• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제14권2호
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• pp.79-91
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• 2010

In this paper, a class of fractional integrodifferential equations of mixed type with nonlocal conditions is considered. First, using contraction mapping principle and Krasnoselskii's fixed point theorem via Gronwall's inequailty, the existence and uniqueness of mild solution are given. Second, the existence of optimal pairs of systems governed by fractional integrodifferential equations of mixed type with nonlocal conditions is also presented.

• Journal of applied mathematics & informatics
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• 제29권3_4호
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• pp.681-696
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• 2011

In this paper, we consider the existence of mild solutions for a certain class of nonlinear impulsive functional evolution integrodifferential equation with nonlocal conditions in Banach spaces. A sufficient condition is established by using Schaefer's fixed point theorem combined with an evolution system. An example is also given to illustrate our result.

• 공업화학
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• 제32권5호
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• pp.532-540
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• 2021

4-도데카노일옥시벤젠술폰산나트륨(sodium dodecanoyl-4-oxybenzenesulfonate; DOBS) 염은 저온에서도 효과적인 표백력과 살균력을 나타내는 물질이다. 본 연구에서는 물(W)-극성 비양자성 용매 계를 사용하는 알칼리 조건하에서 dodecanoyl chloride와 sodium 4-hydroxybenzene sulfonate로부터 DOBS의 온화하고 효율적인 합성방법을 조사하였다. 먼저 물만을 용매로 사용하고 온도 또는 시간을 변화시키며 반응한 결과, 수율은 30 ℃와 1 h 이상의 반응 조건에서 대부분 약 5% 정도로 낮게 나타났다. 효율적인 용매 계를 발견하기 위하여 극성 비양자성 용매의 종류를 변화시키며 물과 혼합하여 제조한 다양한 용매계에서 수율에 미치는 영향을 평가하였다. 수율은 아세톤(acetone; AC)과 물을 혼합한 용매 계에서 가장 우수하였으며, 온화한 반응조건(30 ℃, 1 h 및 상압)의 반응에서 약 82%의 높은 값을 나타냈다. 제조한 DOBS는 높은 표백력 및 살균력을 보여 표백활성화제로서 활용이 가능함을 확인하였다.

• Corrosion Science and Technology
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• 제10권1호
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• pp.1-5
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• 2011

The major purpose of the present study is to evaluate the performance of various galvanized (GI) or galvannealed (GA) mild steels and AHSS in stamping applications. Finite Element Analysis (FEA) of selected stamping operations was conducted to estimate the critical pressure boundary conditions that exist in practice. Using this information, laboratory tribotests, e.g. Twist Compression (TCT), Deep Drawing (DDT) and Strip Drawing (SDT) Tests, were developed to evaluate the performance of selected lubricants and die materials/coatings in forming galvanized steels of interest. The sheet materials investigated included mild steels and AHSS (e.g. DP600 GI/GA, DP780 GI/GA, TRIP780 GA and DP980 GI/GA). Experimental results showed that galvanized material resulted in more galling, while galvannealed material showed more powdering and flaking. The surface roughness and chemical composition of galvanized sheet materials affected the severity of galling under the same testing conditions, i.e. lubricants and die materials/coatings. The results of this study helped to determine the critical interface pressure that initiates lubricant failure and galling in stamping selected galvanized sheet materials. Thus, to prevent or postpone the critical interface conditions, the results of this study can be used to select the optimum combination of galvanized sheet, die material, die coating and lubricant for forming structural automotive components.

• 한국치위생학회지
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• 제24권4호
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• pp.333-341
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• 2024

Objectives: This study aimed to identify the key components and tools for Comprehensive Dental Hygiene Care (CDHC) among dental hygienists and provide foundational data for widespread implementation in dental institutions. Methods: A third Delphi survey involving experts derived the CDHC components and materials. Dental hygienists' characteristics and the CDHC application status were analyzed for frequency. The perceived need for and willingness to apply the CDHC components based on general characteristics were assessed using t-tests. Results: The results of the Delphi survey identified the following CDHC components: 11 for medical history; three, dental history; five, oral hygiene practices; seven, dental conditions; three, occlusion conditions; six, periodontal conditions; and, three, other examinations. Planning included 3 items for healthy gums and 4 for gingivitis and mild periodontitis. Evaluation included 7 items for mild periodontitis, 5 for patient education, and totally 27 CDHC-related materials. Dental hygienists' needs and willingness varied, with higher levels among those in clinics, university graduates, those in counseling or managerial roles, team leaders or those at higher positions, and those with >6 years of experience (p<0.05). Conclusions: The Delphi survey identified the CDHC clinical application process, confirming the strong desire of dental hygienists to apply it in practice.

• 한국재료학회지
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• 제22권11호
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• pp.591-597
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• 2012

For heat exchanger applications, 2-ply clad materials were fabricated by rolling of aluminum (Al) and mild steel sheets. Effects of annealing temperature on interface properties, especially on inter-layer formation and softening of strain hardened mild-steel, for Al/mild steel clad materials, were investigated. To obtain optimum annealing conditions for the Al/mild steel clad materials, annealing temperature was varied from room temperature to $600^{\circ}C$. At the annealing temperature about $450^{\circ}C$, an inter-layer was formed in an island-shape at the interface of the Al/mild steel clad materials; this island expanded along the interface at higher temperature. By analyzing the X-ray diffraction (XRD) peaks and the energy dispersive X-ray spectroscopy (EDX) results, it was determined that the exact chemical stoichiometry for the inter-layer was that of $Fe_2Al_5$. In some samples, an X-layer was formed between the Al and the inter-layer of $Fe_2Al_5$ at high annealing temperature of around $550^{\circ}C$. The existence of an X-layer enhanced the growth of the inter-layer, which resulted in the delamination of the Al/mild-steel clad materials. Hardness tests were also performed to examine the influence of the annealing temperature on the cold deformability, which is a very important property for the deep drawing process of clad materials. The hardness value of mild steel gradually decreased with increasing annealing temperature. Especially, the value of hardness sharply decreased in the temperature range between $525^{\circ}C$ and $550^{\circ}C$. From these results, we can conclude that the optimum annealing temperature is around $550^{\circ}C$ under condition of there being no X-layer creation.

• 한국전산유체공학회지
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• 제22권1호
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• pp.15-25
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• 2017

Swirl flow is often found in proximal coronary arteries, because the aortic valves can induce swirl flows in the coronary artery due to vortex formation. In addition, the curvature and tortuosity of arterial configurations can also produce swirl flows. The present study was performed to investigate fractional flow reserve alterations in a post-stenotic distal part due to the presence of pre-stenotic swirl flow by computational fluid dynamics analysis for virtual stenotic models by quantifying fractional flow reserve(FFR). Simplified stenotic coronary models were divided into those with and without pre-stenotic swirl flow. Various degrees of virtual stenosis were grouped into three grades: mild, moderate, and severe, with degree of stenosis of 0 ~ 40%, 50 ~ 60%, and 70 ~ 90%, respectively. In this study, three-dimensional computational hemodynamic simulations were performed under hyperemic conditions in virtual stenotic coronary models by coupling with a zero-dimensional lumped parameter model. The results showed that the influence of pre-stenotic swirl inflow is dominant on FFR alteration in mild stenosis, whereas stenosis is dominant on FFR alteration in moderate/severe stenosis. The decrease in FFR caused by swirl flow is more significant in mild stenosis than moderate/severe stenosis. Biomechanical modeling is useful for clinicians to provide insight for medical intervention strategies. This hemodynamic-based parameter study could play a critical role in the development of a non-invasive imaging-based strategy-support system for percutaneous transluminal angioplasty in cases of mild/moderate stenosis.

• 청정기술
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• 제8권1호
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• pp.1-9
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• 2002

유연탄 2종과 무연탄 2종을 대상으로 mild pyrolysis 조건 하에서 탈황특성과 무게감량 및 발열량 손실에 대하여 열분해 온도는 $350{\sim}550^{\circ}C$, 열분해 시간은 5~20분, 입자크기는 0~3.35mm인 실험조건에서 수행하였다. 연구 결과 유연탄과 무연탄이 $550^{\circ}C$에서 10분 동안 열분해 시 탈황율은 각각 38%와 28%였으며, 열분해 조건은 10~15분, $450{\sim}550^{\circ}C$ 정도가 적절한 것으로 나타났다. 열분해 온도가 올라감에 따라 유기황과 무기황 모두 감소하는 것으로 보아 열분해법이 유기황의 탈황에도 효과가 있음을 알 수 있다. 열분해 후 char의 발열량은 원탄에 비해 5% 정도 높거나 비슷한 값을 갖는 것으로 나타났다. 입자 크기가 탈황에 미치는 영향은 거의 나타나지 않았다.

• Journal of applied mathematics & informatics
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• 제34권3_4호
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• pp.193-206
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• 2016

In this paper, we study boundary value problems for fractional integrodifferential equations involving Caputo derivative in Banach spaces. A generalized singular type Gronwall inequality is given to obtain an important priori bounds. Some sufficient conditions for the existence solutions are established by virtue of fractional calculus and fixed point method under some mild conditions.

• East Asian mathematical journal
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• 제19권1호
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• pp.91-102
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• 2003

In this paper we prove the existence of mild and strong solutions of nonlinear delay integrodifferential equations with nonlocal conditions. The results are obtained by using the Schauder fixed point theorem and resolvent operator.