• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1995년도 가을 학술발표회 논문집
• /
• pp.15.2-22
• /
• 1995

Evaluating stiffness of near-surface materials has been one of the critically important tasks in many civil engineering works. It is the main goal of geotechnical characterization. The so-called deflection-response method evaluates the stiffness by measuring stress-strain behavior of the materials caused by static or dynamic load. This method, however, evaluates the overall stiffness and the stiffness variation with depth cannot be obtained. Furthermore, evaluation of a large-area geotechnical site by this method can be time-consuming, expensive, and damaging to many surface points of the site. Wave-propagation method, on the other hand, measures seismic velocities at different depths and stiffness profile (stiffness change with depth) can be obtained from the measured velocity data. The stiffness profile is often expressed by shear-wave (S-wave) velocity change with depth because S-wave velocity is proportional to the shear modulus. that is a direct indicator of stiffiiess. The crosshole and downhole method measures the seismic velocity by placing sources and receivers (geophones) at different depths in a borehole. Requirement of borehole installation makes this method also time-consuming, expensive, and damaging to the sites. Spectral-Analysis-of-Surface-Waves (SASW) method places both source and receivers at the surface, and records horizontally-propagating surface waves. Based upon the theory of surfacewave dispersion, the seismic velocities at different depths are calculated by analyzing the recorded surface-wave data. This method can be nondestructive to the sites. However, because only two receivers are used, the method requires multiple measurements with different field setups and, therefore, the method often becomes time-consuming and labor-intensive. Furthermore. the inclusion of noise wavefields cannot be handled properly, and this may cause the results by this method inaccurate. When multi-channel recording method is employed during the measurement of surface-waves, there are several benefits. First, usually single measurement is enough because multiple number (twelve or more) of receivers are used. Second, noise inclusion can be detected by coherency checking on the multi-channel data and handled properly so that it does not decrease the accuracy of the result. Third, various kinds of multi-channel processing techniques can be applied to f1lter unwanted noise wavefields and also to analyze the surface-wavefields more accurately and efficiently. In this way, the accuracy of the result by the method can be significantly improved. Fourth, the entire system of source, receivers, and recording-processing device can be tied into one unit, and the unit can be pulled by a small vehicle, making the survey speed very fast. In all these senses, multi-channel recording of surface waves is best suited for a routine method for geotechnical characterization in most of civil engineering works.

• 대한의용생체공학회:의공학회지
• /
• 제28권2호
• /
• pp.258-264
• /
• 2007

Spatiotemporal changes of brain rhythmic activity at a certain frequency have been usually monitored in real time using scalp potential maps of multi-channel electroencephalography(EEG) or magnetic field maps of magnetoencephalography(MEG). In the present study, we investigate if it is possible to implement a real-time brain activity monitoring system which can monitor spatiotemporal changes of cortical rhythmic activity on a subject's cortical surface, neither on a sensor plane nor on a standard brain model, with a high temporal resolution. In the suggested system, a frequency domain inverse operator is preliminarily constructed, considering the individual subject's anatomical information, noise level, and sensor configurations. Spectral current power at each cortical vertex is then calculated for the Fourier transforms of successive sections of continuous data, when a single frequency or particular frequency band is given. An offline study which perfectly simulated the suggested system demonstrates that cortical rhythmic source changes can be monitored at the cortical level with a maximal delay time of about 200 ms, when 18 channel EEG data are analyzed under Pentium4 3.4GHz environment. Two sets of artifact-free, eye closed, resting EEG data acquired from a dementia patient and a normal male subject were used to show the feasibility of the suggested system. Factors influencing the computational delay are investigated and possible applications of the system are discussed as well.

• 전기학회논문지
• /
• 제61권1호
• /
• pp.179-185
• /
• 2012

Since the eco-era is getting closer, the importance of noise reducing in the passenger cars of high-speed train is very important. The active noise control is best choice to reduce low frequency noise because the passive one is too heavy for high speed trains where weight is so critical. Also ANC is able to reduce the ambient noise when the environmental-factor changes. To reduce a three-dimensional closed-space sound field like a car of a high-speed rail is hard to do using single channel ANC control system. We used multi-channel FXLMS algorithm which calculation speed is fast and the secondary path estimation is possible in order to take into account the physical delay in electro acoustic hardware control loudspeaker and power amplifier. Firstly, we have measured interior noise of KTX and estimated noise path in KTX test-bed. However there was some problem related to algorithm divergence and increasing the filter order. We have made a simulation of interior environment of KTX car by using three frequency bands of 120Hz, 280Hz, 360Hz as the most important for KTX ANC system. During this research the interior noise reduction of KTX car was made by using the multi-channel FXLMS algorithm. Reduction performance was evaluated and compared each other for open space section and tunnel section. in-situ experiment for the KTX noise reduction by proposed ANC was performed based on data obtained in simulation and they were compared for open space section and tunnel section as well.

• IUGG한국위원회:학술대회논문집
• /
• IUGG한국위원회 2003년도 정기총회 및 학술발표회
• /
• pp.20-20
• /
• 2003

In the summers of 1997 and 1998 and in February of 2000 we made 570 measurements of the ambient geomagnetic field 120 cm above the pavement surface of State Route 130, south of Pahoa, the island of Hawaii using a three-component fluxgate magnetometer. We measured at every 15.2 m (50 feet) interval covering a distance of 6, 310 m (20, 704 ft) where both historic and pre-historic highly magnetic basalt flows underlie. We also collected 197 core samples from eight road cuts, 489 specimens of which were subject to AF demagnetizations at 5 - 10 mT level up to a maximum field of 60 mT. We observed significant inclination anomalies ranging from a minimum of $31^{\circ}$ to a maximum $40^{\circ}$ where a uniform inclination value of $36.7^{\circ}$ (International Geomagnetic Reference Field, IGRF) was expected. Since the mean of the observed inclinations is approximately $35^{\circ}$ we assume that the study area is slightly affected by the magnetic terrain effect to a systematically shallower inclinations for being located in the regionally sloping surface of the southern side of the island (Baag, et al., 1995). We observed inclination anomalies showing wider (spacial) wavelength (160 - 600 m) and higher amplitudes in the historic lava flows area than in the northern pre-historic flows. Our observations imply that preexisting inclination anomalies such as those that we observed would have been interpreted as paleosecular variation (PSV). These inclination anomalies can best be attributed to concealed underground highly magnetic dikes, channel type lava flows, on-and-off hydrothermal activities through fissure-like openings, etc. Both the within- and between-site dispersions of natural remanent magnetization (NRM) are largest (up to ${\pm}7^{\circ}$) above the flows of 1955, while the area of pre-historic flows in the northern part of the study area exhibit the smallest dispersion. Nevertheless, mean inclinations of each historic flow of 1955 and 1790 are almost identical to that of the corresponding present field, whereas mean of NRM (after AF demagnetization) inclinations for each of the four pre-historic lava flow units is twelve to thirteen degrees lower than the present field inclination. We observed three cases of very large inclination variations from within a single flow, the best fitting curves of which are linear, second and third order polynomials each from within a single flow, whereas no present field variations are observed. This phenomena can be attributed to the notion that local magnetic anomalies on the surface of an active volcano are not permanent, but are transient. Therefore we believe that local magnetic anomalies of an active volcano may be constantly modified due to on going subsurface injections and circulations of hot material and also due to wide spacial and temporal distribution of highly magnetic basaltic flows that will constantly modify the topography which will in turn modify the local ambient geomagnetic field (Baag, et al., 1995). Our observations bring into question the general reliability of PSV data inferred from volcanic rocks, because on-going various geologic and geophysical activities associated with active volcano would continuously deflect and modify the ambient geomagnetic field.

• Annals of Clinical Neurophysiology
• /
• 제8권2호
• /
• pp.163-170
• /
• 2006

Backgrounds: MEG can measure the task-specific neurophysiologic activity with good spatial and time resolution. Language lateralization using noninvasive method has been a subject of interest in resective brain surgery. We purposed to develop a paradigm for language lateralization using MEG and validate its feasibility. Methods: Magnetic fields were obtained in 12 neurosurgical candidates and one volunteer for language tasks, with a 306 channel whole head MEG. Language tasks were word listening, reading and picture naming. We tested two word listening paradigms: semantic decision of meaning of abstract nouns, and recognition of repeated words. The subjects were instructed to silently name or read, and respond with pushing button or not. We decided language dominance according to the number of acceptable equivalent current dipoles (ECD) modeled by sequential single dipole, and the mean magnetic field strength by root mean square value, in each hemisphere. We collected clinical data including Wada test. Results: Magnetic fields evoked by word listening were generally distributed in bilateral temporoparietal areas with variable hemispheric dominance. Language tasks using visual stimuli frequently evoked magnetic field in posterior midline area, which made laterality decision difficult. Response during task resulted in more artifacts and different results depending on responding hand. Laterality decision with mean magnetic field strength was more concordant with Wada than the method with ECD number of each hemisphere. Conclusions: Word listening task without hand response is the most feasible paradigm for language lateralization using MEG. Mean magnetic field strength in each hemisphere is a proper index for hemispheric dominance.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 1999년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.363-370
• /
• 1999

Remotely sensed data is regarded as a potentially effective data source for the measurement of water quality and for the environmental change of water bodies. In this study, we measured the spectral reflectance by using multi-spectral image of low resolution camera(LRC) which will be loaded in the OSMI multi-purpose satellite(KOMPSAT) scheduled to be launched on 1999 to use the data in analyzing water pollution. We also investigated the possibility of extraction of water quality factors in water bodies by using remotely sensed low resolution data such as NOAA/AVHRR. In this study, Shiwha-District and Sang-Sam Lake was set up as the subject areas for the study. In this part of the study, we measured the spectral reflectance of the water surface to analyze the radiance of the water bodies in low resolution spectral band and tried to analyze the water quality factors in water bodies by using radiance feature from another remotely sensed data such as NOAA/AVHRR. As the method of this study, first, we measured the spectral reflectance of the water surface by using SFOV( Single Field of View) to measure the reflectance of water quality analysis from every channel in LRC spectral band(0.4~O.9${\mu}{\textrm}{m}$). Second, we investigated the usefulness of ground truth data and the LRC data by measuring every spectral reflectance of water quality factors. Third, we analyzed water quality factors by using the radiance feature from another remotely sensed data such as NOAA/AVHRR. We carried out ratio process of what we selected Chlorophyll-a and suspended sediments as the first factors of the water quality. The results of the analysis are below. First, the amount of pollutants of Shiwha-Lake has been increasing every you since 1987 by factors of eutrophication. Second, as a result of the reflectance, Chlorophyll-a represented high spectral reflectance mainly around 0.52${\mu}{\textrm}{m}$ of green spectral band, and turbidity represented high spectral reflectance at 0.57${\mu}{\textrm}{m}$. But suspended sediments absorbed high at 0.8${\mu}{\textrm}{m}$. Third, Chlorophyll-a and suspended sediments could have a distribution chart as a result of the water quality analysis by using NOAA/AVHRR data.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2004년도 춘계학술발표회
• /
• pp.807-814
• /
• 2004

Land seismic reflection survey has been increasingly demanded in various civil engineering works because of its own ability to delineate layers, water table, to detect cavities or fracture zones, to estimate seismic velocities of each layer. However, our shallow subsurface structures are very complex. The relatively thin layer(mostly soil) to the wavelength directly followed by a basic rock with high impedance used to generate complicated surface waves, kind of channel waves with high amplitude that is dominate in entire seismograms and hence the useful reflection events will be almost hopelessly immersed in the undesired surface waves. Thus, it would seem that the use of traditional seismic survey could not be likely to provide in itself a satisfactory information about our exploration targets. This paper hence introduces an efficient measuring strategy illustrating a properly controlled arrangement of the vertical single force sources commonly used, yielding a very sharply elongated form of P-energy with a minimum of S radiation energy, what we call, P-beam source. Abundant experiments of physical modeling showed that in that way the surface waves could be enormously reduced and the reflection events would be additive and thus reinforced. Examples of field data are also illustrated. The contribution of P-beam source will be great in civil engineering area as well as in general geological exploration area.

• 한국의학물리학회지:의학물리
• /
• 제19권4호
• /
• pp.256-262
• /
• 2008

자기공명분광법(magnetic resonance spectroscopy: MRS)은 인체내 대사물질을 정량분석하여 병변의 조기진단 및 정밀진단에 도움을 주고 있으며, 최근 임상에 이용되고 있는 자기공명분광법은 single voxel spectroscopy (SVS) 기법과 multi voxel spectroscopy (MVS) 기법이 있다. 본 연구에서는 SENSE와 NEX를 변화시킨 multi voxel spectroscopy (MVS)의 데이터와 기존 single voxel spectroscopy (SVS)의 데이터를 비교 분석하여, 각각의 데이터의 유의성 차이를 평가하고자 하였다. 정상 성인 지원자 13명(남자: 5명, 여자: 8명, 평균 41세, 표준편차 11.65세)을 대상으로 chemical shift image (CSI)를 이용한 MVS검사를 시행하였다. 장비는 3.0T Achieva Release Version 2.1 (Philips Medical System, Netherland)을 이용하였고, 8 channel head coil을 사용하여 brain thalamus 부위에서 CSI spectrum을 1 slice 획득하였다. Scan parameter로는 FOV (field of view): $230{\times}184mm^2$, TR (time to repetition): 2000 msec, TE (time to echo): 288 msec, matrix: $15{\times}12$, VOI(view of interest): $110{\times}110mm^2$, voxel size: $15{\times}15{\times}15mm^3$로 하였다. SENSE factor (S)와 NEX (N)는 S1*N1, S2*N1, S2*N2, S3*N2로 변화하여 스펙트럼을 획득하였고, 각 scan time은 5분 54초, 3분 32초, 6분 20초, 4분 20초였다. 얻은 모든 MRS 데이터는 jMRUI 3.0 Version 프로그램에서 분석하였고, SENSE factor와 NEX를 변화시켜 얻은 MVS data 그룹들이 정상 성인 뇌 대사물질의 변화에 영향을 주는지 검증하기 위해 그룹 간에 ANOVA분석을 실행하여 P 값이 0.05보다 크게 나오면 그룹들 사이에 유의한 차이가 없다고 분석하였다. NAA/Cr과 Cho/Cr의 상대적 비율은 MV와 SVS사이에서는 유의한 차이가 없었다. 즉, SENSE factor와 NEX를 변화시켜 얻은 MVS data에서 정상 성인 뇌조직의 대사물질의 변화를 관찰한 결과, S1*N1의 NAA/Cr은 $1.45{\pm}0.03$, Cho/Cr은 $0.88{\pm}0.03$이고, S2*N1의 NAA/Cr은 $1.44{\pm}0.03$, Cho/Cr은 $0.87{\pm}0.05$, S2*N2의 NAA/Cr은 $1.43{\pm}0.02$, Cho/Cr은 $0.87{\pm}0.04$이며, S3*N2의 NAA/Cr은 $1.45{\pm}0.03$, Cho/Cr은 $0.87{\pm}0.03$으로 나타났다(F-value : 1.37, D.F : 3, P-value : 0.262). 그러나 데이터의 질을 측정하기 위한 MVS 데이터의 NAA Peak line-width는 SVS 데이터의 NAA Peak line-width 보다 약 3배 정도 넓었다. 본 연구에서는 MVS에서 SENSE factor와 NEX 값을 다양하게 변화시킨 MVS의 데이터와 SVS의 데이터가 큰 차이가 없음을 확인하였다. 즉, 어는 특정 부위의 뇌 조직의 대사물질은 MVS와 SVS 기법 모두 큰 차이가 없음을 확인할 수 있었다. 그러므로 MVS는 SVS보다 광범한 부위를 짧은 시간 안에 검사할 수 있으므로 매우 유용한 방법이라고 사료된다.

• 한국수자원학회논문집
• /
• 제45권8호
• /
• pp.783-794
• /
• 2012

시간에 따른 하도의 수위 및 유량 변화에 영향을 많이 받는 수리구조물의 설계에 있어서 부정류 흐름 해석은 반드시 필요하다. 일반적으로 부정류 흐름 해석에는 수치모형이 많이 활용되고 있으나 수치모형의 검 보정을 위한 현장 자료의 획득이 어려운 경우가 많다. 또한 자료구축이 가능하더라도 인력과 비용이 많이 소모되며, 측정 정확도를 신뢰하기 어려운 경우가 많다. 이러한 경우 수치모형의 검 보정을 위해 부정류 수리실험을 통해 획득되는 자료를 활용하는 것이 대안이 될 수 있다. 따라서 본 연구에서는 다양한 형태의 부정류 수문곡선을 실험에서 재현할 수 있는 유량공급장치를 개발하고자하며, 개발된 부정류 유량공급장치를 이용하여 수리실험 수로에서 재현되는 수문곡선과 목표 수문곡선을 비교 분석함으로써 재현 정확도를 정량적으로 평가하고자 한다. 본 연구에서는 유량이 급격하게 증가 또는 감소하는 사각형 형태, 첨두유량 발생 시간이 짧은 삼각형 형태 및 일반적인 홍수 수문곡선 형태의 종(bell) 형태 수문곡선을 대상으로 재현 오차 및 Root Mean Square Error (RMSE)를 분석하였다. 재현 정확도 분석 결과, 사각형 형태의 수문곡선 재현 오차는 약 59% 정도로 가장 크게 나타났으며, 삼각형 형태의 수문곡선은 단일첨두와 이중첨두 형태 모두 약 10% 정도의 재현 오차가 나타났지만 홍수 수문곡선 형태인 종 모양의 수문곡선의 재현 오차는 최대 2% 이내인 것으로 나타났다.

• 지질공학
• /
• 제25권3호
• /
• pp.349-356
• /
• 2015

물리탐사의 대표적인 한계는 위아래 지층의 물성이 크게 차이나지 않을 경우 취득 신호가 작다는 점이다. 이 경우에는 서로 다른 물성에 기인하는 여러 가지 탐사들을 수행하고 그 결과들을 복합적으로 해석하여 그 효율성을 높인다. 레이더 및 고분해능 탄성파반사법 탐사는 천부 지질구조 및 매설 구조물을 신속하고 정확하게 찾아낼 수 있는 방법으로서 각각 유전율 경계면과 속도 경계면을 찾아내는데 효과적이다. 특히 이 연구에서는 전기적인 성질에 크게 반응하는 레이더 이벤트와 탄성적인 성질에 기인하는 탄성파 이벤트를 단일 단면도에 통합적으로 재건하는 기법을 모델링자료를 통해 구축하고 이를 바탕으로 청주 화강암부지의 얕은(3 m) 깊이의 지하수면, 그 하부의 풍화암, 연암 경계면을 효과적으로 파악하였다. 지반 강성에 중요한 인자인 밀림 탄성률(강성률)을 평가하기 위해 검층 자료를 통해 얻은 S파 속도를 여러 채널 S파 분석(MASW)과 공중점 교차상관 기법(CMPCC)에서 나온 값과 비교한 결과, 일반적인 MASW보다 이상대의 정확한 지점과 높은 S/N을 목적으로 고안된 CMPCC을 통해 얻은 속도가 실제 검층 자료에 보다 접근하였다.