• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3459-3469
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• 2022

Matrix composites of n-WO₃/n-Bi₂O₃/PVA with different loadings of n-WO₃/n-Bi₂O₃ mixtures (0-15 wt%) and starch (0 and 3 wt%) were fabricated by using melt-mixing method. The X-ray attenuation capability were evaluated based on mass attenuation coefficient (μ/⍴) using a general diagnostic X-ray machine at 40-100 kVp. The effect of starch addition on the dispersion of the fillers in the PVA matrix were observed by using FESEM through morphological analysis. The fabricated samples have shrunken and caused their thickness to be decreased (0.35 mm-0.55 mm) after the drying process even though fixed thickness (2.0 mm) was set initially. The density and HVL values of the samples with 3 wt% starch was seen lower than samples without starch (0 wt%), however the former have provided improvement in filler dispersion and better X-ray attenuation capability compared to the latter. As conclusion, the matrix composite of n-WO₃/n-Bi₂O₃/PVA with 15 wt% of n-Bi₂O₃, 8 wt% of n-WO₃ and 3 wt% starch can be selected as the best promising candidate for X-ray shielding materials.

• 한국학교보건학회지
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• 제20권1호
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• pp.63-75
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• 2007

Purpose: With economic development and prolonged longevity, the level of health and health disparities have became growing concerns for individual and society as well. Since youth's health status are influenced by households' socioeconomic status and associated with heath status in later stage of life, assessing health inequality in the youth is a significant step toward lessening health disparity and promoting health. We measured health inequality in high school students and decomposed it into health factors. Methods: The subjects included 3,787 high school students of 12th graders from the Korea Education and Employment Panel (KEEP) in 2004. True health status was assumed as a latent variable and estimated by ordered logistic regression model. The predicted health was used as a measure of individual health after rPSraling to [0,1] interval. Total health inequality was then measured by Gini coefficient and was decomposed into health factors. Results: Health inequality in high school students was observed. Of total health inequality, 44% was explained by biological factors such as body mass index (BMI) (32.5%) and gender (13.5%). Behavioral factors such as smoking, drinking, physical activity, hours in bed and hours of computer ussge added to 11.7%. Household income and work experiences explained 5.6% and 8.8%, respectively. School satisfaction explained 14.6%. Other school related factors such as self-assessed achievement and experience of being bullied accounted for 15.5%. Conclusion: Among the health factors, biological factor was the most important contributor in health disparity. Other factors such as health behaviors, socioeconomic factors, school satisfaction and school related factors exhibited somewhat similar magnitude. For policy purposes, it is recommended to look into modifiable factors depending BM, gender and school surroundings.

• 한국철도학회논문집
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• 제20권2호
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• pp.241-247
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• 2017

장대레일이 부설된 철도 교량은 궤도-교량 상호작용으로 인하여 경간장 연장에 제약이 있다. 이러한 한계를 극복하기 위하여 궤도와 교량 사이에 저마찰 슬라이드층을 두어 교량과 궤도의 종방향 거동을 분리시켜 상호작용을 원천적으로 저감시키는 슬라이딩 궤도가 개발되고 있다. 본 연구에서는 슬라이드층을 포함하는 궤도 시스템을 실규모로 제작하여 종방향으로 반복하중을 재하하는 시험을 통하여 슬라이딩 궤도의 저마찰 거동을 종합적으로 평가하고자 하였다. 하중 재하 속도를 0.2, 1.0, 5.0, 10mm/min.으로 변화를 주었으며, 5,000, 10,000kg의 부가질량이 재하된 경우에 대한 마찰거동를 비교 검토하였다. 실험 결과 제안된 슬라이드층의 마찰계수는 0.22~0.33인 것으로 확인되었다. 더불어, 30년에 해당하는 10,000회의 반복하중을 재하하여 마찰계수 변화를 관찰한 결과, 마찰계수 증가는 7%에 머물러 반복하중에 대한 장기적인 내구성을 확보한 것으로 확인되었다. 슬라이드층의 마찰계수의 변화에 따른 영향을 상호작용 해석을 통하여 추가로 검토하였다.

• Journal of electromagnetic engineering and science
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• 제12권1호
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• pp.101-106
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• 2012

In this study, we investigated the effect of groove pattern and gap-fill with lossy materials at 15 GHz frequency of Ku-band. We used Epoxy/MWCNT composite materials as gap-fill materials. Although epoxy does not have an absorbance capability, epoxy added conductive fillers, which are multi-walled carbon nanotubes (MWCNT), can function as radar absorbing material. Specimens were fabricated with different MWCNT mass fractions (0, 0.5, 1.0, 2.0 wt%) and their permittivity in the Ku-band was measured using the waveguide technique. We investigated the effect of gap-fill on monostatic RCS by calculating RCS with and without gap-fill. For arbitrarily chosen thickness and experimentally obtained relative permittivity, we chose the relative permittivity of MWCNT at 2 wt% (${\varepsilon}_r$=8.8-j2.4), which was the lowest reflection coefficient for given thickness of 3.3 mm at V-pol. and $80^{\circ}$ incident angle. We also checked the monostatic RCS and the field intensity inside the groove channel. In the case of H-pol, gap-fill was not affected by the monostatic RCS and magnitude was similar with or without gap-fill. However, in the case of V-pol, gap-fill effectively reduced the monostatic RCS. The field intensity inside the groove channel reveals that different RCS behaviors depend on the wave polarizations.

• 한국식품과학회지
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• 제24권3호
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• pp.221-225
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• 1992

국내에서 대량생산될 수 있는 자생가능한 자원인 배추의 비전통적 이용을 위해 배추즙액에 효모 Candida utilis를 배양하여 단세포단백을 생산하는 연구를 하였다. 배추의 당함량은 $2.1{\sim}4.0%$의 범위에 있었고 배추원액을 그대로 사용하여 C. utilis를 배양했을 때보다는 배추즙액을 적절히 희석하여 배양하였을 때 증식속도가 빨라졌고 소비된 당에 대한 건조균체생산율도 17%에서 약 50% 정도로 향상되었다. 배추즙액에 C. utilis를 배양하여 단세포단백을 생산하고자 할 때는 당의 함량이 1.0% 정도로 희석하는 것이 적절하였고 당함량을 1.0%되게 조정한 배추희석액에 영양원을 첨가하여 그 영향을 평가해 보았을 때 glucose, $KH_2PO_4$나 $(NH_4)_2SO_4$는 첨가효과가 없거나 오히려 균체생산량을 감소시킨데 비하여 yeast extract나 peptone은 건조균체 생산 및 균체의 단백질 함량을 $10{\sim}20%$씩 증가시키는 효과가 있었으나 yeast extract나 peptone의 첨가량에 비해 건조균체생산량의 증가가 적어서 배추즙희석액 자체로만도 효모배양을 위한 좋은 기질임이 확인되었다.

• 한국해안해양공학회지
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• 제17권1호
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• pp.41-46
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• 2005

항만구조물의 유체-구조물-지반 상호작용(FSSI)을 고려한 지진응답해석을 수행하였다. 우리나라 동남해안에 위치한 방파제 구조물을 대상으로 장주기 및 단주기파로 구분된 지진을 비롯하여 최근 우리나라에서 발생한 울진지진에 대한 지진응답특성에 대하여 고찰하였다. FSSI 효과를 고려하기 위하여 유체요소는 평면변형해석에 사용하는 4절점 사변형요소를 수정한 요소를 이용하여 모델링 하였다. 그리고 FSSI해석, 진도법, 부가질량법에 의한 지진응답특성을 비교하였다. 고유치해석을 통하여 방파제의 고유주기를 찾고, 기존의 지진 및 최근 우리나라에서 발생한 지진에 대한 지진응답특성 결과로부터 방파제 구조물이 장주기성분에 대한 영향을 더 많이 받는 것을 확인하였다.

• Structural Engineering and Mechanics
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• 제67권4호
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• pp.359-368
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• 2018

In this paper, a method is presented to identify the physical and modal parameters of multistory shear building based on substructural technique using block pulse generalized operational matrix and genetic algorithm. The substructure approach divides a complete structure into several substructures in order to significantly reduce the number of unknown parameters for each substructure so that identification processes can be independently conducted on each substructure. Block pulse functions are set of orthogonal functions that have been used in recent years as useful tools in signal characterization. Assuming that the input-outputs data of the system are known, their original BP coefficients can be calculated using numerical method. By using generalized BP operational matrices, substructural dynamic vibration equations can be converted into algebraic equations and based on BP coefficient for each story can be estimated. A cost function can be defined for each story based on original and estimated BP coefficients and physical parameters such as mass, stiffness and damping can be obtained by minimizing cost functions with genetic algorithm. Then, the modal parameters can be computed based on physical parameters. This method does not require that all floors are equipped with sensor simultaneously. To prove the validity, numerical simulation of a shear building excited by two different normally distributed random signals is presented. To evaluate the noise effect, measurement random white noise is added to the noise-free structural responses. The results reveal the proposed method can be beneficial in structural identification with less computational expenses and high accuracy.

• 한국축산식품학회지
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• 제35권1호
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• pp.121-129
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• 2015

${\beta}$-agonists are anabolic compounds that promote fat loss and muscle gain, and their administration to livestock may provide economic benefits by increasing growth rate and feed efficiency. For these reasons, ${\beta}$-agonists are also commonly added to livestock feed as growth promoters. This can introduce a significant risk of secondary human poisoning through intake of contaminated meat. A new method for the simultaneous determination of three ${\beta}$-agonists (clenbuterol, ractopamine, and zilpaterol) was developed in this study and applied to various meat samples. The limits of quantification, derived through a validation test following Codex guidelines, were $0.2{\mu}g/kg$ for clenbuterol and zilpaterol, and $0.4{\mu}g/kg$ for ractopamine. The average recoveries for clenbuterol, ractopamine, and zilpaterol ranged from 109.1% to 118.3%, 95.3% to 109.0%, and 94.1% to 120.0%, respectively. The recovery and coefficient of variation (CV) values fell within the acceptable range according to the Codex guidelines. This method reduced the analysis time without decreasing detection efficiency by modifying the pretreatment steps. This method could be utilized to manage the safety of imported meat products from countries where zilpaterol use is still permitted, thereby improving public health and preventing ${\beta}$-agonist poisoning due to secondary contamination.

• 한국해양공학회지
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• 제27권4호
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• pp.76-82
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• 2013

Motion reduction of an offshore structure at resonant frequency is essential for avoiding critical damage to the topside and mooring system. A damping plate has a distinct advantage in reducing the motion of a floating structure by increasing the added mass and the damping coefficient. In this study, the heave motion responses of a circular cylinder with an impermeable and a permeable damping plate attached at the bottom of the cylinder were investigated thru a model test. The viscous damping coefficients for various combinations of porosity were obtained from a free-decay test by determining the ratio between any pair of successive amplitudes. Maximum energy dissipation occurred at a porous plate with a porosity P = 0.1008. Experimental results for regular and irregular waves were compared with an analytical solution by Cho (2011). The measured heave RAO and spectrum reasonably followed the trends of the predicted values. A significant motion reduction at resonant frequency was pronounced and the heaving-motion energy calculated by the integration of the area under the heave motion spectrum was reduced by more than 75% by the damping plate. However, additional energy dissipation by eddies of strong vorticity and flow separation inside a porous damping plate was not found in the present experiments.

• 한국지능시스템학회논문지
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• 제24권3호
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• pp.245-250
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• 2014

중독은 크게 매개체 자체가 중독성을 가진 매개성 중독과 매개체 자체가 중독성을 가진 것이 아니라 예민한 개인과 잠재된 어떤 행동과 결합하여 중독을 유발하는 유발성 중독으로 나눌 수 있다. 매개성 중독은 약물 중독, 알코올 중독과 주로 화학물질의 직접 적인 원인이 되어 중독현상을 일으킨다. 유발성 중독은 쇼핑 중독, 일 중독, 게임 중독, 인터넷 중독, TV중독, 도박 중독 등의 사이버 중독이 있다. 유발성 중독은 개인의 감수성의 문제로서 개인에 따른 편차가 존재한다. 본 논문에서는 전기 시스템의 R-L-C 직렬 회로와 기계 시스템의 Spring-Damper-Mass를 이용하여 등가적으로 동일한 2차원의 중독 모델을 제안한다. 제안한 중독 모델에 비선형 항을 추가하여 Duffing을 구성한 후 파라미터 변화에 의해 주기운동과 카오스 운동을 시계열과 위상공간으로 나타내었다. 또한 파라미터 중 통제계수의 변화에 의해 주기 운동은 중독 되기 전의 상태를 카오스 운동은 중독된 상태임을 확인하였다.