• 생태와환경
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• 제42권4호
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• pp.441-451
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• 2009

The major objectives of this study were to evaluate trophic state of reservoirs using major water quality variables and its relations in terms of trophic guilds and tolerance guilds with dominant lentic fishes. For this study, we selected 6 artificial reservoirs such as Namyang Reservoir ($N_yR$), Youngsan Reservoir ($Y_sR$), Daechung Reservoir ($D_cR$), Chungju Reservoir ($Cj_R$), Chungpyung Reservoir ($C_pR$), and Paldang Reservoir ($P_dR$), and collected fish during 2000~2007 along with data analysis of water quality monitored by the ministry of environment, Korea. Biological oxygen demand (BOD) and chemical oxygen demand (COD), indicators of organic matter pollution, varied depending on types of the reservoirs and the spatial patterns in terms of trophic gradients were similar to patterns of nutrients, Secchi depth and chlorophyll-a. Analysis of trophic state index (TSI) showed that reservoirs of $D_cR$ and $C_jR$ were mesotrophy and other 4 reservoirs were eutrophic state. The relations of trophic relations showedthat TSI (Chl-a) had a positive linear function [TSI (CHL)=0.407 TSI (TP)+28.2, n=138, p<0.05] with TSI (TP) but had a weak relation with TSI (TN). Also, TSI (TP) were negatively correlated ($R^2=0.703$, p<0.05) with TSI (SD), whereas TSI (TN) was not significant (p>0.05) relations with TSI (SD). Tolerance guilds of lentic fishes, based on three types of the reservoirs, reflected the exactly water quality in the TN, TP, BOD, and COD, and similar trends were shown in the fish feeding/trophic guilds.

• Journal of Pharmaceutical Investigation
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• 제27권3호
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• pp.199-205
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• 1997

In order to formulate biphenyl dimethyl dicarboxylate(DDB) aqueous solutions, the effects of various solubilizing agents such as cosolvents(PG, PEG 400, glycerin, ethanol), surfactants,$(poloxamer\;407,\;Cremophor^{\circledR}\; RH40,\;Solutol^{\circledR},\;Tween\;80,\;sodium\;lauryl\;sulfate)$, complexation agent$(CELDEX^{\circledR}\;CH-20)$ and others(urea, niacinamide, propylene carbonate, HPMC) on the solubility of DDB in water were evaluated. The solubility of DDB in water was about $0.21\;{\mu}g/ml\;at\;20^{\circ}C$, while its solubility in PEG 400 was 5,000 times higher than that in water. 60% PEG 400 aqueous solution was selected as an optimum solvent system, and surfactants or other solubilizing agents were added to prevent DDB from recrystalization. The addition of surfactants in water increased the solubility of DDB from 15- to 34-fold, however, $CELDEX^{\circledR}\;CH-20$ and other agents studied showed negligible effects on the solubility of DDB in water. The 60% PEG 400 aqueous solution containing 5% $Cremophor^{\circledR}$　RH40 was appeared as the formula of choice. It showed acceptable physical stability after stored for 7 days at $4^{\circ}C$.

• 설비공학논문집
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• 제12권3호
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• pp.315-324
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• 2000

R-410A, R-407C, and four refrigerant mixtures composed of R-32, R-l34a, R-l43a, R-l52a, R-600(butane), and R-600a(isobutane) were tested in an attempt to replace R-22 used in most of the residential air conditioners. The performance evaluation was carried out in a psychrometric calorimeter test facility using a residential spilt type air conditioner under the KS rating conditions. Except for the lubricant and hand-operated expansion valve, the other parts of the air conditioner were the same with the commercial system. Performance characteristics were measured; COP, capacity, compressor power, and VCR. R-410A was shown to have 5.5% higher COP and 3.5% lower capacity than R-22. R-32/134a/600a (42.8/ 46.0/11.2 wt%) mixture have the best performance among the four refrigerant mixtures composed of hydrofluorocarbon and hydrocarbon. This inixture have 3.0% lower COP and 1.6% lower capacity than R-22.

• 한국진공학회지
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• 제17권5호
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• pp.400-407
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• 2008

본 연구에서는 축전 결합형 플라즈마원에 대한 전자기장의 2차원 공간 의존성을 계산하였다. 1차원 유체 방정식을 기반으로 축전 전기장과 전도 전류 밀도의 axial 방향 공간 의존성을 계산한 후, radial 방향으로는 맥스웰 방정식의 해를 ${\omega}r/c$에 대한 power series로 전개하여 전자기장의 2차원 공간 의존성을 계산하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1995년도 제22회 학술대회
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• pp.28-37
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• 1995

To protect the ozone layer depeletion the CFC (chlorofluorocarbon). HCFC(hydrochlorofluorocarbon) refrigerants will be replaced with HFCs (hydro-fluorocarbon) as an alternative refrigerant. In recent years a good deal of effort has been made to develop new compressors which are compatible to the new referigent. This paper focused on developing accelerated screening test for predicting tribological characteristics of the rotary compressor in atmosphere of R407C as an alternative refrigerant with polyolester lubricant. Falex wear test machine with high pressure chamber has been used to simulate friction and wear behavior of the common contact geometries found in rotary compressors.

• 대한화학회지
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• 제67권6호
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• pp.407-414
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• 2023

The present study uses quasi-classical trajectory procedures to examine the vibrational relaxation and dissociation of the methyl and ring C-H bonds in excited methylpyrazine (MP) during collision with either N₂ or O₂. The energy-loss (-ΔE) of the excited MP is calculated as the total vibrational energy (E_T) of MP is increased in the range of 5,000 to 40,000cm^-1. The results indicate that the collision-induced vibrational relaxation of MP is not large, increasing gradually with increasing E_T between 5,000 and 30,000 cm^-1, but then decreasing with the further increase in E_T. In both N₂ and O₂ collisions, the vibrational relaxation of MP occurs mainly via the vibration-to-translation (V→T) and vibration-to-vibration (V→V) energy transfer pathways, while the vibration-to-rotation (V→R) energy transfer pathway is negligible. In both collision systems, the V→T transfer shows a similar pattern and amount of energy loss in the ET range of 5,000 to 40,000cm^-1, whereas the pattern and amount of energy transfer via the V→V pathway differs significantly between two collision systems. The collision-induced dissociation of the C-H_methyl or C-H_ring bond occurs when highly excited MP (65,000-72,000 cm^-1) interacts with the ground-state N₂ or O₂. Here, the dissociation probability is low (10^-4-10^-1), but increases exponentially with increasing vibrational excitation. This can be interpreted as the intermolecular interaction below E_T = 71,000 cm^-1. By contrast, the bond dissociation above E_T = 71,000 cm^-1 is due to the intramolecular energy flow between the excited C-H bonds. The probability of C-H_methyl dissociation is higher than that of C-H_ring dissociation.

• 설비공학논문집
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• 제10권4호
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• pp.411-422
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• 1998

In this study, experiments were carried out to provide nucleate pool boiling heat transfer data for a plain tube and 4 different low fin tubes employing 2 refrigerant mixtures of R410A, R407C, and 12 pure fluids. Low fin tubes were machined on a 19.05mm nominal outside diameter copper block according to the manufacturer's low fin tube specifications. Cartridge heaters were used to generate uniform heat flux on the tubes. For all refrigerants, heat flux varied from 10㎾/$\m^2$ to 80㎾/$\m^2$. It is found that heat transfer coefficients(HTCs) of high vapor pressure refrigerants are usually higher than those of low pressure fluids. On the other hand, the fin effect was more prominent with low pressure refrigerants than with high pressure ones. Optimum fin density as well as the increase in heat transfer coefficient with the increase in fin density were found to be strongly fluid dependent. HTCs of Rl23, a low pressure alternative refrigerant, were similar to those of Rll while HTCs of R134a, an intermediate pressure alternative refrigerant, were roughly 20% higher than those of Rl2. Finally, HTCs of R32, R125, R143a, and R410A were all higher than those of R22 by 30~50%.

• 대한설비공학회지:설비저널
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• 제31권7호
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• pp.65-70
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• 2002

지구의 오존층을 보호하기 위한 몬트리올 의정서가 1987년 채택된 이후 오존층 파괴물질의 사용이 점차 감소되고 있다. 선진국의 경우 1995년 말부터 CFC냉매의 생산을 전폐하였고, HCFC냉매의 경우는 2020년 전폐를 목표로 대체냉매를 이용한 응용 기술개발 및 제품 생산이 진행되고 있다. 가정용 냉장고 및 차량용 에어컨에는 R-12의 대체냉매로 R-134a가 도입되었으며, 유럽을 중심으로 냉장고에는 HC계 냉매인 R-600a도 대체냉매로 사용되고 있다. 가정용 에어컨에는 혼합냉매인 R-407c 와 R-410a가 R-22 냉매를 대체하여 적용되고 있다. 그러나 현재, CFC및 HCFC 대체 냉매로 많이 사용되고 있는 HFC계 냉매도 지구 온난화 지수가 대단히 큰 문제를 가지고 있다. 1997년 채택된 교토의 정서에는 HFC계 냉매가 온실효과가 가스 배출규제물질에 포함되어 있다. 이에 따라서 오존층의 파괴지수가 영이고 지구온난화지수도 거의 없는 자연냉매가 주목을 받게 되었으며, 자연 냉매의 하나인 이산화탄소 ($CO_2$R744) 냉매의 응용기술 및 제품개발 연구가 선진국을 중심으로 폭넓게 진행되고 잇다. 본고에서는 $CO_2$냉매의 일반적인 특성을 간단히 소개하고 일본에서 진행되고 있는 $CO_2$냉매를 적용한 급탕시스템의 제품개발 및 시장현황에 대해서 기술하기로 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.83-89
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• 2000

This paper presents a pressure drop correlation for evaporation and condensation of alternative refrigerant with oil in micro-fin tubes. The correlation was developed from a data base consisting of oil-free pure and mixed refrigerants in micro-fin tube; Rl25 R134a. R32 R410a(R32/R125 50/50% mass), R22, R407c(R32/R125/R134a, 23/25/52% mass) and R32/R134a(25/75% mass). The micro-fin tube used in this paper had 60 0.2mm high fins with a 18 helix angle. The cross sectional flow area $(A_c)$ was $60.8 mm^2$ giving an equivalent smooth diameter$(D_e)$ of 8.8mm. The hydraulic diameter $(D_h)$ was estimated to the 5.45mm. The new correlation was obtained by replacing the friction factor and the tube-diameter in Bo Pierre correlation by a friction factor derived from pressure drop data for a micro-fin tube and the hydraulic diameter, respectively. This correlation was also used to predict some pressure data with a lubricant after using a mixing viscosity rule of lubricants and refrigerants. As a result, the new correlation was also well predicted to the measured data within a mean deviation of 19.0%.

• 한국자원식물학회지
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• 제27권2호
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• pp.111-118
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• 2014

주요한 꽃차의 재료로 이용되고 있는 백목련, 매화 및 홍화의 성분 및 생리활성 차이를 검토하고자 폴리페놀 함량, 플라보노이드 함량, 카테킨류 함량 및 항산화성을 분석하였다. 각종 시료의 에탄올 추출물로부터 총 페놀 함량을 Folin-Denis 방법으로 측정한 결과 표준물질을 catechin, chlorogenic acid, tannic acid로 각각 달리하여 측정한 결과 백목련이 72.6 ~ 118.0 mg/kg 범위로 가장 높게 나타났고 그 다음이 매화와 홍화 순으로 나타났다. 한편, 총 플라보노이드 함량은 백목련이 25.1 mg/kg으로 높게 나타났으나 다른 꽃과의 유의적인 차이는 없는 것으로 나타났다. 항산화성을 알아보기 위해 DPPH 라디컬 소거능을 측정한 결과 250 mg/kg의 추출물 농도에서 백목련과 매화는 각각이 93.0과 92.6%로 높게 나타났으나, 홍화는 23.0%로 낮은 활성을 보였다. 총 catechin 함량에 있어서 백목련이 총 8종의 카테킨류 중 6종의 화합물이 함유되어 있었고 9,425.5 mg/kg으로 가장 높게 나타났고, 매화와 홍화는 각각 5종과 2종의 화합물이 함유되어 각각 3,407.8과 190.6 mg/kg으로 낮게 나타났다. 한편 카페인 함량은 매화에서 비타민 C함량은 매화와 홍화가 가장 높은 함량을 보였다. 백목련 꽃은 다른 꽃에 비해 폴리페놀과 플라보노이드 함량이 높고 항산화성이 높아 유망한 기능성 꽃차로서 이용성이 높을 것으로 기대된다. 또한 꽃차의 총 페놀, 총 플라보노이드 및 총 카테킨류 함량은 그들의 항산화성과의 높은 상관계수를 보임으로써 연관성이 높음을 알 수 있었다.