• 멤브레인
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• 제9권1호
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• pp.36-42
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• 1999

본 연구에서는 Si 미립자를 함유한 반도체 세정폐수의 관형막을 이용한 한외여과특성을 검토하였다. 관형막의 시간변화에 따른 투과유속의 감소현상은 막표면에 형성된 케익층의 증가 및 기공막힘에 기인하며, cross flow는 케익여과에 의한 막오염 형태를 보였으나 dead-end flow는 기공막힘과 케익여과에 의한 혼합형태를 보였다. Cross Flow의 케익저항의 크기는 3.16$\times$$10^{12}$ ~4.34$\times$$10^{12}$ $m^{-1}$ 였고, dead-end flow 는 6.6 $\times$$10^{12}$ ~12.19$\times$$10^{12}$ $m^{-1}$였다. 운전초기의 흐름형태에 따른 투과유속은 cross flow 가 dead-end flow 의 약 7 배였다. Cross flow 투과유속은 약 42 $\ell$/$m^2$ hr, 용질배제율은 약 96 % 였으며, 분리막공정을 거친 투과수 중의 Si 입자의 평균크기는 20nm였다.

• 식물조직배양학회지
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• 제24권2호
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• pp.77-81
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• 1997

감자 실생개체들의 내서성계통을 조기 선발하기 위해 CIP575015 $\times$Katahdin CIP 575015 x B6603-6, 84 I 35-4 $\times$Katahdin, CIP 575015 $\times$Nooksack 그리고 CIP575015 $\times$Superior 등 5조합을 교배하여 획득된 총 750립의 진정종자를 기내에서 각각의 조합을 온도별로 처리하여 괴경 형성 반응을 조사한 결과 온도가 2$0^{\circ}C$에서 3$0^{\circ}C$로 증가할 경우 평균 괴경형성율이 2$0^{\circ}C$에 비해 평균 43% 정도가 감소하였으며 특히 CIP575015 $\times$Katahdin조합은 21%로 가장 낮았다. 반면에 CIP575015 $\times$B6603-6 조합은 3$0^{\circ}C$에서도 58%의 괴경형성율을 보여 고온에서도 괴경형성이 잘되는 내서성 조합으로 생각되었다. 기내 고온조건하에 선발된 계통을 고온기 포장에서 내서성을 검정하기 위해 기내소괴경에서 생산된 괴경을 저지대 난지인 강릉 포장에 재배하였다. 조합별 괴경특성 및 수량을 조사한 결과 2$0^{\circ}C$에서 선발된 계통 중 1계통, 3$0^{\circ}C$에서 선발된 계통중 3계통의 내서성계통을 선발하였다. 수량성에서는 89ML75-8 계통이 수미품종 대비 88%의 증가로 다수성이었으며, 89ML64-11 계통은 건물율이 18.8%로 수미 품종보다 11%가 증가되어 전분용으로 유망시 되었다.

• Preventive Nutrition and Food Science
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• 제12권3호
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• pp.167-172
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• 2007

This study was conducted to determine the effect of hygienic processing (HP) on the reduction of microorganisms during manufacturing of saengshik with two vegetables (carrots and cabbage) and two grains (barely and glutinous rice) compared to general processing (GP). For GP, distilled water was used for washing raw materials and equipment. For HP, aqueous ozone (3 ppm) in combination with 1% citric acid and 70% alcohol were used for washing raw materials and the equipment, respectively. In carrots, after cutting, total aerobic bacteria (TAB), yeast and mold (YM) and coliforms were significantly increased to 5.19, 8.04 and 2.08 ($log_{10}$ CFU/g), respectively (p<0.05). Washing effectively reduced the increased microorganisms from cross contamination during cutting, but cross contamination increased with subsequent GP drying and milling procedures to 8.56, 8.27 and 3.71 ($log_{10}$ CFU/g) for TAB, YM and coliforms, respectively (p<0.05). On the other hand, HP washing of carrots with 3 ppm ozone in combination with 1% citric acid showed higher antimicrobial effect than GP washing, significantly decreasing the number of microorganisms (p<0.05). Further cross contamination did not occur through drying and milling due to cleaning the equipments with 70% alcohol prior to processing. After milling, the number of TAB, YM and coliforms were significantly decreased to 3.89, 4.47 and not detectable level ($log_{10}$ CFU/g), respectively (p<0.05). Similar results were observed in cabbage and grains. During storage for two months at different temperatures (22 or $4^{\circ}C$), there were no changes in numbers of spoilage microorganisms in the packaged saengsik after either processing. This suggests the importance of HP for the reduction of microorganisms during saengsik production, and demonstrates the effectiveness of disinfection at each processing stage in minimizing contamination levels to enhance microbial safety of saengshik products.

• 동력기계공학회지
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• 제17권3호
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• pp.35-43
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• 2013

Generally, the chassis of an indoor RAC is composed of a rear-guider and a stabilizer. The aerodynamic performance of a cross-flow fan is strongly influenced by the various design factors of the chassis of an indoor RAC. The purpose of this paper is to select the optimum design factors through the aerodynamic performance of a cross-flow fan. The design factors are the leading angle of a rear-guider (${\theta}_1$), a stabilizer setup angle(${\theta}_2$), a rear-guider clearance(${\epsilon}_1$), and a stabilizer clearance(${\epsilon}_2$), respectively. As a result, the optimum design factors of an indoor RAC can be presented as a combination of ${\theta}_1=33^{\circ}$, ${\theta}_2=55^{\circ}$, ${\epsilon}_1=6{\sim}8mm$, and ${\epsilon}_2=7mm$ through the analysis of a static pressure coefficient and a static pressure efficiency.

• 설비공학논문집
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• 제17권1호
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• pp.1-7
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• 2005

The heat transfer characteristics of an internal heat exchanger for $CO_2$ refrigeration cycle are numerically investigated. The numerical model is verified using the published experimental results for the concentric tube type internal heat exchanger. The Hardy-Cross Method gives very good agreement between the calculation and experimental results on the heat transfer rates and exit temperatures. Also, appropriate combination of heat transfer correlations is found. The operating parameters of the heat exchanger are calculated at transcritical region of $CO_2.$ The heat transfer rate of the counter flow type heat exchanger shows the $32\%$ greater than that of the parallel flow type heat exchanger. The increase of heat exchanger length enhances the heat transfer rate. The thermodynamic characteristics and heat transfer coefficient of $CO_2$ in the internal heat exchanger are estimated.

• 대한기계학회논문집B
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• 제23권2호
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• pp.218-225
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• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.

• ETRI Journal
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• 제33권2호
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• pp.184-193
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• 2011

Tailored for wireless local area networks, the present paper proposes a cross-layer resource allocation scheme for multiple-input multiple-output orthogonal frequency-division multiplexing systems. Our cross-layer resource allocation scheme consists of three stages. Firstly, the condition of sharing the subchannel by more than one user is studied. Secondly, the subchannel allocation policy which depends on the data packets' lengths and the admissible combination of users per subchannel is proposed. Finally, the bits and corresponding power are allocated to users based on a greedy algorithm and the data packets' lengths. The analysis and simulation results demonstrate that our proposed scheme not only achieves significant improvement in system throughput and average packet delay compared with conventional schemes but also has low computational complexity.

• Structural Engineering and Mechanics
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• 제71권2호
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• pp.153-163
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• 2019

Longitudinal fracture behavior of non-linear elastic beam configurations is studied in terms of the strain energy release rate. It is assumed that the beams exhibit continuous material inhomogeneity along the width as well as along the height of the crosssection. The Ramberg-Osgood stress-strain relation is used for describing the non-linear mechanical behavior of the inhomogeneous material. A solution to strain energy release rate is derived that holds for inhomogeneous beams of arbitrary cross-section under combination of axial force and bending moments. Besides, the solution may be applied at any law of continuous distribution of the modulus of elasticity in the beam cross-section. The longitudinal crack may be located arbitrary along the beam height. The solution is used to investigate a longitudinal crack in a beam configuration of rectangular cross-section under four-point bending. The crack is located symmetrically with respect to the beam mid-span. It is assumed that the modulus of elasticity varies continuously according a cosine law in the beam cross-section. The longitudinal fracture behavior of the inhomogeneous beam is studied also by applying the J-integral approach for verification of the non-linear solution to the strain energy release rate derived in the present paper. Effects of material inhomogeneity, crack location along the beam height and non-linear mechanical behavior of the material on the longitudinal fracture behavior are evaluated. Thus, the solution derived in the present paper can be used in engineering design of inhomogeneous non-linear elastic structural members to assess the influence of various material and geometrical parameters on longitudinal fracture.

• Ocean Systems Engineering
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• 제11권1호
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• pp.43-58
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• 2021

In the present work, a 3D numerical model is proposed to study local scouring around single vertical piers with different cross-section shapes under steady-current flow. The model solves the flow field and sediment transport processes using a coupled approach. The flow field is obtained by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in combination with the k-ω SST turbulence closure model and the sediment transport is considered using both bedload and suspended load models. The proposed model is validated against the empirical measurements of local scour around single vertical piers with circular, square, and diamond cross-section shapes obtained from the literature. The measurement of scour depth in equilibrium condition for the simulations reveal the differences of 4.6%, 6.7% and 13.1% from the experimental measurements for the circular, square, and diamond pier cases, respectively. The model displayed a remarkable performance in the prediction of scour around circular and square piers where horseshoe vortices (HSVs) have a leading impact on scour progression. On the other hand, the maximum deviation was found in the case of the diamond pier where HSVs are weak and have minimum impact on the formation of local scour. Overall, the results confirm that the prediction capability of the present model is almost independent of the strength of the formed HSVs and pier cross-section shapes.

• 한국강구조학회 논문집
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• 제16권1호통권68호
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• pp.1-10
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• 2004

본 논문에서는 수직 및 수평 브레이싱을 생략하고 I-형 거더를 가로보만으로 연결한 강합성 2-거더교에서 가로보의 적정 배치간격 및 소요 휨강성의 산정을 위한 연구를 수행하였다. 이를 위해 지간 40m의 단순교와 40+50+40m의 2차로 연속교를 예제교량으로 시산 설계하였다. 본 교량에 대해 중간가로보의 배치 간격과 휨강성을 매개변수로 하여 합성전 후 고정하중, 활하중, 풍하중 및 지진하중에 대한 해석을 수행하고 설계하중조합에 대한 응력 및 활하중 분배효과를 분석하였다. 한편, 강재 거더와 가로보의 격자구조에 대해 합성전 고정하중을 고려한 재료-기하 비선형해석으로부터 횡비틀림 좌굴강도를 평가하였다. 이상의 해석 결과를 토대로 지점부 및 중간가로보의 적정 배치 간격과 소요 휨강성을 제안하였다.