• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1266-1276
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• 2021

The mask parameters of a coded aperture are critical design features when optimizing the performance of a gamma-ray camera. In this paper, experiments and Monte Carlo simulations were performed to derive the minimum detectable activity (MDA) when one seeks a real-time imaging capability. First, the impact of the thickness of the modified uniformly redundant array (MURA) mask on the image quality is quantified, and the imaging of point, line, and surface radiation sources is demonstrated using both cross-correlation (CC) and maximum likelihood expectation maximization (MLEM) methods. Second, the minimum detectable activity is also derived for real-time imaging by altering the factors used in the image quality assessment, consisting of the peak-to-noise ratio (PSNR), the normalized mean square error (NMSE), the spatial resolution (full width at half maximum; FWHM), and the structural similarity (SSIM), all evaluated as a function of energy and mask thickness. Sufficiently sharp images were reconstructed when the mask thickness was approximately 2 cm for a source energy between 30 keV and 1.5 MeV and the minimum detectable activity for real-time imaging was 23.7 MBq at 1 m distance for a 1 s collection time.

• 한국항공우주학회지
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• 제45권9호
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• pp.775-783
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• 2017

본 논문에서는 서로 다른 궤도상에 있는 두 우주비행체의 랑데부를 위한 최소 에너지 순간추력을 구하는 문제를 다룬다. 두 우주비행체의 궤도는 공면 궤도나 원 궤도 같이 특정 지어진 궤도가 아닌 일반적인 궤도이다. 이러한 최적화 문제를 다루기 위해 범용변수를 사용한 케플러 방정식과 두 우주비행체의 최종 위치 및 속도를 구속조건으로 사용하며, 전이 궤도의 정보를 얻기 위해 라그랑지 계수를 이용한다. 이 방법은 최소 에너지를 고려한 예시와 대기시간까지 고려한 예시를 통해 보여 지며, 최소 에너지 궤도로 알려진 호만 궤도와 비교함으로써 검증된다. 비록 닫힌 형태의 해를 얻을 수는 없었지만, 수치해석적 방식을 적용함으로써 다양한 궤도 전이 문제의 해를 구할 수 있음을 보여준다.

• 한국정보과학회논문지:정보통신
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• 제32권2호
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• pp.261-277
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• 2005

센서 네트워크에서는 베이스 노드와 다수의 센서 노드들간의 데이타 중심 (Data-centric) 기반의 통신 모델을 사용한다는 특징을 활용하여, 오버헤드를 최소화 하면서 최저 전력 라우팅 경로를 찾고, 또한 전체 네트워크의 수명을 최대화 시킬 수 있는 PAD (Power Aware Data-centric routing protocol)를 제안한다. PAD는 최저전력 라우팅 경로와는 상관없는 통신 링크를 제거한 최저전력특징그래프(Minimum Energy Property Graph)를 찾은 후, 오버혜드를 최소화 하고 slow convergence와 라우팅 경로의 루프 문제를 해결한 Distributed Data-centric Bellman-Ford Algorithm을 사용하여 라우팅 경로를 결정한다. 특히 PAD가 제안한 최저전력특징그래프를 찾는 알고리듬은 기존의 방식에 비해서 훨씬 빠르며, 간단하여 구현이 용이하면서도 가장 적은 수의 에지를 가지는 그래프를 구한다. 이는 기존의 방식이 사용하던 path-loss 모델만을 이용한 기하학적 계산과 복잡한 알고리듬을 path-loss 모델로부터 독립시켜 전력소모를 예측할 수 있는 어떠한 방법이든지 사용 가능하게 하고 또한 최단거리 알고리듬을 사용한 결과이다. PAD는 모든 과정을 분산된 방식으로 수행하며, 또한 최소의 오버헤드만을 가지므로, 다양한 센서 네트워크 응용에서 사용할 수 있을 것으로 기대한다.

• 한국통신학회논문지
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• 제28권1C호
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• pp.32-36
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• 2003

Based on oriented minimum output energy (OMOE) criterion, a new blind multiuser receiving scheme of linear minimum mean square error (MMSE) detector is proposed, then an adaptive algorithm for implementing the new scheme is given by the steepest descent method, and the convergence property of the algorithm is analyzed in this paper. The numerical results demonstrate the performance of the proposed scheme.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.125-126
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• 2012

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 춘계학술대회 논문집
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• pp.20-26
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• 2005

A running-profile generation method has been developed that efficiently generates the minimum-energy running profile, even in railway lines which have complicated speed limit sections. In the developed method, the problem of minimizing energy consumption is formulated as a resource allocation problem by dividing a running profile into several blocks, and is solved by the incremental method. A concept of Uni-Braking Block (UBB) which has only one brake section within it is introduces for the formulation. This paper proposes a specific method for running profile in the railway lines by using UBB. And proposes the algorithm to generate the running profile with minimum-energy.

• Progress in Superconductivity
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• 제8권2호
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• pp.193-201
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• 2007

Since the margins for the minimum quench energy and for the operating current in the superconducting magnet determine the operating regime of the magnet, a thermal stability analysis for the KSTAR superconducting magnet system is performed using 1-D Gandalf code. The result shows that the minimum quench energy is about 500 mJ/cc and the operating current margin is about 70 %. These values are larger than those of the KSTAR design criteria and the KSTAR superconducting magnet system can be operated stably under various experimental environments.

• 한국태양에너지학회 논문집
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• 제25권4호
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• pp.119-123
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• 2005

The main purpose of this study is to define an optimum slope of the roof that demands minimum cooling load of the building, when the roof is affected by the solar and wind energy. Two different roof shapes were chosen: hip, gabled. The cooling load of building having those roof shapes was calculated through the computer simulation, using DOE program. For the simulation, the angle of the roof and angle of the orientation was changed. In the conclusion of this paper, an optimum slope of the roof which causes minimize cooling load is presented according to the roof shape and orientation. The result of this study could provide a practical design guideline for determining the roof angle for various climatic conditions.

• 한국안전학회지
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• 제15권4호
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• pp.95-100
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• 2000

This study was performed in Hartmann type dust explosion apparatus in order to research the dust explosion characteristics of hydroxypropyl methyl cellulose(HPMC): minimum explosive limit, minimum ignition energy, limiting oxygen concentration, maximum explosion pressure, rate of pressure rise, etc. The samples of HPMC dust were distributed into 120-140 mesh, 170-230 mesh and 325 under, and the gap distance of the discharge electrode was setted up at 5mm. The experimental results were obtained as follows: (1) The minimum explosive limit for HPMC dust was founded at 180g/㎥. the minimum ignition energy at 9.8mJ and the limiting oxygen concentration at 12%. (2) The maximum explosion pressure of HPMC dust was $8.1kg/cm^2\;{\cdot}\;$abs at the concentration of $500g/m^3$ and the maximum rate of pressure rise was 203.98 bar/sec at the concentration of $480g/m^3$ for 325 under.

• 한국안전학회지
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• 제16권3호
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• pp.83-88
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• 2001

This study was preformed by measuring the minimum ignition temperature of MBS according to the change of sample vessel size and the minimum ignition temperature of MBS dust cloud The minimum ignition temperature of MBS product decreased as the vessel size was large, and it was obtained in the range from $120.5^{\circ}C$ to $94.5^{\circ}C$ and the apparent activation energy was obtained with 32.94Kcal/mol. The minimum ignition temperature of MBS dust cloud was measured by using Godbert-Greenwald furnace and it was obtained at $407^{\circ}C$ with the sample of 0.4g in the air and the ignition of dust cloud was not occurred below 13% oxygen concentration.