• 한국자동차공학회논문집
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• 제16권5호
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• pp.179-189
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• 2008

The performance of Lean NOx Trap (LNT) based on the catalysts of Pt/K/Ba/$\gamma-Al_2O_3$ with proprietary washcoat formulation is studied using a bench flow reactor system. To investigate the effect of temperature and gas hourly space velocity (GHSV) on the nitrogen oxides (NOx) trapping capacity as well as NOx breakthrough time and final ratio of $NO_2$ to NO of LNT, series of adsorption isotherms are carried out with simulated exhaust gases of the lean burn engines. Since typical operation of LNT requires periodic regeneration with a short rich excursion, where the stored or trapped NOx is released and subsequently reduced to $N_2$, the effect of the duration of lean and rich phase and type of reductants on the NOx conversion is investigated. NOx storage capacity and breakthrough time obtained from adsorption isotherms shows a volcano-type dependence on the temperature with a maximum NOx storage capacity occurring $350^{\circ}C$ and with a maximum breakthrough time occurring $400^{\circ}C$ at all GHSVs investigated in this study. Also, maximum ratio of $NO_2$ to NO is obtained at $400^{\circ}C$ with a GHSV of $75,000\;hr^{-1}$ Lean/rich cycle of 100 s lean and 5 s rich used with a concentration of 1.33% of $H_2$ and 4% of CO in the rich phase is found to be optimum at operating temperature of $350^{\circ}C$ and a GHSV of $50,000\;hr^{-1}$.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2002년도 생물공학의 동향 (X)
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• pp.504-507
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• 2002

A separation/purification process for enzymatic sugar ester production was investigated The crude reaction mixture contained sugar ester and unreacted fatty acid in acetone. The reaction mixture was mixed with KOH/phosphate buffer. Hexane was then added to enhance phase separation. Three phases formed: a lower aqueous phase containing nothing of interest, a polar organic solvent middle phase that contained mostly fatty acid soaps, and a hexane-rich upper phase that contained mostly sugar ester. Distribution coefficient of each component was measured.

• Korean Chemical Engineering Research
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• 제47권4호
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• pp.476-480
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• 2009

본 연구는 리튬 이차전지용 고분자 전해질 복합재료에 관한 것으로, 고분자는 poly(ethylene oxide)(PEO)와 poly(methyl methacrylate) (PMMA) 블렌드를 사용하고, 용매로는 Ethylene carbonate(EC), 그리고 $LiClO_4$를 리튬염으로 하는 전해질 복합체 필름을 제조하였으며, PMMA의 함유량에 따른 고분자 전해질의 전기화학적 특성을 관찰하였다. 제조된 고분자 전해질의 결정화도와 이온전도도는 시차주사열량계(DSC)와 주파수반응분석기(FRA)로 분석하였다. 그 결과 PMMA의 함량을 증가시킴에 따라서, PEO의 결정 영역이 감소하고 이온전도도가 증가하였다. 또한, PMMA의 함량이 20 wt.% 이상인 경우, 고분자 블렌드필름에서 상분리되는 현상을 관찰하였다. 즉, SEM 분석결과에 의해서, PMMA 주성분 영역과 PEO 주성분 영역의 구분이 가능하였다. 고분자 전해질의 이온전도도는 20 wt.% 첨가한 경우 가장 큰 이온전도도를 가지며, 함유량이 20 wt.% 이상에서는 PMMA 상의 증가로 인해 다소 감소된 이온전도도 변화를 나타내었다.

• 한국분말재료학회지
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• 제22권6호
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• pp.426-431
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• 2015

Microstructural examination of the Nb-Si-B alloys at Nb-rich compositions is performed. The Nb-rich corner of the Nb-Si-B system is favorable in that the constituent phases are Nb (ductile and tough phase with high melting temperature) and $T_2$ phase (very hard intermetallic compound with favorable oxidation resistance) which are good combination for high temperature structural materials. The samples containing compositions near Nb-rich corner of the Nb-Si-B ternary system are prepared by spark plasma sintering (SPS) process using $T_2$ and Nb powders. $T_2$ bulk phase is made in arc furnace by melting the Nb slug and the Si-B powder compact. The $T_2$ bulk phase was subsequently ball-milled to powders. SPS is performed at $1300^{\circ}C$ and $1400^{\circ}C$, depending on the composition, under 30 MPa for 600s, to produce disc-shaped specimen with 15 mm in diameter and 3 mm high. Hardness tests (Rockwell A-scale and micro Vickers) are carried out to estimate the mechanical property.

• 한국재료학회지
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• 제3권6호
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• pp.678-683
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• 1993

MBE법으로 $580^{\circ}C$에서 성장한 $GaAs_{0.5}Sb_{0.5}$/(001)GaAs 에피층의 원자 배열을 TEM을 이용하여 분석하였다. 1/2(111) 형의 장범위 규칙상이 $GaAs_{0.5}Sb_{0.5}$/(001)GaAs 에피층에서 발견되었다. 이 규칙상의 원자 배열은 As의 농도가 높은 {111}As 면과 Sb의 농도가 높은 {l1l}Sb 면이 V족 소격자에 교대로 나열된 구조이며, 주기는 {111} 면간 거리의 2배이다. 이 구조는 R3m 의 공간군에 속하며, 단위포는 능면체정이다.

• Corrosion Science and Technology
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• 제10권1호
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• pp.6-12
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• 2011

The selective surface oxidation of a transformation-induced-plasticity (TRIP) steel containing 1.6 wt.% Mn and 1.5 wt.% Si during annealing at $800^{\circ}C$ was investigated for its influence on the formation of an inhibition layer during hot-dip galvanizing. The selective oxidation of the alloying elements and the oxide morphology were significantly influenced by the annealing atmosphere. The pure $N_{2}$ atmosphere with a dew point $-40^{\circ}C$ promoted the selective oxidation of Mn as a crystalline $Mn_{2}SiO_{4}$ phase, whereas the $N_{2}$ + 10% $H_{2}$ atmosphere with the same dew point $-40^{\circ}C$ promoted the selective oxidation of Si as an amorphous Si-rich oxide phase. During hot-dip galvanizing, the $Mn_{2}SiO_{4}$ phase was reduced more readily by Al in the Zn bath than the Si-rich oxide phase. Consequently, the pure $N_{2}$ atmosphere resulted in a higher formation rate of $Fe_{2}Al_{5}$ particles at the Zn/steel interface and better galvanizability than the $N_{2}$ + 10% $H_{2}$ atmosphere.

• 폴리머
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• 제30권2호
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• pp.108-111
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• 2006

본 연구에서는 아크릴계 고분자의 소수성 차이에 따른 막 모폴로지 변화를 조사하였다. 막은poly(methyl methacrylate)(PMMA), poly(ethyl methacrylate)(PEMA), poly(butyl methacrylate)(PBMA), poly(isobutyl, methacrylate)(PIBMA) 및 이들의 블렌드를 사용하여 습식 상 역전 방법으로 제조하였다. 상대적으로 소수성이 적은 PMMA와 PEMA는channel-like 형태의 막 구조를, 소수성이 큰 PBMA와 PIBMA는 finger-like 형태의 막 구조를 보여주었다. 이러한 막 구조의 변화는 polymer-rich상의 고상화 과정에서 속도론적 차이가 있었기 때문이었다. 이성분 블렌드 막의 구조는 주 성분 고분자에 의해 결정되었다.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2002년도 봄 학술발표회 논문집
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• pp.466-469
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• 2002

Polyurethane(PU)은 segmented 블록공중합체로써 상온보다 높은 유리전이온도(glass transition temperature, Tg)를 갖는 hard segment(H.S)와 상온보다 낮은 Tg를 갖는 soft segment (S.S)로 구성되어 있다. 이들 두 segment간의 열역학적 불친화성으로 인해 미세 상분리 구조를 갖는다$^1$. 그 결과 hard segment-rich hard domain과 soft segment-rich soft matrix의 구조를 이룬다. 이중 hard domain(HD)은 상온에서 glassy한 성격을 띄므로 물리적 가교점과 충진제의 역할을 하며 soft domain(SD)은 rubbery한 성질을 가지므로 polurethane에 탄성을 부여하는 역할을 한다. (중략)

• 천문학회보
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• 제37권2호
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• pp.140.2-140.2
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• 2012

The silicate carbon star IRAS 09425-6040 shows very conspicuous crystalline silicate dust features and excessive emission at far infrared. To investigate properties of dusty envelopes around the object, we use radiative transfer models for axisymmetric and sphericallly symmetric dust distributions. We perform model calculations for various possible combinations of dust shells and disks with various dust species. We compare the model results with the observed spectral energy distributions (SEDs) including the IRAS, ISO, AKARI, MSX and 2MASS data. We find that a model with multiple disks of amorphous and crystalline silicate and multiple spherical shells of carbon dust can reproduce the observed SED fairly well. This supports the scenario for the origin of silicate carbon stars that oxygen-rich material was shed by mass loss when the primary star was an M giant and the O-rich material is stored in a circumbinary disk. Highly (about 75 %) crystallized forsterite dust in the disk can reproduce the conspicuous crystalline features of the ISO observational data. This object looks to have a detached silicate and H2O ice shell with a much higher mass-loss rate. It could be a remnant of the chemical transition phase. The last phase of stellar winds of O-rich materials looks to be a superwind.

• ETRI Journal
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• 제6권1호
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• pp.3-9
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• 1984

This paper presents a direct adaptive poleplacement control scheme which is applicable to discrete-time non-minimum phase systems. It is proved that by this scheme the poles can be placed at the desired locations and the overall state vector of the system is uniformly bounded if the reference input is sufficiently rich, and also proved that in case of insufficiently rich reference input the overall system can still be stabilized though the poles may not be placed exactly at the desired locations. The effectiveness of this scheme is verified by digital computer simulations.