• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3874-3897
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• 2023

A high-fidelity computational fluid dynamics (CFD) analysis was performed using the Large Eddy Simulation (LES) model for the lower plenum of the High-Temperature Test Facility (HTTF), a ¼ scale test facility of the modular high temperature gas-cooled reactor (MHTGR) managed by Oregon State University. In most next-generation nuclear reactors, thermal stress due to thermal striping is one of the risks to be curiously considered. This is also true for HTGRs, especially since the exhaust helium gas temperature is high. In order to evaluate these risks and performance, organizations in the United States led by the OECD NEA are conducting a thermal hydraulic code benchmark for HTGR, and the test facility used for this benchmark is HTTF. HTTF can perform experiments in both normal and accident situations and provide high-quality experimental data. However, it is difficult to provide sufficient data for benchmarking through experiments, and there is a problem with the reliability of CFD analysis results based on Reynolds-averaged Navier-Stokes to analyze thermal hydraulic behavior without verification. To solve this problem, high-fidelity 3-D CFD analysis was performed using the LES model for HTTF. It was also verified that the LES model can properly simulate this jet mixing phenomenon via a unit cell test that provides experimental information. As a result of CFD analysis, the lower the dependency of the sub-grid scale model, the closer to the actual analysis result. In the case of unit cell test CFD analysis and HTTF CFD analysis, the volume-averaged sub-grid scale model dependency was calculated to be 13.0% and 9.16%, respectively. As a result of HTTF analysis, quantitative data of the fluid inside the HTTF lower plenum was provided in this paper. As a result of qualitative analysis, the temperature was highest at the center of the lower plenum, while the temperature fluctuation was highest near the edge of the lower plenum wall. The power spectral density of temperature was analyzed via fast Fourier transform (FFT) for specific points on the center and side of the lower plenum. FFT results did not reveal specific frequency-dominant temperature fluctuations in the center part. It was confirmed that the temperature power spectral density (PSD) at the top increased from the center to the wake. The vortex was visualized using the well-known scalar Q-criterion, and as a result, the closer to the outlet duct, the greater the influence of the mainstream, so that the inflow jet vortex was dissipated and mixed at the top of the lower plenum. Additionally, FFT analysis was performed on the support structure near the corner of the lower plenum with large temperature fluctuations, and as a result, it was confirmed that the temperature fluctuation of the flow did not have a significant effect near the corner wall. In addition, the vortices generated from the lower plenum to the outlet duct were identified in this paper. It is considered that the quantitative and qualitative results presented in this paper will serve as reference data for the benchmark.

• Information Systems Review
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• v.20 no.4
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• pp.79-96
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• 2018

This study started by focusing on the internalization of the technology appraisal model into the credit rating model to increase the discriminative power of the credit rating model not only for SMEs but also for all companies, reflecting the items related to the financial stability of the enterprises among the technology appraisal items. Therefore, it is aimed to verify whether the technology appraisal model can be applied to identify high-stability SMEs in advance. We classified companies into industries (manufacturing vs. non-manufacturing) and the age of company (initial vs. non-initial), and defined as a high-stability company that has achieved an average debt ratio less than 1/2 of the group for three years. The C5.0 was applied to verify the discriminant power of the model. As a result of the analysis, there is a difference in importance according to the type of industry and the age of company at the sub-item level, but in the mid-item level the R&D capability was a key variable for discriminating high-stability SMEs. In the early stage of establishment, the funding capacity (diversification of funding methods, capital structure and capital cost which taking into account profitability) is an important variable in financial stability. However, we concluded that technology development infrastructure, which enables continuous performance as the age of company increase, becomes an important variable affecting financial stability. The classification accuracy of the model according to the age of company and industry is 71~91%, and it is confirmed that it is possible to identify high-stability SMEs by using technology appraisal items.

• Economic and Environmental Geology
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• v.44 no.1
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• pp.83-94
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• 2011

Extra heavy oil reservoirs are distributed over the world but most of them is deposited in the northern part of the Orinoco River in Venezuela, in the area of 5,500 $km^2$, This region, which has been commonly called "the Orinoco Oil Belt", contains estimated 1.3 trillion barrels of original oil-in-place and 250 billion barrels of established reserves. The Venezuela extra heavy oil has an API gravity of less than 10 degree and in situ viscosity of 5,000 cP at reservoir condition. Although the presence of extra heavy oil in the Orinoco Oil Belt has been initially reported in the 1930's, the commercial development using in situ cold production started in the 1990's. The Orinoco heavy oil deposits are clustered into 4 development areas, Boyaco, Junin, Ayachoco, and Carabobo respectively, and they are subdivided into totally 31 production blocks. Nowadays, PDVSA (Petr$\'{o}$leos de Venzuela, S.A.) makes a development of each production block with the international oil companies from more than 20 countries forming a international joint-venture company. The Eastern Venezuela Basin, the Orinoco Oil Belt is included in, is one of the major oil-bearing sedimentary basins in Venezuela and is first formed as a passive margin basin by the Jurassic tectonic plate motion. The major source rock of heavy oil is the late Cretaceous calcareous shale in the central Eastern Venezuela Basin. Hydrocarbon materials migrated an average of 150 km up dip to the southern margin of the basin. During the migration, lighter fractions in the hydrocarbon were removed by biodegradation and the oil changed into heavy and/or extra heavy oil. Miocene Oficina Formation, the main extra heavy oil reservoir, is the unconsolidated sand and shale alternation formed in fluvial-estuarine environment and also has irregularly a large number of the Cenozoic faults induced by basin subsidence and tectonics. Because Oficina Formation has not only complex lithology distribution but also irregular geology structure, geological evolution and characteristics of the reservoirs have to be determined for economical production well design and effective oil recovery. This study introduces geological formation and evolution of the Venezuela extra heavy oil reservoirs and suggest their significant geological characteristics which are (1) thickness and geometry of reservoir pay sands, (2) continuity and thickness of mud beds, (3) geometry of faults, (4) depth and geothermal character of reservoir, (5) in-situ stress field of reservoir, and (6) chemical composition of extra heavy oil. Newly developed exploration techniques, such as 3-D seismic survey and LWD (logging while drilling), can be expected as powerful methods to recognize the geological reservoir characteristics in the Orinoco Oil Belt.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.8
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• pp.831-838
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• 2008

This study investigated the characteristics of nitrogen removal and microbial community in a lab-scale A$_2$O activated sludge process filled with the fluidized media at an aerebic basin. The change of microbial community was monitored based on quinone profiles of activated sludge according to feeding sewage with/without external carbon source. Low C/N ratio(COD$_{Cr}$/T-N of 1.24) sewage was fed. The obtained results from this study were as follows; Ubiquinone(UQ) in the influent was in the descending order of UQ-8, UQ-10 and UQ-9. Menaquinone(MK) was simpler and much less than UQ. The ratio of UQ/MK was less than 0.41 and the dissimilarity was below 0.26. Without an external carbon source, MK-8 was the dominant species and there were 3 kinds of quinone species and low DQ and EQ values in an anaerobic basin. The ratio of UQ/MK increased to 2.3 in an anoxic basin. In an oxic basin, UQ-7 and UQ-8 were the dominant species. UQ-7 was dominating in suspended microorganisms, while UQ-8 was in attached microorganisms. With an external carbon source addition, MK-8 decreased but UQ-8 increased in an anaerobic basin. So did quinone species, DQ and EQ values. There was also a change in an anoxic basin with the improvement of denitrification. UQ-8 decreased instead, MK-7 and MK-8 increased. UQ/MK ratio decreased 2.3 to 1.4. It means that the dominant species change from Pseudomonas sp. to Bacillus and Micrococcus species. etc. In an oxic basin, UQ-8 replaced UQ-7 in suspended microorganisms and UQ-10 replaced UQ-8 in attached microbials. This seemed related with the growth of Nitrosomonas and Nitrobactor species.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.124-128
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• 2016

We have investigated the electronic structures of intermetallic multilayer (ML) films of [$Co(2{\AA})/Pd(x{\AA})$] (x: the thickness of the Pd sublayer; x = $1{\AA}$, $3{\AA}$, $5{\AA}$, $7{\AA}$, $9{\AA}$) by employing soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD). Both Co 2p XAS and XMCD spectra are found to be similar to one another, as well as to those of Co metal, providing evidence for the metallic bonding of Co ions in [Co/Pd] ML films. By analyzing the measured Co 2p XMCD spectra, we have determined the orbital magnetic moments and the spin magnetic moments of Co ions in [$Co(2{\AA})/Pd(x{\AA})$] ML films. Based on this analysis, we have found that the orbital magnetic moments are enhanced greatly when x increases from $1{\AA}$ to $3{\AA}$, and then do not change much for $x{\geq}3{\AA}$. This finding suggests that the interface spin-orbit coupling plays an important role in determining the perpendicular magnetic anisotropy in [Co/Pd] ML films.

• Journal of Technologic Dentistry
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• v.21 no.1
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• pp.27-41
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• 1999

The Ag-Pd-Cu alloys containing a small amount of Au is commonly used for dental purposes, because this alloy cheaper than Au-base alloys for clinical use. However, the most important characteristic of this alloy is age-hardenability, which is not exhibited by other Ag-base dental alloys. The specimens used were Ag-30Pd-10Cu ternary alloy and Au addition alloy. These alloys were melted and casted by induction electric furnace and centrifugal casting machine in Ar atmosphere. These specimens were solution treated for 2hr at $800^{\circ}C$ and were then quenched into iced water, and aged at 350-$550^{\circ}C$ Age-hardening characteristic of the small Au-containing Ag-Pd-Cu dental alloys were investigated by means of hardness testing, X-ray diffraction and electron microscope observations, electrical resistance, differential scanning calorimetric, energy dispersed spectra and electron probe microanalysis. Principal results are as follows ; Maximum hardening occured in two co-phases of ${\alpha}_2$ + PdCu In stage II, decomposition of the $\alpha$ solid solution to a PdCu ordered phase($L1_o$ type) and an Ag-rich ${\alpha}_2$ phase occurred and a discontinuous precipitation occurred at the grain boundary. From the electron microscope study, it was concluded that the cause of age-hardening in this alloy is the precipitation of the PdCu redered phase, which has AuCu I type face-centered tetragonal structure. Precipitation procedure was ${\alpha}{\to}{\alpha}_1+PdCu{\to}{\alpha}_2+PdCu$ at Pd/Cu = 3 Pd element of Ag-Pd-Cu alloy is more effective dental alloy on anti-corrosion and is suitable to isothermal ageing at $450^{\circ}C$.

• Journal of the Korean earth science society
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• v.21 no.4
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• pp.437-448
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• 2000

The Middle Carboniferous Gabsan Formation is distributed in the Cheongrim area of southern Yeongwol and the Mt. Gachang area of Chungbuk Province. This study was carried out to investigate the lithological characters and geochemical composition of the limestones and to find out controlling structures of the limestones of the formation. The limestones of the Gabsan Formation are characterized by the light gray to light brown in color and fine and dense textures. The limestone grains are composed of crinoid fragments, small foraminfers, fusulinids, gastropods, ostracods, etc. Due to the recrystallization, some limestones consist of fine crystalline calcites. The chemical analysis of limestones of the formation was conducted to find out the contents of CaO, MgO, Al$_2$O$_3$, Fe$_2$O$_3$ and SiO$_2$. The content of CaO ranges from 49.78-60.63% and the content of MgO ranges from 0.74 to 4.63% The contents of Al$_2$O$_3$ and Fe$_2$O$_3$ are 0.02-0.55% and 0.02${\sim}$0.84% , respectively. The content of SiO$_2$ varies from 1.55 to 4.80%, but some samples contain more than 6.0%. The limestones of the formation can be grouped into two according to the CaO content: One is a group of which CaO content ranges from 49.78 to 56.26% and the other is a group of which CaO content varies from 59.36 to 60.38%. In the first group, the contents of Al$_2$O$_3$, Fe$_2$O$_3$ and SiO$_2$ range very irregularly according to the CaO content. In the second group, the values of MgO, Al$_2$O$_3$, Fe$_2$O$_3$ and SiO$_2$ are nearly same. Detailed structural analysis of mesoscopic structures and microstructures indicates the five phase of deformation in the study area. The first phase of deformation(D$_1$) is characterized by regional scale isoclinal folds, and bedding parallel S$_1$ axial plane foliation which is locally developed in the mudstone and sandstone. Based on the observations of microstructures, S$_1$ foliations appear to be developed by grain preferred orientation accompanying pressure-solution. During second phase of deformation, outcrop scale E-W trending folds with associated foliations and lineations are developed. Microstructural observations indicate that crenulation foliations were formed by pressure-solution, grain boundary sliding and grain rotation. NNW and SSE trending outcrop scale folds, axial plane foliations, crenulation foliations, crenulation lineations, intersection lineations are developed during the third phase of deformation. On the microscale F$_3$ fold, axial plane foliations which are formed by pressure solution are well developed. Fourth phase of deformation is characterized by map scale NNW trending folds. The pre-existing planar and linear structures are reoriented by F$_4$ folds. Fifth phase of deformation developed joints and faults. The distribution pattern of the limestones is mostly controlled by F$_1$ and F$_4$ folds.

• Journal of the Korean Geographical Society
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• v.31 no.2
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• pp.295-308
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• 1996

1. Retrospect of Political Geographic Studies since Liberation, 1945 : 1) Period from 1945 to mid 1960s : There was not political geography as a science in Korea at the time of liberation from Japan 1945. At that time were not pure political geographers in Korea. In 1947, Moon-Hwa Pyo, economics professor, published a book titled Outline of Korean Geopolitics. This book was a first one in the field of political geography and available at that time in the logical descriptions. Bok-Hyon Choi was a first political geographer who in 1959 wrote a book titled Political geography for the collegians of Seoul National University. Professor Choi introduced American-style political geography through the book above mentioned. In 1963, Kie-Joo Hyong published an article titled "Korean Unification: Possibility from the Geopolitical Viewpoint" which was a first article published by Korean young scholar who studied geography in this country. 2) Period from late 1960s to late 1980s : Both Yoon Cha and Duck-Soon Im published frequently several articles of political geography or geopolitics respectively in 1968-1969. And they issued geopolitical disputes on Korean geopolitical structure and an application of rimland theory to Korean peninsula in 1969 through a magazine named Joung-Kyong Younku (the political and economic researches). The disputes played an important role of showing political geography (or geopolitics) to political sciences especially international political Science. Active researches still continued in 1970s. In that atmosphere the first Korean book of political geography written by a post-liberation scholar (Duck-Soon Im) titled Principles of Political Geography was published in 1973. This book was influenced much by American political geography after Second World War. In 1980s, the researches continued more actively. Especially administrative districts, capital cities, and sub-capital cities were frequently studied during this period. 3) Period from late 1980s to Present: Recent Studies : 1985 was a year of much production of articles of political geography. The first Ph.D thesis of political geography published in the same year in our country. And since 1985 produced many M.A. articles. Several categories of esearches of political geography was made in the period from late 1980s to present. Capital cities, Korean unification, administrative districts, urban politics, elections, sub-capital cities, and defense walls were important research categories. Reviewing the researches from 1945 to present. I found eight categories of political geography in Korea: capital cities, administrative districts, geopolitical structure of Korean peninsula, division and unification of Korea, sub-capital cities, defense walls, elections, and urban politics. Each category includes several scholars respectiveiy. 2. Study Tasks and Prospects in Korean Political Geography: In relation to Korean circumstances there are three study-tasks. The first task of Korean people is unification of two Koreas. Political geographers of Korea must al survey titled Survey Methods of Human Geography for collegians. This book was first one on survey part in Korea. The book however, is insufficient in comprehensiveness in aspects too. I think that the important tasks of general-synoptic human geography in Korea are \circled1 publication of comprehensive books of human geography in the aspects and methodologies for collegians and \circled2 acceptance of academic world of human geography in Korea of variety in methodologies of human geography for future progress. progress.

• Korean Journal of Soil Science and Fertilizer
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• v.6 no.1
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• pp.1-8
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• 1973

This study examined the morphological, physical and chemical characteristics of the Yesan and the Songjeong series derived from residuum of the granite developed on gently sloping to rolling relief in Honam reclamable land Area. The results of this study are summarized as follows. 1. The morphological characteristics. In the Yesan series, the surface soils(Ap horizons) are brown to dark brown sandy loam. The subsoils(B horizons) are yellowish red to red sandy clay loam to sandy loam and the soil profile development is weak. The Songjeong series, the surface soils (Ap horizons) are washed by erosion, so the subsoils are revealed on the surface, and these are dark red silty clay loam. The subsoils (B horizons) are red silty clay loam and thin clay cutans are formed on the ped faces of the structure. The substrata of two soil series are deeply weathered granitic saprolite. 2. The physical and chemical characteristics. The distribution of clay content tends to increase from surfaces to subsoils with depth gradually. On the Yesan series, the content of clay is less than 18%, soil pH (6.0 in the surface-soil, 4.5-5.0 in the subsoil), the content of organic matter (1.8% in the surface soil, 0.1~0.4% in the subsoil), available phosphate (40 ppm), the cation exchange capacity(4~8 me/100 gr) are very low, and the base saturation (57.8% in the surface soil, 46.3% in the subsoil) is moderate. On the Songjeong series, the content of clay is 30~40%, pH (5.7-6.0), the content of in organic matter (1.25% in the surface soil, 0.1~0.4% in the subsoil), available phosphate(4 ppm), the cation exchange capacity(6.2 me/100 gr in the surface soil, 2~6 me/100gr in the subsoil) are very low, and the base saturation(28.1% in the surfacesoil, 16~23% in the subsoil) is also low. 3. The Yesan and Songjeong series are for med under a temperate humid climate, and classified as Red Yellow Soils in the old classification system. According to U.S.D.A. 7th approximation the former belongs to Typic Dystrochrepts in Inceptisols, and the latter, Typic Hapludults in Ultisols.

• Journal of the Korean Vacuum Society
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• v.6 no.2
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• pp.129-135
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• 1997

Undoped and Co-doped $ZnIn_2Se_4$ single crystals crystallized in the tetragonal space group 142m, with lattice constants a=5.748 $\AA$ and c=11.475 $\AA$, and a=5.567 $\AA$ and c=11.401 $\AA$. The optical absorption measured near the fundamental band edge showed that the optical energy band structure of these compounds had an indirect band gap, the direct and the indirect energy gaps of these compounds decreased as temperature changed from 10 to 300 K. The temperature coefficients of the direct energy gaps were found to be $\alpha=3.71\times10^{-4}$eV/K and $\beta$=519 K for $\alpha=3.71\times10^{-4}$eV/K and $\beta$=421K for $ZnIn_2Se_4$: Co. The temperature coefficients of the indirect energy gaps were also found to be $\alpha=2.31\times10^{-4}$ eV/K and $\beta$=285 K for $ZnIn_2Se_4$, and $\alpha=3.71\times10^{-4}$eV/K and $\beta$=609 K for $ZnIn_2Se_4$:Co, respectively. Six impurity optical absorption peaks due to cobalt are observed in $ZnIn_2Se_4$:Co single crystal. These impurity optical absorption peaks can be attibuted to the electronic transitions between the split energy levels of$CO^{2+}$ ions located at Td symmetry site of $ZnIn_2Se_4$ host lattice. The 1st order spin-orbit coupling constant ($\lambda$), Racah parameter (B), and crystal field parameter (Dq) ARE GIVEN AS -$243\textrm{cm}^{-1}, 587\textrm{cm}^{-1}, \;and\;327\textrm{cm}^{-1}$, respectively.