• Asian-Australasian Journal of Animal Sciences
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• 제16권9호
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• pp.1332-1338
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• 2003

This study was undertaken to examine the influence of soluble non-starch polysaccharides on growth performance, mucin secretion, and endogenous amino acid flows in weaner pigs. Different levels (0, 4 and 7.5%) of purified corn arabinoxylan (AX) or barley $\beta$-glucan extract (BG) were substituted for cellulose in a purified diet based on starch, sucrose and enzymatically hydrolyzed casein. All diets contained titanium oxide as an indigestible marker. Each experimental diet was fed to five, 6-wk old weaner pigs for 21 days. Average daily gain (p<0.05) and feed conversion ratio (p<0.01) were improved with dietary inclusion of 7.5% AX and BG, indicating high degradation rates of AX and BG in pigs. Crude mucin contents and endogenous nitrogen flow were increased (p<0.05) with increased levels of AX, but not with BG. Numerical increases in endogenous amino acid flow (EAAF) were observed with increased levels of AX but no definite trend with BG. Endogenous amino acid flow in pigs fed mixed NSP diets (4% BG and 3.5% cellulose) was significantly higher (p<0.05) than those fed 7.5% BG diets. Among diets containing pure sources of soluble non-starch polysaccharides, endogenous amino acid flows were highest in 7.5% AX (p<0.05), intermediate in BG, and lowest in control diet. Increased flows (p<0.01) of threonine, proline and serine in pigs fed 7.5% AX diets are consistent with the increased flow of crude mucin determined in this treatment. In conclusion, mucin and endogenous amino acid flows were increased with dietary inclusion of AX, which could be related to its physicochemical property, particularly its high water-holding capacity. In contrast, $\beta$-glucan, due to its high degradation rate in pig, may be considered as unimportant factor in inducing mucin and endogenous amino acid secretions, at least at levels such as those used in this study.

• 대한의용생체공학회:의공학회지
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• 제16권4호
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• pp.431-438
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• 1995

Tailored RF 경사자계 영상법을 이용하여 혈류효과를 배제한 자화율 효과만의 뇌기능 영상을 얻을수 있었다. 일반적인 RF를 이용한 경사자계 뇌기능 영상법은 빠른 경사자계 영상법으로 인해 정맥뿐만 아니라 동맥에서의 혈류효과와 $T2^{*}$ 효과가 합쳐진 영상을 얻게되는 반면, tailored RF를 이용한 경사자계 영상법은 산소소모와 관계된 자화율 변화에 의한 뇌기능 영상을 얻을 수 있었다. 본 논문에서 tailored RF를 이용하여 뇌기능 영상에서 자화율효과와 혈류효과를 명확히 구분할 수 있음을 보였다. 그리고 실험결과로 얻은 신호는 충분히 크고 산소 소모의 변화를 보다 더 정확히 표현하므로 지금까지 다른 경사자계 영상법으로는 어려웠던 뇌기능 영상에서 정량화된 산소 신진대사 연구의 가능성을 보여주었다.

• 한국항공우주학회지
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• 제31권1호
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• pp.73-84
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• 2003

항공기내 연료온도의 변화가 유한차분식에 의하여 해석되었다. 항공기의 여러 임무 가운데 근접항공지원 임무가 20% hot day 외부대기 조건과 함께 이음속 영역에서 고려되었다. 수정 Dufort-Frankel기법의 explicit방법에 의해 수치계산이 수행되었다. 항공기는 난류유동장내에 있는 것으로 가정되었다. 추가 연료공급-회송 개념을 갖는 항공기 연료시스템 모델이 고려되었다. 본 해석의 결과로써, 추가연료 공급이 증가함에 따라 연료탱크의 온도는 상승함을 보인 반면, 엔진 입구에서의 연료온도는 몇몇 비행단계 및 엔진 연료요구량이 많은 구간을 제외하고는 감소함을 보였다. 본 해석으로부터, 추가 연료공급-회송개념을 사용한 연료시스템이 엔진입구 연료온도를 낮추기 위한 효과적인 방법임을 나타났다. 또한, 연료/오일 열교환기로 흐르는 연료유동량이 연료온도 변화에 중요한 인자임이 밝혀졌다.

• Journal of Magnetics
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• 제20권1호
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• pp.40-46
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• 2015

This study investigated the accuracy of magnetic resonance angiography (MRA) and computed tomography angiography (CTA) in terms of reflecting the actual vascular length. Three-dimensional time of flight (3D TOF) MRA, 3D contrast-enhanced (CE) MRA, volume-rendering after CTA and maximum intensity projection were investigated using a flow model phantom with a diameter of 2.11 mm and area of $0.26cm^2$. 1.5 and 3.0 Tesla devices were used for 3D TOF MRA and 3D CE MRA. CTA was investigated using 16 and 64 channel CT scanners, and the images were transmitted and reconstructed by volume-rendering and maximum intensity projection, followed by conduit length measurement as described above. The smallest 3D TOF MRA measure was $2.51{\pm}0.12mm$ with a flow velocity of 40 cm/s using the 3.0 Tesla apparatus, and $2.57{\pm}0.07mm$ with a velocity of 71.5 cm/s using the 1.5 Tesla apparatus; both images were magnified from the actual measurement of 2.11 mm. The measurement with the 16 channel CT scanner was smaller ($3.83{\pm}0.37mm$) than the reconstructed image on maximum intensity projection. The images from CTA from examination apparatus and reconstruction technique were all larger than the actual measurement.

• Corrosion Science and Technology
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• 제18권2호
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• pp.61-71
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• 2019

Flow-Accelerated Corrosion (FAC) is a phenomenon in which a protective coating on a metal surface is dissolved by a flow of fluid in a metal pipe, leading to continuous wall-thinning. Recently, many countries have developed computer codes to manage FAC in power plants, and the FAC prediction model in these computer codes plays an important role in predictive performance. Herein, the FAC prediction model was developed by applying a machine learning method and the conventional nonlinear regression method. The random forest, a widely used machine learning technique in predictive modeling led to easy calculation of FAC tendency for five input variables: flow rate, temperature, pH, Cr content, and dissolved oxygen concentration. However, the model showed significant errors in some input conditions, and it was difficult to obtain proper regression results without using additional data points. In contrast, nonlinear regression analysis predicted robust estimation even with relatively insufficient data by assuming an empirical equation and the model showed better predictive power when the interaction between DO and pH was considered. The comparative analysis of this study is believed to provide important insights for developing a more sophisticated FAC prediction model.

• Wind and Structures
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• 제34권1호
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• pp.43-58
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• 2022

The BARC flow is studied via Direct Numerical Simulation at a relatively low turbulent Reynolds number, with focus on the geometrical representation of the leading-edge (LE) corners. The study contributes to further our understanding of the discrepancies between existing numerical and experimental BARC data. In a first part, rounded LE corners with small curvature radii are considered. Results show that a small amount of rounding does not lead to abrupt changes of the mean fields, but that the effects increase with the curvature radius. The shear layer separates from the rounded LE at a lower angle, which reduces the size of the main recirculating region over the cylinder side. In contrast, the longitudinal size of the recirculating region behind the trailing edge (TE) increases, as the TE shear layer is accelerated. The effect of the curvature radii on the turbulent kinetic energy and on its production, dissipation and transport are addressed. The present results should be contrasted with the recent work of Rocchio et al. (2020), who found via implicit Large-Eddy Simulations at larger Reynolds numbers that even a small curvature radius leads to significant changes of the mean flow. In a second part, the LE corners are fully sharp and the exact analytical solution of the Stokes problem in the neighbourhood of the corners is used to locally restore the solution accuracy degraded by the singularity. Changes in the mean flow reveal that the analytical correction leads to streamlines that better follow the corners. The flow separates from the LE with a lower angle, resulting in a slightly smaller recirculating region. The corner-correction approach is valuable in general, and is expected to help developing high-quality numerical simulations at the high Reynolds numbers typical of the experiments with reasonable meshing requirements.

• 대한기계학회논문집B
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• 제39권3호
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• pp.223-229
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• 2015

배플과 관군간의 누설유동이 쉘-관 열교환기 성능에 미치는 영향을 FLUENT 를 사용하여 조사하였다. 쉘측 출구온도를 최대로 하는 최적누설유동을 찾기 위해 쉘측 단면적에 대한 누설단면적 비가 0%-40% 범위의 5 가지 누설유동을 가진 쉘-관 열교환기에 대하여 CFD 모델이 개발되었다. 관 입구 및 벽면온도를 일정하게 유지하고 Reynolds 수를 4952 부터 14858 증가시키면서 유동장 및 온도장을 계산하였다. 해석결과, 출구온도, 압력강하, 열전달률은 Reynolds 수뿐만 아니라 누설유동에도 크게 영향을 받는 것으로 나타났다. 누설유동은 열전달률과 압력강하를 동시에 낮추는 결과를 제시한 기존의 결과와는 달리, 본 연구에서는 적정의 누설유동은 배플 주위의 재순환영역에 추가적인 모멘텀을 공급함으로써 최대출구온도, 작은 압력강하, 높은 열전달률을 유도하는 효과를 발휘하는 새로운 결과를 얻었다. 20%의 누설단면적이 최적의 누설단면적으로 나타났다.

• 한국의학물리학회지:의학물리
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• 제23권3호
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• pp.177-187
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• 2012

자기공명 혈관조영술은 혈관협착, 동맥류, 동정맥기형 등의 혈관질환 진단에 널리 사용되고 있다. 특히 위상대조도 자기공명 혈관조영술은 조영제를 사용하지 않는 자기공명 혈관조영술로서 혈관의 해부학적인 정보를 제공함과 동시에 혈류 속도측정이 가능하다. 본 연구에서는 저자장 자기공명영상 시스템에 적합한 2차원 및 3차원 위상대조도 혈관조영술의 펄스열을 개발하여 유속팬텀과 정상인의 뇌에 적용한 후 획득한 혈관영상과 위상분석을 통한 속도측정을 바탕으로 저자장 자기공명영상 시스템에서의 위상대조도 혈관조영술의 유용성을 평가하고자 한다. 2차원 및 3차원 위상대조도 혈관조영술을 제작된 유속팬텀과 인체 내에 적용하여 상시상 정맥동, 곧은 정맥동 및 두 혈관의 합류지점에 대한 속도측정을 시행하였다. 결과로서 2차원 위상대조도 혈관조영술의 사용은 큰 혈관에 대해서는 높은 가시도를 나타내지만, 작은 혈관에 대한 가시도는 상대적으로 저하됨을 확인할 수 있었다. 3차원 위상대조도 혈관조영술을 사용한 혈관영상은 2D PC MRA 영상에 비해 큰 혈관은 물론이고 작은 혈관에 대한 가시도가 향상되었으나 작은 혈관에서 영상의 신호가 불균일하여 작은 혈관의 진단에 사용하기에는 적합하지 않았다. 한편 2차원 위상대조도 혈관조영술을 통한 영상에서 큰 혈관의 가시도는 혈류속도를 측정하기에 충분했다. 측정된 결과는 상시상 정맥동의 경우 $25.46{\pm}0.73cm/sec$, 곧은 정맥동의 경우 $24.02{\pm}0.34cm/sec$, 상시상 정맥동과 곧은 정맥동의 합류지점의 경우 $26.15{\pm}1.50cm/sec$으로 나타났으며 이는 앞선 연구결과에서 알려진 전체 심장운동주기를 고려한 정상인들의 각 해당 부위별 혈류속도의 오차범위 내에 포함되는 좋은 결과를 나타내었다. 앞선 결과들을 토대로 본 연구는 현재 국내에서 제작하여 보급중인 저자장 자기공명영상 시스템에서 위상대조도 혈류영상화 기법의 적용 및 응용 가능성을 보여주고 있으며 이를 실용화하기 위한 중요한 기초자료를 제공할 수 있을 것이다.

• 생태와환경
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• 제43권4호
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• pp.492-502
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• 2010

The study objects were to analyze long-term and seasonal variations of nutrients (N, P), suspended solids, N:P ratios, algal chlorophyll, and trophic state along with general water quality parameters in four sampling sites including two intake tower sites supplying drinking water in Daechung Reservoir. For the analysis, we used water quality long-term data sampled during 1998~2007 by the Ministry of Environment, Korea. Interannual and seasonal trends in inflow and discharge near the intake tower facilities over the ten years were directly influenced by rainfall pattern. The distinct difference between wet year (2003) and dry year (2001) produced marked differences in water temperature, pH, dissolved oxygen, organic matter contents, nutrients, and these variables influenced algal biomass and trophic state. Values of TP varied depending on the year and locations sampled, but monthly mean TP always peaked during July~August when river inflow and precipitation were maxima. In contrast, TN varied little compared to TP, indicating lower influence by seasonal flow compared to phosphorus. The number of E. coli were highest in Site 2 (Chudong intake tower) and varied largely, whereas at other sites, the numbers were low and low variations. Contents of chlorophyll-${\alpha}$ (CHL), as an estimation of primary productivity, varied largely depending on the year and season. The maximum of CHL occurred at Muneu intake tower (S4) during 2006 when the precipitation and inflow were lowest. In contrast, another CHL peak was observed in Site 2 (Chudong intake tower) in 2006 when one of the largest typoons (Ewinia) occurred and river runoff were maximum. So the CHL maxima were associated with both wet year (high flow, high nutrient supply) and dry year (low flow, nutrient supply by littoral zone). Such conditions influenced trophic states, based on Trophic State Index of nutrients and CHL. Based on all analyses, we can provide some clues for management and protection strategies of two intake tower sites.

• Food Science and Biotechnology
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• 제17권3호
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• pp.470-474
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• 2008

The whole berry, pulp, and seed of sea buckthorn fruit were extracted with supercritical $CO_2$ to produce edible oils. The effects of extraction pressure, temperature, and $CO_2$ flow rate on the oil yield and extraction rate were investigated, and the fatty acid composition, tocopherol, and carotenoid contents of the oils were compared. The results showed that the extraction rate was affected by pressure, temperature, and $CO_2$ flow rate and, in general, the yield increased with a rise in any of the 3 variables. Fatty acids in the whole berry and pulp oil were dominated by monounsaturated fatty acids (>64%), followed by saturated fatty acids (about 30%). In contrast, fatty acids in the seed oil consisted mainly of polyunsaturated (>60%) and monounsaturated fatty acids (>24%). The seed oil had a slightly higher content of tocopherols, but a much lower content of carotenoids, compared with the whole berry or pulp oil.