• Title/Summary/Keyword: 분광 특성

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Variation of Water Content and Thermal Behavior of Talc Upon Grinding: Effect of Repeated Slip on Fault Weakening (활석 분쇄에 따른 함수율 및 열적거동 변화: 단층의 반복되는 미끌림이 단층 약화에 미치는 영향)

  • Kim, Min Sik;Kim, Jin Woo;Kang, Chang Du;So, Byung Dal;Kim, Hyun Na
    • Journal of the Mineralogical Society of Korea
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    • v.32 no.3
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    • pp.201-211
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    • 2019
  • The particle size and crystallinity of fault gouge generally decreases with slip. Phyllosilicates including talc are known to be present in fault gouge and play an important role in fault weakening. In particular, the coefficient of friction varies depending on the presence of a water molecule on the surface of mineral. The purpose of this study is to investigate the effect of talc on fault weakening by changing the water content and dehydration behavior of talc before and after grinding, which systematically varied particle size and crystallinity using high energy ball mill. Infrared spectroscopy and thermal analysis show that the as-received talc is hydrophobic before grinding and the water molecule is rarely present. After grinding up to 720 minutes, the particle size decreased to around 100 ~300 nm, and in talc, where amorphization proceeded, the water content increased by about 8 wt.% and water molecule would be attached on the surface of talc. As a result, the amount of vaporized water by heating increased after grinding. The dihydroxylation temperature also decreased by ${\sim}750^{\circ}C$ after 720 minutes of grinding at ${\sim}950^{\circ}C$ before grinding due to the decrease of particle size and crystallinity. These results indicate that the hydrophobicity of talc is changed to hydrophilic by grinding, and water molecules attached on the surface, which is thought to lower the coefficient of friction of phyllosilicates. The repeated slip throughout the seismic cycle would consistently lower the coefficient of friction of talc present in fault gouge, which could provide the clue to the weakening of matured fault.

Crystallograpbic and Magnetic Properties of $Ni_{0.65}Zn_{0.35}Cu_{0.3}Fe_{1.7}O_4$ ($Ni_{0.65}Zn_{0.35}Cu_{0.3}Fe_{1.7}O_4$의 결정학적 및 자기적 특성 연구)

  • 김우철;김삼진;김철성;이승화
    • Journal of the Korean Magnetics Society
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    • v.9 no.3
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    • pp.136-142
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    • 1999
  • $Ni_{0.65}Zn_{0.35}Cu_{0.3}Fe_{1.7}O_4$ has been studied with x-ray diffraction, Mossbauer spectroscopy, and vibrating sample magnetometer. The crystal structure is found to be a cubic spinel with the lattice constant $a_0=8.403{\AA}$. Mossbauer spectra of have been taken at various temperatures ranging from 12 K to 665 K. as the temperature increases toward $T_N$ a systematic line broadening effect in the Mossbauer spectrum is observed and interpreted to originate from different temperature dependencies of the magenetic hyperfine fields at various iron sites. Also, by using binomial distribution equation we obtained the hyperfine fields of tetrahedral[A] and octahedral sites[B], $H_{hf}(A)=470\;kOe,\; H_{hf}(B0)=495 \;kOe,\; H_{hf}(B1)=485\;kOe, \;H_{hf}(B2)=453\;kOe,\; H_{hf}(B3)=424\;kOe,\; H_{hf}(B4)=390\;kOe,\; H_{hf}(Bavr)=451\;kOe$ respectively at room temperature. The isomer shift indicates that the iron ions are ferric at tetrahedral[A] and octahedral sites[B], respectively. The Neel temperature is determined to be $T_N=665\;K$. The results of the VSM data gave the magnetic moment and coercivity values of $M_S=66\; emu/g\;and\;H_C=36\;Oe$.

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Analysis of the Cloud Removal Effect of Sentinel-2A/B NDVI Monthly Composite Images for Rice Paddy and High-altitude Cabbage Fields (논과 고랭지 배추밭 대상 Sentinel-2A/B 정규식생지수 월 합성영상의 구름 제거 효과 분석)

  • Eun, Jeong;Kim, Sun-Hwa;Kim, Taeho
    • Korean Journal of Remote Sensing
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    • v.37 no.6_1
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    • pp.1545-1557
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    • 2021
  • Crops show sensitive spectral characteristics according to their species and growth conditions and although frequent observation is required especially in summer, it is difficult to utilize optical satellite images due to the rainy season. To solve this problem, Constrained Cloud-Maximum Normalized difference vegetation index Composite (CC-MNC) algorithm was developed to generate periodic composite images with minimal cloud effect. In thisstudy, using this method, monthly Sentinel-2A/B Normalized Difference Vegetation Index (NDVI) composite images were produced for paddies and high-latitude cabbage fields from 2019 to 2021. In August 2020, which received 200mm more precipitation than other periods, the effect of clouds, was also significant in MODIS NDVI 16-day composite product. Except for this period, the CC-MNC method was able to reduce the cloud ratio of 45.4% of the original daily image to 14.9%. In the case of rice paddy, there was no significant difference between Sentinel-2A/B and MODIS NDVI values. In addition, it was possible to monitor the rice growth cycle well even with a revisit cycle 5 days. In the case of high-latitude cabbage fields, Sentinel-2A/B showed the short growth cycle of cabbage well, but MODIS showed limitations in spatial resolution. In addition, the CC-MNC method showed that cloud pixels were used for compositing at the harvest time, suggesting that the View Zenith Angle (VZA) threshold needsto be adjusted according to the domestic region.

Estimation of Leaf Area Index Based on Machine Learning/PROSAIL Using Optical Satellite Imagery (광학위성영상을 이용한 기계학습/PROSAIL 모델 기반 엽면적지수 추정)

  • Lee, Jaese;Kang, Yoojin;Son, Bokyung;Im, Jungho;Jang, Keunchang
    • Korean Journal of Remote Sensing
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    • v.37 no.6_1
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    • pp.1719-1729
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    • 2021
  • Leaf area index (LAI) provides valuable information necessary for sustainable and effective management of forests. Although global high resolution LAI data are provided by European Space Agency using Sentinel-2 satellite images, they have not considered forest characteristics in model development and have not been evaluated for various forest ecosystems in South Korea. In this study, we proposed a LAI estimation model combining machine learning and the PROSAIL radiative transfer model using Sentinel-2 satellite data over a local forest area in South Korea. LAI-2200C was used to measure in situ LAI data. The proposed LAI estimation model was compared to the existing Sentinel-2 LAI product. The results showed that the proposed model outperformed the existing Sentinel-2 LAI product, yielding a difference of bias ~ 0.97 and a difference of root-mean-square-error ~ 0.81 on average, respectively, which improved the underestimation of the existing product. The proposed LAI estimation model provided promising results, implying its use for effective LAI estimation over forests in South Korea.

A Scientific Analysis of Gold Threads Used in Donggungbi-Wonsam(Ceremonial Robe Worn by a Crown Princess, National Folklore Cultural Heritage No.48) (동궁비 원삼에 사용된 금사의 과학적 분석)

  • Lee, Jang-Jon;An, Boyeon;Han, Kiok;Lee, Ryangmi;Yoo, Ji Hyun;Yu, Ji A
    • Journal of Conservation Science
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    • v.37 no.5
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    • pp.525-535
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    • 2021
  • This study identified material properties through scientific analysis on Jikgeumdan(satin with gold threads) from Donggungbi-Wonsam and the gold threads used in the embroidery. The Donggungbi-Wonsam's base of gold threads were estimated to have used mulberry fiber's Korean paper(Hanji) because non-wood-based fibers were observed. The X-ray spectrometer showed that the Tongsuseulan of Donggungbi-Wonsam was a flat gold thread of pure gold and Jikgeumdan of flat silver thread of its Saekdong and Hansam. High sulfur levels were detected in the flat silver thread, which appeared to have formed silver sulfide by either manufacturing process using sulfur or conservation environment. he dragon insignia's embroidery is also described as two types twisted gold threads; pure gold and alloying-gold and silver. while dragon insignia's border line is decorated with a twisted gold thread of pure gold. In particular, it was investigated that adhesives such as an animal glue, a protein-based compound by gas chromatography mass spectrometry. Additionally, XRF and Raman spectroscopy analysis on the mixture substances between the metal surface and the base paper of gold threads identified talc and quartz in the gold threads and Seokganju(hematite) in the flat silver threads.

Recent Progress in Membrane based Colorimetric Sensor for Metal Ion Detection (색 변화를 활용한 중금속 이온 검출에 특화된 멤브레인 기반 센서의 최근 연구 개발 동향)

  • Bhang, Saeyun;Patel, Rajkumar
    • Membrane Journal
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    • v.31 no.2
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    • pp.87-100
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    • 2021
  • With a striking increase in the level of contamination and subsequent degradations in the environment, detection and monitoring of contaminants in various sites has become a crucial mission in current society. In this review, we have summarized the current research areas in membrane-based colorimetric sensors for trace detection of various molecules. The researches covered in this summary utilize membranes composed of cellulose fibers as sensing platforms and metal nanoparticles or fluorophores as optical reagents. Displaying decent or excellent sensitivity, most of the developed sensors achieve a significant selectivity in the presence of interfering ions. The physical and chemical properties of cellulose membrane platforms can be customized by changing the synthesis method or type of optical reagent used, allowing a wide range of applications possible. Membrane-based sensors are also portable and have great mechanical properties, which enable on-site detection of contaminants. With such superior qualities, membrane-based sensors examined in the researches were used for versatile purposes including quantification of heavy metals in drinking water, trace detection of toxic antibiotics and heavy metals in environmental water samples. Some of the sensors exhibited additional features like antimicrobial ability and recyclability. Lastly, while most of the sensors aimed for a detection enabled by naked eyes through rapid colour change, many of them investigated further detection methods like fluorescence, UV-vis spectroscopy, and RGB colour intensity.

Comparison of Pixel-based Change Detection Methods for Detecting Changes on Small Objects (소형객체 변화탐지를 위한 화소기반 변화탐지기법의 성능 비교분석)

  • Seo, Junghoon;Park, Wonkyu;Kim, Taejung
    • Korean Journal of Remote Sensing
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    • v.37 no.2
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    • pp.177-198
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    • 2021
  • Existing change detection researches have been focused on changes of land use and land cover (LULC), damaged areas, or large vegetated and water regions. On the other hands, increased temporal and spatial resolution of satellite images are strongly suggesting the feasibility of change detection of small objects such as vehicles and ships. In order to check the feasibility, this paper analyzes the performance of existing pixel-based change detection methods over small objects. We applied pixel differencing, PCA (principal component analysis) analysis, MAD (Multivariate Alteration Detection), and IR-MAD (Iteratively Reweighted-MAD) to Kompsat-3A and Google Map images taken within 10 days. We extracted ground references for changed and non-changed small objects from the images and used them for performance analysis of change detection results. Our analysis showed that MAD and IR-MAD, that are known to perform best over LULC and large areal changes, offered best performance over small object changes among the methods tested. It also showed that the spectral band with high reflectivity of the object of interest needs to be included for change analysis.

Automatic selection method of ROI(region of interest) using land cover spatial data (토지피복 공간정보를 활용한 자동 훈련지역 선택 기법)

  • Cho, Ki-Hwan;Jeong, Jong-Chul
    • Journal of Cadastre & Land InformatiX
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    • v.48 no.2
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    • pp.171-183
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    • 2018
  • Despite the rapid expansion of satellite images supply, the application of imagery is often restricted due to unautomated image processing. This paper presents the automated process for the selection of training areas which are essential to conducting supervised image classification. The training areas were selected based on the prior and cover information. After the selection, the training data were used to classify land cover in an urban area with the latest image and the classification accuracy was valuated. The automatic selection of training area was processed with following steps, 1) to redraw inner areas of prior land cover polygon with negative buffer (-15m) 2) to select the polygons with proper size of area ($2,000{\sim}200,000m^2$) 3) to calculate the mean and standard deviation of reflectance and NDVI of the polygons 4) to select the polygons having characteristic mean value of each land cover type with minimum standard deviation. The supervised image classification was conducted using the automatically selected training data with Sentinel-2 images in 2017. The accuracy of land cover classification was 86.9% ($\hat{K}=0.81$). The result shows that the process of automatic selection is effective in image processing and able to contribute to solving the bottleneck in the application of imagery.

Recovery of Nickel from Waste Iron-Nickel Alloy Etchant and Fabrication of Nickel Powder (에칭 폐액으로부터 용매추출과 가수분해를 이용한 니켈분말제조에 관한 연구)

  • Lee, Seokhwan;Chae, Byungman;Lee, Sangwoo;Lee, Seunghwan
    • Clean Technology
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    • v.25 no.1
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    • pp.14-18
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    • 2019
  • In general after the etching process, waste etching solution contains metals. (ex. Nickel (Ni), Chromium (Cr), Zinc (Zn), etc.) In this work, we proposed a recycling process for waste etching solution and refining from waste liquid contained nickel to make nickel metal nano powder. At first, the neutralization agent was experimentally selected through the hydrolysis of impurities such as iron by adjusting the pH. We selected sodium hydroxide solution as a neutralizing agent, and removed impurities such as iron by pH = 4. And then, metal ions (ex. Manganese (Mn) and Zinc (Zn), etc.) remain as impurities were refined by D2EHPA (Di-(2-ethylhexyl) phosphoric acid). The nickel powders were synthesized by liquid phase reduction method with hydrazine ($N_2H_4$) and sodium hydroxide (NaOH). The resulting nickel chloride solution and nickel metal powder has high purity ( > 99%). The purity of nickel chloride solution and nickel nano powders were measured by EDTA (ethylenediaminetetraacetic) titration method with ICP-OES (inductively coupled plasma optical emission spectrometer). FE-SEM (field emission scanning electron microscopy) was used to investigate the morphology, particle size and crystal structure of the nickel metal nano powder. The structural properties of the nickel nano powder were characterized by XRD (X-ray diffraction) and TEM (transmission electron microscopy).

Highly-permeable Mixed Matrix Membranes Based on SBS-g-POEM Copolymer, ZIF-8 and Ionic Liquid (SBS-g-POEM 공중합체, ZIF-8, 이온성 액체에 기반한 고투과성 혼합 매질 분리막)

  • Kang, Dong A;Kim, Kihoon;Kim, Jong Hak
    • Membrane Journal
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    • v.29 no.1
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    • pp.44-50
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    • 2019
  • In this paper, we developed mixed matrix membranes (MMMs) consisting of SBS-g-POEM block-graft copolymer, ionic liquid (EMIMTFSI) and ZIF-8 nanoparticles to separate a $CO_2/N_2$ gas pair. The SBS-g-POEM is a rubbery block-graft copolymer synthesized through low-cost free-radical polymerization. The EMIMTFSI was dissolved into the SBS-g-POEM matrix and solution synthesized ZIF-8 nanoparticles were also dispersed into the copolymer matrix. The physico-chemical properties of manufactured membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD), which showed that the components were compatible with each other. The gas separation performance was confirmed by time-lag measurements showing $CO_2$ permeability of 537.0 barrer and $CO_2/N_2$ selectivity of 15.2. The result represents the EMIMTFSI and ZIF-8 nanoparticles improves the gas permeability more than two-times, without significantly sacrificing the $CO_2/N_2$ selectivity.