• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.5
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• pp.445-455
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• 2010

In order to effectively predict thermo-acoustic instability within real combustors of rocket engines and gas turbines, in the present study, the Helmholtz equation in conjunction with the time lag hypothesis is discretized by the finite element method on three-dimensional hybrid unstructured mesh. Numerical nonlinearity caused by the combustion response term is linearized by an iterative method, and the large-scale eigenvalue problem is solved by the Arnoldi method available in the ARPACK. As a consequence, the final solution of complex valued eigenfrequency and acoustic pressure field can be interpreted as resonant frequency, growth rate, and modal shape for acoustic modes of interest. The predictive capabilities of the present method have been validated against two academic problems with complex impedance boundary and premixed flame, as well as an ambient acoustic test for liquid rocket combustion chamber with/without baffle.

• Smart Structures and Systems
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• v.9 no.3
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• pp.231-251
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• 2012

The stochastic optimal control for a piezoelectric spherically symmetric shell subjected to stochastic boundary perturbations is constructed, analyzed and evaluated. The stochastic optimal control problem on the boundary stress output reduction of the piezoelectric shell subjected to stochastic boundary displacement perturbations is presented. The electric potential integral as a function of displacement is obtained to convert the differential equations for the piezoelectric shell with electrical and mechanical coupling into the equation only for displacement. The displacement transformation is constructed to convert the stochastic boundary conditions into homogeneous ones, and the transformed displacement is expanded in space to convert further the partial differential equation for displacement into ordinary differential equations by using the Galerkin method. Then the stochastic optimal control problem of the piezoelectric shell in partial differential equations is transformed into that of the multi-degree-of-freedom system. The optimal control law for electric potential is determined according to the stochastic dynamical programming principle. The frequency-response function matrix, power spectral density matrix and correlation function matrix of the controlled system response are derived based on the theory of random vibration. The expressions of mean-square stress, displacement and electric potential of the controlled piezoelectric shell are finally obtained to evaluate the control effectiveness. Numerical results are given to illustrate the high relative reduction in the root-mean-square boundary stress of the piezoelectric shell subjected to stochastic boundary displacement perturbations by the optimal electric potential control.

• Journal of Drive and Control
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• v.17 no.2
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• pp.1-8
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• 2020

Recently, industrial systems are becoming quicker and lighter to enable the reduction of energy consumption and increase productivity. So the latest systems are more flexible and rapid than the previous systems. But, with this improvement, another problem has emerged, such as the increase in residual vibration when a system is started or stopped. The input shaper is a command generation method that can remove residual vibration. It can provide a solution to the problem of residual vibration in industrial systems. However, it is difficult to generate the input shaper in high order systems, such as a typical industrial system because the input shaper is induced from the system's vibration characteristics. This study focused on the extra insensitivity shaper that can compensate for the system's modeling error such as input dynamics, and the high order's system affection. A genetic algorithm was deployed to adjust a vibration limitation for the extra insensitivity of the input shaper. A plant is a low damping system that includes one zero and a pole. The fitness functions are an error signal of the system's response with normalized frequency variations. Verification of the suggested system is satisfied by comparison between the zero vibration derivative input shaper's response and the suggested one.

• Journal of The Korean Association of Information Education
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• v.15 no.3
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• pp.375-385
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• 2011

Computer education is moving its focus from skill oriented education to improving students' creativity and problem solving ability. Thus, the importance of programming education is being strengthened. However, programming education was biased to grammar oriented language that has been limits of students' interest. Robot programming is problem solving itself, and by allowing students to directly see the robot which is the output of programming, can help interest and motivate to the students. In fact, it is still observed that the students are facing difficulties due to various kinds of errors during the programming education. Therefore, this study categorizes and analyzes the errors students are facing during robot programming, and based on that, a support tool to help treat errors developed. The developed supporting system for error solving reduces the frequency of errors and provides the set of coding instruction, NXC language and error message in Korean, examples and detailed information for each stage of education, function removing major coding errors, and code sorting and indication of row number. This study also confirmed that the supporting tool is helpful in reducing and solving errors after input.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.2
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• pp.545-563
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• 2015

Energy harvesting (EH) and network coding (NC) have emerged as two promising technologies for future wireless networks. In this paper, we combine them together in a single system and then present a time switching-based network coding relaying (TSNCR) protocol for the two-way relay system, where an energy constrained relay harvests energy from the transmitted radio frequency (RF) signals from two sources, and then helps the two-way relay information exchange between the two sources with the consumption of the harvested energy. To evaluate the system performance, we derive an explicit expression of the outage probability for the proposed TSNCR protocol. In order to explore the system performance limit, we formulate an optimization problem to minimize the system outage probability. Since the problem is non-convex and cannot be directly solved, we design a genetic algorithm (GA)-based optimization algorithm for it. Numerical results validate our theoretical analysis and show that in such an EH two-way relay system, if NC is applied, the system outage probability can be greatly decreased. Moreover, it is shown that the relay position greatly affects the system performance of TSNCR, where relatively worse outage performance is achieved when the relay is placed in the middle of the two sources. This is the first time to observe such a phenomena in EH two-way relay systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2178-2187
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• 2015

Bluetooth Low Energy (Bluetooth LE) is a representative break-through communication technology for wireless personal area networks on nowaday. In this environment, most of significant performance should be aiming to energy efficiency due to the policy for manufacturing light-weighted communication devices derived from requirement of world IoT market, and many researches have been developed to satisfy this requirement. While Bluetooth LE has been leading the low power communication technology required from the current market by employing duty cycle and frequency hopping approaches, it couldn't address the problem of reliability on broadcast transmissions. The main goal of this paper is aiming to addressing this problem by suggesting a new method. Furthermore analytic evaluations would also be proceeded to find objective results in the view point of broadcast transmission efficiency from Master device.

• Women's Health Nursing
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• v.14 no.4
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• pp.290-296
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• 2008

Purpose: The O'Leary Symptom Index and Problem Index(ICSI/ICPI) have been used widespread in clinical studies and research. This research was aimed to determine the reliability and validity of the ICSI/ICPI-K that was translated into Korean. Methods: The research design was a methodological study to test the measurements. Subjects were 301 elderly women in Seoul, Chungnam and Gyungbuk. They were recruited through a formal announcement and they responded after informed consent. Data was analyzed with SPSS 15.0. The internal consistency was assessed by Cronbach's alpha coefficient and the criterion validity was assessed by Pearson correlation with the Geriatric Depression Scale(GDS) and inter-subscales. Results: The elderly women were on average 74.3 years old. As to the reliability of the scale, ICSI/ICPI-K had a Cronbach alpha of .832. In addition, the results showed that ICSI/ICPI-K was valid through the Pearson correlation. That is, the ICSI-K and ICPI-K had a significant relationship with GDS(r=.295; r=.374, respectively) and strong correlations of subscale to subscale(ICSI-K & ICPI-K: r=.676). The most common symptom of the lower urinary tract by the ICSI/ICPI-K was nocturia 249(83.3%) followed by frequency 187(62.8%), urgency 148(49.8%). and pelvic pain 71(23.9%) in the elderly women. Conclusion: We can conclude that the ICSI/ICPI-K is reliable and valid in Korean elderly women. It needs to be evaluated in the clinical area.

• Journal of Environmental Health Sciences
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• v.46 no.1
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• pp.65-77
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• 2020

Objectives: This study investigated the average number of drinkers in Korea, the number of high-risk drinkers, the average amount of alcohol consumed by high-risk drinkers, and the types of alcohol consumed according to the characteristics of the group of dependent drinkers. Methods: The results were obtained by analyzing the following data: The Global Status Report on Alcohol and Health; Country Profile 2014; WHO Country Profile 2014; Korea National Health and Nutrition Examination Survey 2014, Korean Statistical Information Service; National Tax Statistics-Liquor Tax; Gallup Drinking Frequency Survey 2015 Results: This study found that a large proportion of drinkers in Korea are already high-risk drinkers, and even among drinkers, alcohol consumption was highly biased. It was reported that 49.8% of men in the problem, abuse, and dependence groups accounted for 92.4% of total alcohol consumption among the male population. Notably, the 9.6% of men making up the dependent group consumed more than 30% of the alcohol ingested among males. Women had significant variations within groups that were considered high-risk and exhibited a large share of alcohol consumption in the problem (10.0% of the female population), abuse (1.8% of the female population), and dependence (1.5% of the female population) groups, constituting 72.8% of total alcohol consumption. The average amount of alcohol consumed by drinkers in Korea seems to have exceeded the level of intake by high-risk groups. Alcohol-dependent groups consumed 900.7 mL of soju, 405.2 mL of table wine, and 2,043.8 mL of beer, which is very similar to the consumption average of 2,031 mL of beer and 895.2 mL of soju in the drinking group. Conclusion: It has been shown that men's dependence on alcohol is serious, and it is possible to infer that alcohol consumption in some vulnerable groups is very high. As the average alcohol intake among alcohol-dependent groups and ordinary drinkers is very similar, it is highly likely that the drinker is an alcohol-dependent consumer in Korea.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.8
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• pp.1195-1208
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• 1997

Bellows is a component in piping systems which absorbs mechanical deformation with flexibility. Its geometry is an axial symmetric shell which consists of two toroidal shells and one annular plate or conical shell. In order to analyze bellows, this study presents the finite element analysis using a conical frustum shell element. A finite element analysis is developed to analyze various bellows. The validity of the developed program is verified by the experimental results for axial and lateral stiffness. The formula for calculating the natural frequency of bellows is made by the simple beam theory. The formula for fatigue life is also derived by experiments. The shape optimal design problem is formulated using multiple objective optimization. The multiple objective functions are transformed to a scalar function by weighting factors. The stiffness, strength and specified stiffness are considered as the multiple objective function. The formulation has inequality constraints imposed on the fatigue limit, the natural frequencies, and the manufacturing conditions. Geometric parameters of bellows are the design variables. The recursive quadratic programming algorithm is selected to solve the problem. The results are compared to existing bellows, and the characteristics of bellows is investigated through optimal design process. The optimized shape of bellows is expected to give quite a good guideline to practical design.

• Research in Community and Public Health Nursing
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• v.11 no.1
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• pp.117-126
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• 2000

For basic data to develop health management program of female workers. this study was intended to characterize factors affecting health problems of women at workplace which has less than 50 workers by Cornell Medical Index(CMI). 195 items of CMI questionnaire were simplified to 57 items which were composed of 35 items concerning physical health problems and 22 items concerning mental health problems. The data was collected during 6 months from July 10 to December 30 and analyzed with frequency, percentage, t-test and ANOVA. The 107 female workers included in this study was characterized to be mainly twenties(64.5%), single(69.2%) and working at production position(89.7%). The most frequent physical problem was fatigability and the next, neurological system and cardiovascular system. Main mental complaints were inadquacy. anger and tension. When the health problems were reviewed according to its general characteristics, anger in young age, adaptiveness in single and respiratory complaints in self-recognized unhealthy group were prevalent. According to life styles. the prevalent complaints were musculoskeletal one in alcoholic group and cardiovascular one in group who are sleeping just for four to five hours. The appropriateness of each items of CMI should be evaluated to reveal the reasons why meaningful results could not come from many items of this questionnaire. The repeated study should be carried out to figure out the health problems and its related factors of female workers at small scale workplace. Also, exercise program and abstinence from drinking and smoking should be carried out for female worker's health.