• Journal of Korean Society of Industrial and Systems Engineering
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• v.31 no.3
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• pp.125-130
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• 2008

Multivariate analysis is a rapidly expanding approach to data analysis. One specific technique in multivariate analysis is Principal Component Analysis (PCA). PCA is a statistical technique that linearly transform a given set of variables into a new set of composite variables. These new variables are orthogonal to each other and capture most of the information in the original variables. PCA is used to reduce the number of control points to be checked by measurement system. Therefore, the structure of the data set is simplified significantly It is also shown that eigenvectors obtained by conducting principal component analysis on the basis of the covariance matrix can be used to physically interpret the pattern of relative deformation for the points. This case study reveals the twisting deformation pattern of the underbody which is the largest mode of the total variation.

• STI Policy Review
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• v.6 no.2
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• pp.105-145
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• 2015

Science, technology and innovation (STI) is crucially important to eradicating poverty, and making advances in various areas such as agriculture, health, environment, transport, industry, and telecommunications. Therefore, it is vital to the overall socioeconomic development of nations. The indispensable role of STI in the competitive globalized economy led to several attempts to measure national STI capacities. The present study outlines STI capacity around three sets of capabilities: technological capabilities, social capabilities, and common capabilities. The Global Science, Technology and Innovation Capacity (GSTIC) index was developed to provide current evidence on the national STI capacities of the countries, and to improve the composite indicators used for such purposes. The GSTIC ranks a large number of countries (167) on the basis of their STI capacities and categories them into four groups: i.e. leaders, dynamic adopters, slow adopters, and laggards. For more meaningful assessment of the STI capacities of nations, it captures the achievement gaps of individual countries with the highest achiever. The study also provides ranking and achievement gaps of nations in the nine GSTIC pillars: technology creation, R&D capacity, R&D performance, technology absorption, diffusion of old technologies, diffusion of recent innovations, exposure to foreign technology, human capital, and enabling factors. A more detailed analysis of the strengths and weaknesses in different pillars of STI capacity of ten selected countries is also provided. The results show that there are significant disparities among nations in STI capacity and its various aspects, and developing countries have much to catch-up with the developed nations. However, different countries may adopt different strategies according to their strengths and weaknesses. Useful insight into the strengths and weaknesses of the national STI capacities of different countries are provided in the study.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.58.1-58.1
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• 2011

WC-Co and other similar cemented carbides have been widely used as hard materials in industrial cutting tools and as mould metals; and a number of techniques have been applied to improve its microstructural characteristics, hardness and ear resistance. Cobalt is used primarily to facilitate liquid phase sintering and acts as a matrix, i.e. a cementing phase between WC grains. A uniform distribution of metal phase in a ceramic is beneficial for improved mechanical properties of the composite. WC-Co, starting from initial powders, is vastly used for a variety of machining, cutting, drilling, and other applications because of its unique combination of high strength, high hardness, high toughness, and moderate modulus of elasticity, especially with fine grained WC and finely distributed cobalt. In this study, that started with two different compositions of initial powders, WC-7.5wt%Co and WC-12wt%Co with initial powder size being 1~3 ${\mu}m$, magnetic pulsed compaction followed by subsequent vacuum sintering were carried out to produce consolidated preforms. Magnetic Pulsed Compaction (MPC), a very short duration (~600 ${\mu}s$), high pressure (~4 Gpa), high-density preform molding method was used with varied pressure between 0.5 and 3.0 Gpa, in order to reach an initial high density that would help improve the sintering behavior. For both compositions and varied MPC pressure, before and after sintering, changes in microstructural behavior and mechanical properties were analyzed. With proper combination of MPC pressure and sintering, samples were obtained with better mechanical properties, densification and microstructural behavior, and considerably improved than other conventional processes.

• Journal of Digital Convergence
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• v.16 no.4
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• pp.267-276
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• 2018

The purpose of the study was to provide basic data for planning and offering nursing intervention to prevent suicide attempts by identifying the factors influencing the suicidal thoughts of depressed adults. The subjects of this study were 1,202 individuals who answered clearly in 2013-2015 National Health and Nutrition Survey. A composite sample plan file was generated using the IBM SPSS 23.0 program, and then the data were weighted and analyzed. Suicidal ideation was influenced by income (50-60s), number of family members (50-60s), marital status (40-50s), subjective health (30-50s, over 70s), stress (30s, over 50s), economic activity status (50s), diabetes (60s or older), alcohol consumption (60s), and Body Mass Index (BMI) (40s). These results suggest that tailor-made interventions for the prevention of suicide need to take into account the general and health-related factors of the subjects.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.101-108
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• 2013

In this paper, we propose a method in which the negative acknowledge (NACK) message is used as command for cooperation and spectrum sharing. This allows for an automatic request for cooperation and sharing when the direct link of the primary user is in outage, and also allows for saving the number of control messages in cooperation-spectrum sharing based paradigm. In the sharing phase, the selected relay shares a power fraction of $1-{\alpha}$ for secondary transmitted signal while the remaining of ${\alpha}$ is for primary retransmitted signal. In the case of no relay collected, primary transmitter uses NACK as a command to retransmit the signal with fully power fraction (${\alpha}=1$). Both systems are assumed to employ BPSK signals. In this scheme, we propose the joint optimal decoding in the secondary user. The frame error rate (FER) performance at both systems is then analyzed. The theoretical and simulation results validate the analysis and confirm the efficiency of the protocol.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.245-259
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• 2003

This paper deals with an Umbrealla Arch Reinforcement Method (UARM) in tunnelling. It is known that the mechanism of the reinforcement system is too complex to be simulated in existent finite element (FE) frameworks when considering its complex geometry of pipe arrangements and contribution of each component of the reinforcement to reinforcing effect. In this study a 3-D elastoplastic FE procedure is, therefore, proposed by introducing homogenisation technique, which is used to define mathematically elastic as well as elastoplastic characteristics of a reinforced ground material as a composite. A number of practical suggestions are addressed considering staged constructions of tunnels. For illustrative purposes, a series of parametric studies are undertaken and anisotropic characteristics of the reinforced ground as well as effects of the reinforcement on tunnel convergences are investigated. It is found that the reinforced ground material defined in homogenisation framework has its mechanical characteristics reasonably representing inherent geometrical and quantitative characteristics of each of constituents.

• Composites Research
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• v.15 no.6
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• pp.1-7
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• 2002

In VARTM process where a sacrificial medium is used to facilitate the resin flow, the velocity of resin varies drastically between the sacrificial medium and the fiber preform. Although the thickness-to-length ratio of a VARTM product is usually small, a 3-D analysis is prerequisite to analyze the lead-lag flow in the two different media. The problem associated with the full 3-D analysis is the CPU time. A full 3-D numerical mesh comprising large number of nodes requires an impractical CPU time on average computer platforms. In this study, a dual-scale analysis technique was developed. The flow analysis for the entire calculation domain was conducted in 2.5-D, and the 3-D analysis was performed for a small area of special concern. In some numerical examples, the local 3-D analysis could discover an eccentric flow pattern as well as the lead-lag flow that will inevitably be neglected in 2.5-D simulations. The global-local analysis technique practiced in this study can be used to analyze the intricate flow of resin through non-uniform media in affordable CPU times.

• The Journal of the Korea Contents Association
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• v.11 no.1
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• pp.422-428
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• 2011

This paper presents results from the theoretical analysis of the lateral load distribution for a railway bridge designed with PSC girders which is one of most popular types of bridge in Korea. Typically, 3 sets of intermediate cross beams within a span have been installed for lateral load distribution. In this paper, the effect on the lateral load distribution by the number of intermediate cross beams were examined by both simple grillage analysis and finite element method. This study showed that at least, one set of cross beams at midspan should be needed to ensure the proper load distribution. However, the effect of cross beams on the load distribution becomes not significant though more than one set of cross beams are installed. Therefore, only one set of cross beans at midspan is recommended for constructibility and economic efficiency.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.39-46
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• 2008

The end plates of fuel cell assemblies are used to fasten the inner stacks, reduce the contact pressure, and provide a seal between Membrane-Electrode Assemblies (MEAs). They therefore require sufficient mechanical strength to withstand the tightening pressure, light weight to obtain high energy densities, and stable chemical/electrochemical properties, as well as provide electrical insulation. The design criteria for end plates can be divided into three parts: the material, connecting method, and shape. In the past, end plates were made from metals such as aluminum, titanium, and stainless steel alloys, but due to corrosion problems, thermal losses, and their excessive weight, alternative materials such as plastics have been considered. Composite materials consisting of combinations of two or more materials have also been proposed for end plates to enhance their mechanical strength. Tie-rods have been traditionally used to connect end plates, but since the number of connecting parts has increased, resulting in assembly difficulties, new types of connectors have been contemplated. Ideas such as adding reinforcement or flat plates, or using bands or boxes to replace tie-rods have been proposed. Typical end plates are rectangular or cylindrical solid plates. To minimize the weight and provide a uniform pressure distribution, new concepts such as ribbed-, bomb-, or bow-shaped plates have been considered. Even though end plates were not an issue in fuel cell system designs in the past, they now provide a great challenge for designers. Changes in the materials, connecting methods, and shapes of an end plate allow us to achieve lighter, stronger end plates, resulting in more efficient fuel cell systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.881-889
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• 2010

A volume integral equation method (VIEM) is introduced for solving the elastostatic problems related to an unbounded isotropic elastic solid; this solid is subjected to remote uniaxial tension, and it contains multiple interacting isotropic inclusions. The method is applied to two-dimensional problems involving long parallel cylindrical inclusions. A detailed analysis of the stress field at the interface between the matrix and the central inclusion is carried out; square and hexagonal packing of the inclusions are considered. The effects of the number of isotropic inclusions and different fiber volume fractions on the stress field at the interface between the matrix and the central inclusion are also investigated in detail. The accuracy and efficiency of the method are clarified by comparing the results obtained by analytical and finite element methods. The VIEM is shown to be very accurate and effective for investigating the local stresses in composites containing isotropic fibers.