• Bulletin of the Korean Chemical Society
• /
• v.32 no.2
• /
• pp.613-619
• /
• 2011

Colloidal silver nanoparticles (AgNPs) have been commercialized as the typically stabilized form via the addition of a variety of surfactants or polymers. Herein, to examine the effects of stabilizing AgNPs in suspension, we modified the surface of bare AgNPs with four type of surfactants (NaDDBS, SDS, TW80, CTAB) and polymers (PVP, PAA, PAH, CMC). The modified AgNPs was applied to compare suspension stability and nanotoxicity test using Escherichia coli (E. coli) as a model organism. Modification of AgNPs surface using chemical stabilizer may be not related with molecular weight, but chemical structure such as ionic state and functional group of stabilizer. In this study, it is noteworthy that AgNPs modified with a cationic stabilizer (CTAB, PAH) were importantly toxic to E. coli, rather than anionic stabilizers (NaDDBS, SDS). Comparing similar anionic stabilizer, i.e., NaDDBS and SDS, the result showed that lipophilicity of chemical structure can affect on E. coli, because NaDDBS, which contains a lipophilic benzene ring, accelerated the cytotoxicity of AgNPs. Interestingly, none of the stabilizers tested, including biocompatible nonionic stabilizers (i.e., TW80 and cellulose) caused a reduction in AgNP toxicity. This showed that toxicity of AgNPs cannot be reduced using stabilizers.

• Computational Structural Engineering
• /
• v.7 no.1
• /
• pp.109-116
• /
• 1994

In this paper, various reliability analysis methods for calculating a probability of failure are investigated for their accuracy and efficiency. Crude Monte Carlo method is used as a basis for the comparison of various numerical results. For the sampling methods, Importance Sampling method and Directional Simulation method are considered for overcoming a drawback of Crude Monte Carlo method. For the approximate methods, conventional Rackwitz-Fiessler method. 3-parameter Chen-Lind method, and Rosenblatt transformation method are compared on the basis of First order reliability method. As a Second-order reliability method, Curvature-Fitting paraboloid method, Point-fitting paraboloid method, and Log-likelihood function method are explored in order to verify the accuracy of the reliability calculation results. These methods mentioned above would have some difficulty unless the limit state equation is expressed explicitly in terms of random design variables. Thus, there is a need to develop some general reliability methods for the case where an implicit limit state equation is given. For this purpose, Response surface method is used where the limit state equation is approximated by regression analysis of the response surface outcomes resulted from the structural analysis. From the application of these various reliability methods to three examples, it is found that Directional Simulation method and Response Surface method are very efficient and recommendable for the general reliability analysis problem cases.

• Journal of Korea Soil Environment Society
• /
• v.2 no.3
• /
• pp.59-67
• /
• 1997

To investigate the effects of organic matter and soil depth on soil water flow in a multi-layered soil, the saturated hydraulic conductivities(Ksat) were measured from the single- and multi-layered soil columns, that the soils were mixed with the oven-dried cow manure compost(CMC) at 4 different ratios such as 0, 2, 4, and 6% on a weight basis. The measured hydraulic conductivities(Ksat) were compared with theoretical hydraulic conductivity (Keff calculated by Jury's equation of effective hydraulic conductivity. In the single layered soil column saturated hydraulic conductivities(Ksat) were significantly decreased with increasing the application rate of compost. In the multi-layered the soil columns Ksat was also decreased with increasing rate of compost and soil depth. Calculated Keff showed the similar results of Ksat as obtained from the measured Ksat, whereas steadily increased with increasing soil depth. Therefore, modification of Jury's equation should be required to adapt theoretical Keff for Held application.

• BMB Reports
• /
• v.31 no.1
• /
• pp.53-57
• /
• 1998

The CMCax gene from Acetobacter xylinum ATCC 23769 was cloned and expressed in E. coli. With this gene, three gene products - mature CMCax, CMCax containing signal peptide(pre-CMCax), and a glutathione-S-transferase(GST)-CMCax fusion enzyme - were expressed. CMCax and pre-CMCax are aggregated to multimeric forms which showed high CMC hydrolysis activity, whereas GST-CMCax was less aggregated and showed lower activity, indicating that oligomerization of CMCax controbutes to the cellulose hydrolysis activity to achieve greater efficiency. The enzyme was identified to be an $\beta$-1,4-endoglucanase, which catalyzes the cleavage of internal $\beta$-1,4-glycosidic bonds of cellulose. The reaction products, cellobiose and cellotriose, from cellopentaose as a substrate, were identified by HPLC. Substrate specificity of cellotetraose by this enzyme was poor, and the reaction products consisted of glucose, cellobiose, and cellotriose in a very low yield. Theses results suggested that cellopentaose might be the oligosaccharide substrate consisting of the lowest number of glucose. The optimum pH of CMCax and pre CMCax was about 4.5, whereas that of GST-CMCas was rather broad at pH 4.5-8. The physiological significance of cellulose-hydrolyzing enzyme, CMCax, having such low $\beta$-1,4-endoglucanase activity and low optimum pH in cellulose-producing A. xylinum is not clearly known yet, but it seems to be closely related to the production of cellulose.

• Nutritional Sciences
• /
• v.9 no.3
• /
• pp.159-166
• /
• 2006

This study was performed to investigate antioxidative and anti-aging action of extracts from Sancho (Zanthoxylum schinifolium) leaves. Two extracts were obtained by 80% methanol extraction followed by subsequent fractionation with methylene chloride (MC) and n-butanol (B) and fed at one or three levels to rats on normal level (5%) of fat (control) and high fat(20%) in diets. Male Sprague-Dawley rats weighing about 100 g were divided into ten groups such as control diet group(C), control diet+0.50%B group (CB), control diet+0.50%MC group (CMC), high-fat diet group (HF), high-fat diet+0.25%B group (HBL), high-fat diet+0.50%B group (HBM), high-fat diet+0.75%B group (HBH), high-fat diet+0.25%MC group (HMCL), high-fat diet+0.50%MC group (HMCM) and high-fat diet+ 0.75%MC group (HMCH) and fed each diet for four weeks. The effects of the extracts on antioxidant enzyme activities and indices of lipid peroxidation and aging were seen only in high fat diet groups. Hepatic superoxide dismutase and aryleaterase activities were not changed by Sancho extracts. But glutathione peroxidase, catalase and paraxonase activities were significantly restored by both MC and B at the level of 0.75% lipid peroxide which was increased by high fat diet was significantly reduced by B and MC at the level of 0.25% and over. Lipofuscin fluorescence and cabonyl value were increased by high fat diet were reduced by B and MC at the level of 0.5% and over. It is concluded that the Sancho extracts can be utilized as functional ingredients of health foods for reducing oxidative stress.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.37 no.11
• /
• pp.1465-1471
• /
• 2008

This study was carried out to make water-soluble tocopherol emulsion which can be applicable directly in water. The molecular weight of tocopherol was 340 to 360 and tocopherol emulsion model was decided as O/O/W/W type. In correlation between stability of emulsion and surface tension, the stability in surface tension of emulsion was from 40 to 46 dyne/cm. In the case of lower than 40 dyne/cm of surface tension, the stability of the emulsion was lower. Lipophilic surfactants, especially for a polyglycerine polyricinoleate in 20%, 30% and 40% tocopherol emulsion, was the most effective in emulsion stability. A higher stability of the emulsion among hydrophilic surfactants in the tocopherol emulsion was obtained in the following order; polyglycerine monostearate> polyglycerine monooleate> polyoxyethylene (20) sorbitan monooleate$\geq$ polyoxyethylene (20) sorbitan monolaurate.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.5
• /
• pp.521-528
• /
• 2009

One of reliability measurements of vehicle is estimated by driving mileage but the reliability of component, such as an hydraulic clutch system, is defined from the number of successful operational cycle. Relationship between these reliability measurement variables(mileage and cycle) should be examined first of all in the reliability estimation of components. Relationship between mileage and cycles is commonly known as linear function. However, the gradient depends on the operational environmental condition. Therefore, estimation of mission profile variable should be done with correlation analysis at the same time. In this paper, we derive mission profile variable of an hydraulic clutch system by field vehicle test and suggest the determination process of durability test parameters of CMC(Clutch Master Cylinder) with mission profile variable.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.6
• /
• pp.488-493
• /
• 2014

This paper presents a carrier-based pulse-width modulation(PWM) method for reducing the common-mode voltage of a three-level four-leg converter. The idea of the proposed PWM method is intuitive and easy to be implemented in digital signal processor-based converter control systems. On the basis of the analysis of space-vector PWM(SVPWM) and sinusoidal PWM(SPWM) switching patterns, the fourth leg pole voltage of the three-phase converter called "f leg pole voltage" is manipulated to reduce the common-mode voltage. To synthesize f leg pole voltage for the suppression of the common-mode voltage, positive and negative pole voltage references of f leg are calculated. An offset voltage is also deduced to prevent the distortion of a, b, and c phase voltages. The feasibility of the proposed PWM method is verified by simulation and experimental results. The common-mode voltage of the proposed PWM method in peak-to-peak value is 33% in comparison with that of the conventional SVPWM method. The transition number of the common-mode voltage is also reduced to 25%.

• Journal of Pharmaceutical Investigation
• /
• v.22 no.1
• /
• pp.41-48
• /
• 1992

Six common tablet disintegrants (corn starch, Avicel PH102, calcium carboxymethylcellulose, Primojel, Kollidon CL and Ac-Di-Sol) were used at the concentration of 0, 2, 4 and 6% (w/w) in salicylamide tablets made with wet granulation method. Certain physical parameters of the disintegrants (moisture sorption, hydration capacity and bulk density) were determined to evaluate their relative efficiency. The disintegration time and dissolution rate of the tablets were correlated well with the ranks of initial rate of moisture sorption for each disintegrant as follows; Ac-Di-Sol, Kollidon CL, primojel, calcium CMC, corn starch and Avicel PH102. The initial rate of moisture sorption was important for the disintegration capacity as well as hydration capacity. The effect of storage at different temperatures and relative humidity upon the tablets containing various disintegrants was evaluated in terms of tablet hardness and disintegration time. Storage at high temperature reduced the hardness substantially and retarded the disintegration of the all tablets studied. Especially, the hardness of tablets containing Kollidon CL was significantly reduced. Although the tablet hardness was decreased and the disintegration time was increased under a moderate humid condition, both of them were decreased under the severely high humid condition of 80 or 90% RH, which was due to the breakrupture of tablet matrix bonds by the excessive uptake of moisture. Therefore, the stability caused by moisture sorption should be considered, when disintegrants having high moisture sorption such as Kollidon CL, Ac-Di-Sol and Primojel were employed in the tablets containing water-labile or hygroscopic drugs.

• Journal of the Korean Geosynthetics Society
• /
• v.15 no.4
• /
• pp.53-62
• /
• 2016

This paper presents the results of a reduced-scale physical model investigation into the effect of drilling fluid with different mix designs for use in offshore bore hole collapse prevention. Compare the bentonite and Attapulgite use. Reduced-scale model tests were then carried out considering field procedures for cases with decomposed granitic soil with fines and a sand with various drilling fluids with different mix designs. The results were indicated that the addition of polymer to the bentonite based drilling fluid decreases the amount of injected drilling fluid and increases the final depth of excavation. Also revealed that the effect of polymer on the performance of drilling fluid is more pronounced in the decomposed granite soil with fines than sand. Practical implications of the findings from this study are discussed in detail.