• Restorative Dentistry and Endodontics
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• 제41권2호
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• pp.114-120
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• 2016

Objectives: The aim of this study was to compare the push-out bond strength and dentinal tubule penetration of root canal sealers used with coated core materials and conventional gutta-percha. Materials and Methods: A total of 72 single-rooted human mandibular incisors were instrumented with NiTi rotary files with irrigation of 2.5% NaOCl. The smear layer was removed with 17% ethylenediaminetetraacetic acid (EDTA). Specimens were assigned into four groups according to the obturation system: Group 1, EndoRez (Ultradent Product Inc.); Group 2, Activ GP (Brasseler); Group 3, SmartSeal (DFRP Ltd. Villa Farm); Group 4, AH 26 (Dentsply de Trey)/gutta-percha (GP). For push-out bond strength measurement, two horizontal slices were obtained from each specimen (n = 20). To compare dentinal tubule penetration, remaining 32 roots assigned to 4 groups as above were obturated with 0.1% Rhodamine B labeled sealers. One horizontal slice was obtained from the middle third of each specimen (n = 8) and scanned under confocal laser scanning electron microscope. Tubule penetration area, depth, and percentage were measured. Kruskall-Wallis test was used for statistical analysis. Results: EndoRez showed significantly lower push-out bond strength than the others (p < 0.05). No significant difference was found amongst the groups in terms of percentage of sealer penetration. SmartSeal showed the least penetration than the others (p < 0.05). Conclusions: The bond strength and sealer penetration of resin-and glass ionomer-based sealers used with coated core was not superior to resin-based sealer used with conventional GP. Dentinal tubule penetration has limited effect on bond strength. The use of conventional GP with sealer seems to be sufficient in terms of push-out bond strength.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.127-132
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• 2003

In a today industry, the welding is doing a many portion in structure manufacture. This study is simulated heat of heat-effected zone and researched a mechanical properties and ultrasonic characteristic in used the SS400 and the STS304. As the result mechanical properties of steel that become drawing decreased because of remaining stress by strain gardening according as simulated heat temperature rises, but according as temperature rises in material that do simulated heat after have done annealing, mechanical propensity was improved. The velocity and attenuation become different by effect of remaining stress than effect of material internal microstructure in ultrasonic wave test. In the case of STS304, there was change in mechanical properties by effect that is by strain hardening, but there was no change in material that simulated heat after annealing. When become drawing in ultrasonic waves test, according as simulated heat temperatures rise, change of attenuation coefficient is looked, but material that simulated heat after annealing was no change almost both the volocity and attenuation.

• 수산해양기술연구
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• 제37권2호
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• pp.140-146
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• 2001

수산 시설물의 내구성을 평가하기 위한 기초 단계로 부력재 또는 프레임용 재질로 많이 사용되고 있는 국산 고밀도 PE 및 고강도 PVC와 노루웨이 고밀도 PE에 대하여 인공 광원을 조사한 후 시간의 경과에 따른 시료의 물성과 그 표면 및 파면의 형태적 변화를 비교$\cdot$분석하였다. 실험에서 얻어진 결과를 요약하면 다음과 같다. 1) 자외선 조사 시간이 경과됨에 따라 세 시료 모두 인장 응력과 탄성률은 미처리된 초기의 그것보다 크게 감소하였으나, 파단 신장률의 경우 처음에는 증가하다가 다시 감소하는 불규칙적인 경향을 나타내었다. 2) 잔여 응력 RS(kg/mm 상(2))와 자외선 폭로 기간 Y(Year)와의 상관 관계는 다음과 같이 나타났다. KHDPE : RS=2.6769-0.0003Y(r 상(2)=0.63) Hi-PVC : RS=5.3470-0.0003Y(r 상(2)=0.91) NHDPE : RS=2.4929-0.0004Y(r 상(2)=0.97) 3) 전자 현미경 촬영 결과, 자외선의 영향으로 시료의 표면에 물방울 형상이 나타났으며, 자외선 조사 시간이 경과됨에 따라 분자 구조의 분해로 인하여 작은 구멍이 확인되었다.

• Steel and Composite Structures
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• 제34권5호
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• pp.715-732
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• 2020

High-strength steel composite Y-eccentrically braced frame (Y-HSS-EBF) is a novel structural system. In this study, the spatial substructure hybrid simulation test (SHST) method is used to further study the seismic performance of Y-HSS-EBF. Firstly, based on the cyclic loading tests of two single-story single-span Y-HSS-EBF planar specimens, a finite element model in OpenSees was verified to provide a reference for the numerical substructure analysis model for the later SHST. Then, the SHST was carried out on the OpenFresco test platform. A three-story spatial Y-HSS-EBF model was taken as the prototype, the top story was taken as the experimental substructure, and the remaining two stories were taken as the numerical substructure to be simulated in OpenSees. According to the test results, the validity of the SHST was verified, and the main seismic performance indexes of the SHST model were analyzed. The results show that, the SHST based on the OpenFresco platform has good stability and accuracy, and the results of the SHST agree well with the global numerical model of the structure. Under strong seismic action, the plastic deformation of Y-HSS-EBF mainly occurs in the shear link, and the beam, beam-columns and braces can basically remain in the elastic state, which is conducive to post-earthquake repair.

• 대한치과교정학회지
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• 제42권1호
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• pp.4-10
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• 2012

Objective: To determine the effect of surface anodization on the interfacial strength between an orthodontic microimplant (MI) and the rabbit tibial bone, particularly in the initial phase aft er placement. Methods: A total of 36 MIs were driven into the tibias of 3 mature rabbits by using the self-drilling method and then removed aft er 6 weeks. Half the MIs were as-machined (n = 18; machined group), while the remaining had anodized surfaces (n = 18; anodized group). The peak insertion torque (PIT) and the peak removal torque (PRT) values were measured for the 2 groups of MIs. These values were then used to calculate the interfacial shear strength between the MI and cortical bone. Results: There were no statistical differences in terms of PIT between the 2 groups. However, mean PRT was significantly greater for the anodized implants ($3.79{\pm}1.39$ Ncm) than for the machined ones ($2.05{\pm}1.07$ Ncm) (p < 0.01). The interfacial strengths, converted from PRT, were calculated at 10.6 MPa and 5.74 MPa for the anodized and machined group implants, respectively. Conclusions: Anodization of orthodontic MIs may enhance their early-phase retention capability, thereby ensuring a more reliable source of absolute anchorage.

• Advances in concrete construction
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• 제10권2호
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• pp.127-140
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• 2020

This study explores the feasibility of granite waste aggregate (GWA) as a partial replacement of natural fine aggregate (NFA) in binary blend self-compacting concrete (SCC) prepared with fly ash. Total of nine SCC mixtures were prepared wherein one was Ordinary Portland cement (OPC) based control SCC mixture and remaining were fly ash based binary blend SCC mixtures which included the various percentages of GWA. Fresh properties tests such as slump flow, T₅₀₀, V-funnel, J-ring, L-box, U-box, segregation resistance, bleeding, fresh density, and loss of slump flow (with time) were conducted. Compressive strength and percentage of permeable voids were evaluated in the hardened state. All the SCC mixtures exhibited sufficient flowability, passing ability, and resistance to segregation. Besides, all the binary blend SCC mixtures exhibited lower fresh density and bleeding, and better residual slump (up to 50% of GWA) compared to the OPC based control SCC mixture. Binary blend SCC mixture incorporating up to 40% GWA provided higher compressive strength than binary blend control SCC mixture. The findings of this study encourage the utilization of GWA in the development of binary blend SCC mixtures with satisfactory workability characteristics as a replacement of NFA.

• 대한물리치료과학회지
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• 제9권4호
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• pp.105-112
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• 2002

When any damage or disease occurs, muscular strength and muscular endurance are lowered, and thus, if one is able to be restored from the damage or the disease, appropriate stimulus is required, since the muscles have to restore their proper functions. For such stimulus, the way of exercising and the way using electric stimulus are used in physical therapy. In order to examine the change in muscular strength, muscular endurance and girth of limbs for Biceps brachii, according to the lands of stimulus, in this article a total of 42 healthy male and female adults in their twenties were randomly sampled, and a series of tests were conducted for 6 weeks, for 15 minutes per once, 3 times per week, respectively, dividing them into the group for RUS(Russian Current Stimulation), PRE(Progressive Resistive Exercise) and P+R(RUS + PRE). The findings showed that the change in muscular strength was most significant as for the group for P+R, since it increased from $62.12{\pm}25.30$ before experiment to $95.78{\pm}34.07$ after 6 weeks: the change in muscular endurance was most significant as for the group for P+R, since it increased from $17.57{\pm}6.63$ to $42.86{\pm}10.24$; and the change in the girth of limbs was slightly significant only in the group for P+R, and the remaining two groups showed no significance.

• Steel and Composite Structures
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• 제11권3호
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• pp.207-223
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• 2011

The results of an experimental investigation are presented in this paper for retrofitting of shear damaged reinforced concrete beams by using U shaped CFRP strips. The experimental program is consisted of seven shear deficient T cross sectioned 1/2 scale simply supported beam specimens. One beam was used as reference specimen, and the remaining six specimens were tested in two stages. At the first stage, specimens were shear damaged severely, and then were retrofitted by using CFRP strips with or without fan type anchorages. Finally, retrofitted beams were tested up to failure. Three different CFRP strip spacing were used such as 125 mm, 150 mm, and 200 mm. The effect of anchorages on shear strength and behavior of the retrofitted specimens is investigated. CFRP strips without anchorages improved the shear strength, but no flexural failure mode was observed. Specimens showed brittle shear failure due to peeling of CFRP strip from RC beam surface. Shear damaged specimens retrofitted with anchoraged CFRP strips showed improved shear strength and ductile flexural failure. Maximum strains at anchoraged strips were approximately 68% larger than that of strips without anchorages.

• 한국공간구조학회논문집
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• 제23권4호
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• pp.81-88
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• 2023

Numerous factors contribute to the deterioration of reinforced concrete structures. Elevated temperatures significantly alter the composition of the concrete ingredients, consequently diminishing the concrete's strength properties. With the escalation of global CO2 levels, the carbonation of concrete structures has emerged as a critical challenge, substantially affecting concrete durability research. Assessing and predicting concrete degradation due to thermal effects and carbonation are crucial yet intricate tasks. To address this, multiple prediction models for concrete carbonation and compressive strength under thermal impact have been developed. This study employs seven machine learning algorithms-specifically, multiple linear regression, decision trees, random forest, support vector machines, k-nearest neighbors, artificial neural networks, and extreme gradient boosting algorithms-to formulate predictive models for concrete carbonation and thermal impact. Two distinct datasets, derived from reported experimental studies, were utilized for training these predictive models. Performance evaluation relied on metrics like root mean square error, mean square error, mean absolute error, and coefficient of determination. The optimization of hyperparameters was achieved through k-fold cross-validation and grid search techniques. The analytical outcomes demonstrate that neural networks and extreme gradient boosting algorithms outshine the remaining five machine learning approaches, showcasing outstanding predictive performance for concrete carbonation and thermal effect modeling.

• The Journal of Advanced Prosthodontics
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• 제10권3호
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• pp.205-210
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• 2018

PURPOSE. The purpose of this study was to evaluate the efficiency of a gas-phase fluorination method under different fluorination periods through using two resin cements. MATERIALS AND METHODS. 84 zirconia specimens in dimensions of $5mm{\times}5mm{\times}2mm$ were prepared and surface treated with $50{\mu}m$ aluminum oxide particles or gas phase fluorination for 2 min, 5 min, or 10 min. One specimen in each group was surface analyzed under scanning electron microscope. The remaining specimens were bonded to composite cylinders in dimensions of 2 mm diameter and 3 mm high with Panavia SA Plus or Variolink N. Then, the specimens were stored in $37^{\circ}C$ distilled water for 24 hours and shear bond strength test was applied at a speed of 1 mm/min. RESULTS. The highest shear bond strength values were observed in the samples fluorinated for 5 minutes and cemented with Panavia SA Plus. Variolink N did not elicit any statistical differences between surface treatments. Panavia SA Plus resin cement and Variolink N resin cements featured statistically significant difference in shear bond strength values only in the case of 5 minutes of fluorination treatment. CONCLUSION. According to the results of this study, application of 5 minutes of fluorination with 10-methacryloyloxydecyl dihydrogen phosphate monomer (MDP) containing Panavia SA Plus resin cement increased the resin bond strength of zirconia. Fluorination of the zirconia surface using conventional resin cement, Variolink N, did not lead to an increase in bond strength.