• Progress in Medical Physics
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• v.14 no.2
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• pp.69-73
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• 2003

In this study, we measured shielding block correction factors for irregular fields and compared them with published data for the square blocked field. We devised a methods to measure the factors at an arbitrary depth in phantom. The measurements were performed for 12 shielding blocks used in radiation therapy. The measured correction factors for irregular blocked fields were consistent within $\pm$0.5% with those of the square blocked fields. Our results show that the shielding block correction factors for the typical square blocked fields can be used in clinical dose calculations for irregular blocked fields. However, for small fields, we suggest that verification be done by measurement.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.137-137
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• 2018

표면영상유속계는 매우 간편하고 신속하게 하천의 유속장을 측정하는 기법이지만 하천의 넓은 구역을 카메라로 촬영하기 때문에 영상왜곡이 필연적으로 발생한다. 이러한 왜곡을 보정하기위해 많이 사용되고 있는 2차원 투영좌표변환법을 이용하여 유속을 분석하였다. 하지만 2차원 투영좌표변환법의 경우 표정점이 수표면의 높이와 같은 위치에 존재하지 않으면 유속 분석 결과에 큰 오차를 유발시킨다. 홍수 시 하천의 수위가 급변할 경우 표정점을 수위 변화에 맞추어 이동시키면서 영상을 촬영한다는 것은 현실적으로 불가능하다. 이러한 문제점을 극복하기위해 하천의 수위 변화에 대응하는 영상왜곡 보정 기법 개발이 필요하다. 이에 본 연구에서는 기존의 2차원 투영좌표변환법을 개선하기 위해 제방근처의 표정점 4개와 카메라의 좌표와 카메라와 수표면까지의 연직거리를 이용한 영상왜곡 보정식을 개발하였다. 그리고 표정점과 수표면의 높이를 다양하게 변화시키면서 개발한 보정식을 적용하였다. 표정점이 수위에 맞게 설정된 경우를 기준으로 수위보다 높게 설정된 표정점에 대하여 보정식을 적용한 경우의 유속은 표정점이 수위보다 높게 설정된 경우의 유속과 비교한 결과 오차가 크게 개선되었음을 확인하였다. 따라서 하천에 CCTV를 고정적으로 설치하여 유량을 산정할 경우 본 연구에서 제시한 표정점 보정식을 활용한다면 수위가 급변하는 상황에서도 정확한 표면유속을 산정할 수 있을 것으로 기대한다.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.166-173
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• 1997

Influence coefficients on two-plane flexible rotor balancing model are derived by using the transfer matrix method. The model has a rigid uniform cylinder at mid-span of flexible shafts. Both faces of the rigid cylinder are used as the balancing planes. Calculated influence coefficients show that there exist the rotating speed ranges which are useless or insensitive for the balancing. Gyroscopic effect and damping are considered in the study and their effects are discussed.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.171-175
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• 2006

Gravity reduction and Bouguer anomaly are frequently misunderstood by many geoscientists as follows; the observed gravity is reduced to a common datum plane, so that gravity effects by all materials above the datum is removed, therefore, Bouguer anomaly is located on the datum plane. In reality, Bouguer anomaly does not lie on a common datum plane, but is difference between observed gravity and reference gravity at the actual point of measurement. Commonly used gravity reduction formulas are approximate formulas. Here, we introduce complete formulas, and suggest to use them for more accurate results. We also suggest to use not the geoid but the reference ellipsoid as the vertical datum.

• Progress in Medical Physics
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• v.12 no.2
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• pp.133-140
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• 2001

The dose calculations for blocked fields were studied. The shielding block correction factors(K$_{b}$) as a function of collimator and blocked field size(r$_{c}$ and r$_{b}$) were measured. A simplified $K_{b}$ as a function of $A_{r}$ (the A/P ratio of r$_{b}$ to r$_{c}$) was determined by measured data and a fitting function for $K_{b}$ was obtained. We found that the corrections of $K_{b}$ for blocked fields in MU(monitor units) calculations need not take into account in common case of $A_{r}$ \ulcorner1 but the errors will be 3.5% in particular case such as $A_{r}$ = 0.5. These results imply that the shielding block correction for blocked fields in clinical dose calculations must be considered.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.1
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• pp.31-36
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• 2006

A study on estimation of the datum level is carried out by combining observed and simulated harmonic constants of 4 major tides ($M_2$tide, $S_2$tide, $K_2$tide, and $O_1$tide). In the coastal zone, the datum level can be estimated by using observed tide harmonic constants at tide station. The observed tide harmonic constants, however, cannot be used to calculate the datum level of the sea because of the lack of tide station. In order to estimate the datum level of the sea, it is necessary to adopt the simulated harmonic constants instead of the observed ones. In this study, the datum level is calculated by using the simulated harmonic constants which is modified by tuning coefficient based on relationship between observed and simulated harmonic constants at tide station. Tuning coefficient of sea is interpolated on TIN (Triangulated Irregular Network) which has node points at tide stations.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.711-717
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• 2006

In order to study gas hydrate, potential future energy resources, Korea Institute of Geoscience and Mineral Resources has conducted seismic reflection survey in the East Sea since 1997. one of evidence for presence of gas hydrate in seismic reflection data is a bottom simulating reflector (BSR). The BSR occurs at the interface between overlaying higher velocity, hydrate-bearing sediment and underlying lower velocity, free gas-bearing sediment. That is often characterized by large reflection coefficient and reflection polarity reverse to that of seafloor reflection. In order to apply depth migration to seismic reflection data. we need high performance computers and a parallelizing technique because of huge data volume and computation. Phase shift plus interpolation (PSPI) is a useful method for migration due to less computing time and computational efficiency. PSPI is intrinsically parallelizing characteristic in the frequency domain. We conducted conventional data processing for the gas hydrate data of the Ease Sea and then applied prestack depth migration using message-passing-interface PSPI (MPI_PSPI) that was parallelized by MPI local-area-multi-computer (MPI_LAM). Velocity model was made using the stack velocities after we had picked horizons on the stack image with in-house processing tool, Geobit. We could find the BSRs on the migrated stack section were about at SP 3555-4162 and two way travel time around 2,950 ms in time domain. In depth domain such BSRs appear at 6-17 km distance and 2.1 km depth from the seafloor. Since energy concentrated subsurface was well imaged we have to choose acquisition parameters suited for transmitting seismic energy to target area.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.240-249
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• 2013

The seismic data quality of marine geological and engineering survey deteriorates because of the sea swell. We often conduct a marine survey when the swell height is about 1 ~ 2 m. The swell effect correction is required to enhance the horizontal continuity of seismic data and satisfy the resolution less than 1 m. We applied the swell correction to the 8 channel high-resolution airgun seismic data and 3.5 kHz subbottom profiler (SBP) data. The correct sea bottom detection is important for the swell correction. To detect the sea bottom, we used maximum amplitude of seismic signal around the expected sea bottom, and picked the first increasing point larger than threshold value related with the maximum amplitude. To find sea bottom easily in the case of the low quality data, we transformed the input data to envelope data or the cross-correlated data using the sea bottom wavelet. We averaged the picked sea bottom depths and calculated the correction values. The maximum correction of the airgun data was about 0.8 m and the maximum correction of two kinds of 3.5 kHz SBP data was 0.5 m and 2.0 m respectively. We enhanced the continuity of the subsurface layer and produced the high quality seismic section using the proper methods of swell correction.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.9-17
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• 2018

With an aim of considering the warping restraint effect, the results of the comparative study for several cases on the correction of the warping functions for the theoretical analysis of composite thin-walled beams with chord wise asymmetric closed cross-sections are presented in this study. To solve this problem, it is necessary to correct the warping function so as to satisfy the warping equilibrium condition like 1) without moving the position of the pole, 2) with only modifying the shape function using the existing pole, and 3) with moving the position of the pole. The cross-sectional characteristics of the cases were compared with each other. Finally, the cases were compared in order to correct the warping functions. The case 2) was observed to be more speedy and simple in computation compared to others.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.364-366
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• 2005

최신 동영상 압축 표준인 H.264는 압축 효율을 높이기 위해 기존의 표준과는 다른 1/2 화소 생성 방법을 사용한다. 그러므로 기존의 동영상 압축표준으로 압축된 비트열을 DCT 상에서 H.264로 트랜스코딩(transcoding)하기 위해서는 추가적인 보정 작업이 필요하다. 본 논문에서는 MPEG-2로 압축된 비트열을 DCT 상에서 H.264로 트랜스코딩 할 때 두 표준 간 1/2 화소 값의 차이를 보정하는 기법을 제안한다. 제안된 1/2 화소 보정 기법에서는 DCT 상태의 창조 프레임을 이용하여 두 표준 간의 차이 값을 구하여 입력으로 들어온 블록의 값에 더하여 보정한다. 픽셀 기반에서 보정하는 기법과 성능을 비교한 결과 제안하는 기법이 화질 면에서 우수하며 움직임이 빠른 비디오의 경우 계산량이 높아지는 것으로 나타났다.