• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.1
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• pp.110-117
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• 2018

Machines and facilities are physically or chemically degenerated by continuous usage. One of the results of this degeneration is the process mean shift. By the result of degeneration, non-conforming products and malfunction of machine occur. Therefore a periodic preventive resetting the process is necessary. This type of preventive action is called 'preventive maintenance policy.' Preventive maintenance presupposes that the preventive (resetting the process) cost is smaller than the cost of failure caused by the malfunction of machine. The process mean shift problem is a field of preventive maintenance. This field deals the interrelationship between the quality cost and the process resetting cost before machine breaks down. Quality cost is the sum of the non-conforming item cost and quality loss cost. Quality loss cost is due to the deviation between the quality characteristics from the target value. Under the process mean shift, the quality cost is increasing continuously whereas the process resetting cost is constant value. The objective function is total costs per unit wear, the decision variables are the wear limit (resetting period) and the initial process mean. Comparing the previous studies, we set the process variance as an increasing concave function and set the quality loss function as Cpm+ simultaneously. In the Cpm+, loss function has different cost coefficients according to the direction of the quality characteristics from target value. A numerical example is presented.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.43 no.3
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• pp.95-100
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• 2020

Machines and facilities are physically or chemically degenerated by continuous usage. One of the results of this degeneration is the process mean shift. The representative type of the degeneration is wear of tool or machine. According to the increasing wear level, non-conforming products cost and quality loss cost are increasing simultaneously. Therefore a periodic preventive resetting the process is necessary. The total cost consists of three items: adjustment cost (or replacement cost), non-conforming cost due to product out of upper or lower limit specification, and quality loss cost due to difference from the process target value and the product characteristic value among the conforming products. In this case, the problem of determining the adjustment period or wear limit that minimizes the total cost is called the 'process mean shift' problem. It is assumed that both specifications are set and the wear level can be observed directly. In this study, we propose a new model integrating the quality loss cost, process variance, and production volume, which has been conducted in different fields in previous studies. In particular, for the change in production volume according to the increasing in wear level, we propose a generalized production quantity function g(w). This function can be applied to most processes and we fitted the g(w) to the model. The objective equation of this model is the total cost per unit wear, and the determining variables are the wear limit and initial process setting position that minimize the objective equation.

• Environmental Engineering Research
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• v.25 no.3
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• pp.366-373
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• 2020

The autonomous vehicles (AVs) could make a positive or negative impact on reducing mobile emissions. This study investigated the changes of mobile emissions that could be caused by large-scale adoption of AVs. The factors of road capacity increase and speed limit increase impacts were simulated using a conceptual modeling approach that combines a hypothetical speed-emission function and a traffic demand model using a virtual transportation network. The simulation results show that road capacity increase impact is significant in decreasing mobile emissions until the market share of AVs is less than 80%. If the road capacity increases by 100%, the mobile emissions will decrease by about 30%. On the other hand, driving speed limit increase impact is significant in increasing mobile emissions, and the environmentally desirable speed limit was found at around 95 km/h. If the speed limit increases to 140 km/h, the mobile emissions will increase by about 25%. This is because some vehicles begin to bypass the congested routes at high speeds as speed limit increases. Based on the simulation results, it is clear that the vehicle platooning technology implemented at reasonable speed limit is one of the AV technologies that are encouraging from the environmental point of view.

• 전자공학회논문지 IE
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• v.46 no.3
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• pp.33-41
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• 2009

Because the stability of obstacle avoidance ability is important for the safe operation of mobile robots, this paper deals with the analysis of dynamic stability of Limit-cycle navigation method that was proposed by authors. Limit-cycle navigation method is fast and easy to implement for fast moving mobile robots using limit-cycle characteristics of the 2nd-order nonlinear function. It can be applied to robots in dynamically changing environment such as the robot soccer. By adjusting the radius of the motion circle and the direction of the obstacle avoidance, the mobile robot can avoid the collision with obstacles and move to the destination point. The stability of Limit-cycle navigation method is analyzed with a linear model. To demonstrate the effectiveness and applicability, it is applied to the robot soccer Simulations and real experiments ascertain the merits of the proposed method.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.8 no.1
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• pp.205-222
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• 2013

As Social Welfare Service Act was revised in 2011 and its enforcement decree was revised in 2012, the function of local social welfare center was classified into 3 functions such as case control function, service supply function and local society systematization function. Therefore, from 2013, local social welfare center faces the assignment to establish its status as a core subjectivity of local social welfare while maintaining function, role, business, program, service and organization system required for local social welfare center. Currently, there are internal and external limit factors for local social welfare center to perform its original function. The external limit factors are competition with similar organization, diversification of welfare desire depending on social change, insufficient service network construction and lack of partnership between private sector and government. The internal limit factors are lack of local social organization's ability, program issue, insufficient resource, insufficient manpower, etc. In order for local social welfare center to overcome the limit factor and establish the core status for improving the life quality of resident, it should concentrate its ability on local society systematization, construct human & material support network related to local social welfare, minimize social education program and simple relief project gradually, suggest the reasonable direction for village to nurture resident organization, develop the program based on the research on local resident's desire and create the partnership between private sector and government.

• Journal of the Korean Data and Information Science Society
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• v.8 no.1
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• pp.49-58
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• 1997

We consider the quantile function for the bootstrapped product limit estimate under left truncation and right censoring model and show its weak convergence. We also obtain bootstrapped confidence bands for the quantile function.

• Communications of the Korean Mathematical Society
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• v.38 no.2
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• pp.389-400
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• 2023

In this paper, some estimations will be given for the analytic functions belonging to the class 𝓡(α). In these estimations, an upper bound and a lower bound will be determined for the first coefficient of the expansion of the analytic function h(z) and the modulus of the angular derivative of the function ${\frac{zh^{\prime}(z)}{h(z)}}$, respectively. Also, the relationship between the coefficients of the analytical function h(z) and the derivative mentioned above will be shown.

• Journal of the Korean Mathematical Society
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• v.32 no.3
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• pp.625-633
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• 1995

Classical Fatous' theorem asserts that the non-tangential limit of the Poisson integral of an integrals function on $[\pi, \pi]$ exists a.e.

• Journal of Educational Research in Mathematics
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• v.27 no.3
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• pp.375-389
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• 2017

The purpose of this study is to analyze the difference and inter-connectivity between the definition of continuity in school mathematics and the definition of academic mathematics in four perspectives. These difference and inter-connectivity have not analyzed in previous papers. According to this study, the definition of 'continuity and discontinuity at one point' in school mathematics depends on the limit processing but in academic mathematics it depends on the topology of the domain. The target function of the continuous function in school mathematics is a function whose domain is limited to an interval or a union of intervals, but the target function of the continuous function in academic mathematics is all functions. Based on these results, the following two opinions are given in relation to the concept of continuity in school mathematics. First, since the notion of local continuity in school mathematics is based on limit processing, the contents of 2009-revised textbooks that deal with discontinuity at special point not belonging to the domain is appropriate. Here the discontinuity appears as types of infinite discontinuity, removable discontinuity, and step discontinuity. Second, the definition of a general continuous function is proposed to "if there is no discontinuity point in the domain of a function y = f(x), we call the function f a continuous function." This definition allows the discontinuity at special point in non-domain, but is consistent with the definition in academic mathematics.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.277-289
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• 2005

The study examines the limit strength for steel cable-stayed bridges. A case studies have been performed in order to evaluate the limit strength lot steel cable-stayed bridges using nonlinear inelastic analysis approach and bifurcation point instability analysis approach, effective tangent modulus $(E_f)$ method. To realize it, a practical nonlinear inelastic analysis condoling the initial shape is developed. In the initial shape analysis, updated structural configuration is introduced instead of initial member forces for beam-column members at every iterative step. Geometric and material nonlinearities of beam-column members are accounted by using stability function, and by using CRC tangent modulus and parabolic function, respectively Besides, geometric nonlinearity of cable members is accounted by using secant value of equivalent modulus of elasticity. The load-displacement relationships obtained by the proposed method are compared well with those given by other approaches. The limit strengths evaluated by the proposed nonlinear inelastic analysis for the proposed cable-stayed bridges with tee dimensional configuration compared with those by the inelastic bifurcation point instability analyses.