• Journal of Drive and Control
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• v.20 no.4
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• pp.64-70
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• 2023

Garlic is classified as one of the three essential seasoning vegetables in Korea. In 2023, it was reported that the area under garlic cultivation was 24,700 ha, and the production stood at 318,220 tons. Garlic harvesting mechanization currently stands at 43.8%, and garlic is still collected manually after digging out using diggers, so the process is labor intensive. To reduce garlic production costs and enhance competitiveness, it is necessary to develop a high-performance gathering type harvester in place of the digging type harvester. Therefore, in this study, a gathering-type garlic harvester that can dig and collect simultaneously was designed and manufactured, and the harvest performance by factor was analyzed through a harvest performance test. As a result of the performance test, it was analyzed to perform optimally at a driving speed of 0.11m/s and a transfer speed of 85rpm. Work performance was calculated using the results obtained from the factor performance test.

• Journal of Surface Science and Engineering
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• v.56 no.6
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• pp.437-442
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• 2023

This research aims to enhance the efficiency of Pt/C catalysts due to the limited availability and high cost of platinum in contemporary fuel cell catalysts. Nano-sized platinum particles were distributed onto a carbon-based support via the polyol process, utilizing the metal precursor H₂PtCl₆·6H₂O. Key parameters such as pH, temperature, and RPM were carefully regulated. The findings revealed variations in the particle size, distribution, and dispersion of nano-sized Pt particles, influenced by temperature and pH. Following sodium hydroxide treatment, heat treatment procedures were systematically executed at diverse temperatures, specifically 120, 140, and 160 ℃. Notably, the thermal treatment at 140 ℃ facilitated the production of Pt/C catalysts characterized by the smallest platinum particle size, measuring at 1.49 nm. Comparative evaluations between the commercially available Pt/C catalysts and those synthesized in this study were meticulously conducted through cyclic voltammetry, X-ray diffraction (XRD), and field-emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FE-SEM EDS) methodologies. The catalyst synthesized at 160 ℃ demonstrated superior electrochemical performance; however, it is imperative to underscore the necessity for further optimization studies to refine its efficacy.

• Journal of Technologic Dentistry
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• v.45 no.4
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• pp.87-94
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• 2023

Purpose: This study aimed to observed changes in the shape of dental barrels based on application time. Machinability measures the angle of alloy specimens. Polishing performance measures the surface roughness of alloy specimens. Methods: The dental barrel polishing equipment used in this study was a Snow Barrel (DK Mungyo). Three types of cobalt-chromium alloys for partial dentures were used as specimens (BC CAST R [BP]; Bukwang, Vera PDI [VP]; Aalbadent, and GM 800+ [GP]; Dentaurum). Specimens were prepared in the form of plates (10 mmx10 mmx2 mm). Dental barrel polishing was performed at 450 rpm for 60 minutes with intervals of 5 minutes. The processing angle was measured using a microscope (SZ61; Olympus). Results: For the angle measurement, the VPC specimen was measured at 78.64°, 36.00° for the VP60 specimen, 79.57° for the BP control (BPC) specimen, 28.07° for the BP60 specimen, 75.01° for the GPC specimen, and 39.92° for the GP60 specimen. For the surface roughness measurements, the average surface roughness of the VPC and VP15 specimens were 1.09 ㎛ and 0.26 ㎛, respectively. The average surface roughness of the BPC and BP20 specimens were 1.77 ㎛ and 0.29 ㎛, respectively. The average surface roughness of the GPC and GP15 specimens were 1.08 ㎛ and 0.27 ㎛. Conclusion: The results were excellent after about 20 minutes of dental barrel polishing conditions presented in this study.

• Journal of Powder Materials
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• v.31 no.2
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• pp.132-136
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• 2024

This study investigated the effects of revolution speed and ball size in planetary milling on the microstructure and dehydrogenation behavior of TiH₂ powder. The particle size analysis showed that the large particles present in the raw powder were effectively refined as the revolution speed increased, and when milled at 500 rpm, the median particle size was 1.47 ㎛. Milling with a mixture of balls of two or three sizes was more effective in refining the raw powder than milling with balls of a single size. A mixture of 3 mm and 5 mm diameter balls was the optimal condition for particle refinement, and the measured median particle size was 0.71 ㎛. The dependence of particle size on revolution speed and ball size was explained by changes in input energy and the number of contact points of the balls. In the milled powder, the endothermic peak measured using differential thermal analysis was observed at a relatively low temperature. This finding was interpreted as the activation of a dehydrogenation reaction, mainly due to the increase in the specific surface area and the concentration of lattice defects.

• Microbiology and Biotechnology Letters
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• v.51 no.4
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• pp.449-456
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• 2023

Sugar or dextrose increases the cost of production of xanthan gum by Xanthomonas campestris. Brewers' Spent Grain (BSG) was chosen as a source of fermentable sugars. BSG is a significant industrial by-product generated in large quantities from the breweries. Primarily used as animal feed due to its high fiber and protein content, BSG holds great potential as an economically and ecologically sustainable substrate for fermenting biomolecules. This study explores BSG's potential as a cost-effective carbon source for producing xanthan, utilizing Xanthomonas campestris NCIM 2961. An aqueous extract was prepared from BSG and inoculated with the bacterium under standard fermentation conditions. After fermentation, xanthan gum was purified using a standard protocol. The xanthan yield from BSG media was compared to that from MGYP media (control). The fermentation parameters, including pH, temperature, agitation and duration were optimized for maximum xanthan gum yield by varying them at different levels. Following fermentation, the xanthan gum was purified from the broth by alcoholic precipitation and then dried. The weight of the dried gum was measured. The obtained xanthan from BSG under standard conditions and commercial food-grade xanthan were characterized using FTIR. The highest xanthan yields were achieved at 32 ℃, pH 6.0, and 72 h of fermentation at 200 rpm using BSG media. The FTIR spectra of xanthan from BSG media closely resembled that of commercial food-grade xanthan. The results confirm the potential of BSG as a cost-effective alternative carbon source for xanthan production, thereby reducing production costs and solid waste.

• Journal of Microbiology and Biotechnology
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• v.33 no.11
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• pp.1531-1541
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• 2023

Lipase is a well-known and highly in-demand enzyme. During the last decade, several lipase optimization studies have been reported. However, production costs have always been a bottleneck for commercial-scale microbial enzyme production. This research aimed to optimize the conditions for lipase production by Limtongozyma siamensis DMKU-WBL1-3 via a One-Factor-At-a-Time (OFAT) approach combined with statistical methods while using a low-cost substrate. Results suggest that low-cost substrates can be substituted for all media components. An optimal medium was found, using response surface methodology (RSM) and central composite design (CCD), to consist of 0.50% (w/v) sweet whey, 0.40% (w/v) yeast extract (food grade), and 2.50% (v/v) palm oil with the medium pH adjusted to 4 under shaking flask cultivation. From an economic point of view, this work was successful in reducing production costs while increasing lipase productivity. The medium costs were reduced by 87.5% of the original cost while lipase activity was increased by nearly 6-fold. Moreover, lipase production was further studied in a 2-L stirred-tank fermentor. Its activity was 1,055.6 ± 0.0 U/ml when aeration and agitation rates were adjusted to 1 vvm and 170 rpm, respectively. Interestingly, under this optimal lipase production, the yeast showed accumulated lipids inside the cells. The primary fatty acid is a monounsaturated fatty acid (MUFA) that is typically linked to health benefits. This study hence reveals promising lipase production and lipid accumulation by L. siamensis DMKU-WBL1-3 that are worthy of further study.

• Microbiology and Biotechnology Letters
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• v.51 no.3
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• pp.257-267
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• 2023

The potential polyhydroxyalkanoates (PHA)-producing bacteria, Bacillus megaterium PP-10, was successfully isolated and studied its feasibility for utilization of pineapple peel waste (PPW) as a cheap carbon substrate. The PPW was pretreated with 1% (v/v) H₂SO₄ under steam sterilization and about 26.4 g/l of total reducing sugar (TRS) in pineapple peel hydrolysate (PPH) was generated and main fermentable sugars were glucose and fructose. A maximum cell growth and PHA concentration of 3.63 ± 0.07 g/l and 1.98 ± 0.09 g/l (about 54.58 ± 2.39%DCW) were received in only 12 h when grown in PPH. Interestingly, PHA productivity and biomass yield (Y_x/s) in PPH was about 4 times and 1.5 times higher than in glucose. To achieve the highest DCW and PHA production, the optimal culture conditions e.g. carbon to nitrogen ratios of 40 mole/mole, incubation temperature at 35℃ and shaking speed of 200 rpm were performed and a maximum DCW up to 4.24 ± 0.04 g/l and PHA concentration of 2.68 ± 0.02 g/l (61% DCW) were obtained. The produced PHA was further examined its monomer composition and found to contain only 3-hydroxybutyrate (3HB). This finding corresponded with the presence of class IV PHA synthase gene. Finally, certain thermal properties of the produced PHA i.e. the melting temperature (T_m) and the glass transition temperature (T_g) were about 176℃ and -4℃, respectively whereas the M_w was about 1.07 KDa ; therefore, the newly isolated B. megaterium PP-10 is a promising bacterial candidate for the efficient conversion of low-cost PPH to PHA.

• Particle and aerosol research
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• v.19 no.4
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• pp.101-110
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• 2023

In order to reduce particulate matters (PM) from marine diesel engines, we developed novel electrostatic diesel particulate matter filtration system. Electrostatic diesel particulate filtration (DPF) system consists of electrostatic charger and filtration part. The electrostatic charger and filtration part are composed of a metal discharge electrode and a metal fiber filter (porosity: 68.1-86.1%), respectively. In the electrostatic charger part, diesel soot particles are reduced by electrostatic force. The filtration part after electrostatic charger part reduces diesel soot particles through inertial and diffusion forces. The filtration efficiency of electrostatic DPF system was examined through the experiments using engine dynamometer system (300 kW) and ship (200 kW). The PM reduction efficiencies due to inertial and electrostatic forces showed about 70-75% and 80-90%, respectively, according to the RPM of the engine. The differential pressure of the electrostatic DPF system applied to the ship was about 1-9 mbar, which was less than the allowable differential pressure for ship engines in South Korea (100 mbar). The results show that the electrostatic DPF system is suitable for application to the PM reduction emitted from ships.

• Journal of Microbiology and Biotechnology
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• v.34 no.4
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• pp.969-977
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• 2024

Indigo is a valuable, natural blue dye that has been used for centuries in the textile industry. The large-scale commercial production of indigo relies on its extraction from plants and chemical synthesis. Studies are being conducted to develop methods for environment-friendly and sustainable production of indigo using genetically engineered microbes. Here, to enhance the yield of bioindigo from an E. coli whole-cell system containing tryptophanase (TnaA) and flavin-containing monooxygenase (FMO), we evaluated tryptophan transporters to improve the transport of aromatic compounds, such as indole and tryptophan, which are not easily soluble and passable through cell walls. Among the three transporters, Mtr, AroP, and TnaB, AroP enhanced indigo production the most. The combination of each transporter with AroP was also evaluated, and the combination of AroP and TnaB showed the best performance compared to the single transporters and two transporters. Bioindigo production was then optimized by examining the culture medium, temperature, isopropyl β-D-1-thiogalactopyranoside concentration, shaking speed (rpm), and pH. The novel strain containing aroP and tnaB plasmid with tnaA and FMO produced 8.77 mM (2.3 g/l) of bioindigo after 66 h of culture. The produced bioindigo was further recovered using a simple method and used as a watercolor dye, showing good mixing with other colors and color retention for a relatively long time. This study presents an effective strategy for enhancing indigo production using a combination of transporters.

• Geomechanics and Engineering
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• v.38 no.5
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• pp.477-486
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• 2024

The process of inspecting and replacing cutting tools in a shield tunnel boring machine (TBM) is called cutterhead intervention (CHI) (Farrokh and Kim 2018). Since CHI is performed by a worker who enters the chamber in TBM, the worker is directly exposed to high water pressure and huge water inflow, especially in areas with high ground water levels, causing health problems for the worker and shortening of available working hours (Kindwall 1990). Ham et al. (2022) proposed a method of reducing the water pressure and water inflow by injecting a grout solution into the ground through the shield TBM chamber, and named it the new face grouting method (NFGM). In this study, the TBM mechanical characteristics including the injection pressure of the grout solution and the cutterhead rotation speed were determined for the best performance of the NFGM. To find the appropriate injection pressure, the water inflow volume according to the injection pressure change was measured by using a water inflow test apparatus. A model torque test apparatus was manufactured to find the appropriate cutterhead rotation speed by investigating the change in the status of the grout solution according to the rotation speed change. In addition, to prove the validity of this study, comprehensive water inflow tests were carried out. The results of the tests showed that the injection pressure equal to overburden pressure + (0.10 ~ 0.15) MPa and the cutterhead rotation speed of 0.8 to 1.0 RPM are the most appropriate. In the actual construction site, it is recommended to select an appropriate value within the proposed range while considering the economic feasibility and workability.