• 대한기계학회논문집B
• /
• 제27권12호
• /
• pp.1667-1672
• /
• 2003

In contrast to the high demand for MEMS devices, microflow analysis is not feasible even for single-phase flow with conventional Navier-Stokes equation because of non-continuum effect when characteristic dimension is comparable with local mean free path. DSMC is one of particle based DNS(Direct Numerical Simulation) methods that uses no continuum assumption. In this paper, gas flow in microchannel is studied using DSMC. Interfacial shear and flow characteristics are observed and compared with the results of gas flow that is in contact with liquid case and solid wall case. The simulation is limited to the case of equilibrium steady state and evaporation/condensation coefficient is assumed to be the same and unity. System temperature remains constant and the interfacial shear appears to be small compared to the result with solid wall. This is because particles evaporated and reflected from the liquid surface form high density layer near the interface with liquid flow.

• 대한지역사회영양학회지
• /
• 제3권2호
• /
• pp.210-217
• /
• 1998

The purpose of this study was to examine changes in energy and macronutrient intakes during the premenstrual(days -10-1) and postmenstrual(days 5-14) phases. Thirty-two college female students recorded their food consumption and dietary patterns over 5 weeks from September 8 to October 12, 1997. Mean daily energy and macronutrient intakes and the percentage of energy intake from protein and carbohydrate were relatively consistent over the two menstrual cycle phases, but the energy intake from fat increased 1%(P<0.05)during the postmenstrual phase. Two different dietary patterns were identified by the shifts in energy intake between postmenstrual and premenstrual phases. Seventy five percent of subjects revealed a consistent pattern with the results of previous studies investigating food intake over the menstrual cycle, in which the premenstrual phase is associated with an increment in energy, carbohydrate, and protein intake. In contrast, energy, protein, and fat intakes increased during the postmenstrual phase in 25% of the subjects. We conclude that cyclical fluctuations in energy and macronutrient intakes occur in both postmenstrual and premenstrual dietary pattern groups across the two menstrual phased with the opposite directions.

• 한국광학회지
• /
• 제23권2호
• /
• pp.71-76
• /
• 2012

Sagnac 형태로 변형된 Mach-Zehnder 간섭계(SMZI)는 모든 광경로가 동일한 광부품을 서로 공유하기 때문에 위상 흔들림을 최소화할 수 있는 안정된 간섭계이다. 본 연구에서는 단일광자 수준까지 감쇄시킨 레이저 광과 제 2형의 매개하향변환에서 발생한 편광 상관관계가 있는 광자로부터 준비된 단일광자를 이용한 간섭실험에서 매우 안정된 간섭무늬를 관측하였다. SMZI의 위상은 약 ${\pm}0.18$ rad으로 안정적인 반면에 보통의 MZI는 ${\pm}1.02$ rad의 위상 요동을 나타내었다.

• 대한전자공학회논문지TC
• /
• 제42권1호`
• /
• pp.105-110
• /
• 2005

본 논문에서는 T-Junction 스위치 구조를 이용하여 이중 대역 전압제어 발진기를 설계, 제작하였다. T-Junction 스위치는 이중 대역 공진을 얻기 위한 스위치로서 공진부에 적용된다. 설계한 공진기를 발진기의 능동부와 결합하여 이중 대역 전압제어 발진기를 만들었다. 상위 주파수 대역 5.715 GHz 에서 전압제어 발진기의 출력 전력은 -1.42 dBm, 위상잡음은 1 MHz offset에서 -94.37 dBc/Hz이고 하위 주파수 대역 2.236 GHz에서 출력 전력은 -2.09 dEm, 위상잡음은 1 MHz offset -104.78 dBc/Hz 이다.

• Preventive Nutrition and Food Science
• /
• 제12권4호
• /
• pp.259-266
• /
• 2007

It has been proposed that the mode of action of nisin against vegetative cells and spores of Clostridium botulinum is different. However, clear explanation is not available. Therefore, nisin action against vegetative cells and spores of C. botulinum was investigated in this study. Nisin was added at various stages of spore-to-vegetative cell transition and changes to sensitivity to the bacteriocin were observed. Different nisin preparation (Nisaplin or pure nisin) was compared for their activity against different stages of spore transformation of C. botulinum ATCC 25763. Germination was measured by determining loss of heat resistance and observing phase darkening of spores under phase-contrast microscope. Nisin acted bactericidally against vegetative cells, but acted sporostatically against spores of C. botulinum under the same concentration. This bactericidal and sporostatic action of nisin was dependent on the concentration of nisin used. Presence of nisin during spore activation by heat increased subsequent phase darkening and germination rates. However, nisin inhibited the germination and the outgrowth, when it was added after heat activation stage. Findings from this study suggest that the time of addition of nisin is very important for the effective control of spores during the heating process of foods. In addition, it may be possible to apply nisin at the stage of processing that coincides with the most sensitive stage of spore transformation.

• Journal of Microbiology and Biotechnology
• /
• 제23권1호
• /
• pp.99-105
• /
• 2013

In this study, nitrous oxide ($N_2O$) emission was compared between the operations of two different sequencing batch reactors, conventional sequencing batch reactor (CNVSBR) and simultaneous nitrification and denitrification sequencing batch reactor (SND-SBR), using synthetic wastewater. The CNV-SBR consisted of anoxic (denitrification) and aerobic phases, whereas the SND-SBR consisted of a microaerobic (low dissolved oxygen concentration) phase, which was achieved by intermittent aeration for simultaneous nitrification and denitrification. The CNV-SBR emitted 3.9 mg of $N_2O$-N in the denitrification phase and 1.6 mg of $N_2O$-N in the nitrification phase, resulting in a total emission of 5.5mg from 432mg of $NH_4^+$-N input. In contrast, the SND-SBR emitted 26.2mg of $N_2O$-N under the microaerobic condition, which was about 5 times higher than the emission obtained with the CNV-SBR at the same $NH_4^+$-N input. From the $N_2O$ yield based on $NH_4^+$-N input, the microaerobic condition produced the highest yield (6.1%), followed by the anoxic (0.9%) and aerobic (0.4%) conditions. It is thought that an appropriate dissolved oxygen level is critical for reducing $N_2O$ emission during nitrification and denitrification at wastewater treatment plants.

• Journal of Power Electronics
• /
• 제19권1호
• /
• pp.288-295
• /
• 2019

Rectifiers are widely used in industrial applications. Although detailed models of rectifiers are usually used to evaluate their performance, they are complex and time-consuming. Therefore, the Average Value Model (AVM) has been introduced to meet the demand for a simple and accurate model. This type of rectifier modeling can be used to simplify the simulations of large systems. The AVM of diode rectifiers has been an area of interest for many electrical engineers. However, healthy diode rectifiers are only considered for average value modeling. By contrast, faults occur frequently on diodes, which eventually cause the diodes to open-circuit. Therefore, it is essential to model bridge rectifiers under this faulty condition. Indeed, conventional AVMs are not appropriate or accurate for faulty rectifiers. In addition, they are significantly different in modeling. In this paper, a novel application of the parametric average value of a three-phase line-commutated rectifier is proposed in which one diode of the rectifier is considered open-circuited. In order to evaluate the proposed AVM, it is compared with experimental and simulation results for the application of a brushless synchronous generator field. The results clearly demonstrate the accuracy of the proposed model.

• 한국가시화정보학회지
• /
• 제21권3호
• /
• pp.75-84
• /
• 2023

In this study, we conducted analysis of bubble dynamics and flow of liquid phase change material(PCM) using shadowgraphy and particle image velocimetry(PIV). Characteristics of internal flow varied depending on locations of injection when solid PCM was liquefied from heated vertical wall. When bubbles rose immediately, they exhibited elliptical shape and zigzag trajectory. In contrast, when bubbles rose after merging at the bottom of solid PCM, with equivalent diameter for the inter-wall distance of 0.64 or greater, they showed a jellyfish shape and strong rocking behavior. It was observed by the PIV that the small ellipse bubbles made most strong flow inside the liquid PCM. Furthermore, the flow velocity was highest in the case of front injection, as the directions of temperature gradients and bubble-driven flow were aligned. The results underscore the significant influence of injection location on various characteristics, including bubble size, shape, rising path of bubbles, and internal flow.

• 대한방사선기술학회지:방사선기술과학
• /
• 제38권1호
• /
• pp.39-49
• /
• 2015

격자 간섭계(grating interferometer)는 방사선 영상분야의 새로운 기술로서, 흡수 영상(absorption imaging)뿐만 아니라 위상차 영상(phase contrast imaging)과 다크필드 영상(dark field imaging)을 제공한다. 격자 간섭계는 크게 탈봇 효과(talbot effect)를 이용하는 탈봇 간섭계와 탈봇-라우 효과(talbot-lau effect)를 이용하는 탈봇-라우 간섭계로 나뉘는데, 일반적인 방사선 영상시스템과 달리 방사선의 간섭을 예측하고 적용하는 것이 중요하다. 본 연구에서는 현재 부산대학교 중성자 및 방사선 공학 연구실에서 보유하고 있는 엑스선 격자 세트와 중성자 격자 세트를 이용하여 탈봇 간섭 패턴 및 탈봇-라우 간섭 패턴을 제작하였다. 이를 통해 방사선의 파동 거동에 따른 간섭 세기의 변화를 예측하고, 격자 간섭계를 구성하는 각 요소들을 계산했다. 그리고 격자의 종류 및 위상차 물체에 대한 탈봇 간섭 패턴 및 탈봇-라우 간섭 패턴을 예측하였다.

• 농업과학연구
• /
• 제39권3호
• /
• pp.387-393
• /
• 2012

In the present study, ${\beta}$-glucanase-assisted extraction of starch from glutinous barley(Hinchal ssalbory) was investigated. ${\beta}$-glucanase was added to a coarse starch suspension obtained after wet milling in the starch extraction process. It was found that in the isolated starch with enzyme treatment, protein content was lower by 0.03%, compared to that with non-enzyme treatment. More importantly it was observed that the extraction yield of starch from enzyme treatment was found to be about 12% higher than the one from non-enzyme treatment (enzyme treated: 90.56%, non-enzyme treated: 78.46%). In order to elucidate this finding, the mass-balance determination of starch in each extraction step was carried out and found that the enzyme treatment might influence on the insoluble residues(R3 and R4 fractions) to hydrolyze ${\beta}$-glucan and other materials (e.g., mucilages etc.), thereby facilitated the separation of starch from it and a next filtration process. With a phase-contrast microscope it was observed that the isolated starch with enzyme treatment contained small starch granules more than the one with non-enzyme treatment and this might result in higher extraction yield observed with the former. In order to confirm this hypothesis, further experiments would be necessary.