• Journal of the military operations research society of Korea
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• v.17 no.1
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• pp.61-83
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• 1991

There has been a great deal of research dealing with the optimal replacement of stochastically deteriorating equipment and research in queueing systems with a finite calling population. However. there has been a lack of research which combines these two areas to deal with optimal replacement for a fixed number of machines and a limited number of repairmen. In this research, an optimal control policy for replacement involving two machines and one repairman is developed by investigating a class of age replacement policies in the context of controlling a G/M/1 queueing system with a finite calling population. The control policy to be imposed on this problem is an age-dependent control policy, described by the control limit $t^{\ast}$. The control limit is operational only when the repairman is idle; that is. if both machines are working, as soon as a machine reaches the age $t^{\ast}$ it is taken out of service for replacememt. We obtain the ${\epsilon}$-optimal control age which will minimize the long-run average system cost. An algorithm is developed that is applicable to general failure time distributions and cost functions. The algorithm does not require the condition of unimodality for implementation.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.2 no.1
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• pp.43-48
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• 2002

This paper discusses the application of fuzzy-ARTMAP neural network to compensate the nonlinearity of satellite communication channel. The fuzzy-ARTMAP is the class of ART(adaptive resonance theory) architectures designed fur supervised loaming. It has capabilities not fecund in other neural network approaches, that includes a small number of parameters, no requirements fur the choice of initial weights, automatic increase of hidden units, and capability of adding new data without retraining previously trained data. By a match tracking process with vigilance parameter, fuzzy-ARTMAP neural network achieves a minimax teaming rule that minimizes predictive error and maximizes generalization. Thus, the system automatically leans a minimal number of recognition categories, or hidden units, to meet accuracy criteria. As a input-converting process for implementing fuzzy-ARTMAP equalizer, the sigmoid function is chosen to convert actual channel output to the proper input values of fuzzy-ARTMAP. Simulation studies are performed over satellite nonlinear channels. QPSK signals with Gaussian noise are generated at random from Volterra model. The performance of proposed fuzzy-ARTMAP equalizer is compared with MLP equalizer.

• Journal of The Korean Astronomical Society
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• v.47 no.6
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• pp.209-214
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• 2014

In this study we develop a set of solar proton event (SPE) forecast models with NOAA scales by Multi Layer Perceptron (MLP), one of neural network methods, using GOES solar X-ray flare data from 1976 to 2011. Our MLP models are the first attempt to forecast the SPE scales by the neural network method. The combinations of X-ray flare class, impulsive time, and location are used for input data. For this study we make a number of trials by changing the number of layers and nodes as well as combinations of the input data. To find the best model, we use the summation of F-scores weighted by SPE scales, where F-score is the harmonic mean of PODy (recall) and precision (positive predictive value), in order to minimize both misses and false alarms. We find that the MLP models are much better than the multiple linear regression model and one layer MLP model gives the best result.

• Korean Journal of Biological Psychiatry
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• v.23 no.3
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• pp.116-121
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• 2016

Objectives Experience of early childhood abuse elevates the risk of developing schizophrenia in later period of life, incidence of psychiatric comorbidity, symptomatic severity and complexity. In this context, we hypothesized that the pattern of psychotropic medication used would reflect this; those with childhood trauma will received more types and higher doses of psychotropic medication. Methods From our database of 102 outpatients diagnosed with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) schizophrenia, we analyzed experiences of childhood trauma measured by the Childhood Trauma Questionnaire-Short Form and types and dose of prescribed psychotropic medication. Results We found significant positive correlations between child sexual abuse and the number of psychotropic medications (p = 0.029) and between child emotional neglect and the number of psychotropic medications other than antipsychotics (p = 0.045). Conclusions This preliminary study suggests that the pattern of psychotropic use may be affected by types of childhood trauma. Further studies will have to shed light on mediating factors such as symptoms or comorbid conditions that lead to prescription of certain psychotropic class.

• Journal of Preventive Medicine and Public Health
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• v.48 no.6
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• pp.319-329
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• 2015

Objectives: Parental socioeconomic status (SES) exerts a substantial influence on children's health. The purpose of this study was to examine factors determining children's private health insurance (PHI) enrolment and children's healthcare utilization according to PHI coverage. Methods: Korea Health Panel data from 2011 (n=3085) was used to explore the factors determining PHI enrolment in children younger than 15 years of age. A logit model contained health status and SES variables for both children and parents. A fixed effects model identified factors influencing healthcare utilization in children aged 10 years or younger, using 2008 to 2011 panel data (n=9084). Results: The factors determining children's PHI enrolment included children's age and sex and parents' educational status, employment status, and household income quintile. PHI exerted a significant effect on outpatient cost, inpatient cost, and number of admissions. Number of outpatient visits and total length of stay were not affected by PHI status. The interaction between PHI and age group increased outpatient cost significantly. Conclusions: Children's PHI enrolment was influenced by parents' SES, while healthcare utilization was affected by health and disability status. Therefore, the results of this study suggest disparities in healthcare utilization according to PHI enrollment.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.3
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• pp.790-798
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• 2016

Currently, web-based online games is becoming popular in supporting learning process due to their effective and efficient tool. However, online games have lack of security aspect, in particular due to increase in the number of personal information leakage. Since the data are transmitted over insecure channel, it will be vulnerable of being intercepted by attackers who want to exploit user's identity. This paper aims to propose an online web-based educational game, Vidyanusa which allows the students to register their personal information using a unique code, a user name and a password. It manages the users according to their schools, subject teachers and class levels. In addition, by adopting a unique code, the confidentiality of the user identity can be kept away from attackers. Moreover, in order to provide a secure data communication between client and server, Secure Socket Layer (SSL) protocol is adopted. The performance of the system after implementing SSL protocol is examined by loading a number of requests for various users. From the experiment result, it can be concluded that the SSL protocol can be applied to web-based educational system in order to offer security services and reliable connection.

• Journal of Forest and Environmental Science
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• v.29 no.4
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• pp.292-299
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• 2013

The study was undertaken to assess the tourist's carrying capacity and to explore ecotourism potential of Bangabandhu Sheikh Mujib Safari Park, the only safari park of Bangladesh. Carrying capacity was assessed both from physical and social aspect. On the other hand, 250 visitors were interviewed with semi structured questionnaire for ecotourism prospect evaluation along with some secondary data. The total daily-allowed visit was 17,300 with rotation coefficient of 3.46. Maximum daily average numbers of tourists were relatively below the physical carrying capacity of the Park (5,000). The social carrying capacity was 4.38 persons per day. As there are different categories of visitors, their choice of encounters and number of expected encounters also varied. Each year, the total tourist's number varied significantly ($p{\leq}0.05$). That proved the safari park had immense tourist prospect. 85 percent visitors were from lower and middle class family as entrance fees and other fees inside were very cheap in relation to other private amusement place. The ecological perspective of the park will remain unaltered if the carrying capacities of the area are followed with sustainability. Therefore, it is the proper time for taking appropriate decision.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.5
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• pp.871-876
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• 2006

In this thesis, to accurately measure 3D face information using the spatial encoding patterns, the new algorithm to segment the pattern images from initial face pattern image is proposed. If the obtained images is non-homogeneous texture and ambiguous boundary pattern, the pattern segmentation is very difficult. Furthermore. the non-encoded areas by accumulated error are occurred. In this thesis, the FCM(fuzzy c-means) clustering method is proposed to enhance the robust encoding and segmentation rate under non-homogeneous texture and ambiguous boundary pattern. The initial parameters for experiment such as clustering class number, maximum repetition number, and error tolerance are set with 2, 100, 0.0001 respectively. The proposed pattern segmentation method increased 8-20% segmentation rate with conventional binary segmentation methods.

• The Mathematical Education
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• v.57 no.3
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• pp.215-229
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• 2018

Despite the importance of learning to do mathematical proofs, researchers have reported that not only secondary school students but also undergraduate students have difficulties in learning proofs. In this study, we introduced a new toll for learning proofs and explored the reliability and the validity of peer assessment on proofs. In the course of a university in Seoul, students were given weekly proof assignments prior to class. After solving the proofs, each student had to assess other students' proofs. The inter-rater reliabilities of weekly peer assessment was higher than .9 over 90 percent of the observed cases. To examine the validity of peer assessment, we check whether students' assessments were similar to expert assessment. Analysis showed that the equivalence has been quite high throughout the semester and the validity was low in the middle of the semester but rose by the end of the semester. Based on these results, we believe instructors can consider the application of peer assessment on proving tasks as a tool to help students learn.

• Journal of Korean Elementary Science Education
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• v.25 no.2
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• pp.109-117
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• 2006

The purpose of this study was to examine the questioning styles of $3rd{\sim}6th$ elementary science textbooks in terms of frequency, type, and placement of questions. This paper also sought to analyse and compare the kinds of scientific inquiry processes elicited by the questions in the content domains of textbooks. The instrument used was the Textbook Questioning Strategies Assessment Instrument (TQSAI). The average number of questions per book was 129 and the ratio of questions to sentences was 31.9%. The results were summarized as followings. First, many science textbook questions were used for the purposes of explanation or identifying levels of teaming. Second, process skills were located in each content domain, although it was not affected meaningfully. Third, the number of text question was below 3 in each elementary science class. Therefore, an effective questioning development framework is clearly needed for elementary science instruction.