• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.356-363
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• 2012

This paper addresses an analytical study on the gas-solid two phase flows in a nozzle. The primary purpose is to get recognition into the gas-solid suspension flows and to investigate the particle motion and its influence on the gas flow field. The present study is the primal step to comprehend the gas-solid suspension flow in the convergent-divergent nozzle. This paper try to made a development of an analytical model to study the back pressure ratio, particles loading and the particle diameter effect on gas-solid suspension flow. Mathematical model of gas-solid two phase flow was developed based on the single phase flow models to solve the quasi-one-dimensional mass, momentum equations to calculate the steady pressure field. The influence of particles loading and particle diameter is analyzed. The results obtained show that the suspension flow of smaller diameter particles has almost same trend as that of single phase flow using ideal gas as working fluid. And the presence of particles will weaken the strength of the shock wave; the bigger particle will have larger slip velocity with gas flow. The thrust coefficient is found to be higher for larger particles/gas loading or back pressure ratio, but it also depends on the ambient pressure.

• 청정기술
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• 제26권4호
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• pp.279-285
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• 2020

Laboratories and industrial processes typically involve the use of flammable substances. An important property used to estimate fire and explosion risk for a flammable liquid is the flash point. In this study, flash point data at 101.3 kPa were determined using a SETA closed cup flash point tester on the following solvent mixtures: {2,2,4-trimethylpentane + methylcyclohexane}, {2,2,4-trimethylpentane + ethylbenzene}, and {2,2,4-trimethylpentane + p-xylene}. The purpose of this work is to obtain flash point data for binary mixtures of 2,2,4-trimethylpentane with three hydrocarbons (methylcyclohexane, ethylbenzene, and p-xylene), which are representative compounds of the main aromatic hydrocarbon fractions of petroleum. The measured flash points are compared with the predicted values calculated using the GE models' activity coefficient patterns: the Wilson, the Non-Random Two-Liquid (NRTL), and the UNIversal QUAsiChemical (UNIQUAC) models. The non-ideality of the mixture is also considered. The average absolute deviation between the predicted and measured lower flash point s is less than 1.99 K, except when Raoult's law is calculated. In addition, the minimum flash point behavior is not observed in any of the three binary systems. This work's predicted results can be applied to design safe petrochemical processes, such as identifying safe storage conditions for non-ideal solutions containing volatile components.

• 한국전자통신학회논문지
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• 제18권2호
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• pp.241-250
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• 2023

본 논문에서는 적응형 초음파 빔포밍 시스템에 LMS 알고리즘을 이용하는 때에 초기치 설정이 스텝 파라미터의 여유도에 미치는 영향을 연구하였다. 이를 위하여 임의로 설정한 빔폭을 갖는 준이상 빔과 회전 빔에 대한 빔포밍에 대해서 검토하였다. 수치 실험은 초음파 빔포밍 시스템에 임의의 초기치(음원수는 임의의 수로 고정)를 설정하고, 이에 대한 스텝 파라미터의 여유도와 수렴 특성 등을 비교하였다.

• 한국전자통신학회논문지
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• 제18권3호
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• pp.535-544
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• 2023

본 논문에서는 희망하는 빔포밍을 실현하기 위하여 LMS 알고리즘(반복법)을 이용하는 경우에 반복 계산과정에서 무게 분포를 조절하기 위한 기울기 벡터의 계산법(해석적인 방법, 중앙유한차분법)이 적응 빔포밍에 미치는 영향을 연구하였다. 이를 위하여 임의로 설정한 빔폭을 갖는 준이상 빔과 회전 빔, 그리고 멀티 빔을 예로 하여 검토하였다. 수치 실험은 적응 빔포밍 시스템에 임의의 초기치와 시행착오를 거쳐서 설정한 적절한 값의 스텝 파라미터를 두 계산법에 동일하게 적용하고, 기울기 벡터의 계산을 위한 두 가지 방법을 이용하여 적응성과 오차를 평가하는 목적 함수의 수렴 특성 등을 비교하였다.

• 센서학회지
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• 제33권3호
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• pp.158-164
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• 2024

We developed a self-operated paper pump that can maintain a nearly constant flow rate of an aqueous solution along a paper strip channel in paper-based analytical devices (PADs). The quasi-stationary flow rate was controlled by increasing the crosssectional channel area (capillary force) using a fan-shaped absorption pad coupled with a paper strip channel. The flow rate is regulated by varying the fan angle of the circular absorbing pad. Furthermore, the flow rate can be increased by furnishing a hollow cavity at the center of a conventional paper strip channel. The rate was regulated by varying the length of the hollow paper channel in the flow rate range of 5.1-26.4 mm/min. As a preliminary work, a paper-pump-coupled PAD was fabricated, and its CV detection capability was evaluated for the redox reaction of Fe(CN)₆^+4/+3. The combination of a paper pump with a PAD resulted in an ideal CV curve with a higher limiting current and faster response time. These results are interpreted well by the Levich equation, which suggests that the paper pump is a very useful component in paper-based sensors.

• 인터넷정보학회논문지
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• 제16권1호
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• pp.91-100
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• 2015

최근 전 세계적인 경기불황의 여파로 인하여 많은 기업들이 비용절감의 압박을 느끼게 되면서, 클라우드 컴퓨팅에 대한 관심 또한 덩달아 증대하고 있다. 클라우드 컴퓨팅이란 단말기에서 인터넷 즉, 네트워크를 이용하여 중앙에 있는 메인 서버의 소프트웨어를 활용하거나 데이터를 저장하는 컴퓨터의 이용 형태를 말한다. 사용자들은 소프트웨어나 하드웨어를 구입해서 사용하는 것이 아니라 원격지에서 빌려서 사용하는 형식이 되며 데이터센터를 이용하는 이용료를 지불하는 형식이 된다. 그런데, 비용절감 효과와 각종 효율성 증대로 인해 폭발적 성장세가 예측되었지만, 실제 클라우드 컴퓨팅 도입은 제한된 범주 내에서 확산되고 있다. 특히 국내 공공부문은 민감한 보안 문제나 보수적인 성향 등 여건으로 인해 도입을 더욱 주저하고 있는 현실이며, 관계자들의 인식이나 이해 또한 아직도 기초적인 수준에만 머물러 있어 현황 파악과 대책 마련이 필요한 실정이다. 그럼에도 불구하고 공공기관의 클라우드 컴퓨팅 도입에 관한 학술연구는 대부분이 기술 연구에만 치중되어 왔고 서비스 도입을 위한 현실적인 참고로 삼을 만한 연구는 찾아보기 힘들다. 본 연구에서는 정부부처의 기획된 업무를 실행하는 위탁형 준정부 기관 근무자들의 클라우드 컴퓨팅에 대한 인식과 이해를 파악하며, BCR모형을 적용해 그들이 실제 중요하게 여기고 우려하는 요인들이 우선순위를 분석하고 현실에 맞는 시사점을 제공하는데 목적을 두었다. 연구 결과로서 공공기관의 클라우드 컴퓨팅 서비스 도입현황과 혜택과 비용, 위험요인에 대해 민감도 분석하여 그 결과에 따른 전략적 대처방안을 제시하였다. 본 연구는 클라우드 컴퓨팅 서비스 도입을 하고자 하는 공공기관, 관련된 상위의 유관기관, 클라우드 서비스 제공업체의 입장에서 어떠한 점을 고려하여 향후 대응을 지속해나가야 하는지 가이드라인을 제공한다.

• International Journal of Aeronautical and Space Sciences
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• 제14권1호
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• pp.30-45
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• 2013

The present work focuses on the unsteady aerodynamics and aeroelastic properties of a small-medium sized wind-turbine blade operating under ideal conditions. A tapered/twisted blade representative of commercial blades used in an experiment setup at the National Renewable Energy Laboratory is considered. The aerodynamic loads are computed using Computational Fluid Dynamics (CFD) techniques. For this purpose, FLUENT$^{(R)}$, a commercial finite-volume code that solves the Navier-Stokes and the Reynolds-Averaged Navier-Stokes (RANS) equations, is used. Turbulence effects in the 2D simulations are modeled using the Wilcox k-w model for validation of the CFD approach. For the 3D aerodynamic simulations, in a first approximation, and considering that the intent is to present a methodology and workflow philosophy more than highly accurate turbulent simulations, the unsteady laminar Navier-Stokes equations were used to determine the unsteady loads acting on the blades. Five different blade pitch angles were considered and their aerodynamic performance compared. The structural dynamics of the flexible wind-turbine blade undergoing significant elastic displacements has been described by a nonlinear flap-lag-torsion slender-beam differential model. The aerodynamic quasi-steady forcing terms needed for the aeroelastic governing equations have been predicted through a strip-theory based on a simple 2D model, and the pertinent aerodynamic coefficients and the distribution over the blade span of the induced velocity derived using CFD. The resulting unsteady hub loads are achieved by a first space integration of the aeroelastic equations by applying the Galerkin's approach and by a time integration using a harmonic balance scheme. Comparison among two- and three- dimensional computations for the unsteady aerodynamic load, the flap, lag and torsional deflections, forces and moments are presented in the paper. Results, discussions and pertinent conclusions are outlined.

• 한국학교보건학회지
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• 제11권1호
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• pp.91-97
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• 1998

The main purpose of this study was to develop, implement, and evaluate a weight control program for overweight elementary school children The results of our previous study in 1996 Identified overweight as one of several health problems among elementary school children in urban areas The research method utilized was a quasi experimental design using one group in a pre and post test comparison The sample consisted of 198 children from 3 elementary schools in Kyung-gi Province who were 20% over the ideal weight for their height Height and weight were measured and a BMI score was calculated at the beginning of the program and monthly thereafter. The program had three components: physical exercise, counseling of children, and health education of children, parents, and teachers. The program lasted from March, 1997 to November, 1997. The data were analyzed using an SAS PC statistical package. The results indicate that the overweight children in two elementary schools had statistically Significant changes in their BMI score after the program while those in one school id not. When the process notes were reviewed it was Identified that the school which showed little change averaged less physical exercise, and less parent and teacher participation in the program In conclusion, a school based weight control program is an effective way to manage and prevent obesity for overweight elementary school children It is suggested that a school wide exercise program may be better accepted by overweight children than a program specifically designed for overweight children only. One of the most important factors which determine the successful outcome of any health promotion project in school is the enthusiasm and cooperation of the principal and school health nurse.

• 종양간호연구
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• 제3권2호
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• pp.103-111
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• 2003

The purpose of this study was to identify the effect of imagery therapy on "coping mechanism and type C personality of the women with mastectomy. To achieve this purpose, 2 hours sessions of imagery therapy were given to the patients with breast cancer twice a week for 6 weeks. The period of data collection was from July, 7th to August, 12th 2002. The participants were 30 patients, 15 experimental group, 15 control group who were treated at the G University hospital in J City. This study was designed using a quasi-experimental approach with non-equivalent Pre test-Post test Design. The themes for the Imagery Therapy Program were composed of Leuner's(1969) 12 Imagery Themes: flower, green-field, stream, mountain, house, woods, significant figures, rose, lion, ideal self-image, cave and volcano. The data were analyzed with ${\chi}2-test$ and MANOVA using the SPSS program. The course of image change of the 12 imagery themes was analyzed by content analysis. The results of this study are as follows: First Hypothesis, 'The score of type C personality in the women with mastectomy who received imagery therapy will be significantly lower than that of the control group' was supported(p<.05). Second Hypothesis, 'The score of coping mechanism' in the women with mastectomy who received imagery therapy will be significantly higher than that of the control group' was rejected. In conclusion, imagery therapy is suggested as an effective nursing intervention to change type C personality of the women with mastectomy, but not effective to improve coping mechanism. Therefore, the program for the women with mastectomy should be developed to change their coping mechanism, method of problem solving and Quality of life.

• 한국음향학회지
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• 제19권1호
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• pp.25-31
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• 2000

이 논문에서는 직적법을 이용하여 반복법인 BFGS법의 초기값을 설정하는 알고리즘을 제안하고, 이를 이용하여 점배열음원 형태의 적응형 초음파 트랜스듀서의 최적 지향성합성을 시도했다. 이의 유효성을 확인하기 위하여 부엽의 레벨을 -30dB 이하로 제한한 임의의 빔폭을 갖는 준이상 빔, 회전 빔, 그리고 다중 빔을 보기로 하여 점배열음원으로 형성되는 2차원 음장내의 지향성합성 문제 및 복수의 주파수에 대한 적응 지향성합성 시스템의 적응성 문제를 검토하였다. 수치계산 결과, 제안한 방법은 BFGS법 단독에 의한 지향성합성보다 수렴속도가 빠르고, 목적 지향성합성을 위한 오차개선도 탁월하며, BFGS법과 같은 반복법에서 문제가 되는 초기치의 선택이 필요하지 않다는 장점도 있다. 또한, 제안법은 직접법 단독으로는 불가능한 적응제어도 가능하다.