• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.358-363
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• 2008

Ultrasonic nonlinearity has been considered as a promising method to evaluate the micro damage of material; however, its magnitude is so small that its measurement is not easy. Thus, in this study, we investigate the effects of such experimental system dependent factors in the measurement of ultrasonic nonlinear parameter by using contact PZT transducer. Experimental results showed that the effect of system dependent nonlinearity is reduced when the contact pressure and transducer input voltage are sufficiently large. These results will be very useful to find out the proper experiment condition to measure rather accurate nonlinear parameter.

• Transactions of Materials Processing
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• v.28 no.5
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• pp.266-274
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• 2019

Metal sealing is used to connecting the parts between valves and fuel pipes for a FCEV which utilizes hydrogen gas of 700 bar. Instead of general carbon steel, stainless steel is the primary material used to manufacture fuel pipes due to hydrogen embrittlement. The shape of deformation between metals is an important factor on the air-tightness of the metal to metal contact. Since the stainless steel pipe is hardened using the plastic forming during the tip shaping stage, this work hardening could have an effect on the deformed shape and characteristics of contact surfaces in fastening of pipes. In this paper, the deformation history of the pipe model was considered in order to analyze the hydrogen-tightness on the metal sealing part. The contact distance and the forward displacement for fastening were compared using experimental results and the simulation results. The simulation of the effect of material change on the fitting body demonstrated that the hardness or the strength of the formed tip of the pipe was designed to a proper valued level since the characteristics of the contact surface was exhibited better when the strength of the pipe was lower than that of the fitting body.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.39-44
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• 2015

We investigated the effect of CNT-Ag composite pad on the contact resistance of flip-chip joints, which were formed by flip-chip bonding of Cu/Au chip bumps to Cu substrate metallization using anisotropic conductive adhesive. Lower contact resistances were obtained for the flip-chip joints which contained the CNT-Ag composite pad than the joints without the CNT-Ag composite pad. While the flip-chip joints with the CNT-Ag composite pad exhibited average contact resistances of $164m{\Omega}$, $141m{\Omega}$, and $132m{\Omega}$ at bonding pressures of 25 MPa, 50 MPa, and 100 MPa, the flip-chip joints without the CNT-Ag composite pad had an average contact resistance of $200m{\Omega}$, $150m{\Omega}$, and $140m{\Omega}$ at each bonding pressure.

• Journal of the Korean Society of Safety
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• v.23 no.1
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• pp.35-45
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• 2008

This study was performed to compare the kinematics among three different safety shoes(type 1: ergonomically designed and high quality shoes, 2: curved and cushioned safety shoes, and 3: regular safety shoes) and to find the effect of insole during walking. Ten healthy subjects were recruited for this study. The range of motion of knee and ankle joint, angle of rear foot and angle of heel contact were measured using a three dimensional motion analysis system. In the second peak, the angle of heel contact showed statistically significant difference between safety shoes and insole, however, there was no statistical significance among three different safety shoes. The angle of ankle increased significantly at initial contact, first peak, the second peak and the toe off phase compared with type 1 and 2 safety shoes, and the angle of ankle showed statistically significant difference between with and without applying the insole. During the first peak, the second peak and the toe off phase, the angle of knee was statistical significance between safety shoes and insole. In heel contact, the angles of Achilles' tendon showed statistically significant difference between safety shoes and insole. The rear foot angles showed statistically significant difference between safety shoes and insole during heel contact and early heel contact. These results suggest that the type 1 safety shoes were superior to others in the statistics, and applying insole could be a possible method to prevent fatigue of lower extremity and musculoskeletal disorders. Further studies are needed to find the effect of ergonomically designed safety shoes and insole on practical value in prevention of musculoskeletal disorder, fatigue and satisfaction of workers.

• The Journal of the Korea Contents Association
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• v.14 no.1
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• pp.409-422
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• 2014

This paper examined the influence of employees' social regard toward the customers, such as, overall service quality, service satisfaction, and service loyalty. The paper proves that the high contact beauty services and the low contact fast-food services have different customer satisfaction level depending on the employees' social regards. A survey study was conducted to collect the data with the actual service purchasers at domestic beauty services and fast-food services. Analysis of structural equation modeling with Amos 18.0 was performed to test the research hypothesis. The results of the study are as follows: First, social regard has positive influences on service quality, service satisfaction, and service loyalty. Second, Social regard has more effect on service satisfaction in a high contact beauty services than in a low contact fast-food services. This paper contribute to identify the effects of employees' social regard on service satisfaction, by comparing the effects on service satisfaction between high and low contact services.

• Structural Engineering and Mechanics
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• v.76 no.2
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• pp.153-162
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• 2020

Aiming at the mechanical and structural characteristics of the contact zone composite rock, the shear tests and numerical studies were carried out. The effects of the differences in mechanical properties of different materials and the normal stress on shear properties of contact zone composite samples were analyzed from a macro-meso level. The results show that the composite samples have high shear strength, and the interface of different materials has strong adhesion. The differences in mechanical properties of materials weakens the shear strength and increase the shear brittleness of the sample, while normal stress will inhibit these effect. Under low/high normal stress, the sample show two failure modes, at the meso-damage level: elastic-shearing-frictional sliding and elastic-extrusion wear. This is mainly controlled by the contact and friction state of the material after damage. The secondary failure of undulating structure under normal-shear stress is the nature of extrusion wear, which is positively correlated to the normal stress and the degree of difference in mechanical properties of different materials. The increase of the mechanical difference of the sample will enhance the shear brittleness under lower normal stress and the shear interaction under higher normal stress.

• Journal of the Ergonomics Society of Korea
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• v.33 no.2
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• pp.143-153
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• 2014

Objective: The aim of this study is to investigate the effects of trunk-forearm supported sitting on trunk flexion angle, trunk extensor fatigue and seat contact pressure. Background: The relationship between sitting posture and musculoskeletal disorders of the trunk extensor fatigue and seat contact pressure has been documented. The trunk-forearm support type ergonomic chair was devised from the fact that trunk-forearm support has been reported to reduce trunk extensor activity and discomfort. Method: Using three different sitting postures, upright ($P_1$), trunk-forearm supported ($P_2$) and normal sitting ($P_3$), six healthy subjects participated in the study. Motion capture system was used to collect head and trunk flexion angle, and surface electromyography (sEMG) was used to collect myoelectric signal of upper trapezius, lower trapezius, erector spinae, multifidus, and pressure mat system was used to measure seat contact pressure. Results: When trunk and forearm were supported by the ergonomic chair, higher head flexion angle showed upright > trunk-forearm supported > normal in order, and muscle fatigue showed less than upright and normal sitting. Mean seat contact pressure decreased 19% than upright sitting. But muscle fatigue was not affected by each condition. Conclusion: Trunk-forearm supported sitting of the ergonomic chair showed positive effect in respect of trunk and head flexion angle, trunk extensor fatigue, seat contact pressure. To acquire comprehensive understanding of the effectiveness of the ergonomic chair, further studies such as anatomical effects from measurement of external applied loading effect to the body from interface pressure analysis are required. Application: The results of the publishing trend analysis might help physiological effects of trunk-forearm support type chair.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.4
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• pp.321-328
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• 2017

Recently EC-MBR (Elctrocoagulation - Membrane Bio Reactor) has been suggested as one of alternative processes to overcome membrane fouling problems. Most important operational parameters in the EC-MBR are known to current density and contact time. Their effect on membrane filtration performances has been reported well, however, quantitative interrelationship between both parameters not been investigated yet. The purpose of this study is to give a kinetic model suggesting the current density and the contact time required to reduce the membrane fouling. The 4 different set of current densities (2.5, 6, 12 and $24A/m^2$) and contact times (0, 2, 6 and 12 hr) were selected as operational parameters. After each electro-coagulation under the 16 different conditions, a series of membrane filtration was carried out. The membrane fouling decreased as the current density and contact time increased, Total fouling resistances under different conditions, $R_t(=R_c+R_f)$ were calculated and compared to those of the controls ($R_0$), which were calculated from the data of experiments without electro-coagulation. A kinetic approach for the fouling reduction rate ($R_t/R_0$) was carried out and the equation ${\rho}^{0.46}_it=7.0$ was obtained, which means that the product of current density and the contact time needed to reduce the fouling in certain amounts (in this study, 10% of fouling reduction) is always constant.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.23 no.1
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• pp.8-22
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• 2010

Objectives : The purpose of this study is to investigate the effects of Gyejijakyakjimo-Tang on the Allergic Contact Dermatitis caused by 2,4-dinitro-chlorobezene(DNCB). Methods : Twenty eight mice were divided into four groups ; normal, control, experimental group A and B. Control and experimental groups were induced allergic contact dermatitis by DNCB. Experimental group A was orally administered the Gyejijakyakjimo-Tang and experimental group B was orally administered the prednisolone. In this study, ear thickness measurement, auricle microphotograph observation, MPO(Myeloperoxidase) activity measurement, Reverse transcription-polymerase chain reaction(RT-PCR) analysis of the mRNA level of TNF-$\alpha$, IL-$1{\beta}$ were performed on these four groups. In addition, the effect of Gyejijakyakjimo-Tang on cell viability and the effect of Gyejijakyakjimo-Tang on the compound 48/80-induced histamine release from HMC and RPMC were measured. Results: 1. Both experimental group A and B had decreased ear thickness compared with control group In contact hypersensitivity assay. 2. In experimental group A, inflammatory edema was similarly observed comparing to control group. Nevertheless, inflammatory edema was obviously reduced in experimental group B. In both experimental group A and B, pathological lesion of dermatitis were alleviated. In addition, the numbers of infiltrated inflammatory cells were decreased compared with control group. 3. Compared to the normal group, there was a noticeable increase in MPO activity in control group. However, in experimental group A and B, it showed remarkable inhibition of the increase in MPO activity comparing with control group. 4. The level of expression of TNF-$\alpha$, IL-$1{\beta}$ in experimental group A and B were meaningfully lower than those in control group. 5. In MTT assay, the concentrations of Gyejijakyakjimo-Tang that were used on the test had no cytotoxicity. 6. Gyejijakyakjimo-Tang dose-dependently inhibited the compound 48/80-induced histamine release from both HMC and RPMC. Conclusions : According to above experiments, Gyejijakyakjimo-Tang was effective on allergic contact dermatitis.

• The Journal of the Korea Contents Association
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• v.21 no.8
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• pp.489-497
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• 2021

This study presents the results of an empirical analysis on whether the experience of contact with North Korea and North Korean settlers affects the perceptions of unification. Specifically, the purpose of this study was to examine whether the contact experience enhances intimacy with the North Korean settlers or raises a friendly perception of North Korea.The results of this study are as follows. First, the experience of contact with North Korea and North Korean defectors had a positive effect on intimacy with North Korean settlers, friendly perception of North Korea, and perceptions of unification. Second, intimacy toward North Korean settlers and perception of North Korea played a mediating role between contact experience and unification consciousness.