• 대한기계학회논문집 C: 기술과 교육
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• 제3권3호
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• pp.217-223
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• 2015

유체채널 내에서의 미세입자의 패터닝은 생물 및 의료 응용분야에서 활용될 가치가 높은 응용 기술이다. 본 연구는 미세유체 채널 내에서 구조물 없이 외부 자석의 배열만을 이용한 미세입자 패터닝 방법을 제안한다. 자석의 같은 극과 서로 다른 극끼리의 배열을 이용한 일렬 배열, 적층 배열 등을 고안하여, 다양한 미세입자 패터닝에 실험적으로 적용하였다. 서로 같은 극끼리의 배열은 입자 포획에 쉽게 적용 가능하여, 독립적 배열이 가능하였다. 특히 적층 배열은 다양한 패터닝을 할 수 있음을 확인할 수 있었다. 자기력 1.08mT 수준에서까지 자석 배열에 의한 일정한 패턴을 관찰할 수 있었고, 패터닝된 입자들은 20 ml/hr 의 유체 속도에서도 안정하게 유지되었다. 본 연구는 간단하면서도 자성 입자의 다양한 패터닝을 가능케 하는 방법으로 면역자기성 입자를 이용한 의학/바이오 분야로의 폭넓은 응용을 기대케 한다.

• Progress in Superconductivity
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• 제11권1호
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• pp.57-61
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• 2009

A superconductor flywheel energy storage(SFES) system is mainly act an electro-mechanical battery which transfers mechanical energy into electrical form and vice versa. SFES system consists of a pair of non-contacting High Temperature Superconductor (HTS) bearings with a very low frictional loss. But it is essential to design an efficient HTS bearing considering with rotor dynamic properties through correct calculation of stiffness in order to support a huge composite flywheel rotor with high energy storage density. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate HTS bearing magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measured axial / radial stiffness and found bearing stiffness can be easily changed by activated vibration direction between PM and HTS bulk. These results are used to determine the optimal design for a 10 kWh SFES.

• Tribology and Lubricants
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• 제31권5호
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• pp.221-228
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• 2015

It is possible to prevent a piston from contacting the cylinder by changing the shape of the piston or by applying micro-textures, such as micro-grooves or micro-holes, over the piston surface. Usually, the minimum radial clearance reaches its minimum value at the beginning of the suction stroke because the pressure around the piston is low and almost axisymmetric such that the net pressure force on the piston is not sufficiently high to support the piston from touching the cylinder. In this study, we apply a series of saw-tooth-shaped grooves on the piston surface, and numerically investigate the effects of groove depth, groove angle, and the number of grooves with radial clearance variations using a finite difference method. We conduct a dynamic analysis of the piston for various changes in groove geometries to obtain the minimum radial clearance variation for the entire compression cycle. The minimum radial clearance increases while friction loss decreases when we apply the series of saw-tooth-shaped grooves on the piston. In addition, we analyze the impact of the change in the groove shape variable due to changes in radial clearance. Leakage variations are relevant to radial clearance, but have almost no effect on the groove parameters.

• 한국운동역학회지
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• 제18권4호
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• pp.201-207
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• 2008

본 연구는 2003년 대구 유니버시아드 대회의 도마 경기에서 Roche 기술 동작을 실시한 세 명의 남자체조선수를 대상으로 연구되어진 결과(2005, 여홍철)를 운동역학적 분석으로 재검토하여 경기력 향상에 기여하고자 하는데 목적이 있다. 각 단계별 각운동량 결과에서는 도마 접촉시 반시계 방향으로 각운동량이 클수록 제2비약 즉 peak시 회전력을 방해하는 요인으로 나타났다. 가장 큰 신체각을 나타낸 국면은 VTD이며 가장 작은 신체각은 BTO 국면으로 나타났으며 도마 접촉 국면과 이륙 국면에서 개인차가 가장 큰 것으로 나타났다. Roche 기술은 앞으로 체공 높이도 중요하지만 앞으로 회전력을 빠르게 증가시켜야 하므로 투사각이 쿠에르보 비틀기 기술보다 작게 나타났으며 각속도 결과에서는 제 2비약에서 앞공중돌기 2회전 동작을 진행하고 있는 peak가 가장 큰 각속도를 나타내고 있다. 이러한 결과에 영향을 미치는 국면은 BTO부터 VTO 국면으로 각속도의 결과로 인해 각운동량에 영향을 미치는 것으로 사료된다.

• Tribology and Lubricants
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• 제34권2호
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• pp.49-54
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• 2018

Hydraulic reciprocating seal has been widely used to prevent fluid leakage in hydraulic systems. Also, hydraulic reciprocating seal plays a significant role to provide lubricant film at contacting interface to minimize tribological problems due to sliding with counter material. To predict lifetime of hydraulic reciprocating seal, quantitative understanding of wear characteristics with respect to operating conditions such as normal force and sliding speed is needed. In this work, effect of sliding speed on wear of polyurethane (PU) hydraulic reciprocating seal were experimentally investigated using a pin-on-disk tribo-tester. The wear characteristics of PU specimens were quantitatively determined by comparing the confocal microscope data before and after test. It was found that the wear rate of PU specimens decreased from $4.9{\times}10^{-11}mm^3$ to $1.1{\times}10^{-11}mm^3/Nm$ as sliding speed increased from 120 mm/s to 940 mm/s. Also, it was observed that the friction decreased slightly as the sliding speed increased. Improvement of lubrication state with increasing sliding speed was likely to be responsible for this enhanced friction and wear characteristics. This result also suggests that decrease in sliding distance between PU elastomer and counter materials at lower sliding speed is preferred. Furthermore, the quantitative assessment of wear characteristics of PU specimen may be useful in prediction of lifetime of PU hydraulic reciprocating seal if the allowed degree of wear for failure of the seal is provided.

• Progress in Superconductivity
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• 제10권1호
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• pp.55-59
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• 2008

A Superconductor Flywheel Energy Storage System(SFES) mainly consists of a pair of non-contacting High Temperature Superconductor(HTS) bearings that provide very low frictional losses, a composite flywheel with high energy storage density. The HTS bearings, which offer dynamic stability without active control, are the key technology that distinguishes the SFES from other flywheel energy storage devices, and great effort is being put into developing this technology. The Superconductor Journal Bearing(SJB) mainly consists of HTS bulks and a stator, which holds the HTS bulks and also acts as a cold head. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate SJB magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measure stiffness in static condition and the results are used to determine the optimal number of HTS bulks for a 100kWh SFES.

• Tribology and Lubricants
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• 제33권5호
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• pp.220-227
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• 2017

In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.354-361
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• 2005

In high speed cutting process, due to the friction between the tool and workpiece, a temperature rise of contacting part is serious. It need to develop cutting tool for overcoming such a poor condition. So now, some studies, the optimization of tool shapes, the fine grains of tool material, multi-layer coating of tools are processing. If mirror finishing on the tool is processed, there is advantage of relation between chip and tool, because of less friction, and also tool's lift would be increased. As a result mirror like finishing is expected efficient enhancement of tool. Generally, it is too difficult to process by a general way for tools of complex shapes, it is required a new method to process such complex shape tools. The magnetic fluid polishing technique can polish the workpiece of complex shape, because the polishing method which polishes as compress the workpiece by the magnetism abrasives to arrange to the linear according to the line of magnetic force. In this paper, We polished the surface of the high speed cutting tool using the magnetic fluid polishing technique, to enhance the performance of the high speed cutting tool.

• Nano
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• 제13권11호
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• pp.1850128.1-1850128.10
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• 2018

Glutathione (GSH), the protective agent and reducing agent, has been widely used to prepare gold nanoclusters (GSH-Au NCs) with stable fluorescence properties and negative charge of the surface. Meanwhile, polyethyleneimine (PEI) was used as the modification agent to synthesize magnetic ferroferric oxide nanoparticles ($Fe_3O_4$) with fantastic dispersibility and positive charge of the surface. Based on the electrostatic adsorption force, magnetic nano-$Fe_3O_4@GSH-Au$ NCs core-shell microspheres composed of magnetic $Fe_3O_4$ nanoparticles modified by PEI as the core and GSH-Au NCs as the shell were assembled. The prepared $Fe_3O_4@GSH-Au$ NCs microspheres harbored a uniform size (88.6 nm), high magnetization (29.2 emu/g) and excellent fluorescence. Due to the coordination bond action between Au atom and sulfhydryl (-SH), amino ($-NH_2$), carboxyl (-COOH) in sweat, $Fe_3O_4@GSH-Au$ NCs could combine with latent fingerprints. In addition, $Fe_3O_4@GSH-Au$ NCs with good fluorescence and magnetism could detect fingerprints on various objects. Significantly, the powders were not easy to suspend in the air, which avoided the damage to the health of forensic experts and the fingerprints by only powder contacting. Above all, $Fe_3O_4@GSH-Au$ NCs was successfully applied to the latent fingerprint visualization, which has great potential in forensic science.

• 한국위성정보통신학회논문지
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• 제8권4호
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• pp.150-158
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• 2013

국내에서 위성이나 잔해물이 대기권으로 진입하는 상황을 공식적으로 감시한 것은 1983년 1월 23일에 본체가, 동년 2월 7일에 핵연료 코어가 추락한 구 소비에트 연방의 위성 코스모스 1402호의 상황주시를 위해 구)과학기술처가 구성한 추락상황대책반 운영이 최초이다. 이 후에 2001년 대기권에 재진입한 러시아 우주정거장 미르의 폐기대책반이 구)과학기술부 주관으로 한국천문연구원과 한국항공우주연구원 등 관련기관의 지원으로 운영되었고, 2011년 9월 24일에 있었던 미국의 고층대기기상위성인 UARS (Upper Atmosphere Research Satellite)의 추락이 한국천문연구원에 의해서 분석되었다. 빈번해진 폐기위성 및 우주잔해물의 대기권 재진입 상황에 따라 2011년 10월 14일 구)교육과학기술부와 우주 관련 기관인 한국천문연구원과 한국항공연구원의 관련 전문가 그룹이 대책회의를 거쳐서 위성추락상황실을 한국천문연구원 내에 설치하고 한국천문연구원 주관으로 운영하기로 결정하였다. 그 결과 이 위성추락상황실은 2011년 10월에는 독일 뢴트겐 위성, 2012년 1월에는 러시아 화성 탐사선 포브스 그룬트, 2013년 1월에는 러시아 위성 코스모스 1484, 그리고 2013년 11월에는 유럽연합의 측지위성 고체 (GOCE)의 대기권 재진입을 감시, 자료 분석, 관련기관 보고, 언론 자료 배포 및 대국민 상황 전파를 실시하였다.