• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4518-4526
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• 2023

NECP-SARAX is a neutronics analysis code system for advanced reactor developed by Nuclear Engineering Computational Physics Laboratory of Xi'an Jiaotong University. In past few years, improvements have been implemented in TULIP code which is the cross-section generation module of NECP-SARAX, including the treatment of resonance interface, considering the self-shielding effect in non-resonance energy range, hyperfine group method and nuclear library with thermal scattering law. Previous studies show that NECP-SARAX has high performance in both fast and thermal spectrum system analysis. The accuracy of TULIP code in fast and thermal spectrum system analysis is demonstrated preliminarily. However, a systematic verification and validation is still necessary. In order to validate the applicability of TULIP code for full energy range, 147 fast spectrum critical experiment benchmarks and 170 thermal spectrum critical experiment benchmarks were selected from ICSBEP and used for analysis. The keff bias between TULIP code and reference value is less than 300 pcm for all fast spectrum benchmarks. And that bias keeps within 200 pcm for thermal spectrum benchmarks with neutron-moderating materials such as polyethylene, beryllium oxide, etc. The numerical results indicate that TULIP code has good performance for the analysis of fast and thermal spectrum system.

• 한국통신학회논문지
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• 제38B권10호
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• pp.832-842
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• 2013

Cognitive Radio has attracted intensive interests of the researchers, recently. The data rate always increases in the emerging technologies. The increased data rate poses mainly two challenges for spectrum sensing. One is that the state of primary user (PU) is fast and alternatively varying between "on/off" in a spectrum sensing window. The other is that the asynchronicity among the reports in a cooperative spectrum sensing setting becomes more apparent. Both of them would deteriorate the spectrum sensing performance. Thus, we propose an asynchronous cooperative spectrum sensing method to cope with these two challenges. A likelihood ratio test based spectrum sensing is developed for a single cooperator. The likelihood ratio is obtained in the setting of fast varying PU state. The likelihood ratio test is uniformly powerful according to the Neyman-pearson lemma. Furthermore, the asynchronicity among the cooperators are studied. Two sets of fusion weights are discussed for the asynchronous time among cooperators. One is designed based on the condition probability of the PU state variation and the other one is designed based on the queueing theory. The simulation results are provided with different fusion methods. The performance improvements are demonstrated.

• 한국멀티미디어학회논문지
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• 제18권12호
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• pp.1439-1444
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• 2015

Measuring spectral reflectance can be regarded as obtaining inherent color parameters, and spectral reflectance has been used in image processing. Model-based spectrum recovering, one of the method for obtaining spectral reflectance, uses ordinary camera with multiple illuminations. Conventional model-based methods allow to recover spectral reflectance efficiently by using only a few parameters, however it requires some parameters such as power spectrum of illuminations and spectrum sensitivity of camera. In this paper, we propose an enhanced model-based spectrum recovering method without pre-measured parameters: power spectrum of illuminations and spectrum sensitivity of camera. Instead of measuring each parameters, spectral reflectance can be efficiently recovered by estimating and using the spectrum characteristic matrix which contains spectrum parameters: basis function, power spectrum of illumination, and spectrum sensitivity of camera. The spectrum characteristic matrix can be easily estimated using captured images from scenes with color checker under multiple illuminations. Additionally, we suggest fast recovering method preserving positive constraint of spectrum by nonnegative basis function of spectral reflectance. Results of our method showed accurately reconstructed spectral reflectance and fast constrained estimation with unmeasured camera and illumination. As our method could be conducted conveniently, measuring spectral reflectance is expected to be widely used.

• ETRI Journal
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• 제37권3호
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• pp.491-501
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• 2015

Spectrum sensing is an elementary function in cognitive radio designed to monitor the existence of a primary user (PU). To achieve a high rate of detection, most techniques rely on knowledge of prior spectrum patterns, with a trade-off between high computational complexity and long sensing time. On the other hand, blind techniques ignore pattern matching processes to reduce processing time, but their accuracy degrades greatly at low signal-to-noise ratios. To achieve both a high rate of detection and short sensing time, we propose fast spectrum sensing with coordinate system (FSC) - a novel technique that decomposes a spectrum with high complexity into a new coordinate system of salient features and that uses these features in its PU detection process. Not only is the space of a buffer that is used to store information about a PU reduced, but also the sensing process is fast. The performance of FSC is evaluated according to its accuracy and sensing time against six other well-known conventional techniques through a wireless microphone signal based on the IEEE 802.22 standard. FSC gives the best performance overall.

• 한국광학회지
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• 제14권3호
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• pp.266-271
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• 2003

수 $\mu\textrm{m}$ 이상의 두께를 가지는 비교적 두꺼운 박막의 경우 박막에 의한 간섭효과로 인하여 나타나는 반사율 스펙트럼에서의 진동주기로부터 막의 두께를 얻는다. 대개 빠른 데이터 처리를 위해서 고속 푸리에 변환(Fast Fourier Transformation, FFI)을 사용하여 진동주기(또는 진동수)를 구한다. 본 연구에서는 반사율 또는 투과율 스펙트럼을 빛의 에너지 축상에서 푸리에 변환하는 종래의 방법을 개선하여 박막의 굴절률 분산을 반영하는 수정된 고속 푸리에 변환 방법을 최초로 도입하였다. 이 새로운 방법은 굴절률 분산에서 유래하는 유효굴절률 결정에서의 오차를 줄여주고 푸리에 변환 피크의 폭 넓어짐을 막아줌으로써 막 두께 결정의 정밀도를 크게 향상시킨다. 수정된 고속 푸리에 변환방법을 80 $\mu\textrm{m}$의 덮게층과 13 $\mu\textrm{m}$의 사이층이 있는 시료의 반사 스펙트럼에 적용하여 고 타당성을 확인하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 추계종합학술대회 B
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• pp.628-631
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• 2008

원격탐지를 목적으로 하는 레이다 시스템에서는 일반적으로 도플러 필터뱅크를 적용하여 목표물 반사 신호들의 스펙트럼을 분석함으로서 반사 신호의 크기 및 속도정보 등을 얻게 된다. 이러한 스펙트럼 추정방법은 오래 전부터 널리 이용되고 있는 FFT(Fast Fourier Transform) 기법을 이용한 것으로 대부분의 레이다 시스템에서 채택하고 있는 방식이다. 그러나 레이다 시스템에서의 목표물 반사 신호 획득시간이 현저히 짧은 경우, 즉 고속으로 이동하는 항공기용 시스템이나 매우 빠른 목표물들의 즉각적인 탐지가 목적인 시스템에서는 기존 FFT 스펙트럼 추정방식으로는 높은 도플러 주파수 해상도를 얻을 수 없기 때문에 정확도가 현저히 떨어질 수 있다. 따라서 본 논문에서는 이러한 문제점을 극복하기 위하여 해상도 문제가 발생하지 않는 파라메터 추정방식인 AR 스펙트럼 추정 방법에 대하여 고찰하였다.

• Nuclear Engineering and Technology
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• 제11권2호
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• pp.133-136
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• 1979

이 논문은 Ge(Li)를 이용하여 고속 중성자 에너지 스펙트럼을 재는데 사용하는 방법을 제시한다. Ge$^{72}$ 의 고속 중성자의 비탄성 충돌에 의한 691.4 KeV에서의 스펙트럼을 분석함으로써 고속중성자와 에너지 스펙트럼을 측정할 수 있는 방법을 가질 수 있음을 시사한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권3호
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• pp.980-998
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• 2023

In Low Earth Orbit (LEO) satellite networks, satellites operate fast and the inter-satellite link change period is short. In order to sense the spectrum state in LEO satellite networks in real-time, a space-based satellite network intelligent spectrum sensing algorithm based on artificial neural network (ANN) is proposed, while Geosynchronous Earth Orbit (GEO) satellites are introduced to make fast and effective judgments on the spectrum state of LEO satellites by using their stronger arithmetic power. Firstly, the visibility constraints between LEO satellites and GEO satellites are analyzed to derive the inter-satellite link building matrix and complete the inter-satellite link situational awareness. Secondly, an ANN-based energy detection (ANN-ED) algorithm is proposed based on the traditional energy detection algorithm and artificial neural network. The ANN module is used to determine the spectrum state and optimize the traditional energy detection algorithm. GEO satellites are used to fuse the information sensed by LEO satellites and then give the spectrum decision, thereby realizing the inter-satellite spectrum state sensing. Finally, the sensing quality is evaluated by the analysis of sensing delay and sensing energy consumption. The simulation results show that our proposed algorithm has lower complexity, the sensing delay and sensing energy consumption compared with the traditional energy detection method.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.197-200
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• 2001

최근의 확산대역 통신 방식에 사용되는 주파수 합성기는 주파수 스위칭 시간이 중요한 요소가 되고 있다. FH-SS(Frequency Hopping Spread Spectrum) 송수신기에서 고속 주파수 합성기 설계는 채널 효율을 높이기 위해 매우 중요하다. 본 논문에서는 기존 PLL방식에 직접 접근 주파수 합성 (DDS) 방식을 응용하여 1 $\mu\textrm{s}$ 이하의 스위칭 시간을 갖는 고속 주파수 합성기를 설계하고, 이를 2.4GHz 대리의FH-SS 송수신기에 적용하여 시뮬레이션 결과 20% 이상의 채널 효율 개선 효과를 얻었다.

• Nuclear Engineering and Technology
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• 제38권7호
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• pp.591-618
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• 2006

An integrated R&D program is being conducted to study, qualify, and in some cases, develop materials with required properties for the reactor systems being developed as part the U.S. Department of Energy's Generation IV Reactor Program. The goal of the program is to ensure that the materials research and development (R&D) needed to support Gen IV applications will comprise a comprehensive and integrated effort to identify and provide the materials data and its interpretation needed for the design and construction of the selected advanced reactor concepts. The major materials issues for the five primary systems that have been considered within the U.S. Gen IV Reactor Program-very high temperature gas-cooled, supercritical water-cooled, gas-cooled fast spectrum, lead-cooled fast spectrum, and sodium-cooled fast spectrum reactors-are described along with the R&D that has been identified to address them.