• 한국자동차공학회논문집
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• 제25권2호
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• pp.257-265
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• 2017

In this work, the effect of field-degradation of automotive polymeric interior parts on the squeak characteristics was studied for a number of used vehicles with various mileages and years of service. The purpose of this study was to characterize the squeak noise related with long-term degradation in service life. The characteristics of field-degraded polymeric samples are analyzed using Fourier transform infrared(FT-IR) spectroscopy and scanning electron microscopy(SEM). Complicated carbonyl spectra from FT-IR were deconvoluted into various carbonyls to trace field-degradation phenomenon. In addition, various mechanical tests, i.e. tensile test, hardness test as well as coefficient of friction test, were performed to analyze the variation in mechanical properties due to field-degradation. Squeak noise was measured and analyzed by frequency analysis. It was shown that the changes in the chemical structures of polymer due to field-degradation influenced the variation in mechanical properties, and squeak noise may worsen by increasing the squeak noise level in the wide frequency range. The results indicated that customer complaints regarding the squeak noise coming from used vehicles might be one of the important reliability issues because the increase in sound pressure level especially in the high frequency range could annoy drivers and passengers.

• 대한본초학회지
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• 제34권3호
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• pp.1-7
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• 2019

Objectives : Amyloid ${\beta}(A{\beta})$ could induce cognitive deficits through oxidative stress, inflammation, and neuron death in Alzheimer's disease (AD). This study was investigated the effect of Angelica keiskei KOIDZUMI (AK) on memory in $A{\beta}$-induced an AD model. Methods : AK was extracted uses 70% ethanol solvent. Total polyphenol and flavonoids content were obtained by the Folin-Ciocalteu and the Ethylene glycol colorimetric methods, respectively. The antioxidant activities were assessed through free radical scavenging assays using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazolin-6-sulfonic acid) (ABTS) methods. Intracerebroventrical (i.c.v) injection of $A{\beta}$ 1-42 was used to induce AD in male ICR mice, followed by administrations of 5, 10 or 20 mg/kg AK on a daily. Animals were subjected to short and long term memory behavior in Y-maze and passive avoidance test. Results : The total polyphenol and flavonoids contents of the AK extract were $88.73{\pm}6.36mg$ gallic acid equivalent/g, $84.21{\pm}5.04mg$ rutin equivalent/g, respectively. The assays of DPPH and ABTS revealed that AK extract in treated concentrations (31.25, 62.5, 125, 250, 500, $1000{\mu}g/m{\ell}$) increased antioxidant activity in a dose-dependent manner. Oral administration of AK extract significantly reversed the $A{\beta}$ 1-42-induced decreasing of the spontaneous alternation in the Y-maze test and $A{\beta}$ 1-42-induced shorting of the step-through latency in the passive avoidance test. Conclusions : The findings suggest that AK indicated the antioxidant protective effects against $A{\beta}$-induced memory deficits, and therefore a potential lead natural therapeutic drug or agent for AD.

• 한국산업정보학회논문지
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• 제28권6호
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• pp.21-27
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• 2023

현대 함정은 외부로 방사되는 적외선 신호를 낮추기 위해 폐기관에 적외선 신호저감 장치(Infra-Red Signature Suppression system, IRSS)를 설치한다. 그리고 함정은 생의 주기가 매우 긴 전략 자산으로 탑재 장비들의 성능에 대한 높은 신뢰성을 충분히 확보해야 한다. 따라서, IRSS와 같은 장비들은 설계 단계에서 모형시험을 통해 성능평가를 하고 있다. IRSS의 모형시험에서는 다양한 계측기기들이 사용된다. 그러므로, 모형시험 단계 이전에 계측기들의 신뢰성을 평가해야 한다. 본 연구에서는 IRSS 모형시험에 사용되는 계측 장비들의 신뢰성 평가에 관한 연구를 수행하였다. 시험 장비와 계측기는 열 풍동 시험기, 피토 튜브와 디지털 차압계, 열전대 센서 그리고 디지털 기록계가 사용되었다. 계측 결과 열 풍동 시험기의 풍속이 증가할수록 유동의 계측 편차가 감소하였으며, 열전대 센서의 온도는 사용 방법에 따라 반응 속도 및 민감도의 차이를 보였다.

• 치위생과학회지
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• 제12권2호
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• pp.93-102
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• 2012

보건의료분야의 제반환경의 개선에도 불구하고 국민들의 구강건강상태는 아직도 OECD국가 중에서 매우 열악한 상태이다. 국민들의 구강건강을 효율적으로 증진유지하기 위해서는 중대구강병인 치아우식증을 예방하고 조기에 치료할 수 있는 구강보건진료가 이루어져야 한다. 특히 평생구강건강유지에 중요한 연령층인 초등학교학생들을 대상으로 정기적인 계속구강건강관리제도가 시급히 필요하나 초등학생 대상 계속구강건강관리방식의 치아우식예방관리법의 효과에 관한 사례가 부족한 실정이다. 따라서 광주광역시 소재의 S 치과에 2005년 12월부터 2006년 2월에 내원한 만6세에서 13세 환자 중 환자보호자의 동의를 받은 총 39명을 대상으로 실험군과 대조군으로 분류하여 치아우식활성도와 치아우식경험도를 조사하여 지역사회 치과의원에서 기초자료로 활용할 목적으로 시행한바 다음과 같은 결과를 얻었다. 1. 계속구강건강관리군의 기간별 Alban's test 및 Lactobacillius test 점수는 6개월경과 후 초진시의 1.4배에서 1.5배 감소되었고, 12개월경과 후 초진시의 1.5배에서 1.6배 감소되었다(p<0.001). 2. 계속구강건강관리군의 기간별 간이구강위생지수는 6개월과 12개월경과 후 초진시의 1.6배 감소되었다(p<0.05). 3. 12개월경과 후 우식경험영구치지수는 계속관리군(1.88개)에서 대조군(2.72개)보다 1.4배 감소되었으며, 우식영구치지수는 계속관리군(0.07개)에서 대조군(0.85개)보다 12배 감소되었다(p<0.05). 4. 12개월경과 후 제1대구치건강도는 계속관리군(98.04%)에서 대조군(95.97%)보다 1.02배 높게 나타났다(p<0.05). 이상과 같은 결과에 의하여 지역사회 치과의원에서 지속적인 계속구강건강관리제도를 시행하여 아동의 평생구강건강상태를 유지시켜야 한다고 사료되었다.

• 한국발생생물학회지:발생과생식
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• 제13권3호
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• pp.183-190
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• 2009

In mammals, puberty is a dynamic transition process from infertile immature state to fertile adult state. The neuroendocrine aspect of puberty is started with functional activation of hypothalamus-pituitary-gonadal hormone axis. The timing of puberty can be altered by many factors including hormones and/or hormone-like materials, social cues and metabolic signals. For a long time, attainment of a particular body weight or percentage of body fat has been thought as crucial determinant of puberty onset. However, the precise effect of high-fat (HF) diet on the regulation of hypothalamic GnRH neuron during prepubertal period has not been fully elucidated yet. The present study was undertaken to test the effect of a HF diet on the puberty onset and hypothalamic gene expressions in immature female rats. The HF diet (45% energy from fat, HF group) was applied to female rats from weaning to around puberty onset (postnatal days, PND 22-40). Body weight and vaginal opening (VO) were checked daily during the entire feeding period. In the second experiment, all animals were sacrificed on PND 36 to measure the weights of reproductive tissues. Histological studies were performed to assess the effect of HF diet feeding on the structural alterations in the reproductive tissues. To determine the transcriptional changes of reproductive hormone-related genes in hypothalamus, total RNAs were extracted and applied to the semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Body weights of HF group animals tend to be higher than those of control animals between PND 22 and PND 31, and significant differences were observed PND 32, PND 34, PND 35 and PND 36 (p<0.05). Advanced VO was shown in the HF group (PND $32.8{\pm}0.37$ p<0.001) compared to the control (PND $38.25{\pm}0.25$). The weight of ovaries (p<0.01) and uteri (p<0.05) from HF group animals significantly increased when compared to those from control animals. Corpora lutea were observed in the ovaries from the HF group animals but not in control ovaries. Similarly, hypertrophy of luminal and glandular uterine epithelia was found only in the HF group animals. In the semi-quantitative RT-PCR studies, the transcriptional activities of KiSS-1 in HF group animals were significantly higher than those from the control animals (p<0.001). Likewise, the mRNA levels of GnRH (p<0.05) were significantly elevated in HF group animals. The present study indicated that the feeding HF diet during the post-weaning period activates the upstream modulators of gonadotropin such as GnRH and KiSS-1 in hypothalamus, resulting early onset of puberty in immature female rats.

• 한국과학교육학회지
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• 제33권6호
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• pp.1139-1153
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• 2013

과학교육에서 오개념은 오래된 주제이지만, 아직도 학교현장에서는 오개념으로 인한 문제들이 제기되고 있다. 본 연구에서는 초등예비교사들과 초등현장교사들을 위해 초등과학 교과의 내용과 직접적으로 관련된 오개념을 조사 분석하고 이의 교정을 위한 오개념 교정 소책자를 개발하였으며, 이를 초등예비교사들을 위한 생명영역 교재연구 강좌에 적용하여 과학 교수 효능감과 생명영역 오개념의 교정 효과를 검증하였다. 소책자의 개발을 위해 선행연구결과를 수집하고, 초등예비교사들의 오개념을 조사하였으며, 이를 2007 개정 과학과 교육과정의 초등과학 생명영역 단원의 내용을 분석틀로 하여 분석하였고, 그 결과를 현장에서 쉽게 사용할 수 있도록 작은 소책자 형태로 제작하였다. 제작한 소책자의 효과 검증을 위해 연구에 참여한 초등예비교사는 총 107명으로 소책자를 활용하여 교재연구강좌를 수강한 실험집단이 46명, 소책자를 사용하지 않고 교재연구강좌를 수강한 비교반이 61명이었다. 두 집단을 대상으로 일원변량분석과 공변량분석, 대응표본 t검정, 상관분석을 실시하였다. 연구 결과 본 연구에서 개발한 소책자를 사용한 실험 집단은 과학교수효능감과 생명영역 오개념 교정에 있어서 통계적으로 매우 유의한 수준에서 비교반보다 높은 점수를 얻었다. 따라서 본 연구에서 개발한 소책자는 초등예비교사들의 과학 교수효능감을 증진하고 오개념을 교정하는데 효과가 있음이 검증되었다. 본 연구를 통해서 초등예비교사들의 생명과학 영역 오개념 교정을 돕고, 궁극적으로 초등학생들의 올바른 생명영역 개념 형성을 도울 수 있으며, 초등예비교사들의 고양된 교수효능감은 초등학생들의 과학 수업에 긍정적인 영향을 줄 수 있을 것으로 기대한다.

• 한국해양생명과학회지
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• 제6권2호
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• pp.80-87
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• 2021

본 연구에서는 과불화합물 PFOA와 PFOS potassium salt가 Mesocentrotus nudus의 10 min-수정률과 48 h-정상유생발생률에 미치는 독성영향을 반수영향농도, 무영향농도, 최소영향농도 등의 독성값 계산을 통해 확인하였다. PFOA와 PFOS potassium salt에 대한 10 min-수정률의 EC₅₀ 값은 각각 1346.43 mg/l와 536.18 mg/l로 나타났으며, 48 h-정상유생발생률의 EC₅₀ 값은 각각 42.67 mg/l와 17.81 mg/l로 나타났다. 최근 연구에 의하면, 환경 내의 PFOA와 PFOS의 농도는 지속적으로 감소하였으며, 성게류에게 급성독성을 나타낼 정도는 아닌 것으로 나타났다. 하지만 생물체내에서는 여전히 높은 농도로 관측되고 있다. 결국, PFOA와 PFOS는 생물체의 생애전주기에 걸쳐 체내 축적이 가능하기 때문에, 연안환경에 서식하는 해양생물을 이용한 생애전주기적 만성독성 연구가 필요할 것이다.

• 생태와환경
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• 제41권4호
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• pp.431-440
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• 2008

Turbid water or suspended sediment is associated with negative effects on aquatic organisms; fish, aquatic invertebrate, and periphyton. Effects of turbid water on fish differ depending on their developmental stage and a level of turbidity. Low turbid water may cause feeding and predation rates, reaction distance, and avoidance in fish, and it could make fish to die under high turbidity and long period. Therefore, it is very important to find out how turbid water or suspended sediment can affect fish in domestic watersheds. The objectives of this study were 1) to introduce international case studies and their standards to deal with suspended sediment, 2) to determine acute toxicity in 4 major freshwater fishes, and 3) to determine in relation to adverse effect of macroinvertebrates and fish. Impacts of turbid water on fish can be categorized into direct and indirect effects, and some factors such as duration and frequency of exposure, toxicity, temperature, life stage of fish, size of particle, time of occurrence, availability of and access to refugia, etc, play important role to decide magnitude of effect. A review of turbidity standard in USA, Canada, and Europe indicated that each standard varied with natural condition, and Alaska allowed liberal increase of turbidity over natural conditions in streams. Even though acute toxicity with four different species did not show any fatal effect, it should be considered to conduct a chronic test (long-term) for more detailed assessment. Compared to the control, dominance index of macroinvertebrates was greater in the turbid site, whereas biotic index, species diversity index, species richness index, and ecological score were smaller in the turbid site. According to histopathological analysis with gills of macroinvertebrate and fishes, morphological and physiological modification of gills due to suspended sediments can cause disturbance of respiration, excretion and secretion. In conclusion, in order to maintain good and healthy aquatic ecosystem, it is the best to minimize or prevent impact by occurrence of turbid water in stream and reservoir. We must make every effort to maintain and manage healthy aquatic ecosystem with additional investigation using various assessment tools and periodic biomonitoring of fish.

• 한국수소및신에너지학회논문집
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• 제16권2호
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• pp.170-179
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• 2005

Electrolyte loss is considered as one of the major obstacles limiting the life time of molten carbonate fuel cells (MCFCs). Unit cells with an effective area of 100 $cm^2$ were prepared and were operated to determine the optimum matrix thickness which contains the maximum amount of electrolyte without serious preformance loss caused by high resistance. Matrices with different thickness, 1.45, 1.8, and 2.3 mm, were used in unit cells and those cells were operared about 5000, 10000, and 4000 hrs. The unit cell used 1.8 mm thick matrix showed 0.85 V (at 150 mA/$cm^2$) as the intial performance and this cell voltage is not lower than the cell voltage obtained in the cell with 1 mm thick matrix. This cell was operated for 10000 hrs. The cell used 1.45 mm thick matrices showed 16.6 % in the electrolyte loss after 5000 hr operation. In the case of the cell with 2.3 mm thick matrix, the initial cell voltage was below 0.80 V (at 150 mA/$cm^2$). For thermal cycle test, the gas crossover amount of unit cell used 1.8 mm thick matrix was much less than that of the cell with 1.0 mm thick matrix.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.80-83
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• 2008

As SOC (Social Overhead Capital) has been expanded, the highway road construction has been accelerated and city road system has been more complicated. So, long road tunnels have been increased and traffic flow rate also has been raised. Accordingly, the exhausting gas of vehicle cars seriously deteriorates the tunnel inside air quality and driving view. In order to improve tunnel inside air quality, we may need to introduce a compulsory ventilation system as well as natural ventilation mechanism. The natural ventilation mechanism is enough for short tunnels, meanwhile longer tunnels require a specific compulsory ventilation facility. Many foreign countries already have been devoting on development of effective tunnel ventilation system and especially, some European nations and Japan have already applied their developed tunnel ventilation system for longer road tunnels. More recently, as the quality of life improved, our concerns about safety of driving and better driving environment have been increased. In order to obtain clearer and longer driving view, we are more interested in EP tunnel ventilation system in order to remove floating contaminants and automobile exhaust gas. Evan though it's been a long time since many European countries and Japan applied more economical and environment-friendly tunnel ventilation system with their self-developed Electrostatic Precipitator, we are still dependant on imported system from foreign nations. Therefore, we need to develop our unique technical know-how for optimum design tools through validity investigation and continuous possibility examination, eventually in order to localize the tunnel ventilation system technology. In this project, we will manufacture test-run products to examine the performance of system in order to develop main parts of tunnel ventilation system such as electrostatic precipitator, high voltage power generator, water treatment system, etc.