Optimal maintenance strategies for repairable systems with general degree of repair

1991 ◽  
Vol 28 (2) ◽  
pp. 384-396 ◽  
Author(s):  
Wolfgang Stadje ◽  
Dror Zuckerman
Keyword(s):  
Optimal Policy ◽  
Planning Horizon ◽  
Spare Parts ◽  
Inventory Systems ◽  
Maintenance Strategy ◽  
Repairable Systems ◽  
Discounted Cost ◽  
Wide Range ◽  
Optimal Maintenance ◽  
New Research

In this study we examine repairable systems with random lifetime. Upon failure, a maintenance action, specifying the degree of repair, is taken by a controller. The objective is to determine an age-dependent maintenance strategy which minimizes the total expected discounted cost over an infinite planning horizon. Using several properties of the optimal policy which are derived in this study, we propose analytical and numerical methods for determining the optimal maintenance strategy. In order to obtain a better insight regarding the structure and nature of the optimal policy and to illustrate computational procedures, a numerical example is analysed. The proposed maintenance model outlines a new research channel in the area of reliability with interesting theoretical issues and a wide range of potential applications in various fields such as product design, inventory systems for spare parts, and management of maintenance crews.

Optimal maintenance strategies for repairable systems with general degree of repair

1991 ◽  
Vol 28 (02) ◽  
pp. 384-396 ◽  
Author(s):  
Wolfgang Stadje ◽  
Dror Zuckerman
Keyword(s):  
Optimal Policy ◽  
Planning Horizon ◽  
Spare Parts ◽  
Inventory Systems ◽  
Maintenance Strategy ◽  
Repairable Systems ◽  
Discounted Cost ◽  
Wide Range ◽  
Optimal Maintenance ◽  
New Research

In this study we examine repairable systems with random lifetime. Upon failure, a maintenance action, specifying the degree of repair, is taken by a controller. The objective is to determine an age-dependent maintenance strategy which minimizes the total expected discounted cost over an infinite planning horizon. Using several properties of the optimal policy which are derived in this study, we propose analytical and numerical methods for determining the optimal maintenance strategy. In order to obtain a better insight regarding the structure and nature of the optimal policy and to illustrate computational procedures, a numerical example is analysed. The proposed maintenance model outlines a new research channel in the area of reliability with interesting theoretical issues and a wide range of potential applications in various fields such as product design, inventory systems for spare parts, and management of maintenance crews.

Integrated maintenance/spare parts management for manufacturing system according to variable production rate impacting the system degradation

2020 ◽  
Vol 28 (1) ◽  
pp. 72-84 ◽  
Author(s):  
Sofiene Dellagi ◽  
Wajdi Trabelsi ◽  
Zied Hajej ◽  
Nidhal Rezg
Keyword(s):  
Production Rate ◽  
Preventive Maintenance ◽  
Manufacturing System ◽  
Planning Horizon ◽  
Sensitivity Study ◽  
Spare Parts ◽  
Rate Variation ◽  
Maintenance Strategy ◽  
Spare Parts Management ◽  
The Impact

This study develops an analytical model in order to determine an optimal integrated maintenance plan and spare parts management. We consider a manufacturing system, producing only one type of product, over a finite planning horizon H equal to the sum of all production periods and the production quantity of each period is known. This system is subject to a continuously increasing degradation rate. That is why a preventive maintenance strategy is adopted in order to face the increasing failure rate. We noted that contrarily to the majority of studies in literature, we take into account the impact of the production rate variation on the manufacturing system degradation and consequently on the adopted optimal maintenance strategy. In addition, the real need of spare parts relative to the scheduled maintenance actions is taken into account. In fact, the purpose of our study consists at determining the optimal preventive maintenance frequency and the optimal quantity of spare parts to order by minimizing a total cost, including maintenance and spare parts management. Numerical examples are presented along with a sensitivity study in order to prove the use of the developed model for deriving the optimal integrated strategy for any instance of the problem.

Optimizing the Reliability and Performance of Remote Vehicle-to-Grid Systems Using a Minimal Set of Metrics

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Annette G. Skowronska ◽  
David J. Gorsich ◽  
Vijitashwa Pandey ◽  
Zissimos P. Mourelatos
Keyword(s):  
Power Systems ◽  
Electrical Power ◽  
Optimal Solution ◽  
Planning Horizon ◽  
Spare Parts ◽  
Careful Consideration ◽  
Repairable Systems ◽  
Minimal Set ◽  
Power Management Strategy ◽  
And Performance

Vehicles connected to electric systems are considered “plug-in” vehicles. They can be an integral part of a microgrid. Ground vehicles have become more electrified over time, providing electrical power for the propulsion system (hybrid) and a complex suite of auxiliary power systems, enhancing their use in microgrids. Optimizing the microgrid system for performance and reliability considering many external loads and sources is a challenging problem. This is especially true when the plug-in vehicles may enter and leave the microgrid randomly becoming either sources or loads. The microgrid is a repairable system. Recent work has shown that multiple metrics are needed to fully account for the performance of repairable systems under uncertainty. In this paper, we propose a decision-based framework to design and maintain repairable systems for optimal performance and reliability using a set of metrics such as minimum failure free period (MFFP), number of failures in planning horizon, and cost. Optimal tradeoffs among a minimal set of metrics (MSOM) can be used in the design and maintenance of these systems. The optimal solution includes the initial design, the system maintenance throughout the planning horizon, and the protocol to operate the system. Critical remote military installations with plug-in vehicles connected to the microgrids require careful consideration of cost and repair strategies because of logistical challenges in performing repairs and supplying necessary spare parts in unsafe locations. We show how a MSOM helps to solve the complex optimization problem of finding the best microgrid power management strategy considering performance, reliability, and cost.

scholarly journals Bad World: The Negativity Bias in International Politics

2019 ◽  
Vol 43 (3) ◽  
pp. 96-140 ◽  
Author(s):  
Dominic D.P. Johnson ◽  
Dominic Tierney
Keyword(s):  
International Relations ◽  
Fundamental Principle ◽  
Human Mind ◽  
Negative Information ◽  
Theory And Practice ◽  
Negativity Bias ◽  
Positive Information ◽  
Psychological Phenomena ◽  
Wide Range ◽  
New Research

A major puzzle in international relations is why states privilege negative over positive information. States tend to inflate threats, exhibit loss aversion, and learn more from failures than from successes. Rationalist accounts fail to explain this phenomenon, because systematically overweighting bad over good may in fact undermine state interests. New research in psychology, however, offers an explanation. The “negativity bias” has emerged as a fundamental principle of the human mind, in which people's response to positive and negative information is asymmetric. Negative factors have greater effects than positive factors across a wide range of psychological phenomena, including cognition, motivation, emotion, information processing, decision-making, learning, and memory. Put simply, bad is stronger than good. Scholars have long pointed to the role of positive biases, such as overconfidence, in causing war, but negative biases are actually more pervasive and may represent a core explanation for patterns of conflict. Positive and negative dispositions apply in different contexts. People privilege negative information about the external environment and other actors, but positive information about themselves. The coexistence of biases can increase the potential for conflict. Decisionmakers simultaneously exaggerate the severity of threats and exhibit overconfidence about their capacity to deal with them. Overall, the negativity bias is a potent force in human judgment and decisionmaking, with important implications for international relations theory and practice.

scholarly journals The CoGenT3 Study: Cognition and Gender Trends in Three American Generations

2020 ◽  
Vol 4 (Supplement_1) ◽  
pp. 817-817
Author(s):  
Shana Stites
Keyword(s):  
Cognitive Impairment ◽  
Quantitative Methods ◽  
Cognitive Testing ◽  
Library Science ◽  
Sexual And Gender Minorities ◽  
Functional Impairments ◽  
Gender Minorities ◽  
Wide Range ◽  
And Gender ◽  
New Research

Abstract Many studies find gender differences in how older adults’ report on their memory, perform on cognitive testing, and manage functional impairments that can accompany cognitive impairment. Thus, understanding gender’s effects in aging and Alzheimer’s research is key for advancing methods to prevent, slow, manage, and diagnosis cognitive impairment. Our study, CoGenT3 – The study of Cognition and Gender in Three Generations – seeks to disambiguate the effects of gender on cognition in order to inform a conceptual model, guide innovations in measurement, and support future study. To accomplish this ambitious goal, we have gathered an interdisciplinary team with expertise in psychology, cognition, sexual and gender minorities, library science, measurement, quantitative methods, qualitative methods, and gender and women’s studies. The team benefits from the intersections of expertise in being able to build new research ideas, gain novel insights, and evaluate a wide-range of actions and re-actions but this novelty can also raise challenges.

scholarly journals Emory Roybal Center for Dementia Caregiving Mastery: Diverse Responses to Letter of Intent Call

2020 ◽  
Vol 4 (Supplement_1) ◽  
pp. 254-254
Author(s):  
Kenneth Hepburn ◽  
Molly Perkins ◽  
Drenna Waldrop ◽  
Leila Aflatoony ◽  
Mi-Kyung Song ◽  
...  
Keyword(s):  
Clinical Trial ◽  
Lewy Body Dementia ◽  
Racial Groups ◽  
Dementia Caregiving ◽  
Wide Range ◽  
Great Heterogeneity ◽  
New Research ◽  
Stage 1 ◽  
Native Alaskan ◽  
Physical Care

Abstract This new NIA-supported Roybal Center seeks to support Stage 1 pilot clinical trials of programs aimed at promoting caregiving competence and confidence in the great heterogeneity of dementia caregiving contexts. During our first cycle, we received 26 letters of intent (LOI) for full applications. Responses reaffirmed the Center’s premise that dementia caregiving is remarkably varied in nature. While most proposed programs focused on generic caregiving, a number addressed caregiving issues facing specific ethnic/racial groups (African American; Korean American; Native Alaskan/American Indian; Latino), and several focused on specific dementing conditions (MCI, Lewy Body Dementia,TBI-based dementia). Most described programs centered on knowledge development and daily management skill issues (e.g., management of behaviors); others specified development of physical care skills. Decision-making and communication constituted the second most common topic. Over 40% proposed adaptation of existing programs; more than 25% proposed apps or technology interventions. Investigators represented a wide range of disciplines: 45% each from Health sciences (nursing, medicine, and social work) and Social/Behavioral sciences (principally psychology) and the rest from engineering and communications. LOIs varied most in their readiness to complete a clinical trial within a year. About 40% were in very preliminary stages; 25% were clearly poised for a Stage 1 trial; 15% did not sufficiently address the Center’s aims. Key criteria for invitations to submit full applications (n=4) included: specificity of context; clinical trial readiness; reasonableness of proposed adaptation. These criteria should guide future LOIs addressing the diversity of important new research and intervention perspectives on the multifaceted work of caregiving.

scholarly journals Minimizing spectral risk measures applied to Markov decision processes

2021 ◽  
Author(s):  
Nicole Bäuerle ◽  
Alexander Glauner
Keyword(s):  
Minimization Problem ◽  
Risk Measures ◽  
Risk Measure ◽  
Sufficient Conditions ◽  
Planning Horizon ◽  
Insurance Company ◽  
Existence Of A Solution ◽  
Discounted Cost ◽  
Spectral Risk Measures ◽  
Markov Decision

AbstractWe study the minimization of a spectral risk measure of the total discounted cost generated by a Markov Decision Process (MDP) over a finite or infinite planning horizon. The MDP is assumed to have Borel state and action spaces and the cost function may be unbounded above. The optimization problem is split into two minimization problems using an infimum representation for spectral risk measures. We show that the inner minimization problem can be solved as an ordinary MDP on an extended state space and give sufficient conditions under which an optimal policy exists. Regarding the infinite dimensional outer minimization problem, we prove the existence of a solution and derive an algorithm for its numerical approximation. Our results include the findings in Bäuerle and Ott (Math Methods Oper Res 74(3):361–379, 2011) in the special case that the risk measure is Expected Shortfall. As an application, we present a dynamic extension of the classical static optimal reinsurance problem, where an insurance company minimizes its cost of capital.

Application of eco-friendly natural dye obtained from Spathodea campanulata on silk using combination of mordants

2016 ◽  
Vol 27 (1) ◽  
pp. 15-21 ◽  
Author(s):  
M Kumaresan
Keyword(s):  
Large Scale ◽  
Potassium Dichromate ◽  
Ferrous Sulphate ◽  
Research Work ◽  
Natural Dye ◽  
Alkaline Media ◽  
Silk Fabric ◽  
Content Type ◽  
Wide Range ◽  
New Research

Purpose – The purpose of this paper is to extract the eco-friendly natural dye obtained from the flower of Spathodea campanulata and apply on silk fabric using combination of mordants. The fastness properties of the flower of Spathodea campanulata dyed silk fabric have been studied using different combination (1:3, 1:1 and 3:1) of various mordants, such as myrobolan: nickel sulphate, myrobolan: aluminium sulphate, myrobolan: potassium dichromate, myrobolan: ferrous sulphate and myrobolan: stannous chloride. The wash, rub, light and perspiration fastness of the dyed samples have been evaluated. Design/methodology/approach – For dyeing there are three methods are used. They are Pre mordanting, Simultaneous mordanting and Post mordanting methods. Dyed silk materials are tested by using wash fastness, rub fastness, light and perspiration fastness methods. Findings – It is found that Spathodea campanulata dye can be successfully used for the dyeing of silk to obtain a wide range colours by using various combinations of mordants. With regards to colour fastness, test samples exhibit excellent fastness to washing, rubbing, except for pre-mordanting using myrobolan: potassium dichromate combination; and good to excellent fastness to perspiration in both acidic and alkaline media. Originality/value – Availability of literature related to this work is not available. The study of combination of mordants of this natural dye on silk is a new research work and the large scale preparation is definitely very useful to the society.

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