• Journal of Korea Spatial Information System Society
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• v.11 no.1
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• pp.115-126
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• 2009

Recent development in wireless communication and mobile positioning technologies makes Location-Based Services (LBSs) popular. However, because, in the LBSs, users request a query to database servers by using their exact locations, the location information of the users can be misused by adversaries. Therefore, a mechanism for users' privacy protection is required for the safe use of LBSs by mobile users. For this, we, in this paper, propose a efficient cloaking region creation scheme using Hilbert curves in distributed grid environment, so as to protect users' privacy in LBSs. The proposed scheme generates a minimum cloaking region by analyzing the characteristic of a Hilbert curve and computing the Hilbert curve values of neighboring cells based on it, so that we may create a cloaking region to satisfy K-anonymity. In addition, to reduce network communication cost, we make use of a distributed hash table structure, called Chord. Finally, we show from our performance analysis that the proposed scheme outperforms the existing grid-based cloaking method.

• The Korean Journal of Applied Statistics
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• v.27 no.2
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• pp.249-261
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• 2014

Ever increasing "Big data" can only be effectively processed by parallel computing. Parallel computing refers to a high performance computational method that achieves effectiveness by dividing a big query into smaller subtasks and aggregating results from subtasks to provide an output. However, it is well-known that parallel computing does not achieve scalability which means that performance is improved linearly by adding more computers because it requires a very careful assignment of tasks to each node and collecting results in a timely manner. Hadoop is one of the most successful platforms to attain scalability. In this paper, we propose a measurement for Hadoop optimization by utilizing a Lorenz curve which is a proxy for the inequality of hardware resources. Our proposed index takes into account the intrinsic overhead of Hadoop systems such as CPU, disk I/O and network. Therefore, it also indicates that a given Hadoop can be improved explicitly and in what capacity. Our proposed method is illustrated with experimental data and substantiated by Monte Carlo simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.1
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• pp.108-114
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• 2012

We propose a dispersive finite-difference time domain(FDTD) algorithm suitable for the electromagnetic analysis of the human body. In this work, the dispersion relation of the human body is modeled by a quadratic complex rational function(QCRF), which leads to an accurate and efficient FDTD algorithm. Coefficients(involved in QCRF) for various human tissues are extracted by applying a weighted least square method(WLSM), referred to as the complex-curve fitting technique. We also presents the FDTD formulation for the QCRF-based dispersive model in detail. The QCRFbased dispersive model is significantly accurate and its FDTD implementation is more efficient than the counterpart of the Cole-Cole model. Numerical examples are used to show the validity of the proposed FDTD algorithm.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.10
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• pp.1028-1033
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• 2009

To detect faults and monitor thinning on a pipe, many people use ultra sonic sensors that are operated in high frequency range. Because there are many modes in high frequency range, it is difficult to find faults and monitor pipe thinning on a structure. If we deal with signals in a low frequency range which include only A0 wave and S0 wave, the information of monitoring and diagnosis can be easily obtained. In this paper, the technique for exciting low frequency range using ultra sonic sensors is proposed. The main idea of the proposed method comes from the beat phenomenon. The beat frequency is equal to the absolute value of the difference in frequency of the two waves. If the beat frequency is tuned by two ultra waves, we can excite A0 mode and S0 mode of structures. To verify the proposed method, we have performed a steel plate and pipe experiments. Experimental results show that two ultra sonic sensors can well excite low frequency range.

• Journal of Digital Convergence
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• v.16 no.3
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• pp.157-167
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• 2018

The shortage of research in Vietnam port evolvement is uncontroversial although a huge amount of investment is observed to upgrade both quantity and quality. This study examines the port system performance, in the context of spatially concentration ratio, in Southern Vietnam for the period 2007-2016, by using prevailing indicators for spatially concentration assessment including concentration ratios (CR), the Herfindahl-Hirschman index (HHI), the Gini coefficient, the Lorenz curve and shift-share analysis (SSA), a trend of deconcentration is described in Southern Vietnam port system, since the traditional ports to new deep-water ports. Also, driving forces of this shifting would be discussed in detail. Implications from this study would enable not only port administrators, port operators but also shipping lines, cargo owners, logistics service providers to comprehensively understand the growth of the port system in Southern Vietnam.

• Journal of Digital Convergence
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• v.16 no.9
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• pp.107-114
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• 2018

Since China's economic reform in 1978, international trade has enormously flourished and the port industry is reckoned as a key factor contributing to this growth. This study examines the Bohai Rim port group in the scope of top three largest ports Qingdao, Dalian and Tianjin. By utilizing indicators including concentration ratio (CR), Herfindahl-Hirschman index (HHI), the Gini coefficient and the Lorenz curve as well as shift-share analysis (SSA), the concentration level of this port group in the period 2004-2016 is discussed. As a results, CR demonstrates a decrease during the studied period with a minor fluctuation, and HHI index shows a trend of deconcentration with Bohai Rim port group. In addition, SSA indicates that during the period 2004-2016, the overall shift index of Qingdao port was -1.371 meanwhile with Tianjin and Dalian port were 0.118 and 1.252 in turn. These results suggest that the growth in regional influence of Tianjin and Dalian ports would motivate to the deconcentration pattern in Bohai Rim region. The findings assist decision makers and scholars to obtain knowledge about the port development this region. Considering the geographic position of these three ports as the gate of northeast China, it is suggested that these three ports could explore their advantages and cooperate with the small ports in the surrounding area to enhance their influences in the future study.

• Journal of Broadcast Engineering
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• v.15 no.2
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• pp.290-303
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• 2010

Recently, researches to improve a quality and a color of a display are being actively studied because of the prosperous growth of the flat panel displays such as LCD, PDP and OLED. Automatically adjusting color temperatures based on user preferences is the one of the researches to provide the optimum display color. In this paper, along with defining the problems of prior methods, the user preferences against the priori defined ranges proposed by the MPEG-7 color temperature descriptor are inspected. Based on the analysis of user preferences, an optimal color temperature conversion curve is proposed. As a result of an analysis by ANOVA, tendencies of the user preferences against each range are proven to be similar to the prior research results. The repetition of the color temperature conversion against an image is not statistically significant.

• Journal of the HCI Society of Korea
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• v.14 no.2
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• pp.21-29
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• 2019

Take-over requests in semi-autonomous cars must be handled properly in the case of road obstacles or curved roads in order to avoid accidents. In these situations, situation awareness and appropriate decision making are essential for distracted drivers. This study used a driving simulator to investigate the components of auditory-visual information systems that affect safety, workload, and trust. Auditory information consisted of either voice guidance providing situation awareness for the take-over or a beep sound that only alerted the driver. Visual information consisted of either a screen showing how to maneuver the vehicle or only an icon indicating a take-over situation. By providing auditory information that increased situation awareness and visual information that aided decision making, trust and safety increased, while workload decreased. These results suggest that the levels of situation awareness and decision making ability affect trust, safety, and workload for drivers.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.3
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• pp.1-17
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• 2018

Over the past five years (2010-2014), the total number of traffic accidents has decreased from 226,878 to 223,552 with decrease of 0.37 percent each year. The death toll has also decreased from 5,505 to 4,762. However, the number of rental car accidents and fatalities has been steadily increased. Despite of its growth, no previous study has been conducted on rental car accident severity. This study analyzed data of 18,050 rental car accidents in South Korea collected from 2010 to 2014 and then processed in order to identify which factors could affect the accident severity. Seventeen factors related to rental car accident severity were grouped into four categories: driver, vehicle, roadways and environment. As a result of the ordered probit model analysis, fourteen variables excluding age, intersection, and day of week were found to affect the severity of rental car accidents. The results of the study summarized as follows. First of all, violation of traffic regulations such as speeding increase the severity of rental car accidents. Secondly, rental accident severity is higher at curved sections of complicated roadway, which the driver's field of view is impaired. The results of this study can be used to reduce the severity of rental car accidents in transportation safety.