• Geophysics and Geophysical Exploration
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• v.5 no.4
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• pp.299-308
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• 2002

We have derived an analytical expression for the sensitivity of the frequency domain small-loop electromagnetic (EM) surveys over a two-layer earth in order to estimate the depth of investigation with an instrument having the source-receiver separation of about 2 m. We analyzed the sensitivities to the lower layer normalized by those to the upper half-space and estimated the depth of investigation from the sensitivity analyses and the mutual impedance ratio. The computational results showed that the in-phase components of the sensitivity to the lower layer dominates those to the upper layer when the thickness of the upper layer is less than 20 m, while the quadrature components are not sensitive to the lower layer over the entire frequency range. Hence we confirmed that the accurate measurement of the in-phase component is essential to increase the depth of investigation in the multi-frequency small-loop EM survey. When conductive basement of 10 ohm-m underlies the upper layer of 100 ohm-m, an accurate measurement of the in-phase components ensures the depth of the investigation more than 10 m even accounting a noise effect, from which we conclude that the small-loop EM survey is quite effective in imaging the conductive plume down to a considerable depth. On the other hand, in the presence of the resistive basement of 1,000 ohm-m, the depth of investigation may not exceed 5 m considering the instrumental accuracy, which implies that the application of the small-loop EM survey is not recommended over the resistive environment other than detecting the buried conductor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1601-1607
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• 2009

As a general rule, the orthogonal modulation scheme which is widely used for wireless communications is not appropriate for the high speed data transmission applications due to the low bandwidth efficiency. Therefore, to increase the bandwidth efficiency of the conventional orthogonal modulation, we propose the multi-code trans-(bi-)orthogonal modulation in this paper. It is the combined scheme of multi-code modulation and trans-orthogonal modulation. We can know that the bandwidth efficiency of the proposed scheme is better than that of the conventional orthogonal modulation. Additionally, the receiver complexity of the proposed scheme is lower than that of the conventional orthogonal modulation. The proposed scheme can be used for the physical layer of the high speed wireless digital data transmission applications such as multimedia communications system and high speed personal area networks.

• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.268-273
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• 2014

In this study, multi-walled carbon nanotubes (MWCNT) were treated with nickel by electroless plating method for improving electromagnetic interference (EMI) shielding performance of MWCNT. The physical properties of electroless plated MWCNT were analyzed by using ultra-high resolution scanning electron microscope (UHR-SEM), thermogravimetry (TGA), sheet resistance analyzer and EMI shielding analyzer. EMI shielding efficiencies of nickel electroless plated MWCNT were measured to be 16 dB from 800 MHz band, which was 1.6 times increased compared to that of the activated MWCNT. Also, the average sheet resistance of nickel electroless plated MWCNT was measured to be $70{\Omega}/sq$, which was 56% decreased compared to that of the activated MWCNT. This result could be attributed to the plating morphology on the surface of MWCNT. This result could be attributed to uniformity of plating morphology on the surface, which has more effect on EMI shielding efficiency than the amount of nickel plating.

• Spatial Information Research
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• v.7 no.2
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• pp.159-173
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• 1999

GIS has been regarded as one of important tools or methodologies for various geoscience applications. Recently, spatial data integration schemes for site-specific or field-specific thematic mapping are newly developed and utilized. However, these kinds of approaches are somewhat insufficient quantitative assessment of integrated layers towards known targets in-detailed . Moreover, GIS analysis scheme is rarely extended to scientific approaches. In this study, simple approach of Multi-Buffer Zone Analysis , related to GIS analystical aspect, is addressed and an actual application for predicting or favorable mapping of mineral occurrences, one of GIS-based geoscientific approaches, is performed, As for geo-processing in GIS itself, this scheme can be regarded as extension or adaptiation of cell-based buffering or proximity analysis to geoscientific data interpretation. This study is based on rationale that surface geological pattern around primitives such as a point, a line, or a polygon in GIS, representing significant geological features, can be efficiently utilized to delineate complex geological behaviors or events, especially handling multiple dta sets originated from multiple sources such as airborne geophysical/radiometric exploration, field survey, and even a classified image of remote sensing. Conclusively, this methodology associated wit GIS is though to be helpful to analyze the spatial pattern of multiple data, pointing given sources, and is expected to effectively utilize for exploratory analysis of cell-based resultant layer integrated with complex or different data sources.

• Journal of the Korean earth science society
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• v.36 no.1
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• pp.16-26
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• 2015

To investigate the applicability of physical prospecting technique in soft ground assessment, the resistivity monitoring data of 6 months are acquired. The Multichannel Analysis Surface Wave (MASW) has been additionally performed to identify the shear wave velocity and strength distribution of soft ground. Moreover, by using the Cone Penetration Test (CPT) and laboratory tests of drilling samples, a relationship with the physical prospect data is checked and the reliability of the physical prospect data is increased. Through these activities, the behavior patterns of soft soil are identified by long term monitoring, and the significant relationship between the shear wave velocity and laboratory tests has been confirmed, both of which can be useful in the surface wave exploration to evaluate the strength of soft ground. Finally, using the geostatistical method, 3-dimensional soil base distribution images are obtained about the combined physical prospecting data with heterogeneous data. Through the studies, the nature of entire area can be determined by long term resistivity monitoring for the soft ground assessment in wider area. It would be more economic and reliable if additional exploring and drilling samples can be analyzed, which can reinforce the assessment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8B
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• pp.1558-1566
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• 1999

While high resolution images are required for various applications, aliased low-resolution images are only available due to the physical limitations of sensors. In this paper, we propose an algorithm to reconstruct a high resolution image from multiple aliased low-resolution images, which is based on the generalized multichannel deconvolution technique. The conventional approaches are based on the discrete Fourier transform (DFT) since the aliasing effect is easily analyzed in the frequency domain. However, the useful solution may not be available in many cases, i.e., the underdetermined cases or the insufficient subpixel information cases. In order to compensate for such ill-posedness, the generalized multichannel regularization was adopted in the spatial domain. Furthermore, the usage of the discrete cosine transform instead of the DFT leads to the computationally efficient reconstruction algorithm. The validity of the proposed algorithm is both theoretically and experimentally demonstrated in this paper. It is also shown that the effect of inaccurate motion information is reduced by regularization.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.112-115
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• 2003

쓰레기매립장의 침출수 누출 탐지를 위한 물리탐사법은 침출수의 전기전도도를 대상으로 한 전기탐사법이 주로 적용되어 왔다. 이 연구는 제주도에 위치한 비위생매립지를 대상으로 주변 수리지질환경 파악을 위한 전기비저항 탐사와 더불어 매립장 경계부와 토양층을 통한 침출수 누출 영역을 효율적으로 규명하기 위하여 다중주파수를 이용한 소형루프 전자탐사를 병행하여 수행하였으며, 아울러 오염지역의 천부 지하수 유동 방향을 추정하기 위하여 침출수의 유동에 의해 발생될 수 있는 자연전위를 모니터링 하였다. 전기비저항 탐사 및 자연전위 모니터링 결과 매립지 주변을 통한 침출수의 누출 가능성은 거의 없는 것으로 나타났으며, 이는 주변 하천에서 정기적으로 실시한 수질 분석 결과와 일치된다. 또한 소형루프 전자탐사 자료에 대하여 공간 필터링 및 1차원 역산법을 적용한 결과 매립장 경계부의 위치 및 매립장 내부의 심도별 매립물에 의한 저비저항 이상대를 효과적으로 도출 할 수 있었다.

• Information and Communications Magazine
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• v.22 no.9
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• pp.175-186
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• 2005

향후 수년 내에 흠, 오피스 및 핫스팟 영역에서 초고속 멀티미디어의 서비스 수요가 폭발적으로 증가할 것으로 전망됨에 따라 IEEE 802.11에서는 200-500Mbps급의 차세대 초고속 무선랜 표준으로서 IEEE 802.11n의 표준안을 제정하는 작업을 진행하고 있다. 새로운 표준에는 무선통신의 다양한 기술들이 표준으로 채택될 전망이다. 논의되고 있는 기술들로는 물리계층에서의 다중 안테나의 사용, 송신 빔 형성, 듀얼 밴드 그리고 LDPC (Low Density Parity Check) 등의 기술과 MAC (Media Access Control) 계층에서의 집합 전송, 블록 전송, 링크 적응 기법 등의 채택이 논의되고 있다. 기존의 무선랜 시스템에서 널리 사용되어온 IEEE 802.11a/b/g와의 호환성을 보장한다. 또한 차세대 무선랜은 차량용 통신 장치를 위한 고속 이동성을 보장하는 표준인 IEEE 802.11p에 대한 논의도 함께 이루어지고 있다. 본 고에서는 표준회의에서 논의되고 있는 후보 기술들과 차세대 무선랜의 기술동향을 살펴본다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.2
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• pp.343-351
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• 2008

In this paper, we investigate the design of the QAM(Quadrature Amplitude Modulation) method for the CACB(Constant Amplitude Coded Multicode Biorthogonal) scheme. The modulation method fan improve the transmission data rate by increasing the BE(Bandwidth Efficiency). Additionally, we can improve the system performance by using the QAM SD(Soft Decision) method with the MDSA(Minimum Distance Selection Algorithm). Finally, the DFE(Decision Feedback Equalizer) for the CACB-QAM is simulated under the MPF(MultiPath Fading) channel for real implementation. The proposed scheme can be used for the PHY(PHYsical layer) standard of the WPAN(Wireless Personal Area Network) requiring high rate data transmission.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.336-348
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• 2010

The Single-channel seismic survey with the source of bubble pulser and drilling survey was carried out in 2008 and 2009 for the site survey of Daecheon-Wonsando area, which was a proposed area of Korea-China subsea tunnel. The goal of this study is to analyze the depth and characteristics of acoustic basement for the stability assessment and tunnel design in this proposed area through combining drilling data with this single-channel seismic data after detailed processing. For this purpose, among the data processing schemes which are usually applied to multi-channel seismic data, we applied the F-K filtering to eliminate the AC(alternating current) noise and the post-stack depth migration to produce depth section. As a result, we verified that the improved depth section could be obtained from single-channel seismic data, and the distribution and characteristics of basement could be analyzed in survey area through the combined analysis with drilling data. However, we could not interpret the detailed structures, fault and fracture zone, due to the quality of bubble pulser source and single-channel data. We expect that those detailed structures can be analyzed when higher resolution seismic data is provided. Therefore, we recommend some items for future seismic survey of subsea tunnel to obtain the high resolution seismic data.