Gyeongnam National University of Science and Technology
Oh H.,Gyeongnam National University of Science and Technology
Korean Journal of Materials Research | Year: 2017
Isosteric heat of hydrogen adsorption is one of the most important parameters required to describe solid-state hydrogen storage systems. Typically, it is calculated from adsorption isotherms measured at 77K (liquid N2) and 87K (liquid Ar). This simple calculation, however, results in a high degree of uncertainty due to the small temperature range. Therefore, the original Sievert type setup is upgraded using a heating and cooling device to regulate the wide sample temperature. This upgraded setup allows a wide temperature range for isotherms (77K~ 117K) providing a minimized uncertainty (error) of measurement for adsorption enthalpy calculation and yielding reliable results. To this end, we measure the isosteric heats of hydrogen adsorption of two prototypical samples: Activated carbon and metal-organic frameworks (e.g. MIL-53), and compared the small temperature range (77~87K) to the wide one (77K~ 117K). © Materials Research Society of Korea.
Nam S.,Gyeongnam National University of Science and Technology |
Jang H.W.,University of California at Davis |
Shibamoto T.,University of California at Davis
Journal of Agricultural and Food Chemistry | Year: 2012
The antioxidant activity of essences of teas prepared from mulberry (Morus alba L.), Camellia sinensis L., and Cudrania tricuspidata (Carr.) Burea plant was examined using two antioxidant assays. Selected volatile chemicals identified in these plants were also tested for antioxidant activity. All extracts exhibited antioxidant activity with a clear dose response in the aldehyde/carboxylic acid and the malonaldehyde/gas chromatography (MA/GC) assays. Antioxidant activity of extracts at the level of 500 μg/mL ranged from 77.02 ± 0.51% (stems of Burea plant) to 52.57 ± 0.92% (fermented tea of Camellia and stems of Mulberry tea) in the aldehydes/carboxylic acid assay. Their antioxidant activity at the level of 160 μg/mL ranged from 76.17 ± 0.27% (roots of Burea plant) to 59.32 ± 0.27% (stems of Mulberry tea) in the MA/GC assay. Among the positively identified compounds (11 terpenes and terpenoids, 15 alkyl compounds, 26 nitrogen containing heterocyclic compounds, 9 oxygen containing heterocyclic compounds, 18 aromatic compounds, 7 lactones, 6 acids, and 4 miscellaneous compounds), eugenol, 2,5-dihydroxyl acetophenone, and isoeugenol exhibited antioxidant activity comparable to that of BHT in both assays. Vanillin and 2-acetylpyrrole showed potent antioxidant activity in the aldehydes/carboxylic acid assay but only moderate activity in the MA/GC assay. These results suggest that consumption of antioxidant-rich beverages prepared from these plants may be beneficial to human health. © 2012 American Chemical Society.
Yoon S.-L.,Gyeongnam National University of Science and Technology
Palpu Chongi Gisul/Journal of Korea Technical Association of the Pulp and Paper Industry | Year: 2017
The shape, physical and strength properties of flyers of various sizes collected in each region were evaluated to assess which types of paper were used according to the sizes of leaflets distributed with newspapers. The flyers were mostly printed double-side and in color, and some of the smaller flyers were single-sided. The distribution range of physical properties was narrow in the leaflet (B5, A4 and 2 jeolji) and with in the other leaflets (B4, A3, 8 jeolji and 4 jeolji) were wide. The distribution range of the tensile strength was wide in A4, B4, 8 jeolji, 4 jeolji, and narrow in B5, A3, and 2 jeolji, respectively. Smaller and larger leaflets were produced with the same paper, and other leaflets were produced with various papers. The quality of leaflets in each region did not show any significant difference due to the limited number of paper types used for each flyer size.
Jung H.R.,Gyeongnam National University of Science and Technology |
Kim K.H.,Gyeongnam National University of Science and Technology
Journal of Coastal Research | Year: 2017
The water depth of Namgang Dam Reservoir is shallow and the water level fluctuation is relatively small, because it is located in a midstream plain of the Nam River. These conditions of Namgang Dam led to the growth of Salix subfragilis communities. Initially, they were distributed over small areas but over time, they rapidly proliferated to cover large areas. They generate large amounts of leaf debris particularly in the dry season, so that water quality could be deteriorated. And, in the flood season, they raise water levels by obstructing the water flow in tributary streams, this consequently leads to flooding damages. In addition, Salix subfragilis periodically undergoes selfthinning and the withered trunks and branches turn into driftwood. These problems pose difficulties to dam management. By the way, these communities began to wither in areas lower than the highest water level, after a longterm period of inundation in 2012. To determine the reason for the withering phenomena in this study, the relationship between water level(turbidity) and the withering of Salix subfragilis in dam reservoir was investigated, and the withering characteristics of Salix subfragilis communities were analyzed through aerial photographys and field surveys. Results of this study show that disruption of photosynthesis due to high turbidity during the long-Term inundation is what was caused their withering. © Coastal Education and Research Foundation, Inc. 2017.
Jung S.,Samsung |
Choo Y.G.,Gyeongnam National University of Science and Technology |
Ji T.,Chonnam National University
IEEE Electron Device Letters | Year: 2012
A lift-off process for direct photolithographic top-contact organic thin-film transistors (TFTs) has been developed using a bilayer of polyvinyl alcohol and SU8. Top-contact pentacene TFTs fabricated by this method, with a fixed channel width of 300 μm but different channel lengths varying from 10 to 80 μm, exhibited mobility values in the range of 0.01-0.03 cm -2V̇s with the average of 0.021 ±0.007 cm -2 V̇s. It is expected that the adoption of SU8 with a high aspect ratio enables the easy fabrication of submicrometer channel devices, giving rise to improved carrier transport characteristics. © 2012 IEEE.
Kim I.-S.,Gyeongnam National University of Science and Technology |
Yang M.,Gyeongnam National University of Science and Technology |
Lee O.-H.,Kangwon National University |
Kang S.-N.,Gyeongnam National University of Science and Technology
LWT - Food Science and Technology | Year: 2011
Stevia rebaudiana (SR), a chrysanthemum herb, has been used as a vegetable-based sweetening additive in health drinks and in other foods. This study was conducted to investigate the antioxidant activity and the bioactive compounds found in water extracts taken from SR leaves and calli. Analysis of vitamins in the leaves showed that folic acid (52.18 mg/100 g) was a major component, followed by vitamin C. The total phenolic and flavonoid contents were found to be 130.76 μg catechin and 15.64 μg quercetin for leaves and 43.99 μg catechin and 1.57 μg quercetin for cellus at mg of water extracts, respectively. Pyrogallol was the major material among the phenolic compounds in both leaf and callus extracts. Furthermore, our results showed that the leaf extracts contained higher amounts of free radicals, hydroxyl radicals and superoxide anion radical scavenging activities than those of the callus extracts. © 2010 Elsevier Ltd.
Yoon S.-L.,Gyeongnam National University of Science and Technology
Palpu Chongi Gisul/Journal of Korea Technical Association of the Pulp and Paper Industry | Year: 2011
This research was performed to investigate the physical and mechanical properties of Chanhoji manufactured with the traditional method. This research would provide a basic information for its application in the manufacture of Korean-style house. A piece of Changhoji was manufactured to have a weight of 3.75 g. The weight was increased with the basic weight and no increase was not found on its density. The strength properties of Changhoji are superior to a copying paper, and the quality showed the first grade in Korean Standard (KS M 7301). The air resistance varied with the thickness from 2 to 19 seconds, but it showed better performance than a copying paper having 38 seconds. This research would be used for the practical use in understanding the ventilation and lightening properties of windows and doors in Korean-style house.
Lee J.H.,NAKDONG River Basin Environmental Office |
Cho K.M.,Gyeongnam National University of Science and Technology
Food Chemistry | Year: 2012
Changes in compositional components of black soybeans, including isoflavone, anthocyanin, protein, oil, and fatty acid, were investigated for the first time in soybeans maintained at room temperature for different storage periods. Isoflavone and anthocyanin profiles in hydrolysed extracts were characterised by column chromatography and HPLC-DAD-ESI/MS spectrometry analysis. These components decreased markedly during storage, whereas protein, oil, and fatty acid showed a slight decrease. The individual isoflavones and anthocyanins observed in black soybeans were as follows, in order of abundance: genistein > daidzein > glycitein; cyanidin-3-O-glucoside > dephinidin-3-O-glucoside > petunidin-3-O-glucoside. In particular, genistein (518.4 → 415.7 → 274.8 μg/g) and cyanidin-3-O-glucoside (6.53 → 2.92 → 1.49 mg/g) showed the greatest decrease for a storage time of two years. The scavenging activities of DPPH and ABTS radicals during storage also decreased in comparison with those of observed before storage. Our results can be used to improve our understanding of the relationship between storage times and the components from black soybeans. © 2011 Elsevier Ltd. All rights reserved.
Yoo C.G.,Iowa State University |
Lee C.W.,Gyeongnam National University of Science and Technology |
Kim T.H.,Iowa State University
Biomass and Bioenergy | Year: 2011
A two-stage process using aqueous ammonia and hot-water has been investigated to fractionate corn stover. To maximize hemicelluloses recovery and purity in the liquid hydrolyzate by optimizing the fractionation process, the experiments were carried out employing response surface methodology (RSM). A central composite design (CCD) was used to evaluate and confirm the effectiveness and interactions of factors. The optimal fractionation conditions were determined to be as follow: (1) First-stage reactor operated in batch mode using a 15% NH4OH solution (wNH3 = 15%) at 1:10 solid:liquid ratio, 60 °C, and 24 h; (2) second stage percolation reactor operated using hot-water at 20 cm3 min-1, 200 °C, and 10 min.The model predicted 51.5% xylan recovery yield and 82.4% xylan purity under these conditions. Experiments confirmed the maximum xylan recovery yield and purity were 54.7% and 83.9% respectively under the optimal reaction conditions.With the solids resulting from the two-stage treatment, 87%-98% glucan digestibilities were obtained with 15 FPU of GC 220 per g-glucan and 30 CBU of Novo 188 per g-glucan enzyme loadings. Xylan digestibility of xylooligomer hydrolysates reached 76% with 8000 GXU per g-xylan of Multifect-Xylanase loading. In the simultaneous saccharification and fermentation (SSF) test using treated solids and Saccharomyces cerevisiae (D5A), 86 % to 98% of ethanol yield was obtained on the basis of the glucan content in the treated solids. © 2011 Elsevier Ltd.
Kwak T.-S.,Gyeongnam National University of Science and Technology
Journal of the Korean Ceramic Society | Year: 2012
This study has been focused on properties of mirror surface grinding technology by ELID(Electrolytic In-process Dressing) for metal matrix ceramic composites using in high precision mirror for optics. The experimental studies have been carried out to get mirror surface by grinding for composites, Al-SiC, Al-graphite and Mg-SiC. Grinding process is carried out with varying abrasive mesh type, depth of cut and feed rate using diamond wheel. The machining result of the surface roughness and condition of ground surface, have been analyzed by use of surface roughness tester and SEM measurement system. ELID grinding technology could be applied successfully for the mirror-surface manufacturing processes in spite of ductility of metal matrix material. As the results of experiments, surface roughness of Al-SiC(45 wt%) has been the most superior in these experimental work-pieces as 0.021 μm Ra.