• Current Optics and Photonics
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• 제1권4호
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• pp.402-411
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• 2017

Combined LIBS-Raman spectroscopy has been widely studied, due to its complementary capabilities as an elemental analyzer that can acquire signals of atoms, ions, and molecules. In this study, the classification of polymorphs was performed by laser-induced breakdown spectroscopy (LIBS) to overcome the limitation in molecular analysis; the results were verified by Raman spectroscopy. LIBS signals of the $CaCO_3$ polymorphs calcite and aragonite, and $CaSO_4{\cdot}2H_2O$ (gypsum) and $CaSO_4$ (anhydrite), were acquired using a Nd:YAG laser (532 nm, 6 ns). While the molecular study was performed using Raman spectroscopy, LIBS could also provide sufficient key data for classifying samples containing different molecular densities and structures, using the peculiar signal ratio of $5s{\rightarrow}4p$ for the orbital transition of two polymorphs that contain Ca. The basic principle was analyzed by electronic motion in plasma and electronic transition in atoms or ions. The key factors for the classification of polymorphs were the different electron quantities in the unit-cell volume of each sample, and the selection rule in electric-dipole transitions. The present work has extended the capabilities of LIBS in molecular analysis, as well as in atomic and ionic analysis.

• 한국표면공학회지
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• 제54권5호
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• pp.238-247
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• 2021

PEO (plasma electrolytic oxidation) was applied to modify the surface of AZ31 magnesium alloy in this study. The mixed solution of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used as the electrolyte, and 0 - 0.05 g/L of Ca-GP (Glycerol Phosphate Calcium salt) was added in the electrolyte as an additive. PEO treatment was conducted at a current density of 30mA/cm² for 5 minutes using a DC power supply. The surface properties were identified by SEM, XRD and surface roughness analyses, and the corrosion resistance was evaluated by potentiodynamic polarization and immersion tests. In addition, the biocompatibility was evaluated by immersion test in SBF solution. As the concentration of Ca-GP was increased, the surface morphology was denser and more uniform, and the amount of Ca and the thickness of oxide layer increased. Only Mg peak was observed in XRD analysis due to very thin oxide layer. The corrosion resistance of PEO-treated samples increased with the concentration of Ca-GP in comparision with the untreated sample. In particular, the highest corrosion resistance was identified at the group of 0.04g Ca-GP through potentiodynamic polarization and immersion tests in saline solution (0.9 wt.%NaCl). During the immersion in saline solution, pH rapidly increased at the beginning of immersion period due to rapid corrosion, and then increase rate of pH decreased. However, the pH value in the SBF temporarily increased from 7.4 to 8.5 during the day, then decreased due to the inhibition of corrosion with HA(hydroxyapatite) formation.

• Progress in Superconductivity
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• 제6권1호
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• pp.52-55
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• 2004

The inductive coupling theory in serially stacked $Bi_2$$Sr_2$$CaCu_2$$O_{8+x}$ intrinsic Josephson junctions predicts that the lattice structure of the Josephson vortices along the c axis gradually changes from the triangular to the rectangular lattice with increasing the vortex velocity. This lattice transition appears as voltage jumps or sub-branch splitting in the Josephson vortex-flow region of current-voltage characteristics (IVC). We report the IVC in external magnetic fields from 2 to 4 T. The stack, with the lateral size of 1.4${\times}$15 $u\m^2$, was fabricated by using the double-side cleaving technique. The sub-branches in the Josephson vortex-flow region, corresponding to a plasma propagation mode in serially coupled intrinsic Josephson junctions, were also observed in the range of 2∼4T. Switching from one branch to another in Josephson vortex-flow region suggests the structural transition of the moving Josephson vortex lattice.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.260-260
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• 1999

We compared c-axis tunneling characteristics of small stacked intrinsic Josephson junctions prepared on the surface of pristine, I-, and HgI$_2$-intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ (Bi2212) single crystals. The R(T) curves are almost metallic in I-Bi2212 specimens, but semiconducting in HgI$_2$-Bi2212 ones.· The transition temperatures were 82.0 K, 73.0 K, and 76.8 K for pristine Bi2212, I-Bi2212, and HgI2-Bi2212 specimens, respectively, consistent with p-T$_c$ phase diagram. Current-voltage (IV) characteristics of both kinds of specimens show multiple quasiparticle branches with well developed gap features, indicating Josephson coupling is established between neighboring CuO$_2$ planes. The critical current I$_c$ of I-Bi2212 is almost the same as of that of pristine crystals, but I$_c$ is much reduced in Hgl$_2$-Bi2212. In spite of expanded interlayer distances, the interlayer coupling is not significantly affected in I-Bi2212due to holes generated by iodine atoms. The coupling in HgI$_2$-Bi2212 is, however, weakened due to inertness of HgI$_2$ molecules and the expansion of interlayer distance. Relation between the superconducting transition temperature T$_c$ and the critical current I$_c$ seems to contradict Anderson's interlayer-pair-tunneling theory but agree with a modified version of it.

• 한국입자에어로졸학회지
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• 제7권3호
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• pp.87-97
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• 2011

In this study, we organized the test results obtained from the performance tests for the CA certificated air cleaners which had been commercially available in Korea since 2003, and analyzed the correlation among the test parameters such as flow rate, particle collection efficiency, clean air delivery rate (CADR), ozone emission, odor removal efficiency and noise level etc. The noise level of 267 air cleaners were increased as concentrated at the 45, 50, 55 dB, which are the required noise level for CA certification according to flow rate, and ozone emissions from the CA air cleaners were significantly lower than the requirement limit, 50 ppb for 24 hour operation. The average particle collection efficiency and odor removal efficiency were 89.3 and 80.8%, approximately 20% higher than the requirement of CA certification, regardless of flow rates. The particle removal performance of an air cleaner was clearly discriminated by its CADR, and the CADR was obtained with a simple calculation: 0.79 x flow rate. The low differentiation of gas removal performance of air cleaners by the current CA gas test method was improved by 3.2, 751.3, 13.4 times for ammonia, acetic acid, respectively, by adopting the CADR concept and the real time measurement method, FTIR, for gas removal performance test.

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.40-43
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• 2003

The phase transformation, variation of secondary phase, and critical current density $(J_c) for (Bi,Pb)_2Sr_2Ca_2Cu_3O_10 (2223)$ tapes have been studied through the thermal slide heat treatment (TSHT) process. This process consists of a multiple variations of oxygen partial pressures and temperatures at the initial heat treatment During the initial heat treatment some secondary phase such as $(Ca,Sr)_2CuO_3(2/1 AEC), (Ca,Sr)_{14}Cu_{24}O_{41} (14/24 AEC), and (Bi,Pb)_2Sr_2CuO_y$(2201, amorphous phase) farm in Bi-2223 tapes, especially at the 2223 grain boundaries. These secondary phases are detrimental to the phase transformation and final properties. In order to control the secondary phase in Bi-2223 tapes the amount and size of secondary phases among the TSHT process were observed. The results indicate that the amount and particle size of AEC particles were smaller when the TSHT process was used than when the normal process at the initial heat treatment was used which results in the improved $J_c$ properties after the final process.

• 한국지하수토양환경학회지:지하수토양환경
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• 제16권1호
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• pp.82-90
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• 2011

Reactive reductants of cement/Fe(II) systems in dechlorinating chlorinated hydrocarbons have not been identified. The previous studies showed that a hematite/CaO/Fe(II) system had TCE degradation characteristics similar to those of cement/Fe(II) systems with regard to degradation kinetics and that lime (CaO) plays an important role in enhancing the reactivity for TCE dechlorination. The current study shows identified the formation of gypsum ($CaSO_4$) in the hematite/CaO/$FeSO_4$ system through the XRD analysis. The amounts of the gypsum increased with increment of the initial CaO dose. However, when CaO in the hematite/CaO/$FeSO_4$ system was replaced with gypsum, TCE degradation was not observed. Ca-removed Portland cement extracts (CPCX) in combination with $FeSO_4(CPCX/FeSO_4)$ showed no TCE degradation. On the other hands, the Portland cement extracts (PCX) in the presence of $FeSO_4(PCX/FeSO_4)$ and CPCX/CaO/$FeSO_4$ systems degraded 0.2 mM TCE within 5 days, indicating that CaO also played an important role dechlorination reactions in the systems. The pseudo-first-order rate constants (k) of the CPCX/CaO/$FeSO_4$ systems were 0.20, 0.24, and 0.72 $day^{-1}$, when the CaO dosages were 25, 50 and 75 g/L, respectively. The XRD analyses showed identified the common peaks having the d-values of 3.02, 2.27, and 1.87 in the reaction systems that showed TCE degradation. However, it was not possible to clearly identify the crystalline minerals having the three peaks from the references in JCPDS cards. This study reveals that the reactive agents in the cement/Fe(II) and the hematite/Fe(II) systems are likely to be those containing CaO and Fe(II).

• 생명과학회지
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• 제30권8호
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• pp.688-694
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• 2020

제주에서 자생하는 식물인 다정큼나무는 장미과에 속하는 관목으로 다정큼나무 잎 에탄올 추출물에서 높은 총페놀 함량이 확인되었다. 이를 바탕으로 본 연구에서는 다정큼나무 추출물에서 헥산, 디클로로메탄, 에틸 아세테이트, 부탄올, 물을 이용하여 분획물을 제조하고, 5가지 분획물의 항산화효과를 확인해보고자 하였다. 특히, 외부환경요인 및 자외선 등을 통해 산화적 스트레스가 많이 발생하는 피부각질세포에서의 항산화효과 및 세포보호효과를 확인하고자 사람 각질세포인 HaCaT세포를 이용하였다. 항산화능은 총 플라보노이드 함량 및 2-azino-bis 3-ethylbenzthiazoline-6-sulfonic acid (ABTS) 라디칼 소거능을 통해 관찰하였고 HaCaT 세포보호효과는 세포에 과산화수소(H₂O₂)와 추출물을 처리한 다음 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay를 통해 확인하였다. 다정큼나무 잎 추출물 및 5가지 분획물 중 에틸 아세테이트 분획물에서 가장 높은 총플라보노이드 함량 및 가장 낮은 라디칼 잔여량이 관찰되었고 H₂O₂에 의한 HaCaT 세포의 산화적 스트레스를 가장 많이 차단하여 높은 생존율을 보였다. 이를 토대로 다정큼나무 잎 에틸 아세테이트 분획물은 높은 항산화 효과를 가지고 있어 사람 각질세포의 산화적 스트레스로부터 세포를 보호하는 효과를 가지고 있음이 확인되었다. 따라서, 본 연구 결과는 다정큼나무 잎 에틸 아세테이트 분획물을 이용하여 산화적 스트레스로 인한 피부 손상을 억제하는 기능성 물질 소재로 활용할 수 있을 것으로 제시한다.

• Geosciences Journal
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• 제22권6호
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• pp.989-1000
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• 2018

The provenance of the Central Yellow Sea Mud (CYSM) in the Yellow Sea has been attracted a great deal of attention over the last three decades, but a consensus is not yet reached. In this study, 101 surface sediment samples collected from the CYSM were investigated to determine provenance and transport mechanisms in the area using the clay minerals and major element components. The Huanghe sediments are characterized by higher smectite, but the Changjiang sediments are more abundant illite contents. Western Korean rivers contain more kaolinite and chlorite than do Chinese rivers. The Chinese rivers have higher $Fe_2O_3$, MgO, and CaO than the Korean rivers at the same $Al_2O_3$ concentration. Therefore, the clay minerals and major element concentrations can be useful indicator for the source. Based on our results, we suggest that the surface sediments in CYSM were composed mainly of Changjiang sediments, mixed a partly with sediments from the Huanghe and the western Korean rivers. Although the northwestern part of CYSM is proximate to the Huanghe, the contents of smectite and CaO were extremely low. It could be evidence that the Huanghe materials do not enter directly into the CYSM due to the Shandong Peninsula Front. Considering the oceanic circulation in the Yellow Sea, the Changjiang sediments could be transported eastward with the Changjiang Diluted Water and then mixed in CYSM via the Yellow Sea Warm Current (YSWC). Huanghe sediments could be provided by coastal currents (Shandong Coastal Current and Yellow Sea Coastal Current) and the YSWC. In addition, sediments from western Korean rivers might be supplied into the CYSM deposit via the Korean Coastal Current, Transversal Current, and YSWC.

• 자원리싸이클링
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• 제10권3호
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• pp.37-42
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• 2001

21세기 철강산업에 요구되는 경제성, 환경친화성, 고효율성을 동시에 만족하는 슬래그 정련조업 조건을 슬래그 엔지니어링 개념에 입각하여 평가하였다. 제선 공정의 경우, 기존의 슬래그 조성에서 염기도를 증가시킴으로써 우수한 로내 통액성 및 향상된 용선품질 확보가 가능할 것으로 평가되었으며, COREX 조업에서는 ($SiO_2$+ $A1_2$$O_3$) 농도를 소량 감소시킴으로써 보다 우수한 유동성 및 정련능 확보가 가능한 것으로 예측되었다. 한편, Stainless Steel-AOD공정의 경우, 소량의 CaO농도 증가를 통하여 현재보다 양호한 정련능 확보가 가능함을 알 수 있었으며, 슬래그 중 (CaO+$A1_2$$O_3$)농도 증가를 통해 $CaF_2$의 사용량 감소를 이룩할 수 있을 것으로 예측되었다.