• 천문학회보
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• 제37권1호
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• pp.48.1-48.1
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• 2012

We present the ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) to investigate the properties of hot stellar populations responsible for the UV excess (UVX). The initial sample of ETGs is selected by the spectroscopic redshift and the morphology parameter from the SDSS DR 7, and then cross-matched with the GALEX far-UV (FUV) and near-UV (NUV) GR6 data. The cross-matched ETG sample is further classified by their emission line characteristics in the optical spectra into quiescent, star-forming, and active galactic nucleus categories. Contaminations from early-type spiral galaxies, mergers, and morphologically disturbed galaxies are removed by visual inspection. By drawing the FUV-NUV (as a measure of UV spectral shape) versus FUV-r (as a measure of UVX strength) diagram for the final sample of -3700 quiescent ETGs, we find that the "old and dead" ETGs consist of a well-defined sequence in UV colors, the "UV red sequence," so that the stronger UVX galaxies should have a harder UV spectral shape systematically. However, the observed UV spectral slope is too steep to be reproduced by the canonical stellar population models in which the UV flux is mainly controlled by age or metallicity parameters. Moreover, 2 mag of color spreads both in FUV-NUV and FUV-r appear to be ubiquitous among any subsets in distance or luminosity. This implies that the UVX in ETGs could be driven by yet another parameter which might be even more influential than age or metallicity.

• 대한토목학회논문집
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• 제35권2호
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• pp.341-351
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• 2015

본 연구는 만경강 유역을 대상으로 하천을 하도경사를 이용하여 구분하고 빈도별 홍수량에 따라 확보해야 하는 공간과 홍수 방어 대책 수립 지역을 선정하였다. 하천 구분에 의한 분석결과 상류하천 유역에서는 빈도별 홍수량이 커져도 홍수범람면적의 변화가 작으나 하류 하천유역의 경우 빈도별 홍수량이 커짐에 따라 범람면적이 크게 증가하는 것으로 나타났다. 또한, 하천구간별에 따라 주거지역 면적비율이 10%이하인 지역에 대해서는 하천공간 확보 가능 지역, 그리고 10% 이상인 지역은 홍수방어 보강지역으로 선정하고 분석 수행하였다. 분석결과 하류지역은 하천공간 확보 가능 지역이 많고, 상류지역은 홍수방어 보강지역이 많은 것으로 분석되었다. 향후 과거 하천 형태 및 습지 분포 위치 등을 고려한 하천공간 확보 가능지역을 분석하고자 한다.

• 센서학회지
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• 제7권2호
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• pp.83-89
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• 1998

$TiO_{2-x}$ 박막 습도센서를 스퍼터링법에 의해 제조하고, 스퍼터링 조건과 열처리조건에 따른 습도 감지특성 및 동작온도에 따른 특성 등을 조사하였으며, Auger 전자 분광기와 전자현미경으로 그 원인을 분석하였다. $TiO_{2-x}$ 박막 습도센서는 부임피던스 습도특성을 보였으며, rf power가 200 W, 압력은 50 mTorr 및 기판 온도는 $200^{\circ}C$ 에서 증착하고, $600^{\circ}C$에서 1시간 동안 열처리한 소자의 상대습도 변화에 따른 임피던스 변화는 $0.794\;K{\Omega}/%RH$로 가장 컸으며, 응답 시간은 흡착시 약 2분, 탈착시 약 3분이었다.

• 한국수소및신에너지학회논문집
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• 제20권6호
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• pp.505-511
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• 2009

The hydriding and electrochemical characteristics of Zr-based $AB_2$ alloy produced by gas atomization have been extensively examined. For the particle morphology of the as-cast and gas-atomized powders, it can be seen that the mechanically crushed powders are irregular, while the atomized powder particles are spherical. The increase of jet pressure of gas atomization process results in the decrease of hydrogen storage capacity and the slope of plateau pressure significantly increases. TEM and EDS studies showed the increase of jet pressure in the atomization process accelerated the phase separation within grain of the gas-atomized alloy, which brought about a poor hydrogenation property. However, the gas-atomized $AB_2$ alloy powders produced by jet pressure of 50 bar kept up the reversible $H_2$ storage capacity and discharge capacity similar to the mechanically crushed particles. In addition, the electrode of gas-atomized Zr-based $AB_2$ alloy of 50 bar showed improved cyclic stability over that of the cast and crushed particulate, which is attributed to the restriction of crack propagation by grain boundary and dislocation with ch/discharging cycling.

• Advances in materials Research
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• 제4권4호
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• pp.215-226
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• 2015

Experiment on roughness and micro pit defects of SUS 430 ferrite stainless steel was investigated in laboratory. The relation between roughness and glossiness with reduction in height, roll surface roughness, emulsion parameters was analyzed. The surface morphology of micro pit defects was observed by SEM, and the effects of micro pit defects on rolling reduction, roll surface roughness, emulsion parameters, lubrication oil in deformation zone and work roll diameter were discussed. With the increasing of reduction ratio strip surface roughness Ra(s), Rp(s) and Rv(s) were decreasing along rolling and width direction, the drop value in rolling direction was faster than that in width direction. The roughness and glossiness were obtained under emulsion concentration 3% and 6%, temperature $55^{\circ}C$ and $63^{\circ}C$, roll surface roughness $Ra(r)=0.5{\mu}m$, $Ra(r)=0.7{\mu}m$ and $Ra(r)=1.0{\mu}m$. The glossiness was declined rapidly when the micro defects ratio was above 23%. With the pass number increasing, the micro pit defects were reduced, uneven peak was decreased and gently along rolling direction. The micro pit defects were increased with the roll surface roughness increase. The defects ratio was declined with larger gradient at pass number 1 to 3, but gentle slope at pass number 4 to 5. When work roll diameter was small, bite angle was increasing, lubrication oil in micro pit of deformation zone was decreased, micro defects were decreased, and glossiness value on the surface of strip was increased.

• 한국수자원학회논문집
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• 제35권4호
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• pp.345-358
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• 2002

수치고도모형을 이용한 흐름분배 알고리즘들은 지형을 따른 흐름의 분산특성을 잘 기술해 주는 방향으로 발달되어 왔지만, 수로격자의 연결성, 지형기복을 따른 다양한 분산특성, 수로격자크기 등과 관련한 한계성을 가지고 있다. 기존 흐름 알고리즘들이 흐름분배 결정에 사용한 지형 데이터들은 수치고도모형에서 산출가능한 흐름누적면적과 경사도로서 유역내 지배적인 흐름경로인 수로격자의 위치와 크기에 대한 고려를 하지 않는다. 따라서 본 연구에서는 기존 알고리즘들의 단점인 수로의 연결성과 복잡한 지형을 따른 다양한 흐름분산 특성을 기술할 수 있는 흐름 분배 알고리즘을 제안하고, 유전자 알고리즘을 이용하여 수로격자의 위치와 크기를 가장 잘 표현할 수 있도록 최적화하였으며, 기존의 방법에 비해 개선된 결과를 얻을 수 있었다.

• 천문학회보
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• 제37권2호
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• pp.68.1-68.1
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• 2012

We present a comprehensive study of the stellar populations in two faint M31 dwarf satellites, And XI and And XIII. Using deep archival images from the Wide Field Planetary Camera 2 (WFPC2) onboard the Hubble Space Telepscope (HST), we characterize the horizontal branch (HB) morphologies and the RR Lyrae (RRL) populations of these two faint dwarf satellites. Our new template light curve fitting routine (RRFIT) detected RRL populations from both galaxies. The mean periods of $RR_{ab}$ (RR0) stars in And XI and And XIII are < $P_{ab}$ > = $0.621{\pm}0.040$, and < $P_{ab}$ > = $0.648{\pm}0.038$ respectively. Even though the RRL populations show a lack of $RR_{ab}$ stars with high amplitudes (Amp(V) > 1.0 mag) and relatively short periods ($P_{ab}$ ~ 0.5 days), their period - V band amplitude (P-Amp(V)) relations track the lower part of the general P-Amp(V) trend in the M31 outer halo RRL populations. The metallicities of $RR_{ab}$ stars were calculated via the [Fe/H]-log $P_{ab}$-Amp(V) relationship of Alcock et al. The metallicities thus obtained ($[Fe/H]_{And}$ $_{XI}=-1.75%$; $[Fe/H]_{And}$ $_{XIII}=-1.74$) are consistent with the values calculated from the RGB slope indicating that our measurements are not significantly affected by the evolutionary effects of RRL stars. We discuss the origins of And XI and And XIII based on a comparative analysis of the luminosity-metallicity (L-M) relation of Local Group dwarf galaxies.

• 한국재료학회지
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• 제33권10호
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• pp.377-384
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• 2023

Exploring earth-abundant, highly effective and stable electrocatalysts for electrochemical water splitting is urgent and essential to the development of hydrogen (H₂) energy technology. Iron-cobalt layered double hydroxide (FeCo-LDH) has been widely used as an electrocatalystfor OER due to its facile synthesis, tunable components, and low cost. However, LDH synthesized by the traditional hydrothermal method tends to easily agglomerate, resulting in an unstable structure that can change or dissolve in an alkaline solution. Therefore, studying the real active phase is highly significant in the design of electrochemical electrode materials. Here, metal-organic frameworks (MOFs) are used as template precursors to derive FeCo-LDH from different iron sources. Iron salts with different anions have a significant impact on the morphology and charge transfer properties of the resulting materials. FeCo-LDH synthesized from iron sulfate solution (FeCo-LDH-SO₄) exhibits a hybrid structure of nanosheets and nanowires, quite different from other electrocatalysts that were synthesized from iron chloride and iron nitrate solutions. The final FeCo-LDH-SO₄ had an overpotential of 247 mV with a low Tafel-slope of 60.6 mV dec^-1 at a current density of 10 mA cm^-2 and delivered a long-term stability of 40 h for the OER. This work provides an innovative and feasible strategy to construct efficient electrocatalysts.

• 자원환경지질
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• 제45권6호
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• pp.685-695
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• 2012

본 연구는 현재까지 수행된 독도 화산체 정상부 해역의 정밀수심 및 지구물리 조사 자료를 종합하고 분석하여 정상부 해역의 정밀해저지형 및 지구물리학적 특성을 연구하였다. 독도 연안역 동도와 서도 사이 연결 수로는 약 10 m 이내의 얕은 수심을 이루고 있다. 독도 화산체 정상부해역의 전체적인 수심은 동도와 서도의 육지부부터 수면 아래 약 30 m 까지는 불규칙하며 급한 경사면을 가지고, 그 후 수심 약 30 m부터 수심 약 80 m 까지는 경사가 점차 낮아지다가 수심 약 80 m 이하로 완만한 경사를 보이면서 외해역으로 깊어진다. 독도 육지부와 그 북동쪽 및 북서쪽으로 연장되는 암반들은 독도를 생성시킨 화구륜의 잔해로 판단되며 동도와 서도는 화구륜의 남쪽 한부분일 가능성이 큰 것으로 생각된다. 또한 정상부 해역의 해저지형에서는 소규모의 움푹 패인 지형들이 나타나는데 이는 독도 형성 후 나중에 생성된 소규모 분화구의 흔적들로 추정된다. 독도 정상부 해역은 주로 암반이 많이 분포하지만 곳곳에서는 모래 퇴적층들도 나타나는 것을 볼 수 있다. 독도 화산체 정상부에는 계단형의 경사면들이 나타나는데 이는 제4 기에 나타난 해침, 해퇴 등 해수면변화에 의해 만들어진 해저단구로 유추되며, 지역별로 차이가 있기는 하지만 주로 약 30 m, 60 m, 80 m 및 약 100 m의 수심대를 위주로 하여 몇 개의 주요 해저단구가 나타나는 것으로 판단된다. 자기이상도 및 아날니틱신호도를 살펴보면 수면 위 독도에서 연장되는 북동 및 북서쪽의 이상대들은 화구륜의 잔해로 예상되는 암반들의 위치와 유사하게 나타난다.

• Archives of Pharmacal Research
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• 제21권6호
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• pp.645-650
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• 1998

The dual drug-loaded alginate beads simultaneously containing drug in inner and outer layers were prepared by dropping plain (single-layered) alginate beads into $CaCl_2$ solution. The release characteristics were evaluated in simulated gastric fluid for 2 h followed by intestinal fluids thereafter for 12 h. The surface morphology and cross section of dual drug-loaded alginate beads was also investigated using scanning electron microscope (SEM). The poorlv water-soluble ibuprofen was chosen as a model drug. The surface of single-layered and dual drug-loaded alginate beads showed very crude and roughness, showing aggregated particles, surface cracks and rough crystals. The thickness of dual drug-loaded alginate beads surrounded by outer layer was ranged from about 57 to 329mcm. The distinct chasm between inner and outer layers was also observed. In case of single-layered alginate bead, the drug was not released in gastric fluid but was largely released in intestinal fluid. However, the release rate decreased as the reinforcing $Eudragit^{\circledR}$ polymer contents increased. When the plasticizers were added into polymer, the release rate largely decreased. The release rate of dual drug-loaded alginate beads was stable in gastric fluid for 2 h but largely increased when switched in intestinal fluid. The drug linearly released for 4 h followed by another linear release thereafter, showing a distinct biphasic release characteristics. There was a difference in the release profiles between single-layered and dual drug-loaded alginate beads due to their structural shape. However, this biphasic release profiles were modified by varying formulation compositions of inner and outer layer of alginate beads. The release rate of dual drug-loaded alginate beads slightly decreased when the outer layer was reinforced with $Eudragit^{\circledR}$ RS1OO polymers. In case of dual drug-loaded alginate beads with polymer-reinforced outer layer only, the initial amount of druc released was low but the initial release rate (slope) was higher due to more swellable inner cores when compared to polymer-reinforced inner cores. The current dual drug-loaded alginate beads may be used to deliver the drugs in a time dependent manner.