• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.89-89
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• 2000

AlN 박막은 Al과 N원자의 부분적 이온결합 특성을 가진 공유결합을 한 육방정계의 wurtzite 경정구조의 화합물 반도체로서, III-V족 반도체 중 가장 큰 에너지 갭(6.2 eV), 결정 구조적 이방성, 화학 양론적 결합구조, 높은 탄성종과 전달속도(약 10$\times$106 m/s)와 높은 열전도도, 고온 안정성, 가시광성.적외선 영역에서의 좋은 투과성과 높은 굴절률, 상온 대기압에서의 유일하게 안정적인 특성을 가지고 있어, 절연재료, 내열재료, 저주파 영역 센서의 압전 트랜스듀서, 광전소자, 탄성파 소자 및 내환경 소자, MIS소자 등으로 주목받고 있다. 본 연구에서는 BAW 공진기의 활용을 목적으로 반응성 마그네트론 스퍼터링 방법으로 AIN 압전박막을 제작하여, 증착 조건-질소 농도, 고주파 출력, 전체 스퍼터링 압력, 기판 온도-에 대한 박막의 특성을 조사하였다. AlN 박막의 c축 우선 방위 결정성 및 낮은 투과성, 적당한 굴절률의 특성이 BAW 공진기의 활용을 위한 요건이므로, 각각의 증착 조건하에 제작된 박막은 XRD의 $\theta$/2$\theta$ 스캔 회절상에 의한 결정성의 분석과 우선 성장 결정면의 rocking curve 및 XRD로 측정한 FWHM과 표준 편차로 결정성의 배열성과 소자 응용가능성을 조사하였다. 박막의 표면.단면 미세 구조 및 평활도는 SEM으로 관찰하였으며, Al-N 결합 상태는 XPS와 FT-IR로 분석 조사하였다. 제작된 AlN 박막의 결정성 분석 결과, c축 우선 방위 성장을 위한 스퍼터링 압력에 대한 임계 질소 농도와 임계 스퍼터링 압력이 관찰되었다. 전체 스퍼터링 압력이 6~8 mTorr의 범위에서 나타난 최소 임계질소 농도는 10%, 최대 임계 질소 농도는 60%이며, 4 m Torr 이하 10 m Torr 이상의 전체 스퍼터링 압력에서 박막의 우선 방위성장이 제재된다. 이는 AlN 박막이 형성에 관여하는 질소 이온 양의 충분한 형성에 필요로 하는 질소 가스의 유입량에 따른 것으로 판단된다. AlN 박막의 c축 결정면인 (002) 결정면의 성장을 유도하며 다른 방향으로의 성장을 제어하여 소자 활용에 유용한 박막을 제작하기 위한 고주파 출력은 300W 정도가 적당하며, 기판을 가열하지 않았을 때 낮은 투과도를 나타낸다. 본 연구에 의한 BAW 공진기 활용을 위한 AlN 압전박막의 제작을 위한 최적 증착 조건은 기판의 가열 없이 6~8 mTorr의 전체 스퍼터링 압력에 20~25%의 질소종도, 300W의 고주파 출력이다. 최적 조건에서의 AlN 박막은 약 0.19$^{\circ}$의 FWHM과 약 0.08$^{\circ}$의 표준편차를 가지며, 균일하고 조밀한 표면 미세구조와 주상정 구조의 측면구조, 파장에 대한 약 2.0의 굴절률, 낮은 투과도와 화학 양론적 구조를 가지는 우수한 박막이 형성되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.317-324
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• 2021

This study deals with keywords from social media on domestic portal sites related to COVID-19, which is spreading widely. The data were collected between January 20 and August 15, 2020, and were divided into three stages. The precursor period is before COVID-19 started spreading widely between January 20 and February 17, the serious period denotes the spread in Daegu between February 18 and April 20, and the stable period is the decrease in numbers of confirmed infections up to August 15. The top 50 words were extracted and clustered based on TF-IDF. As a result of the analysis, the precursor period keywords corresponded to congestion of the Situation. The frequent keywords in the serious period were Nation and Infection Route, along with instability surrounding the Treatment of COVID-19. The most common keywords in all periods were infection, mask, person, occurrence, confirmation, and information. People's emotions are becoming more positive as time goes by. Cafes and blogs share text containing writers' thoughts and subjectivity via the internet, so they are the main information-sharing spaces in the non-face-to-face era caused by COVID-19. However, since selectivity and randomness in information delivery exists, a critical view of the information produced on social media is necessary.

• Economic Analysis
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• v.25 no.2
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• pp.1-53
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• 2019

This paper examines monetary policy quantitatively in a two-agent and small-scale New-Keynesian economy with debt-constrained households that cannot smooth their consumption intertemporally and frictionlessly since highly indebted households are not allowed to borrow above a certain debt ceiling in incomplete financial markets without additional risk premiums due to information asymmetry between savers and borrowers. We find that, in the event of cost shocks, the asymmetric responses of borrowing households without, and saving households with, dividend incomes lead to different labor supplies and consumptions over heterogeneous households, and eventually to an extension of the monetary policy transmission channels. The income effect and low elasticity of the labor supply play key roles in such asymmetric responses over heterogeneous households. We also find that the social welfare in a flexible inflation targeting (FIT) monetary policy, in which both the inflation gap and the output gap are considered in an integrated manner when policy-making, is similar to that of the Ramsey optimal monetary policy (ROP), in which the shares of debt-constrained households, as well as all economic states, including both the inflation gap and output gap, are considered comprehensively for policy-making, and that it is greater than that of simple inflation targeting (SIT) monetary policy, in which only the inflation gap is considered mechanically for policy-making. Such social welfare implies that a FIT policy may still work even in an economy with a sizable number of debt-constrained households. Further, the responses of cost shocks to consumption and labor supply are dying out more slowly under FIT and ROP policies than under an SIT policy.

• Journal of Life Science
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• v.31 no.1
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• pp.17-27
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• 2021

This study was performed to investigate the antioxidant activities of subfractions of Peucedanum insolens Kitagawa root in various organic solvents and their anti-inflammatory effects on LPS-treated RAW264.7 cells. First, P. insolens Kitagawa roots were dried at room temperature for one week, chopped, and extracted with 70% ethanol. The resulting extracts were successively sub-fractionated with hexane, chloroform, ethyl acetate, and water. The antioxidant potential of the fractions was evaluated using a DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging assay and by measuring total polyphenol and flavonoid contents. The anti-inflammatory potency of the fractions was evaluated by measuring the inhibition levels of the expressions of inflammatory-mediated genes and proteins (e.g., iNOS, COX-2, IL-1β, and IL-6) in RAW264.7 cells. The results clearly showed that the ethyl acetate fraction of the P. insolens Kitagawa root contained relatively high total flavonoid (34.08±1.68 ㎍ of quercetin equivalents per mg) and total polyphenol (154.1±3.2 ㎍ of gallic acid equivalents per mg) contents. The DPPH assay results showed that the P. insolens Kitagawa root possessed strong free radical scavenging activity in the ethyl acetate fraction. Both the ethyl acetate and hexane fractions showed strong inhibitory potencies to nitric oxide production induced by lipopolysaccharide (1 ㎍/ml) treatment for 24 hr in RAW264.7 cells. The results also showed that both the hexane and ethyl acetate fractions of the P. insolens Kitagawa root strongly inhibited mRNA levels of iNOS, IL-1β, and IL-6, which were overexpressed by LPS treatment for 24 hr in the RAW264.7 cells. These results suggest that P. insolens Kitagawa root may contain compounds that possess strong potency for anti-inflammatory activity. Further studies are needed to discover more detailed modes of action of P. insolens Kitagawa root fractions against inflammation modulation, such as the regulation of cytokine signaling and inflammatory signaling pathways.

• Journal of Life Science
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• v.24 no.2
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• pp.173-180
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• 2014

Estrogen can promote or inhibit cellular proliferation depending on tissue cell types and physiological condition and acts through the signal transduction pathways mediated primarily by estrogen receptors. This study examined the effects of fulvestrant (Ful), a well-known antagonist for the estrogen receptor, on the action of $17{\beta}$-estradiol (E2) with respect to the proliferation and apoptosis of Chinese hamster ovarian (CHO) cells. We used different concentrations of E2, Ful, and E2 plus Ful during different treatment durations. Treatment with 15-40 ${\mu}M$ E2 significantly inhibited proliferation in a time-dependent manner, although it had no influence in concentrations up to 1 ${\mu}M$. Interestingly, Ful at 10-40 ${\mu}M$ also inhibited cellular proliferation in both a concentration- and time-dependent manner. In addition, Ful enhanced rather than decreased the inhibitory effect on cellular proliferation by E2 in combined treatment for 10 days. Thus, Ful does not appear to have an antagonistic effect on estrogen's anti-proliferative action in CHO cells. In TUNEL assays to confirm DNA fragmentation by E2 and/or Ful, CHO cells treated with 20 ${\mu}M$ E2 showed a TUNEL-positive reaction in most DAPI-stained nuclei, and cells treated with either 40 ${\mu}M$ Ful or 40 ${\mu}M$ Ful plus 20 ${\mu}M$ E2 also exhibited a TUNEL-positive reaction but at a lower rate compared to the E2-treated cells. These results indicate that Ful does not have an antagonistic effect on estrogen's anti-proliferative action in CHO cells, suggesting that the anti-proliferative and apoptosis-related mechanism(s) through DNA fragmentation by E2 and Ful may be mediated by different signal transduction pathways.

• Journal of the Korean Society of Food Science and Nutrition
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• v.38 no.4
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• pp.409-414
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• 2009

The aim of this study was to investigate the ameliorating effects of deer antler extract on the learning and memory impairments induced by the administration of scopolamine (2 mg/kg, i.p.) in rats. Tacrine was used as a positive control agent for evaluating the cognition enhancing activity of deer antler extract in scopolamine-induced amnesia models. The results showed that the deer antler extract-treated group (200 mg/kg, p.o.) and the tacrine-treated group (10 mg/kg, p.o.) significantly ameliorated scopolamine-induced amnesia based on the Morris water maze test. Although there was no statistical significance of brain ACh contents among the experimental groups, the brain ACh contents of the deer antler extract-treated group was slightly higher than that of the scopolamine-treated group. The inhibitory effect of deer antler extract on the acetylcholinesterase activity in the brain was significantly lower than that of scopolamine-treated group. The tacrine- and the deer antler-treated groups reduced the MAO-B activity compared to the scopolamine-treated group, but not significantly. These results suggest that the deer antler extract could be an effective agent for the prevention of the cognitive impairment induced by cholinergic dysfunction.

• The korean journal of orthodontics
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• v.41 no.1
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• pp.6-15
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• 2011

Objective: The aim of this study was to evaluate the biomechanical aspects of peri-implant bone upon root contact of orthodontic microimplant. Methods: Axisymmetric finite element modeling scheme was used to analyze the compressive strength of the orthodontic microimplant (Absoanchor SH1312-7, Dentos Inc., Daegu, Korea) placed into inter-radicular bone covered by 1 mm thick cortical bone, with its apical tip contacting adjacent root surface. A stepwise analysis technique was adopted to simulate the response of peri-implant bone. Areas of the bone that were subject to higher stresses than the maximum compressive strength (in case of cancellous bone) or threshold stress of 54.8MPa, which was assumed to impair the physiological remodeling of cortical bone, were removed from the FE mesh in a stepwise manner. For comparison, a control model was analyzed which simulated normal orthodontic force of 5 N at the head of the microimplant. Results: Stresses in cancellous bone were high enough to cause mechanical failure across its entire thickness. Stresses in cortical bone were more likely to cause resorptive bone remodeling than mechanical failure. The overloaded zone, initially located at the lower part of cortical plate, proliferated upward in a positive feedback mode, unaffected by stress redistribution, until the whole thickness was engaged. Conclusions: Stresses induced around a microimplant by root contact may lead to a irreversible loss of microimplant stability.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.1
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• pp.87-96
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• 2009

In conventional method, flight model is discribed to differential equation by linealization of nonlinear object motion equation. As state equation from differential equation of moving object, the controller is designed by transfer functions of each module under discrimination of stability criteria. But this conventional method is designed under limitation of nonlinearity from object's shape and speed. In other word, The greater part of guidance/navigation system was satisfied with the result of good performance for normal figure of flight object, not sudden changed flight condition, not high speed. But it is not able to give full play to its ability on flight object which has abnormal figure, sudden changeable motion, high speed. Therefore, in this paper was presented performance analysis of load control model for navigation/guidance system on flying object being uncertainty, non-linear like abnormal figure, sudden changeable motion, high speed and is presented method of trajectory control(controllability) ahead of controllability and stability to achieve flight mission. In other word, this paper shows the first step of Min-design method and flight control model.

• Journal of the Korean earth science society
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• v.29 no.6
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• pp.506-519
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• 2008

This article explores the potential learning materials and methods of science practice from exhibits, and how those are presented in natural history museums as a feasible science inquiry community. The idea of science inquiry community was offered as a form of science practice that ended with science learning. A grasp of 'scientific practice to learning' is understood as a way to conceive scientific methods as well as facts and understanding knowledge. To get educational implications on the scientific practice of 'earthquake' as a socioscientific topic in the communities, we analyzed 1) the relationship between earth science curriculum and exhibits related to 'earthquake', 2) the educational goals and intentions of educators, and 3) the characteristics of the exhibits in the American Museum of Natural History and in the Smithsonian National Museum of Natural History. The results of this study showed that those museums presented the exhibits consisting of various and practical cases and events of 'earthquakes' as a socioscientific topic related to their curriculum. At the target museum, it was clearly stated that the pursuing educational goals focused on relations with local interests and socioscientific issues. For making earthquakes relevant to visitors, delivering lived experiences with raw data and interactive media was emphasized in exhibit characteristics.

• Journal of dental hygiene science
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• v.13 no.1
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• pp.1-12
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• 2013

This study aims to measure oral health knowledge and practice level among dental clinic patients, and examine their relationships with decayed, missing and filled teeth (DMF) index and the oral health-related quality of life (QOL). Empirical data have been collected from 311 patients through structured questionnaires and dental examinations conducted in Busan area. According to the analysis of causal relationship, oral health knowledge turned out to have a direct effect on oral health practices, which exerted both direct and indirect effects on DMF index and oral health-related QOL. While DMF index directly affected the oral health-related QOL, oral health knowledge proved to have only an indirect effect on DMF index and oral health-related QOL, mediated by oral health practices. Considering all these findings, effective oral health education and other intervention programs should focus on motivating people to participate in the active practices of desirable oral health behaviors, which will lead to the prevention of oral diseases and the subsequent improvement in the QOL.