• 대한디지털의료영상학회논문지
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• 제12권1호
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• pp.27-31
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• 2010

The purpose of this study was to investigated the usefulness of MR perfusion image comparing with SPECT image. A total of pediatric 30 patients(average age : 7.8) with Moyamoya disease were performed MR Perfusion with 32 channel body coil at 3T from March 01, 2010 to June 10, 2010. The MRI sequences and parameters were as followed : gradient Echo-planar imaging(EPI), TR/TE : 2000ms/50ms, FA : $90^{\circ}$, FOV : $240{\times}240$, Matrix : $128{\times}128$, Thickness : 5mm, Gap : 1.5mm. Images were obtained contrast agent administrated at a rate of 1mL/sec after scan start 10s with a total of slice 1000 images(50 phase/1 slice). It was measured with visual color image and digitize data using MRDx software(IDL version 6.2) and also, it was compared of measurement with values of normal and abnormal ratio to analyze hemodynamic change, and a comparison between perfusion MR with technique using Warm Color at SPECT examination. On MR perfusion examination, the color images from abnormal region to the red collar with rCBV(relative cerebral blood volume) and rCBF(relative cerebral blood flow) caused by increase cerebral blood flow with brain vascular occlusion in surrounding collateral circulation advancement, the blood speed relatively was depicted slowly with blue in MTT(Mean Transit Time) and TTP(Time to Peak) images. The region which was visible abnormally from MR perfusion examination visually were detected as comparison with the same SPECT examination region, would be able to confirm the identical results in MMD(Moyamoya disease)judgments. Hymo-dynamic change in MR perfusion examination produced by increase and delay cerebral blood flow. This change with digitize data and being color imaging makes enable to distinguish between normal and abnormal area. Relatively, MR perfusion examination compared with SPECT examination could bring an excellent image with spatial resolution without radiation expose.

• International Journal of Automotive Technology
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• 제6권1호
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• pp.45-52
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• 2005

Interrupted creep tests for investigating the structural degradation during creep were conducted for a Mod.9Cr-1Mo steel in the range of stress from 71 to 167 MPa and temperature from 873 to 923 K. The change of hardness and tempered martensitic lath width was measured in grip and gauge parts of interrupted creep specimens. The lath structure was thermally stable in static conditions. However, it was not stable during creep, and the structural change was enhanced by creep strain. The relation between the change in lath width and creep strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep LCR(life consumption ratio). Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep LCR. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

• Journal of Information Processing Systems
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• 제19권2호
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• pp.149-163
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• 2023

Affected by external factors, errors in time series data collected by sensors are common. Using the traditional method of constraining the speed change rate to clean the errors can get good performance. However, they are only limited to the data of stable changing speed because of fixed constraint rules. Actually, data with uneven changing speed is common in practice. To solve this problem, an online cleaning algorithm for time series data based on dynamic speed change rate constraints is proposed in this paper. Since time series data usually changes periodically, we use the extreme learning machine to learn the law of speed changes from past data and predict the speed ranges that change over time to detect the data. In order to realize online data repair, a dual-window mechanism is proposed to transform the global optimal into the local optimal, and the traditional minimum change principle and median theorem are applied in the selection of the repair strategy. Aiming at the problem that the repair method based on the minimum change principle cannot correct consecutive abnormal points, through quantitative analysis, it is believed that the repair strategy should be the boundary of the repair candidate set. The experimental results obtained on the dataset show that the method proposed in this paper can get a better repair effect.

• 반도체디스플레이기술학회지
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• 제21권2호
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• pp.74-84
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• 2022

As the semiconductor industry develops, the difficulty of newly required process technology becomes difficult, and the importance of production yield and product reliability increases. As an effort to minimize yield loss in the manufacturing process, interests in the process defect process for facility diagnosis and defect identification are continuously increasing. This research observed the plasma condition changes in the multi oxide/nitride layer deposition (MOLD) process, which is one of the 3D-NAND manufacturing processes through optical emission spectroscopy (OES) and monitored the result of whether the change in plasma characteristics generated in repeated deposition of oxide film and nitride film could directly affect the film. Based on these results, it was confirmed that if a change over a certain period occurs, a change in the plasma characteristics was detected. The change may affect the quality of oxide film, such as the film thickness as well as the interfacial surface roughness when the oxide and nitride thin film deposited by plasma enhenced chemical vapor deposition (PECVD) method.

• 재무관리연구
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• 제25권2호
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• pp.191-213
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• 2008

본 연구는 1999년부터 2006년까지 유가증권 시장 및 코스닥 시장의 인수합병 공시에 따른 주주와 채권자의 부의 변화 및 그들의 상호관계를 연구하여, 인수합병에 대한 부의 이전가설을 재검증한다. 주주 부의 변화는 공시에 따른 주가반응(Cumulative Abnormal Return, CAR)으로 측정하며, 채권자 부의 변화는 공시기업의 일반사채 수익률의 변화(Yield Spread Change, YSC) 및 신용등급의 변화로 측정한다. 실증분석 결과, 총 344개의 표본기업을 대상으로 한 인수합병의 합병기업(acquiring firm)의 CAR은 3.59%를 나타내어 인수합병 공시에 따른 주주의 부가 증가한다는 기존의 연구결과를 지지하였다. 채권관련 자료를 얻을 수 있는 2001년부터 2006년까지 총 35개의 합병기업의 표본을 대상으로 한 채권수익률 변화는 벤치마크로서 자기등급의 채권수익률과 국채수익률을 사용하는 경우 모두 음(-)의 값을 나타내어 채권자의 부 또한 증가한다는 것을 알 수 있었다. 또한 신용등급도 인수합병 1년 이후에 상승하는 것으로 나타나서, 기업의 인수합병 의사결정이 채권자의 부를 증가시키는 것을 발견하였다. 이러한 연구의 결과는 채권자의 부가 증가한다는 해외 선행연구와 일치하는 결과이다. 즉, 국내의 인수합병에서 합병 의사결정으로 인해 주주에게로 채권자의 부가 이전되기 보다는 채권자의 부 또한 증가한다는 것을 의미한다.

• 한국수자원학회논문집
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• 제51권spc1호
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• pp.1127-1134
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• 2018

기후변화에 관한 정부 간 협의체의 5차 평가보고서에 기술된 바와 같이 기후변화로 인해 이상기후 현상의 발생빈도가 증가하고 있다. 이에 홍수, 가뭄 등 수자원과 관련된 재해의 발생빈도 또한 증가하고 있다. 이 중 가뭄은 용수공급에 가장 큰 영향을 미치는 재해이다. 최근 우리나라의 가뭄피해 사례를 보면 가뭄의 강도와 발생빈도가 증가하는 것을 확인할 수 있다. 따라서 안정적인 용수공급을 위한 수자원 확보 기술이 필요한 시점이다. 수자원장기종합계획에서는 수자원에도 예비율 개념의 대책 도입이 필요하다고 언급한 바 있다. 현재 국내 대부분의 다목적댐들은 평상시 용수공급에 이용되는 이수용량 외에 비상시 활용 가능한 비상용량을 확보하고 있지만 명확한 활용 기준이 없어 이를 활용하지 못하고 있는 실정이다. 따라서 본 연구에서는 안정적인 용수공급을 위해 비상용량을 예비량으로 활용하는 방안에 대해 연구하였다. 기후변화의 영향을 고려하기 위해 AR5 기반 수문시나리오를 저수지 모의운영 모형의 유입량 자료로 이용하였다. 비상용량과 용수공급 조정기준의 활용 조건에 따라 저수지 모의 운영을 실시하였고 모의 결과를 이용하여 다목적댐별 적정 예비율을 산정하였다.

• 대한원격탐사학회지
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• 제38권6_1호
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• pp.1231-1244
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• 2022

이상기상으로 인해 노지 작물이 스트레스 상황에 노출되는 빈도가 증가하고 있다. 우리나라에서도 대표적인 벼 재배지역에서 대규모의 병해가 발생하는 사례가 나타났으며, 특정 시기에 대규모 필지에서 발생하는 피해를 현장방문으로 조사하는 것은 한계가 있다. 위성 기반의 원격탐사 기법은 시군 영역을 대상으로 작물을 모니터링하기에 유용하나 작물의 생육이상에 따른 민감도 평가가 선행되어야 한다. 본 연구에서는 벼 병해 발생 지역에서 서로 다른 공간해상도를 가지는 위성 기반의 정규화식생지수(normalized difference vegetation index, NDVI)를 드론 영상을 이용하여 평가하였다. 10 m와 30 m의 공간해상도를 가지는 Sentinel-2, Landsat-8 위성 영상을 평가하였으며, 드론 영상은 약 8-10 cm의 공간해상도를 가졌다. 위성 영상에 맞춰 리샘플링(resampling)된 드론 NDVI는 Sentinel-2 NDVI 와 0.867-0.940의 상관관계를 가졌으며, Landsat-8 NDVI와는 0.813-0.934의 상관관계를 가졌다. 센서의 차이, 관측 시점의 차이 등으로 인한 편향(bias) 영향을 최소화하였을 때, Sentinel-2 NDVI는 Landsat-8 NDVI에 비해 드론 NDVI와 0.2-2.8% 더 적은 정규화된 평균 제곱근 오차를 가졌다. 또한, Sentinel-2 NDVI는 드론 NDVI와 병해 피해 정도와 관계없이 일정한 오차를 가졌으나 Landsat-8 NDVI는 병해 피해 정도에 따라 드론 NDVI와 오차 특성이 다르게 나타났다. 농경지 경계에서 오차가 크다는 것을 고려했을 때 공간해상도가 높은 영상을 활용하는 것이 작물 모니터링에 효과적이라고 판단된다.

• 산업경영시스템학회지
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• 제20권44호
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• pp.69-79
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• 1997

We investigate both of central and dispersion tendencies of the observed test statistics in control charts in order to judge whether a production process is abnormal or not. In order to do it, first, we study about detection of changes of the population mean as a central tendency The $\bar{x}$ and x control charts are used for detecting the change of the population mean $\mu$. We shows the probability detecting the change of population mean using the $\bar{x}$ and x control charts. Secondly, we study about detection of changes of the population standard deviation as a dispersion tendency in the s control chart. In our studies, for the given several parameters the detection probabilities of changes of central and dispersion tendencies are calculated, the necessary sample size values n are suggested for detecting the changes, and their informations are given as various tables.

• 한국농공학회논문집
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• 제49권5호
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• pp.3-9
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• 2007

In this study, the effect of the purification materials is analyzed and tested by Flow 3D and Hydraulic model test. Three dimension numerical analysis led from the research that sees abnormal form and the size back of the water purification material conferred the flowing water conduct inside the test channel against the test condition. Comparison it analyzed the flux distribution, a water depth of the channel which establishes the water purification materials the cross section, an interval of the water purification material, a conference with general channel, it change executed. As a result, the cross section ratio of the purification materials against and a flux change from the test which it sees. The interval of the purification materials in order to prevent three dimension that follows in decrease of increase and flux must decide an interval.

• East Asian mathematical journal
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• 제36권1호
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• pp.81-90
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• 2020

Many compartment models assume a kinetically homogeneous amount of materials that have well-stirred compartments. However, based on observations from such processes, they have been heuristically fitted by exponential or gamma distributions even though biological media are inhomogeneous in real environments. Fractional differential equations using a specific kernel in Pharmacokinetic/Pharmacodynamic (PKPD) model are recently introduced to account for abnormal drug disposition. We discuss a tumor growth inhibition (TGI) model using fractional-order derivative from it. This represents a tumor growth delay by cytotoxic agents and additionally show variations in the equilibrium points by the change of fractional order. The result indicates that the equilibrium depends on the tumor size as well as a change of the fractional order. We find that the smaller the fractional order, the smaller the equilibrium value. However, a difference of them is the number of concavities and this indicates that TGI over time profile for fitting or prediction should be determined properly either fractional order or tumor sizes according to the number of concavities shown in experimental data.