• Journal of electromagnetic engineering and science
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• v.16 no.3
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• pp.169-181
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• 2016

This work presents a new method for enhancing the performance of a dual band Planer Inverted-F Antenna (PIFA) and its lumped equivalent circuit formulation. The performance of a PIFA in terms of return loss, bandwidth, gain, and efficiency is improved with the addition of the proposed open stub in the radiating element of the PIFA without disturbing the operating resonance frequencies of the antenna. In specific cases, various simulated and fabricated PIFA models illustrate that the return loss, bandwidth, gain, and efficiency values of antennas with longer optimum open stub lengths can be enhanced up to 4.6 dB, 17%, 1.8 dBi, and 12.4% respectively, when compared with models that do not have open stubs. The proposed open stub is small and does not interfere with the surrounding active modules; therefore, this method is extremely attractive from a practical implementation point of view. The second presented work is a simple procedure for the development of a lumped equivalent circuit model of a dual band PIFA using the rational approximation of its frequency domain response. In this method, the PIFA's measured frequency response is approximated to a rational function using a vector fitting technique and then electrical circuit parameters are extracted from it. The measured results show good agreement with the electrical circuit results. A correlation study between circuit elements and physical open stub lengths in various antenna models is also discussed in detail; this information could be useful for the enhancement of the performance of a PIFA as well as for its systematic design. The computed radiated power obtained using the electrical model is in agreement with the radiated power results obtained through the full wave electromagnetic simulations of the antenna models. The presented approach offers the advantage of saving computation time for full wave EM simulations. In addition, the electrical circuit depicting almost perfect characteristics for return loss and radiated power can be shared with antenna users without sharing the actual antenna structure in cases involving confidentiality limitations.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.2
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• pp.61-65
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• 2009

In this paper, we report on the growth and optical characteristics of white-LED without fluorescent material. The growth of DH(double heterostructure) with AlGaN active layer was performed on a n-GaN/(0001) $Al_{2}O_{3}$ by the mixed-source HVPE and multi-sliding boat. The CRI(color rendering index) of packaging device charged in the range 72-93 with CIE chromaticity coordinates(x=$0.26{\sim}0.34$, y=$0.31{\sim}0.40$). And CCT(correlated color temperature) values was measured $5126{\sim}10406K$ with increasing injection current. The CIE point of conventional phosphor white LED shifts blue region, but cm point of non-phosphor white LED shifts opposite direction. These results show the mixed-source HVPE can be possible to newly fabricate method of phosphor free white LED with high CRI value.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.68.1-68.1
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• 2013

Infrared Medium-Deep Survey is a near-infrared imaging survey geared toward understanding the formation and the evolution of quasars and galaxies at high redshift, and studying transient and time-variable objects such as gamma-ray bursts, supernovae, and young stellar objects. The survey uses a multi-tier structure, with deep imaging survey of 100 $deg^2$ using UKIRT to the depth of 23 AB mag, and a shallower imaging of interesting sources using the CQUEAN camera on the 2.1m telescope at McDonald observatory. This talk will give an overview of the survey strategy, the instrument development, and science highlights. The science highlights will include the discovery of high redshift quasars, high redshift galaxy clusters, GRBs, and other interesting sources. At the end of the talk, we will also present the future prospects of our study.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.7 s.110
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• pp.648-658
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• 2006

We propose a thin frequency selective surface(FSS) superstrate etched on a substrate for dual-band directivity enhancement, and present a design method of the superstrate. In the proposed new design, two FSS arrays with the same periodicity, but with different alignments are placed above and below a thin dielectric layer to overcome the problem of conventional superstrates for dual band directivity enhancements. Based on the unit-cell simulation, several important parameters that characterize the thin FSS superstrate are investigated, and the procedure for designing such a superstrate is described. We compare the resonant frequencies and the qualify factors of the unit cell with those of three FSS antenna composites with different quality factors, and identify the quality factors which support similar directivity enhancement at the dual-band directivity enhancement. It was found that there is an optimum FSS array size of a superstrate to enhance the directivity most efficiently. Measured results for a fabricated superstrate show a good agreement with the simulated ones.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.10
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• pp.1031-1041
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• 2009

A small microstrip monopole antenna for macro-micro frequency tuning over multiple bands is presented. The meander-shape antenna is fabricated on a conventional printed circuit board(FR-4, $\varepsilon_r=4.4$ and tan $\delta=0.02$). The antenna operates over WiBro(2.3~2.4 GHz) and WLAN a/b(2.4~2.5 GHz/5.15~5.35 GHz) service bands with an essentially constant antenna gain within each service band. Two diodes, a PIN diode and a varactor, are embedded into the antenna for frequency reconfiguration. The PIN diode is used for frequency switching(macro-tuning) between 2 GHz and 5 GHz bands while the varactor is used for frequency tuning(micro-tuning) within the service bands, 2.3~2.5 GHz and 5.15~5.35 GHz. Unwanted resonances between the two frequency bands(2 GHz and 5 GHz) are suppressed by filling up the gaps between the meander lines. The antenna gain is essentially constant and higher than 2 dBi within each service band. The measured performance of the proposed antenna system suggests the macro-micro frequency tuning techniques be useful in reconfigurable wireless communication systems.

• Journal of Distribution Research
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• v.11 no.1
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• pp.99-124
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• 2006

The purposes of the study are two-folds. First, it analyzes how factors other than price(e.g. delivery service, saving point policies, free gifts) impact total price for various products and different types of stores. Second, it analyzes how to increase market efficiencies through price level, price differences, and the frequency of price changes for different shops, various products and different types of transactions. By analyzing the price level within different types of stores, there found that prices at on-line store were lower than off-line shops. It also found price differences between pure on-line, hybrid, and off-line store. Comparing prices by product size, there found that pure on-line shops have a lower price compared to others. The results showed that on-line store had lower price variation compared to off-line shops. When comparing pure on-line store to hybrid store, hybrid store had lower price variation. In terms of the frequency of price changes, hybrid stores had higher price fluctuations. In terms of total price differences for delivery distances, pure on-line store had great price fluctuation, excluding cosmetic goods. In conclusion, if we consider price level and price fluctuations, on-line store had more efficiencies and was superior in terms of price effectiveness. Hybrid shops, on the other hand, had greater advantages for seasonal goods and dominant products. Therefore, market entry strategies should differ based on order quantity, type of store(pure on-line, hybrid, off-line), product characteristics(seasonality, product life), etc.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.5 s.108
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• pp.476-482
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• 2006

In this paper, a multimode feed horn antenna is suggested for a high power microwave(HPM) antenna system. The proposed HPM feed horn antenna which is connected with a mode converter is located between source and reflector antenna. A multimode feed horn antenna which has reduced -25 dB beamwidth is designed and fabricated for miniaturization of reflector antenna because -25 dB beamwidth which is determined by considering spillover of feed horn antenna decides a size of reflector in case of HPM. As a result, feed system which uses the multimode feed horn antenna has high gain about 27 dBi and return loss is less than -22 dB at 10 GHz. The measured -25 dB beamwidths of the radiation pattern at vertical, horizontal-plane equal to $20.24^{\circ},\;28.92^{\circ}$ which is less than about $10^{\circ}$ beamwidth of conventional feed system. Thus the suggested feed hem antenna is suitable to feed horn for miniaturization of HPM antenna system.

• Science of Emotion and Sensibility
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• v.10 no.2
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• pp.155-168
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• 2007

Social and psychological experiences in human-agent interactions are becoming more important than the task-oriented efficiency, as the influence of computer agents increases and human-agent interaction develops similarly with interpersonal interaction. Many previous studies aimed to increase social presence in human-agent interaction, in order to derive users' positive psychological experiences, by applying the factors of interpersonal communication to verbal and non-verbal communication of the agents. This study examined the effects of the exchanges of mutual self-disclosure, one of the most important communication acts in interpersonal communication, between users and interface agents. Users' attachment styles towards the perception of social presence, the evaluations toward the agents, user experiences, and the intentions for future interaction were also studied. The mediating role of social presence in dependent variables was, also, examined in this research. The results showed that exchanging self-disclosures with an agent increased the perceptions of social experience, friendly evaluations toward the agent, positive user experience, and the intentions for future interaction. Participants' attachment styles, also, affected the perceptions of the dependent variables. The effects of the exchanges of self-disclosure and participants' attachment styles were mediated by perceived social presence toward the agent. The findings of this study imply that the social and communicational aspects need to be considered in design of the agents seriously. The results also suggest that there may be differences in the psychological effects of agents on users according to the users' personality.

• The KIPS Transactions:PartB
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• v.9B no.3
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• pp.351-358
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• 2002

Video compression based on DCT (Discrete Cosine Transform) has weakpoints of blocking artifacts and pixel loss when the resolution is changed. DWT (Discrete Wavelet Transform) based method can overcome such problems. In SAMCoW (Scalable Adaptive Motion Compensation Wavelet), one of wavelet based video coding algorithm, both intra frames and motion compensated error frames are encoded using EZW(Embedded Zerotree Wavelet) algorithm. However the property of wavelets transform coefficients of motion compensated error frames are different from that of still images. Signal energy is not highly concentrated in the lower bands which is true for most still image cases. Signal energy is rather evenly distributed over all frequency bands. This paper suggests a new video coding algorithm utilizing these properties. Spatial band coding which is known to be very effective for encoding images with relative1y high frequency components and not utilizing the interband coefficients correlation is applied instead of EZW to encode both intra and inter frames. In spatial band coding, the position and value of significant wavelet coefficients in each band are progressively transmitted. Unlike EZW, inter band coefficients correlations are not utilized in spatial band coding. It has been shown that spatial band coding gives better performance than EZW when applied to wavelet based video compression.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.3 no.3
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• pp.22-30
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• 2010

3D TV was been able to see in the market in early in this year. Tablet PC such as ipad by Apple and Galaxytab by Samsung were introduced recently. Those are possible by developing H/W and S/W of computer technology. The needs of interactive contents in many areas including education and entertainment area are increasing rapidly according to the various information devices are or will be in the market. Fore the more, GoogleTV and AppleTV are compete each other to dominate the world market in advance recently. CookTV tries to dominate in the domestic market by upgrading the current system. Diverse information devices are in the market means various size of displayers are able to be shown in our life. As TV is fused to computer, the displayer is substituted to TV's screen and the trend of TV is became bigger. The evolved TV is able to replace the computer by connecting to the network and people want to do interactions with contents by using the bidirectional communication. Therefore, it is expected to changing the human lifestyle. It is natural that contents for all members of family are needed, since TV's screen become bigger. It is required that the contents should guarantees the accessability of information to the all of family members and the easy interaction with contents. Our goal of experiment are to analyse the influence of interaction with contents as the size of images and to analyse a learning effect of contents quantitatively by applying a statistical method. Users interacted with contents without any difficulty when they met a same dimension and shape of objects as ame dimension and shape objects in their experiences or learning, was confirmed. And the learning effect were analysed and explained by applying the correlation.