• Journal of the Korean Society for Precision Engineering
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• v.21 no.11
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• pp.186-194
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• 2004

In this research, microfabrication technique using localized electrochemical deposition (LECD) with ultra short pulses is presented. Electric field is localized near the tool tip end region by applying a few hundreds of nano second pulses. Pt-Ir tip is used as a counter electrode and copper is deposited on the copper substrate in 0.5 M CuSO$_4$ and 0.5 M H$_2$SO$_4$ electrolyte. The effectiveness of this technique is verified by comparison with LECD using DC voltage. The deposition characteristics such as size, shape, surface, and structural density according to applied voltage and pulse duration are investigated. The proper condition is selected from the results of the experiments. Micro columns less than 10 $\mu$m in diameter are fabricated using this technique. The real 3D micro structures such as micro pattern and micro spring can be fabricated by this method. It is suggested that presented method can be used as an easy and inexpensive method for fabrication of microstructure with complex shape.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.28 no.3
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• pp.193-199
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• 2022

Sustainable energy supplies without the recharging and replacement of charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. The TENG harvests electrical energy from wasted mechanical energy in the ambient environment. TENG devices are very likely to be used in next-generation renewable energy and energy harvesting. TENG devices have the advantage of being able to manufacture very simple power devices. In this experiment, various organic dielectrics and inorganic dielectrics were used to improve the open voltage of TENG, Among the various organic dielectrics, Teflon-based FEP, which has the highest electron affinity, showed the highest open voltage and Al electrode was fabricated on Teflon substrate by sputtering deposition process. And AAO (Anodized Aluminum Oxide) nanostructures were applied to maximize the specific surface area of the TENG device. The power generation of TENG within the acceleration level (0.25, 0.5, 1.0, 1.5 and 2 G) and the frequency range (5-120 Hz) of the domestic transport environment was up to 4 V.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.5
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• pp.227-231
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• 2005

We have developed a microsystem with a capillary electrophoresis (CE) and an electrochemical detector (ECD). The microfabricated CE-ECD systems are adequate for a disposable type and the characteristics are optimized for an application to the electrochemical detection. The system was realized with polydimethylsiloxane (PDMS)-glass chip and indium tin oxide electrode. The injection and separation channels (80 um wide$\ast$40 um deep) were produced by moulding a PDMS against a microfabricated master with relatively simple and inexpensive methods. A CE-ECD systems were fabricated on the same substrate with the same fabrication procedure. The surface of PDMS layer and ITO-coated glass layer was treated with UV-Ozone to improve bonding strength and to enhance the effect of electroosmotic flow. For comparing the performance of the ITO electrodes with the gold electrodes, gold electrode microchip was fabricated with the same dimension. The running buffer was prepared by 10 mM 2-(N-morpholino)ethanesulfonic acid (MES) titrated to PH 6.5 using 0.1 N NaOH. We measured olectropherograms for the testing analytes consisted of catechol and dopamine with the different concentrations of 1 mM and 0.1 mM, respectively. The measured current peaks of dopamine and catechol are proportional to their concentrations. For comparing the performance of the ITO electrodes with the gold electrodes, electropherograms was measured for CE-ECD device with gold electrodes under the same conditions. Except for the base current level, the performances including sensitivity, stability, and resolution of CE-ECD microchip with ITO electrode are almost the same compared with gold electrode CE-ECD device. The disposable CE/ECD system showed similar results with the previously reported expensive system in the limit of detection and peak skew. When we are using disposable microchips, it is possible to avoid polishing electrode and reconditioning.

• KSBB Journal
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• v.17 no.4
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• pp.333-338
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• 2002

This study was targeted to isolate and characterize a bacterium producing lactic acid in a large amount. Lactic acid bacteria of about fifty strains were isolated from kimchi, a Korean traditional fermented vegetable food. Strain KH-1 of them was most effective in the lactic acid production and showed 99% homology with Lactobacillus casei from analysis of 16S rRNA sequencing. The conversion ratio of lactic acid from glucose by 1. casei KH-1 was 98% in anaerobic condition, and the lactic acid was composed as racemic mixture of D(-)-and L(+)-lactic acid, 7% and 93%, respectively. This result indicated that L. casei KH-1 was a homofermentative bacterium mainly producing L(+)-lactic acid. The strain KH-1 used glucose as a preferential substrate but not utilized lactose. In investigation of more inexpensive nitrogen source for cultivation of strain KH-1 using industrial MRS medium, when yeast extract and corn steep liquor were used at the ratio of 1 to 1, the molar yield of lactic acid produced per mole of glucose(Yp/s) was 1.09.

• Current Photovoltaic Research
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• v.1 no.1
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• pp.17-26
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• 2013

In contrast to conventional crystalline cells, back-contact solar cells feature high efficiencies, simpler module assembly, and better aesthetics. The highest commercialized cell and module efficiency was recorded by n-type back-contact solar cells. However, the mainstream PV industry uses a p-type substrate instead of n-type due to the high costs and complexity of the manufacturing processes in the case of the latter. P-type back-contact solar cells such as metal wrap-through and emitter wrap-through, which are inexpensive and compatible with the current PV industry, have consequently been developed. In this paper the characteristics of EWT (emitter wrap-through) solar cells and their status and prospects for development are discussed.

• Korean Journal of Materials Research
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• v.19 no.4
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• pp.224-227
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• 2009

Nanofabrication is an essential process throughout industry. Technologies that produce general nanofabrication, such as e-beam lithography, dip-pen lithography, DUV lithography, immersion lithography, and laser interference lithography, have drawbacks including complicated processes, low throughput, and high costs, whereas nano-transfer printing (nTP) is inexpensive, simple, and can produce patterns on non-plane substrates and multilayer structures. In general nTP, the coherency of gold-deposited stamps is strengthened by using SAM treatment on substrates, so the gold patterns are transferred from stamps to substrates. However, it is hard to apply to transfer other metallic materials, and the existing nTP process requires a complicated surface treatment. Therefore, it is necessary to simplify the nTP technology to obtain an easy and simple method for fabricating metal patterns. In this paper, asnTP process with poly vinyl alcohol (PVA) mold was proposed without any chemical treatment. At first, a PVA mold was duplicated from the master mold. Then, a Mo layer, with a thickness of 20 nm, was deposited on the PVA mold. The Mo deposited PVA mold was put on the Si wafer substrate, and nTP process progressed. After the nTP process, the PVA mold was removed using DI water, and transferred Mo nano patterns were characterized by a Scanning electron micrograph (SEM) and Energy Dispersive spectroscopy (EDS).

• Mycobiology
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• v.43 no.3
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• pp.184-194
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• 2015

A compressive description of tropical milky white mushroom (Calocybe indica P&C var. APK2) is provided in this review. This mushroom variety was first identified in the eastern Indian state of West Bengal and can be cultivated on a wide variety of substrates, at a high temperature range ($30{\sim}38^{\circ}C$). However, no commercial cultivation was made until 1998. Krishnamoorthy 1997 rediscovered the fungus from Tamil Nadu, India and standardized the commercial production techniques for the first time in the world. This edible mushroom has a long shelf life (5~7 days) compared to other commercially available counterparts. A comprehensive and critical review on physiological and nutritional requirements viz., pH, temperature, carbon to nitrogen ratio, best carbon source, best nitrogen source, growth period, growth promoters for mycelia biomass production; substrate preparation; spawn inoculation; different supplementation and casing requirements to increase the yield of mushrooms has been outlined. Innovative and inexpensive methods developed to commercially cultivate milky white mushrooms on different lignocellulosic biomass is also described in this review. The composition profiles of milky white mushroom, its mineral contents and non-enzymatic antioxidants are provided in comparison with button mushroom (Agaricus bisporus) and oyster mushroom (Pleurotus ostreatus). Antioxidant assay results using methanol extract of milky white mushroom has been provided along with the information about the compounds that are responsible for flavor profile both in fresh and dry mushrooms. Milky white mushroom extracts are known to have anti-hyperglycemic effect and anti-lipid peroxidation effect. The advantage of growing at elevated temperature creates newer avenues to explore milky white mushroom cultivation economically around the world, especially, in humid tropical and sub-tropical zones. Because of its incomparable productivity and shelf life to any other cultivated mushrooms in the world, milky white mushroom could play an important role in satisfying the growing market demands for edible mushrooms in the near future.

• Journal of Applied Biological Chemistry
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• v.64 no.3
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• pp.309-316
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• 2021

Kaempferol 3-O-galactoside (Trifolin), a member of the flavonol group, has been reported to have anticancer effects against promyelocytic leukemia, histocytic lymphoma, skin melanoma and lung cancer. Trifolin has been extracted and used from several plants, but the extraction process is complicated and the final yield is low. Biotransformation is an alternative tool to produce high value-added chemicals from inexpensive compounds. To synthesis trifolin from naringenin, three genes (PeFLS and OsUGE-PhUGT) were introduced into Escherichia coli, respectively. In order to synthesis trifolin from naringenin, a co-culture fermentation system was established by optimizing the cell concentration, biotransformation temperature and medium, isopropyl-β-D-thiogalactoside (IPTG) concentration, substrate supply concentration, and recombinant protein induction time. The established optimal conditions for trifolin production were a 3:1 ratio of BL-UGTE to BL-FLS, induction of recombinant protein at 25 ℃ for 4 h after addition of 2.0 mM IPTG, biotransformation at 30 ℃, and supply of 300 μM naringenin. Through the optimized co-culture fermentation system, trifolin was biosynthesized up to 67.3 mg/L.

• Journal of Applied Biological Chemistry
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• v.62 no.1
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• pp.1-6
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• 2019

The flavonoid, isokaempferide, has various biological activities such as hepatoprotective, antimicrobial and antiproliferative effect and is extracted from Amburana cearensis and Cirsium rivulare (Jacq.). Biotransformation is an alternative tool for the synthesis of value-added flavonoids with inexpensive substrates. Here, to synthesize isokaempferide from naringenin, two genes, PFLS and Rice O-mthyltransferae-9 were introduced in Escherichia coli. Although isokaempferide was successfully synthesized, the amount of biosynthesis was no high. In order to increase the yields of isokaempferide, S-adenosylmethionine (SAM) used as a methyl donor was increased by deleting MetJ, which is a transcriptional regulator related to SAM biosynthetic pathway. Next we optimized the cell concentration and substrate feed concentration with the engineered E. coli strain. Through these strategies, the biosynthesis of isokaempferide was increased up to 87 mg/L.

• Applied Chemistry
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• v.15 no.1
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• pp.17-20
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• 2011

A disposable light exposure detector kit has been developed by UV curing of a hydrogel material. The devised light exposure detector kit consisted of light sensitive structures, bottom plate, character sheet and sticky back plate. A light exposure detector kit has a serial light sensitive structures that contain various light sensitive dyes such as rhodamine and fluorescein. The light sensitive structure composed of UV curable hydrogel polymer material as a supporing material and photosensitive dye in a certain concentration. The fabrication procedure of the ligh exposure detector kit is very simple and fast due to UV curing procedure of a photopolymerizable hydrogel material such as poly(ethylene glycol) methyl ether acrylate (PEGMEA) and poly(ethylene glycol) diacrylate (PEGDA) with a photosensitive dye. By the proposed fabrication method, various size and shape of a light exposure detector kit could be fabricated using a flexible elastomer mold. Due to a fast and inexpensive fabrication method, the light exposure detector kit could be use a single use for various industrial applications. According to light irradation, the light sensitive structure on a light exposure detector kit could be lose its color by decomposition of a photosensitive dye chemical in the structure. Thus the amount of the exposed light on a substrate could easily be recognised by changing color or transparency of the structure.