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In this paper, a new repairable k-out-of-n system model is proposed, in which the deviation cost of the system is taken into account. Firstly, the standard k-out-of-n system is replaced at planned time or at the failure time. Next, replacement policies are studied at planned time or periodic time when k is a constant. Thirdly, replacement policies are studied at planned time or periodic time when k is a random number, respectively. Finally, replacement policies are planned at the completion of random working time. The expected cost rate functions and its optimum replacement policies are derived analytically for each model. Meanwhile, optimum number of units is designed. The analytical solution of replacement policies for each model is discussed. Numerical examples are given to demonstrate our results. [ABSTRACT FROM AUTHOR]

This article revisits the optimization problems of age-based replacement models for exponential failure distributions. First, we show the steps how an age replacement time goes to an infinite value when the lifetime of a unit has an exponential distribution, and then, we give two discussions of possible replacement times, by introducing a new concept of cost named as deviation cost per unit of time between replacement and failure. Second, similar discussion is given for a random replacement model when the age replacement time is a random variable with a uniform distribution. Third, the models of age-based replacement first and last with deviation costs are discussed when a random replacement is taken into account for an age replacement model. Numerical examples are illustrated to show the results of the analytical discussions. Finally, necessary proofs are provided in the Appendixes. [ABSTRACT FROM AUTHOR]

A ZIF-8@MXene nanosheet reinforced polymer composite electrolyte was developed. In this electrolyte, abundant interactions and ion transport channels were generated by virtue of well-compatibility and plentiful functional groups and Lewis acid sites, enabling to high ionic conductivity and superior thermostability and flame retardance. This shows splendid potential for developing polymer electrolytes by cooperating two dimensional materials with MOFs. [Display omitted] • Developed Ti 3 C 2 -MXene nanosheets with horizontally extended ZIF-8 on the surface (ZIF-8@MXene) and a well compatible polymer composite electrolyte (PE- ZIF-8@MXene). • ZIF-8@MXene decreased the coupling of Li ion and polymer chain and provided ion transport channels to improve Li+ transportation. • Intrinsically stable ZIF-8@MXene enhanced the thermostability and flame resistance of electrolyte. • PE-ZIF-8@MXene presented a high ionic conductivity of 4.4 mS cm−1. • Assembled lithium batteries revealed a long cycling life up to 2000 h at 0.5 mA cm−2. Though polymer electrolytes have been regarded as promising separators for solid-state lithium metal batteries, their low ionic conductivity, poor thermostability and inflammability limit their practical applications. Herein, a polymer composite electrolyte consisting of metal–organic frameworks modified Ti 3 C 2 -MXene nanosheets (ZIF-8@MXene) and polymer mixture (PE-ZIF-8@MXene) was fabricated. The fabricated nonflammable ZIF-8@MXene nanosheets have abundant functional groups and Lewis acid sites as well as high specific surface area. In the composite electrolyte, ZIF-8@MXene nanosheets increased the dissociation of lithium salts and provided channels for transporting ions, accelerating the Li ion transportation. They also enhanced the tensile strength, thermostability and flame resistance of PE-ZIF-8@MXene. Consequently, the fabricated flame-retardant PE-ZIF-8@MXene presented high ionic conductivity (4.4 mS cm−1), impressive Li+ transference number (0.76) and enhanced tensile strength (3.77 MPa). In addition, the assembled Li|PE-ZIF-8@MXene|Li had a long cycle life of 2000 h, and Li|PE-ZIF-8@MXene|LiFePO 4 batteries displayed a capacity retention of 89.6% after 500 cycles. [ABSTRACT FROM AUTHOR]

When a unit should provide reliability at mission time, the mission success probability or failure probability becomes an important constraint to plan inspection policies. From this viewpoint, this paper considers the optimization problems of periodic and sequential inspection policies with mission failure probabilities. In this paper, a mission time is considered as a renewal point for inspection polices, but the failure cost occurred at mission time is higher than the total cost of inspection and failure detection. We give an upper limit of the failure probability at mission time, that is, mission failure probability, to minimize the total expected costs and the expected cost rates of inspection policies. In addition, the extended models of inspection policies for an interval mission, possible random times, and operating interval are discussed. [ABSTRACT FROM AUTHOR]

In order to balance the deviation time between replacement and failure, a new notion of cost named as deviation cost is taken into account for planning replacement policies. We firstly take up a standard parallel system with n identical units and model replacement policies that are done at planned time and at periodic times. Next, we model again the above replacement policies when the number of units is a random variable that has a Poisson distribution. Thirdly, replacement policies are planned preventively at the completion of random working times. Optimum number of units is scheduled for a total working interval that is constantly and randomly given. Finally, we give reliability functions of k-out-of-n systems for extensions of parallel systems. We give analytical discussions for the above replacement policies and illustrate numerical examples when the failure time of each unit has an exponential distribution. [ABSTRACT FROM AUTHOR]

In this paper, in order to improve microhardness and wear resistance of grinding layers for metal-bonded laser cladding grinding tools, the integrity of CBN grits during laser cladding process is protected and bonding quality between metal matrix and CBN grits is improved. 0%, 1.25%, 2.5%, 3.75%, and 5% of B4C as additive for CBN/CuSnTi laser cladding layers were conducted. The surface morphology of these laser cladding layers was observed. The elements distribution and species of phases in cross section of these laser cladding layers were analyzed by scanning electron microscopy (SEM)/energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD), and reaction mechanism was analyzed by Gibbs free energy theory. The microhardness and wear resistance of these laser cladding layers were tested. Then, grinding tests with 0%, 2.5%, and 5% B4C added CBN/CuSnTi LCGTs were conducted. The results show that no cracks and intact CBN cutting edges were on laser cladding layer when 5% B4C was added. The mechanical quality involved microhardness and wear resistance of 5% B4C added laser cladding layer were better than that of other B4C contents of laser cladding layers. The surface roughness of 5% added LCGT is the best. 5% B4C can be the additive for CBN/CuSnTi LCGT. [ABSTRACT FROM AUTHOR]

It has been proposed that if replacement time is planned too early prior to failure, a waste of operation cost, i.e., excess costs, would incur because the system might run for an additional period of time to complete critical operations, and if replacement time is too late after failure, a great failure cost, i.e., shortage cost, is incurred due to the delay in time of the carelessly scheduled replacement. In order to make the preventive replacement policies perform in a more general way, the above two variable types of costs are taken into considerations for periodic replacement policies in this paper. We firstly take up a standard model in which the unit is replaced preventively at periodic times. Secondly, the modeling approaches of whichever occurs first and last are applied into periodic and random models, and replacement first and last policies are discussed to find optimum periodic replacement times for a random working time. Furthermore, optimum working numbers are obtained for the extended models. We give analytical discussions of the above replacement policies, and finally, numerical examples are illustrated. [ABSTRACT FROM AUTHOR]

Though lithium metal has long been regarded as an ideal anode material for high-density batteries, the potential safety hazards greatly hampered its applications due to the non-uniform lithium nucleation and subsequent uncontrollable growth of lithium dendrites. To address these problems, herein, we developed carbon nanoribbons (LBCRs) with linearly distributed nucleation seeds and longitudinally bent structure. In the unique LBCRs, not only nucleation seeds located along edges decreased the nucleation barrier of lithium, inducing selective lithium nucleation, but also conductive carbon skeleton with bent structure regulated Li ion flux, preventing the formation of lithium dendrites. Moreover, LBCRs alleviated the volume change during cycling by guiding the lithium deposition inside the cavity. On the consequence, controllable lithium deposition was realized within LBCRs, and resulted composite anodes exhibited superior cycling stability including a low voltage hysteresis of 47.4 mV with a long cycle life over 700 h and a stable Coulombic efficiency above 94%. Longitudinally bent carbon nanoribbons with linearly distributed nucleation seeds along the exposed edges and a bent structure are developed. Such unique features not only realize well controlled nucleation and deposition of lithium inside the cavity, but also relieve volume change of lithium during cycling processes. Therefore, resulted anodes exhibit enhanced electrochemical performances including a long cycle life and a stable Coulombic efficiency. [Display omitted] • Developed carbon nanoribbons (LBCRs) with linearly distributed nucleation seeds and longitudinally bent structure. • In LBCRs, nucleation seeds induced selective Li nucleation while bent carbon skeleton guided uniform Li deposition inside. • LBCRs alleviated the volume change during cycling with the lithium deposition inside the cavity. • Li-LBCRs anode exhibited a low voltage hysteresis of 47.4 mV with a cycle life over 700 h at 1 mA cm-2, 1 mAh cm-2. [ABSTRACT FROM AUTHOR]

It is always difficult to discuss the analytical formulas, in which optimum solutions of replacement policies satisfy, due to the mathematical complexity. This paper proposes several approximate calculations for age-based random replacement policies, such that the unit is replaced at time T, at random time Y j (j = 1 , 2 , ...) over time T, and at random time YN for Y j (j = 1 , 2 , ... , N). We use the inequality properties of the formulas and the bounds of the extended failure rate functions to find the approximate calculations of replacement times in analytical ways. It is shown from numerical examples that these approximate calculations would become useful references for the optimum age-based random replacement times. [ABSTRACT FROM AUTHOR]

In this investigation, in order to improve bonding strength between superabrasive/metal matrix/grinding substrate, life span of grinding wheel, and grinding using small grits in continuous grinding simultaneously to fit for high speed and high precision machining in industry, coaxial powder feeding laser cladding method with CAD/CAM technology is introduced to manufacture textured CBN/CuSnTi–grinding wheels. The morphology of CBN grit on laser-cladding layer under optimized laser-cladding parameters and a pit created by fallen-off CBN on laser-cladding layer with lower laser–cladding energy density are observed by scanning electron microscope (SEM). The element distributions of interfaces of CBN/CuSnTi/AISI 1045 are analyzed by SEM and energy disperse spectroscope (EDS). The morphology and elements distribution of residual resultants on the surface of CBN grits etched by nitric acid are analyzed by SEM and EDS. Comparative-grinding process between laser cladding–grinding wheel (LCGW) and customized electroplated grinding wheel (EGW) is analyzed with grinding forces and temperature aspects respectively. The wear morphology of CBN grits on LCGW after grinding is observed by SEM. The results show that CBN grit with integrate cutting edges can protrude 50% height of its diameter on laser-cladding layer under optimized laser–cladding parameters. Fe, N, Ti, and B segregates attached to the interfaces of CBN/CuSnTi/AISI 1045 with Cu and Sn distributed uniformly in the laser-cladding layer. Residual resultants on CBN can be divided into two parts based on the distances from the surface of CBN grits. The grinding forces (Fz and Fy) and grinding temperature from LCGW are lower than those from EGW. The wear conditions of CBN on laser cladding are three parts: microfracture, cleavage plane, and wear-out. [ABSTRACT FROM AUTHOR]

Identifying purchase intention by analyzing the Query and the Document of the product description (Q &D) text is one of the most important means of promoting Purchase Rate (PR). In view of that customers sometimes cannot describe their purchasing intention in queries, this paper aims to identify purchase intention from implicit queries by computing semantic similarity between Q &D and proposes a novel model based on Word2Vec algorithm, Long Short-term Memory (LSTM) and Deep Structured Semantic Model (DSSM). Besides, an empirical analysis is conducted through the Keras framework and based on the factual retrieval data of the Home Depot, an E-commerce website selling building materials in America. The results show that the proposed model has achieved improving F1-score on test dataset compared with other existing models. The novel model combines Word2Vec and LSTM to extract text features and applies DSSM to further fetch high-dimension representations by maximizing semantic similarity between the user query and the description of the correct merchandise. Our proposed model can be used to remove or minimize subjective factors in extracting features, improves the performance of purchasing intention identification, and also improves the customer experience of online shopping. [ABSTRACT FROM AUTHOR]

It would be of interest to formulate the general replacement models, combing the constant and random policies to satisfy the commonly planned and randomly needed replacement times. This paper takes up age and periodic replacement models again to formulate their general models when replacement actions are also conducted at random times Y i (i = 1 , 2 , ... , n) . The classic approach of whichever occurs first and the newly proposed approach of whichever occurs last are used for such general models, whose models are named as replacement first, modified replacement first, replacement last and modified replacement last, respectively. We compare all of the replacement models analytically and numerically to find which policy should be selected from the viewpoint of cost. It is shown that the modified replacement policies with combined approaches of whichever occurs first and last are more economical than others. In addition, the replacement models with different replacement costs are extended for further studies. [ABSTRACT FROM AUTHOR]

Zhao, X.; Yu, T.; Zhao, Y.; Zhang, Y.; Yang, L.; Jiang, S., and Wang, W., 2018. Laser cladding Ti coated CBN/CuSnTi alloy on steel for grinding tools of ocean ship. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 571–578. Coconut Creek (Florida), ISSN 0749-0208. In this study, laser cladding CBN/CuSnTi alloy mixed powder on the AISI 1045 steel substrate for grinding tools of ocean ship was investigated. Various laser cladding processing parameters were conducted to find the appropriate laser cladding parameters to fabricate grinding tools of ocean ship in the continuous fiber laser beam with coaxial powder nozzle. The morphology of the laser cladding layer was analyzed by laser scanning confocal microscopy (LSCM) and the CBN grits with specific laser process parameters was observed by scanning electron microscopy (SEM). The interface conditions among the CBN grit/alloy matrix/substrate were detected by SEM and EDS to analyze the elements distribution and the morphology qualities of the bonding interface. The scratching test for the laser cladding layer with a simulated grinding force was operated to testify the bonding strength of the CBN grits embedded in the laser cladding layer for satisfying the grinding process in the industrial operation. The results showed that the cross-section and the surface of the laser cladding layer exerted by the laser process parameters of laser power of 205 W, laser scanning speed of 5 mm/s, defocus distance of 4 mm, powder feed rate of 0.8 rad/min were free of microcracks and porosities. On the other hand, the integrity and uniformity of CBN remain. Element Ti in the CuSnTi alloy matrix played a significant role in the experiment not only of the interface between matrix and CBN but also matrix and substrate. The diffusion and segregation of element Ti to the interface of CBN and substrate formed Ti-B, Ti-N, Ti-Fe compounds respectively, which caused the metallic bonding of the interfaces. During the scratching test, the phenomenon of the pull-out of the CBN embedded in the laser cladding layer was not found. CBN grits were fixed steadily with the fractured cleavage plane. It was concluded that the uniformity, integrity and metallic bonding with metal matrix of the CBN in the laser cladding layer can be carried out, which is fundamental for the laser cladding abrasive grinding tools of ocean ship produced in the industry. [ABSTRACT FROM AUTHOR]

Zhao, X.; Yu, T.; Zhao, Y.; Zhang, Y.; Sun, X.; Ma, Z.; Li, M., and Zhang, T., 2018. The investigation of the morphology and failure types of pre-placed CBN on Cu-Ni-Sn-Ti bonded to steel by laser process. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 486–489. Coconut Creek (Florida), ISSN 0749-0208. Pre-placed CBN on Cu-Ni-Sn-Ti was bonded to AISI 1045 steel with various process parameters by laser in the present paper. The wettability and the oxidization condition of the CBN in laser bead were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) respectively. The failure types of the CBN in laser bead were observed by optical microscopy (OM). The results show that the wettability of the CBN and Cu-Ni-Sn-Ti mixed powder is pronounced because of active element Ti regardless the CBN size and laser processing parameters. Oxidization is serious after laser process even though the protected gas argon being added during the laser process. The failure types can be identified into two types, mechanical press process failure and laser process failure. [ABSTRACT FROM AUTHOR]

Periodic replacement policies modeled with the history of minimal repairs have been studied extensively. However, in the viewpoint of cost rate, there is no literature to compare replacement polices which are carried out at some periodic times and at a predetermined number of repairs. In this paper, we compare these two types of replacement policies analytically from the optimizations of the integrated models. It will be shown that there always exists a degradation model when any bivariate replacement policy is optimized and this is just the best choice of the comparisons. Not only that, the approaches of whichever occurs first and last are applied to model the above two types of policies, which are named as replacement first and replacement last, respectively, and their comparisons are also made. In addition, we delay the policy at repair to periodic time for easier replacement, and the modified replacement model, which is named as replacement overtime, is compared with the original ones. Numerical examples are also given and agree with all analytical discussions. [ABSTRACT FROM AUTHOR]

• Recent progress of alloy-containing lithium anodes are introduced. • Common fabrication approaches of alloy-containing lithium anodes are introduced. • The action mechanism of alloy components in lithium anodes are summarized and discussed in focus. • The shortcomings and challenges as well as the prospects of alloy-containing lithium anodes are also analyzed.Abstract. Lithium metal is regarded as one of the most ideal anode materials for next-generation batteries, due to its high theoretical capacity of 3860 mAh g−1 and low redox potential (−3.04 V vs standard hydrogen electrode). However, practical applications of lithium anodes are impeded by the uncontrollable growth of lithium dendrite and continuous reactions between lithium and electrolyte during cycling processes. According to reports for decades, artificial solid electrolyte interface (SEI), electrolyte additives, and construction of three-dimensional (3D) structures are demonstrated essential strategies. Among numerous approaches, metals that can alloy with lithium have been employed to homogenize lithium deposition and accelerate Li ion transportation, which attract more and more attention. This review aims to summarize the lithium alloying applied in lithium anodes including the fabricating approaches of alloy-containing lithium anodes, and the action mechanism and challenges of fabricated lithium anodes. Based on summarizing the literature, shortcomings and challenges as well as the prospects are also analyzed, to impel further research of lithium anodes and lithium-based batteries. [ABSTRACT FROM AUTHOR]

It has been modeled for several replacement policies in literatures that the whole life cycle or operating interval of an operating unit should be finite rather than infinite as is done with the traditional method. However, it is more natural to consider the case in which the finite life cycle is a fluctuated parameter that could be used to estimate replacement times, which will be taken up in this article. For this, we first formulate a general model in which the unit is replaced at random ageU, random timeYfor the first working number, random life cycleS, or at failureX, whichever occurs first. The following models included in the general model, such that replacement done at ageTwhen variableUis a degenerate distribution, and replacement done at working numbersNsummed by numberNof variableY, are optimized. We obtain the total expected cost until replacement and the expected replacement cost rate for each model. Optimal ageT, working numberN, and a pair of (T,N) are discussed analytically and computed numerically. [ABSTRACT FROM AUTHOR]

This paper takes up the reliability and preventive replacement problems for a K -out-of- n system, where K is a stochastic parameter provided. Firstly, we consider the case when K is predefined as constant numbers as is done with the traditional method, and obtain the system reliability R ( t ), mean time to failure (MTTF), and replacement policies, in which the number n of units for replacement and replacement time T of operation are, respectively, optimized. Secondly, we focus on the above discussions again when K cannot be predefined constantly, but it is a random variable with an estimated probability function. Furthermore, we give approximate computations in an easier way for MTTF, optimal number n * and replacement time T *, respectively. [ABSTRACT FROM AUTHOR]

Age replacement models are fundamental to maintenance theory. This paper summarizes our new perspectives and hods in age replacement models: First, we optimize the expected cost rate for a required availability level and vice versa. Second, an asymptotic model with simple calculation is proposed by using the cumulative hazard function skillfully. Third, we challenge the established theory such that preventive replacement should be non-random and only corrective replacement should be made for the unit with exponential failure. Fourth, three replacement policies with random working cycles are discussed, which are called overtime replacement, replacement first, and replacement last, respectively. Fifth, the policies of replacement first and last are formulated with general models. Sixth, age replacement is modified for the situation when the economical life cycle of the unit is a random variable with probability distribution. Finally, models of a parallel system with constant and random number of units are taken into considerations. The models of expected cost rates are obtained and optimal replacement times to minimize them are discussed analytically and computed numerically. Further studies and potential applications are also indicated at the end of discussions of the above models. [ABSTRACT FROM AUTHOR]

Increasing research efforts have been devoted to mission-oriented preventive maintenance (PM) policies that are restricted mainly to certain missions. This paper investigates the optimization problem of a repair-replacement policy for systems subject to intermittent missions of random types and random durations, which is more realistic in practice. When a mission is completed, the system is assigned a new mission with the type dependent on the previous type and the duration following a general distribution. The randomness of missions affects the failure rate of the system, the penalty for failed missions, and the schedules of PM actions. Taking advantage of the shutdown opportunity of switching missions, the decision maker determine among three possible actions: do-nothing, preventive repair, and preventive replacement to minimize the long-run average cost rate. The optimization problem is formulated as a semi-Markov decision process and is solved by the policy iteration algorithm. An extended policy involving two monotonic control limits is proposed and optimized by a modified policy iteration algorithm. Two numerical examples illustrate the effectiveness of the proposed approach. • Integrate random mission type and random mission duration into maintenance decision-making. • Formulate the optimization problem in the semi-Markov decision process framework. • Extend the proposed policy by considering monotonic control limits. • Develop modified policy-iteration algorithms for optimization. [ABSTRACT FROM AUTHOR]

This paper studies a new large-scale emergency medical services scheduling (EMSS) problem during the outbreak of epidemics like COVID-19, which aims to determine an optimal scheduling scheme of emergency medical services to minimize the completion time of nucleic acid testing to achieve rapid epidemic interruption. We first analyze the impact of the epidemic spread and assign different priorities to different emergency medical services demand points according to the degree of urgency. Then, we formulate the EMSS as a mixed-integer linear program (MILP) model and analyze its complexity. Given the NP-hardness of the problem, we develop two fast and effective improved discrete artificial bee colony algorithms (IDABC) based on problem properties. Experimental results for a real case and practical-sized instances with up to 100 demand points demonstrate that the IDABC significantly outperforms MILP solver CPLEX and two state-of-the-art metaheuristic algorithms in both solution quality and computational efficiency. In addition, we also propose some managerial implications to support emergency management decision-making. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to propose several new maintenance policies that can be performed at suitable middle times for trivariate preventive maintenance scenarios. Firstly, characteristics and limitations for the approaches of whichever occurs first and whichever occurs last are analyzed, and their respective maintenance models, which are called first maintenance and last maintenance, are given directly. Secondly, a combined approach of first and last is employed and middle maintenance is proposed. Thirdly, the aforementioned policy is modified to be performed at discrete working cycles, using the method of overtime maintenance. Finally, a new approach of whichever occurs middle is proposed for modelings. We give the analyses of how to formulate the middle maintenances and obtain their expected maintenance cost rates, using the technique of cumulative damage models. Numerical examples are given to compare the optimal policies among first, last, and middle maintenances. Finally, a potential application of middle maintenance is provided for future studies. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Water hydraulic variable ballast system (WHVBS) is a competitive mechanism to realize the hovering system which is one of the most popular ways to expand the maneuvering capability of AUVs. However, the WHVBSs equipped in AUVs almost were on–off type without controlling the flow rate of the in/out ballast water, which limits the hovering performance of the AUVs operated in complex underwater environment. In this paper, three novel types of WHVBS, which supports one or two low cost means to control the flow rate of ballast water, have been proposed to improve the performance of an AUV hovering system. A torpedo-like AUV equipped with WHVBS was used as a simulation platform to verify the effectiveness of the proposed WHVBSs. Numerical simulation results support the idea that compared with the commonly used on–off type WHVBS, the WHVBSs introduced flow rate control can significantly improve the hovering performance of the AUV, especially in the situations with unfavorable sea wave disturbances. Additionally, the statistics on water usage of different WHVBSs in numerical simulation indicated that the novel WHVBSs have the potential to extend the mission duration of AUV. [ABSTRACT FROM AUTHOR]

When a unit is running successive works with cycle times, it would be uneconomical or impractical to do maintenances during any working cycle. This paper firstly reviews two replacement models proposed in literatures as follows: (1) replacement is done over a planned time $$T$$ at the completion of the working cycle, which is called over-time replacement, and (2) replacement is done over damage level $$Z$$ at the completion of the forthcoming working cycle, which is called over-level replacement. From the viewpoint of replacement cost savings, we secondly focus on comparisons of over-time replacement and its standard age-based policy, over-level replacement and its standard condition-based policy. Furthermore, modified over-time and over-level replacement costs are obtained to specify critical points at which these new replacements, rather than their standard polices, would save more replacement costs. Discussions in this paper are given analytically and computed numerically. [ABSTRACT FROM AUTHOR]

It has been assumed in most maintenance models that (i) the number of units for a parallel system can be predefined precisely, (ii) maintenance cost after failure should be avoided, and (iii) age replacement can always be performed at its optimized times. However, these assumptions are challenged from practical perspectives in this paper. For this purpose, shortage and excess costs, which claim that replacement done too early before failure involves a waste of operation, are introduced into replacement models, such as replacement plans with time T or distribution G ( t ) for constant n or random N of units. Furthermore, the number N of working times and the number n of available units for a scheduled replacement time T are discussed. For each model, the expected replacement cost for one cycle and expected replacement cost rate for a long run are optimized, and numerical examples are given. [ABSTRACT FROM AUTHOR]

To make effective use of a running system, this paper proposes that, when replacement times could be scheduled at a planned time T of operation, and at a number N of minimal repairs, the newly proposed approach of whichever occurs last should be employed into optimizations for policy consideration. The replacement policy with the classical approach of whichever occurs first is also used to make comparison with the approach of whichever occurs last. Further, using the overtime technique, a replacement scheduled at time T in this paper is modified to be done at the first failure after T has arrived, to avoid probable interruptions for running jobs. That is, the system is replaced at failure N before time T, or at the first failure after T has arrived, whichever occurs first, and last, respectively. The policies acting on the approaches of first and last with minimal repairs are analyzed in detail, and their expected cost rates are formulated. Optimal solutions for separate and bivariate T and N are obtained and compared analytically. [ABSTRACT FROM PUBLISHER]

It might be difficult sometimes to derive theoretical and numerical solutions for analytical maintenance modelings due to the computational complexity. This paper takes up several approximate models in maintenance theory, by using the cumulative hazard function H ( t ) and the newly proposed asymptotic MTTF (Mean Time to Failure) skilfully. We firstly denote by t x the time when the expected number of failures is x . Using H ( t x ) = x , we estimate failure times, model age and periodic replacements, and sequential imperfect maintenance. Motivated by the asymptotic method of computation of MTTF, we secondly model the expected cost rate for a parallel system when replacement is made at system failure, and give approximate computations for the sequential inspection policy. Optimizations of each model are obtained approximately in an easier way. When failure times have a Weibull distribution, it is shown from numerical examples that the obtained approximate optimal solutions have good approximations of the exact ones. [ABSTRACT FROM AUTHOR]

Retinal pigment epithelium (RPE) dysfunction, manifested as drusen formation and RPE mottling, is a characteristic lesion of aging. The mechanism of RPE dysfunction remains unknown. Previous animal studies have proven that the activation of NLRP3 inflammasome in RPE leads to apoptosis and pyroptosis, which may play a very important role in the development of age-related macular degeneration (AMD). However, there is a lack of clinical evidence to support the above hypothesis. Herein, we report a 38-year-old Chinese Han woman who had NLRP3-associated autoinflammatory disease (NLRP3-AID) with widely scattered drusen at the posterior pole in both eyes. NLRP3-AID is a rare disease caused by mutations of the NLRP3 gene, leading to NLRP3 inflammasome activation. This report of early-onset drusen provides clinical evidence that the NLRP3 inflammasome might contribute to the occurrence of RPE dysfunction and is a potential cause of age-related macular degeneration (AMD). [ABSTRACT FROM AUTHOR]

A widely use of environment-friendly batteries would reduce carbon emissions for the power battery supply chain in industries. From the point of consumers, it is an interesting problem to find optimal post-warranty replacement policies to ensure the batteries’ lifetime and maintain the required reliability for mission executions. For this, we firstly model replacement policies that are planned at the completion of the executed missions after the expiration of warranty. Secondly, the extended policies of replacement first and last are modeled in terms of reliability, cost, and maintainability. All of the expected cost rates are modeled and their optimal solutions are found in analytical ways. Finally, we give a case illustration of maintaining a lithium-ion battery pack in an electric van. [ABSTRACT FROM AUTHOR]

The water hydraulics is a competitive mechanism to adjust the ballast water and also is the only choice for ultra-deep sea applications. In order to improve the control performance and reduce the energy consumption of the water hydraulic variable ballast system (WHVBS), a novel type WHVBS, which introduces a servo motor to drive the pump and uses four fast response direct-acting solenoid valves to control the water flow direction, has been proposed. The proposed WHVBS has two novel flow control modes: changing the speed of servo motors (pump controlled mode) or changing the opening time of solenoid valves (valve controlled mode). The mathematical model of WHVBS was built up for the purpose of predicting the flow rate under both control modes. A generalized predictive controller with forgetting factor recursive least square (FFRLSGPC) was proposed for WHVBS to improve the control performance. Finally, based on the tracing experiments performed on a WHVBS experiment platform, the comparative discussion of control performance and the analysis of energy efficiency were presented. The experimental results show that the mean tracing error can be maintained within 0.27% by the proposed FFRLSGPC in valve controlled mode and the pump controlled mode is an energy-efficient control method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to observe where the classical assumption “whichever occurs first” holds for preventive maintenance (PM) modelings. We firstly take up a bivariate maintenance policy where “whichever occurs first” and the newly proposed “whichever occurs last” are respectively used. Modification of PM performance is introduced into modelings to avoid interruptions of job executions, that is, PMs are done only at the end of working cycles. From the points of performability and maintenance cost, we secondly compare the optimized “first” and “last” policies in detail and find two critical points of comparisons analytically. Further, by comparing the “first” and “last” policies with the standard maintenance, modified PM costs are obtained to observe whether it is easy to save PM cost for “whichever occurs first”. For a trivariate maintenance policy, we thirdly propose an entirely new assumption “whichever occurs middle” and give another one model that considers both assumptions of “first” and “last”. We analyze maintenance probabilities for each model and then obtain directly their expected maintenance cost rates for further studies. [ABSTRACT FROM AUTHOR]

It has been assumed for a standby unit that periodic inspection is performed more easily to detect failures, but such a strict periodic mode would be impractical if the unit is executing some procedures without stops. From the above viewpoint, this paper first optimises a random inspection policy in accordance with random procedure times, compares it with periodic inspection and computes a modified checking cost for random inspection to determine the case where such a random inspection would be adopted. Second, this paper proposes three new inspection models in which inspections with deterministic policies are scheduled strategically while their performances need to be limited by completion times of operation procedures. These policies are called inspection first, inspection last and inspection overtime. The total expected inspection and downtime costs of each model until failure detection are obtained, and optimal policies which minimise them are derived analytically. Furthermore, the three inspection policies are compared with periodic inspection, inspection first and last are compared with each other, and a modified checking cost for inspection overtime is discussed when the policy would be better than periodic inspection. [ABSTRACT FROM AUTHOR]

This paper proposes age and periodic replacement last models with continuous, and discrete policies. That is, an operating unit is replaced preventively at time T of operation as a strategic policy, or at a number N of working cycles to satisfy successive job completion, whichever occurs last. Such policies are named as replacement last, and their expected cost rates and optimal policies are obtained. However, the focus of this paper is to compare replacement last with replacement first policies, which are formulated under the classical assumption of whichever occurs first. From the points of cost and performability, different comparative methods for continuous and discrete optimizations are demonstrated to determine in what cases we should adopt replacement last rather than replacement first. All theoretical discussions in this paper are made analytically, and are computed numerically. [ABSTRACT FROM AUTHOR]

Abstract: From the economical viewpoint of several combined PM policies in reliability theory, this paper takes up a standard cumulative damage model in which the notion of maintenance last is applied, i.e., the unit undergoes preventive maintenances before failure at a planned time T, at a damage level Z, or at a shock number N, whichever occurs last. Expected cost rates are detailedly formulated, and optimal problems of two alternative policies which combine time-based with condition-based preventive maintenances are discussed, i.e., optimal for N, for T, and for T are rigorously obtained. Comparison methods between such maintenance last and conventional maintenance first are explored. It is determined theoretically and numerically which policy should be adopted, according to the different methods in different cases when the time-based or the condition-based PM policy is optimized. [Copyright &y& Elsevier]

Purpose – The purpose of this paper is to consider maintenance policies for an operating system which works at random times for jobs. Each job causes some damage to the system and these damages are additive, and the system fails when the total damage has exceeded a failure level K. Design/methodology/approach – Using techniques of cumulative damage models, the maintenance is made at the N-th completion of working time for the first model and at a damage level Z with a limit number of working times N for the second model. Findings – The system is maintained at the first completion of the working time over time T for the third model. The system fails with probability p(x) when the total damage is x and undergoes minimal repair at failure for the fourth model. The expected cost rates are obtained and optimal maintenance policies are discussed analytically and computed numerically. Originality/value – The paper discusses four maintenance policies for an operating system which works at successive random times for jobs, where the system fails due to damage that can be additive caused by jobs. [ABSTRACT FROM AUTHOR]

In some practical situations, it may be more economical to work a used system than do a new one. From this viewpoint, this article considers three basic preventive maintenance (PM) policies for a used system: the system with initial variable damage Y 0 begins to operate at time 0, and suffers damage due to shocks. It fails when the total damage exceeds a failure level K and corrective maintenance is made immediately. To prevent such failure, it undergoes PM at a planned time T, a shock number N and a damage level k, but maintenances are imperfect. However, failure rate of a used system maybe higher than that of a new one, so some maintenance is applied to the policies at each shock in the extended models. Using the theory of cumulative processes, expected cost rate models are obtained, optimal policies which minimise them are derived analytically and discussed numerically. [ABSTRACT FROM PUBLISHER]

This paper considers a parallel system with a random number of units according to a Poisson distribution. The fracture of an aircraft fuselage with multiple site damage serves as a real world application for this problem. The mean time to failure is obtained. Using this result, an optimal number of units and replacement time for the system which minimize the expected cost rates are derived analytically, and numerically, when the failure time has a Weibull distribution. It is of interest that these results also give good approximations to those of the system with a constant number of units. Further, similar discussions for a scheduling problem of a job with random working times are made, when a parallel system is provided. [ABSTRACT FROM AUTHOR]

This paper studies age and periodic replacement policies in general replacement models by considering major failures and minor failures, meanwhile, random replacement policies are applied as alternatives for regular policies into replacement first and last models. We obtain the expected cost rates for each planned replacement policies. Optimal regular replacement and random replacement policies are discussed and compared from the point of cost in analytical ways. Furthermore, exponential minor failure, exponential major failure, and Weibull major failure with an increasing hazard rate of minor failure are illustrated in numerical analyses. • Age and periodic replacement policies are modeled into general replacement models. • Regular and random replacement policies are modeled into general replacement models. • Replacement first and last policies are modeled for general replacement models. • Replacement first and last policies are compared from the point of cost. [ABSTRACT FROM AUTHOR]

Rotor-bearing systems play a vital role in machine tools, aero engines, and wind turbines. Generally, worn-induced degradation quantities and manufacturing errors of components are the main error sources that influence the precision reliability of rotor-bearing systems. The current precision reliability evaluation models are focusing on several error sources in only a few key components without agreeable results. Therefore, a precision reliability evaluation model is proposed considering all time-variant error sources and random error sources. Firstly, time-variant wear models for commonly occurred degradation types in a rotor-bearing system are developed. Secondly, the constructed time-variant wear models are inserted into the precision model with all moving components in the rotor-bearing system using meta-action structural decomposition method. Finally, the time-variant stochastic process discretization method is employed to establish the precision reliability evaluation model, and solve the precision reliability of the rotor-bearing systems. Case investigations are carried out to verify the performance of the present model, which provides a more accurate precision reliability evaluation model to estimate the conditions of rotor-bearing systems during the service period. [ABSTRACT FROM AUTHOR]

Although metallic lithium is one of the most potential anode candidates for next-generation batteries, its applications are still restricted by several problems, especially the formation of lithium dendrites. However, insufficient emphasis has been placed on dealing with the incipient lithium dendrites. Herein, a three-dimensional insulating glass-fiber skeleton with gradient-distributed trigger-type carbonized ZIF-8 (GF-cZIF8) was developed. In this structure, plentiful conductive cZIF-8 on the collector/skeleton interface guided uniform lithium nucleation, while highly conductive and lithophilic cZIF-8 on the skeleton passivated and reversed lithium dendrites to a stable part of lithium anode when trigged by lithium dendrites. In addition, insulating glass fibers improved the homogeneity of Li ions. As a consequence, the GF-cZIF8/Cu collector exhibited a high and stable coulombic efficiency of 98 % after 280 cycles, and the GF-cZIF8-Li anode exhibited a low voltage hysteresis of 17 mV and a long cycling life up to 1100 h. A three-dimensional insulating glass-fiber skeleton with gradient-distributed trigger-type carbonized ZIF-8 (GF-cZIF8) is developed. Such unique features not only guide uniform lithium nucleation and deposition through plentiful conductive cZIF-8 on the collector/skeleton interface, but also passivate and reverse lithium dendrites during cycling processes. Therefore, resulted anodes exhibit enhanced electrochemical performances including a long cycle life and a stable Coulombic efficiency. [Display omitted] • A three-dimensional with gradient-distributed trigger-type carbonized ZIF-8 (GF-cZIF8) was developed. • Plentiful conductive cZIF-8 guides uniform lithium nucleation. • Highly conductive/lithophilic cZIF-8 gradient passivated and reversed lithium dendrites. • Insulating glass fibers improve the homogeneity of Li ion flux. [ABSTRACT FROM AUTHOR]

Studying the distribution and history of residual stresses through different laser impact strategies is essential to assess alloy components structure, failure mechanisms, and alloy properties. Commercial modelling methods, including finite element methods, have been introduced to predict residual stress, while the analysis is computationally expensive due to complex engineering conditions. Here we combine the machine learning algorithm and an experimentally validated efficient FEM model to predict the residual stresses of laser shock peening (LSP) induced LD-TC4 alloy. Multiple machine learning algorithms were used to build the predictive models, including ensemble learning and neural networks-based algorithms. Subsequently, the ensemble learning algorithms are able to make highly accurate predictions with different process parameters. Moreover, data-based machine learning methods are an excellent alternative to FEM models in view of the significant reduction in computational cost. • The FEM can function as a generator of the training set of data-driven methods. • In the residual stress predictions, the proposed methods have excellent performance. • The efficient data-driven models are promising as an alternative to FEM simulations. • The influence of the relevant parameters on the residual stress distribution is investigated. [ABSTRACT FROM AUTHOR]

Heterogeneous multi-cores and parallel architectures have recently gained much attention owing to utilizing the strength of different architectures for offering higher performance. In this paper, we study the real-time scheduling of the directed acyclic graph (DAG) tasks upon the heterogeneous multi-core platform, i.e., a task contains different types of vertices, and the workload of each vertex must execute on its particular type of cores. Traditional researches use the work-conserving scheduling strategy to schedule such a typed DAG task and lead to pessimistic schedulability tests. To this end, we propose a novel scheduling algorithm for typed DAG tasks, which assigns each vertex a varying criticality that depends on the remaining workload of the vertex, and moreover, the vertex with higher criticality is more urgent to be executed. Under this scheduling strategy, we propose a new worst-case response time (WCRT) bound to verify the schedulability of DAG task supporting heterogeneous computing. Experiments with randomly generated workload show that the accuracy of our new WCRT is about 20% higher on average than the existing bounds. [ABSTRACT FROM AUTHOR]

This paper proposes the generalized maintenance policies for a computing system when the copula functions model the interdependency. In this paper, the dependence between the components has been modeled by three copula functions. We deal with random maintenance policies for repairable parallel systems with n dependent or independent components. Firstly, we discuss the maintenance first and last policies for parallel systems composed of dependent components. We consider the random maintenance policy for parallel systems that are dependent and attempt to find the optimal maintenance time by considering the copula framework. The expected cost rate is considered as objective function to minimize. For each policy, the optimal maintenance time that minimizes the mean cost rate is analyzed and discussed numerically. And we study the effects of model parameters on the optimal maintenance policy and compare the copula. The findings of the paper extend the results in the literature from system with independent components to dependent components. Numerical results are presented for components lifetime follow Weilbull distribution. Therefore manager can use the results to formulate the optimal decision problem of their parallel systems with dependent components. [ABSTRACT FROM AUTHOR]

In data-driven prognostics and health management (PHM), most studies focus only on prognostics performance but rarely consider maintenance decision problems. However, simple predictive maintenance decisions are not effective in dealing with the complex operating conditions faced in modern industrial systems. Thus, we propose a complete data-driven dynamic predictive maintenance strategy for system remaining useful life (RUL) prediction via deep learning ensemble method to solve this problem. This deep learning ensemble method is composed of a convolutional neural network (CNN) and a bidirectional long short-term memory network (Bi-LSTM), which aims to effectively predict the system RUL. Then, we consider a dynamic predictive maintenance strategy with uncertain system mission cycles based on the RUL predicted by deep learning ensemble method. Meanwhile, this dynamic predictive maintenance strategy includes order, stock, and maintenance decisions. In addition, the number of missions performed by the system and the reliability of the last performed mission are presented based on the mission cycle and the predicted RUL. Finally, experimental results from the NASA turbofan engine dataset C-MAPSS show the favorable performance of the proposed dynamic predictive maintenance strategy compared to the existing maintenance strategy. • We propose a complete data-driven dynamic predictive maintenance strategy based on prognostics information. • We consider the impact of the system mission cycles on the maintenance strategy according to the predicted RUL. • A cost-effective order and stock management decision is considered in dynamic predictive maintenance strategy, in addition to making maintenance strategy. • Based on the predicted RUL, the number of missions performed by the system and the reliability of the performed mission are presented. [ABSTRACT FROM AUTHOR]

When we consider the improvement of the functional performances that are released by the new updates of the products, it is an interesting problem to revisit the existing replacement policies. For such a viewpoint, four replacement models with product update announcements, i.e., PUA for abbreviation, are given in this paper: Model 1, the unit is replaced at time T or at PUA over time T. Model 2, the unit is replaced at the Kth failure or at PUA over the Kth failure. By considering both time T and failure K, Models 3 and 4 are obtained based on the approaches of replacement first and last. We obtain the expected cost rates for four models and discuss analytically their optimal replacement policies Further, numerical examples are given when the time for PUA has an exponential distribution. [ABSTRACT FROM AUTHOR]

Background: Public access of automated external defibrillator (AED) is an important public health strategy for improving survival of cardiac arrest. Major metropolitan cities in China are increasingly investing and implementing public access defibrillator programs, but the effectiveness of these programs remains unclear. This study aims to evaluate the public accessibility of AED in Shanghai, a major metropolitan city in China.Methods: From July 1 to September 30, 2018, all AED locations indicated by AED Access Map Apps were visited and investigated in three most densely distributing areas of AED (Huangpu District, Xuhui District, and Central Area of the Pudong New District) in Shanghai. Two AED Access Map APPs were used to identify the location of AEDs. Characteristics of and the barriers to access, the AED sites were recorded. Awareness and skills of first aid and AED among on-site staff of the AED installation sites were evaluated.Results: A total of 283 sites were marked on two AED Apps. One hundred and seventy (60%) locations were accessible, and 142 (50%) were actually with AEDs installed. Among those AED installed sites, 112 (79%) were completely identifiable to the information on the maps, 20 (14%) were inconsistent and 10 (7%) were inaccurate on the maps. Ninety-four (66%) AEDs had visible signs and information around the location, 7 (5%) AEDs had signs outside of the location, and 107 (75%) sites had educational instructions. In addition, 230 individuals who were around the AED site were interviewed. Among them, 79 (34%) had good knowledge of AED. After shown the picture of AED, 112 (49%) knew whether there was AED in the site, and 108 (47%) knew the AED's location. Eighty-seven (38%) staff have received first aid training, and among them 26 (30%) reported that they had skills in operating the AED.Conclusions: Public placement and accessibility of AEDs, related public signs and information on AED, and staff's awareness about AED were not optimal in Shanghai. Continuing efforts should be made to improve public accessibility and public awareness, knowledge, and user skills of AED. [ABSTRACT FROM AUTHOR]

To achieve lithium metal batteries with high safety and good electrochemical performances, electrolytes with superior ionic conductivity and mechanical strength are urgently desired. Herein, a diphasic multilayered quasi-solid polymer electrolyte (dmlSPE) with glass fiber cloth/metal-organic framework (GFC/ZIF-8) as the skeleton layer and polymers as the surface layer was developed. In such a unique structure, GFC/ZIF-8 layer with nanowetted interfaces substituted the fast Li ion transfer kinetics of the liquid phase for the slow one of solid polymers, efficiently accelerating the Li ion transportation. And polymer surface layers realized stable electrolyte/anode interfaces. Moreover, GFC/ZIF-8 skeleton enhanced the thermostability and mechanical strength of dmlSPE. As a consequence, the dmlSPE exhibited a high ionic conductivity of 0.713 mS cm−1 at 0 °C, a high tensile strength of 21 Mpa, and superior thermostability. In addition, related lithium symmetric cells exhibited a long cycling life of up to 2000 h, and Li|dmlSPE|NCM811 cells exhibited a high capacity of 180 mAh g−1 at 0.2 C. [Display omitted] A diphasic multilayered quasi-solid polymer electrolyte with nanowetted GFC/ZIF-8 skeleton interlayer and soft polymer surface layers was developed. Such unique features enabled highly enhanced Li ion transfer kinetics and outstanding electrolyte/anode interface reactions. And the inorganic skeleton increases the thermal stability and tensile strength. Therefore, this hybrid and batteries exhibited superior physical properties and electrochemical performances. [ABSTRACT FROM AUTHOR]

Purpose: To determine whether the rare NLRP3-Associated Autoinflammatory Disease (NLRP3-AID) is associated with retinal changes and to assess the ocular involvement. Methods: A retrospective cohort study of 20 patients(40 eyes) diagnosed with rare NLRP3-AID at Peking Union Medical College Hospital, from April 2015 to August 2022. Patients underwent a comprehensive ophthalmological examination, including visual acuity, intraocular pressure examination, slit-lamp examination, fundus photography, optical coherence tomography(OCT), and fluorescence angiography (FA). Some patients also underwent optical coherence tomography angiography (OCTA). Results: This study analyzed 40 eyes of 20 patients (11 [55.0%] male; median age, 25.0 years [range, 12–52 years]) and 13 patients (26 eyes, 65%) demonstrated ocular involvement. The most common ophthalmologic manifestation was conjunctivitis (22 eyes, 84.6%), followed by papilledema (14 eyes, 53.8%), retinopathy (10 eyes, 38.5%), optic atrophy (6 eyes, 23.1%), uveitis (4 eyes, 15.4%), reduced pupil light reflex (3 eyes, 11.5%) and cataracts (2 eyes, 7.7%). Ocular involvement was bilateral in 11 patients (55.0%). Five kinds of retinal lesions were seen in 5 patients (10 eyes, 25%) with NLRP3-AID, including peripheral retinal vascular leakage, microaneurysms, macular ischemia, macular epiretinal membrane formation and drusen. Conclusions: Peripheral retinal vascular leakage, macular ischemia, microaneurysms and drusen are newly identified retinal findings in patients with NLRP3-AID, which suggests the importance of detailed retinal examination in these patients. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the static structure resilience and dynamic disrupt resilience of the aircraft manufacturing core products supply chain (AMCPSC) from the perspective of the international trade network. Firstly, this paper employs the supply chain theory and complex network methodology to establish the trade networks of aircraft manufacturing core products. Based on the real data from the UN Comtrade, the global trade value trends of aircraft manufacturing core products from 2000 to 2022 are analyzed. Then, the research quantifies the structural topological characteristics (i.e., hierarchy, agglomeration, transmission, and diversity) of the international trade networks for aircraft manufacturing core products, investigating the network resilience from a static perspective. Further, we simulate random attacks and targeted attacks from a dynamic perspective to evaluate the resilience of the trade networks under disruptions. Using the centrality metrics and the entropy weight method, we identify the core countries (regions) in the aircraft manufacturing core products trade networks. The results show that the global trade value of aircraft manufacturing core products has presented a generally upward trend in the past two decades, but major external shocks, such as the financial crisis and the COVID-19 epidemic, can lead to a decline in global trade value of core products. In the core products trade networks, there are main aircraft manufacturing countries led by the United States, which play a leading role in the trade network. The core products trade networks have obvious hierarchy and agglomeration, and generally obey the power-law distribution. Trade networks show good resilience under random attacks. While under targeted attacks, especially under betweenness centrality attacks, network performance degrades faster. Based on the findings, managerial insights for improving the resilience of the AMCPSC are derived. [ABSTRACT FROM AUTHOR]