• 대한치과교정학회지
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• 제43권5호
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• pp.242-247
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• 2013

Objective: To test the null hypothesis that no difference exists between the effects of at-home bleaching and in-office bleaching on shear bond strength (SBS) with bracket bonding at 4 different time intervals after dental bleaching. Methods: Ninety extracted human premolars were randomly divided into 9 groups (n = 10) according to the bleaching methods used (at-home bleaching and in-office bleaching) and the storage time in artificial saliva (30 min, 1 day, 2 weeks, and 3 weeks before bonding). The control group was stored in artificial saliva for 7 days. Brackets were bonded with the Transbond XT adhesive system, and SBS testing was performed. The adhesive remnant index (ARI) was used to assess the amount of resin remaining on the enamel surfaces after debonding. The SBS data were analyzed by analysis of variance (ANOVA) and the Tukey test. For the ARI, the Kruskal-Wallis test was performed. Significance for all statistical tests was predetermined to be p < 0.05. Results: The SBS of the unbleached group was significantly higher (p < 0.05) than that of the bleached groups (except for the group bonded 30 min after at-home bleaching). Conclusions: The null hypothesis was not totally rejected. All bleaching groups tested had decreased SBS of the brackets to the enamel, except for the group bonded 30 min after at-home bleaching. The SBS returned to values close to those of the unbleached enamel within 3 weeks following bleaching.

• 한국환경농학회지
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• 제11권3호
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• pp.261-268
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• 1992

식물 세포의 미토콘드리아와 엽록체는 광 증감제로 작용할 가능성이 있는 여러 가지 색소들을 함유하고 있다. 이들 색소들은 대부분이 막에 결합되어있으며 청색광 영역에서 강한 흡수대를 가지므로 청색광하에서 노출된 이들 소기관에서는 활성산소가 발생되어 막의 구조적, 기능적 피해를 유발하는 요인이 된다. 활성산소의 광발생에 따른 막구조의 변화는 일차적으로 막지질 지방산성분의 산화적 파괴에 기인할 것이다. 본 연구에서는 식물이 고광도의 가시광선(특히 청색광선)하에서 일어나는 막지질 지방산의 산화적 파괴에 지방산 대신 상대적으로 둔감한 포화 지방산의 조성비를 높일 것이라고 가정하고, 이를 뒷받침할만한 실험결과를 얻었다. 즉, 광질이 서로 다른 가시광선 처리조건하에서 생장중인 식물 및 그 소기관들을 대상으로 막지질의 과산화, 지방산조성 및 불포화도, 막결합 단백질의 활성 등을 측정하고 이를 제시하였다.

• The Journal of Asian Finance, Economics and Business
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• 제7권7호
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• pp.349-360
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• 2020

The study aims to empirically examine the determinants of bank margins from Pakistan, an emerging South Asian economy. To elucidate the importance of the Pakistani banking sector, secondary data has been used, which was extracted from the annual accounts of twenty-four Pakistani scheduled commercial banks (20 conventional, four full-fledged Islamic) over a sample period of 2006 to 2017. The factors identified in the dealership model and the subsequent empirical developments in the dealership model categorized as bank-specific, diversification, regulatory, and industry concentration are analyzed by applying the most-common linear dynamic panel-data estimator, the Generalized Method of Moments (GMM) estimator, developed by Arellano and Bond (1991). The findings reveal that, among the bank-specific variables, funding cost, credit risk, managerial efficiency, market share, and operating cost are significant predictors of bank margins. For diversification variables employed in the study, both variables including net non-interest income and asset diversity are as well significant predictors of bank margins. It is also found that the market concentration variable proxied by the Herfindahl-Hirschman Index (HHI) is significantly predicting bank margins. Subsequently, one of the regulatory variables, the opportunity cost of holding reserves, and one bank-specific variable, the degree of risk aversion, are insignificant in the model.

• 대한치과교정학회지
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• 제48권3호
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• pp.163-171
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• 2018

Objective: The aim of this study was to evaluate the mechanical and biological properties of orthodontic bonding agents containing silver- or zinc-doped bioactive glass (BAG) and determine the antibacterial and remineralization effects of these agents. Methods: BAG was synthesized using the alkali-mediated solgel method. Orthodontic bonding agents containing BAG were prepared by mixing BAG with flowable resin. $Transbond^{TM}$ XT (TXT) and $Charmfil^{TM}$ Flow (CF) were used as controls. Ion release, cytotoxicity, antibacterial properties, the shear bond strength, and the adhesive remnant index were evaluated. To assess the remineralization properties of BAG, micro-computed tomography was performed after pH cycling. Results: The BAG-containing bonding agents showed no noticeable cytotoxicity and suppressed bacterial growth. When these bonding agents were used, demineralization after pH cycling began approximately 200 to $300{\mu}m$ away from the bracket. On the other hand, when CF and TXT were used, all surfaces that were not covered by the adhesive were demineralized after pH cycling. Conclusions: Our findings suggest that orthodontic bonding agents containing silver- or zinc-doped BAG have stronger antibacterial and remineralization effects compared with conventional orthodontic adhesives; thus, they are suitable for use in orthodontic practice.

• 폴리머
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• 제35권5호
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• pp.444-450
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• 2011

천연 알지네이트를 저분자화시키기 위해 과산화수소/초음파를 사용하였다. 이때 반응 온도 시간, 과산화수소 농도 그리고 초음파 조사 조건 등이 저분자화 생성물에 미치는 영향을 검토하였다. 생성된 저분자 알지네이트의 화학적 구조를 규명한 결과 주로 1,4-glycosidic bond가 끓어져서 저분자화가 진행되고 특정조건에서 생성물에 formate 그룹이 형성됨을 확인할 수 있었다. 생성물의 분자량은 MALS가 부착된 GPC를 사용하여 측정하였다. 2 wt%의 고분자 알지네이트 용액을 50 $^{\circ}C$의 초음파 분위기에서 0.5시간 동안 반응시켰을 때 분자량이 450 kDa에서 15.9 kDa로 저하되었다. 또한 분자량분포도는 상당히 좁고 반응 조건에 따라 큰 변화 없이 일정함(~2)을 확인할 수 있었다.

• Steel and Composite Structures
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• 제37권2호
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• pp.211-227
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• 2020

To explore the feasibility of eliminating the longitudinal rebars and stirrups by using ultra-high-performance fiber reinforcement concrete (UHPFRC) in concrete encased steel composite stub column, compressive behavior of UHPFRC encased steel stub column has been experimentally investigated. Effect of concrete types (normal strength concrete, high strength concrete and UHPFRC), fiber fractions, and transverse reinforcement ratio on failure mode, ductility behavior and axial compressive resistance of composite columns have been quantified through axial compression tests. The experimental results show that concrete encased composite columns with NSC and HSC exhibit concrete crushing and spalling failure, respectively, while composite columns using UHPFRC exhibit concrete spitting and no concrete spalling is observed after failure. The incorporation of steel fiber as micro reinforcement significantly improves the concrete toughness, restrains the crack propagation and thus avoids the concrete spalling. No evidence of local buckling of rebars or yielding of stirrups has been detected in composite columns using UHPFRC. Steel fibers improve the bond strength between the concrete and, rebars and core shaped steel which contribute to the improvement of confining pressure on concrete. Three prediction models in Eurocode 4, AISC 360 and JGJ 138 and a proposed toughness index (T.I.) are employed to evaluate the compressive resistance and post peak ductility of the composite columns. It is found that all these three models predict close the compressive resistance of UHPFRC encased composite columns with/without the transverse reinforcement. UHPFRC encased composite columns can achieve a comparable level of ductility with the reinforced concrete (RC) columns using normal strength concrete. In terms of compressive resistance behavior, the feasibility of UHPFRC encased steel composite stub columns with lesser longitudinal reinforcement and stirrups has been verified in this study.

• 품질경영학회지
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• 제51권2호
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• pp.171-184
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• 2023

Purpose: First, this paper suggests an alternative approach to find optimal portfolio (stocks, bonds and ESG stocks) under the maximizing utility of investors. Second, we include ESG stocks in our optimal portfolio, and compare improvement of welfares in the case with and without ESG stocks in portfolio. Methods: Our main method of analysis follows Brennan et al(2002), designed under the continuous time framework. We assume that the dynamics of stock price follow the Geometric Brownian Motion (GBM) while the short rate have the Vasicek model. For the utility function of investors, we use the Power Utility Function, which commonly used in financial studies. The optimal portfolio and welfares are derived in the partial equilibrium. The parameters are estimated by using Kalman filter and ordinary least square method. Results: During the overall analysis period, the portfolio including ESG, did not show clear welfare improvement. In 2017, it has slightly exceeded this benchmark 1, showing the possibility of improvement, but the ESG stocks we selected have not strongly shown statistically significant welfare improvement results. This paper showed that the factors affecting optimal asset allocation and welfare improvement were different each other. We also found that the proportion of optimal asset allocation was affected by factors such as asset return, volatility, and inverse correlation between stocks and bonds, similar to traditional financial theory. Conclusion: The portfolio with ESG investment did not show significant results in welfare improvement is due to that 1) the KRX ESG Leaders 150 selected in our study is an index based on ESG integrated scores, which are designed to affect stability rather than profitability. And 2) Korea has a short history of ESG investment. During the limited analysis period, the performance of stock-related assets was inferior to bond assets at the time of the interest rate drop.

• 대한치과교정학회지
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• 제39권4호
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• pp.213-224
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• 2009

본 연구에서는 세라믹 브라켓 제거에 Er:YAG 레이저 조사가 도움이 되는지 알아보고, 브라켓 제거에 적합한 레이저 조사 방법을 연구하였으며, 또 이렇게 적용된 레이저가 치수와 법랑질에 손상을 주는지도 알아보았다. 총 190개의 치아, 단결정 세라믹 브라켓(MISO), 다결정 세라믹 브라켓(Transcend series 6000)과 KEY Laser3를 사용하였다. 실험군은 세라믹 브라켓의 종류(단결정, 다결정)와 레이저의 에너지(140, 300, 450, 600 mJ)에 따라 분류하였으며, 레이저를 브라켓당 두 곳에 1펄스씩 조사하고, 전단 강도를 측정하였다. 대조군은 레이저를 조사하지 않는 군으로 하였다. 레이저 조사에 의한 열 효과는 브라켓 하방 법랑질과 치수강에서 측정하였으며, 전단 강도 측정 후 치면에 남아있는 접착제의 양을 접착제 잔류 지수(adhesive remnant index)를 이용하여 평가하였다. 레이저 조사로 인한 접착제의 파괴 양상과 법랑질 표면 변화를 주사전자현미경으로 관찰하였다. 모든 세라믹 브라켓군에서 레이저 에너지가 증가할수록 전단 강도는 유의하게 감소하였다. 또한, 브라켓 하방 법랑질에서 최대 온도 변화는 평균 $3.78^{\circ}C$ 상승에 그쳤으며, 치수강에서 최대 온도 변화는 평균 $0.9^{\circ}C$ 상승에 그쳤다. 주사전자현미경을 이용한 법랑질과 접착제 단면 관찰에서 접착제 표면이 레이저에 의해 붕괴되어 분화구 모양의 구덩이로 관찰되었으며, 일부 시편에서 약 $10\;-\;30{\mu}m$의 법랑질 손상이 발견되었다. Transbond XT로 부착된 단결정 도재 브라켓(MISO)의 디본딩에 Er:YAG 레이저를 이용할 경우, 300 - 450 mJ의 레이저 에너지를, 그리고 다결정 도재 브라켓(Transcend series 6000)의 경우는 450 mJ 정도의 에너지를 사용하는 것이 효과적이고 안전할 것으로 생각된다.

• KDI Journal of Economic Policy
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• 제14권4호
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• pp.3-26
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• 1992

본고(本稿)에서는 물가변동(物價變動)의 구조(構造), 주요거시정책변수(主要巨視政策變數)의 변동이 물가에 미치는 영향 및 파급구조(波及構造) 등을 파악하고 물가안정을 위한 적절한 정책대응방안을 제시하기 위하여 물가모형(物價模型)을 작성하였다. Keynesian 거시경제모형(巨視經濟模型) 형태로 작성하되, 임금(賃金), 이자율(利子率), 물가(物價)와 같은 주요가격변수(主要價格變數)를 내생화(內生化)하고 잠재(潛在)GNP의 추정 역시 내생화(內生化)함으로써 가격 및 실물변수의 장기적(長期的) 상호변동관계(相互變動關係)를 파악하였다. 어떠한 충격에 의해 초과수요(超過需要)(실질GNP-잠재GNP)가 변화하면 이는 임금(賃金), 금리(金利), 물가(物價), 실질실효환율(實質實效換率) 등과 같은 가격변수에 영향을 미치고 이는 다시 초과수요(超過需要)를 변동시키는 실물(實物)-가격(價格)-실물(實物)의 순환변동관계(循環變動關係)에 의해 물가가 변동되는 것으로 나타났다. 본 모형(模型)은 Keynesian모형(模型)이나, 장기(長期)에는 고전파적(古典派的)(Classical) 정책함의를 가지는바, 통화공급증가(通貨供給增加), 재정지출증가(財政支出增加), 환율절하(換率切下) 등은 단기(短期)에는 경기부양효과를 가지나 장기(長期)에는 이러한 경기부양효과가 소멸되는 반면 물가(物價)는 높은 수준을 유지하는 결과를 초래하는 것으로 나타났다.

• 유통과학연구
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• 제11권10호
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• pp.73-79
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• 2013

Purpose - This study examines the impact of oil price volatility on economic activities in Korea. The new millennium has seen a deregulation in the crude oil market, which invited immense capital inflow into Korea. It has also raised oil price levels and volatility. Drawing on the recent theoretical literature that emphasizes the role of volatility, this paper attends to the asymmetric changes in economic growth in response to the oil price movement. This study further examines several key macroeconomic variables, such as interest rate, production, and inflation. We come to the conclusion that oil price volatility can, in some part, explain the structural changes. Research design, data, and methodology - We use two methodological frameworks in this study. First, in regards to the oil price uncertainty, we use an Exponential-GARCH (Exponential Generalized Autoregressive Conditional Heteroskedasticity: EGARCH) model estimate to elucidate the asymmetric effect of oil price shock on the conditional oil price volatility. Second, along with the estimation of the conditional volatility by the EGARCH model, we use the estimates in a VECM (Vector Error Correction Model). The study thus examines the dynamic impacts of oil price volatility on industrial production, price levels, and monetary policy responses. We also approximate the monetary policy function by the yield of monetary stabilization bond. The data collected for the study ranges from 1990: M1 to 2013: M7. In the VECM analysis section, the time span is split into two sub-periods; one from 1990 to 1999, and another from 2000 to 2013, due to the U.S. CFTC (Commodity Futures Trading Commission) deregulation on the crude oil futures that became effective in 2000. This paper intends to probe the relationship between oil price uncertainty and macroeconomic variables since the structural change in the oil market became effective. Results and Conclusions - The dynamic impulse response functions obtained from the VECM show a prolonged dampening effect of oil price volatility shock on the industrial production across all sub-periods. We also find that inflation measured by CPI rises by one standard deviation shock in response to oil price uncertainty, and lasts for the ensuing period. In addition, the impulse response functions allude that South Korea practices an expansionary monetary policy in response to oil price shocks, which stems from oil price uncertainty. Moreover, a comparison of the results of the dynamic impulse response functions from the two sub-periods suggests that the dynamic relationships have strengthened since 2000. Specifically, the results are most drastic in terms of industrial production; the impact of oil price volatility shocks has more than doubled from the year 2000 onwards. These results again indicate that the relationships between crude oil price uncertainty and Korean macroeconomic activities have been strengthened since the year2000, which resulted in a structural change in the crude oil market due to the deregulation of the crude oil futures.