• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1690-1695
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• 2003

In order to investigate the mechanism of brake squeal noise, the sound and vibration of an actua1 brake system were measured using a brake dynamometer. The experimental results show that disc run-out varies with brake line pressure and the factor of squeal generation is the run-out due to the misalignment of brake disk. A three degrees of freedom friction model is developed for the disk brake system where the run-out effect and nonlinear friction characteristic are considered. The results of numerical analysis of the model agree well with the experimental results. Also, the stability analysis of the model was performed to predict the generation of brake squeal due to the design parameter modification of brake systems. The results show that the squeal generation depends on the nm-out rather than the friction characteristic between the pad and the disk of brake.

• 한국자동차공학회논문집
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• 제22권5호
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• 설비공학논문집
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• 제23권12호
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• pp.805-814
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• 2011

In the present study, the detailed flow structure and heat transfer characteristics in the newly-designed heat transfer surface geometry were investigated. The surface geometry proposed in the present study is a traditional dimple structure combining with a protrusion inside the dimple, which is named a protrusion-in-dimple in this study. The basic idea underlying the present surface geometry is to enhance the flow mixing and the corresponding heat transfer in the flow re-circulating region generated by a conventional dimple cavity. The present study was performed by the direct numerical simulation at a Reynolds number of 2800 based on mean velocity and channel height and Prandtl number of 0.71. Three different protrusion heights for protrusion-in-dimples were considered as the main design parameter of the present study. The calculated pressure drop and heat transfer capacity were assessed in terms of the Fanning friction factor and Colburn j factor. The overall performances estimated in terms of the volume and area goodness factor for protrusion-in-dimple cases were higher than the conventional dimple case.

• 동서간호학연구지
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• 제14권2호
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• pp.47-53
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• 2008

Purpose: Metabolic syndrome (also known as insulin resistance syndrome) represents a constellation of hypertriglyceridemia, hypertension, impaired glucose tolerance, and obesity. Presently, the influence of various factors on metabolic syndrome was assessed in patients of a university hospital comprehensive medical examination center. Methods: Age, sex, blood pressure, height, weight, triglyceride level, high-density lipoprotein cholesterol, and glucose levels were measured in 67 people (37 males and 30 females). These factors were correlated with tobacco use, alcohol consumption, and exercise habits. Metabolic syndrome and abdominal obesity were assessed according to NCEP-ATP III criteria and the Asia-Pacific guidelines (male obesity defined as a waist circumference exceeding 90 cm), respectively. Data was analyzed using t-test, 2-test, and logistic regression. Results: Respective percentages were: tobacco use (14.9% of the 67 people), no tobacco use (85.1%), alcohol consumption (62.7%), no alcohol consumption (37.3%), regular exercise (25.4%), no regular exercise (74.6%). Logistic regression analysis revealed a gender-related odds ratio of 2.3 for metabolic syndrome and no exercise. Conclusions: Weight reduction and physical exercise may decrease the prevalence of metabolic syndrome. Early identification of metabolic syndrome and risk factor modification is prudent in cases of obesity, diabetes, hyperlipidemia, and hypertension.

• Wind and Structures
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• 제18권1호
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• pp.83-101
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• 2014

Lamps installed on stay cables of cable-stayed bridges may alter the configuration of circular cross section of the cables and therefore result in aerodynamically unstable cable vibrations. The background of this study is a preliminary design of lamp installation on the cable-stayed He-dong Bridge in Guangzhou, China. Force measurements and dynamic response measurements wind tunnel tests were carried out to validate the possibility of cable galloping vibrations. It is observed that galloping will occur and the critical wind velocity is far less than the design wind velocity at Guangzhou City stipulated in Chinese Code. Numerical simulations utilizing software ANSYS CFX were subsequently performed and almost the same results as the wind tunnel tests were obtained. Moreover, the pressure and velocity contours around cable-lamp model obtained from numerical simulations indicated that the upstream steel wire in the preliminary design is the key factor for the onset of the galloping vibrations. A modification for the preliminary design of lamp installation, which suggests to remove the two parallel steel wires, is proposed, and it effectiveness is validated in further wind tunnel tests.

• 한국정밀공학회지
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• 제12권8호
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• 천문학회지
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• 제45권5호
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• pp.127-138
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• 2012

We explore how wave-particle interactions affect diffusive shock acceleration (DSA) at astrophysical shocks by performing time-dependent kinetic simulations, in which phenomenological models for magnetic field amplification (MFA), Alfv$\acute{e}$nic drift, thermal leakage injection, Bohm-like diffusion, and a free escape boundary are implemented. If the injection fraction of cosmic-ray (CR) particles is ${\xi}$ > $2{\times}10^{-4}$, for the shock parameters relevant for young supernova remnants, DSA is efficient enough to develop a significant shock precursor due to CR feedback, and magnetic field can be amplified up to a factor of 20 via CR streaming instability in the upstream region. If scattering centers drift with Alfv$\acute{e}$n speed in the amplified magnetic field, the CR energy spectrum can be steepened significantly and the acceleration efficiency is reduced. Nonlinear DSA with self-consistent MFA and Alfv$\acute{e}$nic drift predicts that the postshock CR pressure saturates roughly at ~10 % of the shock ram pressure for strong shocks with a sonic Mach number ranging $20{\leq}M_s{\leq}100$. Since the amplified magnetic field follows the flow modification in the precursor, the low energy end of the particle spectrum is softened much more than the high energy end. As a result, the concave curvature in the energy spectra does not disappear entirely even with the help of Alfv$\acute{e}$nic drift. For shocks with a moderate Alfv$\acute{e}$n Mach number ($M_A$ < 10), the accelerated CR spectrum can become as steep as $E^{-2.1}$ - $E^{-2.3}$, which is more consistent with the observed CR spectrum and gamma-ray photon spectrum of several young supernova remnants.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.44-45
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• 2010

We are currently conducting studies on culturing and biocompatibility assessment of various cells such as neural stem cells and induced pluripotent stem cells(IPS cells) on carbon nanotube (CNT), on nerve regeneration electrodes, and on silicon wafers with a focus on developing nerve integrated CNT based bio devices for interfacing with living organisms, in order to develop brain-machine interfaces (BMI). In addition, we are carried out the chemical modification of carbon nanotube (mainly SWCNTs)-based bio-nanosensors by the plasma ion irradiation (plasma activation) method, and provide a characteristic evaluation of a bio-nanosensor using bovine serum albumin (BSA)/anti-BSA binding and oligonucleotide hybridization. On the other hand, the researches in the case of "novel plasma" have been widely conducted in the fields of chemistry, solid physics, and nanomaterial science. From the above-mentioned background, we are conducting basic experiments on direct irradiation of body tissues and cells using a micro-spot atmospheric pressure plasma source. The device is a coaxial structure having a tungsten wire installed inside a glass capillary, and a grounded ring electrode wrapped on the outside. The conditions of plasma generation are as follows: applied voltage: 5-9 kV, frequency: 1-3 kHz, helium (He) gas flow: 1-1.5 L/min, and plasma irradiation time: 1-300 sec. The experiment was conducted by preparing a culture medium containing mouse fibroblasts (NIH3T3) on a culture dish. A culture dish irradiated with plasma was introduced into a $CO_2$-incubator. The small animals used in the experiment involving plasma irradiation into living tissue were rat, rabbit, and pick and are deeply anesthetized with the gas anesthesia. According to the dependency of cell numbers against the plasma irradiation time, when only He gas was flowed, the growth of cells was inhibited as the floatation of cells caused by gas agitation inside the culture was promoted. On the other hand, there was no floatation of cells and healthy growth was observed when plasma was irradiated. Furthermore, in an experiment testing the effects of plasma irradiation on rats that were artificially given burn wounds, no evidence of electric shock injuries was found in the irradiated areas. In fact, the observed evidence of healing and improvements of the burn wounds suggested the presence of healing effects due to the growth factors in the tissues. Therefore, it appears that the interaction due to ion/radicalcollisions causes a substantial effect on the proliferation of growth factors such as epidermal growth factor (EGF), nerve growth factor (NGF), and transforming growth factor (TGF) that are present in the cells.

• 대한의생명과학회지
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• 제19권1호
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• pp.61-69
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• 2013

The aim of this study was to evaluate the effect of exercise-based cardiac rehabilitation on pro- and anti-inflammatory markers in patients with acute coronary syndrome (ACS). ACS patients who underwent percutaneous coronary intervention (PCI) and took medicine during phase II of rehabilitation were recruited for study. Subjects were divided into two groups; exercise group (EX, n=21) and a non-exercise group (non-EX, n=13). Supervised exercise program in hospital consisted of treadmill and bicycle exercise was performed three times per week for 6 weeks. Patients of EX received individual counseling, including knowledge of heart disease, risk factor modification, and physical training. Cardiopulmonary fitness, body composition, and biochemical blood factors were analyzed before and after experiment. There was no significant difference in serum levels of hs-CRP and TGF-${\beta}1$ between groups, and between time intervals. But there was a significant decrease in serum levels of IL-18 (P<.001). And there was a significant increase in ratio of IL-18 to IL-10 (P<.01) and serum levels of IL-10 (P<.001). After cardiac rehabilitation, there was significant increase in exercise duration (P<.001), maximal oxygen uptake ($VO_{2peak}$; P<.001) and decrease in submaximal rate-pressure product (sRPP; P<.05) in EX. In conclusion, exercise-based cardiac rehabilitation during phase II in patients with ACS after PCI decreased serum IL-18 (pro-inflammatory) content and ratio of IL-18 to IL-10 in serum (highly related with disease recurrence), and increased serum IL-10 (anti-inflammatory) content. In addition, it led to improved cardiopulmonary fitness.

• 한국임상수의학회지
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• 제30권2호
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• pp.95-99
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• 2013

본 연구는 정상개에서의 계절에 따른 안압의 변화를 평가하기 위해서 실시되었다. 총 474마리의 안질환이 없는 삽살개의 양안에 대해서 편평안압계(Tonopen$^{(R)}$ XL)를 이용해서 안압을 측정하였다. 측정된 결과를 바탕으로, 안압에 영향을 줄 것으로 예상되는 요소의 유의성과, 각 요소의 군내 차이를 통게적 방법을 통하여 검증을 실시 하였다. 전체 삽살개의 평균 안압 및 표준 편차는 $19.1{\pm}3.7$ mmHg (범위: 8 to 28 mmHg) 이었다. 계절적 요소에서만 안압 변화에 대한 유의성이 검증 되었고(P < 0.001), 그 외 나이, 성별, 모색과 관련된 유의성은 확인되지 않았다. 겨울에 측정된 평균 안압 수치($20.4{\pm}3.4$ mmHg)와 여름에 측정된 평균 안압 수치($17.1{\pm}3.6$ mmHg) 는 다른 계절의 평균 안압에 비하여서 신뢰구간 내로 각각 높게 그리고 낮게 측정 되었다. 이상의 결과를 바탕으로 계절적 변화는 정상 개의 안압에 영향을 줄 것으로 판단되며, 본 연구는 후속되는 수의 안과 연구와 수의 안과 임상에 유용한 자료가 될 것으로 사료된다.