A biomimetic approach for effective reduction in micro-scale friction by direct replication of topography of natural water-repellent surfaces

In this paper, we report on the replication of surface topographies of natural leaves of water-repellent plants of Lotus and Colocasia onto thin polymeric films using a capillarity-directed soft lithographic technique. The replication was carried out on poly(methyl methacrylate) (PMMA) film spin coated on silicon wafer using poly(dimethyl siloxane) (PDMS) molds. The friction properties of the replicated surfaces were investigated at micro-scale in comparison with those of PMMA thin film and silicon wafer. The replicated surfaces exhibited superior friction property when compared to those of PMMA thin film and silicon wafer. The superior friction behaviour of the replicated surfaces was attributed to the reduced real area of contact projected by them.     

Characteristics of critical solid-liquid separation and its effect on the performance of an anaerobic sequencing batch reactor treating municipal sludge

Solid-liquid separation and its type greatly affected the stability and performance of an anaerobic sequencing batch reactor (ASBR) for municipal sludge digestion. Flotation thickening occurred in the mesophilic ASBR, while solid-liquid separation in the thermophilic ASBR followed gravity thickening. Hydraulic retention times (HRT) and cycle period as well as type of thickening were key parameters governing sludge thickenability and critical solids accumulation. Thickened sludge bed volume was a critical operating variable in the ASBR with gravity thickening, which had poor performance because of the loss of thickened solids, and sludge interface disruption or instability of sludge bed due to internal gas evolution. A cyclic mutual effect between thickened volume and gas production was serious in gravity thickening, whereas it was insignificant in flotation thickening.     

On-line monitoring and quantitative analysis of biofouling in low-velocity cooling water system

To monitor and analyze the biofouling phenomenon caused primarily by microbial suspended solids (MSS), a ‘biofouling tube’ apparatus consisting of a carbon steel tube, a differential pressure transmitter, a corrator, and a cooling water circulation device was designed and fabricated. By measuring continuously the pressure drop across the biofouling tube and using the correlation between the fluid’s friction factor and surface roughness, we quantitatively analyzed the influence of MSS concentration, temperature, and fluid velocity on the rate of biofilm growth on the metal surface. The result indicated that the fluid velocity had the most profound impact, e.g., lowering the linear velocity from 0.3 to 0.15 m/sec resulted in about a four times higher biofouling rate. Up to 50 ppm MSS, the biofouling rate was proportional to the MSS concentration. The biofouling rate at 35°C was about 1.75 times higher than that of 45°C., probably due to the diminishing effect of thermolabile microorganisms exposed at 45°C. It was also demonstrated that the biofouling could be significantly reduced by incorporating cooling water treatment programs such as protective pre-filming and adding corrosion inhibitors. This apparatus, if installed on-site at a sidestream of a cooling water system, could be used to monitor the biofouling tendency on-line and to suggest timely preventive maintenance actions.     

Impacts of fouling and cleaning on the performance of plate fin and spine fin heat exchangers

An experimental study was conducted to investigate the effects of air-side fouling and cleaning on the performances of various condenser coils used in unitary air-conditioning systems. A total of six condenser coils with different fin geometry and row number were tested. Performance tests were performed at three different conditions: clean-as-received, after fouling, and after cleaning. In all cases, it was observed that the fouling was mostly confined to the frontal face of the heat exchanger as reported in the previous investigations. The amount of deposited dust was more dependent on fin geometry for the single-row heat exchangers than for the double-row heat exchangers. The predominant effect of fouling was to cause a more significant increase in air-side pressure drop than a degradation in heat transfer performance. For the single-row heat exchangers, the pressure drop increased by 28 to 31%, while the heat transfer performance decreased by 7 to 12% at the standard air face velocity of 1.53 m/s depending on fin shape. For the double-row heat exchangers, the pressure drop increased by 22 to 37%, and heat transfer performance decreased by only 4-5% at the same air face velocity. Once the contaminated coils were cleaned according to the given cleaning procedure the original performance of the heat exchangers could almost be recovered completely. The pressure drop could be restored within 1 to 7% and the heat transfer performance could be recovered to within 1 to 5% of the originally clean heat exchangers. Therefore, it is concluded that a periodic application of the specified cleaning technique will be effective in maintaining the thermal performance of the condenser coils.     

The evolution of recrystallization textures in plastically deformed face centered cubic metals

The recrystallization texture of axisymmetrically deformed fcc metals having major <111> + minor <100> fibers and major <100> + minor <111> fibers is the <100> orientation. The evolution of the 100<001> recrystallization texture from the 112<111> deformation texture and near 031<20 1 3> recrystallization texture from plane strain compressed bicrystal 123<412> and the recrystallization texture of axisymmetrically deformed fcc metals have been discussed based on the energy release maximization theory in which the absolute maximum stress direction in deformed state becomes parallel to the minimum Young’s modulus direction after recrystallization.     

Performance test and component characteristics evaluation of a micro gas turbine

This study aims to analyze engine performance and component characteristics of a micro gas turbine based on detailed measurement of various parameters. A test facility to measure performance of a micro gas turbine was set up and performance parameters such as turbine exit temperature, exhaust gas temperature, engine inlet temperature, compressor discharge pressure and temperature, and fuel and air flow rates were measured. The net gas turbine performance (power and efficiency based on the gas turbine shaft end) was isolated and analyzed. With the aid of measurement based simulation, component characteristic parameters such as turbine inlet temperature, compressor efficiency, turbine efficiency and recuperator effectiveness were estimated. Behaviors of the estimated characteristic parameters with operating condition change were examined and sensitivities of estimated parameters to the measured parameters were analyzed.     

Efficient cell surface display of organophosphorous hydrolase using N-terminal domain of ice nucleation protein in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Recombinant Escherichia coli systems expressing organophosphorous hydrolase (OPH) have been used for detoxifying toxic organophosphate compounds. However, a whole cell biocatalyst system has an intrinsic problem due to substrate diffusion limitation by its cell membrane. As a strategy for reducing this diffusion barrier limitation to enhance whole cell biocatalytic activity, we engineered E. coli cells to target OPH on cell surface using ice nucleation protein (InaK) as a surface targeting motif, especially N-terminal domain of InaK (InaK-N). The whole cell OPH activities of the cells expressing InaK/OPH fusion constructs were higher (∼2.5-fold for InaK-N and ∼5.7-fold for combined N-and C-terminal domain of InaK (InaK-NC)) than that of the cells expressing cytosolic OPH. Interestingly, the membrane targeting efficiency of the cells expressing InaK-N/OPH fusion proteins was ∼2.2-fold higher compared to the cells expressing InaK-NC/OPH even though both whole cell and total cell lysate OPH activities were lower. Therefore, we found that the small size N-terminal domain of InaK is more efficient for targeting OPH on the cell surface, and the surface display of OPH using N-terminal InaK domain can reduce the mass-transfer problem in whole cell bioconversion system. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007     

Development of an aircraft worst case flutter prediction with Mach variation using robust stability analysis

Modern aircraft are under a severe operating environment, in which uncertainties in mass, stiffness, and aerodynamic characteristics could play an important role in determining the safety of an airplane. Recently, several analysis methodologies have been proposed to find a new critical flight condition in the presence of the system uncertainties. In the present paper, a variation is assumed to exist in the aerodynamic characteristics. A robust aeroelastic analysis is established which accounts for aerodynamic variation due to a different level of compressibility and atmospheric density. Mathematically, the variations in Mach number and atmospheric density are treated as aerodynamic uncertainties. A robust flutter stability boundary is obtained by using the mu method. It is found that the worst case flutter speed, dynamic pressure, and atmospheric density results are all more conservative than the nominal flutter results. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo ChanHoon Chung received M.S degree in Mechanical Engineering from Korea University in 2004. Since 2005, he has been a Ph.D student at the School of Mechanical and Aerospace Engineering in Seoul National University. His research interests include robust aeroelasticity and aeroservoelasticity. SangJoon Shin received S.M. and Ph.D. degrees in Aeronautics and Astronautics from Massachusetts Institute of Technology in 1999 and 2001, respectively. During 1991–1996, he worked at the Helicopter Systems Department, Korean Agency for Defense Development. During 2001–2003, he worked at the Department of erospace Engineering, University of Michigan, Ann Arbor. Since 2003, he has been a professor at the School of Mechanical and Aerospace Engineering in Seoul National University. His research interests include aeroelasticty, rotorcraft dynamics, and smart structures. Taehyoun Kim earned a Ph.D. in Aeronautics and Astronautics from Massachusetts Institute of Technology in 1992. Since 1996 he has worked in Loads and Dynamics Group of Boeing Commercial Aircraft, Seattle, Washington, USA. Prior to joining the Boeing Company he worked in Computational Mechanics Laboratory at Georgia Institute of Technology. Since 2005, he has been teaching a short course, “Computational Methods in Aeroelasticity” at SDM Conference, Boeing Ed Wells, National Aerospace Laboratory in India, and NASA Langley. Dr. Kim’s specialties are aeroservoelasticity/structural dynamics, computational and experimental methods in aeroelasticity, system identification and model reduction of large-scaled dynamic systems, and composite structures.     

Efficient purification and morphology characterization of paclitaxel from cell cultures of Taxus chinensis

Paclitaxel was purified from cell cultures of Taxus chinensis by a combination of extraction, low‐pressure chromatography, precipitation and HPLC. A crude extract (purity 6.9%) was obtained by methanol extraction of plant cell cultures, followed by liquid–liquid extraction using dichloromethane. The extract was purified to greater than 32% with a 97% step yield by low‐pressure chromatography. After acetone/pentane precipitation, the resulting purity and step yield were 75.8% and 97.4%, respectively. High performance liquid chromatography steps, which were composed of an HPLC step with column‐packed ODS and an HPLC step with column‐packed silica, were applied to give over 99.5% purity with high yield. Amorphous paclitaxel with a fine particle size, which has a solubility advantage compared with the stable crystalline form, was obtained by dissolving in dichloromethane, followed by spray‐drying. Copyright © 2004 Society of Chemical Industry