• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.422-424
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• 2002

The accuracy of DXA(Dual Energy X-ray Absorptiometry) highly depends on the detection and separation capability of dual energy X-ray X-ray photons. In addition both of scan time and patient exposure are affected by detection efficiency. A CZT detector with a good energy resolution and high detection efficiency was evaluated for the application of bone densitometry. Its performance was compared to a photomultiplier tube with a NaI(T1) scintillator in terms of energy resolution, detection efficiency and the accuracy of bone mineral density measurement. The comparison study was performed with CZT detector and PM tube using DXA equipments(OSTEO Plus, OSTEO Prima, ISOL Technology). The energy spectrum was acquired using MCA(Multi-Channel Analyzer). The used X-ray energy ranged from 20keV to 86keV. The MCA result of the CZT detector showed a slightly sharper energy spectrum than that of NaI(T1). Detection efficiency of the CZT detector at 59.5keV was 1.4 times better. Remarkably the final results of bone mineral density measurements demonstrate only less than 1% difference. The CZT detector appears to have many benefits for the application of bone densitometry. Its excellent energy resolution can enhance the counting accuracy of dual energy X-ray spectrum. Furthermore its compactness in physical dimension and no cooling requirement will be additional benefits for a more compact and accurate bone densitometer.

• 대한방사선기술학회지:방사선기술과학
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• 제28권2호
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• pp.117-122
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• 2005

1999년 개정된 국내 원자력법 시행령 제2조 5항에 의하면 2003년부터 원전 작업종사자들에 대해 외부 피폭 선량뿐만 아니라 내부피폭 선량도 합산하여 평가하도록 하였으며 또한 각 선량평가에 대한 오차도 50% 이내로 유지되어야 한다고 규정한 바 있어 전신이나 갑상선 계측기와 같은 내부피폭선량 측정 장비의 정밀한 계측이 요구되고 있다. 이러한 국내 원자력법의 개정에 부합하여 본 연구에서는 내부피폭 선량측정 결과치의 정확도를 향상시키기 위해서 현재 개발 중인 갑상선 내부피폭선량 측정 시스템의 검출효율을 계산하기 위한 몬테카를로 모의실험 코드(CALEFF)를 개발하였으며, 이 코드를 사용하여 다양한 실험조건에서 검출효율을 계산하였다. 향후 갑상선 내부피폭선량 측정 시스템의 보정인자로 사용하고자 한다.

• 천문학회보
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• 제38권2호
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• pp.72.1-72.1
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• 2013

Even though current microlensing follow-up observations focus on high-magnification events due to the high efficiency of planet detection, it is very difficult to do a confident detection of planets in high-magnification events with extremely weak central perturbations (i.e., the fractional deviation is ${\delta}{\leq}0.02$). For the confident detection of planets in the extremely weak central perturbation events, it is needed both the high cadence monitoring and the high photometric accuracy. A next-generation ground-based observation project, KMTNet (Korea Microlensing Telescope Network), satisfies both the conditions. Here we investigate how well planets in high-magnification events with extremely weak central perturbations are detected by KMTNet. First, we determine the probability of occurrence of events with ${\delta}{\leq}0.02$. From this, we find that for ${\leq}100M_E$ planets in the separation of $0.2AU{\leq}d{\leq}20AU$, events with ${\delta}{\leq}0.02$ occur with a frequency of more than 70%, in which d is the projected planet-star separation. Second, we estimate the efficiency of detecting planetary signals in the events with ${\delta}{\leq}0.02$ via KMTNet. We find that for main-sequence and subgiant source stars, ${\geq}1M_E$ planets can be detected more than 50% in a certain range that has the efficiency of ${\geq}10%$ and changes with the planet mass.

• 한국멀티미디어학회논문지
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• 제7권2호
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• pp.156-163
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• 2004

본 논문에서는 적응적 얼굴영역 검출과 얼굴 특징자 평가함수를 사용한 실시간 얼굴인식 알고리즘을 제안하였다. 제안한 알고리즘은 명암도 정보와 타원마스킹 기법뿐만 아니라 인종별 얼굴피부색을 사용하여 정확한 얼굴영역을 적응적으로 검출 가능하다. 또한 제안한 알고리즘은 얼굴 특징자 및 얼굴특징자간 기하학적 평가함수를 사용하여 얼굴 인식 효율을 개선하였다. 제안한 알고리즘은 생체인증 및 보안 시스템 분야에 사용 가능하다. 실험에서는 제안한 방법의 우수성을 입증하기 위해 실 영상을 사용하였으며 실험 결과 기존의 방법보다 얼굴 영역 검출뿐만 아니라 얼굴인식 성능을 개선하였다.

• 한국입자에어로졸학회지
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• 제13권4호
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• pp.159-164
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• 2017

The detection efficiency and characteristics of an optical particle counter (OPC), with various sample nozzle outlet diameters, were experimentally investigated. The OPC system, which was built with original design, was made up of a diode laser, two photodetectors, and a variety of optics such as a beam splitter and a concave mirror. The cone-shaped sampling nozzle was designed to be changeable to alter the outlet diameter, within the range of 1 to 3 mm. For samples, sets of polystyrene latex (PSL) standard particle with various sizes of 1 to $3{\mu}m$, were used. As a result, detection efficiency of the OPC greatly decreased with larger nozzle outlet diameter. Moreover, increased nozzle outlet diameter means broader sample flow, thus caused light interference and multiple scattering which results in abnormal high peaks in scattered light signal. The ratio of abnormal peaks to regular signal of single particle increased with larger nozzle outlet diameter.

• 한국정보통신학회논문지
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• 제12권4호
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• pp.737-743
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• 2008

소프트웨어의 신뢰도 모델링에서 테스트노력과 결함검출비를 동시에 고려하여 효과적인 파라미터 분석 기법을 이용하여 기존의 방법과 비교하고자 한다. 일반적으로, 소프트웨어 결함검출/제거 메카니즘은 이전의 검출/제거 결함과 테스트노력을 어떻게 활용하느냐에 달려 있다. 결함 제거 효율은 개발중인 소프트웨어의 신뢰도 성장이나 테스트 및 수정비용에 영향을 크게 미친다. 이는 소프트웨어 개발의 모든 과정에서 매우 유용한 척도로서 개발자가 디버깅 효율을 평가하는데 크게 도움이 될 뿐더러, 추가로 소요되는 작업량을 예측할 수 있게 해준다. 그러므로 개발 소프트웨어의 신뢰도와 비용면에서 불완전 디버깅의 영향을 연구하는 것은 매우 중요하다고 할 수 있으며, 이는 최적 인도 시각이나 운영 예산에도 영향을 줄 수 있다. 본 논문에서는 개발중인 소프트웨어를 대상으로 하여 디버깅이 완전하지 않으며, 따라서 결함검출비가 완벽하지 않다는 가정 하에 보편적으로 사용되는 신뢰도 모델을 대상으로 불완전 디버깅 범위로까지 소프트웨어의 신뢰도와 비용 문제를 확장하여 연구한다.

• Journal of Communications and Networks
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• 제12권6호
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• pp.605-615
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• 2010

Intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems, which causes substantial performance degradation in time-varying fading channels, is analyzed. An equivalent spreading code formulation is derived based on the analogy of OFDM and code division multiple access (CDMA) systems. Techniques as linear multiuser detection in CDMA systems are applied to suppress the ICI in OFDM systems. The performance of linear detection, measured using multiuser efficiency and asymptotic multiuser efficiency, is analyzed given the assumption of perfect channel state information (CSI), which serves as an upper bound for the performance of practical systems. For systems without CSI, time domain and frequency domain channel estimation based linear detectors are proposed. The performance gains and robustness of a linear minimum mean square error (LMMSE) filter over a traditional filter (TF) and matched filter (MF) in the high signal-to-noise ratio (SNR) regime are demonstrated with numerical simulation results.

• Journal of Mechanical Science and Technology
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• 제20권7호
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• pp.929-940
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• 2006

Early detection and diagnosis of incipient induction machine faults increases machinery availability, reduces consequential damage, and improves operational efficiency. However, fault detection using analytical methods is not always possible because it requires perfect knowledge of a process model. This paper proposes a neural network based expert system for diagnosing problems with induction motors using vibration analysis. The short-time Fourier transform (STFT) is used to process the quasi-steady vibration signals, and the neural network is trained and tested using the vibration spectra. The efficiency of the developed neural network expert system is evaluated. The results show that a neural network expert system can be developed based on vibration measurements acquired on-line from the machine.

• Smart Structures and Systems
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• 제23권1호
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• pp.45-60
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• 2019

This paper is devoted to proposing a new approach for damage detection of structures. In this technique, the biconjugate gradient method (BCG) is employed. To remedy the noise effects, a new preconditioning algorithm is applied. The proposed preconditioner matrix significantly reduces the condition number of the system. Moreover, based on the characteristics of the damage vector, a new direct search algorithm is employed to increase the efficiency of the suggested damage detection scheme by reducing the number of unknowns. To corroborate the high efficiency and capability of the presented strategy, it is applied for estimating the severity and location of damage in the well-known 31-member and 52-member trusses. For damage detection of these trusses, the time history responses are measured by a limited number of sensors. The results of numerical examples reveal high accuracy and robustness of the proposed method.

• 대한전자공학회논문지
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• 제22권2호
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• pp.44-54
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• 1985

양전자 방출 CT에서는 고해상도를 얻기 위해서 즙은 폭의 검출기와 충분히 큰 검출효률이 동시에 요구된다. 검출기의 폭을 수 mm까지 줄이면 검출기준이 급감소하고 누설률이 급상승하여 이를 사용함이 인난하여진다. 특히 사각으로 입사하는 포톤의 경우 후각하다. 이를 해결하는 방법으로 쐐기형 검출기를 제안하였고 이에 관련된 문제들을 탐구하였다. 4∼8mm BGO 검출기의 쐐기형을 사용한 시스템이 종미 요육양체형을 사용한 시스템보다 해상도가 증가하였다. 예를들면 회 8mm의 BGO 검출기 200개를 난제하게 배치한 시스템이 이점 샘플링할 경우 쐐기형의 해상도가 5.4mm FWHM으로 같은 조건의 직육면체형의 6.6mm FWHM보다 향상됨을 시뮬레이션으로 확인하였다. 3∼7mm FWHM의 초고해상도 시스템의 검출기에 대하여 형태와 크기에 따른 특성도 시뮬레이션으로 구하여 제시하였다. The high resolution of positron emission tomography, in particular, requires the use of detector crystals of narrow width but still with sufficiently high detection efficiency. If the crystal width is reduced to several millimeters, degradation of detection efficiency and leakage coefficient becomes significant, particularly in case of obliquely incident photons. Alleviation of such a problem can be made possible by modification of the detector shape from the conventional rectangular type to a wed농e type. The Proposed wedge shape makes the absorption length longer for obliquely incident photons, thus increasing the detection efficiency and suppressing leakage coefficient. For the BGO detectors of 4-8mm width, the computer simulation result of the system using wedge detectors reveals resolution improvement to the system using conventional detectors. For the system composed of 200 BGO detectors of 8mm width with 2 point sampling motion, the simulation resolution system using conventional detectors. For the very high resolution system of 3-7mm FWHM, the characteristics of the detector shape and size is studied by computer simulation.