• 대한기계학회논문집 C: 기술과 교육
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• 제2권1호
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• pp.29-37
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• 2014

본 연구에서는 저 레이놀즈수에서의 Kline-Fogleman 익형과 이를 적용한 날개의 공력특성을 분석하였다. 레이놀즈수 $2.4{\times}10^5$ 이하 영역에서 양항비가 향상됨을 확인하였으며, 특히 레이놀즈수 $1{\times}10^4$에서 양항비가 26% 향상되었다. 양항비 측면에서 Kline-Fogleman 익형이 날개 중앙에 위치하는 것이 가장 유리하며, 전체 날개에 대한 Kline-Fogleman 익형의 면적이 80%일 때 양항비가 20% 증가함을 확인하였다. 이 때 항속시간은 12% 향상되었다. 또한 날개의 구조적 안정성과 양항비 향상률을 고려하였을 때 Kline-Fogleman 익형의 면적을 50%에서 80%사이로 설계하는 것이 유리할 것으로 판단된다.

• 한국항공우주학회지
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• 제40권6호
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• pp.467-474
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• 2012

무인항공기의 정찰 및 정보 수집 능력을 효율적으로 수행하기 위해 장기 체공 능력이 요구된다. 분산 추진 장치는 대형 추진 장치를 복수의 소형 추진 장치들로 대체하여 추력을 얻는 장치이다. 날개의 스팬 길이를 따라 넓게 분포하여 효율이 증가하며, 유동의 흡입을 통해 경계층을 제어하고 출구에서 분사되는 흐름이 항공기에 부착되어 흐르기 때문에 양항비가 증가한다. 본 연구에서는 전익기 융합익기와 분산 추진 장치가 장기 체공 성능을 향상시키는 점에 착안하여 연구를 수행하였다. Eppler 337 에어포일 유닛에 추진 장치의 위치 및 입 출구 가로세로비 변화에 따라 나타나는 공력특성을 분석했다. CFD를 사용하여 공력해석을 수행하였고, 빠른 해석 결과를 얻을 수 있도록 팬 영역에 작동판 이론을 적용하였다. 양항비와 모멘트 비교를 통해 추진 장치의 위치 및 형상을 결정하고자 한다.

• 한국전문물리치료학회지
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• 제29권3호
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• pp.180-186
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• 2022

Background: The craniocervical flexion test (CCFT) was developed for the activation and endurance of deep cervical flexors. However, the muscle thickness and muscle thickness changing ratio of the sternocleidomastoid (SCM) and deep cervical flexor (DCF) muscles in subjects with and without forward head posture (FHP) have not been reported. Objects: To determine the difference in thickness of the SCM and DCF muscles and the difference in the muscle thickness changing ratio between SCM, DCF, and DCF/SCM 20 mmHg and DCF/SCM 30 mmHg between subjects with and without FHP. Methods: Thirty subjects with and without FHP were enrolled. The muscle thickness of the SCM and DCF was measured when maintained at a baseline pressure of 20 mmHg and a maximum pressure of 30 mmHg using a pressure biofeedback unit during the CCFT. Ultrasonography was used to capture images of SCM and DCF muscle thickness during the CCFT, which was calculated using the picture archiving and communication system (PACS). Results: We observed a significant difference within the pressure main effect between SCM and DCF at a baseline pressure of 20 mmHg and a maximum pressure of 30 mmHg (p < 0.05). However, there was no significant difference in the muscle thickness and muscle thickness changing ratio for SCM and DCF during CCFT between subjects with and without FHP. Conclusion: There was no significant difference in the muscle thickness recruitment pattern during CCFT in posture changes between subjects with and without FHP.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• Journal of Nutrition and Health
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• 제43권3호
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• pp.260-272
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• 2010

This study examined how the participation rates contribute to subjects' outcomes after a nutrition education (once/week) and exercise (3 times/week) intervention program for 12 weeks in 44 obese female subjects. The subjects were divided into two groups: high-participator (HP) or low-participator (LP) groups according to their participation levels based on the median visit value (30 visits out of a total of 48 visits). Daily nutrient intakes assessed by a 24-hour recall, body composition, blood lipid profiles and physical fitness were measured at baseline and after 12 weeks. After the intervention, weight, BMI, percent body fat, and the waist-hip ratio were significantly decreased in the HP group. In addition, the HP group had a greater rates of changes in weight (HP group: -6.6% and LP group: -3.1%, p < 0.01), BMI (-7.0% and -3.2%, p < 0.01), percent body fat (-7.8% and -4.2%, p < 0.05), and waist-hip ratio (-3.1% and -0.4%, p < 0.01) compared to the LP group. Energy-adjusted protein, fiber, potassium, vitamin $B_1$, vitamin $B_6$, and vitamin C were significantly increased in the HP group. The HP group showed a significant increase in HDLcholesterol and a decrease in blood pressure, total cholesterol, LDL-cholesterol, triglycerides, and atherogenic index (AI). While the muscle endurance, muscle strength, power, agility and flexibility were significantly increased in the HP group, agility and balance were improved in the LP group. In addition, dietary behavior score was significantly increased and stress score decreased in the HP group compared to the LP group. High participation rates were correlated with the improvement of the nutrient density (protein, fiber, potassium, Vitamin $B_1$, Vitamin $B_2$, Vitamin $B_6$ and folate), anthropometric parameters (body weight, BMI and percent body fat), serum lipid profiles (HDL-cholesterol, Triglyceride, and AI) and physical fitness (muscle endurance) adjusted for age, menopausal status, alcohol drinking, nutritional supplement use and baseline BMI. Our results suggest that high participation in nutrition education and exercise program was effective not only for weight reduction but also for the improvement of physical fitness in obese women.

• 대한물리치료과학회지
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• 제3권2호
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• pp.951-961
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• 1996

Isokinetic exercise is dynamic, but the spped of movement must be regulated so that the resistance is in ratio to the force applied at each point throughout the full range of motion. The purpose of this study is to comparise with trunk flexors & extensors of isokinetic evaluation of pre-exercise and post-exercise in operated laminectomy & disectomy patients. 7 subjects were examined at $120^{\circ}$/sec and $60^{\circ}$/sec each 15 days. The results were as follows; 1. Peak torque of extensors on $60^{\circ}$/sec showed significant difference statistically(p<0.05), but peak torque of flexors on $60^{\circ}$/sec showed no significant difference statistically. 2. Trunk flexors/extensors ratio of peak torque of $60^{\circ}$/sec showed no significant difference ststistically. 3. Peak torque % B.W of extensors on $60^{\circ}$/sec showed significant difference statistically(p<0.05), but peak torque % B.W of flexors on $60^{\circ}$/sec showed no significant difference statistically. 4. TAE of extensors on $60^{\circ}$/sec showed significant difference statistically (p<0.05), but TAE of flexors on $60^{\circ}$/sec showed no significant difference. 5. Total work of flexors & extensors on $60^{\circ}$/sec showed significant difference statistically (p<0.05). 6. Average power of flexors & extensors on $120^{\circ}$/sec showed significant difference statistically(p<0.05). 7. Endurance ratio of flexors & extensors on $120^{\circ}$/sec showed no significant difference statistically. 8. Set total work of flexors & extensors on $120^{\circ}$/sec showed significant difference statistically(p<0.05). 9. TAE of extensors on $120^{\circ}$/sec showed significant difference statistically(p<0.05), TAE of flexors on $120^{\circ}$/sec showed no significant difference statistically. 10. Total work of flexors & extensors on $120^{\circ}$/sec showed significant difference statistically (p<0.05).

• Journal of Korean Vacuum Science & Technology
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• 제4권4호
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• pp.93-96
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• 2000

Microchannel plates (MCPs) have been developed by introducing new materials and process technologies. Main body was made of alumina by programmable punching, laminating, and firing. The channel walls of pore arrays of an MCP were deposited with thin films by electroless copper plating and sol-gel process. Our MCP has advantages such as easy fabrication, durability, high temperature endurance, and applicability to the large size comparing with the conventional MCPs. Experiments on the brightness of an MCP incorporated FED revealed that the FED with a MCP is three to four times brighter than a conventional FED. Moreover, the focusing in a FED is improved. Incorporating an MCP into a FED is one of promising methods to enhance the characteristics of the FED. In addition, amplification yield of the MCP is measured for varying the aspect ratio and the input current.

• 한국생산제조학회지
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• 제22권3호
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• pp.414-420
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• 2013

Research on decreasing the weight of composite sandwich panels is in progress. This paper reports the experimental results for the mechanical behavior of a composite sandwich panel. The skins of sandwich panels were made of glass fiber sheets and plywood matrix composites. Their interior layers consisted of glass fiber pultrusion pipes and gold foam. Experimental tests were performed to obtain the mechanical properties and complex mechanical behavior. Before fatigue tests, tensile tests and 3-point bending tests were carried out to obtain the optimal design and determine their strength and failure mechanisms in the flat-wise position. After the static test, a fatigue test were conducted at a load frequency of 5 Hz, stress ratio (R) of 0.1, and endurance limit for the S-N curve. It showed that the failure modes were related to both the core design and skin failure.

• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.132-138
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• 2016

Korea Aerospace Research Institute (KARI) is developing an electric-driven HALE UAV in order to secure system and operational technologies since 2010. Based on the flight tests and design experiences of the previously developed electric-driven UAVs, KARI has designed EAV-3, a solar-powered HALE UAV. EAV-3 weighs 53kg, the structure weight is 22kg, and features a flexible wing of 19.5m in span with the aspect ratio of 17.4. Designing the main wing and empennage of the EAV-3 the amount of the bending due to the flexible wing, 404mm at 1-G flight condition based on T-800 composite material, and side wind effects due to low cruise speed, $V_{cr}=6m/sec$, are carefully considered. Also, unlike the general aircraft there is no center of gravity shift during the flight because of the EAV-3 is the solar-electric driven UAV. Thus, static margin cuts down to 28.4% and center of gravity moves back to 31% of the Mean Aerodynamic Chord (MAC) comparing with the previously designed the EAV-2 and EAV-2H/2H+ to upgrade the flight performance of the EAV-3.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.331-334
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• 2006

Air foil bearings have been attempted for application to industrial turbo machines, since they have several advantages over oil bearings in terms of endurance, simplicity, environment-friendliness, efficiency, sound and vibration, and small turbo machines with air foil bearings are in the market as the result. Recently, researches on widening the application spectrum of air foil bearings are in progress worldwide. In this paper, a 300 HP class turbo blower using air foil bearings is introduced. The turbo blower has a high speed PMSM(Permanent Magnet Synchronous Motor) driving a compressor, and air flow rate is designed to be $180\;m^3/min$ at pressure ratio of 1.6. The maximum rotational speed is set to 17,000 RPM to maximize the total efficiency with the result that the weight of rotor assembly is 26kg, which is expected to be the largest turbo machine with air foil bearings ever developed in the world.