• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2648-2656
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• 2011

A simple HPLC-DAD method was developed and validated to determine B group vitamin content (thiamine, riboflavin, nicotinamide, pantothenic acid, pyridoxine and folic acid) in supplemented food samples, i.e., infant formula, cereal, low-calorie food, a multi-vitamin pill and a vitamin drink. In this study, the most significant advantages were simultaneous determination of the six B group vitamins in various food matrices and a small number of sample treatment steps that required only an organic solvent, acetonitrile. Moreover, this method prevents reduction of column durability, because the mobile phase does not contain ion-pairing reagents. Analytes were separated on a Develosil RPAQUEOUS $C_{30}$ (4.6 mm ${\times}$ 250 mm, 5 ${\mu}M$ particle size) column with a gradient elution of acetonitrile and 20 mM phosphate buffer (pH 3.0) at a flow rate between 0.8 and 1.0 mL/min. Detection was performed at 275 nm, except for that of pantothenic acid (205 nm). The calibration curves for all six vitamins showed good linearity with correlation coefficients ($r^2$) higher than 0.995. The developed method was validated with respect to linearity, intra- and inter-day accuracy and precision, limit of quantification (LOQ), recovery and stability. The method showed good precision and accuracy, with intra- and inter-assay coefficients of variation less than 15% at all concentrations. The recovery was carried out according to the standard addition procedure, with yields ranging from 89.8 to 104.4%. This method was successfully applied to the determination of vitamin B groups in supplemented food products.

• Structural Engineering and Mechanics
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• v.30 no.6
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• pp.713-732
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• 2008

Serviceability and durability of the concrete members can be seriously affected by the corrosion of steel rebar. Carbonation front and or chloride ingress can destroy the passive film on rebar and may set the corrosion (oxidation process). Depending on the level of oxidation (expansive corrosion products/rust) damage to the cover concrete takes place in the form of expansion, cracking and spalling or delamination. This makes the concrete unable to develop forces through bond and also become unprotected against further degradation from corrosion; and thus marks the end of service life for corrosion-affected structures. This paper presents an analytical model that predicts the weight loss of steel rebar and the corresponding time from onset of corrosion for the known corrosion rate and thus can be used for the determination of time to cover cracking in corrosion affected RC member. This model uses fully the thick-walled cylinder approach. The gradual crack propagation in radial directions (from inside) is considered when the circumferential tensile stresses at the inner surface of intact concrete have reached the tensile strength of concrete. The analysis is done separately with and without considering the stiffness of reinforcing steel and rust combine along with the assumption of zero residual strength of cracked concrete. The model accounts for the time required for corrosion products to fill a porous zone before they start inducing expansive pressure on the concrete surrounding the steel rebar. The capability of the model to produce the experimental trends is demonstrated by comparing the model's predictions with the results of experimental data published in the literature. The effect of considering the corroded reinforcing steel bar stiffness is demonstrated. A sensitivity analysis has also been carried out to show the influence of the various parameters. It has been found that material properties and their inter-relations significantly influence weight loss of rebar. Time to cover cracking from onset of corrosion for the same weight loss is influenced by corrosion rate and state of oxidation of corrosion product formed. Time to cover cracking from onset of corrosion is useful in making certain decisions pertaining to inspection, repair, rehabilitation, replacement and demolition of RC member/structure in corrosive environment.

• Advances in concrete construction
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• v.9 no.1
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• pp.55-70
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• 2020

In this research article, acid resistance, sulphate resistance and sorptivity of self compacted concrete (SCC) prepared from C&D waste have been discussed. To improve the above properties of self compacted recycled aggregate concrete (SCRAC) along with mechanical and durability properties, different two stage mixing approaches (TSMA and TSMAsfc) were followed. In the proposed two stage mixing approach (TSMAsfc), silica fume, a proportional amount of cement and a proportional amount of water were mixed in premix stage which fills the pores and cracks of recycled aggregate concrete (RAC). The concrete specimen prepared using above mixing approaches were immersed in 1% concentration of sulphuric acid (H2SO4) and magnesium sulphate (MgSO4) solution for 28, 90 and 180 days for evaluating the acid resistance of SCRAC. Experimental results concluded that the proposed two stage mixing approach (TSMAsfc) is most suitable for acid resistance and sulphate resistance in terms of weight loss and strength loss due to the elimination of pores and cracks in the interfacial transition zone (ITZ). In modified two stage mixing approach, the pores and cracks of recycled concrete aggregate (RCA) were filled up and make ITZs of SCRAC stronger. Microstructure analysis was carried out to justify the reason of improvement of ITZs by electron probe micro analyser (EPMA) analysis. X-ray mapping was also done to know the presence of strength contributing elements presents in the concrete sample. It was established that SCRAC with modified mixing approach have shown improved results in terms of acid resistance, sulphate resistance, sorptivity and mechanical properties.

• Journal of Applied Reliability
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• v.15 no.4
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• pp.241-247
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• 2015

Purpose : The demand for higher fuel economy vehicles has helped develop fuel-efficient vehicles such as a CVVL called continuous variable valve lift. Existing CVVL has been applying DC type motor to control intake valve, but recently some car parts manufacturers have been developing a BLDC type CVVL motor for improvements of endurance performance. The purpose of this study is to find the potential failure mechanism of the CVVL BLDC moto in early stage of development based on the design properties and design the accelerated life test model. Methods : CVVL BLDC is consist of brushs, coil, magnetic, PCB, bearing and so on. Each component has a latent failure mechanism caused by temperature, humidity, vibration. By analysis result of the failure mechanism, thermal fatigue is the most important factor of a durability of CVVL BLDC motor. So, we designed a new accelerated life test model for guarantee of the CVVL BLDC motor. Results : A crack occurred on via hole in test using the conditions we designed, so we did change the design to avoid this failure. The via hole dimension is changed a little larger, as a result we achieve improvements in reliability of the CVVL BLDC motor. By applying various kinds and extreme level of stresses, we can find the operating limits of products. Conclusion : In thesis, We analyzed the failure mechanism of CVVL BLDC and designed an accelerated life test method to give a guarantee for reliability. Based on the test results, we could improve the reliability of developments by change of design.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.177-188
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• 2006

Conventional nonlinear finite element analysis requires complicated modeling and analytical technique. Furthermore, it is difficult to interpret the analytical results presented as the stress-strain relationship. In the present study, a design-oriented analytical method using the truss model was developed. A reinforced concrete member to be analyzed was idealized by longitudinal, transverse, and diagonal line elements. Basically, each element was modeled as a composite element of concrete and re-bars. Simplified cyclic models for the concrete and re-bar elements were developed. RC beams and walls with various reinforcement details were analyzed by the proposed method. The inelastic strength, energy dissipation capacity, deformability, and failure mode predicted by the proposed method were compared with those of existing experiments. The results showed that the proposed model accurately predicted the strength and energy dissipation capacities, and to predict deformability of the members, the compression-softening model used for the concrete strut element must be improved.

• Korean Journal of Social Welfare
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• v.58 no.4
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• pp.313-339
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• 2006

The purpose of this study is to analysis empirically the socio-structural causes of working poor. This study used raw data of of Korea National Statistical Office from 1982 to 2004, and put in operation time series multiple regression analysis to use socio-economic factors of macro-economy environment, labor market, distribution system. Contrary to assertion of growth-concentrated people, economic growth rate has had significantly positive effect on the change of working poor size. In the growth period there has been trickle down effect of economic growth, but in the post-Fordism period there has not been valid circular relation. Recent introduction of the U. S. type capitalism resulted in negative phenomenon like aggravation of income distribution, deterioration of employment quality, enlargement of working poor. And there rise a question on socio-economic durability due to de-compensation on intra-institution. It is necessary to grope transition to the high road social market model - that is stable and sustainable - correspond to Korea that is stable and sustainable.

• Journal of Hydrogen and New Energy
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• v.13 no.4
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• pp.259-269
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• 2002

A battery based on the lithium/elemental sulfur redox couple has the advantage of high theoretical specific capacity of 1,675 mAh/g-sulfur. However, Li/S battery has bad cyclic durability at room temperature due to sulfur active material loss resulting from lithium polysulfide dissolution. To improve the cycle life of Li/S battery, PEGDME (Poly(ethylene glycol) dimethyl ether) 500 containing 1M LiTFSI salt which has high viscosity was used as electrolyte to retard the polysulfide dissolution and nano-sized $Mg_{0.6}Ni_{0.4}O$ was added to sulfur cathode as additive to adsorb soluble polysulfide within sulfur cathode. From experimental results, the improvement of the capacity and cycle life of Li/S battery was observed( maximum discharge capacity : 1,185 mAh/g-sulfur, C50/C1 = 85 % ). Through the charge-discharge test, we knew that PEGDME 500 played a role of preventing incomplete charge-discharge $behavior^{1,2)$. And then, in sulfur dissolution analysis and rate capability test, we first confirmed that nano-sized $Mg_{0.6}Ni_{0.4}O$ had polysulfide adsorbing effect and catalytic effect of promoting the Li/S redox reaction. In addition, from BET surface area analysis, we also verified that it played the part of increasing the porosity of sulfur cathode.

• Journal of the Korean Society of Costume
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• v.53 no.2
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• pp.35-55
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• 2003

The purpose of the study is to get some pieces of prior information to eventually develop competitive swimming suit designs with Korean traditional images. The study has been accomplished in following steps. First, as theoretical research, the history of swimming suit design and the requirements in designing competitive swimming suits were studied. Second, as practical research, at first, the trend of the competitive swimming suit designs in the national swimming suit market was examined. And then. the questionnaire surveys of both professional and amateur swimmers about their design preferences with purchasing and fabric-related tendencies were conducted for understanding professionals' characters more exactly. This data were analyzed through cross-analysis and multi-response analysis and x 2 was used. The results of this study can be summarized as follows : First, athletes' preferential design tendency for the swimming suit designs were examined in the aspects of style, color, pattern, logo, and accessary. In style, female athletes preferred an athletic one-piece style and male ones preferred a brief style. In color. neutral, mostly black was preferred most and cold color group like dark blue and navy blue next, regardless of sex. In addition, they preferred similar color coordination. In pattern, though solid fabrics were mostly preferred in both sexes, especially Taeguk motive were considered the most appropriate pattern to show Korean image. Besides, logo was considered importantly, and swimming caps and goggles of accessaries were generally used. Second, athletes' swimming suit purchasing tendency was as a following. the number of swimming suits possessed was more than 4 pieces. the durable period was less than 3 months. and the most important point considered in purchasing was an easy fitting for men and a design with an easy fitting for women. And most of swimming athletes preferred foreign products than domestic ones, which was attributed to excellent quality, easy fitting, and good design. and so on. Third, in fabric-related tendency, food touch, easy fitting. and opaqueness were considered importantly. and durability to chlorine, elasticity, color fastness, easy draining, lightness, and so on were demanded forward.

• Journal of the Korean Society of Clothing and Textiles
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• v.36 no.8
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• pp.828-836
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• 2012

This study provided the data for the planning of knit apparel by analyzing structural effects of intarsia and jacquard knit on mechanical properties, subjective hand measurements, and preference. Intarsia and 7 types of color jacquard (floating jacquard, normal jacquard, bird's eye jacquard, tubular jacquard, ladder's back jacquard, blister jacquard, and transfer jacquard) were used. The samples (with a gauge of 14) were knitted using 100% wool 2/48's yarn by a Shima Seiki SIG computer knitting machine. Mechanical properties and hand values were measured by a KES-FB system. Subjective hand and favorable images were surveyed based on women in their 20s and 30s. The data were analyzed by a factor analysis, ANOVA and correlation analysis using SPSS 12.0. The subjective hand of intarsia and jacquard knits was categorized into 'thermofeeling', 'weight/flexibility', and 'durability'. The results of the favorable image survey for F/W outer knitwear showed that tubular jacquard was most favorable; however, the transfer jacquard was least favorable. Among the three factors that explain the subjective hand, thermofeeling had a strong influence on the favorable image of consumers. Bird's eye jacquard and tubular jacquard turned out to be most suitable for suits, intarsia and floating jacquard were suitable for cardigans and sweaters, ladder's back jacquard was suitable for hats or mufflers, and transfer jacquard was suitable for home fashion rather than garments.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.3
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• pp.299-304
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• 2014

The need of reusing sewage sludge is highly increasing as the amount of domestic sewage sludge is growing and sewage management strategies were reinforced. Accordingly, in this research, we studied the composting possibility of sludge in sewage treatment plant J, using dryer facility with indirect system by conducting component analysis of dried sludge and experiment on cultivating crops. It was observed from the component analysis, that the dried sludge is appropriate for both decomposed manure standard of Ministry of Environment and fertilizer standard of Rural Development Administration. Besides, in the experiment on cultivating lettuce, the experimental group(soil + dried sludge) was superior to the control group(soil + bed soil) in apparent condition of leaves tensity and damage by disease and pest. In case of cultivating tomato, the experimental group showed stronger durability of fruits dangling on stems compared to the control group after 9 weeks. Consequently, the excess sludge dried by indirect heating system in the sewage treatment plant J is appropriate for the standard of both Ministry of Environment and Rural Development Administration and show good result in experiment on cultivating crops therefore it can be reused for composting.