• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1388-1393
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• 2004

Investigators have been perplexed with the thermal phenomena behind the recently discovered nanofluids, fluids with unprecedented stability of suspended nanoparticles although huge difference in the density of nanoparticles and fluid. For example, nanofluids have anomalously high thermal conductivities at very low fraction, strongly temperature-dependent and size-dependent conductivities, and three-fold higher critical heat flux than that of base fluids. Traditional conductivity theories such as the Maxwell or other macroscale approaches cannot explain why nanofluids have these intriguing features. So in this paper, we devise a theoretical model that accounts for the fundamental role of dynamic nanoparticles in nanofluids. The proposed model not only captures the concentration and temperature-dependent conductivity, but also predicts strongly size-dependent conductivity. Furthermore, we physically explain the new phenomena for nanofluids. In addition, based on a proposed model, the effects of various parameters such as the ratio of thermal conductivity of nanofluids to that of a base fluid, volume fraction, nanoparticle size, and temperature on the thermal conductivities of nanofluids are investigated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.55-58
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• 2005

During braking at a train, thermal energy is generated due to the frictions between disk and lining and wheel and shoe. In general, the braking transfers the kinetic energy into thermal energy. Therefore, the frictional characteristics are varied according to the braking force, the thermal resistance, and the thermostable, etc. Using a Dynamo testing we have studied the frictional characteristics and the thermal distribution to investigate a stable speed and to improve the testing method through comparing and analysing in the measurement of the thermocouple temperature and infrared camera.

• 한국정밀공학회지
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• 제17권11호
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• pp.115-121
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• 2000

In this paper, track tension estimation methods are developed for tracked vehicles which are subject to various maneuvering tasks such as turning and pivoting on flat road. The information of the track tension is very important for the tracked vehicles because the track tension is closely related to the maneuverability and the durability of the tracked vehicles. Kinetic models for the six road-wheels are obtained and used for calculating the track tension around the sprocket. This method does not require the tuning of the turning resistance, which makes it difficult to estimate the track tension in turning. The tension estimation performance of the proposed methods is verified through the simulation of the Multi-body Dynamics tool. The simulation results demonstrate the effectiveness of the proposed method under steering and pivoting of the tracked vehicles.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.57-68
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• 2018

The main objective of this study is to prepare the bionanocomposite films using mungbean starch (MBS), PVA, ZnS, and plasticizers, and to evaluate the physical properties, thermal stability, and photocatalytic activity. The bionanocomposite films were cross-linked by heat-curing process. The ZnS and bionanocomposite films were characterized by FT-IR, XRD, and SEM. The results indicated that the mechanical properties and water resistance enhanced up to 1.2-1.5 times by the addition of nano-ZnS particles, and the thermal stability was improved by the addition of nano-ZnS particles. The photocatalytic activity of the bionanocomposite films added nano-ZnS particles was examined using bisphenol A (BPA) and methyl orange (MO). In addition, the photodegradation efficiency of BPA and MO was evaluated using the pseudo-first order kinetic model (PFOK).

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1761-1765
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• 2008

In the braking of a railroad car, mechanical brake systems using wheel tread and brake disk are applied as well as electrical brake systems by regenerator and rheostat. It is very important to consider the frictional characteristic because kinetic energy of the vehicle is dissipated as converted thermal energy through friction between disk and brake pad during disk braking. A friction coefficient and wear characteristic are decided from the interrelationship of disk and friction material in the disk brake system. Lab-scale dynamometer test on developed brake disk materials for increasing heat resistance was performed in this study. Each candidate material was tested at various braking speeds and pressures and we obtained the friction coefficient and wear characteristic. And we executed comparative evaluation of the result from the test.

• 한국식품영양학회지
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• 제16권3호
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• pp.180-186
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• 2003

가열살균 처리시의 온도값을 이용하여 다양한 미생물들의 가열살균 효과를 D값, z값 등의 미생물 내열성 특성치와 kinetic 모델 및 수식을 이용하여 살균치 계산을 컴퓨터를 이용하여 수행함으로써 target 미생물의 살균정도를 예측하고자, Excel과 Visual Basic을 연동하여 작성된 시스템으로 Excel을 기본으로 사용한 프로그램을 개발하였다. 가열살균 target 미생물을 선택하고자 야채식품을 기반으로 하는 식품에서의 미생물을 검토하여, 내열성인 가장 큰 호기성 포자형성균인 Bacillus spp. 계통이 산을 형성하여 맛 등의 품질을 저하시켜 변패를 유발하며, 위생적인 면에서 포자수를 줄이거나 사멸할 필요가 있어서 선택하였다. 병원성 균 중에서 $D_{121.1}$이 0.0065분, z값이 7.8$^{\circ}C$인 Bacillus cereus와 부패현상 관련 균 중에서 $D_{121.1}$이 0.5분, z값이 12$^{\circ}C$인 Bacillus subtilis를 대상으로 해서 개발되었으며, 필요시에는 D값과 z값을 직접 대입하므로서, 여러 가지 미생물에 대해서도 적용이 가능하게 하였다.

• 한국운동역학회지
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• 제16권2호
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• pp.121-134
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• 2006

The purpose of this study was to analyze the effect of different types of rehabilitation training program on the kinetic and kinematic parameters during sit-to-stand movement(STS) in chronic stroke patients. Two groups of hemiparetic patients, experimental and control, participated in the study. The experimental group participated in a 10-week training program (three sessions/wk, $1{\sim}1.5\;hr/session$) consisting of a warm-up, aerobic exercises, lower extremity strengthening. and a cool-down. The control group participated in an aerobic exercise. Three dimensional kinematic analysis and force platform; were used to analyze the duration of STS, lower extremity angle, and weight bearing ability. The experimental group which had more strength of lower extremity displayed decrease in duration of STS. However, the control group showed increases in duration during sit-to-stand movement. The control group flexed their trunk more than the group did Therefore, it took more time to extend their trunk during STS. The duration in sit-to-stand was affected by the strength of lower extremity and the angle of trunk movement. The angles of ankle and knee joint had an influenced on duration of STS. The post experimental group performed with their feet near the front leg of the chair during sit-to-stand, therefore the duration was decreased. The repetitive sit-to-stand movements as a resistance exercise was effective to hemiparetic patients in learning mechanism of sit-to-stand. The control group showed decreased differences in the vertical ground reaction forces between paretic and non-paretic limbs. Their training program included strengthening exercise that may help improving weight bearing ability. The control group showed increases in the center of pressure in the anteroposterior and mediolateral displacement. This means that the stability of movement was low in the control group. Their training program which combined aerobic and strengthening exercises that are more effective to improve the stability of movement.

• 상하수도학회지
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• 제33권2호
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• pp.111-119
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• 2019

Electro-coagulation process has been gained an attention recently because it could overcome the membrane fouling problems in MBR(Membrane bio-reactor). Effect of the key operational parameters in electro-coagulation, current density(${\rho}_i$) and contact time(t) on membrane fouling reduction was investigated in this study. A kinetic model for ${\rho}_i$ and t required to reduce the membrane fouling was suggested under different MLSS(mixed liquor suspended solids) concentration. Total 48 batch type experiments of electro-coagulations under different sets of current densities(2.5, 6, 12 and $24A/m^2$), contact times(0, 2, 6 and 12 hr) and MLSS concentration(4500, 6500 and 8500mg/L) were carried out. After each electro-coagulation under different conditions, a series of membrane filtration was performed to get information on how much of membrane fouling was reduced. The membrane fouling decreased as the ${\rho}_i$ and t increased but as MLSS decreased. Total fouling resistances, Rt (=Rc+Rf) were calculated and compared to those of the controls (Ro), which were obtained from the experiments without electro-coagulation. A kinetic approach for the fouling reduction rate (Rt/Ro) was carried out and three equations under different MLSS concentration were suggested: i) ${\rho}_i^{0.39}t=3.5$ (MLSS=4500 mg/L), ii) ${\rho}_i^{0.46}t=7.0$ (MLSS=6500 mg/L), iii) ${\rho}_i^{0.74}t=10.5$ (MLSS=8500 mg/L). These equations state that the product of ${\rho}_i$ and t needed to reduce the fouling in certain amounts (in this study, 10% of fouling reduction) is always constant.

• 한국구조물진단유지관리공학회 논문집
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• 제19권4호
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• pp.92-100
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• 2015

본 연구는 폴리비닐 알코올 섬유 및 강섬유를 체적비율로 1.5% 혼입한 고인성 섬유보강 시멘트복합체에 대한 비상체의 고속충돌시험을 실시하고, 충돌조건에 따른 파괴특성을 실험적으로 검토하는 것을 목적으로 하였다. 비상체의 충돌에 의한 고인성 섬유보강 시멘트복합체의 파괴특성을 평가하기 위하여 화약압력식 충격시험장치를 활용하였으며, 충돌속도의 범위는 약 150~1,000m/s로 설정하였다. 파괴특성에 대한 평가결과, 고인성 섬유보강 시멘트복합체는 섬유를 혼입하지 않은 Plain시험체의 약 3배 이상의 비상체 운동에너지가 작용하는 범위에서도 표면관입의 파괴등급으로 평가되었으며, 시험체가 파단되지 않는 내충격성능이 확인 되었다. 또한, 충돌시험 전후에 대한 시험체의 질량감소율의 경우, Plain시험체는 비상체의 운동에너지의 증가율과 비례적인 관계를 보였지만, 고인성 섬유보강 시멘트복합체는 비상체의 운동에너지의 영향을 크게 받지 않는 것으로 나타났다. 특히, 이와 같은 경향은 시험체 배면의 파괴특성과 밀접한 관계를 가지며, S시험체에 비해 PVA시험체의 배면박리 억제효율이 큰 것으로 평가되었다. 한편, 국부손상에 대한 표면관입깊이 및 배면박리깊이의 관계를 검토한 결과, 고인성 섬유보강 시멘트복합체는 Plain과 달리 시험체 단면의 중앙선을 기준으로 배면에 가까운 영역에서 배면박리가 발생하는 것을 알 수 있었다. 본 연구를 통해 비상체의 충돌에 대한 고인성 섬유보강 시멘트복합체의 주요 파괴거동이 검토되었으며, Plain과 비교하여 내충격성능의 향상을 명확히 확인하였다.

• Journal of Microbiology and Biotechnology
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• 제18권3호
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• pp.410-416
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• 2008

The gene SfXyn10, which encodes a protease-resistant xylanase, was isolated using colony PCR screening from a genomic library of a feather-degrading bacterial strain Streptomyces fradiae var. k11. The full-length gene consists of 1,437bp and encodes 479 amino acids, which includes 41 residues of a putative signal peptide at its N terminus. The amino acid sequence shares the highest similarity (80%) to the endo-1,4-${\beta}$-xylanase from Streptomyces coelicolor A3, which belongs to the glycoside hydrolase family 10. The gene fragment encoding the mature xylanase was expressed in Escherichia coli BL21 (DE3). The recombinant protein was purified to homogeneity by acetone precipitation and anion-exchange chromatography, and subsequently characterized. The optimal pH and temperature for the purified recombinant enzyme were 7.8 and $60^{\circ}C$, respectively. The enzyme showed stability over a pH range of 4.0-10.0. The kinetic values on oat spelt xylan and birchwood xylan substrates were also determined. The enzyme activity was enhanced by $Fe^{2+}$ and strongly inhibited by $Hg^{2+}$ and SDS. The enzyme also showed resistance to neutral and alkaline proteases. Therefore, these characteristics suggest that SfXyn10 could be an important candidate for protease-resistant mechanistic research and has potential applications in the food industry, cotton scouring, and improving animal nutrition.