This research models the behavior of a multi-task system with respect to time. The type of multi-task system considered here is one in which not all system components are required to perform each task. Each component may, however, be used for more than one task. Also, it is possible that some of the components may be required for every task that the system performs. The components that are required for a subset of the tasks are considered to be intermittently demanded components and those components required for every task are continuously demanded components. This modeling approach assumes that the system is subject to a Modified Age Replacement Policy (MARP). With a MARP the intermittently demanded components are maintained during their idle periods and the continuously demanded components are replaced according to their age replacement times. A renewal theory approach is used to develop an availability expression for the multi-task system. Past research has focused on systems consisting of continuously demanded components and typically does not distinguish between elapsed clock time and elapsed operating time in the renewal density function expressions. This research recognizes that the operational age of an intermittently demanded component is different than the chronological age of the component. The renewal density function and availability measures are modeled using joint density functions defined on both clock time and operating time. The expressions are evaluated numerically using a multidimensional numerical integration routine. The results show logical behavior of the joint density functions used to define the availability measure. The availability measure also displays behavior consistent with the definition of a multi-task system. This model is an important development in the need for stochastic models of highly complex systems. The model is also a first step in defining performance measures for systems composed of both intermittently demanded components and continuously demanded components. / Ph. D.

This investigation studied the level of knowledge that principals have concerning the maintenance of their schools. A questionnaire was developed to address three research questions. These research questions were: (1) what is the extent that facilities maintenance is an important issue for school principals? (2) in what specific areas of facilities maintenance do principals lack knowledge? and (3) in what specific areas does the lack of facilities maintenance knowledge by principals exceed 30%? A questionnaire was developed to gather data to analyze comparative relationships to the research questions. Data indicated that principals do believe facilities maintenance is an important issue. Reponses to the questionnaire indicated most principals have a general understanding of facilities maintenance in its broadest sense. However, the data supported that most principals lack knowledge concerning the specific facilities maintenance information and issues. Recommendations were made to address the lack of knowledge principals have concerning facilities maintenance. Recommendations were also made for additional research in the area of the principal's knowledge concerning facilities maintenance.

Indiana University-Purdue University Indianapolis (IUPUI) / This investigation compared the spring characteristics of three space closing assemblies; the classic "Bull" loop and two new spring designs currently being used in the Department of Orthodontics at Indiana University. Using interbracket distance and the degree of gable preactivation as variables, a complete laboratory analysis was carried out on each spring design. A total of two hundred springs were tested. A statistical investigation was conducted to determine if the spring designs had significantly different load-deflection rates, moment to force ratios, and range of activation. The range of activation for all three spring designs was large enough to be of some minor importance in determining the difference in efficiency of each design. However, when the load-deflection rates and moment to force ratios of the "Bull" loop and the two new spring designs were compared, the new spring designs invariably proved to be superior. From this laboratory study, it was concluded that the two new spring designs have the potential of providing a more efficient method of orthodontic space closure.

Examensarbetet genomfördes på AstraZeneca, Snäckviken hos fabriken API. Dess ångsystem har länge drabbats av oavsiktliga avbrott och detta har inte åtgärdats trots förebyggande insatser, vilket i sin tur har resulterat i produktionsbortfall. Syftet med denna studie är därmed att ta fram en långsiktig underhållsplan på komponentnivå som ska minska samtliga avbrott i ångsystemet. För att genomföra detta var det nödvändigt med litteraturstudier, avbrottanalys, nulägesanalys, besök på Snäckviken samt intervjuer. Studiens teoriavsnitt omfattades bland annat av väsentliga begrepp såsom underhåll, tidsbaserat- och tillståndsbaserat underhåll. Dessa termer bidrog till förståelsen av arbetet och framtagningen av resultatet och i sin tur även diskussionen. Det slutliga resultatet påvisade faktumet att det fanns tre komponenter som orsakade flest avbrott i systemet, och för en av dessa skapades det en underhållsplan. Planen omfattas av en underhållsbeskrivning, reservdelar/utbyteskomponenter, tidsutförande samt underhållsreperationer som inkluderar rekommenderad utförarkompetens. / The project was carried out at AstraZeneca, Snäckviken at the API factory. Its steam system has long been affected by unintentional interruptions and this has not been remedied despite preventive measures, which in turn has resulted in production losses. The purpose of this study is therefore to develop a long-term maintenance plan at component level that will reduce all interruptions in the steam system. To implement this, it was necessary with literature studies, current situation analysis, interruption analysis, visits to Snäckviken and interviews. The theoretical section of the study included, among other things, essential concepts such as maintenance, time-based- and condition-based maintenance. These terms contributed to the understanding of the study and the result, and in turn also the discussion. The result demonstrated the fact that there were three components that caused the most interruptions in the steam system, and for one of these a maintenance plan was created. The plan is covered by a maintenance description, spare parts / replacement

This research explores optimal sequencing of aircraft engine maintenance events. Due to the high ongoing maintenance costs and large capital investments required for supporting an aircraft engine fleet, the timing and associated costs of maintenance events are key to minimizing overall costs for an airline. This paper examines a novel application of particle swarm optimization techniques in order to create a decision tool which may be easily implemented by the practitioner. Numerical experiments demonstrate the quality of this solution method under multiple maintenance pricing structures and operational constraints.

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This study addressed the relational maintenance strategies and the meaning 23 to 35 year old students attributed to their long-distance dating relationships. Ten participants completed in depth interviews exploring the thoughts and feelings individuals held about their current long-distance partner and relationship. Also, commitment and quality of alternatives were addressed including the strengths and weaknesses of the respondent's relationship. Common themes of strong friendship, absolute trust, commitment to one partner, and using the technique of reminiscing were all dominant issues that emerged from the interview data. Social network approval as well as positive role models in the form of older siblings was also instrumental in lending support to the success and general positive attitude felt by participants about the geographic separation. Methods of communication included the telephone and e-mail, which was substituted or supplementary when high phone bills created financial concerns for the respondents. Variation in physical visitation was due to the intersection of academic schedule, affordable transportation, attitude towards work disruptions, geographic distance, and a general willingness to travel. Participants told a story of the geographic separation as both a temporary and necessary inconvenience, rather than a major obstacle or focal point of the relationship. Future directions for studying long-distance dating relationships include collecting couple data and examining gender differences to determine if sex has an impact on how geographic separation is viewed. / Master of Science

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Problem statement: Manufacturing and production plants operate machines and equipment that deteriorate with usage and time thus requiring maintenance actions to restore them back to their original operational conditions. Approach: This study investigates the current standard of maintenance planning at a steel manufacturing facility in South Africa. The study begins with a thorough literature study to find good characteristics of planning which should be present at any facility that is optimally engaged in performing excellent maintenance planning effectively and efficiently. A number of key observations from the literature are made indicating that planning is a key component of maintenance and affects excellence in maintenance significantly. The literature recommends that planning should be set and based on key principles to allow for standardisation and efficiency. An empirical study in the form of a survey is then completed to benchmark the current maintenance-planning environment of the steel facility against the good characteristics of maintenance planning found in literature. Results: The results from the empirical study show that the current maintenance environment at the steel manufacturer is not optimal. The following issues are uncovered from the study: no schedulers employed to relieve the planners’ work overload, no guiding principles for planning and standardisation of work planning, no efficient shutdown planning and also no existent measures for tracking some of the key performance areas. Conclusion: Key recommendations to be considered for implementation for improving the status of the maintenance environment at the works include: introducing the scheduler position, standardising planning methodologies according to specific principles and rigorously focusing on overall maintenance improvement using standardised methodologies. / MBA (Business Administration), North-West University, Potchefstroom Campus, 2015