• 자원환경지질
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• 제55권2호
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• pp.127-135
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• 2022

Excessive presence of As level in groundwater is a major health problem worldwide. In the Red River Delta in Vietnam, several million residents possess a high risk of chronic As poisoning. The As releases into groundwater caused by natural process through microbially-driven reductive dissolution of Fe (III) oxides. It has been extracted by Red River residents using private tube wells for drinking and daily purposes because of their unawareness of the contamination. This long-term consumption of As-contaminated groundwater could lead to various health problems. Therefore, a predictive model would be useful to expose contamination risks of the wells in the Red River Delta Vietnam area. This study used four machine learning algorithms to predict the As probability of study sites in Red River Delta, Vietnam. The GBM was the best performing model with the accuracy, precision, sensitivity, and specificity of 98.7%, 100%, 95.2%, and 100%, respectively. In addition, it resulted the highest AUC of 92% and 96% for the PRC and ROC curves, with Eh and Fe as the most important variables. The partial dependence plot of As concentration on the model parameters showed that the probability of high level of As is related to the low number of wells' depth, Eh, and SO₄, along with high PO₄^3- and NH₄⁺. This condition triggers the reductive dissolution of iron phases, thus releasing As into groundwater.

• 광물과 암석
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• 제35권2호
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• pp.111-123
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• 2022

본 연구는 자연계에서 가장 흔하게 관찰되는 두 그린 러스트(green rust) 광물인 carbonate green rust (CGR)과 sulfate green rust (SGR)을 공침법(co-precipitation)을 통해 각각 합성하고, 이들의 형성 메커니즘 및 이화학적 특성들을 체계적으로 규명하였다. X-선 회절(XRD) 분석 및 리트벨트 정련 수행 결과, 본 합성 조건에서 이차광물상 없이 이중층수산화물로서 CGR과 SGR이 합성됨을 확인하였다. 또한, 각각의 구조 파라미터는 CGR의 경우 a(=b)축 = 3.17 Å, c축 = 22.52 Å이고, SGR의 경우 a(=b)축 = 5.50 Å, c축 = 10.97 Å이며, 이들의 미결정 크기는 각각 (003)면 기준 57.8 nm와 (001)면 기준 40.1 nm로 밝혀졌다. 주사전자현미경/에너지 분산형 분광분석(SEM/EDS) 결과, CGR과 SGR은 모두 육각 판상의 전형적인 이중층수산화물 결정 형상을 보이지만 탄소(C)와 황(S)의 함량은 서로 다르게 나타났다. 퓨리에 변환 적외선(FT-IR) 분광 분석결과, 탄산염(CO₃^2-)와 황산염(SO₄^2-) 이온들이 각각 CGR과 SGR의 층간 음이온으로 밝혀졌고, 이는 XRD를 활용한 광물상 동정 결과와 잘 일치한다. 철 용액으로의 수산화이온(OH^-) 주입 시간에 따른 혼합 용액의 pH와 Eh, 그리고 잔류 철 농도의 비율(Fe(II):Fe(III)) 측정 결과, 시간에 따른 차이는 있지만 두 green rusts 모두 1단계 전구체 형성, 2단계 중간 생성물로의 상변환, 그리고 3단계 green rust로의 상변환과 에이징에 의한 결정성장으로 이어지는 결정 형성 메커니즘을 보이는 것으로 판단된다. 본 연구는 공침법을 통해 CGR과 SGR을 안정적으로 합성하고 이들의 형성 메커니즘과 이화학적 특성을 규명함으로써, green rust를 활용한 응용 연구 및 산업 활용에 원천 기초자료를 제공할 것으로 기대된다.

• 자원환경지질
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• 제26권3호
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• pp.311-325
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• 1993

The Ohto and Tohyun copper mine which are located 4 km southeast of Euiseong, Gyeongsangbukdo, Republic of Korea show various common geologic and mineralogic features. Both copper deposits are of hydrothermal-vein types, and associated with fracture system developed during formation of the Geumseong-san caldera in late Cretaceous age. According to structures and mineral assemblages, the mineralization processes have progressed in four stages: three hypogene mineralization stages and one supergene stage. Three hypogene stages are 1) stage I forming $N5{\sim}20^{\circ}E$ veins in the Ohto mine, 2) stage II building $N5^{\circ}W{\sim}N5^{\circ}E$ veins in the Tohyun mine, and 3) stage ill bringing $N80^{\circ}E$ veins which crosscut veins of the stage II. The vein ores consist mainly of pyrite, arsenopyrite, galena and chalcopyrite, minor or trace amounts of magnetite, hematite, pyrrhotite, stannite, bournonite, boulangerite, stibnite, galenobismutite, native bismuth, marcasite, geothite and malachite. The main gangue minerals are quartz and calcite. Wallrock is altered by sericitization, chloritization, pyritization, carbonitization and argillization. Arsenic and copper contents in arsenopyrite increase from stage I to stage III (from 31.28 to 33043 atom.% As) and (from 0.04 to 0040 atom.% Co). Going from stage I to stage III Fe and Mn contents in sphalerite decreases from 12.56 to 0.44 wt.% and from 0.24 to 0.01 wt.%, respectively. The compositional data of arsenopyrite in the early stage I indicate a temperature of $420{\sim}365^{\circ}C$ and sulfur fugacity of $10^{-6.5}{\sim}10^{-8.3}$ atm. Chalcopyrite and pyrrhotite assemblage suggest that Middle stage I was deposited at below $334^{\circ}C$. The compositional data of arsenopyrite in early stage II suggest a temperature range of $425{\sim}390^{\circ}C$ and sulfur fugacity codition of $10^{-6.4}{\sim}10^{-7.3}$ atm. Based on fluid inclusion the Middle stage II was regarded as to be deposited at $420{\sim}337^{\circ}C$ (Chi et al., 1989). Referring composition of sphalerite and stannite middle-late stage II seem to be deposited around $246^{\circ}C$ and $10^{-16.5}$ atm. sulfur fugacity. The ${\delta}^{34}S$ values of sulfide minerals in the Stage I, II, III range from 4.9 to 7.6%0 and indicate igneous ore fluid origin. Based on differences in mineral assemblages, chemical composition and chemical environments of Ohto and Tohyun mine its mineralization are considered to be formed at diffent mineralization ages and by different ore fluids.

• Restorative Dentistry and Endodontics
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• 제30권3호
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• pp.204-214
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• 2005

본 연구는 상아질에 2단계와 단일 단계 자가 산부식 접착제를 적용하여 복합레진을 접착한 후 저장기간에 따른 미세 인장 결합강도와 접착계면의 변화를 상호 비교하기 위하여 시행하였다. 발거된 상 하악 대구치 48개의 교합면측 상아질을 노출시켜 12개씩 4개의 군으로 분류하였다 사용된 접착제의 종류에 따라 SE Bond 군, AdheSE 군, Adper 군, Xeno III 군으로 분류하여 접착제를 적용한 후, 동일 회사의 복합레진 을 4 mm두께로 접착시켰다. 각 군당 4개의 치아를 선택하여 증류수가 담겨진 용기에 집어넣고 37$^{\circ}C$의 항온기에 각각 1일 15일, 30일 동안 저장한 후 시편을 제작하여 각각 미세인장 결합강도의 측정과 주사전자 현미경 관찰 하여 다음과 같은 결과를 나타내었다. 2단계 자가 산부식 접착제는 1일에서 30간의 저장기간 동안 결합강도가 점차적으로 감소하였지만 통계학적으로 유의한 차이를 나타내지 않았고, 상아질과 접착제 간에 긴밀한 접착관계를 보였다. 반면에 단일 단계자가 산부식 접착제는 1일의 저장기간에 비해 30일의 저장기간에서 통계학적인 결합강도의 감소를 나타내었으며, 상아질과 접착제 간에 넓은 간극이 관찰되었다. 따라서 본 연구에서 나타난 두 종류의 30일 동안의 접착내구성은 2단계 자가 산부식 접착제가 단일 단계 자가 산부식 접착제보다 우수한 것으로 나타났다.

• International Journal of Industrial Entomology and Biomaterials
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• 제22권2호
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• pp.83-93
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• 2011

Biochemical and enzymatic characterization for extracellular protease isolated from Cordyceps militaris cultivated on rice bran medium was investigated. C militaris produced proteolytic enzymes from 10 days after inoculation, maximum enzyme production was found at 25 days. The optimum temperature and pH of proteases production was at $25^{\circ}C$ and pH 7.0, respectively. The protease activity was observed in the four peaks (Pro-I, Pro-II, Pro-III, and Pro-IV) separated through Sephadex G-100 column chromatography. The separated protease was optimally active at $25^{\circ}C$. Optimum pH of the protease was between 7 and 8. Enzyme was also stable over at $30-80^{\circ}C$. The enzyme was highly stable in a pH range of 4-9. Protease activity was found to be slightly decreased by the addition of $Mg^{2+}$, $Mn^{2+}$, $Zn^{2+}$, $Fe^{2+}$ and $Cu^{2+}$, whereas inhibited by the addition of $Ca^{2+}$ and $Co^{2+}$ Protease activity was inhibited by protease inhibitor PMSF. On the other hand, the partially purified protease was investigated on proteolytic protease activity by zymogram gel electrophoresis using three substances (casein, gelatin and fibrin). Four active bands (F-I, FII, F-III, and F-IV) of fibrin degradation were revealed on fibrin zymogram gels. Both of F-II and FIII showed caseinolytic, fibrinolytic and gelatinolytic activities in three gels. Thermostability, pH stability, and pH-thermostability of the enzyme determined the residual fibrinolytic activity also displayed on fibrin zymogram gel. The only one enzyme (F-II) displayed over a broad range of temperature at $30-90^{\circ}C$. The FII displayed fibrinolytic activity in the pH range 3-5, but was inactivated in the range of pH 6-11. The F-I and F-III showed enzyme activity in the pH range of 6-11. In the pH-thermostability, the F-II only kept fibrinolytic activity after heating at $100^{\circ}C$ for 10, 20 and 30 min at pH 3 and pH 7, respectively. On the other hand, the F-II was retained activity until heating for 10 min under pH 11 condition. By using fibrin zymogram gel electrophoresis, extracellular fibrinolytic enzyme F-II from C. militaris showed unusual thermostable under acid and neutral conditions.

• 대한화학회지
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• 제56권1호
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• pp.34-46
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• 2012

Dopants and defects can be introduced as well as the intercalation of metals into single wall carbon nanotubes (SWCNTs) to modify their electronic and magnetic properties, thus significantly widening their application areas. Through spinpolarized density functional theory (DFT) calculations, we have systemically studied the following: (i) (10,0) and (5,5) SWCNT doped with nitrogen ($CN_xNT$), (ii) (10,0) and (5,5) SWCNT with pyridine-like defects (3NV-$CN_xNT$), and (iii) chemical functionalization of (10,0) and (5,5) 3NV-$CN_xNT$ with 12 different transition metals (TMs) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, and Pt). Attention was done in searching for the most stable configurations, deformation, calculating the formation energies, and exploring the effects of the doping concentration of nitrogen and pyridine-like nitrogenated defects on the electronic properties of the nanotubes. Also, calculating the corresponding binding energies and effects of chemical functionalization of TMs on the electronic and magnetic properties of the nanotubes has been made. We found out that the electronic properties of SWCNT can be effectively modified in various ways, which are strongly dependent not only on the concentration of the adsorbed nitrogen but also to the configuration of the adsorbed nitrogen impurities, the pyridine-like nitrogenated defects, and the TMs absorbed; due to the strong interaction between the d orbitals of TMs and the p orbitals of N atoms, the binding strengths of TMs with the two 3NV-$CN_xNT$ are significantly enhanced when compared to the pure SWCNTs.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.535-546
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• 2018

The objective of this study is to understand the behaviour of hollow core slabs strengthened with FRP and hybrid techniques through numerical and analytical studies. Different strengthening techniques considered in this study are (i) External Bonding (EB) of Carbon Fiber Reinforced Polymer (CFRP) laminates, (ii) Near Surface Mounting (NSM) of CFRP laminates, (iii) Bonded Overlay (BO) using concrete layer, and (iv) hybrid strengthening which is a combination of bonded overlay and NSM or EB. In the numerical studies, three-dimensional Finite Element (FE) models of hollow core slabs were developed considering material and geometrical nonlinearities, and a phased nonlinear analysis was carried out. The analytical calculations were carried out using Response-2000 program which is based on Modified Compression Field Theory (MCFT). Both the numerical and analytical models predicted the behaviour in agreement with experimental results. Parametric studies indicated that increase in the bonded overlay thickness increases the peak load capacity without reducing the displacement ductility. The increase in FRP strengthening ratio increased the capacity but reduced the displacement ductility. The hybrid strengthening technique was found to increase the capacity of the hollow core slabs by more than 100% without compromise in ductility when compared to their individual strengthening schemes.

• 말소리와 음성과학
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• 제1권2호
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• pp.119-128
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• 2009

Many researchers have argued about the relationship between information structure and intonation. Their results can be summarized in three main points: the intonation of topic and focus in English information structures is implemented as i) a pitch accent, ii) a tune (a pitch accent + (an) edge tone(s)), or iii) a boundary tone. The purpose of this paper is to study various intonational patterns of topic and focus in English information structures, using natural conversations. In this paper, the types of topics and foci are divided, based on contrastiveness. The topics are classified as five non-contrastive and four contrastive topics. The foci are classified as neutral focus, informational focus, and contrastive focus. The results show that the intonation of the topic in English information structures is mainly implemented as a pitch accent, except for the type of the pronoun topic (Lp) which is not implemented as a pitch accent or a tune. However, the intonation of the focus is implemented as a tune in the neutral focus (Fn) and as a pitch accent or a tune in the informational focus (Fi) and the contrastive focus (Fe). In our discussion and conclusion, we suggest that it is not always true that for the meaning of contrast, the topic or the focus is represented as a $L+H^{\ast}$ pitch accent, which has been the main contrastive intonation from earlier studies.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권4호
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• pp.179-184
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• 2003

The pulsed power system is widely used for many industries and environments. Generally, we call the "RUST", the reddish brown surface, that was made on iron surface or some other metals, when they are contacted by water and air the main substance of rust is oxide-ionization. In other words, the chemical symbol of rust on iron surface is iron oxide(III) hydrate Fe203.nH2O. In this study, we have designed and fabricated our system which has a compact pulse generator with switching MOSFET. Also we have studied the metal-oxide removing characteristics using in the atmospheric arc discharge. It has been investigated their removing characteristics by the change of charging voltage and pulse repetition rates. From this result, we can find out that the removal area Is increased from 3.80 to 8.04[$\textrm{cm}^2$], when pulse duration is increased from 100[pps] to 400[pps]. 400[pps].

• 천문학회보
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• 제38권2호
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• pp.54-54
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• 2013

We performed spectroscopic and photometric monitoring observations of a QSO, PG0934+013 for a reverberation-mapping analysis, using the 9-m Southern African Large Telescope (SALT) for spectroscopy and the 2-m Faulkes Telescope North and the South for photometry. The monitoring campaign was carried out for 5 month between December 2012 to April 2013, providing 20 spectroscopic epochs and ~40 photometric epochs. Based on the obtained spectra, which typically have a signal-to-noise ratio to 30-60, we performed multicomponent decomposition using various components, i.e., power-law continuum, FeII emission complex, and broad and narrow emission lines, to properly measure the Hbeta line flux. After a flux normalization using [O III] 5007 line luminosity, we obtained a rms spectrum from all epochs, which shows clear variability of Hbeta line. We find that Hbeta line flux decreases by ~20% during the monitoring period while the continuum flux obtained from the aperture photometry based on the imaging data, shows similar variability. The current Hbeta light curve shows monotonic decrease and a reliable cross correlation analysis between Hbeta and continuum light is difficult. Nevertheless, we obtained a preliminary lag measurements as ~24 light days.