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Preparation of Mesoporous SiCBN Ceramic Templated by Mesoporous Carbon
Nghiem, Quoc Dat,Ryoo, Hyang-Im,Kim, Dong-Pyo The Korean Ceramic Society 2007 한국세라믹학회지 Vol.44 No.7
Well-ordered mesoporous SiCBN ceramics have been successfully synthesized by infiltrating a polymeric precursor, which was prepared from borazine and 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane via a hydroboration reaction, into a mesoporous carbon (CMK-3) as a hard template. This was followed by pyrolysis at $1400^{\circ}C$ under nitrogen gas and subsequent oxidative removal of the carbon template without chemical etching. The prepared mesoporous SiCBN ceramic was characterized by a small-angle XRD, TEM, and BET surface area. The resulting mesoporous SiCBN ceramic revealed a BET surface area of $275 m^2g^{-1}$ and a pore volume of $0.8 cm^3 g$ with no crystallization.
Synthesis of Inorganic–Organic Diblock Copolymers as a Precursor of Ordered Mesoporous SiCN Ceramic
Nghiem, Q. D.,Kim, D. J.,Kim, D.-P. WILEY-VCH Verlag 2007 Advanced Materials Vol.19 No.17
<B>Graphic Abstract</B> <P>A novel poly(vinyl)silazane-block-polystyrene diblock copolymer is successfully synthesized by living free-radical polymerization via a reversible addition fragmentation chain transfer (RAFT) route (see figure). The obtained diblock copolymer, having an inorganic volume fraction of 0.69, leads to phase-separation at the nanoscale to form an ordered nanostructure, which is converted to well-ordered mesoporous SiCN ceramic after heating at 800 °C and maintained up to 1400 °C. <img src='wiley_img/09359648-2007-19-17-ADMA200602348-content.gif' alt='wiley_img/09359648-2007-19-17-ADMA200602348-content'> </P>
Nghiem, N. P.,Montanti, J.,Kim, T. H. Springer Science + Business Media 2016 Applied biochemistry and biotechnology Vol.179 No.2
<P>Dried distillers grains with solubles (DDGS), a co-product of corn ethanol production in the dry-grind process, was pretreated by soaking in aqueous ammonia (SAA) using a 15 % w/w NH4OH solution at a solid/liquid ratio of 1:10. The effect of pretreatment on subsequent enzymatic hydrolysis was studied at two temperatures (40 and 60 A degrees C) and four reaction times (6, 12, 24, and 48 h). Highest glucose yield of 91 % theoretical was obtained for the DDGS pretreated at 60 A degrees C and 24 h. The solubilized hemicellulose in the liquid fraction was further hydrolyzed with dilute H2SO4 to generate fermentable monomeric sugars. The conditions of acid hydrolysis included 1 and 4 wt% acid, 60 and 120 A degrees C, and 0.5 and 1 h. Highest yields of xylose and arabinose were obtained at 4 wt% acid, 120 A degrees C, and 1 h. The fermentability of the hydrolysate obtained by enzymatic hydrolysis of the SAA-pretreated DDGS was demonstrated in ethanol fermentation by Saccharomyces cerevisiae. The fermentability of the hydrolysate obtained by consecutive enzymatic and dilute acid hydrolysis was demonstrated using a succinic acid-producing microorganism, strain Escherichia coli AFP184. Under the fermentation conditions, complete utilization of glucose and arabinose was observed, whereas only 47 % of xylose was used. The succinic acid yield was 0.60 g/g total sugar consumed.</P>
Determinants of Technical Efficiency of Microenterprises in Vietnam
Nghiem Tan LE,Hau Long LE,Truc Viet Thanh TRAN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.6
The aim of this study is to examine the determinants of technical efficiency (TE) of microenterprises (MEs) operating in the coconut handicraft industry in the Mekong Delta of Vietnam. In the first stage of analysis, output-oriented Data Envelopment Analysis (DEA) method is employed to estimate the technical efficiency of the 120 microenterprises operating in the coconut handicraft industry in the Mekong Delta, specifically in Ben Tre province over the year 2019 by using pre-determined three input and one output variables. The estimation results reveal that on average, variable returns to scale technical efficiency (VRS TE), constant returns to scale technical efficiency (CRS TE) and scale efficiency (SE) are 68.4%, 58.0%, and 87.3%, respectively. Tobit regression is applied in the second stage to examine the influences of the determinant factors on VRS TE. The empirical findings of the study imply that firm size, membership in economic association, application of science and technology, and cost-to-revenue ratio positively affect the technical efficiency of the microenterprises operating in the coconut handicraft industry in the Mekong Delta of Vietnam. Considering the results, several governance recommendations are given for business owners to improve firm technical efficiency in order to enhance the brand name of coconut handicrafts.
Nghiem, Quoc Dat,Pham, Anh Tuan,Kim, Dong Pyo Trans Tech Publications, Ltd. 2006 Materials science forum Vol.510 No.-
<P>Microelectromechanical systems (MEMS) including microchemical devices have been widely concerned, in particular, when made of an extremely stable ceramic material for their use at harsh conditions. SiCBN preceramic polymer was derived from borazine (B3N3H6) modified allylhydridopolycarbosilane (AHPCS) via hydroboration of allyl groups with B-H groups at 0oC for 24 h by following the standard Schenk technique. The extent of polymer-to-ceramic conversion with an ultimate ceramic yield of 92 wt% was investigated by simultaneous TGA, 1H, 13C-NMR, IR, and XRD measurements. The polymer-derived SiCBN ceramic remained as an amorphous solid up to 1400oC. The ceramic product obtained after pyrolysis at 1000-1400oC exhibited excellent oxidation resistance in air. In addition, ceramic microstructures were fabricated by employing soft lithographic technique.</P>