• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.123-124
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• 2023

Despite the acuuracy, stability, and economic feasibility of geomagnetic field-based indoor positioning, its applicability in construction sites needs to be thoroughly discussed due to the issue of distortion of geomagnetic fields around ferromagnetic objects such as rebars. In this study, the possibility of applying the geomagnetic field-based indoor positioning in construction sites was reviewed through the Student's t-test after measuring the changes in geomagnetic field values depending on the presence or absence of rebars. The statistical analysis revealed that there is a high probability (over 80%) of significant changes in geomagnetic field values when measuring points are located within 60cm from the rebars. On the other hand, the probability of minimal changes in geomagnetic field values is over 90% when measuring points are located more than 60cm from the rebars. This suggests the application of geomagnetic-based indoor positioning in construction sites would be possible if the issue of distortion in geomagnetic field values near rebars within 60cm is resolved.

• 정보저장시스템학회:학술대회논문집
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• 정보저장시스템학회 2005년도 추계학술대회 논문집
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• pp.12-13
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• 2005

Near field recording (NFR) technology with SIL has been thought as the most promising generation optical storage device. A gap distance between the SIL and the disc should be controlled to be 20${\~}$40nm. We observed gap error signal in our NFR test-bed using a blue LD (405nm). The digital gap servo filter and control algorithm were developed to maintain a constant air gap by adopting a conventional actuator.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.69-76
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• 2002

In this paper, several improved Element-Free Galerkin (EFG) methods containing singular expression in their approximation functions are compared one another through a patch test with near-tip field. Intrinsic enrichments that expand the basis function partially and fully with known near-tip displacement field and a local enrichment using auxiliary supports based on the partition of unity concept are examined by evaluating a relative stress norm error and the stress intensity factor. Some numerical examinations graphically show that how the size of compact support, dilation parameter and the diffraction parameter can affect the accuracy of the improved EFG methods in the error and the stress intensity factor.

• 전기학회논문지
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• 제62권9호
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• pp.1223-1227
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• 2013

If the factory test efficiency and field operation efficiency of water turbine are different from each other, issues for efficiency warranty can be raised. So, This paper shows the result for comparative analysis of field operating efficiency vs plant testing efficiency of the water turbine generator installed in agricultural reservoir. The efficiency of the induction generator is analyzed by the change of rotational speed with the parameter obtained by test, the efficiency of water turbine is calculated by the change of head with the design flow. Efficiency deviation of induction generator is lower but the variation of developed power is pretty high near the rated speed and the efficiency variation of water turbine is high by the fluctuation of head for constant flow. It was found that factory test efficiency and total efficiency of water turbine generator calculated according to the rotational speed are very close.

• 한국초전도ㆍ저온공학회논문지
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• 제15권1호
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• pp.35-39
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• 2013

The superconducting Homopolar motor is manufactured and tested. Homopolar motor system is simple and solid as the field coil of the motor is fixed near the stator coil without rotating system. In this paper, a 5 kW fully superconducting homopolar motor which has high temperature superconducting armature and field coils is manufactured and tested in liquid nitrogen. The critical current test results of the used 2G superconducting wire, pancake coil for rotor winding and race-track coils for armature winding are reported. Also, the test result of rotating and operating performance is presented. The operating frequency is to be 5 Hz for low-speed rotating. The developed fully superconducting Homopolar motor is the world's first.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 총회 및 춘계학술발표회
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• pp.31-34
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• 2004

Feasibility of electrokinetic(EK)-Fenton process and Ozone chemical oxidation were investigated for tile removal of organic contaminants and heavy metals from the contaminated soil. In EK-Fenton process, accumulated electroosmotic flow(EOF) was 80 L for 26 days. Removal efficiency of TPH, As, and Ni were 61%, 36%, and 47%, respectively. The concentration of As was high near the anode due to the transport of anionic As toward the anode, while the concentration of Ni was high near the cathode by the movement of cationic Ni to the cathode. Field scale application of in-situ ozonation was carried out for removal of TPH in 3-D test cell (3 m$\times$2 m$\times$2 m). After 25 days of ozone injection, more than 80% of removal rate was observed through the test cell.

• 한국전자파학회논문지
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• 제28권4호
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• pp.318-327
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• 2017

능동위상배열안테나는 정밀한 빔의 형성과 성능 확인을 위해 근접전계 수신시험이 요구된다. 그에 따른 근접전계 수신시험을 통해 모노펄스 기능을 활용하기 위한 보상값을 획득하게 된다. 하지만, 많은 주파수 채널을 사용하는 레이다의 경우 많은 시간과 노력이 요구된다. 효율적인 레이다 개발과 생산을 위해서는 선택적으로 주파수 채널을 선정하고, 그 측정값을 기준으로 측정하지 않은 주파수 채널의 보상값을 보간법을 통해 예측하여 획득할 수 있다. 이와 같은 방법으로 보상값의 위상각 정보를 획득할 경우, 합, 차 채널간의 위상변화량을 확인할 필요성이 있다. 위상의 측정은 랩핑으로 인하여 비선형 현상이 나타날 수 있기 때문이다. 일반적인 레이다의 경우, 합, 차 채널의 전기적 길이가 유사하게 설계되지만, 특정 목적으로 전기적 길이 차이가 발생할 경우, 랩핑 현상으로 인해 보간법의 오류를 발생할 수 있다. 본 논문에서는 전기적 길이 차이에 의해 발생되는 보간법의 오류를 확인하고, 하나의 주파수 선택 방안을 제시한다.

• Journal of Astronomy and Space Sciences
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• 제28권2호
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• pp.117-122
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• 2011

In this paper, the anisotropic nature of the magnetic turbulence associated with magnetic dipolarizations in the Earth's plasma sheet is examined. Specifically, we determine the power spectral indices for the perpendicular and parallel components of the fluctuating magnetic field with respect to the background magnetic field, and compare them in order to identify possible anisotropic features. For this study, we identify a total of 47 dipolarization events in February 2008 using the magnetic field data observed by the THEMIS A, D and E satellites when they are situated near the neutral sheet in the near-Earth tail. For the identified events, we estimate the spectral indices for the frequency range from 1.3 mHz to 42 mHz. The results show that the degree of anisotropy, as defined by the ratio of the spectral index of the perpendicular components to that of the parallel component, can range from ~0.2 to ~2.6, and there are more events associated with the ratio greater than unity (i.e., the perpendicular index being greater than the parallel index) than those which are anisotropic in the opposite sense. This implies that the dipolarization-associated turbulence of the magnetic field is often anisotropic, to some non-negligible degree. We then discuss how this result differs from what the theory of homogeneous, anisotropic, magnetohydrodynamic turbulence would predict.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2001년도 학술대회 논문집
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• pp.121-124
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• 2001

The research results on the superconducting magnet for whole body MRI are presented. The magnet consists of main coil with 6 solenoid coils, shielding coil with 2 solenoid coils and 6 sets of cryogenic shim coil. The ferromagnetic shim assembly is installed on the inside wall of the room temperature bore for shimming inhomogeneous field components generated due to manufacturing tolerances, installation misalignments and external ferromagnetic materials near the magnet. Also, the magnet is enclosed with the horizontal type cryostat with 80cm room temperature bore to keep the magnet under the operating temperature. The magnetic field distributions within the imaging volume were measured by the NMR field mapping system. Through the test, the central field of magnet was 1.5 Tesla and the field homogeneity of 9.3 ppm has been obtained on 40cm DSV(the diameter of spherical volume) and using this magnet, comparatively good images for human body, fruits and water phantoms have been achieved.

• 한국환경복원기술학회지
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• 제2권3호
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• pp.1-9
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• 1999

This paper described the results of the characteristics of the near-bottom flow and field analysis of the tidal flats sediment. It was the aim of this paper to grasp current flow of tidal flat's environment and influence factor for environmental change forecast of tidal flats. Field measurement of water velocity, water elevation, bed materials test, and temperature distribution of tidal flat were conducted. Thereafter, current flow, turbidity and temperature distribution of tidal flat sediment have been discussed. The field research results showed that the fluctuating velocity near the seabed before and after its appearance at low tide was strongly affected by the wind wave. The resuspension of the sea-bottom sediment took place with great intensity before and after the appearance of the seabed at low tide. Both the sea water level and the weather condition were a significant influential factors. Such as, temperature and turbidity just on the surface and the shallow layer of seabed sediments were varied largely with time and weather conditions, but that its deeper layers was almost constant. Temperature on the seabed sediments was strongly influenced by irradiance and water depth. The temperature variation of the tidal flat and the variation characteristics of the current flow and turbidity depend greatly on the inhabiting environment of the tidal flat benthic organism.