumulated work piece material within the scroll groove (pick up material-PUM), evaluating the effect of welding parameters on the shoulder flow zone formation, and documenting the shoulder flow zone flow pattern. The major finding was that there is a simple banded structure which forms in a layer to layer manner in the bottom portion of the shoulder flow zone, but it disappears in the top portion of the shoulder flow zone. Accordingly, the forming mechanism of the shoulder flow zone for the scroll shoulder tool was suggested as follows. Firstly, the tool pin is plunged into the work piece; the work piece material is extruded by the pin and pushed up into the scroll groove forming the PUM. Secondly, after the tool shoulder is plunged into the work piece to a certain depth, the scroll groove is fully filled up with the PUM. Finally, during the forward movement of the tool, the central portion of PUM is driven downward by the root portion of the pin and then detaches from the pin (tip portion) in a layer to layer manner. It has also found that the thickness of the shoulder flow zone varies with a thicker on the advancing side than on the retreating side, and there is a positive linear relationship between the mass of PUM and the weld quality. This study has revealed for the first time the forming mechanism of the shoulder flow zone, and has improved the understanding of the shoulder flow zone formation using a scroll shoulder tool. It is recommended that a ‘shoulder-breaking’ technique is developed to break the rotating shoulder suddenly and hence embed it into the work piece during FSW, in which a real-time shoulder-work piece couple could be produced for a better three-dimensional examination of the shoulder flow zone.

Sociala manipulatörer besitter förmågan att använda social interaktion som medel för att övertyga en individ eller organisation till samtycke för en specifik förfrågan. Syftet är att uppnå ett mål i form av exempelvis ekonomisk vinning, obehörig åtkomst eller serviceavbrott. En social manipuleringsattack föranleds utav bakomliggande processer och innefattar en datorrelaterad enhet för antingen den sociala interaktionen, för övertalningen till samtycke eller för manipulatörens förfrågan. Syftet med arbetet var att kartlägga säkerhetsåtgärder mot sociala manipuleringsattacker och på så vis ge uttryck för en utveckling av området över tid. Resultatet förväntades med andra ord att ge uttryck för en mognad inom området och bidra med ökade insikter i hur attacker på ett tidstroget vis kan tacklas inom administrativ- och teknisk säkerhet. En kartläggande granskning genomfördes utifrån ett urval utifrån de tre databaserna; IEEE Xplore Digital Library, Springer Link och DBLP Computer Science Bibliography. Studier primär- och sekundärkategoriserades utifrån en kodningsprocess i syfte att understödja en narrativ analys. Fyra primärkategorier utav säkerhetsåtgärder uppstod; modellering, sårbarhetsbedömning, datasystem och (in)direkt utbildning. Sökstrategi och bedömningsprocess gav en inkluderad datamängd av totalt 28 studier. Säkerhetsåtgärder mot social manipulering från 2008 representerades av fem studier; en föreslog modellering, tre föreslog datasystem och en föreslog (in)direkt utbildning. Säkerhetsåtgärder från 2018 representerades av 23 studier; fyra föreslog modellering, två föreslog sårbarhetsbedömning; nio föreslog datasystem och åtta föreslog (in)direkt utbildning. Kodningsprocessen gav även upphov till sekundära kategorier – samtliga kategorier återgavs en dynamisk återspegling utav säkerhetsåtgärder mot social manipulering 2008 kontra 2018. Fyra av fem studier från 2008 definierade social manipulering med avsaknad av teoretiska förklaringar till bakomliggande processer för en attack – respektive 13 av 23 studier från 2018. Analysen mynnade ut i insikter om att framtida forskning behöver eftersträva ett holistiskt synsätt för de bakomliggande processer som föranleder en social manipuleringsattack – på så vis kan en ökad säkerhetsmedvetenhet och motståndskraft mot social manipulering uppnås. / Social engineers possess the ability to use social interaction as a means of convincing an individual or organization to consent to a specific request. The purpose is to achieve a goal in the form of, for example, financial gain, unauthorized access or service interruption. A social engineering attack is caused by underlying processes and includes a computer-related device for either the social interaction, for the persuasion to consent or for the social engineer's request. The purpose of the thesis was to map security measures against social engineering attacks and thus express the development of the area over time. In other words, the result was expected to express a maturity in the area and contribute with increased insights into how attacks in a timely manner can be tackled in administrative and technical security. A survey was conducted based on a selection based on the three databases; IEEE Xplore Digital Library, Springer Link and DBLP Computer Science Bibliography. Studies were primary and secondary categorized based on a coding process in order to support a narrative analysis. Four primary categories of security measures occurred; modelling, vulnerability assessment, computer systems and (in)direct education. Search strategy and assessment process provided an included data set of a total of 28 studies. Security measures against social manipulation from 2008 were represented by five studies; one proposed modeling, three suggested computer systems and one suggested (in)direct education. Security measures from 2018 were represented by 23 studies; four proposed modeling, two suggested vulnerability assessment; nine proposed computer systems and eight suggested (in)direct education. The coding process also gave rise to secondary categories - all categories were given a dynamic reflection of security measures against social manipulation 2008 versus 2018. Four out of five studies from 2008 defined social manipulation with the absence of theoretical explanations for underlying processes for an attack - and 13 of 23 studies from 2018. The analysis resulted in insights that future research needs to strive for a holistic approach to the underlying processes that cause a social manipulation attack - in this way increased security awareness and resistance to social engineering can be achieved.

Un nouveau facteur de transcription, appartenant à la famille des protéines à domaine bHLH, a récemment été isolé dans notre laboratoire. Initialement appelé « clone bc8 » puis HRT1, ce facteur présentait des similitudes avec les protéines Hairy and Enhancer of split qui interviennent notamment dans le phénomène d’inhibition latérale lors de la formation du tissu neural. Des études d’hybridation in situ réalisées chez l'embryon de xénope ont suggéré un rôle important de XHRT1, la protéine HRT1 de xénope, dans le développement neural. Nous avons recherché les partenaires protéiques de XHRT1 par la technique du double-hybride afin de mieux comprendre son mécanisme d’action moléculaire dans la neurogenèse.<p>Tout d’abord nous avons construit les outils appropriés pour l’élaboration du travail, à savoir, les clones de levures exprimant les appâts spécifiques des domaines de la protéine étudiée et la création d’une banque d’ADNc du xénope au stade de la neurulation. Ensuite, trois criblages ont été réalisés. Dans le premier cas, nous avons recherché les partenaires des domaines bHLH et Orange (bHLH-O). Le domaine bHLH est en effet responsable de la dimérisation de ce type de protéine. Le domaine Orange qui suit le domaine bHLH, pourrait participer dans le choix du partenaire d’hétérodimérisation. Nous avons isolé deux facteurs de type bHLH-Orange apparentés à HRT1, XHairy1 et XHairy2b et confirmé leur interaction avec XHRT1. Les domaines impliqués dans ces interactions sont les bHLH-O pour les trois facteurs. Ce même criblage nous a permis d’isoler un nouvel ADNc qui code une protéine sans domaine apparent connu actuellement. Nous avons montré que cette protéine reconnaissait spécifiquement le domaine Orange de HRT1 mais pas celui des autres facteurs de type bHLH-O. Elle a été baptisée BOIP pour Bc8 Orange Interacting Protein. Le rôle physiologique de cette interaction n’a pu être démontré. Nous avons établi que la protéine BOIP pouvait aussi s’homodimériser. Nous avons aussi déterminé son profil d’expression chez le xénope et la souris. Son transcrit est hautement présent dans les testicules adultes. La protéine pourrait donc jouer un rôle important dans la spermatogenèse. Les deux autres criblages, utilisant les domaines situés dans la partie C-terminale de XHRT1, ont apporté des nouveaux partenaires potentiels, mais ces interactions n’ont pu être confirmées dans un système indépendant. <p>Enfin, en étudiant plus en détail les interactions entre XHRT1 et XHairy1 ou XHairy2b, nous avons mis à jour une possible fonction de spécificité dans le choix du partenaire dans la région C-terminale de HRT1. La formation de ces dimères pourrait jouer un rôle dans la formation du tube neural mais également dans d’autres différenciations tissulaires.<p> / Doctorat en sciences, Spécialisation biologie moléculaire / info:eu-repo/semantics/nonPublished