• Journal of Surface Science and Engineering
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• v.35 no.4
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• pp.199-205
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• 2002

TiN and TiAlN films were deposited on SKD 11 steel substrates by an arc ion plating (AIP) technique. The crystallinity and morphology for the deposited films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mechanical properties of both films were investigated through the indentation, impact, and wear test. Those films fairly adherent to SKD 11 steel substrate, showed hardness values of 2300 $\pm$ 100kg/$\textrm{mm}^2$ and 3200 $\pm$ 100kg/$\textrm{mm}^2$ with a load of 25g, respectively. During impact test, TiAlN films showed much superior impact wear resistance to TiN films. It could be suggested that the TiN films was failed relatively by plastic deformation with oxidation during impact test, while TiAlN films was failed by brittle fracture and resisted the oxidation by the impact energy. The friction coefficient of TiAlN films became lower than that of TiN films at high sliding speed condition although it was higher than that of TiN films at low speed. Therefore, TiAlN films was suggested to be more advantageous than TiN films for high speed machining fields.

• Smart Structures and Systems
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• v.24 no.1
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• pp.95-110
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• 2019

The semi-active impact damper (SAID) is proposed to improve the damping efficiency of traditional passive impact dampers. In order to investigate its damping mechanism and vibration control effects on realistic engineering structures, a 20-story nonlinear benchmark building is used as the main structure. The studies on system parameters, including the mass ratio, damping ratio, rigid coefficient, and the intensity of excitation are carried out, and their effects both on linear and nonlinear indexes are evaluated. The damping mechanism is herein further investigated and some suggestions for the design in high-rise buildings are also proposed. To validate the superiority of SAID, an optimal passive particle impact damper ($PID_{opt}$) is also investigated as a control group, in which the parameters of the SAID remain the same, and the optimal parameters of the $PID_{opt}$ are designed by differential evolution algorithm based on a reduced-order model. The numerical simulation shows that the SAID has better control effects than that of the optimized passive particle impact damper, not only for linear indexes (e.g., root mean square response), but also for nonlinear indexes (e.g., component energy consumption and hinge joint curvature).

• Steel and Composite Structures
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• v.52 no.6
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• pp.609-620
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• 2024

The impact problem of imperfect beams is crucial in engineering fields such as water conservancy and transportation. In this paper, the low velocity impact of graphene reinforced metal foam beams with geometric defects is studied for the first time. Firstly, an improved Hertz contact theory is adopted to construct an accurate model of the contact force during the impact process, while establishing the initial conditions of the system. Subsequently, the classical theory was used to model the defective beam, and the motion equation was derived using Hamilton's principle. Then, the Galerkin method is applied to discretize the equation, and the Runge Kutta method is used for numerical analysis to obtain the dynamic response curve. Finally, convergence validation and comparison with existing literature are conducted. In addition, a detailed analysis was conducted on the sensitivity of various parameters, including graphene sheet (GPL) distribution pattern and mass fraction, porosity distribution type and coefficient, geometric dimensions of the beam, damping, prestress, and initial geometric defects of the beam. The results revealed a strong inhibitory effect of initial geometric defects on the impact response of beams.

• Culinary science and hospitality research
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• v.22 no.3
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• pp.79-91
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• 2016

This research was conducted over one month from May 1st to May 30th, 2015. Data were collected after confirming purpose of current study with eating house manager from the restaurant consumers. This study investigated the impact of nostalgia tendency on the propensity to revisit the eating house. Nostalgia impact on the propensity of the perceived emotional food repurchase also had the effect of significantly positive (+) on the road to repurchase B=0.767(p<.001). The coefficient of determination for measuring the adequacy of the model to determine the coefficient that measures the suitability of the model was explaining 58.9% of the variation in the premises 0.589, models with F=431.234(p<.001) to verify the significance of the model is significantly It has been described. Second, nostalgia tendency and social tendencies of the bond part had a strong impact in moderating effects of (-). The lower the social bond was investigated by increasing the propensity nostalgia.

• Journal of Korean Society of Forest Science
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• v.106 no.4
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• pp.424-430
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• 2017

With its rapid velocity and wide deposition, debris flow is a natural disaster that causes loss of human life and destruction of facility. To design effective debris barriers, impact force of debris flow should be first considered. Debris flow velocity is one of the key features to estimate the impact force of debris flow. In this study, we conducted small-scale flume experiments to analyze flow characteristics of debris flow, and determine flow resistance coefficients with different slope gradients and sediment mixtures. Flow velocity significantly varied with flume slope and mixture type. Debris flow depth decreased as slope increased, but difference in depth between sediment mixtures was not significant. Among flow resistance coefficients, Chezy coefficient ($C_1$) showed not only relatively highest goodness of fit, but also constant value ($20.19m^{-1/2}\;s^{-1}$) regardless the scale of debris flow events. The overall results suggested that $C_1$ can be most appropriately used to estimate flow velocity, the key factor of assessing impact force, in wide range of debris flow scale.

• Culinary science and hospitality research
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• v.23 no.5
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• pp.169-177
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• 2017

Smoking bans at restaurants and bars have recently been introduced in Korea. Researchers and stakeholder are interested in the resulting changes in sales of restaurants and bars and their impact on overall national economy including employment. We examined the input-output tables (2013) issued by The Bank of Korea. The result showed that the production inducement coefficient was about 2.16; employment inducement coefficient was 13.1 for the restaurant and bar industry. The amount of inducement in the national production was calculated by 93,100 billion KRW. Employment inducement was calculated by 1,219,610 persons overall industries for a year. Assuming there comes a change (3%, 5%, 10%) in restaurant and bar production in consequence of the smoking bans, we computed following change in the national production and employment. The resulting changed in national production was 6,033 billion, 10,055 billion, and 20,110 billion KRW, respectively. The impact of employment overall industries was calculated 79,032, 131,720 and 263,441 persons, respectively.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.3
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• pp.187-195
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• 2018

Ship's bottom slamming has been studied by many researchers for a very long time. But still some ships suffer structure damages caused by the bottom slamming impacts. This paper presents a practical computation method of the design impact pressure due to ship's bow bottom slamming. Large heave and pitch motions of a rigid hull ship are simulated by the nonlinear strip method in time domain and the relative colliding velocity between the bow bottom and the water surface is calculated using the simulated ship motions. The bottom slamming impact pressure is calculated as a product of the relative colliding velocity squared and the bottom slamming pressure coefficient that is obtained by modification of the SNAME pressure coefficients based on Ochi's slamming experiments. Not only the bottom slamming pressures but also the required bottom plate thicknesses are calculated and compared with those of the classification society rules. The comparisons show good agreements and it is confirmed that the present method is practically very useful for the bottom structure design against ship's bow bottom slamming impacts.

• Research in Community and Public Health Nursing
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• v.23 no.3
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• pp.338-346
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• 2012

Purpose: The purpose of this study was to examine the association between oral health impact profile, depression and quality of life among community-dwelling elderly persons in South Korea. Methods: The design of this research was cross-sectional descriptive study. The participants were 266 community-dwelling individuals aged 65 and older. Data were collected from November 20 to December 20, 2011. The measurements for assessing the subjects' oral health, depression, quality of life were OHIP-14, GDS-SF and QOL. Data were collected using self-administered or interviewer-administered questionnaires. Collected data were analyzed using descriptive statistics, Pearson's correlation coefficient and stepwise multiple regression. Results: The participants' mean age was 77.68, and 86.5% were female, 42.9% were living-alone elders. Pearson's correlation coefficient analysis found that oral health impact profile was significantly associated with depression (r=-.622, p<.001), QOL (r=-.400, p<.001), number of disease (r=.298, p<.001), age (r=.198, p=.002), education (r=-.149, p=.015), eating habit (r=.185, p=.003). The QOL was explained 54.7% by depression (${\beta}$=-.619), oral health impact profile (${\beta}$=-.127), number of benefited welfare service (${\beta}$=.235), perceived health (${\beta}$=-.327), eating habit (${\beta}$=-.094) using stepwise multiple regression analysis. Conclusion: These results indicate that the intervention program of oral health promotion for community-dwelling elders is needed from now on.

• Korean Journal of Applied Biomechanics
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• v.26 no.2
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• pp.167-174
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• 2016

Objective: The purpose of this study was to determine the interrelationship between ranges of motion of the knee and ankle joints on the sagittal plane and the attenuation magnitude of impact shock at high frequency (9~20 Hz) in the support phase during downhill running. Method: Fifteen male heel-toe runners with no history of lower extremity injuries were recruited for this study (age, $25.07{\pm}5.35years$; height, $175.4{\pm}4.6cm$; mass, $75.8{\pm}.70kg$). Two uniaxial accelerometers were mounted to the tuberosity of tibia and sacrum, respectively, to measure acceleration signals. The participants were asked to run at their preferred running speed on a treadmill set at $0^{\circ}$, $7^{\circ}$, and $15^{\circ}$ downhill. Six optical cameras were placed around the treadmill to capture the coordinates of the joints of the lower extremities. The power spectrum densities of the two acceleration signals were analyzed and used in the transfer function describing the gain and attenuation of impact shock between the tibia and the sacrum. Angles of the knee and ankle joints on the sagittal plane and their angle ranges were calculated. The Pearson correlation coefficient was used to test the relationship between two variables, the magnitude of impact shock, and the range of joint angle under three downhill conditions. The alpha level was set at .05. Results: Close correlations were observed between the knee joint range of motion and the attenuation magnitude of impact shock regardless of running slopes (p<.05), and positive correlations were found between the ranges of motion of the knee and ankle joints and the attenuation magnitude of impact shock in $15^{\circ}$ downhill running (p<.05). Conclusion: In conclusion, increased knee flexion might be required to attenuate impact shock during downhill and level running through change in stride or cadence while maintaining stability, and strong and flexible ankle joints are also needed in steeper downhill running.

• Journal of the Korea Institute of Building Construction
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• v.5 no.1 s.15
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• pp.53-61
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• 2005

The purpose of this study presents useful data on the choice or development of floor covering from slip viewpoint by examining closely the impact of the changes in sliding experiments due to the wear of floor covering by walk. The result of wear practical test per ten thousand walks enforces some kind of popular floor covering and measure of coefficient of slip resistance as follows: (1) When surface of floor covering is in the state of wet, the degree of wear doesn't affect greatly in slip. (2) When surface of floor covering is in dry and clean state, most floor coverings have the tendency to lower the coefficient of slip resistance with the amount of walk on it. (3) Change in the tendency of slip resistance by wear appeared mainly due to the differences in the state of floor covering and organic floor covering appeared to have great reduction of coefficient of slip resistance than the inorganic ones. (4) According to the result of investigation on changes in tendency of coefficient of slip resistance due to the increase in the number of walk and if two hundred thousand walks were done, regardless of surface shape or kind of site, etc, the safety of floor covering, in slip viewpoint, greatly reduces.