This research develops the availability function for a continuously demanded component which is maintained by an age replacement preventive maintenance policy. The availability function, A(t), is a function of time and is defined as the probability that the component functions at time t. The component is considered to have two states: operating and failed. In this policy, the component is repaired or replaced at time of failure. Otherwise, if the component survives T time units, a preventive maintenance service is performed. T is known as the age replacement period or preventive maintenance policy. The component is considered to be as good as new after either service action is completed. A renewal theory approach is used to develop A(t). Past research has concerned infinite time horizons letting analysis proceed with limiting values. This research considers component economic life that is finite. The lifetime, failure service time and preventive maintenance service time probability distributions are unique and independent. Laplace transforms are used to simplify model development. The age replacement period, T, is treated as a parameter during model development. The partial Laplace transform is developed to deal with truncated random time periods. A general model is developed in which the resulting availability function is dependent on both continuous time and T. An exact expression for the Laplace transform of A(t, T) is developed. Two specific cases are considered. In the first case, the lifetime, repair and preventive maintenance times are unique exponential distributions. This case is used to validate model performance. Tests are performed for t→0, t→∞ and for times in between these extremes. Results validate model performance. The second case models the lifetime as a Weibull distribution with exponential failure repair and preventive maintenance times. Results validate model performance in this case also. Exact infinite series for the partial and normal Laplace transform of the Weibull distribution and survivor function are presented. Research results show that the optimum infinite time horizon age replacement period does not maximize average availability for all finite values of component economic life. This result is critical in lifecycle maintenance planning. / Ph. D.

This research develops the availability function for a two component series system in which a component is replaced because of component failure or because it reaches a prescribed age. Also each component replacement provides an opportunity for the replacement of the other component. This last maintenance policy is called an opportunistic replacement strategy. The system functions only if the both components of the system are functioning. The system fails if either of the components fails. Component i is replaced if it fails before attaining age T_i since it was last replaced or maintained. The component i is preventatively maintained if is has not failed by the age T_i. This type of replacement plan is called age replacement policy. When component 1 is being replaced or preventatively maintained, if the age of component j ≠ i exceeds τ_j then both components i and j are replaced at the same time. This type of replacement is called opportunistic replacement of component j and τ_j is called the opportunistic replacement time for component j. The time dependent and long run availability measures for the system are developed. A nested renewal theory approach is used is used to develop the system availability function. The nesting is defined by considering the replacement of a specific one of the components as an elementary renewal event and the simultaneous replacement of both components as the macroscopic renewal event. More specifically, the renewal process for the system represents a starting point for the entire system and is in fact a renewal process. The intervals between system regeneration points are called “major intervals". The age replacement time T_i and opportunistic replacement time τ_i are treated as decision parameters during the model development. The probability distribution of the major interval is developed and the Laplace transform of the system availability is developed. Four replacement models are obtained from the main opportunistic age replacement policy. These are a failure replacement policy, an opportunistic failure model, a partial opportunistic age replacement policy and an opportunistic age replacement policy. These models are obtained as specific cases of the general model. The long run availability measure for the failure replacement model is proven to be the same measure as that developed by Barlow and Proschan. This proof validates the modeling approach. / Ph. D.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment Of the requirements for the degree of Master of Science in Engineering. Johannesburg, 1993 / Renewal is the extraction of the intellectual content (algorithms, data structures) from an existing program, and then puilding a new more maiatainable program using more modem progra1Tlming methods and languages. A survey of software structure on maintenance. highlighted the different hierarchies produced by functional and object-oriented design methods. Elecsim, a linear circuit sL~ulator written in Pascal, was chosen as the existing program to be renewed, The new version follows the approach of decoupling the user interface and introducing an explicit scheduler. The object-oriented design technique is used extensively. Other issues addressed include online-help and. documentation for the program. Conclusions are drawn which are generally applicable from the specificlessons learnt from the Elecsim/Elector case study. / MT2017

Most modern systems are equipped with very complex, expensive, and high technology components whose maintenance costs have become an increasingly large portion of the total operating cost of these systems. Thus, the efficacy of the maintenance policy for these and related systems has become a major concern to both manufacturing and design engineers. Different kinds of maintenance strategies have been proposed to solve the problem. While some of these have proven effective, there is yet no definitive approach that has been found that support the maintainability requirements of transient systems or systems that exhibit transient behavior. Transient behavior is the notion of non-steady state operation, which is the characteristic of system operation during its useful life. For designing convenience most of the maintenance strategies have assumed negligible maintenance or repair time which is not practical.In this research an opportunistic maintenance (OM) approach is implemented on a multi-unit system that exhibits transient behavior. Under OM policy, if a maintenance event has been scheduled for certain components and in the process of implementing the scheduled maintenance of these targeted components, the maintenance of other components whose maintenance times are in close proximity is also implemented at the same time. As a result, the time and cost of marshalling and staging maintenance resources are reduced. As part of the system effectiveness measure, the instantaneous system availability based on the transient nature of the system, is estimated using the renewal theory approach.

The aim of the research conducted in To Reach Everyone – The Regional Councils’ Communication to Foreign-Born During the COVID-19 Pandemic is to explore how communications officers on Swedish regional councils have thought and resonated about the strategies used to reach foreign-born during the COVID-19 pandemic. Discourse psychology is the main theoretical framework and is combined with a late modern view on crisis communication and the Discourse of Renewal Theory. The study can be placed in the field of strategic communication. The material consists of qualitative semi-structured interviews with six communications officers from different regional councils. The interviews were conducted in the spring of 2021. The results show that all of the six regional councils have taken foreign-born into consideration in their communication. Furthermore, six interpretative repertoires were identified: responsibility, resources, cooperation, wide selection of channels, constantly changing information and learning. The communications officers feel a huge responsibility to reach the entire population, however, often lack the resources needed. The main strategies to reach foreign-born has been cooperation with other actors and using a wide selection of channels in the communication efforts. The communications officers have been challenged by the constantly changing information and use their experiences for learning for future situations.

La thèse est consacrée à l'étude de modèles bivariés en Fabilité, qui tiennent compte de différents types de dépendance entre composants. Dans un premier temps, nous nous intéressons au cas d'un système formé de deux composants, dont la dégradation est modélisée par un processus de Lévy croissant bivarié (subordinateur bivarié). Sous cette hypothèse, eux études sont faites : l'une sous l'hypothèse de surveillance continue et de réparation parfaite du système, l'autre sous une hypothèse d'inspections périodiques et de réparation imparfaite. Dans un deuxième temps, la thèse est consacrée à un autre modèle de survie bivarié, sous influence d'un environnement stochastique stressant ponctuel. La dépendance entre composants est ici induite par un environnement stressant commun, qui induit des détériorations différentes sur chacun des composants (augmentation du taux de panne pour l'un, du niveau de détérioration pour l'autre). Pour chacun des modèles étudiés, nos résultats montrent l'importance de la prise en compte de la dépendance entre les composants d'un système. / The thesis is devoted to the study of bivariate models in reliability, which take into account several types of dependence between components. As a first step, we are interested in a two-component system with accumulating deterioration modeled by a bivariate increasing Lévy process (bivariate subordinator). Under this hypothesis, two different studies are made : one under the assumption of continuous monitoring and perfect repair, the other one under the assumption of periodic inspections and imperfect repair. In a second step, the thesis is devoted to the study of another bivariate survivalmodel, under the influence of a stochastic and stressful environment. The dependence between components is here induced by the common stressful environment, with different incidence on the two components (increment of failure rate for one, of deterioration level for the other). For each of the studied models, our results show the importance of taking into account the dependence between the components of a system.

隨著經濟不斷的發展，企業間的競爭也愈趨激烈，因此在以利潤最大、付出成本最小的前提下，一些可能造成成本增加的因素就不能不重視。在量測產品的特性所使用的量測機器，可能因為量測設備的不精確造成誤差，進而影響測量產品品質特性的實際值。是以量測儀器測量產品特性時的誤差對於管制圖的設計參數的影響及使用管制圖監控製程的能力是我們所關切的課題。 本文探討量測誤差對 — 管制圖的效應。運用George Tagaras非對稱管制圖的概念，及同時考慮Taguchi的損失函數和測量誤差下，以更新理論方法建立 — 管制圖，並推導出目標函數，再透過最佳化的技巧以決定 — 管制圖的最佳經濟設計參數值。另外討論管制圖在統計層面的表現，並與經濟設計的結果作比較。 在資料分析方面，本研究考慮32組製程和成本參數組合，透過最佳化技巧找出 — 經濟及經濟統計管制圖之最小單位時間平均成本及最佳設計參數組合。再利用敏感度分析，觀察量測誤差對設計參數的影響，另外得知重要的製程和成本參數為何。這些可作為製程工程師決策參考之用。

Over the past century the study of gas exchange rates between the atmosphere and the ocean has received increased attention because of concern about the fate of greenhouse gases such as CO2 released into the atmosphere. Of interest is the oceanic uptake of CO2 in shallow water coastal regions as biological productivity in these regions is on average about three times larger than in the open ocean. It is well-known that in the absence of breaking surface waves, the water side turbulence controls gas transfer of sparingly soluble gases such as CO2 from the air to the water. The dependence of gas transfer on wind-driven shear turbulence and convection turbulence generated by surface cooling has been investigated previously by others. However, the effect of Langmuir turbulence generated by wave-current interaction has not been investigated before. More specifically, Langmuir turbulence is generated by the interaction of the wind-driven shear current with the Stokes drift velocity induced by surface gravity waves. In this dissertation, large-eddy simulations (LES) of wind-driven shallow water flows with Langmuir turbulence have been conducted and scalar transport and surface scalar transfer dynamics analyzed. The scalar represents the concentration of a dissolved gas such as CO2 in the water. In flows with Langmuir turbulence, the largest scales of the turbulence consist of full-depth Langmuir circulation (LC), parallel downwind-elongated, counter-rotating vortices acting as a secondary structure to the mean flow. LES guided by the full-depth LC field measurements of Gargett & Wells (2007) shows that Langmuir turbulence plays a major role in determining scalar transport throughout the entire water column and scalar transfer at the surface. Langmuir turbulence affects scalar transport and its surface transfer through 1. the full-depth homogenizing action of the large scale LC and 2. the near-surface vertical turbulence intensity induced by the Stokes drift velocity shear. Two key parameters controlling the extent of these two mechanisms are the dominant wavelength (λ) of the surface waves generating the turbulence and the turbulent Langmuir number, Lat , which is inversely proportional to wave forcing relative to wind forcing. Furthermore, LES representative of the field measurements of Gargett et al. (2004) shows that Langmuir turbulence increases transfer velocity (a measure of mass transfer efficiency across the air-water interface) dramatically with respect to shear-dominated turbulence. Finally, direct resolution of the surface mass transfer boundary layer allows for the LES to serve as a testing ground for bulk parameterizations of transfer velocity. Several wellestablished parameterizations are tested and a new parameterization based on Stokes drift velocity shear is proposed leading to encouraging results.

In this thesis examples of spectral triples, which represent fractal sets, are examined and new insights into their noncommutative geometries are obtained. Firstly, starting with Connes' spectral triple for a non-empty compact totally disconnected subset E of {R} with no isolated points, we develop a noncommutative coarse multifractal formalism. Specifically, we show how multifractal properties of a measure supported on E can be expressed in terms of a spectral triple and the Dixmier trace of certain operators. If E satisfies a given porosity condition, then we prove that the coarse multifractal box-counting dimension can be recovered. We show that for a self-similar measure μ, given by an iterated function system S defined on a compact subset of {R} satisfying the strong separation condition, our noncommutative coarse multifractal formalism gives rise to a noncommutative integral which recovers the self-similar multifractal measure ν associated to μ, and we establish a relationship between the noncommutative volume of such a noncommutative integral and the measure theoretical entropy of ν with respect to S. Secondly, motivated by the results of Antonescu-Ivan and Christensen, we construct a family of (1, +)-summable spectral triples for a one-sided topologically exact subshift of finite type (∑{{A}} {{N}}, σ). These spectral triples are constructed using equilibrium measures obtained from the Perron-Frobenius-Ruelle operator, whose potential function is non-arithemetic and Hölder continuous. We show that the Connes' pseudo-metric, given by any one of these spectral triples, is a metric and that the metric topology agrees with the weak*-topology on the state space {S}(C(∑{{A}} {{N}}); {C}). For each equilibrium measure ν[subscript(φ)] we show that the noncommuative volume of the associated spectral triple is equal to the reciprocal of the measure theoretical entropy of ν[subscript(φ)] with respect to the left shift σ (where it is assumed, without loss of generality, that the pressure of the potential function is equal to zero). We also show that the measure ν[subscript(φ)] can be fully recovered from the noncommutative integration theory.

管制圖設計的經濟模式在最近三十年已經被廣泛的研究。本研究利用更新 理論方法(Renewal Theory Approach) 解出兩個非隨機因素下之S 經濟管 制圖。與其它的多重非隨機因素製程模式相比較，我們的模式不僅假設更 合理且以此方法表示平均循環時間(The Expected Cycle Time) 及平均循 環成本(The Expected Cycle Cost)會比擴展Duncan的方法或其它的方法 簡單容易。文中以數值例子說明建立 S 經濟管制圖的過程，並比較 S經 濟管制圖與Shewhart S 管制圖成本的大小及偵錯能力。另外，當製程上 有多重非隨機因素發生時，其成本模式也可容易的以更新理論方法擴展而 得。在實務上，若業者希望以最小成本維持製程之穩定，則可依本文所提 出的方法建立經濟管制圖。