• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2433-2443
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• 1996

In this paper, a new technique is proposed for obtaining the error probabilities of the VSB(vestigial sideband modulation) signal in the presence of the cochannel interference and frequency-selective fading channel. For the receivers, a suboptimal matched filter receiver and the MLSE(maximum likelihood sequence estimation) receiver, which is known to be optimal on the fading channel, are considered. First, for the matched filter receiver, the distributions of the random variables, which determine the SER(symbol error rate) are obtained by decomposing the multi-path fading channel into Rayleigh distributed main path and Gaussian distributed remained path channels. the random variables mean the energy of the main path and subpath respecitively, and SER can be calculated from the distribution of them. Next, for the case of the MLSE receover, it is found that the random variables are expressed as a function of integrals. In order to obtain the distribution for the random variables, we expanded each element of integrals with the KL(Karhunen-Loeve) transformation. And it is derived that the distributions for the transformed random variables are given by a sum of chi-square distributions. Finally, we calculated the error rate derived formula on the two-ray fading channel, which is one of widely used models for the frequency-selective fading channel. From the numerical results, it is found that for the matched filer receiver, performance degradation is significant, while the performance degradation at the MLSE receiver is insignificant on the frequency-selective fading channel. However, in case of cochannel interference environment, the error rateis found to increase significantly both at the matched filter and at the MLSE receiver.

• Journal of Korean Society of Transportation
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• v.33 no.2
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• pp.192-203
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• 2015

Pedestrians not only walk along pedestrian pathways, but also choose unusual routes such as passing through buildings or crossing large scale open spaces. This study defines these unusual paths as social path, and includes them into one of the pedestrian road categories. Previous pedestrian accessibility and route choice studies could not evaluate correctly the space connectivity or optimal route because the social path was not considered properly. Therefore, this study analyzes the effectiveness of the social path in view of space connectivity focused on Coex and Seoul stations in Seoul, which are representative transit oriented development(TOD) areas. Global integration, which is widely used in network analysis, is selected (as performance index) to identify the space hierarchy and define new pedestrian links. The study results show that the network connectivity is improved especially in the main streets and social paths. This study demonstrated that the social path should be considered in finding the pedestrian optimal route from the practical perspective.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.5
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• pp.824-830
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• 2010

It is not easy job to find a underwater target using sonar system in the ASW operations. Many researchers have tried to solve anti-submarine search problem aiming to maximize the probability of detection under limited searching conditions. The classical 'Search Theory' deals with search allocation problem and search path problem. In both problems, the main issue is to prioritize the searching cells in a searching area. The number of possible searching path that is combination of the consecutive searching cells increases rapidly by exponential function in the case that the number of searching cells or searchers increases. The more searching path we consider, the longer time we calculate. In this study, an effective algorithm that can maximize the probability of detection in shorter computation time is presented. We show the presented algorithm is quicker method than previous algorithms to solve search problem through the comparison of the CPU computation time.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.208-214
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• 2000

Reduction of structure-borne noise of the compartment in a car is an important task in automotive engineering. Transfer path analysis using vibroacoustic reciprocity technique or multiple path decomposition method has generally been used for structure-borne noise path analysis. These methods are useful in solving particular problem but do not quantify the effectiveness of vibration isolation of each isolator of a vehicle. To quantify the effectiveness of vibration isolation, the vibrational power flow has been used for a simple isolation system or a laboratory based isolation system. It is often difficult to apply the vibrational power flow technique to the complex isolation system like a car. In this paper, a simple equation is derived for calculation of the vibrational power flow of an isolation system with multiple isolators such as a car. It is successfully applied to not only quantifying the relative contributions of eighteen isolators but also reducing structure-borne noise of a passenger car. According to the results, the main contributor of eighteen isolators is the rear roll mount of an engine. The reduced structure-borne noise level is about 5dBA.

• The Journal of the Korea Contents Association
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• v.14 no.10
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• pp.562-569
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• 2014

The purpose of this study was to investigate the determinants of total payment for mental and behavioral disorders patients admitted through the emergency room. Study data was selected from the Korean National Health Insurance sample data in 2009. This data was consisted of 753 inpatients who are 331 inpatients with only main sick(F31-F39) and 422 inpatients with main sick codes(F31-F39) and sub sick(F00-F99) admitted through the emergency room. SPSS v.18 was used for the statistical analysis such as descriptive analysis, t-test, ANOVA, and multiple regression analysis. In multiple regression analysis, significant variables affecting total payment of main sick patients were gender(p<.01), treatment result(p<.001), path of the emergency room(p<.001), and length of stay(p<.001). Also, main sick patients with sub sick were gender(p<.01), age(p<.001), treatment result(p<.001), path of the emergency room(p<.001), and length of stay(p<.001). These findings implied that it is necessary to build short, middle, and longterm program and system for high risk mental and behavioral disorders groups.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.183-188
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• 2003

This study is to make the fundamentals of sound quality evaluation in regard of acoustical characteristics of passenger compartment. The deviation of frequency response function level within audible frequency is evaluated at receiving point in the research of room acoustics. In this study, frequency response function is the one between speaker and driver's ear positions. The positions of driver and audio speakers are optimized by analysis of acoustic mode of acoustic cavity. The main reflection planes are determined by analysis sound ray path diffused at optimized speaker positions. Finally, designer selects acoustical material by analysis of absorption effect of acoustical materials on the main reflection planes in order to avoid to distortion and fluctuation of frequency response function..

• Korean Management Science Review
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• v.27 no.2
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• pp.1-20
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• 2010

Many firms are trying to acquire innovative technologies and relative knowledge by offshoring R&D work. Although research to date has focused on the multinational corporations' motivations of R&D offshoring, such as cost reduction and market expansion, little is known about external or environmental factors influencing the performance of global R&D activities. We investigated the relationship between the offshore R&D performance and the technical capabilities of the parent company, the host country and the home country as enhancers from outside R&D facilities. The analysis uses European patent data and EU R&D scoreboard of 134 overseas R&D labs from 46 multinational corporations in 2005. Also, we calculated total patent number of each country for this. Results from path analysis supported our main hypothesis that the technological capabilities of the parent company and the host country positively affect the overseas R&D performances. By multi-group analysis, we also found that the relationships among the variables are different for each industry.

• International Journal of Automotive Technology
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• v.4 no.1
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• pp.21-30
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• 2003

In this paper a systematic test procedure for evaluation of road-induced noise of a vehicle and guidelines for each test are presented. Also, a practical application of the test procedure to a small SUV is presented. According to the test procedure, all the tests were performed to evaluate road-induced booming noise that is in low frequency range. First of all the information on characteristics of road-induced noise was obtained through baseline test. Coupling effects between body structure and acoustic cavity of a compartment were obtained by means of modal tests for a structure and an acoustic cavity. Local stiffness of joint areas between chassis system and car-body was determined by test for measurement of input point inertance. Noise sensitivities of body joints to operational forces were obtained through test for measurement of noise transfer functions. Operational deflection shapes made us analyze behaviors of chassis system under running condition and then find sources of noise due to resonance of the chassis system. Finally, Principal Component Analysis and Transfer Path Analysis were utilized to investigate main paths of road-induced noise. In order to evaluate road-induced booming noise exactly, all of tests mentioned above should be performed systematically.

• Journal of Information Technology Services
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• v.17 no.4
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• pp.37-52
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• 2018

With the increasing severity of the shortage of highly-skilled IT personnel, more and more attention is being paid to the professional career path and systematic career management of IT employees. Although some studies have been conducted to describe the current status of IT personnel, limited attempts have been made to analyze the career paths or career patterns of IT professionals from a longitudinal perspective. In this context, this study explored the job career patterns of IT professionals in Korea and examined their relationship with subjective and objective career success. To identify job career patterns over time, detailed information about jobs and positions were used and an optimal matching analysis (OMA) was conducted to calculate the dissimilarity matrix between employees' career sequences, while a cluster analysis was used to categorize the meaningful groups based on this dissimilarity data. This analysis revealed that career patterns among Korean IT personnel are more varied than previously thought. These career types have a significant relationship with individual profiles, such as age, education, industry and company size, and account for significant variations in the three main career success variables, i.e. quality of life, assessment of software quality, and wage level. It is expected that the findings of this study will contribute to refining the Korean career path so as to retain IT personnel, and raise the need to improve the low quality of life and poor SW work environment of IT personnel.

• Computers and Concrete
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• v.29 no.1
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• pp.1-14
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• 2022

Several aspects influence corrosive processes in reinforced concrete (RC) structures such as environmental conditions, structural geometry and mechanical properties. Since these aspects present large randomnesses, probabilistic models allow a more accurate description of the corrosive phenomena. Besides, the definition of limit states in the reliability assessment requires a proper mechanical model. In this context, this study proposes a straightforward methodology for the mechanical-probabilistic modelling of RC structures subjected to reinforcements' corrosion. An improved damage approach is proposed to define the limit states for the probabilistic modelling, considering three main degradation phenomena: concrete cracking, rebar yielding and rebar corrosion caused either by chloride or carbonation mechanisms. The stochastic analysis is evaluated by the Monte Carlo simulation method due to the computational efficiency of the Lumped Damage Model for Corrosion (LDMC). The proposed mechanical-probabilistic methodology is implemented in a computational framework and applied to the analysis of a simply supported RC beam and a 2D RC frame. Curves illustrate the probability of failure evolution over a service life of 50 years. Moreover, the proposed model allows drawing the probability of failure map and then identifying the critical failure path for progressive collapse analysis. Collapse path changes caused by the corrosion phenomena are observed.