• Korean Journal of Plant Tissue Culture
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• v.21 no.2
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• pp.85-90
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• 1994

Attempts were made to regenerate plants from petiole explane of Forest Pimpinella barchycarpa via repetitive somatic embryogenesis. Effective induction of somatic emb교ogenesis was achieved on both MS and modified $B_{5}\;(mB_{5})$ media containing BA + 2,4-D or BA + 2,4-D + NAA under light condition (16-h photoperiod/day) cultures. The explants exposed to the ligt produced numerous somatic embryos while those kept under the dark did not form any on the same medium. Somatic embryos at different developmental stages were observed to arise within a individual explants. Plantlets could be regenerated on $mB_{5}$ basal medium or $mB_{5}$ containing 0.1 mg/L NAA Secondary adventive embryos were formed on the surface of the somatic embryos. Therefore, repetitive somatic embryogenesis could be achieved by secondary embryogenesis. Although the treatment of 2,4-D or NAA alone was effective in callus formation and growth, but not in induction of somatic embryogenesis. Some explants, cultured on NAA-containing media in darkness, produced only adventive roots. The embryogenic potential was maintained for two years when subcultured to BA and 2,4-D containing media with 5 weeks inteval. Regenerated plantlets were maintained on $mB_{5}$ or MS basal media for 4 to 6 more weeks and transferred to soil of an artificial mixture for acclimation. Most plantlets (more than 97%) survived, and grew without any deformity.

• Tribology and Lubricants
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• v.11 no.5
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• pp.128-135
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• 1995

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales, ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer, and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of single-crystal silicon, natural diamond, magnetic media (magnetic tapes and disks) and magnetic heads have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurements of atomic-scale friction of a freshly-cleaved highly-oriented pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement has been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macro scales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than the macrofriction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load approaching to the macrofriction at contact stresses higher than the hardness of the softer material. Wear rate for single-crystal silicon is approximately constant for various loads and test durations. However, for magnetic disks with a multilayered thin-film structure, the wear of the diamond like carbon overcoat is catastrophic. Breakdown of thin films can be detected with AFM. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nono scratches. AFM has been modified to obtain load-displacement curves and for nanoindentation hardness measurements with depth of indentation as low as 1 mm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin fdms. Detection of material transfer on a nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thichness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolyers and chemically-bonded lubricant films with a mobile fraction are superior in wear resistance. Finally, AFM has also shown to be useful for nanofabrication/nanomachining. Friction and wear on micro-and nanoscales have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help def'me the regimes for ultra-low friction and near zero wear.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.6
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• pp.9-16
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• 2000

In order to achieve stiction-free polysilicon surfaces, we have suggested a new class of chemical coating precursors and confirmed their excellent characteristics. The strategy is to adopt dialkyldichlorosilanes (DDS, $R2SiCl_2$) instead of monoalkyltrichlorosilanes (MTS, $RSiCl_3$) such as octadecyltrichlorosilane (OTS) or 1H,1H2H,2H-perfluorodecyltrichlorosilane (FDTS). Dichlorodimethylsilane (DDMS, $(CH_3)2SiCl_2$) in this study is commercially available DDS with two short chains. DDMS in aprotic media spontaneously deposits on the hydrophilic polysilicon surface, which is completely changed to hydrophobic one. When polysilicon surface is exposed to DDMS solution at room temperature, anti-stiction property and hydrophobicity are clearly comparable to FDTS. DDMS is even superior to MTS in reliability and easy handling, which provides high yield. Since interactions among precursor molecules are reduced, conglomeration both in homogeneous solution and on surface can be effectively avoided. Even the cantilevers of 3 mm in length can be protected successfully from the stiction and the final quality of the modified surfaces is much less dependent on temperature. And no difference was found between the processes in ambient environment and in dry box. In addition, DDMS has advantages of remarkably reduced process time and low cost.

• Microbiology and Biotechnology Letters
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• v.46 no.1
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• pp.9-17
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• 2018

The aims of this work were to characterize and determine bioactivities of crude exopolysaccharide (EPS) extract from Bacillus tequilensis PS21 isolated from milk kefir from Kampaeng Petch, Thailand. B. tequilensis PS21 produced 112.1 mg dried EPS/l from initial 80 g/l lactose in modified TSB media at 52 h, with EPS product yield of 8.9 mg EPS/g lactose and specific product yield of 0.3 mg EPS/mg biomass. The FTIR result confirmed EPS to be a protein-bound polysaccharide and SEM analysis showed the morphology to be a grainy appearance with an uneven surface, covered with pores. HPLC analysis determined EPS as a heteropolysaccharide consisting of five sugar units with the following molar ratios; xylose (17.65), glucose (2.54), ribose (1.83), rhamnose (1.23), and galactose (1). Chemical components of this EPS were predominantly carbohydrate at 697.8 mg/g EPS (65%), protein 361.4 mg/g EPS (34%), and nucleic acid 12.5 mg/g EPS (1%). The EPS demonstrated antioxidant activities at 57.5% DPPH scavenging activity, $37.2{\mu}M\;Fe(II)/mg$ EPS and $34.9{\mu}M\;TEAC\;{\mu}M/mg$ EPS using DPPH, FRAP and ABTS assays, respectively. EPS also exhibited anti-tyrosinase activity at 34.9% inhibition. This work represents the first finding of EPS produced by Bacillus sp. from Thai milk kefir which shows potential applications in the production of antioxidant functional foods and whitening cosmetics. However, optimization of EPS production for industrial exploitation requires further study to ascertain the economic potential.

• Membrane and Water Treatment
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• v.11 no.1
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• pp.41-48
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• 2020

Lead is a highly toxic heavy metal that causes serious health problems. Nonetheless, it is increasingly being used for industrial applications and is often discharged into the environment without adequate purification. In this study, Pb(II) was removed by powdered waste sludge (PWS) based on the biosorption mechanism. Different PWSs were collected from a submerged moving media intermittent aeration reactor (SMMIAR) and modified Ludzack-Ettinger (MLE) processes. The contents of extracellular polymeric substances were similar, but the surface area of MLE-PWS (2.07 ㎡/g) was higher than that of SMMIAR-PWS (0.82 ㎡/g); this is expected to be the main parameter determining Pb(II) biosorption capacity. The Bacillaceae family was dominant in both PWSs and may serve as the major responsible bacterial group for Pb(II) biosorption. Pb(II) biosorption using PWS was evaluated for reaction time, salinity effect, and isotherm equilibrium. For all experiments, MLE-PWS showed higher removal efficiency. At a fixed initial Pb(II) concentration of 20 mg/L and a reaction time of 180 minutes, the biosorption capacities (q_e) for SMMIAR- and MLE-PWSs were 2.86 and 3.07 mg/g, respectively. Pb(II) biosorption using PWS was rapid; over 80% of the maximum biosorption capacity was achieved within 10 minutes. Interestingly, MLE-PWS showed enhanced Pb(II) biosorption with salinity values of up to 30 g NaCl/L. Linear regression of the Freundlich isotherm revealed high regression coefficients (R² > 0.968). The fundamental Pb(II) biosorption capacity, represented by the K_F value, was consistently higher for MLE-PWS than SMMIAR-PWS.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.36 no.3
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• pp.186-196
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• 2010

Introduction: The first aim of this study was to isolate the dental tissue-derived stem cells from the dental follicle (DF), dental pulp (DP), and root apical papilla (RAP) of the extracted wisdom teeth. Second was to evaluate their characterization with the expressions of transcription factors and cell surface markers. Finally, their ability of the in vitro multi-lineage differentiations into osteogenic and adipogenic cells were compared, respectively. Materials and Methods: Dental tissues, including dental follicle, dental pulp, and root apical papilla, were separated in the extracted wisdom teeth. These three dental tissues were cultured in Dulbecco’s modified Eagle’s medium (DMEM) with supplements, respectively. After passage 3, the homogeneous shaped dental tissue-derived cells were analyzed the expression of transcription factors (Oct-4, Nanog and Sox-2) and cell surface markers (CD44, CD90 and CD105) with reverse transcription polymerase chain reaction (RT-PCR) and fluorescence-activated cell sorting (FACS) analysis. In order to evaluate in vitro multi-lineage differentiations, the culture media were changed to the osteogenic and adipogenic induction mediums when the dental tissue-derived cells reached to passage 3. The characteristics of these three dental tissue-derived cells were compared with immunohistochemistry. Results: During primary culture, heterogenous and colony formatted dental tissue-derived cells were observed in the culture plates. After passage 2 or 3, homogenous spindle-like cells were observed in all culture plates. Transcription factors and mesenchymal stem cell markers were positively observed in all three types of dental tissue-derived cells. However, the quantity of expressed transcription factors was most large in RAP-derived cells. In all three types of dental tissue-derived cells, osteogenic and adipogenic differentiations were observed after treatment of specific induction media. In vitro adipogenic differentiation was similar among these three types of cells. In vitro osteogenic differentiation was most strongly and frequently observed in the RAP-derived cells, whereas rarely osteogenic differentiation was observed in the DP-derived cells. Conclusion: These findings suggest that three types of human dental tissue-derived cells from extracted wisdom teeth were multipotent mesenchymal stem cells, have the properties of multi-lineage differentiations. Especially, stem cells from root apical papilla (SCAP) have much advantage in osteogenic differentiation, whereas dental follicle cells (DFCs) have a characteristic of easy adipogenic differentiation.

• Journal of Broadcast Engineering
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• v.18 no.1
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• pp.21-30
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• 2013

It is a challenging problem to most of the image processing when the light source is unknown. The color of the light source must be estimated in order to compensate color changes. To estimate the color of the light source, additional assumption is need, so that we assumed color distribution according to the light source. If the pixels, which do not satisfy the assumption, are used, the estimation fails to provide an accurate result. The most popular color distribution assumption is Grey-World Assumption (GWA); it is the assumption that the color in each scene, the surface reflectance averages to gray or achromatic color over the entire images. In this paper, we analyze the characteristics of the camera response function, and the effect of the Grey-World Assumption on the pixel value and chromaticity, based on the inherent characteristics of the light source. Besides, we propose a novel method that detects important pixels for the color estimation of the light source. In our method, we firstly proposed a method that gives weights to pixels satisfying the assumption. Then, we proposed a pixel detection method, which we modified max-RGB method, to apply on the weighted pixels. Maximum weighted pixels in the column direction and row direction in one channel are detected. The performance of our method is verified through demonstrations in several real scenes. Proposed method better accurately estimate the color of the light than previous methods.

• Economic and Environmental Geology
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• v.53 no.2
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• pp.213-220
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• 2020

When CO₂ foam is injected into the saline aquifer, the relative permeability of CO₂ decreases and its viscosity increases, thereby reducing mobility in porous media and ultimately improving CO₂ storge with enhanced sweep efficiency. In general, surfactants were used to fabricate CO₂ foam. Recently, nanoparticles have been used to form stable foam than surfactant. This paper introduces CO₂ storage technology using nanoparticle stabilized CO₂ foam. If the surface of the hydrophilic nanoparticles is partially modified into a CO₂-philic portion, the particles have an affinity for CO₂ and water, thus forming a stable CO₂ foam even in deep saline aquifers under high temperature and high salinity conditions, thereby it can be stored in the pores of the rock. In terms of economics, injection method using nanopaticle-stabilized CO₂ foam is more expensive than the conventional CO₂ injection, but it is estimated that it will have price competitiveness because the injection efficiency is improved. From an environmental point of view, it is possible to inject chemical substances such as surfactants and nanomaterials into aquifers or reservoirs for specific purposes such as pollutant removal and oil production. However, some studies have shown that nanoparticles and surfactants are toxic to aquatic animals, so environmentally proven substances should be used. Therefore, further research and development will be needed to study the production and injection of nanoparticle-stabilized CO₂ foam that are environmentally safe and economically reasonable.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.287-293
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• 2009

This study investigated the influence of ionic strength on the adhesion and release of bacteria (Escherichia coli, Bacillus subtilis, and Staphylococcus aureus) in quartz and iron-coated sands using column experiments. Results show that the mass recovery remained constant (E. coli = 13.7${\pm}$0.5%, B. subtilis = 9.8${\pm}$1.3%, S. aureus = 13.0${\pm}$2.1%) in iron-coated sand while it decreased from 80.7 to 45.3% (S. aureus) in quartz sand with increasing ionic concentrations from 1 to 100 mM. As the ionic concentrations of leaching solution was lowered from 100 to 0.1 mM, average 39.1% of bacterial detachment was quantified from quartz sand, but no bacterial release was observed in iron-coated sand. The phenomenon observed in iron-coated sand can be attributed to the inner-sphere complexes between bacteria and coated sand, which have minimal effect from ionic strength. This study improves our knowledge regarding the bacterial interaction with surface-modified porous media.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.119-125
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• 2018

The particle based computational fluid dynamics (CFD) method, which follow Lagrangian approach for fluid dynamics, fluid particle behavior by tracking all particle calculation physical quantities of each particle. According to basic concept of particle based CFD method, it is difficult to satisfy continuum theory and measure influences from neighboring particle. Article number density and weight function were used to solve aforementioned issue. Difficulties continuum mean simulate non-continuum particles such as solid including granular and sand. In this regard, the particle based CFD method modified solid particle problems by replacing viscous and surface tension forces friction and drag forces. In this paper, particle interaction model for solid particle friction model implemented to simulate solid particle problems. The broken dam problem, which is common to verify particle based CFD method, used fluid or solid particles. The angle of repose was observed in the simulation results the solid particle not fluid particle.