• Journal of electromagnetic engineering and science
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• v.13 no.1
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• pp.44-50
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• 2013

In this paper, we present a circularly polarized (CP) composite cavity-backed crossed dipole antenna for global positioning system (GPS) applications. We produce the CP radiation by crossing two dipoles through a $90^{\circ}$ phase delay line of a vacant-quarter printed ring, which also has a broadband impedance matching characteristic. Two techniques, insertion of meander lines in the dipole arm and arrowhead-shaped trace at its end, are employed to reduce the sizes of the primary radiation element. The compact radiator is backed by a cavity reflector to achieve a wide CP radiation beamwidth. The proposed antenna exhibits a measured bandwidth of 1.450~1.656 GHz for a voltage standing wave ratio (VSWR) < 2 and 1.555~1.605 GHz for AR < 3-dB. At 1.575 GHz, the antenna has a gain of 7 dBic, a frontto-back ratio of 27 dB, AR of 1.18 dB, and 3-dB AR beamwidths of $130^{\circ}$ and $132^{\circ}$ in the x-z and y-z planes, respectively.

• The Journal of Information Technology
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• v.1 no.2
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• pp.15-24
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• 1998

C.I.F. and F.O.B. contracts are the chief terms used in international trade contracts. But, in recently, the multimodal transport which is based on the containerization and the improvement of air transport has been grown gradually, Regardless of theese change in international trade environment, most of the contract of sale is made by C.I.F. and F.O.B. contracts which are based on the traditional port to port transport. In other words, there are some limitation in terms of legal base in which traditional C.I.F. and F.O.B. contract is applied to the changed environment. Especially, problems arised in marine insurance which export by F.O.B. trade terms. Therefore, when the parties of the contracts of sale make an sale contracts by using the container ship and Multimodal Transport, they should use the F.C.A. and C.I.P. contracts Instead of F.O.B. and C.I.F. contracts for the transport of goods. And parties of the contracts of sale need to gain a better understanding of the characteristic of F.C.A. and C.I.P. terms and the problem of the F.C.A. and C.I.P. contracts used in the performance on international multimodal transport.

• Journal of Korea Multimedia Society
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• v.10 no.12
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• pp.1632-1644
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• 2007

Wireless Mesh Networks aim to attain large connectivity with minimum performance degradation, as network size is increase. As such, scalability is one of the main characteristics of Wireless Mesh Networks that differentiates it from other wireless networks. This characteristic creates the need for bandwidth efficiency strategies to ensure that network performance does not degrade as the size of the network increase. Several researches have been done to realize mesh networks. However, the researches conducted were mostly focused on a per TCP/IP layer basis. Also, the studies on bandwidth efficiency and bandwidth improvement are usually dealt with as separate issues. This paper aims to simultaneously study bandwidth efficiency and improvement. Aside from optimizing the bandwidth given a fixed capacity, the capacity is also increased using results of physical layer studies. In this paper, the capacity is improved by using the concept of non-overlapping channels for wireless communication. A channel allocation scheme is conceptualized to choose the transmission channel that would optimize the network performance parameters with consideration of chosen Quality of Service (QoS) parameters. Network utility maximization is used to optimize the bandwidth after channel selection. Furthermore, a routing scheme is proposed using the results of the network utilization method and the channel allocation scheme to find the optimal path that would maximize the network gain.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.9
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• pp.2003-2008
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• 2013

In this paper, a design method for a ultra-wideband printed semi-circular-shaped dipole antenna operating in the band of 1-15 GHz is studied. The effects of the gap between the two arms of the semi-circular-shaped dipole and the radius of the semi-circle on the input reflection coefficient and gain characteristics are examined to obtain the optimal design parameters. The optimized printed semi-circular-shaped dipole antenna is fabricated on an FR4 substrate and the experimental results show that the antenna has a desired extremely wideband characteristic with a frequency band of 1-15 GHz (175%) for a VSWR < 2.

• Proceedings of the KIPE Conference
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• 2001.12a
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• pp.97-101
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• 2001

Recently, as the development of industry, the nonlinear load becomes increased. Because of nonlinear load, the variation of source voltage is generated by the impedace of source side flowed harmonic currents. For blocking harmonic currents by nonlinear load, a series active power filter operates blocking resistance of harmonic currents. The value of blocking resistance shows ideal compensating characteristic out of theoretically infinite value. But the blocking resistance is limited by the problem of the system stability and the capacity of inverter. In this paper, the value of optimum blocking resistance is found by a simulation in the applied system. In the case of unbalanced source voltages, each relation of the blocking resistance is shown. It is proved that blocking resistance of series active power filter relates to a passive filter.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.664-672
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• 2010

This paper provides the target observability analysis of time-to-go polynomial guidance law with bearing-only measurement. In this study, a direct approach is used to analyze the target observability. Since the observability condition of a constant-velocity target is given by the function of LOS angle only, the target observability characteristic is determined by substituting the closed form solution of LOS angle to the observability condition directly. The analysis results show that the target observability is depended on the choice of guidance gain, initial intercept condition and guidance command shape. After that this mathematical analysis result is evaluated and demonstrated by number of simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.415-419
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• 1999

Many bipolar logic circuit of conventional occurred problem of speed delay according to deep saturation state of vertical NPN Transistor. In order to remove minority carries of the base region at changing signal in conventional bipolar logic circuit, we made transistor which is composed of NPN transistor shortened buried layer under the Base region, PNP transistor which is merged in base, epi layer and substrate. Also the Ring-Oscillator for measuring transmission time-delay per gate was designed as well. The structure of Gate consists of the vertical NPN Transistor, substrate and Merged PNP Transistor. In the result, we fount that tarriers which are coming into intrinsic Base from Emitter and the portion of edge are relatively a lot, so those make Base currents a lot and Gain is low with a few of collector currents because of cutting the buried layer of collector of conventional junction area. Merged PNP Transistor's currents are low because Base width is wide and the difference of Emitter's density and Base's density is small. we get amplitude of logic voltage of 200mv, the minimum of transmission delay-time of 211nS, and the minimum of transmission delay-time per gate of 7.26nS in AC characteristic output of Ring-Oscillator connected Gate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.710-716
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• 2003

OFDM is a very attractive technique for achieving high-bit-rate data transmission and high spectrum efficiency. However one of disadvantages of OFDM signal is the high PAPR characteristic when multicarriers are added up coherently. In this paper, we propose an adaptive PTS scheme using two threshold levels for PAPR reduction and reducing the amount of PAPR calculations with clipping scheme. Simulation results show that it is almost same between average bit error rate performance of the proposed scheme and that of a conventional scheme. Also, we obtain a great performance gain in the amount of calculations compared to the conventional scheme. Therefore, proposed system has a good performance in data processing time in OFDM wireless communication systems.

• Sleep Medicine and Psychophysiology
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• v.1 no.1
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• pp.3-8
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• 1994

With the recent development of sleep medicine, insomnia has been perceived as a disease from a simple symptom. As there are various causes in a disease, proper treatment according to each cause is necessary for a more effective treatment In general, insomnia is classified into five categrories of physical, physiological, psychological, psychiatric and pharmacological aspects. However, such categorizations are often insufficient in treating insomnia. Furthermore understanding of the developmental mechanisms of insomnia is required. The function of sleep is developed and maintained through the balance of the reciprocal forces of sleep and arousal. These forces are contantly regulated by what is called a circadian rhythm. Sleep is induced by this rhythm which is affected by factors such as awakening time in the morning, amount of intellectual function, amount and time length of physical exercise and sunlight Insomnia could develop when this rhythm is delayed and leads to a "forbidden zone" which is a very difficult period for inducing sleep about two to four hours before the routine bedtime. Whereas sleep gradually develops in line with the circardian rhythm, arousal can occur very abruptly by any cause triggered by emotional discomfort or anxiety. Such characteristic and emotional factors as perfectionism, separation anxiety, secondary gain, insecurity, and negative cognition may provoke the inner anxiety and fear for insomnia, which can lead acute insomnia to a chronic one. As chronic insomnia is developed by multiple causes and factors, integrated approaches through analysis of above mentioned factors will be more effective in the treatment of insomnia than a simple administration of hypnotics.

• Journal of Construction Engineering and Project Management
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• v.4 no.3
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• pp.13-20
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• 2014

Estimating time and cost is an important mission in the early phase of a construction project, especially in feasibility study. It provides a foundation for making decision whether or not the project is performed on schedule and within budget. Thus, reliability of this estimate plays a key role in measuring the success of a project. This study was carried out to investigate the time-cost relationship in building construction projects in Bangladesh. The mathematical equation used in this study is based on Bromilow's equation. The research data were collected from sixty-three completed building projects through questionnaire survey. Type of clients, type of projects, and tender methods are the project characteristics considered in this study. The results of analysis indicated that the Bromilow's time-cost (BTC) models developed for each project characteristic are appropriate due to quite high coefficient of determination and relatively small mean percent errors. Among them, the forecasted model for time and cost according to tender methods is the best fit model. It is concluded that the BTC model could be applied in building construction project to predict its time and cost in Bangladesh. Four different regression models were also developed in this study. The results of BTC model between some selected countries were compared to gain the comprehensive view.