• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2444-2451
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• 2024

This work demonstrates a new sol-gel approach for synthesizing PbO₂-doped zirconia using zircon mineral precursors. The streamlined methodology enables straightforward fabrication of the doped zirconia composites. Comprehensive materials characterization was performed using XRD, SEM, and TEM techniques to analyze the crystal structure, microstructure, and morphology. Quantitative analysis of the XRD data provided insights into the nanoscale crystallite sizes achieved, along with their relationship to lattice imperfections. Furthermore, the gamma-ray shielding capacity for the PbO₂-doped zirconia samples was estimated by the Monte Carlo simulation, which proves an increase in the gamma ray shielding properties by raising the Pb concentration. The linear attenuation coefficient increased between 0.467 and 0.499 cm^-1 (at 0.662 MeV) by increasing the Pb content between 11 and 21 wt%. By increasing the Pb content to 21 wt%, the synthesized composites' lead equivalent thickness reaches 2.49 cm. The radiation shielding properties for the synthesized composites revealed a remarkable performance against low and intermediate γ-ray photons, with radiation shielding capacity of 37.3 % and 21.4 % at 0.662 MeV and 2.506 MeV, respectively. As a result, the developed composites can be employed as an alternative shielding material in hospitals and radioactive zones.

• Journal of the Mineralogical Society of Korea
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• v.20 no.4
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• pp.351-356
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• 2007

The crystal structure of $Li(ND_4)SO_4$ was analyzed by X-ray and neutron diffraction methods. The crystal is a deuterated $Li(NH_4)SO_4$ and one of the ferroelectric materials with hydrogen atoms. The crystal is orthorhombic at room temperature, $P2_1nb$, with lattice parameters of $a=5.2773(5)\;{\AA},\;b=9.1244(23)\;{\AA},\;c=8.7719(11)\;{\AA}$ and Z=4. Neutron intensity data were collected on the Four-Circle diffractometer (FCD) at HANARO in Korea Atomic Energy Research Institute and X-ray date were given by Prof. Y. Noda of Tohoku University Japan. The structure was refined by full-matrix least-square to final R value of 0.070 for 1450 observed reflections by X-ray diffraction and to final R=0.049 for 745 observed reflections by neutron diffraction. With X-ray data we obtained only one hydrogen atomic position. However, not only all atomic positions of four hydrogen atoms at $NH_4$ but also the occupation factors of D and H were refined with neutron data. From this results we obtained the average chemical structure of this sample, $LiND_{3.05}H_{0.95}SO_4$.

• Journal of the Korean Vacuum Society
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• v.16 no.5
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• pp.322-329
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• 2007

The interaction of oxygen with the ordered $Ni_3Al(111)$ alloy surface at 800 K and 1000 K has been investigated using LEED, STM, HREELS, UPS, and PAX. The clean $Ni_3Al(111)$ surface exhibits a "$2{\times}2$" LEED pattern corresponding to the ordered bulk-like terminated surface structure. For an adsorption of oxygen at 800 K, LEED shows an unrelated oxygen induced superstructure with a lattice spacing of $2.93\;{\AA}$ in addition to the ($1{\times}1$) substrate spots. The combined HREELS and the UPS data point to an oxygen chemisorption on threefold aluminum sites while PAX confirms an islands growth of the overlayer. Since such sites are not available on the $Ni_3Al(111)$ surface, we conclude the buildup of an oxygen covered aluminum overlayer. During oxygen exposure at 1000 K, however, we observe the growth of ${\gamma}'-Al_2O_3$ structure on the reordered $Ni_3Al(111)$ substrate surface. This structure has been identified by means of HREELS and STM. The HREELS data will show that at 800 K the oxidation shows a very characteristic behavior that cannot be described by the formation of an $Al_2O_3$ overlayer. Moreover, the STM image shows a "Strawberry" structure due to the oxide islands formation at 1000 K. Conclusively, from the oxygen interaction with $Ni_3Al(111)$ alloy surface at 800 K and 1000 K an islands growth of the aluminum oxide overlayer has been found.

• Journal of the Korean Chemical Society
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• v.38 no.12
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• pp.873-879
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• 1994

A series of samples of solid solutions in the $Sr_xEu_{1-x}FeO_{3-y}(0.00{\leq}x{\leq}1.00)$ system has been prepared at $1200^{\circ}C$ under an atmospheric air pressure. The structures of solid solutions are studied by X-ray diffraction, thermal, Mohr salt, and Mossbauer spectroscopic analyses. Their physical properties are also discussed with the electrical conductivities. X-ray diffraction data for the compositions of x = 0.00, 0.25, and 1.00 are assigned to the orthorhombic and the compositions of x = 0.50 and 0.75 to the cubic systems. The lattice volume reduced to cubic cell increases with the x value. The mole ratio of $Fe^{4+}$ iometric chemical formulas of the system are formulated from the x, $\tau$, and y values. The mixed valency state of Fe ions, the oxygen coordination, and covalent bond character are discussed with the Mossbauer spectroscopic data. The activation enegy of the electrical conductivities depends on the $\tau$ value in the temperature range of -$100^{\circ}C$ to $600\circC$ under the air pressure. The Mossbauer spectrum and electrical conductivity of the solid solutions are discussed with nonstoichiometric chemical compositions.

• Journal of the Korean Chemical Society
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• v.27 no.3
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• pp.183-188
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• 1983

The catalytic oxidation of $SO_2$ has been investigated in the presence of vacuum-activated 10 mol % Ni-doped ${\alpha}-Fe_2O_3$ under various partial pressures of $SO_2\;and\;O_2$ at temperatures from 320 to $440{\circ}C$. Over the temperature range $320{\sim}440{\circ}C$, the activation energy is 13.8 $kcal{\cdot}mol^{-1}$. The oxidation rates have been correlated with 1.5 order kinetics; first order with respect to $SO_2$ and 0.5 order with respect to $O_2$. From the kinetic data and conductivity measurements, the adsorption, oxidation mechanism of $SO_2$ and the defect structure of vacuum-activated 10 mol % Ni-doped {\alpha}-Fe_2O_3$ are suggested. $O_2\;and\;SO_2$ appear to be adsorbed essentially as ionic species. Two surface sites, probably an $O^{2-}$ lattice and an oxygen vacancy which is induced by Ni-doping, might be required to adsorb $SO_2\;and\;O_2$. The conductivity measurements and kinetic data indicate that the adsorption process of $SO_2\;{(SO_2+O^{2-}}_{(latt)}{\rightleftharpoons}{{SO_3}^-}_{(ads)}+e')$ is the rate-determining step.

• Journal of Korea Water Resources Association
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• v.40 no.6 s.179
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• pp.469-483
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• 2007

Nitrate and chloride are the most common contaminants in groundwater and their concentrations increase easily due to fertilizer consumption and urbanization. The number of time series data for groundwater quality at a single site was not sufficient to analyze trends on Jeju Island. Therefore rectangle grids were drawn for the whole island and single grid was determined to be $500m{\times}500m$ after considering similar stream density, homogeneous hydraulic coefficients, geologic features of volcanic rock and low topographic slopes. All data within each lattice were collected and arranged in time series order and analyzed using Sen's method. 10.6 % of the total lattices for chloride and 22.4% for nitrate showed upward trends from the early 1990's to the early 2000's. Especially, upward trends for nitrate concentration are distinct in the low mid-mountainous areas of western and southern watersheds. Many septic tanks and much domestic waste from the urbanization of the low mid-mountainous area have produced this upward trend. Additionally, the agricultural region has dramatically increased since the 1990's and this has led to an increase of fertilizer consumption and, as a result, nitrate concentration. Therefore, the target of any management plan for groundwater quality on Jeiu Island needs to be focused on careful land use decisions in the mid-mountainous areas which are near Halla Mountain.

• Analytical Science and Technology
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• v.11 no.3
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• pp.189-193
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• 1998

Binary alloys, $MoRu_3$ and $MoRh_3$, have been prepared using arc melting furnace. Mo and the noble metals Ru and Rh are the constituents of metallic insoluble residues, which were found in the early days of the post-irradiation studies on uranium oxide fuels. Detailed structural informations about these alloys have not been reported on JCPDS files of ICDD (International Centre for Diffraction Data). The results of X-ray diffraction study showed that the alloy was crystallized in hexagonal close-packing, well known as ${\varepsilon}$-phase. The X-ray diffraction patterns of these alloys matched well to that of $WRh_3$ with $P6_3/mmc$ of space group. The lattice parameters, a and c, were calculated using the least squares extrapolation. It was found from X-ray photoelectron spectroscopic measurements that Mo on the surface of the alloy was oxidized to Mo(6+), which could be removed by sputtering with Ar ions for approximately 15 minutes. The changes in binding energy of Mo, Ru, and Rh on the surface of the alloy were not observed. Magnetic susceptibility measurements resulted in the typical Pauli-paramagnetic behavior in the temperature range of 2 to 300 K.

• Journal of the Korean Geotechnical Society
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• v.37 no.5
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• pp.47-63
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• 2021

Recently, the demand for three-dimensional (3D) underground maps from the perspective of digital twins and the demand for linkage utilization are increasing. However, the vastness of national geotechnical survey data and the uncertainty in applying geostatistical techniques pose challenges in modeling underground regional geotechnical characteristics. In this study, an optimal learning model based on multi-layer perceptron (MLP) was constructed for 3D subsurface lithological and geotechnical classification in Seoul, South Korea. First, the geotechnical layer and 3D spatial coordinates of each borehole dataset in the Seoul area were constructed as a geotechnical database according to a standardized format, and data pre-processing such as correction and normalization of missing values for machine learning was performed. An optimal fitting model was designed through hyperparameter optimization of the MLP model and model performance evaluation, such as precision and accuracy tests. Then, a 3D grid network locally assigning geotechnical layer classification was constructed by applying an MLP-based bet-fitting model for each unit lattice. The constructed 3D geotechnical layer map was evaluated by comparing the results of a geostatistical interpolation technique and the topsoil properties of the geological map.

• Journal of Internet Computing and Services
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• v.16 no.1
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• pp.67-74
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• 2015

In recent years, frequent itemset mining for considering the importance of each item has been intensively studied as one of important issues in the data mining field. According to strategies utilizing the item importance, itemset mining approaches for discovering itemsets based on the item importance are classified as follows: weighted frequent itemset mining, frequent itemset mining using transactional weights, and utility itemset mining. In this paper, we perform empirical analysis with respect to frequent itemset mining algorithms based on transactional weights. The mining algorithms compute transactional weights by utilizing the weight for each item in large databases. In addition, these algorithms discover weighted frequent itemsets on the basis of the item frequency and weight of each transaction. Consequently, we can see the importance of a certain transaction through the database analysis because the weight for the transaction has higher value if it contains many items with high values. We not only analyze the advantages and disadvantages but also compare the performance of the most famous algorithms in the frequent itemset mining field based on the transactional weights. As a representative of the frequent itemset mining using transactional weights, WIS introduces the concept and strategies of transactional weights. In addition, there are various other state-of-the-art algorithms, WIT-FWIs, WIT-FWIs-MODIFY, and WIT-FWIs-DIFF, for extracting itemsets with the weight information. To efficiently conduct processes for mining weighted frequent itemsets, three algorithms use the special Lattice-like data structure, called WIT-tree. The algorithms do not need to an additional database scanning operation after the construction of WIT-tree is finished since each node of WIT-tree has item information such as item and transaction IDs. In particular, the traditional algorithms conduct a number of database scanning operations to mine weighted itemsets, whereas the algorithms based on WIT-tree solve the overhead problem that can occur in the mining processes by reading databases only one time. Additionally, the algorithms use the technique for generating each new itemset of length N+1 on the basis of two different itemsets of length N. To discover new weighted itemsets, WIT-FWIs performs the itemset combination processes by using the information of transactions that contain all the itemsets. WIT-FWIs-MODIFY has a unique feature decreasing operations for calculating the frequency of the new itemset. WIT-FWIs-DIFF utilizes a technique using the difference of two itemsets. To compare and analyze the performance of the algorithms in various environments, we use real datasets of two types (i.e., dense and sparse) in terms of the runtime and maximum memory usage. Moreover, a scalability test is conducted to evaluate the stability for each algorithm when the size of a database is changed. As a result, WIT-FWIs and WIT-FWIs-MODIFY show the best performance in the dense dataset, and in sparse dataset, WIT-FWI-DIFF has mining efficiency better than the other algorithms. Compared to the algorithms using WIT-tree, WIS based on the Apriori technique has the worst efficiency because it requires a large number of computations more than the others on average.

• Korean Security Journal
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• no.40
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• pp.209-242
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• 2014

This study is to understand sure the primary crime prevention has been incidence as a social problem intended for parents through the analysis of the Crime Prevention Design (CPTED) CPTED element of recognize elements that target crime prevention strategy to effectively help students be and an object of the present invention is to provide a policy suggestion haryeoneunde proposed basic data required for orientation. To achieve the study objectives such as the core framework in this study IPA: Importance-Performance Analysis) also was selected. Subjects of study in 2010 Gyeongju Elementary parents name and were 203 first research group investigating the secondary school population of the region in 2014 to nomadic parents of 297 people sampled selection. Questionnaire that use by this study applies "Important-Performance Analysis : IPA" technique that Martilla & James(1977) presented and analyzed awareness for CPTED elements of strategy for student's crime prevention to elementary school pupil students' parentse. It was the first group, 0.886, 0.920, 0.895 and 2nd group 0.880, 0.906, 0.878 that reliability of (Cronbach' s ${\alpha}$) the importance, and believability of run chart was the first group, 0.880, 0.917, 0.878 and 2nd group, 0.735, 0.840, 0.830. Analysis of the data carried out frequency analysis, reliability analysis, Frequency analysis was performed, paired sample t-Test for the reliability analysis, and the technical statistical analysis of the data is. The analysis of lattice bars execution through the IPA, the importance of the primary parents elements of CPTED strategies are generally very high, but found that the variation depending on the components that Performance. This study, an important element of the strategy to eliminate the school building for students from inside and outside the criminal fears CPTED is a mechanical surveillance in the first group, organizational surveillance, and the second group is the region intensified I'll showed mechanically and organizational factors in the investigation, and request that the investment is urgently important element is also execution low, crime prevention personnel security higher importance than expanding the front door. The analysis result of this study expects that basic data can be used in policy direction presentation that examines closely CPTED elements of strategy for crime prevention of students and applies CPTED's component effectively at elementary school hereafter.