It is essential for the managers to make investment on hardware based on the utilization information of the equipment. From December 2014, a pool of hardware and a scheduling and resource sharing system is implemented by one of the software testing sections in Ericsson. To monitor the efficiency of these equipment and the workflow, a model of non-homogeneous M/M/c queue is developed that successfully captures the main aspects of the system. The model is decomposed into arrival, service, failure and each part is estimated. Mixture exponential is estimated with EM algorithm and the impact of scheduling change is also examined. Finally a simulation of workflow is done with Python module and the optimized number of hardware is proposed based on this M/M/c queue system.

This thesis is the summation of two publications with the motivation to move reliability analysis earlier in the design process. Current analyses aim to improve reliability after components have been selected. Moving specific analyses earlier in the design process reduces the cost to the designer. These early design analyses provide information to the designer so that critical design changes can be made to avoid failures. The first presents failure rates for function-flow pairs. These function-flow failure rates are used in the Early Design Reliability Method (EDRM) to calculate system level reliability during functional design. This methodology is compared to the traditional reliability block diagram for three examples to show its usefulness during early conceptual design. Next, an extension to the Function Failure Design Method (FFDM) is presented. A more robust knowledge base using Failure Mode/Mechanism Distributions 1997 (FMD-97) has been implemented. Then failure rates from Nonelectric Parts Reliability Data (NPRD-95) are added to more effectively determine the likelihood that a failure mode will occur. The proposed Functional Failure Rate Design Method (FFRDM) uses functional inputs to offer recommendations to mitigate failure modes that have a high likelihood of occurrence. This work uses a past example where FFDM and Failure Modes and Effects Analysis (FMEA) are compared to show that improvements have been made. A four step process is presented to show how the FFRDM is used during conceptual design. / Graduation date: 2012

Die Dimensionierung einer Betonfahrbahn zielt darauf ab, den Anteil der im Nutzungszeitraum versagenden Platten auf ein akzeptables Maß zu begrenzen. Der Anteil ausgefallener Platten entspricht der Versagenswahrscheinlichkeit der einzelnen Platte. Damit ergibt sich die Notwendigkeit, die Versagenswahrscheinlichkeit zu berechnen. Innerhalb der vorliegenden Arbeit werden grundlegende Methoden und Verfahrensweisen zur Lösung dieser Aufgabe entwickelt. Es wird gezeigt, wie die für die Quantifizierung der Versagenswahrscheinlichkeit entscheidenden Streuungen der Einflussgrößen mathematisch beschrieben und im Dimensionierungsverfahren berücksichtigt werden können. Dabei wird regelmäßig Bezug genommen auf das in Deutschland eingeführte Dimensionierungsmodell der RDO Beton [2]. Die Grundlage für die Berechnung der Versagenswahrscheinlichkeit liefern die Methoden der Statistik und Wahrscheinlichkeitsrechnung, sowie der Zuverlässigkeitstheorie. Es wird gezeigt, dass sowohl die mathematisch exakte Lösung, wie auch verschiedene Näherungsverfahren für die Problematik der Betonfahrbahnen anwendbar sind. Näher untersucht werden die Zuverlässigkeitstheorie 1. Ordnung (FORM) sowie die Monte-Carlo-Methode. Die jeweiligen Vor- und Nachteile werden analysiert. Es zeigt sich, dass für die Anwendung des FORM-Algorithmus das Berechnungsmodell der RDO Beton modifiziert werden muss. Der zeitliche Bezug der Berechnung kann über die Benutzung von Extremwertverteilungen, die Modellierung stochastischer Prozesse oder die Einführung einer Schadensakkumulationshypothese hergestellt werden. Besondere praktische Bedeutung hat die Berechnung der Versagenswahrscheinlichkeit für den Nutzungszeitraum mit zeitlich varianten Bedingungen. Für diesen Fall werden vier verschiedene Lösungsansätze aufgezeigt. Um die teilweise sehr hohen Rechenzeiten zu minimieren, werden Näherungslösungen entwickelt. Die praktische Eignung wird mit beispielhaften Berechnungen demonstriert. Es zeigt sich, dass die Berechnungsergebnisse stark davon abhängen, wie sich die Werte einzelner Parameter über den Nutzungszeitraum entwickeln. Die betreffenden zeitlichen Verlaufsfunktionen sind gegenwärtig nur unzureichend bekannt. Um eine hinreichend verlässliche Prognose zu berechnen, sind alle Berechnungsverfahren möglichst objektbezogen zu kalibrieren. / The dimensioning of a concrete pavements aims to limit the percentage of failing slabs to an acceptable level. The proportion of failed slabs corresponds to the probability of failure of each slab. This results in the need to calculate the probability of failure. Within the present work, basic methods and procedures for solving this problem are being developed. It is shown how the variations of parameters can be mathematically described and considered in the dimensioning process. Reference is frequently made to the model of RDO Beton [2]. The methods of statistics and probability theory, and reliability theory provide the basis for calculating the probability of failure. It is shown that both the mathematically exact solution and various approximation methods as well are applicable to the problem of concrete pavements. Be examined more closely the reliability theory 1st order (FORM) and Monte Carlo method. The respective advantages and disadvantages are analyzed. It turns out that the calculation model of the RDO concrete has to be modified for the use of FORM algorithm. The temporal relation of the calculation can be made on the use of extreme value distributions, modeling of a stochastic process or the introduction of a damage accumulation hypothesis. Particular practical significance has to calculate the probability of failure for the period of use with time-variant conditions. In this case, four different approaches are discussed. Approximate solutions to minimize the sometimes very high computation times has been developed. The practical suitability is demonstrated by exemplary calculations. It turns out that the calculation results depend strongly on how to develop the values of individual parameters over the period of use. These time course functions are insufficiently known at present. To calculate a sufficiently reliable forecast, all calculation methods are possible to calibrate object-related.

Die Dimensionierung einer Betonfahrbahn zielt darauf ab, den Anteil der im Nutzungszeitraum versagenden Platten auf ein akzeptables Maß zu begrenzen. Der Anteil ausgefallener Platten entspricht der Versagenswahrscheinlichkeit der einzelnen Platte. Damit ergibt sich die Notwendigkeit, die Versagenswahrscheinlichkeit zu berechnen. Innerhalb der vorliegenden Arbeit werden grundlegende Methoden und Verfahrensweisen zur Lösung dieser Aufgabe entwickelt. Es wird gezeigt, wie die für die Quantifizierung der Versagenswahrscheinlichkeit entscheidenden Streuungen der Einflussgrößen mathematisch beschrieben und im Dimensionierungsverfahren berücksichtigt werden können. Dabei wird regelmäßig Bezug genommen auf das in Deutschland eingeführte Dimensionierungsmodell der RDO Beton [2]. Die Grundlage für die Berechnung der Versagenswahrscheinlichkeit liefern die Methoden der Statistik und Wahrscheinlichkeitsrechnung, sowie der Zuverlässigkeitstheorie. Es wird gezeigt, dass sowohl die mathematisch exakte Lösung, wie auch verschiedene Näherungsverfahren für die Problematik der Betonfahrbahnen anwendbar sind. Näher untersucht werden die Zuverlässigkeitstheorie 1. Ordnung (FORM) sowie die Monte-Carlo-Methode. Die jeweiligen Vor- und Nachteile werden analysiert. Es zeigt sich, dass für die Anwendung des FORM-Algorithmus das Berechnungsmodell der RDO Beton modifiziert werden muss. Der zeitliche Bezug der Berechnung kann über die Benutzung von Extremwertverteilungen, die Modellierung stochastischer Prozesse oder die Einführung einer Schadensakkumulationshypothese hergestellt werden. Besondere praktische Bedeutung hat die Berechnung der Versagenswahrscheinlichkeit für den Nutzungszeitraum mit zeitlich varianten Bedingungen. Für diesen Fall werden vier verschiedene Lösungsansätze aufgezeigt. Um die teilweise sehr hohen Rechenzeiten zu minimieren, werden Näherungslösungen entwickelt. Die praktische Eignung wird mit beispielhaften Berechnungen demonstriert. Es zeigt sich, dass die Berechnungsergebnisse stark davon abhängen, wie sich die Werte einzelner Parameter über den Nutzungszeitraum entwickeln. Die betreffenden zeitlichen Verlaufsfunktionen sind gegenwärtig nur unzureichend bekannt. Um eine hinreichend verlässliche Prognose zu berechnen, sind alle Berechnungsverfahren möglichst objektbezogen zu kalibrieren. / The dimensioning of a concrete pavements aims to limit the percentage of failing slabs to an acceptable level. The proportion of failed slabs corresponds to the probability of failure of each slab. This results in the need to calculate the probability of failure. Within the present work, basic methods and procedures for solving this problem are being developed. It is shown how the variations of parameters can be mathematically described and considered in the dimensioning process. Reference is frequently made to the model of RDO Beton [2]. The methods of statistics and probability theory, and reliability theory provide the basis for calculating the probability of failure. It is shown that both the mathematically exact solution and various approximation methods as well are applicable to the problem of concrete pavements. Be examined more closely the reliability theory 1st order (FORM) and Monte Carlo method. The respective advantages and disadvantages are analyzed. It turns out that the calculation model of the RDO concrete has to be modified for the use of FORM algorithm. The temporal relation of the calculation can be made on the use of extreme value distributions, modeling of a stochastic process or the introduction of a damage accumulation hypothesis. Particular practical significance has to calculate the probability of failure for the period of use with time-variant conditions. In this case, four different approaches are discussed. Approximate solutions to minimize the sometimes very high computation times has been developed. The practical suitability is demonstrated by exemplary calculations. It turns out that the calculation results depend strongly on how to develop the values of individual parameters over the period of use. These time course functions are insufficiently known at present. To calculate a sufficiently reliable forecast, all calculation methods are possible to calibrate object-related.

No description available.

Yes / It is shown that the probability generating function of a lifetime random variable T on a finite lattice with polynomial failure rate satisfies a certain differential equation. The interrelationship with Markov chain theory is highlighted. The differential equation gives rise to a system of differential equations which, when inverted, can be used in the limit to express the polynomial coefficients in terms of the factorial moments of T. This then can be used to estimate the polynomial coefficients. Some special cases are worked through symbolically using Computer Algebra. A simulation study is used to validate the approach and to explore its potential in the reliability context.

In a world with unlimited travel options, railways play a key role in transportation. In order to serve the demand at a satisfactory level, it is important that the infrastructure quality remains high and safe. Maintenance is then the most important aspect of railway infrastructure.  This project’s aim is to develop a tool that would evaluate the cost differences and maintenance needs during the life cycle of turnouts, bent with different radii to straight, as a crucial part of the infrastructure, not only technically but also financially. When the cost over a life cycle is provided then design decisions can get more efficient.  Maintenance history of seven years of preventive and corrective maintenance data from databases Bessy and 0felia for single turnouts across the Swedish rail network were studied, analysed and evaluated.  Along with information from interviews with key informants the cost driving parameters were specified. The calculator was developed in Microsoft Excel, giving results for bent turnouts in 4 different radii categories and the respective straight turnouts. An EV-UIC60-760-1:14 turnout was used as a case study for different radii categories and 3 different scenarios were run in order to test the robustness of the tool.  The results showed that bent turnouts have a higher life cycle cost than straight in the order of 1 to 3 mkr depending on the radius, the bigger share of which is usually the preventive maintenance cost, with the specifics to vary between the categories and different scenarios tested. The way maintenance data are registered and classified plays an important role in the analysis.

The main aim of the study was to investigate change of programmes of study at University of the Western Cape (UWC). This involved examining the extent, nature and possible range of factors which shape change of programmes. The factors influencing choice to study at UWC and choice of programmes formed the background for understanding the link between choice and change of programmes. The study focused on first-time entering undergraduates in selected faculties: Arts, Economics and Management Sciences (EMS) and Community and Health Sciences (CHS). The progression “pathways” of these students were tracked from first year of enrolment in 2001 to 2004. The findings of the longitudinal data showed that the percentage of students who changed their programmes in the Faculty of Arts and in CHS was very minimal. In total 5% changed their programmes in CHS in three-year programmes while in four-year programmes only 2% changed their programmes. In the Faculty of Arts in three-year and four-year programmes change of programmes ranged from 6% to 10%. The significant change of programmes of study happened in EMS which also had the highest enrolments. In total 18% of the students changed their programmes. It appeared from the statistical data that failure and academic exclusion could be associated with change of programmes of study. Other factors such as financial problems, poor grouping of courses, exploring and changing to preferred programmes as well came out from the interviews as major influences of change of programmes.

The main aim of the study was to investigate change of programmes of study at University of the Western Cape (UWC). This involved examining the extent, nature and possible range of factors which shape change of programmes. The factors influencing choice to study at UWC and choice of programmes formed the background for understanding the link between choice and change of programmes. The study focused on first-time entering undergraduates in selected faculties: Arts, Economics and Management Sciences (EMS) and Community and Health Sciences (CHS). The progression “pathways” of these students were tracked from first year of enrolment in 2001 to 2004. The findings of the longitudinal data showed that the percentage of students who changed their programmes in the Faculty of Arts and in CHS was very minimal. In total 5% changed their programmes in CHS in three-year programmes while in four-year programmes only 2% changed their programmes. In the Faculty of Arts in three-year and four-year programmes change of programmes ranged from 6% to 10%. The significant change of programmes of study happened in EMS which also had the highest enrolments. In total 18% of the students changed their programmes. It appeared from the statistical data that failure and academic exclusion could be associated with change of programmes of study. Other factors such as financial problems, poor grouping of courses, exploring and changing to preferred programmes as well came out from the interviews as major influences of change of programmes.

L'emploi salarié hors cursus durant l'année universitaire peut-il affecter les résultats universitaires ? A partir des données tirées d'enquêtes nationales (les enquêtes « Conditions de Vie » de l'Observatoire national de la Vie Etudiante (OVE) et Panel 1995 du Ministère de l'Education National), cette thèse a pour ambition d'analyser à l'échelle de la France, le travail salarié des étudiants sous toutes ses formes et de relever les différents impacts qu'il pourrait avoir sur la réussite universitaire. Il ressort de l'analyse que le travail salarié a une influence négative et significative sur les résultats académiques. Cependant, ce n'est pas le travail en lui-même qui porte préjudice aux étudiants mais plutôt tout un ensemble de caractéristiques propres à l'emploi telles que l'intensité du temps accordée à l'emploi et le secteur d'embauche. De plus, il semblerait que ce soient les meilleurs étudiants qui font le choix de travailler pendant les études tandis que les étudiants non-salariés n'auraient pas intérêt à cumuler emploi et études. En somme, l'exercice d'une activité professionnelle pendant les études peut constituer une première expérience professionnelle utile, à condition qu'elle n'empiète pas trop sur le temps d'études et qu'elle soit liée aux études. Une politique publique qui inciterait les étudiants à ne pas travailler au-delà du temps partiel pourrait leur être favorable. Enfin, l'étude particulière des étudiants de première année de Licence nous montre que la majorité des étudiants-travailleurs inscrits en L1 et ayant abandonné leur année universitaire ne travaillait pas de manière intensive. L'activité professionnelle hors cursus n'est donc pas le seul élément qui peut justifier du taux d'échec alarmant des L1. / Students' employment during the academic year can it affect academic performance? Using data from national surveys (surveys "Living Conditions" of the National Observatory of Student Life (OVE) and Panel 1995 of the Ministry of National Education), this thesis aims to analyze, at the scale of France, students' employment in all its forms and to identify the different impacts it could have on academic achievement. This analysis shows that students' employment has a negative and significant influence on academic achievement. However, it's not the employment itself that is detrimental to students but some characteristics of these activities, such as the job intensity and the hiring sector. Moreover, it seems that they are the best students who work while studying, whereas unemployed students would have no incentive to combine jobs and education. In short, combine study and job can become a first professional experience useful for students, provided that job is linked to studies and does not interfere too much on school time. Public policy that would encourage students not to work beyond the part-time could be favorable to them. Finally, the particular study on students in university first year shows that the majority of students-workers enrolled in L1 who have abandoned their academic year not working intensively. Employment outside the curriculum is not the only factor that can justify the alarming failure rate of L1.