Ram D. Srivastava and Anil K. Agarwal
Urea and thiourea have been investigated as corrosion inhibitors for 94/6 and 80/20 copper‐cadmium alloy electroplates in nitric acid solutions by weight‐loss and polarisation…
Abstract
Urea and thiourea have been investigated as corrosion inhibitors for 94/6 and 80/20 copper‐cadmium alloy electroplates in nitric acid solutions by weight‐loss and polarisation measurements. Both inhibitors are found to be quite effective for shorter duration of immersion. Potential and polarisation data indicate a predominant role of local cathodic areas in corrosion protection.
D.R. Barot and M.N. Patel
This paper aims to deal with the estimation of the empirical Bayesian exact confidence limits of reliability indexes of a cold standby series system with (n+k−1) units under the…
Abstract
Purpose
This paper aims to deal with the estimation of the empirical Bayesian exact confidence limits of reliability indexes of a cold standby series system with (n+k−1) units under the general progressive Type II censoring scheme.
Design/methodology/approach
Assuming that the lifetime of each unit in the system is identical and independent random variable with exponential distribution, the exact confidence limits of the reliability indexes are derived by using an empirical Bayes approach when an exponential prior distribution of the failure rate parameter is considered. The accuracy of these confidence limits is examined in terms of their coverage probabilities by means of Monte-Carlo simulations.
Findings
The simulation results show that accuracy of exact confidence limits of reliability indexes of a cold standby series system is efficient. Therefore, this approach is good enough to use for reliability practitioners in order to improve the system reliability.
Practical implications
When items are costly, the general progressive Type II censoring scheme is used to reduce the total test time and the associated cost of an experiment. The proposed method provides the means to estimate the exact confidence limits of reliability indexes of the proposed cold standby series system under this scheme.
Originality/value
The application of the proposed technique will help the reliability engineers/managers/system engineers in various industrial and other setups where a cold standby series system is widely used.
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Sakshi Soni, Ashish Kumar Shukla and Kapil Kumar
This article aims to develop procedures for estimation and prediction in case of Type-I hybrid censored samples drawn from a two-parameter generalized half-logistic distribution…
Abstract
Purpose
This article aims to develop procedures for estimation and prediction in case of Type-I hybrid censored samples drawn from a two-parameter generalized half-logistic distribution (GHLD).
Design/methodology/approach
The GHLD is a versatile model which is useful in lifetime modelling. Also, hybrid censoring is a time and cost-effective censoring scheme which is widely used in the literature. The authors derive the maximum likelihood estimates, the maximum product of spacing estimates and Bayes estimates with squared error loss function for the unknown parameters, reliability function and stress-strength reliability. The Bayesian estimation is performed under an informative prior set-up using the “importance sampling technique”. Afterwards, we discuss the Bayesian prediction problem under one and two-sample frameworks and obtain the predictive estimates and intervals with corresponding average interval lengths. Applications of the developed theory are illustrated with the help of two real data sets.
Findings
The performances of these estimates and prediction methods are examined under Type-I hybrid censoring scheme with different combinations of sample sizes and time points using Monte Carlo simulation techniques. The simulation results show that the developed estimates are quite satisfactory. Bayes estimates and predictive intervals estimate the reliability characteristics efficiently.
Originality/value
The proposed methodology may be used to estimate future observations when the available data are Type-I hybrid censored. This study would help in estimating and predicting the mission time as well as stress-strength reliability when the data are censored.
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The purpose of this paper is to present the results of some corrosion inhibition studies of brass in 3N HNO3 by gemini surfactants.
Abstract
Purpose
The purpose of this paper is to present the results of some corrosion inhibition studies of brass in 3N HNO3 by gemini surfactants.
Design/methodology/approach
Gemini surfactants namely: N‐trimethyl butane‐diyl‐1,2‐ethane‐bis‐ammonium bromide (BEAB), N‐hexane‐diyl‐1,2‐ethane‐bis‐ammonium bromide (HEAB), N‐dodecane‐diyl‐1,2‐ethane‐bis‐ammonium bromide (DDEAB) and N‐hexadecane‐diyl‐1,2‐ethane‐bis‐ammonium bromide (HDEAB) were synthesized in the laboratory and their influence has been investigated for controlling the dissolution of brass in 3N HNO3. Weight loss, potentiodynamic polarization and electrochemical impedance have been employed for the study. Weight loss experiments were performed as per standard method (ASTM, 1987). Potentiodynamic polarization studies were carried out using EG&G PARC potentiostat/galvanostat (model 173), universal programmer (model 175) and X‐Y recorder (model RE 0089) and impedance measurements were carried out with an EG&G PAR (model 5301 A) lock‐in‐amplifier, using an IBM computer.
Findings
The inhibition efficiency for all the gemini surfactants increases with increase in concentrations. The maximum inhibition efficiency of each inhibitor was achieved at 250 ppm concentration. The inhibition efficiency of all the inhibitors decreases on increasing the temperature from 30 to 50°C. The results of potentiodynamic polarization studies revealed that all the compounds were mixed type inhibitors and inhibit the corrosion of brass by blocking the active sites of the metal. The adsorption of the compounds on brass surface in 3N HNO3 has been found to obey the Langmuir adsorption isotherm.
Originality/value
The paper provides information regarding corrosion inhibition of brass in 3N HNO3, the mechanism of the inhibition on the basis of molecular structures of the inhibitors, activation energy and free energy of adsorption.
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Soumya Roy, Biswabrata Pradhan and Annesha Purakayastha
This article considers Inverse Gaussian distribution as the basic lifetime model for the test units. The unknown model parameters are estimated using the method of moments, the…
Abstract
Purpose
This article considers Inverse Gaussian distribution as the basic lifetime model for the test units. The unknown model parameters are estimated using the method of moments, the method of maximum likelihood and Bayesian methods. As part of maximum likelihood analysis, this article employs an expectation-maximization algorithm to simplify numerical computation. Subsequently, Bayesian estimates are obtained using the Metropolis–Hastings algorithm. This article then presents the design of optimal censoring schemes using a design criterion that deals with the precision of a particular system lifetime quantile. The optimal censoring schemes are obtained after taking into account budget constraints.
Design/methodology/approach
This article first presents classical and Bayesian statistical inference for Progressive Type-I Interval censored data. Subsequently, this article considers the design of optimal Progressive Type-I Interval censoring schemes after incorporating budget constraints.
Findings
A real dataset is analyzed to demonstrate the methods developed in this article. The adequacy of the lifetime model is ensured using a simulation-based goodness-of-fit test. Furthermore, the performance of various estimators is studied using a detailed simulation experiment. It is observed that the maximum likelihood estimator relatively outperforms the method of moment estimator. Furthermore, the posterior median fares better among Bayesian estimators even in the absence of any subjective information. Furthermore, it is observed that the budget constraints have real implications on the optimal design of censoring schemes.
Originality/value
The proposed methodology may be used for analyzing any Progressive Type-I Interval Censored data for any lifetime model. The methodology adopted to obtain the optimal censoring schemes may be particularly useful for reliability engineers in real-life applications.
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Amit Kumar Yadav and Dinesh Kumar
The already-strained vaccine supply chain (VSC) of the expanded program for immunization (EPI) require a more robust and structured distribution network for pandemic/outbreak…
Abstract
Purpose
The already-strained vaccine supply chain (VSC) of the expanded program for immunization (EPI) require a more robust and structured distribution network for pandemic/outbreak vaccination due to huge volume demand and time constraint. In this paper, a lean-agile-green (LAG) practices approach is proposed to improve the operational, economic and environmental efficiency of the VSC.
Design/methodology/approach
A fuzzy decision framework of importance performance analysis (IPA)–analytical hierarchy process (AHP)–technique for order for preference by similarity in ideal solution (TOPSIS) has been presented in this paper to prioritize the LAG practices on the basis of the influence on performance indicators. Sensitivity analysis is carried out to check the robustness of the presented model.
Findings
The derived result indicates that sustainable packaging, coordination among supply chain stakeholders and cold chain technology improvement are among the top practices affecting most of the performance parameters of VSC. The sensitivity analysis reveals that the priority of practices is highly dependent on the weightage of performance indicators.
Practical implications
This study's finding will help policymakers reframe strategies for sustainable VSC (SVSC) by including new management practices that can handle regular immunization programs as well as emergency mass vaccination.
Originality/value
To the best of the authors' knowledge, this is the first study that proposes the LAG framework for SVSC. The IPA–Fuzzy AHP (FAHP)–Fuzyy TOPSIS (FTOPSIS) is also a novel combination in decision-making.
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The aim of this chapter is to study catastrophic pandemics which have occurred in the twentieth and twenty-first centuries and their disruptive impact on tourism mobility. A…
Abstract
The aim of this chapter is to study catastrophic pandemics which have occurred in the twentieth and twenty-first centuries and their disruptive impact on tourism mobility. A detailed study of past pandemics is conducted starting from the black death or bubonic plague of 1346 to the recent COVID-19 outbreak and effect of these diseases on the tourism and economy of the infected countries. Studies show that influenza pandemics will prove to be the most dangerous in future, and the next outbreak could occur from any of the 16 known HA (haemagglutinin) subtypes. Also, it is found that tourism itself has been responsible for spread of pandemic outbreaks as countries around the world put an enormous emphasis on increased growth of tourist numbers. Among recent pandemics, it was severe acute respiratory syndrome (SARS) that caused the major decrease in international tourist arrivals although for a short term. Such pandemics have a negative effect on tourism destinations by damaging their image and competitiveness, and as a result, leading to disruptions in mobility of tourists, with Asian countries being the most at risk of such disruptions. Therefore, the findings of this study stress the need for pre-crisis management to handle such outbreaks, better traveller tracking system to check infected persons and the need for tourism destinations to diversify their economies to reduce dependency on tourism.
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José A. Ramírez‐Hernández, Emmanuel Fernandez, Matilda O'Connor and Nipa Patel
The aim of this paper is to present the rationale, a numerical example and a case study of the application of an algorithm to convert non‐calendar based preventive maintenance…
Abstract
Purpose
The aim of this paper is to present the rationale, a numerical example and a case study of the application of an algorithm to convert non‐calendar based preventive maintenance (PM) schedules into calendar‐time format for semiconductor manufacturing systems (SMS). The resulting calendar‐time PM schedules can be utilized as a baseline within a PM scheduling optimization process.
Design/methodology/approach
The algorithm utilizes estimations of work‐in‐process (WIP) and system parameters to estimate an equivalent calendar‐time schedule for PM schedules based on different units. A numerical example based on fictitious data illustrates the utilization of the conversion algorithm within a mixed PM scheduling scenario, including wafer, processing‐time and energy‐based PM tasks for multi‐chamber tools. In addition, a case study illustrates the accuracy of the algorithm by comparing estimated PM targets (i.e. due, warning and late dates) with historical data from a real semiconductor fabrication facility.
Findings
Results from the case study validated the conversion algorithm by showing accurate estimations of PM targets (i.e. due, warning and late dates). The accuracy of the algorithm depends, however, on good estimates for WIP levels within the planning horizon.
Originality/value
The conversion algorithm may be utilized not only in SMS but also in other industries that require the conversion of non‐calendar based PM schedules into calendar‐time format for PM optimization and operational purposes.