• Korean Journal of Metals and Materials
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• v.50 no.9
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• pp.659-667
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• 2012

Alloy 617 is a Ni-base superalloy and a candidate material for the intermediate heat exchanger (IHX) of a very high temperature gas reactor (VHTR) which is one of the next generation nuclear reactors under development. The high operating temperature of VHTR enables various applications such as mass production of hydrogen with high energy efficiency. Alloy 617 has good creep resistance and phase stability at high temperatures in an air environment. However, it was reported that the mechanical properties decreased at a high temperature in an impure helium environment. In this study, high-temperature corrosion tests were carried out at $850^{\circ}C-950^{\circ}C$ in a helium environment containing the impurity gases $H_2$, CO, and $CH_4$, in order to examine the corrosion behavior of Alloy 617. Until 250 h, Alloy 617 specimens showed a parabolic oxidation behavior at all temperatures. The activation energy for oxidation in helium environment was 154 kJ/mol. The SEM and EDS results elucidated a Cr-rich surface oxide layer, Al-rich internal oxides and depletion of grain boundary carbides. The thickness and depths of degraded layers also showed a parabolic relationship with time. A normal grain growth was observed in the Cr-rich surface oxide layer. When corrosion tests were conducted in a pure helium environment, the oxidation was suppressed drastically. It was elucidated that minor impurity gases in the helium would have detrimental effects on the high-temperature corrosion behavior of Alloy 617 for the VHTR application.

• Steel and Composite Structures
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• v.38 no.5
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• pp.477-496
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• 2021

The main objective of this paper is to study vibration of sandwich open cylindrical panel with damaged core and FG face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions. It is seen that for the large amount of power-law index "P", increasing this parameter does not have significant effect on the non-dimensional natural frequency parameters of the FG sandwich curved panel. Results indicate that by increasing the value of isotropic damage parameter "D" up to the unity (fully damaged core) the frequency would tend to become zero. One can dictate the fiber variation profile through the radial direction of the sandwich panel via the amount of "P", "b" and "c" parameters. It should be noticed that with increase of volume fraction of fibers, the frequency parameter of the panels does not increase necessarily, so by considering suitable amounts of power-law index "P" and the parameters "b" and "c", one can get dynamic characteristics similar or better than the isotropic limit case for laminated FG curved panels.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.6
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• pp.723-732
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• 2022

Cracking ammonia inside solid oxide fuel cell (SOFC) stack is a compact and simple way. To prevent sharp temperature fluctuation and increase cell efficiency, the decomposition reaction should be spread on whole cell area. This leading to a question that, how does anode thickness affect the conversion rate of ammonia and the cell voltage? Since the 0D model of SOFC is useful for system level simulation, how accurate is it to use equilibrium solver for internal ammonia cracking reaction? The 1D model of ammonia fed SOFC was used to simulate the diffusion and reaction of ammonia inside the anode electrode, then the partial pressure of hydrogen and steam at triple phase boundary was used for cell voltage calculation. The result shows that, the ammonia conversion rate increases and reaches saturated value as anode thickness increase, and the saturated thickness is bigger for lower operating temperature. The similar cell voltage between 1D and 0D models can be reached with NH₃ conversion rate above 90%. The 0D model and 1D model of SOFC showed similar conversion rate at temperature over 750℃.

• Analyses & Alternatives
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• v.2 no.2
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• pp.93-110
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• 2018

Due to its speciality, Johannesburg has drawn wide attention from the international academia, which the existing urban theory cannot easily explain. This paper focuses on the spatial pattern of Johannesburg, and finds that it is highly fragmented: first North-South Division due to apartheid and gold mining, secondly, the continuous sprawl due to population densification, and thirdly formation of city-region due to the fill-in spatial policy. The fragmented spatial pattern undermines the social integration and weakens the potential economic sustainability, which make the balanced multi-core spatial pattern inevitable under the influence of the international planning thought. The Johannesburg's spatial transformation comes not only from social integration, but also from the development vison of world-class status of an African city. In reality, since the collapse of apartheid, the municipal government has released series of strategic planning in different executive phase. These different plannings unanimously focus on the world class status although since 2008, the social inclusiveness is more emphasized. Thus, Johannesburg implements some spatial policies, as promoting the corridor of freedom, identifying the key nodes in the city then developing with high density, implementing the in-filling policy, managing the urban growth boundary, effectively preserving the natural system. However, the industrial structure in Johannesburg is already quite high-ended which cannot produce many jobs and also require much investment in advanced infrastructure. Thus, the strategic goals of world-class status of an African city and social inclusiveness which really need widely shared public services to some extent are in tension. After evaluation, we can see that spatial transformation is quite limited. Obviously spatial transformation largely depends on the social-economy. The population is still in flow. In this sense Johannesburg must energetically support the employment-based industry, effectively control the spatial sprawl and carry out institutional innovation which further incentive investment, gradually build an integrated regional governance. In general, how Johannesburg combines globalization and its own condition is still worth thinking in both theory and practice.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.43.1-43.1
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• 2020

Cassiopeia A (Cas A) is a young supernova remnant (SNR) where we observe the interaction of SNR blast wave with circumstellar medium. From the early optical studies, dense, slowly-moving, N-rich "quasi-stationary flocculi" (QSF) have been known. These are probably dense CNO-processed circumstellar knots that have been engulfed by the SNR blast wave. We have carried out near-infrared, high-resolution (R=45,000) spectroscopic observations of ~40 QSF, and here we present the result on a QSF knot (hereafter 'Knot 24') near the SNR boundary of Cas A. The average [Fe II] 1.644 um spectrum of Knot 24 has a remarkable shape with a narrow (~8 km/s) line superposed on the broad (~200 km/s) line emitted from shocked gas. The spatial morphology and the line parameters indicate that Knot 24 has been partially destroyed by a shock wave and that the narrow line is emitted from the unshocked material heated/ionized by the shock radiation. This is the first detection of the emission from the pristine circumstellar material of the Cas A supernova progenitor. We also detected H Br gamma and other [Fe II] lines corresponding to the narrow [Fe II] 1.644 um line. For the main clump where we can clearly identify the shock emission associated with the unshocked material, we analyze the observed line ratios using a shock model that includes radiative precursor. The analysis indicates that the majority of Fe in the unshocked material is in the gas phase, not depleted onto dust grains as in the general interstellar medium. We discuss the non-depletion of Fe in QSF and its implications on the immediate progenitor of the Cas A supernova.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.467-475
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• 2023

To ensure the safety of the pipeline against large deformation of the pipeline during lowering construction, the analysis for pipeline becomes emphasized. The FE analysis has a lower efficiency at calculating time, while it could be obtained high accuracy. In this paper, a reasonable analytical model for analysis of pipeline is proposed during lowering-in. This analytical model is partitioned considering the geometrical characteristics and modeled as two parameters Beam On Elastic Foundation and Euler-Bernoulli beam considering the boundary condition. This takes into account the pipeline-soil interaction and the axial forces acting on the pipeline. Previous model can only be applied to standardized conditions, whereas the proposed model defined as Segmented Pipeline Model can be considered for the majority of construction conditions occurred during lowering-in. In addition, minimized assumptions and segmented elements lead to improve the convenience and applicability of modeling. Nevertheless, the model shows accurate results compared to the FE model. Accordingly, it is expected that it will be used efficiently for configuration management as well as safety assessment of pipeline during lowering-in.

• Journal of Biomedical Engineering Research
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• v.25 no.4
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• pp.261-268
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• 2004

Osteoporosis is a clinical condition in which the amount of bone tissue is reduced and the likelihood of fracture is increased. It is known that the electrical property of the bone is related to its density, and, in particular, the electrical resistance of the bone decreases as the bone loss increases. This implies that the electrical property of bone may be an useful parameter to diagnose osteoporosis, provided that it can be readily measured. The study attempted to evaluate the electrical conductivity of bone using a technique of electrical impedance tomography (EIT). It nay not be easy in general to get an EIT for the bone due to the big difference (an order of 2) of electrical properties between the bone and the surrounding soft tissue. In the present study, we took an adaptive mesh regeneration technique originally developed for the detection of two phase boundaries and modified it to be able to reconstruct the electrical conductivity inside the boundary provided that the geometry of the boundary was given. Numerical simulation was carried out for a tibia phantom, circular cylindrical phantom (radius of 40 mm) inside of which there is an ellipsoidal homeogenous tibia bone (short and long radius are 17 mm and 15 mm, respectively) surrounded by the soft tissue. The bone was located in the 15 mm above from the center of the circular cross section of the phantom. The electrical conductivity of the soft tissue was set to be 4 mS/cm and varies from 0.01 to 1 ms/cm for the bone. The simulation considered measurement errors in order to look into its effects. The simulated results showed that, if the measurement error was maintained less than 5 %, the reconstructed electrical conductivity of the bone was within 10 % errors. The accuracy increased with the electrical conductivity of the bone, as expected. This indicates that the present technique provides more accurate information for osteoporotic bones. It should be noted that tile simulation is based on a simple two phase image for the bone and the surrounding soft tissue when its anatomical information is provided. Nevertheless, the study indicates the possibility that the EIT technique may be used as a new means to detect the bone loss leading to osteoporotic fractures.

• Korean Journal of Materials Research
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• v.2 no.6
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• pp.408-416
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• 1992

Stable TiS$i_2$was formed by RTA on single-Si and on poly-Si. Subsequently, an Al-1% Si layer with 600-nm thick was deposited on top of the TiS$i_2$, Finally, the specimens were annealed for 30min at 400-60$0^{\circ}C$in $N_2$ambient. The thermal stability of Al-1% Si/TiS$i_2$bilayer and interfacial reaction were investigated by measuring sheet resistance, Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The composition and phase of precipitates formed by the reaction of Al-1% Si with Ti-silicide were studied by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD). In the case of single-Si substrate the reaction of Al-1% Si layer with TiS$i_2$layer resulted in precipitates, consuming all TiS$i_2$layer at 55$0^{\circ}C$. On the other hand, the disappearance of TiS$i_2$on poly-Si occurred at 50$0^{\circ}C$ and more precipitates were formed by the reaction of Al-1% Si/TiS$i_2$on potty-Si substrate than those of the reaction on single-Si substrate. This phenomenon resulted from the fact that Ti-silicide formed on poly-Si was more unstable than on single-Si by the effect of grain boundary. By EDS analysis the precipitates were found tobe composed of Ti, Al, and Si. X-ray diffraction showed the phase of precipitates to be theT$i_7$A$l_5$S$i_12$ternary compound.

• Journal of the Korean earth science society
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• v.32 no.3
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• pp.276-293
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• 2011

In this study a modeling system consisting of Weather Research and Forecasting (WRF), Sparse Matrix Operator Kernel Emissions (SMOKE), the Community Multiscale Air Quality (CMAQ) model, and the CMAQ-Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (MADRID) model has been applied to estimate enhancements of $PM_{10}$ during Asian dust events in Korea. In particular, 5 experimental formulas were applied to the WRF-SMOKE-CMAQ (MADRID) model to estimate Asian dust emissions from source locations for major Asian dust events in China and Mongolia: the US Environmental Protection Agency (EPA) model, the Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model, and the Dust Entrainment and Deposition (DEAD) model, as well as formulas by Park and In (2003), and Wang et al. (2000). According to the weather map, backward trajectory and satellite image analyses, Asian dust is generated by a strong downwind associated with the upper trough from a stagnation wave due to development of the upper jet stream, and transport of Asian dust to Korea shows up behind a surface front related to the cut-off low (known as comma type cloud) in satellite images. In the WRF-SMOKE-CMAQ modeling to estimate the PM10 concentration, Wang et al.'s experimental formula was depicted well in the temporal and spatial distribution of Asian dusts, and the GOCART model was low in mean bias errors and root mean square errors. Also, in the vertical profile analysis of Asian dusts using Wang et al's experimental formula, strong Asian dust with a concentration of more than $800\;{\mu}g/m^3$ for the period of March 31 to April 1, 2007 was transported under the boundary layer (about 1 km high), and weak Asian dust with a concentration of less than $400\;{\mu}g/m^3$ for the period of 16-17 March 2009 was transported above the boundary layer (about 1-3 km high). Furthermore, the difference between the CMAQ model and the CMAQ-MADRID model for the period of March 31 to April 1, 2007, in terms of PM10 concentration, was seen to be large in the East Asia area: the CMAQ-MADRID model showed the concentration to be about $25\;{\mu}g/m^3$ higher than the CMAQ model. In addition, the $PM_{10}$ concentration removed by the cloud liquid phase mechanism within the CMAQ-MADRID model was shown in the maximum $15\;{\mu}g/m^3$ in the Eastern Asia area.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.36 no.1
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• pp.120-128
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• 2018

The purpose of this study is to establish basic data for the continuous protection management policy of domestic natural world heritage and mixed world heritage, and to examine the present situation and characteristics of the protection management according to the World Heritage Convention on the World Heritage listed Huangshan. The results of this study are as follows. First, Huangshan began to be protected by the establishment of the Huangshan Construction Committee in 1933, and after the designation of national park in 1982, laws and regulations were established in the central ministries, And various projects related to utilization have been implemented. Secondly, the establishment of the boundary for protection was actively intervened by the central government, such as the reorganization of the boundary of Huangshan through the administrative district plan. In order to protect the ecological and landscape value as well as the cultural factor, And designated a heritage designated area. Third, the protection management of Huangshan was divided into four major stages. The first phase was divided into the period when administrative measures were taken to manage the protection of Huangshan. The second phase was designated as a national park in Huangshan. The third period was the time of the protection-oriented project according to the recommendation of the international organizations after the World Heritage listed. The fourth period was the expansion of the tourism industry for the continuous use of protection of Huangshan city, My preservation business was being implemented. Fourth, Huangshan is managed by the central government and the city government. Huangshan, which is a mixed heritage, is managed jointly by the Ministry of Cultural Heritage Administration and the Ministry of Natural Heritage Administration. The protection and management of Huangshan promoted the efficiency and expertise of the heritage-related work through the establishment of the administrative unit-specific management system, and the local governments were entrusted with the authority to implement the protection management policies that meet local characteristics. Fifth, the preservation area of Huangshan has been destroyed by the development policy centered on the mountain. In addition, according to the operation of accommodation facilities, there are problems such as sewage, garbage disposal, and environmental pollution caused by tourists, and the damage caused by pests and diseases in planted plantations around the area and changes in ecosystem due to the composition of cable cars. Sixth, for the continuous protection of Huangshan, strict regulations on new construction, extension and management of accommodation are required, and it is necessary to install facilities to limit and control the number of visitors.