• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1225-1232
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• 2023

The ¹⁸⁰W is the lightest isotope of Tungsten with small abundance ratio. It is slightly radioactive (α decay), with an extremely long half-life. Its separation is possible by non-conventional single withdrawal cascades. The ¹⁸⁰W is used in radioisotopes production and study of metals through gamma-ray spectroscopy. In this paper, single withdrawal cascade model is developed to evaluate multicomponent separation in non-conventional transient cascades, and available experimental results are used for validation. Numerical studies for separation of ¹⁸⁰W in a transient single withdrawal cascade are performed. Parameters affecting the separation and equilibrium time of cascade such as number of stages, cascade arrangements, feed location and flow rate for a fixed number of gas centrifuges (GC) are investigated. The Salp Swarm Algorithm (SSA) as a bio-inspired optimization algorithm is applied as a novel method to minimize the feed consumption to obtain desired concentration in the collection tank. Examining different cascade arrangements, it is observed in arrangements with more stages, the separation is further efficient. Based on the obtained results, with increasing feed flow rate, for fixed product concentration, the cascade equilibrium time decreases. Also, it is shown while the feed location is the farthest stage from the collection tank, the separation and cascade equilibrium time are well-organized. Finally, using SSA optimal parameters of the cascade is calculated, and optimal arrangement to produce 5 gr of ¹⁸⁰W with 90% concentration in the tank, is proposed.

• 천문학회보
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• 제44권2호
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• pp.36.2-36.2
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• 2019

Fe II emission is a prominent and ubiquitous feature in the spectra of broad-line Active Galactic Nuclei (AGN) by producing a pseudo-continuum from UV to optical with complex and strong blends of the numerous emission lines themselves, other emission lines, and continuum. Since theoretical modeling of such intricate Fe II emission is very difficult and still far from able to reproduce observed data in detail, an empirical iron emission template, derived from observations of a narrow-line Seyfert 1 galaxy, is an essential and practical tool to obtain accurate measurements of all the emission lines and continuum in AGN spectra. However, the existing iron templates, based on the single prototypical strong Fe II emitter I Zw 1, are suffering from inadequate S/N and non-simultaneous, inconsistent data with limited wavelength coverage, which consequently limit the accuracy of all the spectral measurements. To overcome the limitations and construct an improved iron template with wide spectral coverage, high-quality UV and optical spectra for the new and better identified template galaxy, Mrk 493, were successfully obtained from our HST STIS program (GO-14744). We will show the preliminary results for multicomponent spectral decomposition of the data and template construction with application tests to various AGN spectra and comparison with previous templates.

• 대한치매학회지
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• 제21권1호
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• pp.1-16
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• 2022

Background and purpose: We investigated existing nonpharmacological programs for people with dementia (PWD) to explore critical factors related to the effectiveness of these types of programs. Methods: We conducted a qualitative systematic literature review to identify nonpharmacological intervention programs developed for PWD and reviewed 36 randomized controlled trials. Among several outcomes reported in each study, we focused on the most common outcomes including quality of life (QoL), neuropsychiatric symptoms, depression, agitation, and cognition for further review. Results: Several factors were identified that might affect the outcomes of nonpharmacological interventions for PWD including study design, characteristics of the intervention, maintaining research participants, heterogeneity issues, and implementation fidelity. About half of studies in this review reported positive program effects on their targeted outcomes such as Well-being and Health for PWD on improving quality of life, neuropsychiatric symptoms and agitation; cognitive stimulation therapy on QoL, neuropsychiatric symptoms and cognition; and a stepwise multicomponent intervention on neuropsychiatric symptoms, depression and agitation. Conclusions: We found some programs even with a rigorous study design did not produce expected outcomes while other programs with poor designs reported positive outcomes, which necessitates further investigation on the validity of the assessments. Factors such as individual tailored and customized interventions, promoting social interactions, ease of administration and compatibility of interventions, and developing program theory need to be considered when developing nonpharmacological intervention programs.

• 한국표면공학회지
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• 제42권6호
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• pp.267-271
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• 2009

Multicomponent transparent conducting oxide films were deposited on glass substrates at 150 by dual magnetron sputtering of AZO and ITO targets. In the case of mixing a limited amount of ITO (10W), resistivity of TCO films was significantly increased compared to the AZO film; from $3.5{\times}10^{-3}$ to $9.7{\times}10^{-3}{\Omega}{\cdot}cm$. Deterioration of the electrical conductivity is attributed to the decreases in carrier concentration and Hall mobility. Improvement of the conductivity could be obtained for the films prepared with ITO powers larger than 40 W. The lowest resistivity ($\rho$) of $7.3{\times}10^{-4}{\Omega}{\cdot}cm$ was achieved when ITO power was 100 W. Effects of $H_2$ incorporation on the electrical and optical properties of AZO-ITO films were investigated in this work. Addition of small amount of hydrogen resulted in the increase of carrier concentration and the improvement of electrical conductivity. It is apparent that the roughness of AZO-ITO films decreases dramatically after the transition of microstructure from polycrystalline to amorphous phase, which gives practical advantages such as an excellent uniformity of surface and a high etching rate. AZO-ITO films grown at sputtering ambient with hydrogen gas are expected to be applicable to optoelectronic devices such as organic light emitting diodes and flexible displays due to their sufficient electrical and structural properties.

• 한국세라믹학회지
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• 제39권1호
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• pp.74-78
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• 2002

본 연구에서는 전구체 용액의 산화환원 발열반응을 이용하여 다성분계 산화물을 제조할 수 있는 용액연소합성법을 이용하여 페로브스카이트 구조 PZT 세라믹스를 합성하고자 하였다. 산화제/환원제 전구체 혼합물의 열분석(DTA/TG) 결과 산화제와 환원제의 열분해 거동의 차이로 인해 214$^{\circ}C$와 35$0^{\circ}C$에서 발열 피크가 나타났다. PZT세라믹스 합성을 위한 승온 과정에서는 37$0^{\circ}C$에서 연소반응이 일어났으나, 페로브스카이트로의 상전이는 일어나지 않았다. 용액연소과정 중 산화제와 연료의 열분해 거동을 고려하여 $600^{\circ}C$에서 제조한 생성물은 결정크기가 50nm인 정방정의 단일상으로 이루어진 PZT세라믹스이었다. 격자상수를 측정한 결과 a는 3.997$\pm$0.001 $\AA$이었으며, c는 4.147$\pm$0.001 $\AA$으로 나타났다.

• 공업화학
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• 제10권1호
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• pp.166-172
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• 1999

폐수중 중금속 이온을 제거하기 위한 방법으로 키토산 비드에 의한 금속 이온의 고정층 흡착 특성을 조사하였다. 게껍질로부터 키틴을 추출하고 이를 탈아세틸화 반응시켜 키토산을 제조하였다. 키토산은 비드로 만들어 중금속 흡착제로 사용하였다. 키토산 비드에 대한 $Cu^{2+}$, $Co^{2+}$, $Ni^{2+}$ 이온의 단성분 평형 흡착 실험 결과로부터 Freundlich와 Langmuir 흡착등온식을 결정하였다. 흡착등온식에 의하면 키토산 비드에 대한 중금속 이온의 흡착 세기는 $Cu^{2+}$>$Co^{2+}$>$Ni^{2+}$의 순서로 나타났다. 키토산 비드에 대한 중금속 이온의 단성분 또는 다성분계 고정층 흡착 실험으로부터 흡착 파과곡선을 구하였다. 단성분 흡착등온식으로 다성분 흡착 평형을 예측할 수 있는 IAS (ideal adsorbed solution) 이론을 적용하여 LDFA (linear driving force approximation)에 의한 고정층 흡착 모델식을 수치해 기법으로 모사하여 실험결과와 비교하였다. LDFA에 의한 모델식을 적용한 결과 키토산 비드에 대한 중금속 이온의 단성분 및 다성분계 고정층 흡착거동을 잘 모사할 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.164-164
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• 2013

Among multicomponent nanostructures, hybrid nanocatalysts consisting of metal nanoparticle-semiconductor junctions offer an interesting platform to study the role of metal-oxide interfaces and hot electron flows in heterogeneous catalysis. In this study, we report that hot carriers generated upon photon absorption significantly impact the catalytic activity of CO oxidation. We found that Pt-CdSe-Pt nanodumbbells exhibited a higher turnover frequency by a factor of two during irradiation by light with energy higher than the bandgap of CdSe, while the turnover rate on bare Pt nanoparticles didn't depend on light irradiation. We also found that Pt nanoparticles deposited on a GaN substrate under light irradiation exhibit changes in catalytic activity of CO oxidation that depends on the type of doping of the GaN. We suppose that hot electrons are generated upon the absorption of photons by the semiconducting nanorods or substrates, whereafter the hot electrons are injected into the Pt nanoparticles, resulting in the change in catalytic activity. We discuss the possible mechanism for how hot carrier flows generated during light irradiation affect the catalytic activity of CO oxidation.

• 한국재료학회지
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• 제20권9호
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• pp.472-477
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• 2010

$Al_2O_3$ has received wide attention with established use as a catalyst and growing application in structural or functional ceramic materials. On the other hand, the boehmite (AlO(OH)) obtained by sol-gel process has exhibited a decrease in surface area during phase transformation due to a decline in surface active site at high temperature. In this work, $Al_2O_3$-CuO/ZnO (ACZ) and $Al_2O_3$-CuO/CeO (ACC) composite materials were synthesized with aluminum isopropoxide, copper (II) nitrate hemi (pentahydrate), and cerium (III) nitrate hexahydrate or zinc (II) nitrate hexahydrate. Moreover, the Span 80 as the template block copolymer was added to the ACZ/ACC composition to make nano size particles and to keep increasing the surface area. The ACZ/ACC synthesized powders were characterized by Thermogravimetry-Differential Thermal analysis (TG/DTA), X-ray Diffractometer (XRD), Field-Emmision Scanning Electron Microscope (FE-SEM), Bruner-Emmett-Teller (BET) surface analysis and thermal electrical conductivity (ZEM-2:M8/L). An enhancement of surface area with the addition to Span 80 surfactant was observed in the ACZ powders from 105 $m^2$/g to 142 $m^2$/g, and the ACC powders from 103 $m^2$/g to 140 $m^2$/g, respectively.

• 폴리머
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• 제25권6호
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• pp.765-773
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• 2001

본 연구에서는 수중의 $Co^{2+}$, $Ni^{2+}$ , $Cr_2O_7\;^{2-}$등의 유해이온을 선택적으로 흡착 제거시키기 위하여 단량체의 몰비를 달리하여 AN-co-(MMA/IA)를 합성하고, 습식방사에 의해 제조한 PAN 섬유를 산가수분해하여 PAN계 다관능성 이온교환섬유를 합성하였다. 또한 합성한 이온교환섬유의 구조, 관능화도, 이온교환용량, 분포계수. 기계적 물성 등을 시험하였다. 이온교환체의 음이온교환 용량은 IA의 mole 함량이 증가함에 따라 4.5~4.2 meq/g으로 감소하고, 양이온교환용량은 1.8-2.2 meq/g으로 증가하는 경향을 보였다. 인장감도는 공중합체 내에 IA의 함량이 0.008 mol%까지 증가하여 216 $kg/cm^2$로 최대값을 나타냈고, AN-co-(MMA/IA) 이온교환체의 분포계수 측정 결과 Co(II)와 Ni(II)는 pH 5-6영역에서 최대를 보였고, Cr(III)는 pH 3-4에서 최대값을 나타냈다. 또한 다성분 계상에서의 연속식 흡착 실험에서 Cr(III > Co(II) > Ni(II)의 순으로 선택능을 나타냈다.

• Nuclear Engineering and Technology
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• 제52권3호
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• pp.597-609
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• 2020

Accident Tolerant Fuels have been widely studied since the Fukushima-Daiichi accident in 2011 as one of the options on how to further enhance the safety of nuclear power plants. Deposition of protective coatings on nuclear fuel claddings has been considered as a near-term concept that will reduce the high-temperature oxidation rate and enhance accidental tolerance of the cladding while providing additional benefits during normal operation and transients. This study focuses on experimental testing of Zr-based alloys coated with Cr-based coatings using Physical Vapour Deposition. The results of long-term corrosion tests, as well as tests simulating postulated accidents, are presented. Zr-1%Nb alloy used as nuclear fuel cladding serves as a substrate and Cr, CrN, Cr_xN_y layers are deposited by unbalanced magnetron sputtering and reactive magnetron sputtering. The deposition procedures are optimized in order to improve coating properties. Coated as well as reference uncoated samples were experimentally tested. The presented results include standard long-term corrosion tests at 360℃ in WWER water chemistry, burst (creep) tests and mainly single and double-sided high-temperature steam oxidation tests between 1000 and 1400℃ related to postulated Loss-of-coolant accident and Design extension conditions. Coated and reference samples were characterized pre- and post-testing using mechanical testing (microhardness, ring compression test), Thermal Evolved Gas Analysis analysis (hydrogen, oxygen concentration), optical microscopy, scanning electron microscopy (EDS, WDS, EBSD) and X-ray diffraction.