• Restorative Dentistry and Endodontics
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• 제45권4호
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• pp.50.1-50.11
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• 2020

Objectives: In this study, we investigated the potential of amoxicillin-loaded polymeric microspheres to be delivered to tooth root infection sites via a bioactive reparative cement. Materials and Methods: Amoxicillin-loaded microspheres were synthesized by a spray-dray method and incorporated at 2.5% and 5% into a mineral trioxide aggregate cement clinically used to induce a mineralized barrier at the root tip of young permanent teeth with incomplete root development and necrotic pulp. The formulations were modified in liquid:powder ratios and in composition by the microspheres. The optimized formulations were evaluated in vitro for physical and mechanical eligibility. The morphology of microspheres was observed under scanning electron microscopy. Results: The optimized cement formulation containing microspheres at 5% exhibited a delayed-release response and maintained its fundamental functional properties. When mixed with amoxicillin-loaded microspheres, the setting times of both test materials significantly increased. The diametral tensile strength of cement containing microspheres at 5% was similar to control. However, phytic acid had no effect on this outcome (p > 0.05). When mixed with modified liquid:powder ratio, the setting time was significantly longer than that original liquid:powder ratio (p < 0.05). Conclusions: Lack of optimal concentrations of antibiotics at anatomical sites of the dental tissues is a hallmark of recurrent endodontic infections. Therefore, targeting the controlled release of broad-spectrum antibiotics may improve the therapeutic outcomes of current treatments. Overall, these results indicate that the carry of amoxicillin by microspheres could provide an alternative strategy for the local delivery of antibiotics for the management of tooth infections.

• Journal of Korea Trade
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• 제27권5호
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• pp.153-166
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• 2023

Purpose - This research empirically analyzes the influence of economic policy uncertainty and free trade agreements (FTAs) on bilateral trade volumes between Korea and its trading partners. The study investigates whether fluctuations in the Economic Policy Uncertainty Index (EPUI) for both Korea and its trading partners significantly impact trade volumes and whether the implementation of FTAs mitigates these effects. Design/methodology - The study employs dynamic panel data analysis using the system generalized method of moments (system GMM) estimation method to achieve its research objectives. It utilizes country-month-level panel data, including the EPUI, trade volume between Korea and its trading partner countries, and other pertinent variables. The use of system GMM allows for the control of potential endogeneity issues and the incorporation of country-specific and time-specific effects. Findings - The analysis yields significant results regarding the impact of economic policy uncertainty on Korea's exports and imports, particularly before the implementation of FTAs. An increase in the EPUI of trading partners leads to a notable increase in Korea's exports to them. Conversely, an increase in Korea's EPUI negatively affects its imports from trading partners. However, post-FTA implementation, the influence of each country's EPUI on trade volume is neutralized, with no significant difference observed. Originality/value - This research contributes to the existing literature by providing empirical evidence on the interaction effects between economic policy uncertainty and FTAs on bilateral trade volumes. The study's uniqueness lies in its examination of how FTAs mitigate the impact of economic uncertainty on trade relations between countries. The findings underscore the importance of trade agreements as mechanisms to address economic risks and promote international trade relations. In a world where global market uncertainties persist, these insights can aid policymakers in Korea and other countries in enhancing their trade cooperation strategies and navigating challenges posed by evolving economic landscapes.

• 한국건축시공학회지
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• 제23권6호
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• pp.703-714
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• 2023

본 연구에서는 효율적인 콘크리트용 당류계 초지연제를 개발하기 위해 현재 시판되고 있는 당 성분의 물질들을 대상으로 이들의 종류 및 혼입률 변화에 따른 시멘트 페이스트의 응결지연 특성, 압축강도 발현 특성 및 미시구조 특성을 분석하고자 하였다. 당류계 초지연성 혼화제 중 백설탕, 슈가파우더 및 스테비오사이드를 사용할 경우 응결지연에 효율적인 것으로 나타났다. 슈가파우더 및 스테비오사이드를 제외한 여타 배합의 경우 Plain 대비 동등한 수준의 압축강도를 발휘하는 것으로 나타났다. 특히, 백설탕의 경우 0.2% 혼입시 재령 1일에서 강도가 발휘되지 않다가 재령 28일에서는 Plain과 비교하여 동등 이상의 강도를 발휘하는 것으로 나타났다. XRD, SEM 및 EDS 분석 결과, XRD를 통해 백설탕에 의한 C₃S의 수화지연(응결 지연)을 확인하였으며, EDS의 정량 분석을 통해 추가적으로 확인할 수 있었다. 수화물의 유무는 SEM를 이용하여 존재를 확인하였다. 본 연구 범위에 한하여 콘크리트용 당류계 초지연성 혼화제로써 백설탕을 사용할 경우 응결지연 성능 및 압축강도 발현 성능에 효과적일 것으로 판단된다.

• Asian-Australasian Journal of Animal Sciences
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• 제8권1호
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• pp.43-50
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• 1995

This study was carried out to investigate the effects of activated carbon (AC) on growth, ruminal charateristics, blood profiles and feed digestibility in sheep, using roughage-based or concentrate-based diets. Twelve Suffolk breed of sheep of similar age and weight were distributed into 4 groups in a $2{\times}2$ factorial design. Two groups were fed a roughage-based diet with (R + AC) and without AC (R - AC), while the other two were fed a concentrate-based diet with (C + AC) and without AC (C - AC), respectively. The addition of 0.3% AC was based on dry matter of feed offered to animals. The incorporation of AC in roughage and concentrate based diets had no marked effects on feed intake, daily gain and feed conversion of the animals within experimental diets. The results obtained might be due to the low level of AC added in the diet. The animal on both concentrate-based diets were higher than the roughage-based diets in terms of daily gain and feed conversion ratio. However, it was observed that the animals provided with AC in the concentrate-based diet did not suffer from diarrhea and easily adjusted to high concentrate feeding. Further, the pH value for all diets before feeding was noted to be similar. After feeding, however, pH was shown to be higher in R + AC (p < 0.05) than in C + AC diet. Rumen protozoa number was decreased after feeding for both + AC diets, but in C - AC diet it was higher than in the roughage-based diets. For ammonia-nitrogen, C - AC was found to be higher than C + AC diet and the roughage-based diets before feeding. Total volatile fatty acid concentration, propionate and valerate molar ratios for both diets and time of collection were not affected. However, acetate, butyrate and valerate molar ratios were observed to be affected by diets and time of collections. The diets with AC increased (p < 0.05) before feeding for acetate molar ratio, but not different within diet, however, the roughage diets were found to be higher (p < 0.05) in acetate than the concentrate diet. In the blood parameters, the glutamic pyruvic transaminase (GPT), red and white blood cell (RBC, WBC) counts and packed cell volume (PCV) did not differ within and among the diets. Likewise, the WBC differential count in both diets with either - AC or + AC were similar in trend. However, lymphocyte count was noted to be increased in R + AC than the R - AC diet. The addition of AC in both diets did not affect nutrient digestibilities within diets.

• Journal of Microbiology and Biotechnology
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• 제10권1호
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• pp.27-34
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• 2000

The chloroform and methanol (2;1, v/v) extract from an edible plant, Actinidia arguta Planchon, appeared to possess antitumor activity against human leukemias Jurkat T and U937 cells through inducing apoptosis. The substance in the solvent extract was purified by silica gel column chromatography, preparative TLC, and Sephadex LH-20 column chromatography. Characteristics of the substance analyzed by UV scanning analysis, $^1H$ and $^{13}C$ NMR spectra suggested that the substance belongs to the chlorophyll derivatives-like group. The $IC_{50}$ value of the chlorophyll derivative (Cp-D) determined by MTT assay was $15\mu\textrm{g}/ml$ for Jurkat, $10\mu\textrm{g}/ml$ for U937, and $11.4\mu\textrm{g}/ml$ for HL-60m and was more toxic to these leukemias than to solid tumors or normal fibroblast. In order to elucidate cellular mechanisms underlying the cytotoxicity, the effect of the Cp-D on Jurkat T cells was investigated. When cells were treated with the Cp-D at a concentration of $15\mu\textrm{g}/ml$, [3H]thymidine incorporation declined rapidly and wa undetectable in 1h. However, no significant changes were made in the cell cycle distribution of the cells by 24h. The sub-Gl peak representing apoptotic cells began to be detectable in 36h, at which time apoptotic DNA fragmentation was also detected on agarose gel electrophoresis, demonstrating that the cytotoxic effect of the Cp-D is attributable to the induced apoptosis. Under the same conditions, although the protein level of cyclin-dependent kinases such as cdc4, csk6, cdk2, and cdc2 was not significantly changed until 24h, the kinase activity of all c안 rapidly declined and reached a minimum level within 1-6h and then recovered to the initial level by 12h and sustained until 24h. These results suggest that inactivation of cdks at an inappropriate time during the cell cycle progression in jurkat T cells following a treatment with the Cp-D leads to induction of apoptotic cell death.

• The Journal of Advanced Prosthodontics
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• 제10권2호
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• pp.113-121
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• 2018

PURPOSE. The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes ($n-TiO_2$) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS. $TiO_2$ nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each $TiO_2$:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of $n-TiO_2$ addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS. SEM images of $n-TiO_2$ exhibited the presence of elongated tubular structures. The XRD pattern of synthesized $n-TiO_2$ represented the anatase crystal phase of $TiO_2$. Moderate to very strong significant positive correlations were observed between the concentration of $n-TiO_2$ and each of the 3 physicomechanical properties of PMMA (Pearson's P value ${\leq}.001$, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% $n-TiO_2$ were significantly higher than those of control ($P{\leq}.001$). Fracture toughness of samples reinforced with 5 wt% $n-TiO_2$ (but not those of 2.5% $n-TiO_2$) was higher than control (P=.002). CONCLUSION. Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.62-62
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• 2018

Pt is still considered as one of the most active electrocatalysts for ORR in alkaline fuel cells. However, the high cost and scarcity of Pt hamper the widespread commercialization of fuel cells. As a strong candidate for the replacement of Pt catalyst, silver (Ag) has been extensively studied due to its high activity, abundance, and low cost. Ag is more stable than Pt in the pH range of 8~14 as the equilibrium potential of Ag/Ag+ being ${\approx}200mV$ higher than that of Pt/PtO. However, Ag is the overall catalytic activity of Ag for oxygen reduction reaction(ORR) is still not comparable to Pt catalyst since the surface Ag atoms are approximately 10 times less active than Pt atoms. Therefore, further enhancement in the ORR activity of Ag catalysts is necessary to be competitive with current cutting-edge Pt-based catalysts. We demonstrate the architectural design of Ag catalysts, synthesized using plasma discharge in liquid phase, for enhanced ORR kinetics in alkaline media. An attractive feature of this work is that the plasma status controlled via electric-field could form the Ag nanowires or dendrites without any chemical agents. The plasma reactor was made of a Teflon vessel with an inner diameter of 80 mm and a height of 80 mm, where a pair of tungsten(W) electrodes with a diameter of 2 mm was placed horizontally. The stock solutions were made by dissolving the 5-mM AgNO3 in DI water. For the synthesis of Agnanowires, the electricfield of 3.6kVcm-1 in a 200-ml AgNO3 aqueous solution was applied across the electrodes using a bipolar pulsed power supply(Kurita, Seisakusyo Co. Ltd). The repetition rate and pulse width were fixed at 30kHz and 2.0 us, respectively. The plasma discharge was carried out for a fixed reaction time of 60 min. In case of Ag nanodendrites, the electric field of 32kVcm-1 in a 200-ml AgNO3 aqueous solution was applied and other conditions were identical to the plasma discharge in water in terms of electrode configuration, repetition rate and discharge time. Using SEM and STEM, morphology of Ag nanowires and dendrites were investigated. With 3.6 kV/cm, Ag nanowire was obtained, while Ag dendrite was constructed with 32 kV/cm. The average diameter and legth of Ag nanowireses were 50 nm and 3.5 um, and thoes values of Ag dendrites were 40 nm and 3.0 um. As a results of XPS analysis, the surface defects in the Ag nanowires facilitated O2 incorporation into the surface region via the interaction between the oxygen and the electron cloud of the adjacent Ag atoms. The catalytic activity of Ag for oxygen reduction reaction(ORR) showed that the catalytic ORR activity of Ag nanowires are much better than Ag nanodendrites, and electron transfer number of Ag nanowires is similar to that of Pt (${\approx}4$).

• 대한화학회지
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• 제54권2호
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• pp.198-207
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• 2010

독스핀 하이드로클로라이드 선택전극의 구조와 성능특징에 대하여 개발하였다. 전극의 3가지 형태가 있다. I. 플라스틱 막 II. 코팅된 선형 III. 흑연으로 된 로드, 이것들은 암모늄 라이네케이트를 갖는 독스핀 하이드로클로라이드의 결합에 기초하여 구성되었다. 막의 조성, 가소제의 종류, 시험용액의 pH, 담궈 놓은 시간 그리고 전극에 있는 이질 이온들의 영향을 조사했다. $25^{\circ}C$에서 전극 I, II, III에 대해 각각 57.41 ${\pm}$ 0.5, 56.22 ${\pm}$ 0.2 and 52.88 ${\pm}$ 0.7 mV 의 평균 보정 그래프 기울기를 갖는 Nernst 반응을 보여준다. 그리고 전극 I, II, III에 대해 $1{\times}10^{-2}-1{\times}10^{-6}M$, $5{\times}10^{-2}-1{\times}10^{-6}M$ 그리고 $1{\times}10^{-3}-5{\times}10^{-6}M$의 독스핀 하이드로클로라이드 농도범위에 있고, $5.0{\times}10^{-7}M$, $6.3{\time}10^{-7}M$ 그리고 $2.5{\times}10^{-6}M$의 검출한계를 갖는다는 것을 보여준다. 만들어진 전극은 pH 3 - 7의 범위에서 선택적으로 정밀하고, 사용 가능한 평균을 보였다. 공통양이온, 알칼로이드, 설탕 아미노산, 그리고 약품첨가제로부터의 방해가 기록되었다. 제안된 전극에 의해 얻어진 결과는 약의 조세와 생물학적 유체에 있어서 약물의 확인에 성공적으로 적용되었다.

• 한국시뮬레이션학회논문지
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• 제15권2호
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• pp.31-39
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• 2006

가시성그래프는 최소 탐색 공간으로 게임환경을 모델링하여 효과적으로 길을 찾을 수 있도록 하는 방법으로 잘 알려져 있다. 일반화 가시성그래프는 가시성그래프의 가장 큰 단점으로 지적되는 "벽-껴안기" 문제를 해결하기 위해 확장된 장애물의 경계 위에 생성된 가시성그래프이다. 일반화 가시성그래프에 의해 구해진 경로는 근사 최적이며 자연스럽게 보이는 장점이 있다. 본 논문에서는 변화하는 출발점과 목표점과 정적인 장애물 사이를 움직이는 게임 캐릭터에 효과적으로 일반화 가시성그래프를 적용하는 방법을 제안한다. 일반화 가시성그래프는 일단 생성되면 최소 탐색공간을 보장하지만 그 생성 자체는 노드사이의 링크의 교차 여부론 일일이 체크하여야 하므로 시간이 많이 소요된다. 아이디어는 먼저 정적인 장애물만으로 지도를 생성해 놓고 출발점과 목표점을 빠르게 포함시키는 것이다. 출발점과 목표점의 포함 부분이 여러 번 반복되어야 하는 과정이므로 출발점과 목표점을 빠르게 포함시키는데에 연산 기하학 분야의 회전 plane-sweep 알고리즘을 이용할 것을 제안한다. 시뮬레이션 결과는 전체 그래프를 매번 생성하는 것보다 제안한 방법의 실행시간이 39%-68% 정도 향상되었음을 보여준다.

• 한국항해항만학회지
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• 제43권3호
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• pp.153-159
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• 2019

항해사나 기관사 등 해기사에 의한 선박운항 과정에서 이들의 과실이나 부주의로 인한 해양사고나 위법행위가 발생한다. 그 결과로 해기사 면허에 대한 행정처분이 따른다. 처분 즉, 면허징계는 올바른 법규와 절차에 따라서 형평성 있게 이루어져야 한다. 하지만, 실제는 그렇지 못한 것으로 나타났다. 이에 대한 현황파악을 위하여 B지방해양수산청에서 2014년부터 2018년까지 5년간 이루어진 737명의 해기사 면허 징계처분 내용을 살펴보았다. 분석내용은 징계처분통보기관, 면허종류, 당시 직책, 징계량, 위반행위, 연도별 처분현황, 징계규정과 절차 그리고 경감규정과 감면 정도 등이다. 분석 결과 관련 규정별 징계량 편차, 징계 규정 미비, 면허종류별 징계 대상자 편차, 징계 경감규정 미비 그리고 선원행정처분심의회 역할 부족 등의 문제점이 식별되었다. 마지막에 드러난 문제점들에 대한 개선방안을 제안하였다. 이 연구는 국내에서 처음으로 해기사에 대한 다수의 실제 행정처분 사례를 분석하고 미비점을 확인하여 개선안을 제시한 것으로, 향후 해기사에 대한 연구나 정책수립에 도움이 될 것으로 기대한다.