• 한국생산제조학회지
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• 제21권1호
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• pp.7-14
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• 2012

CFRP composite material has the superior specific strength and rigidity compared to metallic materials, and is widely adopted in the various fields. However, CFRP composite material has the weakness in hygrothermal and crash environment. Especially, moisture ingress into composite material under hygrothermal environment can change molecule arrangement and chemical properties. In addition, interface characteristics and material component properties can be degraded. A collapse experiment has been made to research the differences of absorbed energy and deformation mode between absorbed specimens of moisture and non-moisture. As a result of this study, the effect of moisture absorption and impact loads of about 30~50% reduction in strength are shown.

• Advances in concrete construction
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• 제8권3호
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• pp.199-206
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• 2019

High performance sandcretes (HPS) are new concretes characterized by particles having a diameter less than 5 mm, as well as very high mechanical strength and durability. This work consists in finding solutions to make sandcretes with good physico-mechanical and durability properties for this new generation of micro-concrete. However, upgrading ordinary sandcrete into high performance sandcrete (HPS) requires a thorough study of formulation parameters (equivalent water/binder ratio, type of cement and its dosage, kind and amount of super plasticizer, and gravel/sand ratio). This research study concerns the formulation, characterization and durability, in a sulphate environment, of a high performance sandcrete (HPS), made from local materials. The obtained results show that the rheological properties of fresh concrete and mechanical strength differ with the mineralogy, density and grain size distribution of sands and silica fume used.

• Advances in materials Research
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• 제9권3호
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• pp.219-231
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• 2020

The aim of this study is to investigate the durability of fly ash based geopolymer mortar with and without protective coatings in aggressive chemical environments. The source materials for geopolymer are Fly ash and Ground Granulated Blast furnace Slag (GGBS) and they are considered in the combination of 80% & 20% respectively. Two Molarities of NaOH solution were considered such as 8M and 10M. The ratio of binder to sand and Sodium silicate to Sodium hydroxide solution (Na₂SiO₃/NaOH) are taken as 1:2 and 2 respectively. The alkaline liquid to binder ratio is 0.4. Compressive strength tests were conducted at various ages of the mortar specimens. In order to evaluate the performance of coatings on geopolymer mortar under aggressive chemical environment, the mortar specimens were coated with two different types of coatings such as epoxy and Acrylic. They were then subjected to different chemical environments by immersing them in 10% standard solutions of each ammonium nitrate, sodium chloride and sulphuric acid. Drop in compressive strength as a result of chemical exposure was considered as a measure of chemical attack and the drop in compressive strength was measured after 30 and 60 days of chemical exposure. The compressive strength results following chemical exposure indicated that the specimens containing the acrylic coating proved to be more resistant to chemical attacks. The control specimen without coating showed a much greater degree of deterioration. Therefore, the application of acrylic coating was invariably much more effective in improving the compressive strength as well as the resistance of mortar against chemical attacks. The results also indicated that among all the aggressive attacks, the sulphate environment has the most adverse effect in terms of lowering the strength.

• 융합보안논문지
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• 제13권2호
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• pp.165-173
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• 2013

국방개혁과 안보환경의 변화, 저출산으로 인한 병역자원 부족 등으로 우리도 병역체계 변화를 준비해야 할 시기가 도래하고 있다. 이에 선진국의 병역체계를 연구하여 우리의 실정에 맞는 제도를 갖춰 나가는 것이 바람직한 방법이다. 미 육군의 경우는 통합된 입대절차를 보장하기 위해 교육사 예하에 입대사령부를 창설하였으며, 그 예하에 모병사령부, 후보생사령부, 육군훈련소를 두고 있으며, 한국 육군은 인사사령부를 창설하여 현행 인사관리와 병력 획득업무를 총괄하고 있다. 한국도 미국이 시행착오를 범하면서 지나온 과정을 겪고 있다. 현재 우리는 사회적 정치적 이슈의 변화와 신세대의 요구 등에서 모병환경이 변하고 있다. 최근의 변화요소들 중에 모병에 유리할 것은 청년인구와 젊은이들이 공무원이나 안정된 직업을 원하고 있다는 것과 실업률 증가, 대학 학기상승과 관련한 재정적인 부담, 아프가니스탄 및 이라크 등 전쟁관련 국민의 관심 증대, 다양한 군복무 지원정책의 개발 등이 있다. 미 육군의 모병업무는 기본적으로 경영학적 모델을 연구하여 적용하고 있으며, 모병 홍보전략을 풍부한 재정적 뒷받침 하에 수립하고, 연방정부로부터 각종 통계자료와 D/B를 제공받아 활용하면서 많은 대학, 연구소들과 연계된 프로그램을 개발하고 타군과도 긴밀히 관계를 유지하며 적극적으로 모병업무를 수행하고 있다. 우리도 과학적인 체계를 구축하여 통합된 모병을 해야하는 시점에 와 있다.

• 한국전문물리치료학회지
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• 제29권4호
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• pp.262-268
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• 2022

Background: Virtual reality (VR) programs based on motion capture camera are the most convenient and cost-effective approaches for remote rehabilitation. Assessment of physical function is critical for providing optimal VR rehabilitation training; however, direct muscle strength measurement using camera-based kinematic data is impracticable. Therefore, it is necessary to develop a method to indirectly estimate the muscle strength of users from the value obtained using a motion capture camera. Objects: The purpose of this study was to determine whether the pedaling speed converted using the VR engine from the captured foot position data in the VR environment can be used as an indirect way to evaluate knee muscle strength, and to investigate the validity and reliability of a camera-based VR program. Methods: Thirty healthy adults were included in this study. Each subject performed a 15-second maximum pedaling test in the VR and built-in speedometer modes. In the VR speedometer mode, a motion capture camera was used to detect the position of the ankle joints and automatically calculate the pedaling speed. An isokinetic dynamometer was used to assess the isometric and isokinetic peak torques of knee flexion and extension. Results: The pedaling speeds in VR and built-in speedometer modes revealed a significantly high positive correlation (r = 0.922). In addition, the intra-rater reliability of the pedaling speed in the VR speedometer mode was good (ICC [intraclass correlation coefficient] = 0.685). The results of the Pearson correlation analysis revealed a significant moderate positive correlation between the pedaling speed of the VR speedometer and the peak torque of knee isokinetic flexion (r = 0.639) and extension (r = 0.598). Conclusion: This study suggests the potential benefits of measuring the maximum pedaling speed using 3D depth camera in a VR environment as an indirect assessment of muscle strength. However, technological improvements must be followed to obtain more accurate estimation of muscle strength from the VR cycling test.

• 대한안전경영과학회지
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• 제11권3호
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• pp.27-32
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• 2009

Human physical activity to lead daily life is performed by a variety of muscular activity strategies. These strategies can be influenced by characteristics, difficulty and muscle fatigue of work. Therefore this study examines muscular strengths (grip and back strength) of workers engaged in electronics industry in Korea, compares them to mean value of muscular strength by sex and age, accumulates related data and then aims to develop improvement methods of working environment and prevention/management program.

• The Journal of Korean Physical Therapy
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• 제25권2호
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• pp.49-55
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• 2013

Purpose: This study was conducted in order to analyze the effect of proprioceptive neuromuscular facilitation lower extremity pattern on muscular strength and flexibility in an aquatic environment. Methods: Ten members of the experimental group and 10 members of the control group were randomly selected from 20 college students who are in their 20s. Bilateral symmetry pattern among proprioceptive neuromuscular facilitation lower extremity patterns was applied in an aquatic environment in the experimental group three times per week for a period of six weeks, and a set consisted of 10 times, which was repeated 10 times. On the other hand, subjects in the control group did not receive any treatment while maintaining daily life. Muscular strength was measured using a dynamometer and electromyogram system for maximum voluntary isometric contraction of hip flexor, hip extensor, knee flexor, and knee extensor. Cervical flexibility was measured using cervical range of motion instrument for cervical flexion, rotation, and lateral flexion. Lumbar flexibility was measured using back range of motion instrument II for lumbar flexion. Results: For the experimental group, significance was observed for hip flexor, extensor, knee flexor, extensor, cervical flexion, rotation, lateral flexion, and lumbar flexion. For the control group, no significance was observed for any other variables except for cervical flexion. As a result of observation of difference between the two groups, relatively high significance was observed in the experimental group, compared with the control group. Conclusion: In conclusion, proprioceptive neuromuscular facilitation lower extremity pattern had a positive effect on muscular strength and flexibility in an aquatic environment.

• 한국안전학회지
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• 제23권3호
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• pp.12-16
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• 2008

For industrial centrifuges, the state of their welding areas, even with a naked-eye observation, offers potential safety problems such as inconsistent bead formation. STS304, which is used mainly in centrifuges, is made of metal alloys with chrome and nickel as the main ingredients, offering excellent corrosion resistance, thermal resistance, and high strength, and thus allowing it to be used for diverse purposes. This paper conducted tensile and fatigue tests of STS304 to improve the safety of centrifuges. In the findings, for the static behavior of the STS304 material, welded specimens increased their yield and tensile strength compared with the base test specimens, but decreased their elongation ratio. Also, the data dispersion phenomenon of welded specimens remarkably increased.

• 한국대기환경학회지
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• 제15권1호
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• pp.33-39
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• 1999

This study has been performed to develop an efficient electrocharged scrubber. To improve collection efficiency of the scrubber, electric-charger was installed at the forefront of the packed crossflow scrubbers, and an experiment of changing discharge electrode shape and fluctuating electric field strength was undertaken. After using a light-oil boiler for generation of particles in the about 80% weight of submicron size particles was exhausted. Collection characteristics of the electrocharged scrubber were similar to those of two-stage electrostatic precipitator. In this study the collection efficiency of submicron size particles has been much improved, compared with the previous ones. In an experiment of changing discharge electrode and electric field strength, a needle-spike shape wire electrode showed a higher collection efficiency than round shape wire. The collection efficiency becomes increased with an increase of electric field strength.

• Journal of Advanced Marine Engineering and Technology
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• 제17권2호
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• pp.52-59
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• 1993

This study is investigated of tensile and fatigue strength for advanced composite materials under hygrothermal environment. The materials used are two types of Carbon/Epoxy reinforced composite materials i.e., 13$0^{\circ}C$ cure-type composite T-1/347, and 18$0^{\circ}C$ cure-type MM-1/982X. These are composed by cross-ply laminates. Test condition is the distilled water of 8$0^{\circ}C$. The separate absorption contents estimated by the Fick's diffusion rule are similar to the experiment results. The tensile strength of T-1/347 wet specimens more increased than that of dry ones, but that of MM-1/982X decreased. The fatigue strengthes of both T-1/347 and MM-1/982X wet specimen more decreased than those of dry specimens.