• Title/Summary/Keyword: Curing effect

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The Effect of Hand Grip Force on the Activity of Shoulder Muscles in the Patterns of Arm Position (팔자세의 유형에서 손의 쥐기 강도가 어깨근육의 활성도에 미치는 영향)

  • Choi, Hyun
    • Journal of Digital Convergence
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    • v.10 no.9
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    • pp.435-441
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    • 2012
  • This study is intended to provide a basic clinical data useful for preventing shoulder injuries related to occupation and curing them, by measuring the shoulder muscle activity of normal adults in an arm posture type of a wide shoulder joint angle, according to several differences of hand grip force. In order to examine the shoulder muscle activity during hand grips at a variety of intensity, according to the arm posture type, MVCs of all subjects were measured, and %MVCs of anterior deltoid, supraspinatus, the upper trapezius and infraspinatus at 0 degree, 90 degrees and 160 degrees of shoulder angle were yielded according to the grip force in an arm posture type, changing the maximum grip force into 30%, 50% and 90%, randomly. When measuring the hand grip at 30%, 50% and 70% of the maximum grip force to compare %MVC of each group depending on the arm posture type, there were no significant differences of muscle activity at 0 degree of shoulder angle among anterior deltoid, supraspinatus, the upper trapezius and infraspinatus, but there were significant differences of it among them at 90 degrees and 160 degrees of should angle(p<.001). According to the results of post-hoc test, also, anterior deltoid had the highest muscle activity, whereas the upper trapezius had the lowest muscle activity.

Shear Strength of Interface between Natural Aggregate Concrete and Recycled Aggregate Concrete (천연골재 콘크리트와 순환골재 콘크리트 접합면의 전단강도)

  • Moon, Hoon;Choi, Ik-Je;Kim, Ji-Hyun;Chung, Chul-Woo;Kim, Young-Chan
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.8 no.1
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    • pp.26-32
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    • 2020
  • Concrete recycling is becoming mandatory rather selective due to depletion of constructional materials and increase of concrete waste. Studies on recycling concrete are conducted in various point of view for long time. However, standard or guideline of many countries for the application of recycled aggregate concrete(RAC) has restrictions such as low replacement rate of coarse aggregate and no fine aggregate allowed due to inferior material properties of recycled aggregate. This study intends to figure out the feasibility of casting natural aggregate concrete(NAC) and RAC separately in a structural member. In making RAC, replacement rate of coarse aggregate was 50, 100% in RAC and treatment of interface of two concretes is introduced. RAC treatment of recycled aggregate or inclusion of additives was not done as it can increase embodied energy of concrete work. Double-shear test with uniformly distributed loading was adopted to evaluate shear strength at the interface of two concretes. After curing it was hard to distinguish interface of two concretes. Experimental result revealed that specimen with higher replacement rate showed higher shear-to-compressive strength ratio, which is possibly attributed to coarse aggregate size and roughness of sheared section. Further study on the effect of various parameters is required and subsequent research activity is on-going.

Development of Self-Repairing Smart Concrete Using Micro-Biologically Induced Calcite Precipitation (미생물의 방해석 석출 작용을 이용한 자기보수 스마트 콘크리트 개발에 관한 연구)

  • Kim, Wha-Jung;Ghim, Sa-Youl;Park, Sung-Jin;Choi, Kil-Jun;Chun, Woo-Young
    • Journal of the Korea Concrete Institute
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    • v.22 no.4
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    • pp.547-557
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    • 2010
  • This paper presents a study on the development of next generation smart concrete in an eco-friendly manner using micro-biologically induced calcite precipitation (MICP) via microbial biomineralization. It seems that currently, the reformation and functional improvement of concrete using MICP can be achieved using Sporosarcina pasteurii, which is a representative microorganism that produces calcite precipitation. Based on previous studies on MICP the biochemical tests and crystallinity evaluation of cement using sporoasrcina pasteurii and four additional micro-organisms from the concrete structures as identified by 16S rDNA sequence analysis were conducted. Also by applying the Sporosarcina pasteurii and separated four effective micro-organisms from the concrete structures to mortar, the compressive strength improvement by varying curing conditions, repair of crack were examined, and plans for future study were suggested. The effect of the application of effective micro-organisms can lead to the development of a new material that will contribute to resolution of environmental problems and facilitate repair work, and this can also serve as a new research theme in the future. In addition, the importance of this study is to use micro-organism, which is found common in concrete structures, this new microbial is not only environmentally safe but also persists in the natural environment for an extended period of time. Therefore, it seems to have a great potential to became a new environmentally low-burdened functional material.

Electrical Property in InAn/GaAs Quantum Dot Infrared Photodetector with Hydrogen Plasma Treatment (수소화 처리된 InAs/GaAs 양자점 적외선 수광소자의 전기적 특성)

  • Nam H.D.;Song J.D.;Choi W.J.;Cho W.J.;Lee J.I.;Choe J.W.;Yang H.S.
    • Journal of the Korean Vacuum Society
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    • v.15 no.2
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    • pp.216-222
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    • 2006
  • In this paper, we investigated the effect of hydrogen-plasma (H-plasma) treatment on the electrical and optical properties of a quantum dot infrared photodetector (QDIP) with a 5-stacked InAs dots in an InGaAs/GaAs well structure and $Al_{0.3}Ga_{0.7}As/GaAs$ SL (superlattice) current blocking layer. It has been observed that H-plasma treatment didn't affect the band structure of QDIP. It has been also observed that the H-plasma treatment on the QDIP not only enhance the electrical property of QDIP by curing the defect channels in $Al_{0.3}Ga_{0.7}As/GaAs$ SL but also introduce defects in QDIP structure. The H-plasma treatment for 10 min with 20 W of RF power provided the lowest dark current, which made it possible to measure the photo-current (PC) of QDIP whose PC was not detectable without the H-plasma treatment due to the high dark current.

Estimation of Aging Effects on Determination of Compressive Strength of Concrete by Non-Destructive Tests (비파괴 시험에 의한 콘크리트 압축강도 및 반발도의 재령계수 추정)

  • 김민수;윤영호;김진근;권영웅;이승석
    • Journal of the Korea Concrete Institute
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    • v.14 no.5
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    • pp.782-788
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    • 2002
  • Several non-destructive test methods have been developed to estimate compressive strength of concrete in other countries. However, their applications are limited in domestic concrete due to their inaccuracies. The purpose of this study is to propose an aging coefficient of compressive strength of structural concrete in rebound number method and ultrasonic pulse velocity method for domestic concrete. The test variables include type of aggregate, curing condition, and compressive strength. Two approaches are used to estimate aging coefficient. One is evaluated by uniform linear regression equation for all ages and shows uniform strength reduction coefficient regardless of material properties and the other is evaluated by individual regression equation for each ages and shows nonuniform strength reduction and rebound increasing coefficients which decrease with increasing of rebound number and compressive strength. The latter result which can include the effect of rebound number and compressive strength is more resonable than the former.

Characteristics of Unconfined Compressive Strength of Dredged Clay Mixed with Friendly Soil Hardening Agent (준설토와 친토양 경화재 혼합지반의 일축강도특성)

  • Oh, Sewook;Yeon, Yonghum;Kwon, Youngcheul
    • Journal of the Korean GEO-environmental Society
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    • v.17 no.10
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    • pp.73-81
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    • 2016
  • In the construction on low strength and high compressible soft ground, the many problems have been occurred in recent construction project. therefore, the soil improvement have been developed to obtain high strength in relatively short period of curing time. Based on the laboratory tests using undisturbed marine clay, the effect of improvement on soft ground was estimated. Deep mixing method by cement have been virtually used for decades to improve the mechanical properties of soft ground. However, previous researches set the focus on the short term strength the about 10% of cement treated clay. In this paper, cement and Natural Soil Stabilizer (NSS) were used as the stabilizing agent to obtain trafficability and mechanical strength of the soft clay. Based on the several laboratory tests, optimum condition was proposed to ensure the mechanical strength and compressibility as the foundation soil using cement and NSS mixed soil. Finally, research data was proposed about the applicability of NSS as the stabilizing agent to soft clay to increase the mechanical strength of soil.

Effects of hydrogen peroxide pretreatment and heat activation of silane on the shear bond strength of fiber-reinforced composite posts to resin cement

  • Pyun, Jung-Hoon;Shin, Tae-Bong;Lee, Joo-Hee;Ahn, Kang-Min;Kim, Tae-Hyung;Cha, Hyun-Suk
    • The Journal of Advanced Prosthodontics
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    • v.8 no.2
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    • pp.94-100
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    • 2016
  • PURPOSE. To evaluate the effects of hydrogen peroxide pretreatment and heat activation of silane on the shear bond strength of fiber-reinforced composite posts to resin cement. MATERIALS AND METHODS. The specimens were prepared to evaluate the bond strength of epoxy resin-based fiber posts (D.T. Light-Post) to dual-curing resin cement (RelyX U200). The specimens were divided into four groups (n=18) according to different surface treatments: group 1, no treatment; group 2, silanization; group 3, silanization after hydrogen peroxide etching; group 4, silanization with warm drying at $80^{\circ}C$ after hydrogen peroxide etching. After storage of the specimens in distilled water at $37^{\circ}C$ for 24 hours, the shear bond strength (in MPa) between the fiber post and resin cement was measured using a universal testing machine. The fractured surface of the fiber post was examined using scanning electron microscopy. Data were analyzed using one-way ANOVA and post-hoc analysis with Tukey's HSD test (${\alpha}=0.05$). RESULTS. Silanization of the fiber post (Group 2) significantly increased the bond strength in comparison with the non treated control (Group 1) (P<.05). Heat drying after silanization also significantly increased the bond strength (Group 3 and 4) (P<.05). However, no effect was determined for hydrogen peroxide etching before applying silane agent (Group 2 and 3) (P>.05). CONCLUSION. Fiber post silanization and subsequent heat treatment ($80^{\circ}C$) with warm air blower can be beneficial in clinical post cementation. However, hydrogen peroxide etching prior to silanization was not effective in this study.

Effect of immediate provisional restoration on the preservation of gingival contour (발치 창에 삽입한 임시 수복물의 치은형태 보존 효과)

  • Lee, Jin-Gyu;Lee, Ju-Youn;Choi, Jeom-Il
    • Journal of Periodontal and Implant Science
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    • v.33 no.4
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    • pp.563-571
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    • 2003
  • One of the central components of periodontal therapy is the improvement of esthetics. The presence and appearance of interdental papillae plays an important role of periodontal esthetics. The aim of the present study was to investigate how immediate provisional restoration preserve the shape of interdental papilla around the extraction socket and the width of bucco-lingual of gingiva. Another aim was to investigate the change in the interdental papilla and the amount of vertical bone fill of a extraction socket in relation to the interdental alveolar bone levels adjacent the alveolar socket. A total of 19 patients (11 male, 8 female, mean age of 50.57${\pm}$8.16), who visited the Department of Periodontology, Pusan National University and had more than one anterior tooth scheduled to be extracted due to an advanced periodontal disease were included in the present study. After initial periodontal therapy, the extracted teeth were reshaped of the root and placed into the socket followed by splinting with adjacent teeth with self-curing resin. The width of hucco-lingual of gingiva and interdental papilla height were measured at baseline, 1, 3, 6, 9 and 12 month and the periapical radiographic examination were taken at baseline, 6 and 12month following the extraction. The amount of vertical bone fill in the extraction socket were calculated. At 12 months following the extraction, the changes in mesial and distal interdental papilla and the width of bucco-lingual showed -1.06${\pm}$0.48mm, -0.844${\pm}$0.50mm, -1.50${\pm}$0.96m, relatively. The positional change in the interproximal papillae was significantly associated with the interdental bone level adjacent to the extraction socket(p=0.028). The higher the interproximal bone level adjacent the extraction socket, the greater the amount of bone fill in the extraction socket(p<0.001). In conclusion, it was thought that immediate provisional restoration could minimize the loss of the width of bucco-lingual and interproximal papillae around the extraction socket. In addition, the higher the interproximal bone level adjacent the extraction socket, the greater the amount of bone fill and the smaller the reduction of papillary height around the extraction socket.

SHEAR BOND STRENGTH OF GIOMER AND SELF-ETCHING PRIMER ON THE DENTIN (Giomer와 자가 산부식 접착제의 상아질에 대한 전단 결합강도)

  • Yoon, Eun-Young;Lee, Nan-Young;Lee, Sang-Ho
    • Journal of the korean academy of Pediatric Dentistry
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    • v.37 no.4
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    • pp.422-428
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    • 2010
  • Giomer is fluoride-releasing, resin-based dental materials that comprise PRG(pre-reacted glass ionomer) filler. The purpose of this study was to evaluate the shear bond strength of Giomer using self-etching primer systems to bovine dentin. Bovine incisors were mounted in self-curing orthodontic resin and the facial surfaces were wet ground on SIC paper to expose the dentin. Total 100 samples were made and divided randomly into 4 groups, Giomer group(I), Composite resin group(II) and Compomer group(III), Giomer and single bottle adhesive group(IV). The shear bond strengths of 25 samples per each group were measured using universal testing machine. And data were analyzed statistically with One-way ANOVA and Scheffe test. Giomer group(I) showed the significantly higher bond strength than Compomer group(III)(p<0.05). There was no significant difference between Giomer group(I) and Composite resin group(II)(p>0.05). And there is no significant difference between gourp(I) and group(IV). Based on the results of present study, the use of Giomer as an esthetic restorative material for primary teeth might be justified. It is considered that more study about the fluoride releasing ability is needed to evaluate the anticariogenic effect of giomer.

Effect of Hardening Accelerators on the Adiabatic Temperature property Properties of Precast Concrete and FEM analysis for Evaluating the Crack Performance (경화촉진제를 사용한 프리캐스트 콘크리트의 단열온도특성 및 FEM해석에 의한 균열성능 평가에 관한 연구)

  • Min, Tae-Beom;Cho, In-Sung;Mun, Young-Bum;Lee, Han-Seung
    • Journal of the Korea Institute of Building Construction
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    • v.15 no.1
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    • pp.25-33
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    • 2015
  • In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.