• Nuclear Engineering and Technology
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• 제54권1호
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• pp.310-317
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• 2022

The mass attenuation coefficient is the primary physical parameter to model narrow beam gamma-ray attenuation. A new machine learning based approach is proposed to model gamma-ray shielding behavior of composites alternative to theoretical calculations. Two fuzzy logic algorithms and a neural network algorithm were trained and tested with different mixture ratios of vanadium slag/epoxy resin/antimony in the 0.05 MeV-2 MeV energy range. Two of the algorithms showed excellent agreement with testing data after optimizing adjustable parameters, with root mean squared error (RMSE) values down to 0.0001. Those results are remarkable because mass attenuation coefficients are often presented with four significant figures. Different training data sizes were tried to determine the least number of data points required to train sufficient models. Data set size more than 1000 is seen to be required to model in above 0.05 MeV energy. Below this energy, more data points with finer energy resolution might be required. Neuro-fuzzy models were three times faster to train than neural network models, while neural network models depicted low RMSE. Fuzzy logic algorithms are overlooked in complex function approximation, yet grid partitioned fuzzy algorithms showed excellent calculation efficiency and good convergence in predicting mass attenuation coefficient.

• Smart Structures and Systems
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• 제30권1호
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• pp.89-106
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• 2022

The negative stiffness of an active or semi-active damper system has been proven to be very effective in reducing dynamic response. Therefore, energy dissipation devices possessing negative stiffness, such as viscous inertial mass dampers (VIMDs), have drawn much attention recently. The control performance of the VIMD for cable vibration mitigation has already been demonstrated by many researchers. In this paper, a new optimal design procedure for VIMD parameters for taut cable vibration control is presented based on the fixed-points method originally developed for tuned mass damper design. A model consisting of a taut cable and a VIMD installed near a cable end is studied. The frequency response function (FRF) of the cable under a sinusoidal load distributed proportionally to the mode shape is derived. Then, the fixed-points method is applied to the FRF curves. The performance of a VIMD with the optimal parameters is subsequently evaluated through simulations. A taut cable model with a tuned VIMD is established for several cases of external excitation. The performance of VIMDs using the proposed optimal parameters is compared with that in the literature. The results show that cable vibration can be significantly reduced using the proposed optimal VIMD with a relatively small amount of damping. Multiple VIMDs are applied effectively to reduce the cable vibration with multi-modal components.

• Earthquakes and Structures
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• 제22권1호
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• pp.95-107
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• 2022

This paper introduces a novel, rigorous, and efficient probabilistic methodology for the performance-based optimal design (PBOD) of semi-active tuned mass damper (SATMD) for seismically excited nonlinear structures. The proposed methodology is consistent with the modern performance-based earthquake engineering framework and aims to design reliable control systems. To this end, an optimization problem has been defined which considers the parameters of control systems as design variables and minimization of the probability of exceeding a targeted structural performance level during the lifetime as an objective function with a constraint on the failure probability of stroke length damage state associated with mass damper mechanism. The effectiveness of the proposed methodology is illustrated through a numerical example of performance analysis of an eight-story nonlinear shear building frame with hysteretic bilinear behavior. The SATMD with variable stiffness and damping have been designed separately with different mass ratios. Their performance has been compared with that of uncontrolled structure and the structure controlled with passive TMD in terms of probabilistic demand curves, response hazard curves, fragility curves, and exceedance probability of performance levels during the lifetime. Numerical results show the effectiveness, simplicity, and reliability of the proposed PBOD method in designing SATMD with variable stiffness and damping for the nonlinear frames where they have reduced the exceedance probability of the structure up to 49% and 44%, respectively.

• 천문학회보
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• 제44권2호
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• pp.63.3-63.3
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• 2019

Nearby young moving groups (NYMGs hereafter) are gravitationally unbound loose young stellar associations located within 100 pc of the Sun. Since NYMGs are crucial laboratories for studying low-mass stars and planets, intensive searches for NYMG members have been performed. For identification of NYMG members, various strategies and methods have been applied. As a result, the reliability of the members in terms of membership is not uniform, which means that a careful membership re-assessment is required. In this study, I developed a NYMG membership probability calculation tool based on Bayesian inference (Bayesian Assessment of Moving Groups: BAMG). For the development of the BAMG tool, I constructed ellipsoidal models for nine NYMGs via iterative and self-consistent processes. Using BAMG, memberships of claimed members in the literature (N~2000) were evaluated, and 35 per cent of members were confirmed as bona fide members of NYMGs. Based on the deficiency of low-mass members appeared in mass function using these bona fide members, low mass members from Gaia DR2 are identified. About 2000 new M dwarf and brown dwarf candidate members were identified. Memberships of ~70 members with RV from Gaia were confirmed, and the additional ~20 members were confirmed via spectroscopic observation. Not relying on previous knowledge about the existence of nine NYMGs, unsupervised machine learning analyses were applied to NYMG members. K-means and Agglomerative Clustering algorithms result in similar trends of grouping. As a result, six previously known groups (TWA, beta-Pic, Carina, Argus, AB Doradus, and Volans-Carina) were rediscovered. Three the other known groups are recognized as well; however, they are combined into two new separate groups (ThOr+Columba and TucHor+Columba).

• Journal of Digestive Cancer Research
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• 제5권1호
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• pp.50-54
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• 2017

Pancreatic neuroendocrine tumors are rare pancreatic neoplasms comprising 1-2% of all pancreatic tumors and typically present high attenuating mass on arterial and venous phase images, due to their rich capillary network. A 70-year-old South Korean female visited our hospital presenting with jaundice and dark urine color. She had received an operation for treatment of small bowel perforation seven years ago. On physical examination, icteric sclera was observed but otherwise unremarkable. Laboratory tests were abnormal liver function test and suspected obstructive jaundice. Computed tomography revealed 4 cm sized cystic mass lesion with homogeneous low attenuation in the head of pancreas and distal common bile duct was compressed by the mass. During review of past medical records, we found that the mass was observed and measured about 1.7 cm seven years ago. To resolve obstructive jaundice, pylorus preserving pancreaticoduodenectomy was performed and diagnosed with well differentiated pancreatic neuroendocrine carcinoma with intermediate grade.

• 한국식품과학회지
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• 제41권6호
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• pp.609-614
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• 2009

참기름은 높은 항산화활성 및 항암작용 등의 우수한 영양학적 가치를 지니는 반면 비싼 가격으로 인하여 가짜 참기름의 유통이 범람함에 따라 이를 판별할 수 있는 분석 방법의 확립이 요구되는 실정이다. 질량분석기를 바탕으로 한 전자코를 이용하여 들기름이 혼합된 참기름을 제조하여 진위 판별을 시도하였다. 각각의 유지를 전자코를 이용하여 분석, 통계처리하였다. 혼합 참기름의 휘발성 향기성분으로부터 생성되는 ion fragment 중 40-160 amu에서 각 시료 간에 차별성이 높은 fragment(m/z)를 선택하여 해당 intensity값을 판별 분석한 결과, 참기름 및 들기름은 뚜렷하게 구분되었다. 미량의 들기름이 혼합된 참기름은 첨가된 들기름의 농도에 비례하여 제1판별함수값(DF1)과 높은 상관관계를 나타내었다. 참기름의 볶음온도 및 시간 등의 제조조건 및 재배환경, 재배 산지, 제조회사 등의 요인에 의하여 순수한 참기름의 향기패턴이 달라지는 것을 인도산과 국산 참기름을 이용하여 분석하였다. 향후 참기름의 위조 여부를 검증하는 방법에 하나로 활용될 수 있을 것이다.

• 터널과지하공간
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• 제25권3호
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• pp.284-292
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• 2015

일반화된 Hoek-Brown 파괴함수는 GSI 지수를 이용하여 현장 암반의 강도정수를 결정하는 경험적 비선형 파괴조건식으로서 오늘날 다양한 암반공학적 설계에 널리 활용되고 있다. 그러나 여전히 많은 암반공학 전문가들이 암반의 강도를 마찰각과 점착력으로 표현하는 것에 익숙하다. 또한 거의 대부분의 암반안정성해석 수치해석 프로그램이 간편한 선형 Mohr-Coulomb 파괴조건식을 채택하고 있다. 이에 따라 Hoek-Brown 파괴함수를 Mohr-Coulomb 파괴함수 틀에서 이해하는 방법의 제시가 필요하다. 이 연구에서는 한계해석 상계정리를 적용하여 유도된 줄기초의 지지력 공식을 활용하여 Hoek-Brown 파괴조건을 따르는 천부 암반의 등가마찰각과 등가점착력을 계산하는 방법을 제안하였다. 일반화된 Hoek-Brown 파괴함수가 내포하는 접선점착력-접선마찰각 관계식을 이용하여 지지력 상계해를 마찰각의 함수로 표현한 후 최소 지지력 조건의 마찰각을 탐색하여 이를 등가마찰각으로 간주하였다. 제안된 방법을 활용하여 GSI, $m_i$, 교란계수 D가 등가마찰각과 등가점착력에 미치는 영향을 분석하였다.

• 한국식품과학회지
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• 제43권4호
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• pp.419-425
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• 2011

머스크멜론의 저장온도 차이에 따른 저장 중 미세한 향기성분의 변화를 질량분석기 기반 전자코를 이용하여 품질 변화 정도를 판단하였다. 저장기간이 증가함에 따라 향기성분이 변화하면서 휘발성분이 증가하였는데, 판별함수분석 결과 DF1값이 99.8%로 큰 영향을 받았으며 향기성분의 변화가 크게 나타날수록 DF1 값이 음의 방향으로 이동하였다. 이후 DF1 뿐만 아니라 DF2도 음의 값으로 변하면서 저장 초기와는 확연히 다른 향기성분의 변화가 일어난 것으로 판단된다. 0$^{\circ}C$ 저장에서는 28일, 4와 7$^{\circ}C$에서는 21일, 10$^{\circ}C$에서는 14일까지 저장 초기와 유사한 향기성분을 나타났으며, 이는 저장 온도가 낮아질수록 휘발성분의 변화가 적게 일어났다. 이러한 향기성분의 변화는 머스크멜론이 저장 중숙기가 지나고 노화가 진행되어지면서 일어난 것으로 유추된다. 또한 전자코로 분석한 DF1 값을 이용하여 일반성분들(비타민 C 함량, 꼭지 수분함량, 산도)의 저장 중 경향도 예측 가능 하였다. 머스크멜론의 저장 중 변화하는 전자코의 mass spectrum에 나타난 주요 향기성분은 이미 보고된 GC/MS의 분석 결과와 유사한 ethyl acetate, butyl acetate, nonanol, dodecanoic acid, hexadecanoic acid, tricosane과 같은 성분들로 나타났으며, 저장 중 전자코에 감지되는 양은 계속적으로 증가하였다.

• 한국식품과학회지
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• 제42권6호
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• pp.699-704
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• 2010

유채유에 감광제나 금속이온을 첨가하거나 UV처리를 하였을 때 어떠한 차이가 있는지 알아보기 위하여 MS-전자코를 이용하여 분석하였다. 유채유를 저장하였을 때 저장기간이 증가함에 따라 지방의 품질이 변화되면서 휘발성분이 증감하였는데 판별함수분석(DFA) 결과 DF1값의 영향을 받았으며 품질 변화가 많이 일어날수록 DF1값이 음의 방향으로 이동하였다. 암소에 비하여 UV를 처리하였을 때가 오히려 DF1값의 변화 폭이 크게 나타났다(DF1 $r^2$=0.9481 F=307.07). 실온(17, $26^{\circ}C$)보다는 냉장온도($4^{\circ}C$)에 보관할 때 휘발성분의 변화가 적게 일어났다. 또한 자외선 처리 유무와 온도를 달리 저장할 경우 온도에 의한 영향에 비해 자외선에 의한 영향이 크게 나타났다. ${\gamma}$DF1 값이 암실에서는 각각 $4^{\circ}C$의 경우 0.099, $17^{\circ}C$에서 0.187, $26^{\circ}C$에서 0.278값을 나타냈고 UV 처리 구에서는 각각 $4^{\circ}C$에서 0.554, $17^{\circ}C$는 0.558, $26^{\circ}C$에서는 0.542값을 나타냈다. 감광제인 cytochrome C을 0.1, 0.3, 0.5 mg/%첨가 하였을 때 첨가량이 증가함에 따라 휘발성분의 패턴 변화가 크게 나타났으며 금속이온인 $Cu^{2+}$를 10, 15, 20 mg% 첨가할 경우에도 첨가량이 증가함에 따라 변화가 크게 일어났다. 또한 유채유의 산패 조건에 따른 전자코의 mass spectrum의 감응도 변화는 이미 보고된 GC/MS의 분석 결과와 유사한 pentane, pentanal, 1-pentanol, hexanal, n-octane, 2-hexenal, heptanal, 2-heptenal, decane, 2-octenal, undecane, dodecane과 같은 성분들로 나타났다.

• Geomechanics and Engineering
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• 제8권6호
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• pp.757-767
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• 2015

Rock mass is an important engineering material. In hydropower engineering, rock mass of bank slope controlled the stability of an arch dam. However, mechanical characteristics of the rock mass are not only affected by lithology, but also joints. On the basis of field geological survey, this paper built rock mass material containing parallel concentrated joints with different dip angle, different number under different stress conditions by PFC (Particle Flow Code) numerical simulation. Next, we analyzed mechanical property and fracture features of this rock mass. The following achievements have been obtained through this research. (1) When dip angle of joints is $15^{\circ}$ and $30^{\circ}$, with the increase of joints number, peak strength of rock mass has not changed much. But when dip angle increase to $45^{\circ}$, especially increase to $60^{\circ}$ and $75^{\circ}$, peak strength of rock mass decreased obviously with the increase of joints number. (2) With the increase of confining stress, peak strengths of all rock mass have different degree of improvement, especially the rock mass with dip angle of $75^{\circ}$. (3) Under the condition of no confining stress, dip angle of joints is low and joint number is small, existence of joints has little influence on fracture mode of rock mass, but when joints number increase to 5, tensile deformation firstly happened at joints zone and further resulted in tension fracture of the whole rock mass. When dip angle of joints increases to $45^{\circ}$, fracture presented as shear along joints, and with increase of joints number, strength of rock mass is weakened caused by shear-tension fracture zone along joints. When dip angle of joints increases to $60^{\circ}$ and $75^{\circ}$, deformation and fracture model presented as tension fracture zone along concentrated joints. (4) Influence of increase of confining stress on fracture modes is to weaken joints' control function and to reduce the width of fracture zone. Furthermore, increase of confining stress translated deformation mode from tension to shear.