• International Journal of Railway
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• v.5 no.2
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• pp.71-76
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• 2012

Recently, axle load, operating speed and traffic density on railroads have had a tendency to increase and thereby cause additional pressure applied on used track. These operating conditions frequently result in service failure due to wear caused by wheel-rail contact and fatigue damage under cyclic loading. Among rail defects, the transverse crack, which has been the most dangerous type of fatigue damages, is developed from the subsurface crack near the rail running face and grows perpendicular to the rail surface. Therefore, it is necessary to investigate systematically the growth behavior of transverse crack for rail steel under mixed mode. In this study, the fatigue crack growth behavior of the transverse crack in rail steel was experimentally investigated under mixed-mode variable amplitude loadings.

• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.63-69
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• 2000

This study investigates a new method of using a concrete disk to calculate stress intensity factor (SIF) for mixed mode cases. The results indicate that the disk method is more accurate than three point bending test (TPB) in obtaining correct SIF values for mixed mode fracture propagation. Stress intensity factors $K_{I}$ and $K_{II}$ are calculated using a center notched disk subjected to splitting load. The notch angle is calculated by finite element (FEM). Fracture toughness $K_\textsc{k}$ of the concrete is obtained from the load intensities at the initiation of crack propagation. According to the finite element analysis(FEA) and disk test, the results show that mode I and mixed mode cracks propagate toward the directions of crack face and loading point, respectively. The results from FEA with maximum stress theory compare well with the experimental date. Unlike TPB method where an accurate fracture toughness value is difficult to obtain due to the irregular shape of load deflection curve and delayed final crack propagation (following slow stable cracking). fracture toughness value is easily measured in the disk test from the crack initial load. Therefore, it is safe to conclude that disk method is more advantageous than TPB method in analyzing combined mode fracture problems.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.701-708
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• 2011

Although Titanium material has superior properties, it belongs to difficult-to-machine materials. The present research applies magnetic abrasive finishing to precision machining of internal-face of titanium pipes, and analyzed & assessed the influence of grinding conditions on magnetic abrasive effects through the removed amount and surface roughness of materials. There was the influence on grinding properties according to change of rotational speed, a total input of mixed powder and an input of grinding liquid, and when the total input, rotational speed and ratio of electrolytic iron versus magnetic abrasives are 8g and 1000rpm, it was most advantageous in aspects of surface roughness and material removal amount, and the grinding liquid remarkably improved the surface roughness and material removal amount only with addition of trace amounts of light oil rather than dry machining conditions. And a result of considering the influence on grinding properties by using an inert gas (Argon gas) for improving grinding properties of the internal-face of titanium pipe, the present research has obtained improvement effects in the removal amount and surface roughness through utilization of an inert gas.

• Journal of Korea Entertainment Industry Association
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• v.14 no.7
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• pp.397-408
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• 2020

This study conducted a focus group interview with 15 college freshman from J college to find out their experiences in non-face-to-face lectures with COVID-19. The contents of the interview were recorded and conducted, and the meaning was analyzed according to the focus group interview procedure through repeated listening. Components were 'Operation of non-face-to-face lectures in unprepared situations', 'Loss of orientation in lectures and departure from learning', 'One way listening', 'The convenience of taking a lectures'. The experience of 'Operating non-face-to-face lectures in unprepared situations' included the start of mixed non-face-to-face lectures, cumbersome and inconvenient online systems, and the demand for tuition refunds. The experience of 'Loss of orientation in lectures and departure from learning' has experienced difficulty in concentrating on lectures, Deficiency in the degree of recognition of learning content, and burden of assignments and exams. The experience of 'One way listening' has experienced lack of interaction between professors and learners and non reflection of liveliness in the field. Finally, participants experienced satisfaction with being able to lectures and repeat lectures at anytime and anywhere they wanted with the convenience of taking lectures. Based on this study, participants called for improvements in the quality lecture contents and interaction between professors and learners, and it is thought that universities will need administrative and financial support and education design and system construction to construct high-quality lecture contents.

• Journal of the Korean Society of Safety
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• v.27 no.1
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• pp.49-54
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• 2012

The objective of this study is to investigate the capacity of epoxy injection method using low pressure mixed with high pressure. Injection depth test and flexural strength test were respectively performed on $40{\times}45{\times}35$ cm and $100{\times}10{\times}40$ cm specimens. Considered as the test variables were injection type(low pressure, low and high pressure), crack width(0.25 mm, 0.50 mm), injection direction(upper, lower, side), and epoxy viscosity(low, medium, high). Test results showed that low viscosity epoxy injection depth of injector using low pressure mixed with high pressure for upper direction were 23 cm and tension strength of crack face repaired by injector using low pressure mixed with high pressure was larger than that of concrete.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.643-648
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• 2001

Class III malocclusion usually becomes manifested at a very early age, most typically evidenced clinically by the appearance of either an edge-to-edge incisor relationship or an anterior crossbite. Anterior crossbite, by it-self, retards growth of maxilla, and accelerates growth of mandible. So, treatment should be started as early as the patient cooperates, removing any factors or forces that inhibit growth and development in the same physiologic maxillary displacement direction. The facial mask is effective in most developing Class III patients, because the appliance system affects virtually all areas contributing to a Class III malocclusion. Thus, the facial mask can be applied to most developing Class If cases regardless of the specific etiology. In these cases, the results were followed. Anterior crossbite was corrected by anterior movement of maxilla and downward backward rotation of mandible and simultaneously, lower facial height was increased. So, it can be concluded that the facial mask is effective in treating growing patients with a deficient maxilla.

• Proceedings of the Korea Contents Association Conference
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• 2007.11a
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• pp.920-923
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• 2007

Cyber Educations of University are increasing in development of Contents and spreading Internet Network. We need to classify a cyber education by the type, and analyze environment. In addition, We need a measurement of effectiveness and the research of method for activation of cyber education. In this paper, we classify into partial cyber which is mixed face-to face lecture and cyber lecture and full cyber which is organized all cyber lecture, and investigate a satisfaction of learner. We analysis also the problem in cyber classes according to their types, and propose a plan for activation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.1
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• pp.19-32
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• 2011

The risk assessment is essential for tunnel design in order to minimize risks associated with uncertainty about geological conditions and tunneling method. This paper provides a comparative risk analysis of a large single bore TBM driven tunnel against sequentially excavated NATM tunnel for a mixed-face large-diameter urban tunnel project near or under a river. The focus of this assessment is on the risks associated with the tunnel excavation methods, in particular whether a TBM or NATM presents more or less risk to achieve the planned excavation duration and bring the project within the estimated bid price. First, the impacts and risks to tunnel construction under each method were discussed, and the risks were scored and ranked in the order of perceived severity and likelihood. Finally, the assessment from a risk based perspective was conducted to decide which alternate tunneling method is more likely to deliver the project with the least time and cost. It is very important to note that this study is only applied to this tunnel project with specific geological conditions and other contract requirements.

• The korean journal of orthodontics
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• v.9 no.1
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• pp.67-84
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• 1979

The author measured the right and left craniofacial skeleton using posteroanterior cephalography of 124 male and 97 female subjects of ages ranging 2-6 years, 7-13 years and adult group on Korean. Statstical parameters were calculated by computer from the data. The results of the study were as follows. 1. In the male and female group of deciduous dentition, the right side measurements were slightly greater than the left side measurements, and generally male measurements were greater than female measurements. 2. In the both sex group of mixed dentition, the right side measurements were greater than the left side measurements, and in comparision of sex, the female recognized more growth, and development than male, especially on the cranial base, lateral maxilla, lower maxilla and dental region. 3. In the permanent dentition group, regardless of sex, the right side measurements were greater than the left side measurements, and in the sex difference, male was conspicuously greater than female on both sides measurements. 4. In the permanent dentition group, the asymmetry of the face was striking than deciduous dentition and mixed dentition group.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.368-375
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• 2010

To alleviate NOx emission, a variety of approaches has been applied. In marine diesels, the application of SCR systems has been considered an effective exhaust aftertreatment method for NOx emission control. Most current SCR systems use a various catalyst for the reaction of ammonia with NOx to form nitrogen and water. In theory, it is possible to achieve 100% NOx if the NH3-to-NOx ratio is 1:1. However, the reaction has a limited non-uniformity of the exhaust gas flow and ammonia concentration distribution. Therefore it is necessary to investigate the optimum flow conditions. In order to achieve uniform flow at monolith front face, we are equipped with a various mixed device. In this paper, it is presented that the mixed devices play an important role improvement of flow patterns and particle distributions of NH3 by numerical simulation.