• The Korean Journal of Applied Statistics
• /
• v.28 no.1
• /
• pp.61-74
• /
• 2015

Structural equation modeling (SEM) is a widely used in social sciences such as education, business administration, and psychology. In SEM, the latent variable score is the estimate of the latent variable which cannot be observed directly. This study uses stagewise structural equation modeling(stagewise SEM; SSEM) by partitioning the whole model into several stages. The traditional estimation method minimizes the discrepancy function using the variance-covariance of all observed variables. This method can lead to inappropriate situations where exogenous latent variables may be affected by endogenous latent variables. The SSEM approach can avoid such situations and reduce the complexity of the whole SEM in estimating parameters.

• Tribology and Lubricants
• /
• v.31 no.6
• /
• pp.272-280
• /
• 2015

Recently, Luu suggested fatigue life equation that uses every term of the Crossland equation with stress gradient effect. Luu’s model, however, has a limit of being unable to coverage small radii that are less than a specified length. Furthermore, rolling model has a very small contact area compared to the rolling element size, and fatigue failure occurs on the small radius such as surface asperity by cyclic loading. Therefore, it is necessary to modify fatigue life equation in order to enable fatigue analysis for a small radius. In this paper, the fatigue life considering a stress gradient effect in rolling contact was obtained using Luu’s modified equation. Fatigue analysis was performed to study the effect of stress gradient on the fatigue life using newly adopted equation and to compare the results with pervious models. In order to do this, a series of simulation such as surface stress analysis, subsurface stress analysis, and fatigue analysis are conducted for two rolling balls of same size that contact each other. Through such a series of processes, the fatigue life can be calculated and equation that is proposed in this paper evaluates the fatigue life in case the contact area is small.

• Tribology and Lubricants
• /
• v.31 no.2
• /
• pp.69-77
• /
• 2015

Recently, there have been reports of severe symptoms of wear in bearings due to foreign substances mixed in lubricants. Therefore, studying the effects of foreign substances (such as combustion products and metallic debris) on the wear characteristics of journal bearings and proposing appropriate management standards for lubricant cleanliness have become necessary. Studies on the effect of particle size and concentration of foreign substances on surface damage have actively progressed in the recent times. These studies indicate the possibility of foreign substances causing direct wear of bearing surfaces. However, experiments conducted until now involve only basic tests such as the Pin-on-Disk test instead of those involving real bearing systems. This study experimentally examines the damage to the surface of a journal bearing due to foreign substances (combustion products and alumina) mixed with the lubricant, as well as the effect of the type and size of particles on its wear characteristics. The study uses an experimental journal bearing similar to a real bearing system for conducting the lubrication test. Hydrodynamic Lubrication (HL) numerical analysis, experiment results, and film parameters are used for calculating the operating conditions required for achieving the desired film thickness, and the results of the analysis are modified for considering the surface roughness. The run-time of the experiment is 10 min including the stabilization process. The experiment results show that alumina particles larger than the minimum film thickness cause significant surface damage.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.257-257
• /
• 2013

In order to selectively remove oil and organic compound from water, silica nanoparticles with hydrophobic coating was used. Since silica nanoparticles are generally hydrophilic, removal efficiency of oil and organic compound, such as toluene, in water can be decreased due to competitive adsorption with water. In order to increase the removal efficiency of oil and toluene, hydrophobic polydimethylsiloxane (PDMS) was coated on silica nanoparticles in the form of thin film. Hydrophobic property of the PDMS-coated silica nanoparticles and hydrophilic silica nanoparticles were easily confirmed by putting it in the water, hydrophilic particle sinks but hydrophobic particle floats. PDMS coated silica nanoparticles were dispersed on a slide glass with epoxy glue on and the water contact angle on the surface was determined to be over $150^{\circ}$, which is called superhydrophobic. FT-IR spectroscopy was used to check the functional group on silica nanoparticle surface before and after PDMS coating. Then, PDMS coated silica nanoparticles were used to selectively remove oil and toluene from water, respectively. It was demonstrated that PDMS coated nanoaprticles selectively aggregates with oil and toluene in the water and floats in the form of gel and this gel remained floating over 7 days. Furthermore, column filled with hydrophobic PDMS coated silica nanoparticles and hydrophilic porous silica was prepared and tested for simultaneous removal of water-soluble and organic pollutant from water. PDMS coated silica nanoparticles have strong resistibility for water and has affinity for oil and organic compound removal. Therefore PDMS-coated silica nanoparticles can be applied in separating oil or organic solvents from water.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.130.1-130.1
• /
• 2013

We made attempts to improve photocatalytic activity of $TiO_2$ nanoparticles under visible light exposure by combining two additional treatments. N-doping of $TiO_2$ by ammonia gas treatment at $600^{\circ}C$ increased absorbance of visible light. By coating thin film of polydimethylsiloxane (PDMS), and subsequent vacuum-annealing at $800^{\circ}C$, $TiO_2$, became more hydrophilic, thereby enhancing photocatalytic activity of $TiO_2$. Four types of $TiO_2$ samples were prepared, bare-$TiO_2$, hydrophilic-modified $TiO_2$ ($h-PDMS/TiO_2$), N-doped $TiO_2$ ($N/TiO_2$) and hydrophilic-modified and N-doped $TiO_2$ ($h-PDMS/N/TiO_2$). Adsorption capability was evaluated under dark condition and photocatalytic activity of $TiO_2$ was evaluated by photodegradation of MB under blue LED (400 nm< ${\lambda}$) irradiation. N-doping on $TiO_2$ was characterized using XPS and hydrophilic modification of $TiO_2$ surface was analyzed by FT-IR spectrometer. It was found that N-doping and hydrophilic modification both had positive effect on enhancing adsorption capability and photocatalytic activity of $TiO_2$ at the same time. Particularly, N-doping enhanced visible light absorption of $TiO_2$, whereas hydrophilic surface modification increased MB adsorption capacity. By combining these two strategies, photocatalytic acitivity under visible light irradiation became the sum of individual effects of N-doping and hydrophilic modification.

• Journal of Physiology & Pathology in Korean Medicine
• /
• v.29 no.1
• /
• pp.51-57
• /
• 2015

Bone destruction is a pathological symptom of some chronic inflammatory diseases, such as rheumatoid arthritis and periodontitis. Inflammation-induced bone loss of these diseases results from increased number and activity of osteoclasts. Paeoniae Radix Alba has been used in korean traditional medicine to treat disease including inflammation, gynecopathy and various pain. However, these effects have not been tested on osteoclasts, the bone resorbing cells that regulate bone metabolism. Here, we investigated the effects of Paeoniae Radix Alba ethanol extract (PRAE) on receptor activator of nuclear factor-kappa B ligand (RANKL)-mediated osteoclast differentiation and formation. Osteoclast differentiation and formation were measured by tartrate resistant acidic phosphatase (TRAP) staining and TRAP solution assay. The treatment of PRAE on bone marrow derived macrophages (BMMs), which is known as osteoclast precursor cells, inhibited osteoclast differentiation and formation in a dose-dependent manner. In addition, the expression of osteoclast differentiation marker genes was suppressed by PRAE treatment. This inhibitory effect of PRAE resulted from significant repression of c-Fos expression, and subsequent reduction of NFATc1 expression which was previously reported as a master transcription factor for osteoclastogenesis in vitro and in vivo. These results demonstrate that PRAE negatively regulates osteoclast differentiation and formation and suggest that PRAE can be used as a potent preventive or therapeutic candidate for various bone diseases, such as postmenopausal osteoporosis, periodontitis and rheumatoid arthritis.

• Journal of The Korean Society of Integrative Medicine
• /
• v.2 no.1
• /
• pp.15-21
• /
• 2014

Purpose : The aim of this study was to find out differences between muscle activity of quadriceps according to hip angle. Method : 40 healthy adults produced maximum isometric muscle contraction of quadriceps femoris and each part of the quadriceps femoris were measured with a surface EMG in hip joint angle of $90^{\circ}$, $135^{\circ}$, $180^{\circ}$. Result : There was no significant difference between muscle activity of vastus medialis and lateralis according to hip angle. But there was significant difference in muscle activity of rectus femoris and the muscle activity was maximum at 135 degrees of hip angle. Conclusion : In conclusion, maximum muscle activation of rectus femoris is affected by hip angle, and the findings from this study may be helpful for physical therapists in selecting hip position when instructing patients to do Q-setting exercise. So, we suggest that patients perform Q-setting exercise at 135 degrees of hip angle for the best result.

• Journal of Fashion Business
• /
• v.20 no.4
• /
• pp.207-225
• /
• 2016

This study aims to analyze the impact of negative review type, brand reputation and opportunity scarcity perception, on preferences of fashion products in social commerce. For the above evaluation, we used the 2 (negative review type: objective/subjective) ${\times}2$ (brand reputation: high/low) ${\times}2$ (opportunity scarcity perception: high/low) model, designed with three mixed elements. We enrolled 260 women in their 20s and 30s, who live in Seoul and have used social commerce; a final total of 207 subjects were considered for analysis. The data were analyzed using the SPSS 18 program and reliability test, t-test and three-way ANOVA were performed. Following observations were made: First, preferences were higher when the subjects read objective negative reviews than subjective negative reviews, and when a fashion product was from a brand of high reputation than a brand of low reputation. Second, the interaction effect between negative review type and brand reputation was greater among the subjects whose opportunity scarcity perception is high, than those having low opportunity scarcity perception. Thus, we conclude that the social commerce should encourage consumers to write more objective reviews, and fashion brands should manage their reputations well. Also, social commerce can use scarcity messages aggressively to increase preferences of global fashion luxury goods, which is actively marketed in social commerce since 2015.

• Nutrition Research and Practice
• /
• v.7 no.4
• /
• pp.326-329
• /
• 2013

Height and weight are important indicators to calculate Body Mass Index (BMI); measuring height and weight directly is the most exact method to get this information. However, it is ineffective in terms of cost and time on large population samples. The aim of our study was to investigate the validity of self-reported height and weight data compared to our measured data in Korean children to predict obese status. Four hundred twenty-two fifth-grade (mean age $10.5{\pm}0.5$ years) children who had self-reported and measured height and weight data were final subjects for this study. Overweight/obese was defined as a BMI of or above the 85th percentile of the gender-specific BMI for age in the 2007 Korean National Growth Charts or a BMI of 25 or higher (underweight : < 5th, normal : ${\geq}5th$ to < 85th, overweight : ${\geq}85th$ to < 95th). The differences between self-reported and measured data were tested using paired t-test. Differences based on overweight/obese status were tested using analysis of variance (ANOVA) and linear trends. Pearson's correlation and Cohen's kappa were tested to examine agreements between the self-reported and measured data. Although measured and self-reported height, weight and BMI were significantly different and children tended to overreport their height and underreport their weight, the correlation between the two methods of height, weight and BMI were high (r = 0.956, 0.969, 0.932, respectively; all P < 0.001), and both genders reported their overweight/non-overweight status accurately (Cohen's kappa = 0.792, P < 0.001). Although there were differences between the self-reported and our measured methods, the self-reported weight and height was valid enough to classify overweight/obesity status correctly, especially in non-overweight/obese children. Due to bigger underestimation of weight and overestimation of height in obese children, however, we need to be aware that the self-reported anthropometric data were less accurate in overweight/obese children than in non-overweight/obese children.

• Nutrition Research and Practice
• /
• v.15 no.5
• /
• pp.613-627
• /
• 2021

BACKGROUND/OBJECTIVES: Despite the widespread use of dietary assessment tools, the validity of food records has not been evaluated in Koreans. We assessed the accuracy of estimated food records and the effect of a short education session in young Korean women. SUBJECTS/METHODS: Thirty women (aged 18-23 yrs) each completed 3 food records during a controlled-feeding study. One educational session was provided on day 2 of the study. Food records were analyzed for the accuracy of food items and portion size estimation according to food group (grains; meat, fish, eggs, and beans; vegetables; fruit; dairy; and oils and sugars) and type of dish (rice, kimchi, soup, side dishes, spreads, beverages, and snacks). Reported food items were categorized as exact, close, or far matches, exclusions, or intrusions. Portion sizes were evaluated as accurate, similar, or inaccurate estimates, or missing. The means of days 2 and 3 were used to assess post-education results. Paired t-tests were performed to assess the effects of the education session. RESULTS: The mean percentages of exact matches, close matches, far matches, and exclusions on day 1 were 80.9%, 10.9%, 2.0%, and 6.2%, respectively, and mean intrusions observed were 0.1. The education session slightly increased the accuracy of recorded food items. The percentages of accurate, similar, and inaccurate estimates, and missing portion sizes were 11.7%, 19.8%, 12.2%, and 56.3%, respectively, at baseline. The percentage of missing portion size estimates decreased to 14.0% after the education session, resulting in an increase in the percentages of all other estimates. An increase was observed in the accuracy of reported portion sizes of vegetables, rice, and kimchi. CONCLUSIONS: In young Korean women, estimated food records are highly accurate for food items but not for portion size estimates without prior education. A short education session can improve the accuracy of portion size estimation.