• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2000년도 춘계학술발표대회
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• pp.141-144
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• 2000

Highly open porous polymer matrices are required for high density cell seeding, efficient nutrient, and oxygen supply to the cells cultured in the three dimensional matrices. However, there are severe problems of mass transfer limitations within the cell/scaffolds culture system. Thus we hypothesize that continuos-flow culture conditioning of cells with the scaffolds may improve the cell viability and the differentiated function. In this study, we fabricated porous PLGA scaffolds by using gas-foaming/salt-leaching method as previous described. Viscous PLGA gel paste contains ammonium bicarbonate particulates, acting as a gas-foaming agent as well as a salt-leaching porogen, were cast into Teflon mold and dried. Ammonium bicarbonate salt upon contact to an acidic aqueous solution evloves gaseous ammonia and carbon dioxide by itself. And we conjugated galactose moiety [AGA; $N-(aminobuty1)-O-{\beta}-D-galactopyranosyl-(1{\rightarrow}4)-D-glucoamide]$ to the terminal end group of a PLGA to increase the cell adhesion and matain the differentiated function of hepatocytes. Cell-seeded scaffolds were secured in a flow bioreactor chamber and exposed to continuous flow at 5 ml/min. As a result of our study, the high yield of hepatocytes attachment was accomplished by increasing the concentration of PLGA-AGA conjugate in polymer scaffolds and cells in the scaffolds under continuos flow condition maintained a high level of viability and albumin secretion rate of cultured hepatocytes showed a higher level that of control groups.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2003년도 생물공학의 동향(XIII)
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• pp.384-387
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• 2003

음식물쓰레기 퇴비화시설에서 발생하는 악취에 대해 90일 동안 입구농도를 측정한 결과 발효기 가동시간에는 $10{\sim}100ppm$, 비가동시간에는 $0{\sim}10ppm$의 농도를 나타냈다. 바이오필터의 제거효율은 초기에 80%정도를 보이다 20일 전후를 해서 90%이상을 나타냈다. 압력손실은 90일 경과 후에도 20 $mmH_2O$를 넘지 않아 바이오필터에 효율적인 악취처리가 이루어졌음을 알 수 있다.

• 한국대기환경학회지
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• 제13권6호
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• pp.439-450
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• 1997

Atmospheric fine particles $(PM_{2.5})$ were collected at the background sites, Kangwha, Taean, and Kosan and characterized to understand their behaviors at the sites. Daily samples of $PM_{2.5}$ mass were measured and ionic species, carbonaceous species, and gaseous species were analyzed. Four-day backward trajectory analysis was also carried out. The mean concentrations of anthropogenic species were highest at Kangwha among three sites, while contributions from sea salts wree highest at Taean during the measurement period due to higher wind speed at Taean. Major chemical components in fine particles were sulfate, organic carbon, nitrate, and ammoniu. Most of the non-sea-salt (nss) sulfates in $PM_{2.5}$ might be present as ammonium sulfates at these sites. Most air parcels arriving at Kangwha and Taean were from northern China. Therefore, both sites were thought to be affected by the same air parcel. At Kosan, during the measurement period, air parcels were from either northern China or sourthern China. The nss sulfate concentration in the air parcels from southern China was higher, while the nss calcium, nitrate, and ammonium concentrations were higher when the air parcels were from northern China.

• 한국세라믹학회지
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• 제32권4호
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• pp.419-428
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• 1995

Polycrystalline silicon carbide (SiC) thick films were depostied by low pressure chemical vapor deposition (LPCVD) using CH3SiCl3 (MTS) and H2 gaseous mixture onto isotropic graphite substrate. Effects of deposition variables on the SiC film were investigated. Deposition rate had been found to be surface-reaction controlled below reactor temperature of 120$0^{\circ}C$ and mass-transport controlled over 125$0^{\circ}C$. Apparent activation energy value decreased below 120$0^{\circ}C$ and deposition rate decreased above 125$0^{\circ}C$ by depletion effect of the reactant gas in the direction of flow in a horizontal hot wall reactor. Microstructure of the as-deposited SiC films was strongly influenced by deposition temperature and position. Microstructural change occurred greater in the mass transport controlled region than surface reaction controlled region. The as-deposited SiC layers in this experiment showed stoichiometric composition and there were no polytype except for $\beta$-SiC. The preferred orientation plane of the polycrystalline SiC layers was (220) plane at a high reactant gas concentration in the mass transfer controlled region. As depletion effect of reactant concentration was increased, SiC films preferentially grow as (111) plane.

• 항공우주기술
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• 제7권2호
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• pp.170-175
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• 2008

본 연구에서는 다양한 기체를 사용한 액체로켓엔진의 시동특성 및 적합성, 그리고 호환성 등에 대해 고찰하였다. 엔진의 시동특성은 파이로 시동기 및 헬륨 기체 시동에 대해 고찰하였으며, 파이로 시동기 및 헬륨, 수소+질소 혼합기체 그리고 공기 등을 구동매질로 할 때의 시험 적합성과 호환성 등에 대해 고찰하였다. 대부분의 기체가 엔진의 시동특성과 호환성을 만족시키는 것을 알 수 있었으나, 공기의 경우 저추력의 경우에만 사용할 수 있는 것을 알 수 있었다.

• 천문학회보
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• 제40권2호
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• pp.35.4-36
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• 2015

Gaseous inner disks are the main controller of the final structure of planetary systems as well as the building place of planets, especially of terrestrial planets. However, the inner disk of <5AU is still difficult to be spatially resolved even at the closest star forming regions. Resolving velocity structure in the disk with high resolution infrared spectroscopic study is the best approach to study the inner disk at this moment. Here, we present the IGRINS (Immersion GRating INfrared Spectrometer) result of the Class I young stellar object, ESO Ha 279a, in the Serpens molecular cloud region. IGRINS has a resolving power of R=40,000, corresponding to the velocity resolution of 7 km/s at K-band, which is perfect to study the hot inner disk structure. We report that NaI and CO overtone emission lines are indeed good tracers of the rotating inner warm disk tracing from ~0.04 to ~7AU of this source. We also report the disk properties using other emission lines.

• 한국수소및신에너지학회논문집
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• 제25권6호
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• pp.643-647
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• 2014

Two types of fuel supply method ar used in CNG vehicles. One is premixed ignition and the other is gas-jet ignition. In premixed ignition, the fuel is introduced with intake air so that homogeneous air-fuel mixture may form. The ignitability of this method depends on the global equivalence ratio. In gas-jet ignition, CNG is introduced directly into the engine combustion chamber. The overall mixture is stratified by retarded fuel injection. In this study, a visualization technique was employed to obtain fundamental properties regarding overall mixture formation of direct injected CNG fuel inside a constant volume chamber. Jet angles, penetrations and projected jet area with respect to ambient pressure are investigated. The penetration decreases apparently and the time reaching the CVC wall was delayed as the chamber pressure increases. This is caused by the higher inertia of the fluid elements that the injected fluid must accelerate and push aside. It is same to liquid fuel such as diesel and gasoline, but this phenomenon is far more prominent for the gaseous fuel.

• 한국전산유체공학회지
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• 제7권3호
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• pp.17-26
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• 2002

Computational fluid dynamic(CFD) analysis has been frequently applied to the waste incinerators to understand the flow performance for various design and operating parameters. Since the computational modeling inevitably requires many simplifications and complicated sub-models, validity of the results should be carefully evaluated. In this study, major computational modeling and procedure of usual simulation methods for the grate-type waste incinerators were assessed. Usual simulation method does not explicitly incorporate the waste combustion, simply by assuming the combustion gas properties from the waste bed which is treated as an inlet plane. However, effect of this arbitrary assumption on the overall flow pattern is not significant, since the flow pattern is dominated by strong pattern of jet flows of the secondary air. Thus, this method is valid in understanding the effect of flow-related parameters. In analyzing the results, deriving conclusive information directly from temperature and chemical species concentration should be avoided, since the model prediction for the gaseous reaction and the radiation reveals significant discrepancies against the actual phenomena. Use of quantitative measures such as residence time is very efficient in evaluating the flow performance.

• 한국전산유체공학회지
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• 제15권1호
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• pp.56-63
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• 2010

Since emission regulations for vehicles have become more stringent, SCR technology has drawn a strong attention in order to reduce NOx emissions. Optimal design of a reductant injection nozzle and a multi-hole plate located between the cone and catalyst is critical in that the uniform distribution of reductant is necessary to maximize the NOx conversion efficiency and minimize the slip of reductant in SCR. In this work, an LPG fuel(C3H8 in vapor state) was used as a reductant for LPG vehicles. A Realizable k-$\varepsilon$ model is used for turbulence, and SCR body is defined as porous media with inertia and viscous resistances measured in this work. Effect of the number of nozzle holes on the flow mixing index was analyzed, which revealed that a four hole nozzle shows the best performance in terms of uniformity of flow. An installment of a multi-hole plate at the entrance of catalyst was evaluated with flow mixing index, uniformity of flow, and pressure drop. A multi-hole plate with gradual hole diameter change in three steps showed the best uniformity of flow within the conditions suggested in this work.

• Journal of Advanced Marine Engineering and Technology
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• 제21권5호
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• pp.564-570
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• 1997

The most important factor for the desalination system is the fresh water production cost dependent upon the possible energy source which should be obtained easily and with low price. Recently in Korea the demand of LNG, as a cheap and clean energy which does not cause an environmental problem, has sharply been increased. In general, LNG is storaged in a tank as a liquid state below -162 'C. When it is serviced, however, the LNG absorbs energy from a heating source and transforms to the gaseous state with high pressure. During this process a huge amount of cold energy accumulated in LNG is wasted. This waste cold energy can be utilized for producing fresh water from sea water using a sea water freezing desalination system. In order to develop a sea water freezing desalination system and to establish its design technique, a qualitative and quantitative data regarding the freezing behavior of sea water is needed in advance. The goal of this study, therefore, are to reveal the freezing mechanism of sea water, to measure the freezing rate, and to investigate the freezing heat-transfer characteristics. The experimental results help to provide a general understanding of the sea water freezing behavior in a Rectangular vessel cooled from below.