• Tunnel and Underground Space
• /
• v.28 no.4
• /
• pp.358-371
• /
• 2018

The stability of openings in the underground mine is major concern in the operation of mines that must ensure productivity and safety. Among many rock conditions affecting cavities stability, the width and height of the opening is an important design factor. In this paper, we consider to determine the maximum unsupported span of a opening in a limestone mine by using the Q system among several rock classification schemes. In order to determine the span of the unsupported opening in the limestone mine, rock mass classifications were carried out at over 200 sites in the underground limestone mines. The relationships by using the Q system and the stability graph proposed by Mathews to determine the maximum span of the unsupported opening were derived and compared. We propose a new classification method that combines GSI and RMR rock classification systems to make it easy to use in a field.

• Journal of the Society of Naval Architects of Korea
• /
• v.48 no.5
• /
• pp.396-403
• /
• 2011

The concept of an air lubrication has long been an object of attention since it can be utilized to reduce the frictional resistance, and what is more, it is eco-friendly. The present study examines the basic characteristics of an air cavity with intention of applying the air lubrication technology to the reduction of the resistance of a ship without excessive power increment. For the purpose, an air cavity was created at the bottom of a flat plate by injecting air behind a backward step and the hydrodynamic properties of the air cavity and the surrounding flow has been investigated experimentally and numerically. The influence of the step height and the air flow rate have been more carefully studied since they are presumed to be the main parameters affecting the characteristics of an air cavity. The results indicates that the shapes of the air cavities attached on the flat plate become "U" or "V" type depending on the incoming flow velocity and air flow rate. The study also confirms that the length of the air cavity increases with increase in air flow rate but there is a certain critical limit in the flow rate above which increase in the air cavity length is no more evident.

• Journal of the Korean Home Economics Association
• /
• v.45 no.4
• /
• pp.113-122
• /
• 2007

The purpose of this study was to investigate weight control and the relative influence of individual variables affecting children's attempts to control weight. The study subjects were 319 elementary school children. First, the average body height and weight of the children who participated in this study was somewhat larger in boys and similar in girls, as compared with the normal body shape of Korean children. More boys were classified as overweight than girls, based on BMI. Both boys and girls were dissatisfied with their body shape, and especially the girls showed higher dissatisfaction rate than the boys did. Almost half of the children were concerned about weight control and girls had higher concern than boys. Of the children, 38.8% had controlled their weight; however there was no difference between their sexes. There were significant differences between children who had and had not experienced weight control in the following variables: stress caused by obesity, body satisfaction, BMI, subjective body shape perception and concern about weight control. Therefore, discriminant function analysis was performed to determine the discrimination of these variables between the two groups. From the analysis results, the most critical factor was BMI in the boys and concern about weight control in the girls. This finding should be reflected in the design of weight control programs for children i.e., boys should be encouraged to perceive correctly their own body shape and to control weight by maintaining a well-balanced diet and moderate exercise over a long period of time, rather than by skipping meals, while girls should be inspired with sound values and attitudes regarding their body shape, rather than provided with the concrete information on how to control weight.

• Korean Journal of Applied Biomechanics
• /
• v.21 no.5
• /
• pp.653-660
• /
• 2011

The purpose of this study was to compare selected kinematic variables between male medalists and a Korean male javelin thrower at the IAAF World Championships, Daegu 2011. The three medalists and one Korean javelin thrower that participated in the Championships were videotaped using three high-speed cameras (300 frames/s, EX-F1 Exilim, Casio, Japan). The results showed that the release and attitude angles of the Korean male javelin thrower (KMJT) were greater than that of the medalists, whereas the attack angle of the KMJT was smaller than that of the medalists. This study also found that the KMJT clearly had a lower release height than the medalists. As a possible adaptation of his physique to the skill, the KMJT used a small trunk inclination angle and produced greater inclination angles at his upper extremities. These results may be linked to an increase in the release angle of the KMJT. There were some difference between the KMJT and the medalists in terms of the length and duration of the delivery phase. In harmony with the shorter length of the delivery phase, its duration was shorter for the KMJT in comparison to the medalists. Because the delivery stride is considered to be a primary generator of endpoint speed, this decrease in the delivery phase time would decrease the javelin velocity at release. The amount of time taken in the delivery phase may be a critical factor to enhance a javelin thrower's performance. Thus, rhythmic movement training specifically designed for the KMJT will help him attain an optimal throwing position.

• Korean Journal of Weed Science
• /
• v.32 no.3
• /
• pp.230-239
• /
• 2012

Coconut (Cocos nucifera L) is one of the predominant plantation crops in Sri Lankan economy which is known to have existed for over thousands of years. During the past decades coconut production had been reduced by a significant quantity. The usage of poor quality planting materials is a major reason for the low coconut production. Thus much attention needs to be paid in coconut nurseries. Weed management is a critical management practice in the nursery. Though glyphosate application is becoming popular in nurseries it can affect weeds as well as coconut seedlings growth. Therefore the effects of glyphosate were evaluated by determining the growth of shoot and root of coconut seedlings. Poly bag nursery was prepared and three treatments were used. Treatments were no glyphosate and manual weeding ($T_1$), application of glyphosate 1.08 ai kg $ha^{-1}$ at 2 monthly interval ($T_2$) and application of glyphosate 1.44 ai kg $ha^{-1}$ at 2 monthly interval ($T_3$). Application of glyphosate at early stage of seedling growth had a no significant effect on growth parameters tested. However, the concentrations of glyphosate negatively affected numbers, volumes and dry weights of secondary, tertiary and quaternary roots at the latter stage of seedling growth. The leaf area and the height of seedling were significantly reduced by the highest concentration of glyphosate. Among the growth parameters tested, seedling girth and shoot dry weight were not affected by the application of glyphosate. These results revealed that the usage of glyphosate at both concentrations negatively affected root growth of coconut seedlings. Based on these results, the both concentration levels of glyphosate should be applied to coconut nurseries before sprouting the seed nuts.

• Journal of IKEEE
• /
• v.18 no.4
• /
• pp.447-455
• /
• 2014

In this research, n-based 4H-MOS Capacitor was fabricated with PECVD (plasma enhanced chemical vapor deposition) process for improving SiC/$SiO_2$ interface properties known as main problem of 4H-SiC MOSFET. To overcome the problems of dry oxidation process such as lower growth rate, high interface trap density and low critical electric field of $SiO_2$, PECVD and NO annealing processes are used to MOS Capacitor fabrication. After fabrication, MOS Capacitor's interface properties were measured and evaluated by hi-lo C-V measure, I-V measure and SIMS. As a result of comparing the interface properties with the dry oxidation case, improved interface and oxide properties such as 20% reduced flatband voltage shift, 25% reduced effective oxide charge density, increased oxide breakdown field of 8MV/cm and best effective barrier height of 1.57eV, 69.05% reduced interface trap density in the range of 0.375~0.495eV under the conduction band are observed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.19 no.5
• /
• pp.587-596
• /
• 2008

For Wireless internet service in Metropolitan area, optimum location selection for base station and cell planning are critical process in determining service coverage by accurate prediction of Wave Propagation Characteristics. Due to different kinds of characteristics in service area such as lay of land, natural feature and material, height and width of artificially made building, it has a great impact on the transmission and distance recovery of wireless network service. Therefore, these facts may cause substantial barriers in predicting & analyzing the expected level of service quality and providing it to subscribers. In this thesis, we have simulated the process to improve quality and coverage of the service by adjusting the location of Base station and the antenna angle that influence the service after the basic location of base station is selected according to the wave prediction model. Based on this simulations test, we have demonstrated the results in which subscribers would get higher quality of wireless internet service along with bigger coverage and the improved quality in the same service coverage area through optimization process of base station.

• Korean Journal of Rural Living Science
• /
• v.7 no.1
• /
• pp.23-29
• /
• 1996

The purpose of this study is to observe the relationship between smoking and control factors to blood pressure, such as sodium and potassium levels of dietary intake and serum in 67 rural university male students(smoker: 35 persons, non smoker: 32 persons). 3-day dietary record and blood sampling were conducted for measurements of the levels of dietary intake and serum. The results were as follows: 1) There are no significance between smokers and non-smokers in height, weight, and BMI. 2) Mean systolic and diastolic blood pressure of smokers and non-smokers were $131.33\pm93.75mmHg, \;119.37\pm80.62mmHg, $ respectively. Blood pressure of smoker was higher than that of non-smokers(p＜0.05). 3) There was no significant difference between smoker and non smoker in dietary potassium intake but dietary sodium intake and Na/K ratio of smoker were higher than those of non-smokers(p＜0.05, p＜0.05). And significant correlation was found between dietary sodium intake and blood pressure of smokers(p＜0.05). 4) Smokers of optimum gustation of salt(0.52%) was higher than that of non-smokers(0.49%). Even though blood pressure of smokers was not critical level, if they smoke continuosely until middle age, their blood pressure will be increased by smoking. The results of this study suggest that no smoking education program for smokers including the information about desirable food habits for prevention of hypertension should be developed.

• Ocean and Polar Research
• /
• v.36 no.2
• /
• pp.145-156
• /
• 2014

Macrobenthic biodiversity in the rocky intertidal areas of the Tae-an region, Republic of Korea, has decreased since the Hebei Spirit oil spill in December 2007. We aimed to investigate ecological roles of Pacific oyster (Crassostrea gigas) because recruitment and growth of oysters are critical to the recovery of damaged rocky shore ecosystem. We surveyed two sites monthly: natural rocky substrate and farming substrate, from July 2012 to January 2013 to identify and compare the changes in macrobenthic fauna. The abundance of young oysters was higher at the natural site. On the other hand, the mean height of oyster on the farming substrate was more than twice as great. The abundance of oyster at the natural site increased until October and then continuously decreased until end of study period. However, the abundance of oyster at the farming site constantly decreased from the beginning of study period. These different growth patterns might be attributable to spatial competition between oyster and a barnacle species (Balanus albicostatus) and environmental factors. At the natural site, physical stress factors including dramatic temperature changes and desiccation a few of the major factors limiting growth during aerial exposure. In addition, motile macrobenthos could be detrimental to oysters because they interrupt filter-feeding activities and hence hamper the growth of oysters. We show the higher recruitment of oysters at the natural site and healthy growth in the farming substrate are due to complicated differences in physical and biological stress factors.

• Ocean and Polar Research
• /
• v.28 no.3
• /
• pp.225-236
• /
• 2006

Seagrass meadows are considered as critical habitats for a wide variety of marine organisms in coastal and estuarine ecosystems. In many cases, studies on the spatial/temporal distribution of seagrass have depended on direct observations using SCUBA diving. As an alternative method fur studying seagrass distribution, an application of hydroacoustic technique has been assessed for mapping seagrass distribution in Dongdae Bay, on the south coast of Korea, in September 2005. Data were collected using high frequency transducer (420 kHz split-beam), which was installed with towed body system. The system was linked to DGPS to make goo-referenced data. Additionally, in situ seagrass distribution has been observed using underwater cameras and SCUBA diving at four stations in order to compare with acoustic data. Acoustic survey was conducted along 23 transects with 3-4 blot ship speed. Seagrass beds were vertically limited to depths less than 3.5m and seagrass height ranged between 55 and 90cm at the study sites. Dense seagmss beds were mainly found at the entrance of the bay and at a flat area around the center of the bay. Although the study area was a relatively small, the vertical and spatial distributions of the seagrass were highly variable with bathymetry and region. Considering dominant species, Zostera marina L., preliminary estimation of seagrass biomass with acoustic and direct sampling data was approximately $56.55g/m^2$, and total biomass of 104 tones (coefficient variation: 25.77%) was estimated at the study area. Hydroacoustic method provided valuable information to understand distribution pattern and to estimate seagrass biomass.