• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.240-247
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• 2004

In order to transmit data at high speed in the wireless environment, OFDM is selected as the transmission method of various high-speed wireless communication system since it has the advantage to deal easily the serious selective frequency fading channel by the multiple path. We evaluate STBC-OFDM and linear STBC-OFDM combining with a class of recently proposed linear scalable space-time block codes and OFDM in MIMO channel environments, and demonstrate the performance for spatial multiplexing and diversity gain. The codes are able to use jointly transmit diversity in combination with spatial multiplexing, and achieve spatial and temporal diversity. Frequency diversity of frequency selective channels can be utilized by combining the linear STBC and OFDM. Simulation results are shown to demonstrate the better performance of proposed approach in comparison with STBC-OFDM.

• Journal of the Korea Society of Computer and Information
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• v.11 no.2 s.40
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• pp.177-186
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• 2006

This paper presents the development of a certain highly efficient authoring tool for constructing realistic 3D virtual space using image-based rendering techniques based on a virtual space map. Unlike conventional techniques such as TIP, for constructing a small 3D virtual space using single image, the authoring tool developed herein produces a wide 3D virtual space using multiple images. This tool is designed for constructing each small 3D virtual space for each input image, and for interconnecting these 3D virtual spaces into a wide 3D virtual space using a virtual space map. The map consists of three elements such as specific room, link point and passageway, and three directions. It contains various information such as the connection structure, the navigation information and so on. Also, the tool contains a user interface that let users construct the wide 3D virtual space easily.

• The Journal of the Korea Contents Association
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• v.10 no.12
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• pp.290-299
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• 2010

This study aims to evaluate the efficiency of superior appraisal corporations using DEA(Data Envelopment Analysis). DEA is known as a method for evaluating relative efficiency of organizations with multiple inputs and outputs. We used CCR-O and BCC-O DEA models to evaluate relative efficiency of superior appraisal corporations. Input variable is number of appraisers, output variables are total sales and net income. Total of 13 appraisal corporations in Korea were selected for this study, and the data were collected from financial reports for 2008 fiscal year. The result of this study is summarized as follows. First, the average of superior appraisal corporation's technical efficiency score is about 88.3% by applying CCR-O model. Second, the average of superior appraisal corporation's pure technical efficiency score is about 90% and scale efficiency score is about 98.2% by applying BCC-O model. According to the result of DEA, the cause of inefficiency is pure technical efficiency.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.1 s.24
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• pp.47-56
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• 2007

The parameters are determined analyzing the hydraulic and hydrological characteristics of design floods, watershed, channel length, and river bed slope. The models are calibrated while the input hydrologic data are the field data of middle size areas in Guem river basin in Korea. The basic equations of design width are suggested by the multiple regression analysis and the results show excelled in comparisons as well as calibrations with the existing empirical formulas and the design criteria, respectively. The basic equations of design width in validation process is determined the regression functions with the design floods, watershed, channel length, river bed slope as the four parameters using other database in the same scales watershed. As a results, this study will be used for apply to determine of design width and river alignmentof the watershed in hydraulic fields.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.7
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• pp.945-951
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• 2007

Noise cancellation is essential for the devices which use speech as an interface. In real environments, speech quality and recognition rates are degraded by the auditive noises coming near the microphone. In this paper, we propose a noise cancellation algorithm using stereo microphones basically. The advantage of the use of multiple microphones is that the direction information of the target source could be applied. The proposed noise canceller is based on the Wiener filter. To estimate the filter, noise and target speech frequency responses should be known and they are estimated by the spectral classification in the frequency domain. The performance of the proposed algorithm is compared with that of the well-known Frost algorithm and the generalized sidelobe canceller (GSC) with an adaptation mode controller (AMC). As performance measures, the perceptual evaluation of speech quality (PESQ), which is the most widely used among various objective speech quality methods, and speech recognition rates are adopted.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.211-216
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• 2012

Control Theory for continuous-time system has been well developed. Due to the development of computer technology, digital control scheme are employed in many areas. When delays are in control systems, it is hard to control the system efficiently. Delays by controller-to-actuator and sensor-to-controller deteriorate control performance and could possibly destabilize the overall system. In this paper, a new approximated discretization method and digital design for control systems with multiple state, input and output delays and a generalized bilinear transformation method with a tunable parameter are also provided, which can re-transform the integer time-delayed discrete-time model to its continuous-time model. Illustrative example is given to demonstrate the effectiveness of the developed method.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.40 no.4
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• pp.211-220
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• 2017

The application of the theoretical model to real assembly lines has been one of the biggest challenges for researchers and industrial engineers. There should be some realistic approach to achieve the conflicting objectives on real systems. Therefore, in this paper, a model is developed to synchronize a real system (A discrete event simulation model) with a theoretical model (An optimization model). This synchronization will enable the realistic optimization of systems. A job assignment model of the assembly line is formulated for the evaluation of proposed realistic optimization to achieve multiple conflicting objectives. The objectives, fluctuation in cycle time, throughput, labor cost, energy cost, teamwork and deviation in the skill level of operators have been modeled mathematically. To solve the formulated mathematical model, a multi-objective simulation integrated hybrid genetic algorithm (MO-SHGA) is proposed. In MO-SHGA each individual in each population acts as an input scenario of simulation. Also, it is very difficult to assign weights to the objective function in the traditional multi-objective GA because of pareto fronts. Therefore, we have proposed a probabilistic based linearization and multi-objective to single objective conversion method at population evolution phase. The performance of MO-SHGA is evaluated with the standard multi-objective genetic algorithm (MO-GA) with both deterministic and stochastic data settings. A case study of the goalkeeping gloves assembly line is also presented as a numerical example which is solved using MO-SHGA and MO-GA. The proposed research is useful for the development of synchronized human based assembly lines for real time monitoring, optimization, and control.

• Journal of Welding and Joining
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• v.35 no.3
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• pp.68-74
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• 2017

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E71T-1C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, Intragranular polygonal ferrite and grainboundary ferrite were formed only in first layer of weld metal. Another layers consisted of acicular ferrite and $Widmannst{\ddot{a}}tten$ ferrite. The amount of acicular ferrite was increased with decreasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered martensite and lower bainite. Lower and upper bainite were formed in heat affected zone of carbon steel. Tensile strengths of dissimilar metal welds decreased with increasing heat inputs. Dissimilar metal welds showed a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals welds showed that the weight loss rate by corrosion below 170 hours was decreased with increasing heat inputs due to the increase of the amount of acicular ferrite.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.22 no.4
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• pp.301-315
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• 2011

DEA(Data Envelopment Analysis) is useful to measure the relative efficiency of organizational units where the presence of multiple inputs and outputs. This study applied DEA-CCR and DEA-BCC to evaluate the technical, pure technical, and scale efficiency of 29 university libraries. The input variables were number of books, print edition expenses, building space, staff, number of seats. As output variables we estimated: reader visits, number of borrowed items, number of visitors. It was found out that number of libraries with 100% relative efficiency among 29 libraries were 13. Also the results shows that main reason of inefficiency was from scale rather than from pure technical. Many inefficient libraries were operations of increasing return to scale.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.3
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• pp.458-464
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• 2015

This paper proposes a portable 3-D scanning technique using a laser pointer. 3-D scanning is a process that acquires surface information from an 3-D object. There have been many studies on 3-D scanning. The methods of 3-D scanning are summarized into some methods based on multiple cameras, line lasers, and light pattern recognition. However, those methods has major disadvantages of their high cost and big size for portable appliances such as smartphones and digital cameras. In this paper, a 3-D scanning system using a low-cost and small-sized laser pointer are introduced to solve the problems. To do so, we propose a 3-D localization technique for a laser point. The proposed method consists of two main parts; one is a fast recognition of input images to obtain 2-D information of a point laser and the other is calibration based on the least-squares technique to calculate the 3-D information overall. To verified our method, we carry out experiments. It is proved that the proposed method provides 3-D surface information although the system is constructed by extremely low-cost parts such a chip laser pointer, compared to existing methods. Also, the method can be implemented in small-size; thus, it is enough to use in mobile devices such as smartphones.