• 대한기계학회논문집
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• 제13권4호
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• pp.764-770
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• 1989

This paper analyze the steady state performance of a self-acting air lubricated slider bearing in hard disk/head system. Modified Reynolds' equation is derived from the steady state compressible Navier-Stokes equation, under slip-flow conditions. Finite difference technique and numerical procedure are described by using Newton-Raphson iteration method to slove the non-linear equations. These techniques are applied to conventional slider bearings and the effects of molecular mean free path(MMFP) for a recording surface of hard disk are shown. The calculation procedure developed here, wide applicabilities in practical head design procedures, and converges rapidly.

• Molecules and Cells
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• 제39권1호
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• pp.26-30
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• 2016

Peroxiredoxins are ubiquitous thiol proteins that catalyse the breakdown of peroxides and regulate redox activity in the cell. Kinetic analysis of their reactions is required in order to identify substrate preferences, to understand how molecular structure affects activity and to establish their physiological functions. Various approaches can be taken, including the measurement of rates of individual steps in the reaction pathway by stopped flow or competitive kinetics, classical enzymatic analysis and measurement of peroxidase activity. Each methodology has its strengths and they can often give complementary information. However, it is important to understand the experimental conditions of the assay so as to interpret correctly what parameter is being measured. This brief review discusses different kinetic approaches and the information that can be obtained from them.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권3호
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• pp.89-99
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• 2008

Indoor ozone has received attention because of its well-documented adverse effects on health. In addition to the inherently harmful effects of ozone, it can also initiate a series of reactions that generate potentially irritating oxidation products, including free radicals, aldehydes, organic acids and secondary organic aerosols (SOA). Especially, ozone reacts actively with terpene. The overarching goal of this work was to better understand ozone and terpene distributions within rooms. Towards this end, the paper has two parts. The first describes the development of a cylindrical test chamber that can be used to obtain the second order rate constant $(k_b)$ for the bi-molecular chemical reaction of ozone and terpene in the air phase. The second consists of model room experiments coupled with Computational Fluid Dynamics (CFD) analysis of the experimental scenarios to obtain ozone and terpene distributions in various turbulent flow fields. The results of CFD predictions were in reasonable agreement with the experimental measurements.

• Tuberculosis and Respiratory Diseases
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• 제85권3호
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• pp.264-272
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• 2022

Background: The current conventional drug susceptibility test (DST) for Mycobacterium tuberculosis (Mtb) takes several weeks of incubation to obtain results. As a rapid method, molecular DST requires only a few days to get the results but does not fully cover the phenotypic resistance. A new rapid method based on the ability of viable Mtb bacilli to hydrolyze fluorescein diacetate to free fluorescein with detection of fluorescent mycobacteria by flow cytometric analysis, was recently developed. Methods: To evaluate this cytometric method, we tested 39 clinical isolates which were susceptible or resistant to isoniazid (INH) or rifampin (RIF), or ethambutol (EMB) by phenotypic or molecular DST methods and compared the results. Results: The susceptibility was determined by measuring the viability rate of Mtb and all the isolates which were tested with INH, RIF, and EMB showed susceptibility results concordant with those by the phenotypic solid and liquid media methods. The isolates having no mutations in the molecular DST but resistance in the conventional phenotypic DST were also resistant in this cytometric method. These results suggest that the flow cytometric DST method is faster than conventional agar phenotypic DST and may complement the results of molecular DST. Conclusion: In conclusion, the cytometric method could provide quick and more accurate information that would help clinicians to choose more effective drugs.

• Korea-Australia Rheology Journal
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• 제11권4호
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• pp.305-311
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• 1999

The shear behavior of polymers obtained by means of devices such as capillary and cone-and-plate rheo-meters is commonly used to assess their processing performance and as a characterization tool. However, the number of instances when two polymers have the same shear properties but perform differently during certain types of processing operations (e.g. film blowing and sheet extrusion) indicate that shear properties alone may not be sufficient to characterize polymeric fluids. We begin by defining the kinematics of shear-free or extensional flow and the associated material functions. The extensional and shear behavior of three different types of polyethylene (PE) are then compared to illustrate the points that one cannot ascertain the extensional properties of polymer melts from their shear properties and, furthermore, there may not be a simple relation between properties obtained from one type of extensional flow and those of another type. The kinematics of most processing flows are extensional rather than shear in nature, and , hence, the performance of polymers during processes such as fiber spinning, film casting, film blowing, thermoforming, blow molding, and even extrusion is more readily accounted for through extensional viscosity measurements. Methods for carrying out extensional flow measurements are then reviewed including approximate methods. To illustrate the sensitivity of extensional viscosity measurements to subtle changes in the molecular architecture of PEs, results are presented for samples with a narrow molecular weight distribution but with varying numbers of long chain branches. Finally, constitutive equations which allow one to separate shear and extensional flow behavior are discussed as any attempts to simulate the subtle processing differences between two polymers will require constitutive equations of this nature.

• Environmental Engineering Research
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• 제23권4호
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• pp.390-396
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• 2018

This study investigated the transformation of dissolved organic matter (DOM) in a free-water surface flow constructed wetland. Pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) coupled with preparative high-performance liquid chromatography (prep-HPLC) was used to analyze the compositions of biopolymers (polysaccharides, amino sugars, proteins, polyhydroxy aromatics, lipids and lignin) in DOM according to the molecular size at three sampling points of the water flow: inflow, midflow, and outflow. The prep-HPLC results verified the decomposition of DOM through the decrease in the number of peaks from three to one in the chromatograms of the sampling points. The Py-GC/MS results for the degradable peaks indicated that biopolymers relating to polysaccharides and proteins gradually biodegraded with the water flow. On the other hand, the recalcitrant organic fraction (the remaining peak) in the outflow showed a relatively high concentration of aromatic compounds. Therefore, the ecological processes in the constructed wetland caused DOM to become more aromatic and homogeneous. This indicated that the constructed wetland can be an effective buffer area for releasing biochemically stable DOM, which has less influence on biological water quality indicators, e.g., biochemical oxygen demand, into an aquatic ecosystem.

• KSTLE International Journal
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• 제7권2호
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• pp.27-34
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• 2006

Knudsen number is the ratio of molecular mean free path versus mm thickness and the criterion to determine the flow form. When its value is lower than 0.01, the flow can be assumed to has no slip boundary condition. And in the case that the value is between 0.01 and 10, then the flow has slip boundary condition at both the adjacent walls. The condition of the air flow between the rotating journal and top foil in the air foil bearing is determined by the rotating speed and load, and the Knudsen number is also varied by those values. Because the molecular mean free path is variable to the pressure and temperature, more exact formulation is necessary to understand and analyze the flow regime. In this study, the analysis considering Knudsen number formulated with those variables (pressure, temperature and mm thickness) was executed. The approximate value was examined using the equation to confirm whether the flow has the slip or no-slip boundary condition. From the analytic investigation, it was decided to range approximately 0.01 to 1.0 and the flow can be supposed to have the slip boundary condition. Under the condition of the slip flow, the static characteristics of the air foil bearing were examined using modified Reynolds equations. The results were compared with those considering no slip condition. It shows that the slip condition makes the flow decelerates and the load carrying capacity decreases compared with no slip condition. And as the bearing number and eccentricity ratio increase, the load carrying capacity also increased at both the cases. From this result, it can be supposed that the bearing torque also increases. In the analysis of the dynamic characteristics, the perturbed Knudsen number was taken into consideration. Because the Knudsen number is expressed as the terms of each variable, the perturbed equation can be simply derived. The results of both cases considering and not considering Knudsen number were compared each other. In the case of the direct terms of the stiffness and damping coefficients, the difference between both cases was little and increased as the bearing number and eccentricity ratio increased. And the cross terms have less or more differences.

• 한국진공학회지
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• 제16권4호
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• pp.298-304
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• 2007

rf 플라즈마 소스가 장착된 분자선 에피택시 장비를 이용하여 Si(111) 기판위에 GaN 나노로드를 성장할 때, N2의 흐름양을 조절하여 나노로드의 구조 및 광학적인 특성을 조사하였다. $N_2$의 양이 1.1sccm에서 2.0sccm으로 변할 때 육각형 모양의 나노로드가 성장되었으며, 평균 직경이 80nm에서 190nm 까지 변화 하였다. 그러나 나노로드와 compact한 영역의 길이 (두께)비는 $N_2$의 양이 1.7sccm 까지는 증가하지만 그 이상에서는 변화지 않았다. PL 측정으로부터, $N_2$의 양이 적은 나노로드에서 자유 엑시톤의 피이크가 더욱 뚜렷하게 관측되었고, 모든 PL 피이크의 위치는 직경이 적을수록 나노로드의 크기 효과에 의해서 고에너지 쪽으로 이동하였다. $N_2$의 양이 1.7sccm 인 시료에서는 온도에 따른 PL의 피이크의 위치가 온도가 증가함에 따라서 "S-형"의 거동을 나타내었다.

• Journal of Korean Vacuum Science & Technology
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• 제2권1호
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• pp.1-8
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• 1998

The uniform distributed pumping model is used to derive analytic expressions of the pressure profile for the molecular flow regime in linearly tapered or flared(conical or pyramidal) tubes with wall sorption. The concept of transmission conductance for sticky tubes of arbitrary shape is newly introduced to calculate the transmission probability using the pressure profile. The transmission probability obtained analytically for a conical sticky tube is compared with that from the Monte Carlo simulation.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.581-584
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• 2008

A generation of a particle beam is the key technique in a flow cytometry that measures the fluorescence and light scattering of individual cell and other particulate or molecular analytes in biomedical research. Recent methods performing this function require a laborious and time-consuming assembly. In the present work, we propose a novel device for the generation of an axisymmetrical focusing beam of microparticles (3-D focusing) in a single capillary without sheath flows. This work uses the concept that the particles migrate toward the centerline of the channel when they lag behind the parabolic velocity profile. Particle focusing of spherical particles was successfully made with a beam diameter of about 10 ${\mu}$m. Proposed device provides crucial solutions for simple and innovative 3-D particle focusing method for the applications to the MEMS-based micro-flow cytometry. We believe that this device can be utilized in a wide variety of applications, such as biomedical/ biochemical engineering.