• Korean Journal of Radiology
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• 제2권4호
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• pp.210-215
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• 2001

Objective: To investigate the efficacy of gadobenate dimeglumine (GdBOPTA) enhanced MR imaging for the detection of liver lesions in patients with primary malignant hepatic neoplasms. Materials and Methods: Thirty-one patients with histologically proven primary malignancy of the liver were evaluated before and after administration of GdBOPTA at dose 0.05 or 0.10 mmol/kg. T1-weighted spin echo (T1W-SE) and gradient echo (T1W-GRE) images were evaluated for lesion number, location, size and confidence by three off-site independent reviewers and the findings were compared to reference standard imaging (intraoperative ultrasound, computed tomography during arterial portography or lipiodol computed tomography). Results were analyzed for significance using a two-sided McNemar's test. Results: More lesions were identified on Gd-BOPTA enhanced images than on unenhanced images and there was no significant difference in lesion detection between either concentration. The largest benefit was in detection of lesions under 1 cm in size (7 to 21, 9 to 15, 16 to 18 for reviewers A, B, C respectively). In 68% of the patients with more than one lesion, Gd-BOPTA increased the number of lesions detected. Conclusion: Liver MR imaging after Gd-BOPTA increases the detection of liver lesions in patients with primary malignant hepatic neoplasm.

• Advances in aircraft and spacecraft science
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• 제5권2호
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• pp.225-237
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• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.

• 한국음향학회지
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• 제16권5호
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• pp.76-82
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• 1997

본 논문은 음원의 절대위치를 정확하게 추정할 수 있는 음향홀로그래픽법에 관하여 계산기상의 시뮬레이션 및 측정시스템을 이용한 실험과결과에 대하여 서술한다. 이 연구에서는 원거리 음장을 만족하도록 측정면을 설정하여 7개의 마이크로폰을 직선으로 배열한다. 음원의 측정은 음원면에 근접한 위치에 한 개의 기준 마이크로폰을 설치하고 측정면의 마이크로폰들을 등간격으로 스캐닝하면서 각지점의 음을 동시 기록한다. 수음한 기준음과 측정음간의 크로스 스펙트럼 알고리즘에 의하여 음원의 절대위치를 측정한다. 그리고 각 마이크로폰의 위상차는 기준 마이크로폰을 대상으로 위상보상 하였으며, 측정시의 시간지연은 제 1열 측정시점을 기준으로 시간보상을 행하였다. 측정면에 설정한 마이크로폰들의 최적 간격은 수치 시뮬레이션에 의하여 정한다. 음원신호는 정현파를 이용하고 S/N비를 30dB의 조건하에서 각각 실험을 행하였다. 시뮬레이션과 실험에서 결정한 최적 마이크로폰 간격은 2KHz인 정현파 음원을 기준으로 하여 공간상의 나이키스트 조건을 만족하도록 설정하였다. 무향실에서 측정한 실험결고, 500Hz 와 1KHz의 신호원에 대한 음원이 2KHz인 경우의 추정된 3차원 홀로그램의 주극폭이 각각 87%와 30%씩 감소하였고, 그 결과 수치 시뮬레이션의 타당성을 확인할 수 있었다. 그러므로 본 연구에서 제안하는 3차원 음향 홀로그래픽법을 이용한 음원위치 추정에 관한 연구의 유용성을 검증하였다.

• 한국산학기술학회논문지
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• 제10권8호
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• pp.1783-1788
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• 2009

스컬 공정으로 제조된 큐빅지르코니아에서 보석용으로 사용되는 부분 외에 일반적으로 버려지는 에지부 폐지르코니아를 분쇄하여 1550$^{circ}C$-2hr의 저온 소결 공정으로 소결한 소결체의 물성을 분석하여 재활용 가능성을 확인해보았다. 비교를 위한 새 지르코니아와 30 mol%-$Y_2O_3$ 혼합분말 (모두 1㎛ 길이의 셀룰러형)로 만든 소결체는 직경 $\sim$10㎛의 조밀 소결체가 결합된 형태를 보였으나, 1$\sim$30㎛의 크기 및 형태가 일정하지 않은 분말로 제조된 폐지르코니아 소결체는 $\sim$30㎛ 이상의 결정립을 가진 미세구조를 보였다. 새 지르코니아 혼합 분말로 만든 소결체는 cubic상인 $Y_2O_3$, $Z_{r0.8}O_{1.9}$와 monoclinic상인 $Z_rO_2$의 혼합상을 보였으나, 폐지르코니아 분말 소결체의 경우 tetragonal 단일상을 보임을 확인하였다. 폐지르코니아 소결체도 70 이상의 비커스 경도와 4.11 g/cc의 소결밀도를 보여서 구조재로 사용이 가능하였다.

• 대한원격탐사학회지
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• 제36권5_1호
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• pp.847-860
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• 2020

2-pass DInSAR (Differential Interferometric SAR) 기법을 이용한 DEM 생성 방법은 SAR 영상쌍 간의 정합, 간섭도 생성, 위상 unwrapping, DEM오차 계산, 좌표계 변환 등 복잡한 단계가 필요하다. 이러한 각 단계별 자료처리 정확도는 최종적으로 생성되는 DEM의 성능에 영향을 미치게 된다. 본 연구에서는 TanDEM-X bistatic SAR 영상의 2-pass DInSAR 기법 기반 DEM 생성 방법에 대한 성능 향상을 위한 개선된 방법을 개발하였다. 개발된 DEM 생성 방법은 unwrapped 위상 내의 DEM 오차와 좌표계 변환 시 발생할 수 있는 DEM오차를 현저히 줄일 수 있는 방법이다. 개발된 알고리즘의 성능 분석은 GPS 측량으로부터 생성한 지상기준점(Ground Control Point, GCP)을 이용하여 기존의 방법과 새로 제안된 알고리즘 적용 결과의 수직정확도(Root Mean Square Error, RMSE)를 비교하여 수행하였다. 실제 unwrapped 위상 및 좌표계변환 오차에 대한 보정을 수행하지 않고 생성한 DInSAR 기반 DEM의 고도 오차는 수직정확도는 39.617 m로 관측되었고, 제안한 방법을 통하여 생성한 DEM의 수직정확도는 2.346 m로 향상됨을 확인할 수 있었다. 제안하는 2-pass DInSAR 기법을 통해 reference로 사용한 SRTM 30 m DEM(수직정확도 5.567 m)에 DInSAR로 관측한 SRTM DEM 오차를 보상하여 최종적으로 공간해상도는 약 5배, 수직 정확도는 약 2.4배 향상된 DEM을 생성할 수 있었다. 또한, 제안한 방법을 통하여 생성한 DEM의 공간해상도를 SRTM 30 m DEM과 TanDEM-X 90 m DEM과 일치시키고 수직정확도를 비교한 결과 각각 약 1.7배 및 1.6배 향상되어 제안하는 2-pass DInSAR 기반 DEM 생성 방법으로 보다 정확한 DEM 생성이 가능함을 확인할 수 있었다. 빈번한 형태학적 변화를 갖는 지역에 대한 DEM의 지속적인 업데이트를 위하여 본 연구에서 도출한 방법을 이용한다면 저비용으로 빠른 시간 내에 효과적으로 DEM을 갱신할 수 있을 것이다.

• 분석과학
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• 제27권2호
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• pp.92-99
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• 2014

본 연구에서는 음이온 고체상 추출법 (AE SPE; anion exchange solid phase extraction)을 사용하여 간섭요인을 제거한 후, 친화 크로마토그래피 AF HPLC; affinity high performance liquid chromatography)와 유도결합 플라스마 질량분석법 (ICP/MS; inductively coupled plasma/mass spectrometry)을 사용하여 한국인의 혈청에서의 셀레노 단백질을 분리하고 정량하였다. 먼저 동위원소 희석법으로 셀레늄 총량을 분석한 결과, 건강한 한국 사람의 혈청내 평균농도는 $94.3{\pm}2.3ngg^{-1}$ 이었다. AE SPE와 AF 컬럼을 online으로 연결하여 셀레노단백질인 glutathione peroxidase (GPx), selenoprotein P (SelP), selenoalbumin (SeAlb)을 분리하고, 후 컬럼 동위원소 희석법 (PC ID; post column isotope dilution)으로 정량하였다. 혈청 인증표준물인 BCR-637을 분석한 결과 전체 셀레노 단백질의 합은 $85.4{\pm}3.4ngg^{-1}$으로 문헌값인 $81{\pm}7ngg^{-1}$과 일치하는 결과를 얻을 수 있었다. 20 명의 건강한 한국인의 혈청에서 얻은 셀레노 단백질 GPx, SelP 및 SeAlb 의 농도는 각각 $12.1{\pm}1.4ngg^{-1}$, $57.2{\pm}2.0ngg^{-1}$, 그리고 $20.0{\pm}1.9ngg^{-1}$ 이었으며 이들의 합인 $89.3ngg^{-1}$은 셀레늄의 총량값인 $94.3ngg^{-1}$과 거의 같은 값으로 혈청에서의 셀레늄은 주로 셀레노 단백질로 구성되어 있음을 알았다. 이 중 GPx의 농도는 간섭을 제거하기 전인 $25.0ngg^{-1}$에 비해 50% 이상 크게 감소하였는데 이로서 간섭은 주로 GPx에 포함되어 있음을 확인할 수 있었다. AE SPE는 간섭요인인 Cl과 Br을 제거 하는데 매우 효과적임을 보여주었다.

• Journal of Electrical Engineering and Technology
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• 제1권2호
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• pp.153-160
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• 2006

This paper presents a new compensating system, which consists of a shunt active filter and passive components for mitigating voltage and current disturbances arising from an Electric Arc Furnace (EAF). A novel control strategy is presented for the shunt active filter. An extended method based on instantaneous power theory in a rotating reference frame is developed for extraction of compensating signals. Since voltages at the point of common coupling contain low frequency interharmonics, conventional methods cannot be used for dc voltage regulation. Therefore, a new method is introduced for this purpose. The passive components limit the fast variations of load currents and mitigate voltage notching at the Point of Common Coupling (PCC). A three-phase electric arc furnace model is used to show power quality improvement through reactive power and harmonic compensation by a shunt active filter using the proposed control method. The system performance is investigated by simulation, which shows improvement in power quality indices such as flicker severity index.

• Journal of Power Electronics
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• 제5권2호
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• pp.109-119
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• 2005

This paper deals with the performance analysis of static compensator (STATCOM) based voltage regulator for self­excited induction generators (SEIGs) supplying balanced/unbalanced and linear/ non-linear loads. In practice, most of the loads are linear. But the presence of non-linear loads in some applications injects harmonics into the generating system. Because an SEIG is a weak isolated system, these harmonics have a great effect on its performance. Additionally, SEIG's offer poor voltage regulation and require an adjustable reactive power source to maintain a constant terminal voltage under a varying load. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC- VSI) known as STATCOM is used for harmonic elimination. It also provides the required reactive power an SEIG needs to maintain a constant terminal voltage under varying loads. A dynamic model of an SEIG-STATCOM system with the ability to simulate varying loads has been developed using a stationary d-q axes reference frame. This enables us to predict the behavior of the system under transient conditions. The simulated results show that by using a STATCOM based voltage regulator the SEIG terminal voltage can be maintained constant and free from harmonics under linear/non linear and balanced/unbalanced loads.

• Bulletin of the Korean Chemical Society
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• 제33권5호
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• pp.1734-1740
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• 2012

Voltammetric characterization of hydrophilic anion transfer processes across a 66 microhole array interface between the water and polyvinylchloride-2-nitrophenyloctylether gel layer is demonstrated. Since the transfer of hydrophilic anions including $Br^-$, $NO_3{^-}$, $I^-$, $SCN^-$ and $ClO_4{^-}$ across the liquid/gel interface usually sets the potential window within a negative potential region, a highly hydrophobic organic electrolyte, tetraoctylammonium tetrakis(pentafluorophenyl)borate, providing a wider potential window was incorporated into the gel phase. The transfer reaction of perchlorate anions across the microhole-water/gel interface was first studied using cyclic voltammetry and differential pulse voltammetry. The full voltammetric response of perchlorate anion transfer was then used as a reference for evaluating the half-wave transfer potentials, the formal transfer potentials and the formal Gibbs transfer energies of more hydrophilic anions such as $Br^-$, $NO_3{^-}$, $I^-$, and $SCN^-$. The current response associated with the perchlorate anion transfer across the micro-water/gel interface versus the perchlorate concentration was also demonstrated for sensing applications.

• Journal of Positioning, Navigation, and Timing
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• 제2권1호
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• pp.59-65
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• 2013

The signal broadcast from a GPS satellite experiences code delay and carrier phase advance while passing through the ionosphere, which causes a signal error. Many ionosphere models have been studied to correct this ionospheric delay error. In this paper, the ionosphere modeling for the Korean Peninsula was carried out using a spherical harmonics based model. In contrast to the previous studies, we considered a real-time ionospheric delay correction model using fewer number of basis functions. The modeling performance was evaluated by comparing with a grid model. Total number of basis functions was set to be identical to the number of grid points in the grid model. The performance test was conducted using the GPS measurements collected from 5 reference stations during 24 hours. In the test result, the modeling residual error was smaller than that of the existing grid model. However, when the number of measurements was small and the measurements were not evenly distributed, the overall trend was found to be problematic. For improving this problem, we implemented the modeling with additional virtual measurements.