Optimal Replacement Strategy Research Articles

Replacement Strategies for Tunneled Hemodialysis Catheters with Complications: A Nationwide Cohort Study.

Tunneled hemodialysis catheters often have infectious or mechanical complications that require unplanned removal and replacement, but the optimal replacement strategy is unknown. This study described the real-world use of two strategies in Australia and compared the survival of replacement catheters inserted by either strategy. Observational data from the REDUCCTION trial, which enrolled a nationwide cohort of 6400 adults who received an incident hemodialysis catheter (2016-2020) was used for this secondary analysis. Tunneled catheters were replaced by either catheter exchange through the existing tunnel tract or removal and replacement through a new tract. The effect of the replacement strategy on the time to catheter removal due to infection or dysfunction was estimated by emulating a hypothetical pragmatic randomized trial among a subset of 434 patients with mechanical tunneled catheter failure. Out of 9974 tunneled hemodialysis catheters inserted during the trial, 380 had infectious and 945 had mechanical complications that required replacement. Almost all infected hemodialysis catheters (97%) were removed and separately replaced through a new tunnel tract, whereas nephrology services differed widely in their replacement practices for catheters with mechanical failure (median = 50% guidewire exchanged, interquartile range= 30%-67%). Service-level differences accounted for 29% of the residual variation after adjusting for patient factors. In the target trial emulation cohort of mechanical failure (N=434 patients), catheter exchange was not associated with lower complication-free survival at one, six, or 12 months (counterfactual survival difference at one month = 5.9%, 95% CI = -2%, 14%). Guidewire exchange for mechanical failure of catheter was not associated with lower catheter survival and may be preferable for patients.

Optimal age replacement time for coherent systems under Geometric Point Process

In spatial context, the understanding of event dynamics and point distributions is a fundamental requirement. This study addresses a critical need by introducing the Geometric Point Process (GPP) and explaining its potential impact on optimizing the determination of optimal replacement ages for coherent systems. Our paper has three overarching aims: firstly, to bridge the gap by presenting the novel GPP model that effectively captures the geometric distribution of points, filling a void in point process theory. Secondly, we calculate the optimal replacement age for the coherent system based on the principles of GPP. This involves employing the Infinitesimal-Look Ahead stopping rule within the framework of Smooth Semi-Martingale (SSM) decomposition. A comprehensive comparative analysis is conducted to assess the distinct features and advantages of the GPP in relation to other point processes, offering valuable insights into its applicability and performance. Lastly, we extend the practical application of GPP by examining optimal replacement strategies for components in coherent systems, offering a bridge between theory and real-world practices, especially in the context of aircraft and wind turbine component deterioration. Additionally, we conduct reliability and sensitivity analyses, providing management suggestions, and present Monte Carlo simulations as an alternative method for validating optimal solutions. This research invites the industrial community to utilize the proposed replacement policy, paving the way for exploring geometric characteristics in stochastic processes. The timeliness and significance of this work are underscored by the relatively unexplored field of smooth semi-martingales, with the most recent publication dating back to 2015 by Bueno.

Evaluating different predictive strategies for filling the global GRACE/-FO terrestrial water storage anomalies gap

The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions provide unprecedented approaches for tracking terrestrial water storage anomalies (TWSA). However, evaluating long-term hydrologic states requires continuous TWSA without the ∼11-month gap between the two GRACE missions. Trend prediction is a challenging problem for TWSA gap-filling. There are three common methods for handling trends in previous efforts, i.e., de-trending the TWSA, adding back the long-term or piecewise trends of GRACE/-FO to the detrended predictions, or not performing such trend replacement. However, a single global application of one of these methods will not produce optimal results. Therefore, we designed a framework to select the optimal trend replacement strategy for each grid in this study. Based on this framework, we better filled the gap (excluding Antarctica) using machine learning techniques adopting the Global Land Data Assimilation System (GLDAS) Noah TWSA, precipitation, and temperature as inputs. The median gridwise Nash-Sutcliffe efficiency of the result generated by our framework improves by 0.08 compared to the result of a single long-term trend replacement strategy. Furthermore, we quantitatively evaluated the impact of three predictive strategies on the results: selection of leader machine learning technique, selection of optimal trend replacement strategy, and selection of most relevant inputs. The results indicate that the selection of trend replacement strategy has the greatest influence, followed by the selection of machine learning technique and then the selection of inputs. In addition, we found that in areas with abundant surface water, utilizing surface water anomalies as an additional predictor benefits the results. Our study is expected to provide suggestions for better TWSA predictive strategies.

Capsulectomy: a safe and effective way to lower shock impedance in S-ICD replacement procedures

Abstract Funding Acknowledgements Type of funding sources: None. Background The safety and efficacy of the subcutaneous implantable cardioverter-defibrillator (S-ICD) has been proven in various clinical trials. Due to intermuscular device placement, higher shock energy is required for effective treatment of ventricular tachyarrhythmia. High shock impedance is a risk marker for ineffective defibrillation. Previous studies have shown reduced shock efficacy in device replacement procedures, possibly due to fibrous encapsulation of the device associated with dwelling time of the system. Therefore, in case of significant capsulation, capsulectomy became part of device replacement procedure in our center. In this study we analyzed the results of intraoperative testing before and after capsulectomy measured by results of high-voltage impedance. Purpose Aim of our study was to show that removal of the fibrous capsulation can help to reduce high voltage impedance without relevant perioperative adverse events at the device replacement procedure. Methods Between January 2018 and November 2022, a total of 68 consecutive patients underwent S-ICD device replacement in our center. Pre-operative high-voltage impedance was determined either through recent therapy deliveries or by a 10J test shock immediately before device replacement. Device replacement was performed according to international standards. In case of significant capsulation, additional capsulectomy was performed. Defibrillation testing was routinely performed by the end of the procedure in the absence of contraindications. Results Of 68 patients, 81% were male, mean age at device replacement was 55 ± 17 years. Most patients were implanted for primary prevention (69%). Defibrillation testing with 65 J at initial device implantation was successful in 87% of patients. Mean dwelling time of the S-ICD System was 61 months (±19 months). Shock impedance increased significantly to 98±33 Ω vs. 80±20 Ω (p=0.013) at initial implantation. Capsulectomy of the S-ICD pocket resulted in a significant decrease of high-voltage impedance to 83±23 Ω as compared to measurement prior to replacement (p=0.03). Defibrillation testing was successful in all patients. First shock efficacy with 65 J was 92%. No acute complications (defined as significant bleeding, prolongation of hospital stay, etc.) were observed in short term follow-up and patients could be discharged as planned. Conclusion Capsulectomy of S-ICD pocket appears to be a safe and effective way to reduce shock impedance which has proven to be a predictor of successful defibrillation in testing as well as in spontaneous episodes. Despite the additional step during device replacement, no complications were observed in our study. Randomized trials regarding defibrillation testing during first implantation are ongoing. Trials addressing the optimal device replacement strategy however are warranted.

Designing optimal proactive replacement strategies for degraded systems subject to two types of external shocks

This article mainly investigates a proactive replacement policy for a stochastically deteriorating system concurrently subject to two types of shocks. First, the closed-form representation of system reliability function suffering from both a degradation process and environmental shocks is derived based on the degradation-threshold-failure (DTS) modeling framework. An age- and state-dependent competing risks model with mutual dependence between the two failure processes is embedded into system reliability modeling, where two types of shocks are taken into consideration upon arrival of an external shock including a minor one and a major one. Based on which, a bivariate maintenance policy is put forward for the deteriorating system, where the system is proactively replaced before failure at a planned time, or at an appropriate number of minimal repairs, whichever takes place first. The expected long-run cost rate (ELRCR) is formulated, and optimal solutions are evaluated analytically for two special cases. Finally, an illustrative example is redesigned to validate the theoretical results, exploring the significance of two types of shocks and mutual dependence in system reliability modeling, and illustrating the potential applications in maintenance decisions in various manufacturing systems.

Abstract 11271: Post TAVR Outcomes Among Patient With Amyloidosis and Aortic Stenosis: A Meta Analysis

Introduction: Aortic stenosis (AS) is one of the most prevalent valvular heart diseases globally. As many as 16% of AS patients have underlying cardiac amyloidosis (CA). To date, there is a paucity of data on outcomes among AS with concomitant CA patients post-TAVR. Hypothesis: This study aimed to evaluate the clinical outcomes post TAVR among patients with CA. Methods: We performed a systematic literature search of databases for relevant articles from inception until June 01, 2022. Unadjusted odds ratios (OR) were pooled using a random-effect model, and a p-value of <0.05 was considered statistically significant. Results: 5 studies with 1,488 patients were involved in the final analysis. The mean age of patients among CA+AS and AS alone was (85 vs 80) years. The number of males affected with dual pathology was higher compared to AS alone (71% vs 59%). 29% of patients were having a right bundle branch block in the CA+AS group, while 12% were among AS alone. Mean IV Septal Thickness (1.53 vs 1.33), mean relative wall thickness (0.60 vs 0.40) and mean LA dimensions (5.19 vs 4.8) were higher among the CA+AS group compared with AS alone. At the mean follow up of 12 months the odds of in-hospital mortality (OR, 2.09(95% CI: 0.77-5.63), P = 0.15), stroke (OR, 0.46(95%CI: 0.06-3.60), P = 0.46), and vascular complication (OR, 0.19(95% CI: 0.01-3.40), P = 0.26) were comparable between both group. In contrast, the incidence of acute kidney injury (OR, 3.09(95% CI: 2.02-4.71), P<0.001), and major bleeding (OR, 1.74(95% CI: 1.02-2.98), P = 0.04) were significantly higher among CA+AS group compared to AS group following TAVR. Conclusions: TAVR appeared to be a safe procedure among patients diagnosed with amyloidosis in aortic stenosis with a similar mortality rate between both groups of patients. Further studies should aim at determining the optimal valve replacement strategy in AS patients with concomitant CA.

Optimal block replacement policy for two-dimensional products considering imperfect maintenance with improved Salp swarm algorithm

Abstract Human society is entering Industry 4.0. Engineering systems are becoming more complex, which increases the difficulties in maintenance support work. Maintenance plays a very important role in the entire life cycle of a system, and in reality, maintenance is not always perfect, and its maintenance degree is between good as new and bad as old, which should be considered in the maintenance strategy. Under the framework of two-dimensional warranty, this work proposes an optimal two-dimensional block replacement strategy based on the minimum expected warranty cost. Two-dimensional block replacement maintenance is imperfect maintenance. The failure rate reduction method is used to describe the maintenance effect of two-dimensional block replacement. In case analysis, the grid search algorithm, genetic algorithm, particle swarm optimization algorithm, and improved salp swarm algorithm (SSA) are used to find the optimal warranty scheme for the laser module. The improved SSA can converge faster and find a warranty scheme that makes the warranty cost lower. Therefore, managers can use these results to reduce costs and get a win-win extended warranty cost. Rationalization suggestions are put forward for managers to make maintenance decisions through comparative analysis and sensitivity analysis.

Improved Estimators of Population Mean under Nonresponse in Successive Sampling

It is well accepted that suitable additional information improves the efficiency of an estimator but at the same time, it faced the situation of nonresponse. The two-occasion successive sampling is useful to handle the absence of a full response from respondents. In this present study, we have developed exponential estimators for population mean using a subsampling nonrespondent procedure. To show the efficacy of the recommended estimators, several properties are derived, and respective optimum replacement strategies are inferred. To evaluate the performance of the recommended estimators empirically, a computational study is carried out as well. It was found that the recommended estimators outperform the existing ones under the nonresponse in successive sampling.

Optimal Hormone Replacement Therapy in Hypothyroidism - A Model Predictive Control Approach.

In this paper, we address the problem of optimal thyroid hormone replacement strategy development for hypothyroid patients. This is challenging for the following reasons. First, it is difficult to determine the correct dosage leading to normalized serum thyroid hormone concentrations of a patient. Second, it remains unclear whether a levothyroxine L-T 4) monotherapy or a liothyronine/levothyroxine (L-T 3/L-T 4) combined therapy is more suitable to treat hypothyroidism. Third, the optimal intake frequency of L-T 3/L-T 4 is unclear. We address these issues by extending a mathematical model of the pituitary-thyroid feedback loop to be able to consider an oral intake of L-T 3/L-T 4. A model predictive controller (MPC) is employed to determine optimal dosages with respect to the thyroid hormone concentrations for each type of therapy. The results indicate that the L-T 3/L-T 4 combined therapy is slightly better (in terms of the achieved hormone concentrations) to treat hypothyroidism than the L-T 4 monotherapy. In case of a specific genetic variant, namely genotype CC in polymorphism rs2235544 of gene DIO1, the simulation results suggest that the L-T 4 monotherapy is better to treat hypothyroidism. In turn, when genotype AA is considered, the L-T 3/L-T 4 combined therapy is better to treat hypothyroidism. Furthermore, when genotype CC of polymorphism rs225014 (also referred to as c.274A>G or p.Thr92Ala) in the DIO2 gene is considered, the outcome of the L-T 3/L-T 4 combined therapy is better in terms of the steady-state hormone concentrations (for a triiodothyronine setpoint at the upper limit of the reference range of healthy individuals). Finally, the results suggest that two daily intakes of L-T 3 could be the best trade-off between stable hormone concentrations and inconveniences for the patient.

Bone Marrow Derived Mesenchymal Stromal Cells Promote Vascularization and Ciliation in Airway Mucosa Tri-Culture Models in Vitro

Patients suffering from irresectable tracheal stenosis often face limited treatment options associated with low quality of life. To date, an optimal tracheal replacement strategy does not exist. A tissue-engineered tracheal substitute promises to overcome limitations such as implant vascularization, functional mucociliary clearance and mechanical stability. In order to advance a tracheal mucosa model recently developed by our group, we examined different supporting cell types in fibrin-based tri-culture with primary human umbilical vein endothelial cells (HUVEC) and primary human respiratory epithelial cells (HRE). Bone marrow-derived mesenchymal stromal cells (BM-MSC), adipose-derived mesenchymal stromal cells (ASC) and human nasal fibroblasts (HNF) were compared regarding their ability to promote mucociliary differentiation and vascularization in vitro. Three-dimensional co-cultures of the supporting cell types with either HRE or HUVEC were used as controls. Mucociliary differentiation and formation of vascular-like structures were analyzed by scanning electron microscopy (SEM), periodic acid Schiff’s reaction (PAS reaction), two-photon laser scanning microscopy (TPLSM) and immunohistochemistry. Cytokine levels of vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), interleukin-6 (IL6), interleukin-8 (IL8), angiopoietin 1, angiopoietin 2, fibroblast growth factor basic (FGF-b) and placenta growth factor (PIGF) in media supernatant were investigated using LEGENDplex™ bead-based immunoassay. Epithelial morphology of tri-cultures with BM-MSC most closely resembled native respiratory epithelium with respect to ciliation, mucus production as well as expression and localization of epithelial cell markers pan-cytokeratin, claudin-1, α-tubulin and mucin5AC. This was followed by tri-cultures with HNF, while ASC-supported tri-cultures lacked mucociliary differentiation. For all supporting cell types, a reduced ciliation was observed in tri-cultures compared to the corresponding co-cultures. Although formation of vascular-like structures was confirmed in all cultures, vascular networks in BM-MSC-tri-cultures were found to be more branched and extended. Concentrations of pro-angiogenic and inflammatory cytokines, in particular VEGF and angiopoietin 2, revealed to be reduced in tri-cultures compared to co-cultures. With these results, our study provides an important step towards a vascularized and ciliated tissue-engineered tracheal replacement. Additionally, our tri-culture model may in the future contribute to an improved understanding of cell-cell interactions in diseases associated with impaired mucosal function.

Deep replacement: Reinforcement learning based constellation management and autonomous replacement

The Deep Reinforcement Learning (DRL) algorithm, Proximal Policy Optimization (PPO2), is deployed on a custom spacecraft (S/C) build and loss model to determine if an Artificial Intelligence (AI) can learn to monitor satellite constellation health and determine an optimal replacement strategy. A custom environment is created to simulate how S/C are built, launched, generate revenue, and finally decay. The reinforcement learning agent successfully learned an optimal policy for two models: a Simplified Model where the financial cost of actions is ignored; and an Advanced Model where the financial cost of actions is a major element. In both models the AI monitors the constellations and takes multiple strategic and tactical actions to replace satellites to maintain constellation performance. The Simplified Model showed that the PPO2 algorithm was able to converge on an optimal solution after ∼200,000 simulations. The Advanced Model was much more difficult for the AI to learn, and thus, the performance drops during the early episodes, but eventually converges to an optimal policy at ∼25,000,000 simulations. With the Advanced Model, the AI is taking actions that are successfully providing strategies for constellation management and satellite replacements which include these actions’ financial implications. Thus, the methods in this paper provide initial research developments towards a real-world tool and an AI application that can aid various Aerospace businesses in managing Low Earth Orbit (LEO) constellations. This type of AI application may become imperative for deploying and maintaining small satellite mega-constellations.

Optimal replacement policy under cumulative damage model and strength degradation with applications

In many real-life scenarios, system failure depends on dynamic stress-strength interference, where strength degrades and stress accumulates concurrently over time. In this paper, we consider the problem of finding an optimal replacement strategy that balances the cost of replacement with the cost of failure and results in the minimum expected cost per unit time under cumulative damage model with strength degradation. In the most general setting, we propose to find optimal choices of three thresholds on operation time, number of arriving shocks and amount of cumulative damage such that replacement of the system due to failure or reaching any of the three thresholds, whichever occurs first, results in the minimum expected cost per unit time. The existing recommendations are applicable only under the assumption of Exponential damage distribution including Poisson arrival of shocks and/or with fixed strength. As theoretical evaluation of the expected cost per unit time turns out to be very complicated, a simulation-based algorithm is proposed to evaluate the expected cost rate and find the optimal replacement strategy. The proposed method is easy to implement having wider domain of application including non-Poisson arrival of shocks and non-Exponential damage distributions. For illustration, the proposed method is applied to real case studies on mailbox and cell-phone battery experiments.

Optimal replacement strategies for warranty products with multiple failure modes after warranty expiry

The optimal replacement problem for a warranty product subject to (M + 1) types of mutually exclusive failure modes, including M repairable failure modes and a catastrophic failure mode, is investigated in this paper. When the product fails with a repairable failure mode, a minimal repair will be conducted to remove the failure. However, if a catastrophic failure mode occurs, the failure product can only be replaced by a new one. Within the warranty period, the seller needs to complete each failure repair within a repair time limit. Once a failure cannot be repaired within the stipulated time, under the rebate warranty, the customer is refunded a proportion of the sale price of the product based on its working time, and the warranty terminates simultaneously; or under the free replacement warranty, the seller is obligated to provide a new product at no charge to the customer. Under both the warranty policies, the repair cost is free of charge to the customer within the warranty time, while the customer is responsible for all the cost for repairs within the post-warranty time. From the customer’s point of view, the expected life cycle cost rate of the product under the rebate and free replacement warranty are respectively derived. The existence and uniqueness of the optimal replacement strategies after warranty expiring are also proved theoretically by minimizing the cost rate. Finally, we give numerical examples to illustrate the two warranty models and show the effectiveness of proposed strategies.

Investigation of Competent Estimation Procedure for Estimating the Finite Population Mean at Current Occasion Addressing Non-response in Two-Occasion Successive Sampling

This paper is an effort to investigate the effect of non-response at the current (second) occasion in successive sampling. Using the subsampling non-respondent procedure, some exponential-type estimators have been proposed to estimate the current population mean. Properties of the proposed class of estimators are examined, and respective optimum replacement strategies are derived. Empirical studies are carried out to evaluate the performances of the suggested estimators. The outcomes are interpreted, and appropriate recommendations have been made.

Generalized Estimation Procedure in Two-Occasion Rotation Patterns

This paper describes some proficient estimation procedures in the presence of multi-auxiliary variables to enhance the precision of estimates in two-occasion rotation sampling. Utilizing information on several auxiliary variables, which are considered to be a positive correlation with the study variables on both occasions, we have suggested some better estimation procedures. The behaviors of the proposed estimation strategies have been examined along with the discussion of optimum replacement strategies, and the results obtained in these estimation procedures are demonstrated numerically through empirical and simulation studies, which present the supremacy in efficiencies of the proposed estimation procedures over the sample mean estimator, natural successive sampling estimator and recently developed estimator.

Primary Aortic Root Replacement Outcomes and Risk Factors in Pediatric Patients

The study sought to identify the optimal aortic root replacement (ARR) strategy for pediatric patients, and a single-center experience was analyzed. Retrospective review of patients undergoing ARR from 1995 to 2018 was performed. Patients were stratified by surgical strategy (pulmonary autograft [Ross procedure], aortic homograft, mechanical valve conduit [Bentall procedure], or porcine xenograft [Freestyle bioprosthesis]) and aortic annulus size. ARR was performed in 206 patients with a median follow-up of 5.0 (interquartile range, 1.4-11.4) years. Root replacements included Ross procedure (n= 98), homograft (n= 83), Bentall procedure (n= 18), and Freestyle bioprosthesis (n= 7). Overall survival was 92%, and freedom from reoperation or death was 81%. Reoperation-free survival was superior in the Ross group when compared with other groups. Because surgical options differ based on the size of the aortic annulus, the analysis was arbitrarily stratified. When the aortic annulus diameter was greater than 19 mm (n= 74), procedures included Ross procedure (n= 23), homograft (n= 29), Bentall procedure (n= 17), and Freestyle bioprosthesis (n= 5). Reoperation-free survival at median follow-up (5 years) was 86%, 58%, 100%, and 100%, respectively. The Bentall procedure offered the longest freedom from reoperation. In the subset with aortic annulus diameter less than 19 mm and a pulmonary valve suitable for a Ross procedure, patients underwent the Ross procedure (n= 75) or homograft ARR (n= 36). At median follow-up (3.8 years), reoperation-free survival was longer after the Ross procedure than after homograft ARR (88% vs 46%; P < .001). In patients with a large aortic annulus, a Bentall ARR offers the longest reoperation-free survival. For patients with small aortic roots, a Ross procedure provides better a reoperation-free survival than does homograft ARR.

Comparison of forecasting models to predict concrete bridge decks performance

AbstractThe accuracy of forecasting models for the prediction of an infrastructure's deterioration process plays a significant role in the estimation of optimal maintenance, rehabilitation, and replacement strategies. Numerous approaches have been developed to overcome the limitations of existing forecasting models. In this article, a direct comparison is made between different models using the same input data to derive conclusions of their distinct performance. The models selected for the comparison were Markov, semi‐Markov, and hidden Markov models together with artificial neural networks (ANNs), which have been reported in literature as reliable deterioration prediction models. A quality of fit was performed to measure how well the observed data corresponded to the predicted values, and therefore objectively compare the performance of each model. The results demonstrated that the most accurate prediction was accomplished by the ANN model. Nevertheless, all models presented differences with respect to typical values of concrete decks life expectancy, which is attributed to the inherent difficulties of the database. Additionally, the problem of the visual inspection subjectivity was also regarded as one of the potential causes for the found deviations. Therefore, this article also discusses the shortcomings of current condition assessment practices and encourages future bridge management systems to replace the classical methods by more sophisticated and objective tools.

A Clustering-based Approach to Segment a Pavement Markings Line

The maintenance of road infrastructure is a classic social challenge, especially in the context of a decreasing maintenance budget and the advent of autonomous vehicle traffic. Road markings need an accurate replacement strategy to guarantee that the markings remain perceptible. The retroreflective luminance of markings is currently dynamically quantifiable only by using a retroreflectometer such as the Ecodyn from MLPC. The main objective of this research is to construct a performance-based approach for retroreflective marking replacement adapted to a given road network. This approach involves three main tasks: localize the strategic area based on past inspections, determine an adapted decay model for a given area, and evaluate the economic impact of replacing markings. This paper focuses on the first task. We apply the Agglomerative Hierarchical Clustering (AHC) method to a given dataset to obtain a suitable markings line segmentation. Markings whose retroreflective luminance exhibits similar evolution over time are interpreted to belong to a specific area of the road network. When no follow-up replacement has occurred, a replacement detector deduces the date at which markings were laid from the clusters. The broken center line of the French National Road 4 illustrates the proposed approach; the road is divided into 5 clusters and 34 lifecycles. A study of markings laid in 2008 and replaced in 2012 shows important variations in the decay of the retroreflective luminance as identified by the clustering approach. Even for a single road, an optimal replacement strategy for retroreflective road markings is necessary and is composed of several local maintenance strategies.

Optimal inspection and replacement strategy for 145 kV gas-insulated switchgear

We deal with an optimization problem of planning a maintenance strategy for 145 kV gas-insulated switchgear and apply reliability-centered maintenance approach to find an efficient and effective strategy. In a three-step sequential process, we use failure mode effects and criticality analysis to define the critical failure modes that cause the major failures of 145 kV gas-insulated switchgear, select the maintenance significant items to remove the major failure modes, and finally apply logic tree analysis to assign the appropriate maintenance task to each critical failure modes in the system. We then compare the assigned maintenance tasks with existing tasks in the installation, operation, and maintenance manuals developed in the system design and development phase. The assigned maintenance tasks in this study are compared with those in the system design and development phase by simulation, and a simple heuristic method is proposed to find optimal solutions.

Exploring Cost and Environmental Implications of Optimal Technology Management Strategies in the Street Lighting Industry

Abstract The market for solid-state lighting (SSL) systems has expanded 40-fold in installed lamps since 2001. At the same time, systems which preserve materials over time and promote material reuse are getting increasing attention in light of calls for reducing consumption of natural resources. As new lighting technology products are designed and brought to market, consideration must be given to how products will be managed throughout the life-cycle as well as their end-of-life (EOL) fate. Lighting-as-a-service (LaaS) business models have emerged as a potential strategy for preserving the materials embedded in lighting products. In this paper, we examine the cost and environmental implications of technology management decisions in the context of the street lighting industry, employing life-cycle assessment and a Markov Decision Process model. The goal of the research is to determine a policy that minimizes expected costs and emissions for the system over a fixed time horizon thus reducing uncertainty for managers. The model used in the paper evaluates the optimal replacement strategies for street lighting products and additionally connects the result to the optimal EOL product trajectory, taking both costs and carbon emissions into account. In doing so, we are able to more deeply understand the role that LaaS business models might play in enabling closed-loop systems within the street lighting industry.