• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.900-909
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• 2002

Fibers play a role to increase the tensile strength and cracking resistance of concrete structures. The post cracking behavior must be clarified to predict cracking resistance of fiber reinforced concrete. The purpose of this study is to develop a realistic analysis method for the post cracking behavior of synthetic fiber reinforced concrete members. For this purpose, the cracked section is assumed to behave as a rigid body and the pullout behavior of single fiber is employed. A probabilistic approach is used to calculate effective number of fibers across crack faces. The existing theory is compared with test data and shows good agreement. The proposed theory can be efficiently used to describe the load-deflection behavior, moment-curvature relation, load-crack width relation of synthetic fiber reinforced concrete beams.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_2
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• pp.675-682
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• 2020

Multi-wire sawing is the prominent technology employed to cut hard material ingots into wafers. This paper aimed to research the effect of diamond toughness index on the cutting performance of electroplated diamond wire. Three different toughness index of diamond abrasives were used to manufacture electroplated diamond wires. The cutting performance of electroplated diamond wire is verified through experiments, in which sapphire ingot are cut using single wire sawing machine. A single wire saw for constant load slicing is developed for the cutting performance evaluation of electroplated diamond wire. Choosing the cutting depth, total cutting depth, cutting force and wear of electroplated diamond wires as evaluation parameters, the performance of electroplated diamond wire is evaluated. The results of this study showed that there was a significant direct relationship between the toughness index of diamond abrasives and the cutting performance. Results demonstrated that diamond abrasive with a high toughness index showed higher cutting performance. However, all diamond abrasives showed similar cutting performance under low load conditions. The results of this paper are useful for the development of cutting large diameter ingots and cutting high hardness ingots at high speed.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.67-80
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• 2014

Long-term stability and delayed failure of granite were evaluated through the laboratory test based on Wilkins method and Brazilian disc test (BDT) which yields tensile strength, mode I fracture toughness and subcritical crack growth parameters. Then, the long-term strength of granite was estimated by using analytical models and long-term stability of compressed air-energy storage (CAES) pilot cavern pressurized up to 5 ~ 6 MPa was evaluated using numerical code, FRACOD with the determined subcritical crack growth parameters. The results of test and analyses showed that the subcritical crack growth index, n was determined as 29.39 and the inner pressure of 5 ~ 6 MPa had an insignificant effect on the long-term stability of pilot cavern. It was also found that the measurement and analysis of acoustic emission events can describe the accumulation of damage due to subcritical crack growth quantitatively. That is, AE monitoring can provide the current status of rock under loading if we make an identical installation condition in the field with that of the laboratory test.

• Journal of the Korean GEO-environmental Society
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• v.9 no.3
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• pp.17-28
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• 2008

In this study, the residual strength prediction models were proposed by measuring various residual strength according to pit characteristics for metallic water pipes such as cast iron pipe (CIP), ductile iron pipe (DIP), and steel pipe (SP). The exponential prediction model was better fitted to measured residual tensile strength for CIP. In case of DIP and SP, the prediction model using loss of strength was more exactly predicted compared with other model types. The fracture toughness were averagely $40.46kgf/mm^2{\sqrt{mm}}$ for CIP, $85.27kgf/mm^2{\sqrt{mm}}$ for DIP, and $92.27kgf/mm^2{\sqrt{mm}}$ for SP, the determination coefficient ($R^2$) of between measured residual tensile strength and predicted values for residual strength prediction models using fracture toughness was estimated from 0.44 to 0.86. Especially, the proposed residual tensile strength prediction models were applied for the verification and reliability to CIPs and DIPs at 14 sites. The determination coefficient ($R^2$) between measured residual tensile strength and predicted values was estimated from 0.76 to 0.78. Therefore it was thought that the proposed residual tensile strength models could help to support resonable and economical decision of rehabilitation/replacement.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.305-311
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• 2000

Applicability of crack arrest load measured from the Charpy V-notch impact test has been investigated to predict the fracture toughness of nuclear reactor pressure vessel (RPV) steels (ASME SA508 Cl.3). The temperature dependence of the crack arrest load was well described by the type of exponential function characterized by an index temperature at which the crack arrest load is 2kN. The specific index temperature, which also well correlated with $T_{NDT}\;and\;T_{41J}$ is expected to be representative index temperature characterizing the crack arrest fracture toughness of RPV steels. Also, the crack arrest load correlated well with the stable crack length measured from the fracture surface. From the measurements of the crack arrest load and the stable crack length, the lower bound fracture toughness, $K_{Ia}$ of RPV steels could be predicted with sufficient accuracy.

• Journal of Oral Medicine and Pain
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• v.33 no.3
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• pp.257-267
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• 2008

The mentophysical disease causes diseases in digestive, respiratory, circulating systems, including chronic pain, through combined reactions from different individual characteristics, mental stress and temperamental factors. The most common symptom related to orofacial area is pain and the contributive factors include biological, behavioral, environmental, social, emotional, recognitive factors. These factors affect the course of the symptom according to individual's character and human nature. In pain, sleep acts as a contributive factor, and pain could bring about sleep disturbance and vice versa. Deterioration of sleep quality would act as a factor that aggravates mental stress. Therefore, relatively accurate and simple mental examinations and sleep quality test should be carried out for the patients with symptoms related to orofacial area. This study evaluated the mental state in relation to the sleep quality which could affect orofacial pain. The number of poor sleeper was 18 in male subjects, and 1 in female subjects and PSQI global index was higher in male($6.11{\pm}2.38$) than female($4.67{\pm}2.18$). SCL-90-R index showed no sex difference. Poor sleeper showed significantly high value in SOM, O-C, I-S, ANX, PHOB, PSY, GSI, PST. When SCL-90-R T scores were compared according to sleep quality, higher the subjective sleep quality score, O-C and I-S showed significant increase. As sleep disturbances score increased, PAR, PSY, PST showed statistically significant increase. In comparison of SCL-90-R T score according to daytime dysfunction, statistically significant increase in DEP, ANX, HOS, PHOB, PAR, GSI was observed. Therefore, the quality of sleep and psychological status have a high correlation. This is likely to influence chronic pain in the orofacial field. As a result, clinicians treating orofacial pain should evaluate the sleep quality and psychological status of the patient. Further studies of larger sample sizes including various age, occupation, and pain groups are necessary in order to apply the results to clinical practice.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.77-82
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• 1999

The compleete joining method for dissimilar hot die punch materials and its real-time evaluation method are not available at present. Brazing method has been used for joining them, but it is known that the welded joint by the brazing has the lower bonding efficiency and reliability than the diffusion welding. The friction wleding with a diffusion mechanism in bonding was applied in this study. So, this work was carried out to determine the optimal friction welding conditions and to analyze mechanical properties of friction welded joints of hot die punch materials (STD61 for the blade part of hot die punch) to alloy steel (SCM440 for the shank park of hot die punch) such as plunger. In addition, acoustic emission test was carried out during friction welding to evaluate the weld quality.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.13-22
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• 2015

This study suggests mixing steel fibers in concrete to secure the toughness of the columns. Therefore, to evaluate the structural behavior of welded built-up square columns filled with steel fiber reinforced concrete, ten stub column specimens were fabricated for compressive loading test with variables of steel fiber mixing ratio and loading condition. It is deduced that the steel fibers continue to provide tensile strength even after the concrete cracks and thus improve the strength and behavior of the column when bending moment is applied to it. A small amount of steel fibers can improve compressive strength and bending strength and thus produce economically efficient results when employed in structural design.

• The Journal of the Korea Contents Association
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• v.16 no.12
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• pp.360-372
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• 2016

South Korea has become richer economically than the past, but still level of happiness is low. This research was conducted to verify the relationships among mental health, self-forgiveness, and psychological well-being. Participants were 232 college students in an university in Seoul. Methods of data analysis were ANOVA, regression analysis, and path analysis. As a result of analyses, first, MMPI-2 clinical scales which showed significant correlation with psychological well-being were as follows: Hs, D, Pd, Pa, Pt, Sc, Si. Second, PSY-5 scales which showed significant correlation with psychological well-being were as follows: PSYC, NEGE, INTR. Third, stepwise regression analysis revealed that Sc, Si and Pd among clinical scales of MMPI-2 were associated with psychological well-being. Fourth, PSYC, NEGE and INTR among clinical scales of PSY-5 scales were associated with psychological well-being. Fifth, self-forgiveness had a significant mediating effect in the relationship between mental health and psychological well-being. Based on the results, implications related to importances of mental health and self-forgiveness were discussed for increasing psychological well-being of college students.

• Journal of The Korean Society of Integrative Medicine
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• v.2 no.1
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• pp.109-116
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• 2014

Purpose : The purpose of this study was to perform the calf-raise exercise on the stable support surface and unstable support surface for comparing deference of the gastrocnemius thickness changes that measured by ultrasonography. Method : Subjects stand on unstable support surface and a stable support surface with both feet. Keeping calf-raise position in the 3 seconds, and then had to return back to the starting position. Total of 3 sets of 15 repetitions performed and give a 30-second rest between each set. In this way, exercise performed 3 times a week, performed a total of 6 weeks. Result : 1. gastrocnemius muscle thickness before and after exercise in experimental group A was significantly different(p<.05). 2. gastrocnemius muscle thickness before and after exercise in experimental group B was significantly different(p<.05). 3. gastrocnemius muscle thickness in experimental group A and experimental group B was significantly difference(p<.05). Conclusion : In conclusion, calf-raise exercise on unstable support surface was more efficient than stable support surface for increasing thickness of gastrocnemius.