• Transactions of Materials Processing
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• v.9 no.4
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• pp.362-371
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• 2000

In order to reduce weight of a high-speed railroad vehicle, the main body has been manufactured by hollow section extrusion using aluminum alloys. A porthole die has utilized for the hollow section extrusion process, which causes complicated die geometry and flow characteristics. Design of porthole die is very difficult due to such a complexity. The three-dimensional finite element analysis for hollow section is also an arduous job from the viewpoint of appropriate mesh construction and tremendous computation time. In the present work, mismatching refinement, an efficient domain decomposition method with different mesh density for each subdomain, is implemented for the analysis of the hollow section extrusion process. In addition, a modified grid-based approach with the surface element layer is utilized lot three-dimensional mesh generation of a complicated shape with hexahedral elements. The effects of porthole design are discussed through the simulation for extrusion of an underframe part of a railroad vehicle. An experiment has also been carried out for the comparison. Comparing the velocity distribution at the outlet with the thickness variation of the extruded part, it is concluded that the analysis results can provide reliable measures whether the die design is acceptable to obtain uniform part thickness. The analysis results are then successfully reflected on the industrial porthole die design.

• Wind and Structures
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• v.10 no.2
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• pp.153-176
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• 2007

The Proper Orthogonal Decomposition (POD) is a statistical method particularly suitable and versatile for dealing with many problems concerning wind engineering and several other scientific and humanist fields. POD represents a random process as a linear combination of deterministic functions, the POD modes, modulated by uncorrelated random coefficients, the principal components. It owes its popularity to the property that only few terms of the series are usually needed to capture the most energetic coherent structures of the process, and a link often exists between each dominant mode and the main mechanisms of the phenomenon. For this reason, POD modes are normally used to identify low-dimensional subspaces appropriate for the construction of reduced models. This paper provides a state-of-the-art and some prospects on POD, with special regard to its framework and applications in wind engineering. A wide bibliography is also reported.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.375-382
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• 2019

In this study, an experimental study on the buildability of the structure using the developed printing materials and equipment was performed. Experimental variables included the moving speed of nozzles(=80 and 100mm/s), the revolutions per minute (RPM) of screw in discharge buckets, and the aspect ratio(=1.67 and 5.00) reflecting wall length of the structures. Buildability of the 3D printed concrete structures was analyzed based on the maximum decomposition layer and collapse patterns of the structures according to the experimental variables. The nozzle movement speed of 80mm/s and the aspect ratio of 1.67 were favorable for 3D printing in this study. The collapse process of structure due to uneven layer decomposition was also analyzed through the relative displacement measurement of the lower part of the structure during printing.

• KDI Journal of Economic Policy
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• v.35 no.2
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• pp.107-131
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• 2013

In this paper, we test and estimate the stochastic non-fundamental trend in Korean stock market. For this, following Kim (2011), we exploit that the long-run equilibrium stock price may be decomposed into fundamental and stochastic non-fundamental trends (i.e., the sum of dividend innovations and a part that are orthogonal with the dividend innovations) by using the Beveridge-Nelson decomposition and projections. In this VAR construction, there is an error correction mechanism through which stock prices converge to their long-run equilibrium, which also contain the stated stochastic non-fundamental trend as well as fundamental trend. The estimation and test results using yearly data from the Korea (1976-2012) indicated that fluctuations in stock prices during that period can be explained mainly not by the stochastic non-fundamental trend but by the dividend trend. However, during some periods like after Seoul Olympic Games, we may observe the non-fundamental trend affected to the stock price variation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3D
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• pp.231-237
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• 2012

The interrelation of integrity degree and country competitive power was known as high. But, according to the CPI announcement of Transparency International, the domestic Corruption Perceptions Index ranked 5 points, as being corrupt. It was investigated that the corruption level of Korea was getting worse most in the construction sector. In this way, it is emergent and inevitable to improve the transparency in the construction industry, accounting for 25-54% of the total corruption cases in our society. Transparency International has opened to the public the source data, utilized in the CPI measures in 2010. In the case of Korea, the 9 data of 6 organizations were utilized. According to the PERC, the corruption level of the private sector in Korea has been estimated as the worst among the 16 countries. In this context, this paper analyses the corruption level of Korea by utilizing the source data of the Transparency International CPI. And it aims to comprehend structural problems in the construction industry and to suggest implicative countermeasures through out the anti-corruption activities in the world. It propose finally an improvement of the structural causes in the construction industry, a promotion of effective punishment against corrupt practices, a reinforcement of the transparency management in the construction sector, etc.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.622-626
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• 2001

Every design activity has a goal of satisfying a set of functional requirement. The commencement of a design, therefore, must have its foundation upon the identification of the functional requirements. Many of the design practices of the industrial examples can be categorized as design of small systems that are defined to have limited and fixed sets of functional requirements to be satisfied at all times. In the case of small systems it facilitates the construction of a knowledge-based system for a specific purpose to decompose the functional requirement and map ones in the lowest level into specific design features. When the number of design features is large, they need to be managed by groups. This paper suggests a grouping method for design process can be regarded as a series of selections of the predefined functional primitives according to the requirements and the preceding selections. An intelligent product design system for automatic transmission lever design is developed as an example.

• The KIPS Transactions:PartD
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• v.13D no.7 s.110
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• pp.889-900
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• 2006

Even though sensor networks are different in user requests and data characteristics depending on each application area, the existing researches on stream data transmission problem focus on the performance improvement of their methods rather than considering the original characteristic of stream data. In this paper, we introduce a hierarchical or distributed sensor network architecture and data model, and then evaluate the multivariate data reduction methods suitable for user requirements and data features so as to apply reduction methods alternatively. To assess the relative performance of the proposed multivariate data reduction methods, we used the conventional techniques, such as Wavelet, HCL(Hierarchical Clustering), Sampling and SVD (Singular Value Decomposition) as well as the experimental data sets, such as multivariate time series, synthetic data and robot execution failure data. The experimental results shows that SVD and Sampling method are superior to Wavelet and HCL ia respect to the relative error ratio and execution time. Especially, since relative error ratio of each data reduction method is different according to data characteristic, it shows a good performance using the selective data reduction method for the experimental data set. The findings reported in this paper can serve as a useful guideline for sensor network application design and construction including multivariate stream data.

• Wind and Structures
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• v.14 no.4
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• pp.301-319
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• 2011

The full-scale measurements are compared with the wind tunnel test results for the long-span roof latticed spatial structure of Shenzhen Citizen Center. A direct comparison of model testing results to full-scale measurements is always desirable, not only in validating the experimental data and methods but also in providing better understanding of the physics such as Reynolds numbers and scale effects. Since the quantity and location of full-scale measurements points are different from those of the wind tunnel tests taps, the weighted proper orthogonal decomposition technique is applied to the wind pressure data obtained from the wind tunnel tests to generate a time history of wind load vector, then loads acted on all the internal nodes are obtained by interpolation technique. The nodal mean wind pressure coefficients, root-mean-square of wind pressure coefficients and wind pressure power spectrum are also calculated. The time and frequency domain characteristics of full-scale measurements wind load are analyzed based on filtered data-acquisitions. In the analysis, special attention is paid to the distributions of the mean wind pressure coefficients of center part of Shenzhen Citizen Center long-span roof spatial latticed structure. Furthermore, a brief discussion about difference between the wind pressure power spectrum from the wind tunnel experiments and that from the full-scale in-site measurements is compared. The result is important fundament of wind-induced dynamic response of long-span spatial latticed structures.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.74-74
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• 2010

One-dimensional nanosturctures such as nanowires and nanotube have been mainly proposed as important components of nano-electronic devices and are expected to play an integral part in design and construction of these devices. Silicon carbide(SiC) is one of a promising wide bandgap semiconductor that exhibits extraordinary properties, such as higher thermal conductivity, mechanical and chemical stability than silicon. Therefore, the synthesis of SiC-based nanowires(NWs) open a possibility for developing a potential application in nano-electronic devices which have to work under harsh environment. In this study, one-dimensional nanowires(NWs) of cubic phase silicon carbide($\beta$-SiC) were efficiently produced by thermal chemical vapor deposition(T-CVD) synthesis of mixtures containing Si powders and hydrocarbon in a alumina boat about $T\;=\;1400^{\circ}C$ SEM images are shown that the temperature below $1300^{\circ}C$ is not enough to synthesis the SiC NWs due to insufficient thermal energy for melting of Si Powder and decomposition of methane gas. However, the SiC NWs are produced over $1300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is about $1400^{\circ}C$ with an average diameter range between 50 ~ 150 nm. Raman spectra revealed the crystal form of the synthesized SiC NWs is a cubic phase. Two distinct peaks at 795 and $970\;cm^{-1}$ over $1400^{\circ}C$ represent the TO and LO mode of the bulk $\beta$-SiC, respectively. In XRD spectra, this result was also verified with the strongest (111) peaks at $2{\theta}=35.7^{\circ}$, which is very close to (111) plane peak position of 3C-SiC over $1400 ^{\circ}C$ TEM images are represented to two typical $\beta$-SiC NWs structures. One is shown the defect-free $\beta$-SiC nanowire with a (111) interplane distance with 0.25 nm, and the other is the stacking-faulted $\beta$-SiC nanowire. Two SiC nanowires are covered with $SiO_2$ layer with a thickness of less 2 nm. Moreover, by changing the flow rate of methane gas, the 300 sccm is the optimal condition for synthesis of a large amount of $\beta$-SiC NWs.