• Proceedings of the IEEK Conference
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• summer
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• pp.302-309
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• 2004

The transmission capacity of wireless communication systems may become dramatically high by employ multiple transmit and receive antennas with space-time coding techniques appropriate to multiple transmit antennas. For large number of transmit antennas and at high bandwidth efficiencies, the receiver may become too complex whenever correlation across transmit antennas is introduced. Reducing decoding complexity at receiver by combining array processing and space-time codes (STC) helps a communication system using STC to overcome the big obstacle that prevents it from achieving a desired high transmission rate. Multi-carrier CDMA (MC-CDMA) allows providing good performance in a channel with high inter-symbol interference. Antenna array, STC and MC-CDMA system have a similar characteristic that transmit-receive data streams are divided into sub-streams. Thus, there may be a noticeable reduction of receiver complexity when we combine them together. In this paper, the combination of array processing and STC in MC-CDMA system over slow selective-fading channel is investigated and compared with corresponding existing MC-CDMA system using STC. A refinement of this basic structure leads to a system design principle in which we have to make a trade off between transmission rate, decoding complexity, and length of spreading code to reach a given desired design goal.

• Computers and Concrete
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• v.2 no.6
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• pp.439-454
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• 2005

When deterioration of concrete is observed in a structure, it is highly desirable to determine the cause of such deterioration. Only by understanding the cause can an appropriate repair strategy be implemented to address both the cause and the symptom. In colder climates, bridge deck deterioration is often caused by chlorides from de-icing salts, which penetrate the concrete and depassivate the embedded reinforcement, causing corrosion. Bridge decks can also suffer from other deterioration mechanisms, such as alkali-silica reaction, freeze-thaw, and shrinkage. There is a need for a comprehensive and integrative system to help with the inspection and evaluation of concrete bridge deck deterioration before decisions are made on the best way to repair it. The purpose of this research was to develop a model to help with the diagnosis of concrete bridge deck deterioration that integrates the symptoms observed during an inspection, various deterioration mechanisms, and the probability of their occurrence given the available data. The model displays the diagnosis result as the probability that one of four deterioration mechanisms, namely shrinkage, corrosion of reinforcement, freeze-thaw and alkali-silica reaction, is at fault. Sensitivity analysis was performed to determine which probabilities in the model require refinement. Two case studies are included in this investigation.

• Wind and Structures
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• v.24 no.3
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• pp.223-247
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• 2017

By using numerical simulation, vast and detailed information and observation of the physics of flow over a train model can be obtained. However, the accuracy of the numerical results is questionable as it is affected by grid convergence error. This paper describes a systematic method of computational grid refinement for the Unsteady Reynolds Navier-Stokes (URANS) of flow around a generic model of trains using the OpenFOAM software. The sensitivity of the computed flow field on different mesh resolutions is investigated in this paper. This involves solutions on three different grid refinements, namely fine, medium, and coarse grids to investigate the effect of grid dependency. The level of grid independence is evaluated using a form of Richardson extrapolation and Grid Convergence Index (GCI). This is done by comparing the GCI results of various parameters between different levels of mesh resolutions. In this study, monotonic convergence criteria were achieved, indicating that the grid convergence error was progressively reduced. The fine grid resolution's GCI value was less than 1%. The results from a simulation of the finest grid resolution, which includes pressure coefficient, drag coefficient and flow visualization, are presented and compared to previous available data.

• Journal of Korean Society for Quality Management
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• v.44 no.1
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• pp.109-120
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• 2016

Purpose: This study developed a method of determining priorities for evaluating and revising defense standards. Methods: The proposed data integration and refinement methods are used to obtain component reliability information and to determine the frequency of component citation based on Pareto analysis. Based on the reliability information and the frequency of cited components, the target components for quality improvement can be determined and improved using various methods, such as engineering changes, special meetings, additional training, and revising the maintenance manual. Results: Based on the proposed process, we identified components that need to be improved in order to enhance the quality and reliability. Conclusion: Our process will improve the quality and reliability of weapon systems. The proposed process can be adopted for various weapon systems to enhance their quality and reliability, and to reduce military spending.

• Transactions of Materials Processing
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• v.21 no.4
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• pp.240-245
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• 2012

With the increasing demand for light-weight materials to reduce fuel consumption, the automobile industry has extensively studied magnesium alloys which are light weight metals. The intrinsic poor formability and poor ductility at ambient temperature due to the hexagonal close-packed (HCP) crystal structure and the associated insufficient number of independent slip systems restricts the practical usage of these alloys. Hot working of magnesium alloys using a forging or extrusion enables net-shape manufacturing with enhanced formability and ductility since there are several operative non-basal slip systems in addition to basal slip plane, which increases the workability. In this research, the thermomechanical properties of AZ80 Mg alloy were obtained by compression testing at the various temperatures and strain rates. Optical microscopy and EBSD were used to study the microstructural behavior such as misorientation distribution and dynamic recrystallization. The results were correlated to the hardening and the softening of the alloy. The experimental data in conjunction with a physical explanation provide the optimal conditions for net-shape forging under hot or warm temperatures through control of the grain refinement and the working conditions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.358-361
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• 2004

This paper describes the development process of high stiffness body for ride and handling performance. High stiffness and light weight vehicle is a major target in the refinement of passenger cars to meet customers' contradictable requirements between ride and handling performance and fuel economy. This paper describes the analysis approach process for high stiffness body through the data level of body stiffness. According to the frequency band, we can suggest the design guideline about Is cornering static stiffness, torsional and lateral stiffness, body attachment stiffness. The ride and handling characteristic of a vehicle is significantly affected by vibration transferred to the body through the chassis mounting points from front and rear suspension. It is known that body attachment stiffness is an important factor of ride and handling performance improvement. And high stiffness helps to improve the flexibility of bushing rate tuning between Handling and road noise. It makes it possible to design the good handling performance vehicle at initial design stage and save vehicles to be used in tests by using mother car at initial design stage. These improvements can lead to shortening the time needed to develop better vehicles.

• Bulletin of the Korean Chemical Society
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• v.11 no.1
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• pp.15-19
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• 1990

The crystal structure of $(C_{12}H_{24}O_6{\cdot}K)_2K[Co(OH)_6Mo_6O_{18}]{\cdot}12H_2O$ has been determined by X-ray diffraction. Crystal data as follows ; monoclinic, space group $C_2/m,\;a\;=\;22.512(4)\;{\AA},\;b\;=\;18.304(4)\;{\AA},\;c\;=\;7.641(1)\;{\AA},\;{\beta}\;=\;90.52(2)\;{\AA}$, and Z = 2. A final conventional R value of 0.044 was obtained by least-squares refinement of 4173 independent observed $[{\mid}Fo{\mid}{\geq}3{\sigma}({\mid}Fo{\mid})]$ reflections. The $[Co(OH)_6Mo_6O_}{18}]^{-3}$ polyanion shows the well-known Anderson-structure and has approximate 3m symmetry. A $[Co(OH)_6Mo_6O_{18}]^{-3}$ polyanion is located between two crown ether complexed cations forming a sandwich structure. One potassium ion interacts with the crown ether via electrostatic interactions. The other potassium ion only interacts with the water molecules and terminal oxygen atoms of the polyanion.

• Bulletin of the Korean Chemical Society
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• v.19 no.4
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• pp.457-462
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• 1998

A chiral pentadentate bis-amide ligand, 1,9-bis(S)-pyrrolidinyl-2,5,8-triazanonane-1,9-dio ne$(S,S-prodienH_2)$ has been synthesized from the reaction of bis(2-aminoethyl)amine(dien) and S-proline, and the structure of $[Co(S,S-prodien)H_2O]ClO_4$ has be en determined by single crystal X-ray diffraction. The geometrical structure of the Co(III) complex has been an αβ -form, where the dien moiety of ligand chelates to a facial in metal center, and the aqua ligand coordinates a cis site to the secondary nitrogen of dien. The Co-N(1), Co-N(3) distances of two amide moiety in S,S-prodien are shorter than the other Co-N(2), Co-N(4), and Co-N(5) distances because of the increased basicity of nitrogen in amide. The complex crystallizes in the monoclinic space group $P2_1$(#4), with a=7.838(1), b=12.675(1), c=9.710(1) Å, β=100.39(1) and z=2. Refinement gives the final R and $R_w$ values of 0.045 and 0.057, respectively for 2130 observed reflections. Based upon the CD and X-ray data, it is identified that the absolute configuration of the αβ -$[Co(S,S-prodien)H_2O]ClO_4$ has a Λ-form.

• Bulletin of the Korean Chemical Society
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• v.12 no.2
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• pp.214-219
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• 1991

To study the effect of solvents and counterions in Z-DNA crystal of d(5BrC-G-5BrC-G-5BrC-G), we performed the local energy analysis and then molecular dynamics simulations. Since counterions raise serious caging problems in crystal simulations, it is very important to search for the possible positions before simulations. For this purpose, the local energy analysis was done for the whole crystal volume. It is shown from our simulation that counterions along with water molecules play a bridging role to bind adjacent oligomers so as to form the crystal. In this crystal, each water molecule bound to Gua-N2H, either directly or indirectly, hydrates the adjacent anionic phosphate oxygen, and thus assists Gua to be in a syn position. From the simulation, the average root-mean-square deviation of allthe DNA heavy atom coordinates from the X-ray data is $0.99{\AA}$ . The bases are less deviated from the X-ray positions than the phosphates. The temperature factors from the simulation are consistent with those from the X-ray refinement, showing that the phosphates are more mobile than the bases.

• Communications for Statistical Applications and Methods
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• v.27 no.6
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• pp.603-624
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• 2020

There is an emerging interest in brain functional connectivity (FC) based on functional Magnetic Resonance Imaging in Alzheimer's disease (AD) studies. The complex and high-dimensional structure of FC makes it challenging to explore the association between altered connectivity and AD susceptibility. We develop a pipeline to refine FC as proper covariates in a penalized logistic regression model and classify normal and AD susceptible groups. Three different quantification methods are proposed for FC refinement. One of the methods is dimension reduction based on common component analysis (CCA), which is employed to address the limitations of the other methods. We applied the proposed pipeline to the Alzheimer's Disease Neuroimaging Initiative (ADNI) data and deduced pathogenic FC biomarkers associated with AD susceptibility. The refined FC biomarkers were related to brain regions for cognition, stimuli processing, and sensorimotor skills. We also demonstrated that a model using CCA performed better than others in terms of classification performance and goodness-of-fit.