Purpose
The maintenance department of today, like many other departments, is under sustained pressure to slash costs, show outcome and to support the assignments of the organization, as it is a ...commonsensical prospect from the business perspective. Therefore, the purpose of this paper is to find out the wastes level present in maintenance and, after that, do the ranking of maintenance wastes currently present in the operations of Indian organizations with the help of a questionnaire survey.
Design/methodology/approach
For this, a database of 421 Indian industries was identified and a structured questionnaire was designed. The questionnaire was divided into two sections A and B to assist with data interpretation. The aim of section A was to build general information of participants and their position, type of organization, number of employees, annual turnover of the organization, etc. Section B was also a structured questionnaire developed based on a five-point Likert scale for assessing the level of maintenance wastes currently present in the maintenance.
Findings
Waste of inventory in terms of spare parts storage and obsolesce, etc., waste of rejects/rework/scrap in case of poor maintenance, waste of processing that leads to increases in maintenance and waste of overproduction/excessive maintenance activity has a high level of presence in the maintenance of Indian organizations and gets the top ranks in all the seven types of maintenance wastes.
Practical implications
This paper will be extremely useful for the researchers, maintenance professionals and others concerned with maintenance to understand the after effects of maintenance wastes in Indian industries.
Originality/value
These findings will be highly valuable for professionals relating to manufacturing sector desiring to implement effective maintenance approach in the maintenance management system.
An MCM4 mutation detected in human cancer cells from endometrium was characterized. The mutation of G486D is located within MCM-box and the glycine at 486 in human MCM4 is conserved in Saccharomyces ...cerevisiae MCM4 and Sulfolobus solfataricus MCM. This MCM4 mutation affected human MCM4/6/7 complex formation, since the complex containing the mutant MCM4 protein is unstable and the mutant MCM4 protein is tend to be degraded. It is likely that the MCM4 mutation affects the interaction with MCM7 to destabilize the MCM4/6/7 complex. Cells with abnormal nuclear morphology were detected when the mutant MCM4 was expressed in HeLa cells, suggesting that DNA replication was perturbed in the presence of the mutant MCM4. Role of the conserved amino acid in MCM4 function is discussed.
Summary
Feasible and sustainable source of power is a burning question nowadays. The offshore wind farms can be a solution to power generation problem, but it is relatively more expensive. Its ...installation cost is more than twice of its similar size onshore counterpart. The cost that matters most is the operations and maintenance (O&M) cost. Expensive and sophisticated transfer vehicles as well as highly skilled technicians are needed to conduct O&M activities, which results in a remarkably higher O&M cost for an offshore wind farm project. Few researchers proposed some strategies that could resolve the problem nicely, although there is no universal maintenance strategy, which will fit all the conditions. Optimal maintenance strategy depends on a lot of factors such as cost of energy, level of reliability needed, weather conditions, availability of skilled technicians, availability of crew transfer vehicles, and to mention a few. Total 190 research articles related to offshore maintenance have been reviewed, and some prominent models have been discussed in detail. Some risk and reliability‐based models reduced annual maintenance cost by 23%, whereas some other opportunistic maintenance strategy was able to minimize 32% of production loss and transportation cost. Compatibility and usability of different models and results are highlighted. This critical review is aimed at identifying the relevant research outcomes and comparing their critical aspects to provide a good guideline about optimal maintenance strategy to the maintenance managers.
All the models related to offshore maintenance were classified into four (04) major categories: opportunistic maintenance, condition‐based maintenance, risk‐based uncertainty management, cost and task breakdown models. Most cost‐efficient opportunistic maintenance model produced 48.2% less cost than corrective maintenance. However, the best CBM strategy was 44.42% less expensive than traditional preventive replacement policy. On the other hand, best risk and reliability‐based model illustrated 23% annual cost reduction.
Abstract
The amino-terminal region of eukaryotic MCM4 is characteristic of the presence of a number of phosphorylation sites for CDK and DDK, suggesting that the region plays regulatory roles in the ...MCM2-7 helicase function. However, the roles are not fully understood. We analyzed the role of the amino-terminal region of human MCM4 by using MCM4/6/7 helicase as a model for MCM2-7 helicase. First we found that deletion of 35 amino acids at the amino-terminal end resulted in inhibition of DNA helicase activity of the MCM4/6/7 complex. Conversion of arginine at amino acid no. 10 and 11 to alanine had similar effect to the deletion mutant of Δ1-35, suggesting that these arginine play a role in the DNA helicase activity. The data suggest that expression of these mutant MCM4 in HeLa cells perturbed the progression of the S phase. Substitution of six CDK phosphorylation sites (3, 7, 19, 32, 54 and 110) in the amino-terminal region by phospho-mimetic glutamic acids affected the hexamer formation of the MCM4/6/7 complex. MCM4 phosphorylation by CDK may play a role in DNA replication licensing system, and the present results suggest that the phosphorylation interferes MCM function by lowering stability of MCM complex.
Summary Chronic insomnia is defined by difficulties in falling asleep, maintaining sleep, and early morning awakening, and is coupled with daytime consequences such as fatigue, attention deficits, ...and mood instability. These symptoms persist over a period of at least 3 months (Diagnostic and Statistical Manual 5 criteria). Chronic insomnia can be a symptom of many medical, neurological, and mental disorders. As a disorder, it incurs substantial health-care and occupational costs, and poses substantial risks for the development of cardiovascular and mental disorders, including cognitive deficits. Family and twin studies confirm that chronic insomnia can have a genetic component (heritability coefficients between 42% and 57%), whereas the investigation of autonomous and central nervous system parameters has identified hyperarousal as a final common pathway of the pathophysiology, implicating an imbalance of sleep–wake regulation consisting of either overactivity of the arousal systems, hypoactivity of the sleep-inducing systems, or both. Insomnia treatments include benzodiazepines, benzodiazepine-receptor agonists, and cognitive behavioural therapy. Treatments currently under investigation include transcranial magnetic or electrical brain stimulation, and novel methods to deliver psychological interventions.
•Impacts of economic and structural dependences are jointly investigated.•Assembly operation and its impact the components degradation are discussed.•An multi-level opportunistic predictive ...maintenance policy is proposed.•An optimization approach is developed to find the optimal decision variables.•A comparison study with a conventional maintenance policy is investigated.
For maintenance optimization of multi-component systems, opportunistic maintenance has been addressed in many studies since it allows considering the advantages of dependences between components in maintenance decision-making process. In the literature, economic dependence, which implies that joint maintenance of several components can reduce the maintenance cost, has been widely studied in the framework of opportunistic maintenance. There are however very few existing studies considering the advantages of structural dependence, whereby maintenance of a component requires disassembly of other components, in maintenance optimization. To face this issue, the objective of this paper is to propose a multi-level opportunistic predictive maintenance approach considering both economic and structural dependence. In that way, the economic and structural dependences between components are firstly formulated. A degradation model considering disassembly impacts is then developed. For opportunistic maintenance decision-making, two opportunistic thresholds are introduced. When corrective/preventive maintenance occurs, the first opportunistic threshold (eRo) is defined to select non-disassembled components for opportunistic maintenance. This first opportunistic decision allows considering the economic dependence between components. In addition, the maintenance of the selected components may require disassembly of other components which could be also good candidates to be opportunistically maintained. So, the second opportunistic threshold, sRo(sRo≥eRo), is then developed to select one or several disassembled components to be opportunistically maintained. To evaluate the performance of the proposed opportunistic maintenance approach, a cost model is developed. Particle swarm optimization algorithm is then applied to find the optimal decision variables. Finally, the proposed opportunistic maintenance approach is illustrated through a conveyor system to show its feasibility and added value in maintenance optimization framework.
Reliable and continuous operation of the equipment is expected in the wastewater treatment plant, as any perturbations can lead to environmental pollution and the need to pay penalties. Optimization ...and minimization of operating costs of the pump station cannot, therefore, lead to a reduction in reliability but rather should be based on preventive works, the necessity of which should be foreseen. The purpose of this paper is to develop an accurate model to predict a pump's mean time to failure, allowing for rational planning of maintenance. The pumps operate under the supervision of the automatic control system and SCADA, which is the source of historical data on pump operation parameters. This enables the research and development of various methods and algorithms for optimizing service activities. In this case, a multiple linear regression model is developed to describe the impact of historical data on pump operation for pump maintenance. In the literature, the least squares method is used to estimate unknown regression coefficients for this data. The original value of the paper is the application of the genetic algorithm to estimate coefficient values of the multiple linear regression model of failure-free time of the pump. Necessary analysis and simulations are performed on the data collected for submersible pumps in a sewage pumping station. As a result, an improvement in the adequacy of the presented model was identified.
In this paper, the reliability allocation and index of overall cost of rotary ultrasonic vibration-assisted EDM machine tool were studied. The failure rate of each module of the rotary ultrasonic ...vibration-assisted EDM machine tool can be accurately predicted by the maximum entropy ordered weighted average algorithm so that the corrected maintenance cost can be predicted. And effective control of preventive maintenance costs can be achieved by selecting the best maintenance times under the premise of reliability. The cost of corrective maintenance can be reduced by improving modules with a high failure rate, so as to realize the purpose of cost optimization under the premise of determining the maintenance time and reliability. The reliability function of the rotary ultrasonic vibration-assisted EDM machine tool is established according to the series-parallel relationship of each module. The results showed that the reliability of rotary ultrasonic vibration-assisted EDM machine tool is stabler at the non-fixed maintenance period according to the comparison between the non-fixed and the fixed maintenance period.
•A novel dynamic maintenance strategy is developed which can sequentially plan the system PM schedule based on the actual maintenance history and health information•Based on the classic rolling ...horizon approach, both preventive and opportunistic maintenance strategies are integrated into the same framework. Some drawbacks of this approach are overcome.•Less mathematical modeling and computation efforts are required, which enables it to address the systems of large scale. An efficient dynamic programming algorithm is developed for optimization.•The dynamic framework of the proposed strategy is flexible and can be further extended to CBM problems.
Maintenance grouping methods such as the rolling horizon approach are effective in reducing maintenance costs of multi-component systems. Despite the theoretical advancements of this approach, it still faces three challenges. First, the extensively adopted minimal repair assumption upon failures limits its application. Second, opportunistic maintenance upon corrective maintenance is overlooked, unable to fully take advantage of economic dependence. Third, maintenance plans are not based on actual maintenance history and health information, which may increase failure risks. To address these challenges, this paper formulates a novel dynamic planning framework that captures economic dependence in both preventive and opportunistic replacement. Unlike conventional approaches that restrict all maintenance activities into a finite planning horizon, our proposal focuses on activity-to-activity scheduling without specifying the horizon. As such, the subsequent maintenance schedule is dynamically updated once a system maintenance is executed. A flexible dynamic programming algorithm is developed to optimize the maintenance grouping, and the strategy framework is further extended to condition-based maintenance scenarios. The effectiveness and generality of the proposed maintenance strategy are demonstrated by numerical experiments.
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