• Journal of the Korean Geotechnical Society
• /
• v.21 no.6
• /
• pp.81-91
• /
• 2005

'Coarse grained material' refers to crushed stones or gravels, and the behaviour of soil containing coarse grained material is not easily defined using the conventional soil mechanics theory due to the influences of large particles, therefore large scale test is essential to investigate their effects. Previous studies have identified the major factors affecting the properties of coarse grained materials by using large scale shear testing apparatus, such as maximum particle size, water content, density and uniformity coefficients. In this paper, the effect of variation of maximum particle size and water content on shear strength was analyzed from the results of large scale shear test. In addition, the fiction coefficient at critical state per vertical load was estimated using the equation proposed by Wood (1998). The sample for the test was obtained from the local quarry sites. Tests results show that the shear strength for 50.8 m maximum particle size is relatively larger than that of 76.3 m and air-dry sample has larger shear strength than saturated sample. In the meantime, the friction coefficient at critical state shows $1.0\sim1.6$ according to the test conditions.

• Journal of the Korean Geotechnical Society
• /
• v.31 no.10
• /
• pp.5-16
• /
• 2015

Considering the conversion of the Korea Construction Standards to Limit State Design (LSD), we analyzed the resistance bias factor for pullout resistance, as a part of the development of the Load and Resistance Factor Design (LRFD) for soil nailing; very few studies have been conducted on soil nailing. In order to reflect the local characteristics of soil nailing, such as the design and construction level, we collected statistics on pullout tests conducted on slopes and excavation construction sites around the country. In this study a database was built based on the geotechnical properties, soil nailing specifications, and pullout test results. The resistance bias factors are calculated to determine the resistance factor of the pullout resistance for gravity and pressurized grouting method, which are the most commonly used methods in Korea; moreover, we have relatively sufficient data on these methods. We found the resistance bias factors to be 1.144 and 1.325, which are relatively conservative values for predicting the actual ultimate pullout resistance. It showed that our designs are safer than those found in a research case in the United States (NCHRP Report); however, there was an uncertainty, $COV_R$, of 0.27-0.43 in the pullout resistance, which is relatively high. In addition, the pressurized grouting method has a greater margin of safety than the gravity grouting method, and the actual ultimate pullout resistance determined using the pressurized grouting method has low uncertainty.

• Journal of Periodontal and Implant Science
• /
• v.46 no.6
• /
• pp.382-395
• /
• 2016

Purpose: Alendronate has been proposed as a local and systemic drug treatment used as an adjunct to scaling and root planing (SRP) for the treatment of periodontitis. However, its effectiveness has yet to be conclusively established. The purpose of the present meta-analysis was to assess the effectiveness of SRP with alendronate on periodontitis compared to SRP alone. Methods: Five electronic databases were used by 2 independent reviewers to identify relevant articles from the earliest records up to September 2016. Randomized controlled trials (RCTs) comparing SRP with alendronate to SRP with placebo in the treatment of periodontitis were included. The outcome measures were changes in bone defect fill, probing depth (PD), and clinical attachment level (CAL) from baseline to 6 months. A fixed-effect or random-effect model was used to pool the extracted data, as appropriate. Mean differences (MDs) with 95% confidence intervals (CIs) were calculated. Heterogeneity was assessed using the Cochrane ${\chi}^2$ and $I^2$ tests. Results: After the selection process, 8 articles were included in the meta-analysis. Compared with SRP alone, the adjunctive mean benefits of locally delivered alendronate were 38.25% for bone defect fill increase (95% CI=33.05%-43.45%; P<0.001; $I^2=94.0%$), 2.29 mm for PD reduction (95% CI=2.07-2.52 mm; P<0.001; $I^2=0.0%$) and 1.92 mm for CAL gain (95% CI=1.55-2.30 mm; P<0.001; $I^2=66.0%$). In addition, systemically administered alendronate with SRP significantly reduced PD by 0.36 mm (95% CI=0.18-0.55 mm; P<0.001; $I^2=0.0%$) and increased CAL by 0.39 mm (95% CI=0.11-0.68 mm; P=0.006; $I^2=6.0%$). Conclusions: The collective evidence regarding the adjunctive use of alendronate locally and systemically with SRP indicates that the combined treatment can improve the efficacy of non-surgical periodontal therapy on increasing CAL and bone defect fill and reducing PD. However, precautions must be exercised in interpreting these results, and multicenter studies evaluating this specific application should be carried out.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.43 no.3
• /
• pp.360-366
• /
• 2014

Kimchi is a Korean traditional fermented food with various health functionalities. However, the protective effects of kimchi against Alzheimer's disease (AD) have not been studied yet. In this study, the protective activities of kimchi extract against oxidative stress and AD were investigated in an amyloid beta ($A{\beta}$)-induced AD model using ICR mice. Kimchi extract exerted strong scavenging activities against 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radical. In addition, T-maze, object cognition, and water maze tests were carried out using the AD model. The $A{\beta}_{25-35}$-injected groups showed impairment of cognition and memory. However, the abilities of novel object recognition and new route awareness were improved by administration of kimchi extract (100 and 200 mg/kg/day) for 2 weeks. Furthermore, the results on water maze test indicated that kimchi extract exerted protective activity against cognitive impairment induced by $A{\beta}_{25-35}$. The present study suggested that kimchi protected against $A{\beta}$-induced impairment of memory and cognition as well as attenuated oxidative stress.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.4
• /
• pp.431-442
• /
• 2013

Most of previous studies have insufficiently investigated the shear behavior and fracturing characteristics, experimentally in respect to the change of size of tooth-shaped surface asperity such as length and slope angle in a broad range. This study investigates the influence of the length and slope angle of a tooth-shaped surface asperity on the fracturing characteristics and the interface shear strength by using direct shear test apparatus. A total of 36 interface direct shear tests were conducted by changing the three types of slope angle of surface asperity, four type of length, and three types of normal stress. The shape of fractured surface after the test was quantified by using a three-dimensional surface roughness measurement apparatus. Through the experimental test results, the characteristics of fractured shape of surface asperity according to the normal stress were investigated. In addition, fractured length and height were quantified at each slope angle of surface asperity under a certain normal stress condition.

• Composites Research
• /
• v.23 no.4
• /
• pp.44-51
• /
• 2010

Recently, to solve the problems associated with the neutralization and corrosion of reinforced concrete compression members, the structural configurations such as CFFT (Concrete Filled GFRP Tube) and RCFFT (Reinforced Concrete Filled GFRR Tube) have been developed and applied to main members of civil engineering structure. These members can increase structural performance in terms of structural stability, ductility as well as chemical resistance compared with conventional concrete structural members. Many researches in numerous institutions to predict the load carrying capacity of the concrete compression member strengthened with FRP materials have been conducted and they have been suggested an equation for the prediction of the load carrying capacity of the members. Through the review of the research results, it was found that their results are similar each other. Moreover, it was also found that the results are not directly applicable to our specimens since the results are largely depended upon the member configurations. Also, since the accurate design criteria for the RC members strengthened with FRP such as RCFFT have not been established properly, relevant theoretical and experimental investigations must be conducted for the application to the practical structures. In this study, structural behavior of RCFFT was evaluated through compressive and quasi-static flexural tests in order to formulate design criteria for the structural design. In addition, the RCFFT members were also investigated to examine their confinement effect and the equations capable of estimating the compressive ultimate strength and flexural stiffness of the RCFFT members were proposed.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.14 no.5
• /
• pp.485-501
• /
• 2012

This study aims to experimentally investigate ground settlement and ground movement around the square pipe by its penetration in sandy ground. A series of laboratory model tests were carried out with a small-scale auger equipment for penetration of a square pipe as well as a newly designed test box with a sand raining equipment. From the experiments, it is shown that a square pipe induces ground movement evenly around it in a low overburden condition. However, as the overburden becomes higher, ground movement by a square pipe is concentrated mainly above it. Especially, horizontal strain above the square pipe was mainly dominated by its penetration. In addition, sand surface movement is the smallest in case of the dimensionless penetration rate equal to 0.2. When its penetration rate of the square pipe is fixed, the rotation speed of auger controls surface movement whether it is settlement or heaving. Therefore, the selection of an optimal dimensionless rate for the square pipe is a key design factor to minimize ground settlement in a trenchless construction.

• Journal of Korean Ophthalmic Optics Society
• /
• v.20 no.4
• /
• pp.519-526
• /
• 2015

Purpose: To evaluate the changes of OSI value according to tear-film instability measured serially by OQAS(Optical Quality Analysis System, Visiometrics, Spain) every seconds. The presented study analyzed the relationship of the OQAS parameter with the results of the tear-film break-up time, Schirmer test, and the McMonies score. Methods: 147 eyes of 82 subjects were randomly selected from university students (age: $21.51{\pm}3.97$, male 45, female 37). Subjects were measured tear-film break-up time, Schirmer test, McMonies score and once every second for 15 seconds after blinking by continuous measurements from OQAS system. Results: The normal eye groups presented OSI values of $2.13{\pm}1.16$ while the dry eye groups had OSI values of $3.76{\pm}1.42$. Therefore, a significant difference between the normal eye group and dry eye group was discovered (p<0.05). In addition, the OSI value of all subjects increased over time. The OSI value, which was measured every second after blinking occurred, significantly increased between 6 seconds and 7 seconds after the start of the measurement (p<0.05). OSI cut off of 30% (sec.) showed a greater correlation; TBUT (r = 0.855, p = 0.000), McMonies test (r = -0.351, p = 0.003), Schirmer (r = 0.316, p = 0.012). Conclusions: Continuous measurement of OQAS showed a high correlation with the value of the existing dry eye tests. Therefore, Analysis of OSI values by utilization of OQAS could be useful in objectively evaluation of tear film in patients.

• Journal of Distribution Science
• /
• v.9 no.1
• /
• pp.49-59
• /
• 2011

Although the South Korean organic food market is in the infancy compared to other industrialized countries, Korean consumers'interest in organic food and retail stores devoting space to organic products have been rapidly increasing. Despite the fact of organic food popularity, the term "organic" is interpreted differently by individuals. As opposed to the US, Japan and the EU where have operated an integrated organic food labelling system, Korea has adopted complex organic labelling systems regulated by several different government bodies. As a result, complicated food labelling standards make consumers confused when purchasing organic foods. Furthermore, in terms of country of origin (COO), it is argued by a lot of researchers that COO effects vary from product to product and from country to country; moreover, other informational cues such as brand and price can influence COO effects. In modern society, COO labelling has been complicated, due to the sourcing, manufacturing and market locations of merchandise spread over the world. Accordingly, the evaluation of COO effects has become complex. In order to examine these issues, a quantitative research was selected to classify the commonfeatures of organic food consumers and construct statistics such as the extent to which people are aware of organic food and COO labellingvia a questionnaire which took place in two cities in Korea with a cluster sample of 161 organic food purchasers. As for the data analysis, one-way analysis of variance (ANOVA), T-tests, bivariate crosstatulations with Cramer's V were conducted,depending on the characteristics of variables and the assumptions the research data need to fit. It has been concluded that in general, Korean organic consumers comprehend the term "organic"in a closer way to the general concept rather than technical term, thus people do not appreciate environmentally labels which include organic food labels, although marital status influence the degree of label awareness, regardless of gender, age, education level and so on. Regarding COO effects on organic food, home organic products were Korean consumers'first choice over those from industrialized countries and developing nations. Specifically, in processed organic product category, domestically cultivated and processed organic products were absolutely preferred to leading national brands produced with imported ingredients and international brands. However, due to a lack of checks of ingredients' COO, consumers tend to purchase a leading national organic food brand, believing that it is a pure organic food sourced domestically. As a consequence, this research has suggested some important managerial implications and future research directions. In order to prevent consumer confusion when buying organic foods, it should be noted that consumers do not comprehend the organic food certifications, due to complicated labelling systems for organic produce and processed organic foods. Therefore, government bodies related to organic food distribution have to know consumers' perception of organic food labels and the significance of customer-oriented labels and reestablish labelling standards. Similarly, public advertising should be followed to raise public awareness of the labelling to enable customers to have the correct information. In addition, not only international marketers but also domestic marketers need to understand COO images and also the influence COO of ingredients has on the image of an organic product.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.10
• /
• pp.259-266
• /
• 2020

In this study, required drill bits and excavation methods were developed for an uneven drilling method that can solve the problem of performance degradation of rock bolts. The developed drill bit's excavation performance was verified using rock with a strength of 100 MPa or more. In addition, for the relative evaluation of the uneven excavation method, experimental specimens were prepared for models with and without irregularities, and tests were performed. As a result of the experiment, the model with unevenness exhibited an average critical draw resistance of 801.6 kN, which is about 1.7 times the value of 468.7 kN for the model without unevenness, thus confirming the effect sufficiently. Therefore, it is expected that the resistance performance will significantly increase despite an increase in the uneven hole diameter of 20 mm. In the future, the results of this study could be used as basic data when performing other studies using numerical analysis models and performance verification through experiments to obtain an optimized rock forming method.