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A general method, of approach to resonant non-linear optical phenomena involving travelling waves has been developed. Maxwell's equations are solved for the electric field in a spherical Fabry-Perot type optical resonator, which encloses uniaxial arisotropic media. The specific case of propagation perpendicular to the optic axis is considered but the theory can be extended to cover the general case including double refraction. In the presence of more than one optical field of this form, when the medium enclosed in the resonator is non-linear, by expanding the polarisation in terms of the electric field in the normal way coupled mode equations are obtained for amplitudes of the eigen modes concerned. This general formalism is then used to examine resonant second harmonic generation in the small conversion approximation from a fundamental beam in the lowest order 0-0 mode. Analytical solutions are obtained in three limiting cases, weak focussing, strong focussing and the focus removed infinitely from the non-linear medium. The general case is solved numerically. From the results the values of the variable parameters can he obtained which give the maximum output in any given mode. Graphs are presented giving the output variation in 0-0 and 0-2 modes with focus position, phase matching, focussing and spot size. From there it can be seen that the optimum focussing for the 0-0 mode occurs at 1/20 = 5.65 (1 crystal length, zo one half the confocal parameter). Secondly degenerate parametric amplification between two lowest order inodes is examined under the approximation that the pump beam is undepleted. An analytic solution is obtained for the single pass amplification in the weak focussing limit and preliminary results of numerical computations for the general case are given. From these results a value for the optimum threshold condition is calculated.

Social groups are a fundamental part of our lives. From early beginnings humans lived in family groups and formed 'tribes' that not only provided protection from the many dangers they faced but by combining their efforts humans learnt that a group could be more than the 'sum of its parts'. Collective action has, and still, provides the basis for much of human activity, while shared knowledge contributes equally to the advancement of humankind. Study into groups has revealed that humans instinctively know when cooperation is the best strategy and that not only is collective action often more efficient and effective than that of independent effort but that groups are good problem solving mechanisms, often making better decisions than individuals through the use of 'collective mindfulness' and a group 'trans-active’ memory. People do not just create a group memory, there is evidence they also ‘become’ the group. As social integration rises, people feel, think, and act more like group members. They automatically associate themselves with the groups that they identify with. Tajfel and Turner’s theory of Social Identity suggests that people not only join groups but take on the ‘group identity’ as their own self-image in a process of ‘depersonalization’. To achieve effective collective action requires more than just 'being' and 'feeling' part of a group. Effective cooperation requires cohesion between group members, good communication and a coherent purpose or goal. Social Identity Theory does not provide evidence of how these mechanisms work other than to identify the formation of group norms. For that we have to turn to cybernetics, the study of 'purposeful action' and Stafford Beer's Viable Systems Model in particular. The Viable Systems Model provides an epistemology for examining the viability of systems. Viability is the ability of systems to achieve cohesion and coherence through autonomy, recursivity and ultimately closure with their environment. This study brings together these two powerful theories to create a more complete picture of purposeful collective action and group membership. By building a Viable Systems Model of salient social groups the research provides a mechanism to understand how individual human social behaviours form and maintain purposeful social groups capable of self-awareness, self-maintenance and the ability to sustain their identity, autonomous from perturbations in the environment. Not every social group is able to maintain viability. Many groups form and expire as the circumstances dictate. Only a few are able to achieve organisational closure from their environment and sustain their identity, This research seeks to identify what is meant by social viability and what factors make some groups achieve it while others do not. It investigates the formation of social groups under different environmental conditions in order to 'tease-out' the invariances that contribute to viability and it tests the validity of the Viable Systems Model of Social Identity Theory developed for the study. In order to answer the research question the study had to address the difficult issue of conducting research on complex social systems and to utilises a process of deduction, induction and abductive reasoning through both analysis and synthesis to achieve its findings.

The dissertation brings together and reports the entire work presented and discussed throughout this pioneering and original research project. This exploratory study utilising primarily semi-structured, qualitative research methodology aimed to develop a model of executive stress by discovering, understanding, describing and sharing knowledge and experience of occupational stress caused by the basic executive functions, among the oil and gas executives in Saudi Arabia. These functions included planning, organising, leading and controlling. This interpretive investigation involved forty-three executives of five major oil and gas firms in Saudi Arabia purposively selected for participation in this exploratory study through audiotape-recorded interviews gathered over a period of eight months from June 2002 to January 2003. In addition, this primary data collection method was triangulated with other secondary methods of observations, focus groups and documentary analysis involving additional twenty executives from other neighboured Arabian Gulf countries. These considerable qualitative data were systematically managed through primarily manual analysis along with the aid of NUD*IST qualitative analysis computer program. Common recurring categories, themes and patterns were identified in relation to sources of stress, manifestations and coping strategies along with stressful factors related to internal and external environments. The study findings revealed four significant interrelated eustressful and distressful themes underpinning the basic executive functions of planning, organising, leading and controlling. These were related to information management, performance management, human resource management and strategic management. The findings revealed that the participants perceived these focused executive functions as a direct source of occupational stress instead of the basic executive functions that were thought of at the beginning of the research. The emerged key patterns related to these focused activities included difficulty of people management, micromanagement behaviour and engineering attitude. Moreover, the study resulted into additional stress factors related to the organisational structure and work style of the internal environment of the organisation. There were also other stressful contributing factors associated with Government interventions, market influences, media focus and social conflict of the external environment of the organisation. Furthermore, the study revealed important personal related factors that could shape and regulate the manifestations of executive eustress or distress. These included experience, personality type, cognitive appraisal and self-esteem factors. Accordingly, a comprehensive framework of executive stress process based on a dynamic system approach was developed summarising the explored executive stress process and its underlying attributes. This present qualitative study was designed interpretively and qualitatively for exploration or discovery of the topic under investigation. Further, the limitations of this approach were acknowledged, as being subjective perceptions, understandings and descriptions of the oil and gas executives under investigation. In view of that, this new and original study was hoped to add to the existing knowledge in various related areas such as occupational health and safety, industrial/ organisational psychology, human resource management, strategic management and organisational culture. This research could add value to the field of occupational stress in Arabic context in particular and the world in general since there was little research about the types and effects of job-related stress at the time of the study.