• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.195-201
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• 2008

In the jet engines on the aircrafts cruising at high altitude over 20 km and subsonic speed, the Reynolds number in terms of the compressor blades becomes very low. In such an operating condition with low Reynolds number, it is widely reported that total pressure loss of the air flow through the compressor cascades increases dramatically due to separation of the boundary layer and the secondary-flow. But the detail of flow mechanisms causes the total pressure loss has not been fully understood yet. In the present study, two series of numerical investigations were conducted to study the effects of Reynolds number on the aerodynamic characteristics of compressor cascades. At first, the incompressible flow fields in the two-dimensional compressor cascade composed of C4 airfoils were numerically simulated with various values of Reynolds number. Compared with the corresponding experimental data, the numerically estimated trend of total pressure loss as a function of Reynolds number showed good agreement with that of experiment. From the visualized numerical results, the thickness of boundary layer and wake were found to increase with the decrease of Reynolds number. Especially at very low Reynolds number, the separation of boundary layer and vortex shedding were observed. The other series, as the preparatory investigation, the flow fields in the transonic compressor, NASA Rotor 37, were simulated under the several conditions, which corresponded to the operation at sea level static and at 10 km of altitude with low density and temperature. It was found that, in the case of operation at high altitude, the separation region on the blade surface became lager, and that the radial and reverse flow around the trailing edge become stronger than those under sea level static condition.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권7호
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• pp.2610-2630
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• 2021

The aim of this paper is to propose the alternative algorithm to finish the process in public key cryptography. In general, the proposed method can be selected to finish both of modular exponentiation and point multiplication. Although this method is not the best method in all cases, it may be the most efficient method when the condition responds well to this approach. Assuming that the binary system of the exponent or the multiplier is considered and it is divided into groups, the binary system is in excellent condition when the number of groups is small. Each group is generated from a number of 0 that is adjacent to each other. The main idea behind the proposed method is to convert the exponent or the multiplier as the subtraction between two integers. For these integers, it is impossible that the bit which is equal to 1 will be assigned in the same position. The experiment is split into two sections. The first section is an experiment to examine the modular exponentiation. The results demonstrate that the cost of completing the modular multiplication is decreased if the number of groups is very small. In tables 7 - 9, four modular multiplications are required when there is one group, although number of bits which are equal to 0 in each table is different. The second component is the experiment to examine the point multiplication process in Elliptic Curves Cryptography. The findings demonstrate that if the number of groups is small, the costs to compute point additions are low. In tables 10 - 12, assigning one group is appeared, number of point addition is one when the multiplier of a point is an even number. However, three-point additions are required when the multiplier is an odd number. As a result, the proposed method is an alternative way that should be used when the number of groups is minimal in order to save the costs.

• 전기학회논문지P
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• 제65권4호
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• pp.262-267
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• 2016

This paper describes a design of a hair drier to improve its performance. the performance of the hair drier can be improved by increasing the wind velocity of its discharge port. the design of the hair drier is accomplished by using the CFD. the validity of design results were verified by comparison with the dry change of the hair drier. In this paper, the initial condition of the applied hair drier is as follows, the number of the blade is 9, the diameter of the suction port is 40[mm], the tip clearance is 12.5[mm], the con angle is $28.5^{\circ}$ and the fan angle is 27.5R. From design results, the enhanced condition of the hair drier can be obtained as follows, the number of the blade is 3, the diameter of the suction port is 50[mm], the tip clearance is 10.5[mm], the con angle is $21.5^{\circ}$ and the fan angle is 75R. At the enhanced condition of the hair drier, the wind velocity of the hair drier is 29[%] increase, and the dry time is 40[%] increase compare to the initial condition of the hair drier.

• Tribology and Lubricants
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• 제33권4호
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• pp.141-147
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• 2017

The vibration data of bearings are very useful for monitoring and determining the condition of the bearings. The defect frequencies of ball bearings have been used for monitoring there condition. However, it is not easy to verify the defect frequencies as the wear progress. Therefore there is a need for an easy method to monitor the damages of bearings in real-time and to observe the variations in vibration characteristics as the wear progress. In this study, a bearing test equipment is constructed to diagnose the damage of bearings. The friction coefficient and vibration data are measured by using a torque sensor and an acceleration sensor, and the correlation between the measured data is analyzed to diagnose the condition of the bearing. We reached the following conclusions from the results. When the ball surface, inner and outer rings of a ball bearing are damaged, the friction coefficient increases to over 0.02 with an adhesion on the surface. Moreover this damage occurs more quickly with an increase in the number of revolutions. In the vibration characteristics, the amplitude of vibration wave appears high with an increase in the friction coefficient. In the high frequency range between 1000 and 2000 Hz, a wide range of frequency components with high amplitude occurs continuously irrespective of the number of revolutions.

• 한국동물위생학회지
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• 제24권3호
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• pp.279-285
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• 2001

The change of the body condition score(BCS) and milk production graph as days in milk by lactation number show that the productivity of cow is on the increase as increase the lactation number, but the health condition is much worse because of the inappropriate nutrition intake. Metabolic profiles test(MPT) results indicate that the early-lactation for directly after the parturition to the peak production of milk during the total lactation period is the time of the more likely to be exposed to lack of energy, protein, minerals. To solve this problem, the early-lactation cows should be sufficiently supplied the required nutrients and should maximum intake the supplied nutrients not to be suddenly decline body weight and BCS from postparturition to the peak production of milk. To maximize the dry matter intake of a cow, there is have got to improve the management of body weight for heifer's skeletal development and in the dry period which is carelessly deal by mostly farms. This study presents that the use of measurement of body weight, graph of body condition score, distribution of milk production, metabolic profiles test in the monitoring for dairy herd health management is very valuable.

• 한국전산유체공학회지
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• 제19권2호
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• pp.40-48
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• 2014

For rarefied gas flow regimes, physical phenomena such as velocity slip and temperature jump occur on the solid body surface. To predict these phenomena accurately, either the Navier-Stokes solver with a slip boundary condition or the direct simulation Monte Carlo method should be used. In the present study, flow simulations of a wedge were conducted in Mach-10 flow of argon gas for several different flow regimes using a two-dimensional Navier-Stokes solver with the Maxwell slip boundary condition. The results of the simulations were compared with those of the direct simulation Monte Carlo method to assess the present method. It was found that the values of the velocity slip and the temperature jump predicted increase as the Knudsen number increases. Also, the results are comparatively reasonable up to the Knudsen number of 0.05.

• Tribology and Lubricants
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• 제37권2호
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• pp.41-47
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• 2021

An experimental device was developed for analysis of hydraulic oil characteristics with dielectric constant sensors. Online analysis is the most effective method of the three methods used for analyzing lubricant oils. This is because it can monitor the machine condition effectively using oil sensors in real time without requiring excellent analysis skill and eliminates human errors. Determining the oil quality usually requires complex laboratory equipment for measuring factors such as density, viscosity, base number, acid number, water content, additive, and wear debris. However, the electric constant is another indicator of oil quality that can be measured on-site. The electric constant is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has a vacuum as its dielectric. The electric constant affects the factors such as the base oil, additive, temperature, electric field frequency, water content, and contaminants. In this study, the tendency of the electric constant is investigated with a variation of temperature, water content, and dust weight. The experimental device can control working temperature and mix the contaminants with oil. A machine condition monitoring program developed to analyze hydraulic oil is described. This program provides graph and digital values with variation of time. Moreover, it includes an alarm system for when the oil condition is bad.

• 한국노년학
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• 제30권1호
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• pp.179-194
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• 2010

본 연구는 만성신부전으로 혈액투석치료를 받고 있는 노인의 건강관련 삶의 질을 고찰해보고, 대상자들의 일반적 특성, 건강상태에 대한 인식, 그리고 건강관련 삶의 질 간의 관계분석을 통해 혈액투석노인의 건강관련 삶의 질에 대한 폭넓은 이해와 함께 건강관련 삶의 질을 향상시키기 위한 체계적인 방안을 모색해 보고자 시도되었다. 연구 대상은 수도권의 인공신장실 부설 병의원 30개에서 현재 1개월 이상 혈액투석치료를 받고 있는 65세 이상 노인으로 연구 참여에 동의한 443명이었다. 조사도구는 건강관련 삶의 질 척도로 SF-36 (Medical Outcome Survey 36-Item Short Form)을 사용하여 건강상태의 변화인식과 건강관련 삶의 질을 측정하였다. 수집된 자료는 변인간의 인과관계 분석을 위해 기술통계분석, 상관관계분석, 신뢰도분석, t-test, ANOVA 및 회귀분석 등에 사용되었다. 연구결과를 요약하면 다음과 같았다. 첫째, 혈액투석노인의 건강관련 삶의 질 총 평점은 57.67이었다. 혈액투석노인의 건강상태에 대한 인식을 작년과 비교하여, 악화된 경우에는 건강관련 삶의 질은 50.63점이었으나, 호전된 노인의 경우에는 62.04점으로 높게 나타났다. 둘째, 혈액투석 노인들 간의 건강관련 삶의 질의 점수는 일반적인 특성 중 성별, 교육정도, 배우자 동거유무, 주수발자, 동반질환수 등에 따라 통계적으로 유의미한 차이를 보이고 있었으며, 또한 건강상태에 대한 인식에 따라 동반질환 수에 있어서도 통계적으로 유의미한 차이를 보였다. 셋째, 혈액투석노인의 건강상태에 대한 인식과 건강관련 삶의 질은 정(+)의 상관관계로 건강상태가 호전 된 것으로 인식할 때 건강관련 삶의 질은 높았고, 동반질환수와 건강관련 삶의 질은 부(-)의 상관관계로 동반질환수가 적을수록 건강관련 삶의 질은 높게 나타났다. 이러한 결과를 바탕으로 혈액투석노인의 건강관련 삶의 질 개선을 위해서는 특성을 고려한 적절한 혈액투석치료와 자기관리를 통해 현재의 건강상태를 유지 증진시키는 것이 무엇보다도 중요하다. 그러므로 적절한 투석치료를 위해 의료서비스를 확대하고, 자기관리를 위한 치료식이, 투약, 일상생활을 영위할 수 있는 생활서비스와 역할상실에 따른 지지와 사회적 고립에 따른 사회적 욕구충족이 반영되는 보건복지통합서비스가 실시되어야 할 것이다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.365-370
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• 2001

This study is the selection of optimum forming condition for RP system using ADS. Program using ADS reduces the required time for feedback between design and manufacturing of workpiece. When we produce rapid prototype using RP system, we investigate the relationship between Facetres in system variable number of AutoCAD and circularity of rapid prototype, and we will find optimum forming condition in RP system.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.996-999
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• 2001

This study is the election of optimum forming condition for RP system using ADS. Program using ADS reduces the required time for feedback between design and manufacturing of workpiece. When we produce rapid prototype using RP system, we investigate the relationship between Facetres in system variable number of AutoCAD and circularity of rapid prototype, and we will find optimum forming condition in RP system.