• Journal of Korean Physical Therapy Science
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• v.24 no.2
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• pp.17-26
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• 2017

Purpose: The importance of core exercise on muscle activation of the lower extremity has been studied. This study investigated the effects of core exercise using pressure biofeedback unit on muscle strength of lower extremity. Method: Fourteen healthy young adults (7 males and 7 females) were recruited. They were randomly separated two groups and performed core exercise using pressure biofeedback unit of one set for three minutes, 10sets per day for three weeks. Result: The mean of muscle strength of lower extremity, maximum power of muscle and peak TQ/BW in core exercise group significantly increased after core exercise using bio feedback unit (p<.05). Conclusion: These findings suggest that core exercise using pressure biofeed-back unit may help improving of muscle strength of lower extremity in young adults.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.3
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• pp.288-299
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• 2003

Statement of problem: Many kinds of post and core systems are in the market, but there are no clear selection criteria for them. Purpose: The purpose of this study was to compare the flexural strength and modulus of elasticity of core materials, and measure the bending strength of post systems made of a variety of materials. Material and Methods: The flexural strength and elastic modulus of thirteen kinds core buildup materials were measured on beams of specimens of $2.0{\times}2.0{\times}24{\pm}0.1mm$. Ten specimens per group were fabricated and loaded on an lnstron testing machine at a crosshead speed of 0.25mm/min. A test span of 20 mm was used. The failure loads were recorded and flexural strength calculated with the measured dimensions. The elastic modulus was calculated from the slopes of the linear portions of the stress-stram graphs. Also nine kinds commercially available prefabricated posts made of various materials with similar nominal diameters, approximately 1.25mm, were loaded in a three-point bend test until plastic deformation or failure occurred. Ten posts per group were tested and the obtained data were anaylzed with analysis of variance and compared with the Tukey multiple comparison tests. Results: Clearfil Photo Core and Luxacore had flexural strengths approaching amalgam, but its modulus of elasticity was only about 15% of that of amalgam. The strengths of the glass ionomer and resin modified glass ionomer were very low. The heat pressed glass ceramic core had a high elastic modulus but a relatively low flexural strength approximating that of the lower strength composite resin core materials. The stainless steel, zirconia and carbon fiber post exhibited high bending strengths. The glass fiber posts displayed strengths that were approximately half of the higher strength posts. Conclusion: When moderate amounts of coronal tooth structure are to be replaced by a post and core on an anterior tooth, a prefabricated post and high strength, high elastic modulus core may be suitable. CLINICAL IMPLICATIONS In this study several newly introduced post and core systems demonstrated satisfactory physical properties. However when the higher stress situation exists with only a minimal ferrule extension remaining a cast post and core or zirconia post and pressed core are desirable.

• Restorative Dentistry and Endodontics
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• v.29 no.2
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• pp.191-199
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• 2004

The purposes of this study were to estimate the material properties of the recently developed domestic composite resins for core filling material (Chemical, Dual A, Dual B；Vericom, Korea) and to compare them with other marketed foreign products (CorePaste, Den-Mat, USA；Ti-Core, Essential Dental Systems, USA；Support. SCI-Pharm. USA). Six assessments were made：working time. setting time. depth of polymerization. flexural strength. bonding strength. and marginal leakage. All items were compared to ISO standards. All domestic products satisfied the minimum requirements from ISO standards (working time：above 90 seconds. setting time：within 5 minutes). and showed significantly higher flexural strength than Core Paste. Dual A and B could. especially. reduce the setting time to 60 seconds when cured with $600mW/cm^2$ light intensity. All experimental materials showed 6 mm depth of polymerization. Bond strengths of Ti-Core and Dual B materials were significantly higher than the other materials. Furthermore. three domestic products and Ti-Core could reduce the microleakage effectively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.193-194
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• 2022

The use of high-strength grout for facility foundations and bridges has recently been expanding in offshore wind farms. Offshore wind farms require a bearing capacity for horizontal loads such as wind, waves. Therefore, in this study, the strength of the high-strength grout discharged through pump pressure was measured and compared with the existing strength to secure the strength after the underwater pump pressure of the high-strength grout used in the offshore wind connection. The compressive strength measurement showed that the strength difference at each position of the core specimen was 1% higher than that of the other specimens, and there was almost no change in the strength according to the height. The strength of the core specimen decreased by 23% compared to the existing strength, which is similar to the result of this study because the strength of the core specimen decreased by approximately 25% compared to the general specimen according to related research. Therefore, it is believed that there is no decrease in strength due to underwater pumping.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1130-1131
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• 2006

We found that the """interface reaction between Ni-based alloy bond, diamond, and steel core is very critical in bond strength of diamond tool. None element from metal bond diffuses into the steel core but the Fe element of steel core was easily diffused into the bond. This diffusion depth of Fe has a great effect on the bonding strength. The Cr in steel core accelerated the Fe diffusion and improved the bond strength, on the other hand, carbon decreased the strength. Ni-based alloy bond including Cr was chemically bonded with diamond by forming Cr carbide. However, the Cr and Fe in STS304 were largely interdiffused, the strength was very low. The Cr passivity layer formed at surface of STS304 made worse strength at commissure in brazing process.

• Computers and Concrete
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• v.11 no.5
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• pp.463-473
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• 2013

As known, concrete classes are described as strength of standard specimens produced and kept in ideal conditions, not including reinforcement and not subjected to any load effect before. Under the circumstances, transforming core strengths to the standard specimen strength is necessary and considering all parameters, affected on the core strength, is inevitable. In fact, effects of the reinforcement and the load history on concrete strength are generally neglected when these mentioned transforms are performing. The main purpose of this paper is investigating the effects of the reinforcement and the load history on the core strength. This investigation is experimentally performed on cores drilled from specimens having different keeping conditions, reinforced, unreinforced, subjected to bending and central pressure in various proportions of failure load during specified periods. Obtained results show that the importance of these effects cannot be neglected.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.397-400
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• 2004

This research aims to estimate the shear strength of the composition of prestressed hollow-core slab and steel beam. The shear strength of prestressed hollow-core slab combined with the steel beam decreases, as the beam deflection increases to a considerable extent. Existing studies on the shear strength of prestressed hollow-core slab are mostly limited to 265mrn- and larger thickness slab on concrete beam. This study investigates the slab of 100mm-thickness combined with steel beam instead of concrete beam. Five shear connector methods are proposed and the shear strength is estimated with or without the beam deflection for each composition method, respectively. Finally the reduction coefficient $(\beta)$ for the transverse shear stress$(\tau_{zx})$, which is critical for the failure of prestressed hollow-core slab, is proposed.

• Journal of the Korean Society of Physical Medicine
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• v.16 no.1
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• pp.111-121
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• 2021

PURPOSE: This study examined the effects of core stability exercise on the strength, activation of the trunk muscle, and pulmonary function in a Guillain-Barre syndrome (GBS) patient. METHODS: A 38-year-old male with GBS was enrolled in the study. A core stability exercise program was implemented for four weeks with a duration of 30 min/day and a frequency of three days/week. The program consisted of abdominal crunch, Swiss ball crunch, bicycle crunch, medicine ball sit-up with a toss, medicine ball rotational chest pass, raised upper body and lower body, and dead bug. Measurements of the strength of the trunk muscle (trunk flexion and hip flexion), activation of trunk muscles (rectus femoris; RA, external oblique abdominal; EOA, internal oblique abdominal; IOA, erector spinae; ES), and pulmonary function (forced expiratory capacity; FVC, forced expiratory volume at one second; FEV1) were taken before and after four weeks of core stability exercise. RESULTS: The strength of trunk muscles increased in the trunk and hip flexion after four weeks of core stability exercise, respectively, compared to the baseline levels. Activation of the trunk muscles increased in RA, EOA, and IOA after four weeks of core stability exercise compared to baseline levels, but decreased in ES after four weeks of core stability exercise compared to the baseline levels. The pulmonary function increased in FVC and FEV1 after four weeks of core stability exercise compared to the baseline levels. CONCLUSION: These results suggest that core stability exercise improves strength, Activation of the trunk muscle, And pulmonary function in patients with GBS.

• Journal of the Korea Convergence Society
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• v.12 no.2
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• pp.185-191
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• 2021

The characteristics of the foundry sand were analyzed for water jacket core required to prevent structural deformation from the heat generated in the cylinder bore during the casting of the cylinder block of an automobile. The sand core tensile strength tester, AFS-GFN, and optical microscope were used to evaluate the its properties. If the SiO2 content is high in the foundry sand, the dimensional defects and veining defects occur due to high temperature expansion. Also, if it is too low, the core breakage, porosities, chemical burn-on defects occur. The particle size index and grain shape influenced the core strength and resin consumption, resulting in fluctuations in defect types. The higher the alkalinity of the dried sand, the lower the core strength. And the more basic, the lower the core strength. At the resin content of 1.6~1.8%, the increase in core strength after 1 hour curing was approximately at its maximum.

• Journal of the Korean Society of Physical Medicine
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• v.13 no.2
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• pp.157-165
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• 2018

PURPOSE: The purpose of this study was carried out to investigate the effect of plyometric training combined with core strength training on the balance and agility of adolescent soccer players. METHODS: A total of 36 subjects participated in this study. Subjects were randomly divided 3 groups and assigned PG (plyometric training group), CSG (core strength training group) and PCG (plyometric training combined with core strength training group). Each group was assigned to 12. Intervention was performed three times a week for 4 weeks. The training was performed for 60 minutes a day. Subjects were warmed up for 10 minutes, and performed main exercise for 40 minutes. Finally, subjects performed cool-down exercise including stretching for 10 minutes. A Statistical analysis was performed the paired t-test for the comparison pre and post intervention. A comparison among the groups was using one-way ANOVA, and the LSD was used for the post-test. RESULTS: The balance and agility were statistically significant differences in all group (p<.05). There was no significant difference in the balance factors between the three groups, but there was a significant difference in the agility factor (p<.05). CONCLUSION: Plyometric training and plyometric training combined with core strength training were effective for the balance and agility of adolescent soccer players.