• Korean Journal of Materials Research
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• v.32 no.12
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• pp.538-544
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• 2022

In existing ceramic mold manufacturing processes, inorganic binder systems (Si-Na, two-component system) are applied to ensure the effective firing strength of the ceramic mold and core. These inorganic binder systems makes it possible to manufacture a ceramic mold and core with high dimensional stability and effective strength. However, as in general sand casting processes, when molten metal is injected at room temperature, there is a limit to the production of thin or complex castings due to reduced fluidity caused by the rapid cooling of the molten metal. In addition, because sodium silicate generated through the vitrification reaction of the inorganic binder is converted into a liquid phase at a temperature of 1,000 ℃. or higher, it is somewhat difficult to manufacture parts through high-temperature casting. Therefore, in this study, a high-strength ceramic mold and core test piece with effective strength at high temperature was produced by applying a Si-Na-Ti three-component inorganic binder. The starting particles were coated with binary and ternary inorganic binders and mixed with an organic binder to prepare a molded body, and then heat-treated at 1,000/1,350/1,500 ℃ to prepare a fired body. In the sample where the two-component inorganic binder was applied, the glass was liquefied at a temperature of 1,000 ℃ or higher, and the strength decreased. However, the firing strength of the ceramic mold sample containing the three-component inorganic binder was improved, and it was confirmed that it was possible to manufacture a ceramic mold and core via high temperature casting.

• Journal of odor and indoor environment
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• v.17 no.4
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• pp.355-361
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• 2018

Mold grows more easily when humidity is higher in indoor spaces, and as such is found more often on wetted areas in housing such as walls, toilets, kitchens, and poorly managed spaces. However, there have been few studies that have specifically assessed the level of mold in the indoor spaces of water-damaged housing in the Republic of Korea. We investigated the levels of airborne mold according to the characteristics of water damage types and explored the correlation between the distribution of mold genera and the characteristics of households. Samplings were performed from January 2016 to June 2018 in 97 housing units with water leakage or condensation, or a history of flooding, and in 61 general housing units in the metropolitan and Busan area, respectively. Airborne mold was collected on MEA (Malt extract agar) at flow rate of 100 L/min for 1 min. After collection, the samples were incubated at $25^{\circ}C$ for 120 hours. The cultured samples were counted and corrected using a positive hole conversion table. The samples were then analyzed by single colony culture, DNA extraction, gene amplification, and sequencing. By type of housing, concentrations of airborne mold were highest in flooded housing, followed by water-leaked or highly condensed housings, and then general housing. In more than 50% of water-damaged housing, the level of airborne mold exceeded the guideline of Korea's Ministry of Environment ($500CFU/m^3$). Of particular concern was the fact that the I/O ratio of water-damaged housing was greater than 1, which could indicate that mold damage may occur indoors. The distribution patterns of the fungal species were as follows: Penicillium spp., Cladosporium spp. (14%), Aspergillus spp. (13%) and Alternaria spp. (3%), but significant differences of their levels in indoor spaces were not found. Our findings indicate that high levels of mold damage were found in housing with water damage, and Aspergillus flavus and Penicillium brevicompactum were more dominant in housing with high water activity. Comprehensive management of flooded or water-damaged housing is necessary to reduce fungal exposure.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.10 no.1
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• pp.115-125
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• 2000

Three major hospitals with over 500 beds located in and near Seoul were surveyed for airbone microorganisms from February 1, 1998 to February 18, 1998. The purpose of the study was to identify and quantify microbiological organisms circulating in the air of three different areas in the hospitals. For the study, a RCS air sampler was utilized equipped with two different collection media, the agar strip GK-A for bacteria and the agar strip HS for fungi. The areas investigated were the intensive care unit (ICU) in the Department of internal medicine, the Newborns room in the Department of Obstetrics, and the microbiology laboratory. The results were as follows; 1. The average numbers of general microbiological particles collected on the agar strip GK-A media were $205CFU/m^3$, $232CFU/m^3$, and $128CFU/m^3$ in each hospitals. The highest concentration of $387CFU/m^3$ was found in the ICU of A hospital at 15:00 during the day. Further analysis of the collected bioaerosols by gram staining, revealed that there were gram positive cocci (89.5%), gram positive bacilli (7.2%), gram negative bacilli (2.8%), and fungi (0.5%), in descending order of frequency. 2. Ten different genes were identified from the agar strip GK-A. The most frequently identified organisms were: the Coagulase negative staphylococcus (55.0%), Micrococcus (21.4%), Enterococcus species(10.4%), and Bacillus species (7.2%). A series of antibiotics susceptibility test were conducted against the aforementioned four(4) organisms. Ninety percent of coagulase negative stapylococcus were sensitive to Penicillins. Pathogenic microbes isolated include: Staphylococcus aureus, Acinetobacter species, Klebsiella pneumonia, Klebsiella oxytoca, and Pseudomonas aeroginosa. 3 Although 56.8% of the microorganisms grown on the strip HS media for fungi could not be identified, some of them were successfully identified. The most frequently found fungi were Aspergillus (35.3%), Yeast or Molds (6.2%), and Penicillium (0.7%). Based on the results obtained from the study, it was concluded that some areas in the hospitals had abnormally high bioaerosol concentrations which could be attributed to human activity. Therefore, it is recommended that periodic assessments of indoor bioaerosols aiming to identify the possible sources should be conducted in order to maintain clean indoor environment in the hospitals.

• Journal of the Korean Society of Food Science and Nutrition
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• v.35 no.5
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• pp.649-654
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• 2006

It was investigated the effects of pre-treatment method on the microbes on the surface of radish (Raphanus sativus L.) leaves. Independent variables put in water washing ($X_1$), microwave treatment ($X_2$) and steam treatment ($X_3$) using central composite design and response surface analysis. It was not detected in the pathogenic microbes, Samonella spp., Camphylobacter spp., Vibrio spp., Shigella spp., Staphyloccocus spp., on the surface of collected radish leaves without pre-treatment. But general microbes showed $3.90{\times}10^5{\sim}1.20{\times}10^7CFU/g$ of total microbes, $1.10{\times}10^2{\sim}2.00{\times}10^5CFU/g$ of E. coli, $2.40{\times}10^3{\sim}3.55{\times}10^6CFU/g$ of yeast/mold on the surface of various radish leaves and lactic acid bacteria was detected or not according to collected samples. The best method of pre-treatment was steam treatment on the microbe reduction effect of samples surface. Also, the multiplex regression coefficients analysis was calculated three independent variables ($X_1,\;X_2,\;X_3$) and dependent variables (total microbes, lactic acid bacteria and yeast/molds). It showed high correlation $R^2$, 0.89, 0.87, 0.85, respectively. For effective reduction of surface microbes, the best method was water washing with microwave or steam treatment at the same time.

• Korean Journal of Pharmacognosy
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• v.48 no.4
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• pp.329-338
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• 2017

This study was investigated the changes of quality stability and physicochemical characteristics of the Korean red ginsengs stored for a long times over 20 years. The Korean red ginsengs were stored for 4 to 22 years in canned packaging with polypropylene film and wooden box at room temperatures. The unusal phenomena such as discoloration and pin hole in packaging were not observed. General bacteria showed the vlaues of below 100 CFU/g, coliform groups and molds were not found in any samples stored for 22 year. Any samples also were not detected in mycotoxins. The contents of moisture, ash and crude saponin were the levels of 10.6~11.1%, 3.8~4.2% and 4.1~4.7% during the whole storage periods, respectively. The contents of maltol, which has been known as characteristic flavour and antioxidant of Korean red ginseng, showed remarkably increasing tendency from 0.10 mg/g for 4 years to 2.53 mg/g for 22 years during the storage. The contents of AFG (arginyl-fructosyl-glucose), arginine and free sugar were slightly decreased. Acidic polysaccharide and ginsenoside were not changed significantly during the storage periods. The contents of acidic polysaccharide and total ginsenosides were the 75.1~76.3 mg/g and 15.1~16.6 mg/g, respectively. The sums of ginsenoside-Rg1,-Rb1 and -Rg3s were the ranges of 9.3~9.9 mg/g and PD (ginsenoside-Rb1, -Rb2,-Rc,-Rd,-Rg3s,-Rg3r)/PT (ginsenoside-Rg1,-Rg2,-Re,-Rf,-Rh1) saponin ratios were the levels of 1.4~1.5. These results suggest that Korean red ginsengs stored for long periods show relatively stable quaility stabilities and not significantly changed the contents of ginsenoside and polysaccharide during the storage up to 22 years.

• Journal of Ginseng Research
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• v.33 no.4
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• pp.361-366
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• 2009

This research aims to develop a new drying technology using super-heated steam to reduce the time required for drying ginseng and to enhance its quality. The drying rate of ginseng powder treated with hot-air drying after drying with super-heated steam was about 40% faster than the drying rate of ginseng powder treated with hot-air drying. Minimal difference was found between hot-air drying and hot-air drying after drying with super-heated steam in the general composition of the ginseng powder, such as its crude lipid, crude protein, crude fiber, and ash. Moreover, no difference was found between hot-air drying and hot-air drying after drying with super-heated steam in terms of the ginseng powder's mineral and free sugar contents. The crude saponin contents was 5.43% in the ginseng treated with hot-air drying and 5.4% in the ginseng treated with hot-air drying after drying with super-heated steam. The ginseng powder that was treated with hot-air drying after drying with super-heated steam had a slightly higher redness compared to the ginseng powder that was treated with hot-air drying alone. The number of microorganisms of the ginseng powder treated with hotair drying after drying with super-heated steam showed a reduction of one log cycle in the total bacteria and two log cycles in the yeast molds compared to the ginseng powder treated with hot-air drying alone.

• Design & Manufacturing
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• v.15 no.2
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• pp.11-16
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• 2021

Recently, three-dimensional (3D) cell culture systems, which are superior to conventional two-dimensional (2D) vascular systems that mimic the in vivo environment, are being actively studied to reproduce drug responses and cell differentiation in organisms. Conventional two-dimensional cell culture methods (scaffold-based and non-scaffold-based) have a limited cell growth rate because the culture cannot supply the culture medium as consistently as microvessels. To solve this problem, we would like to propose a 3D culture system with an environment similar to living cells by continuously supplying the culture medium to the bottom of the 3D cell support. The 3D culture system is a structure in which microvascular structures are combined under a scaffold (agar, collagen, etc.) where cells can settle and grow. First, we have manufactured molds for the formation of four types of microvessel-mimicking chips: width / height ①100 ㎛ / 100 ㎛, ②100 ㎛ / 50 ㎛, ③ 150 ㎛ / 100 ㎛, and ④ 200 ㎛ / 100 ㎛. By injection molding, four types of microfluidic chips were made with GPPS (general purpose polystyrene), and a 100㎛-thick PDMS (polydimethylsiloxane) film was attached to the top of each microfluidic chip. As a result of observing the flow of the culture medium in the microchannel, it was confirmed that when the aspect ratio (height/width) of the microchannel is 1.5 or more, the fluid flows from the inlet to the outlet without a backflow phenomenon. In addition, the culture efficiency experiments of colorectal cancer cells (SW490) were performed in a 3D culture system in which PDMS films with different pore diameters (1/25/45 ㎛) were combined on a microfluidic chip. As a result, it was found that the cell growth rate increased up to 1.3 times and the cell death rate decreased by 71% as a result of the 3D culture system having a hole membrane with a diameter of 10 ㎛ or more compared to the conventional commercial. Based on the results of this study, it is possible to expand and build various 3D cell culture systems that can maximize cell culture efficiency by cell type by adjusting the shape of the microchannel, the size of the film hole, and the flow rate of the inlet.

• Applied Biological Chemistry
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• v.48 no.2
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• pp.132-139
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• 2005

The major obstacle in the popularization of Chungkookjang is the short shelf-life of $2{\sim}3$ months and some problems concerning storage including the growth of molds even in the products even within shelf-life. To solve these problems we conducted a research to improve its storage by using the vacuumed packaging and sanitary method through seed culture, innoculation and sterilization. For the optimization of storage time, temperature and sterilization temperature, we measured viable cell numbers of bacteria and fungi, amount of gas outbreak and contents of amino type nitrogen and monitored these experimental results by response surface methodology of SAS program, so that we could observe the quality changes of Chungkookjang during shelf-life. Especially fungi, which are the biggest troublemaker in Chungkookjang shelf-life, couldn't be detected from the generally and vacuum-packed samples; also, viable cell numbers were highly influenced by sterilization temperature and in vacuum-packed samples. In the case of vacuum-packed samples, amount of gas outbreak was highly influenced by sterilization temperature of its storage conditions and it was higher in generally packed samples as compared to vacuum-packed samples even at any storage conditions. The changes of pH in generally and vacuum-packed samples were highly influenced by the storage temperature. As the temperatures of storage and sterilization were higher and the storage time was longer, so the amount of gas outbreak was accordingly lower. These results showed that amino type nitrogen contents in generally and vacuum-packed samples were systematically influenced by the temperature, storage time and sterilization temperature. Also the result showed that the change of amino type nitrogen contents during storage was less in vacuum-packed samples than in general ones. Based on the above results, we can produce Chungkookjang products with extended shelf-life of as far as 6 months without any quality change using sanitary manufacturing method, vacuumed packaging condition, sterilization in $70^{\circ}C$ for 60 minutes and storage under $10^{\circ}C$ during shelf-life. According to this research, we have the possibility to greatly increase the goods value of Chungkookjang by developing the manufacture processing and packaging.

• Food Science and Preservation
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• v.17 no.4
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• pp.494-499
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• 2010

Pasteurization by radiation was performed to improve the microbiological quality of fresh yam juice. Samples were irradiated at doses of up to 5 kGy and microbiological, physicochemical, and sensory qualities were investigated during storage at 5oC for 8 days. Total aerobic bacterial, coliform bacterial, and yeast and mold counts in pre-irradiation samples were 7.09, 6.91, and 3.42 log CFU/g, respectively. Total aerobic bacterial and coliform counts fell significantly, in a dose-dependent manner, after irradiation, and these organisms were completely eliminated after 1 day of storage when 3 kGy or 5 kGy of radiation was applied. Yeast and molds were eliminated by irradiation at 3 kGy. Irradiation reduced sample viscosity. The $L^*$ value decreased after irradiation, whereas the $b^*$ value rose. Sensory evaluation testing revealed no significant difference between control samples and those irradiated with 1 kGy, except in color and texture, but sensory scores fell when irradiation of 3 kGy or over was employed, except in the taste domain. The results indicate that gamma irradiation with 1 kGy is effective to ensure the microbiological safety of fresh yam juice, without significant alteration in sensory characteristics, although further work should seek to reduce the detrimental effects of irradiation.

• Korean Journal of Heritage: History & Science
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• v.39
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• pp.59-93
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• 2006

Wolseong in Gyeongju is a historic fortress site of Silla constructed under the reign of Pasanisageum that played politically and militarily important roles. The moat surrounding Wolseong had a function of protecting the fortress in wartimes but became a part of gardening in the unified Silla era. Lots of relics have been excavated from Wolseong moat since 1985. Among them a great number and kinds of convex roofing tiles are regarded as invaluable sources to show different aspects of Silla, from its earlier time through to the unified and on. Roofing tiles were widely used for national buildings such as royal palaces, temples and fortresses and even for other popular architecture and have been dug out a lot more than any other relics. Research on them, however, has been done poorly. Vigorous study is in progress with increasing number of roofing tiles coming from many recent excavations, though it has been limited to the studies on general genealogy of patterns and manufacture processes. Thus this essay seeks to find which are dongbeomwas, roofing tiles of a same mold, out of convex tiles with the pattern of a unilobed lotus flower dug out of Wolseong moat. It also attempts to identify dongbeomwas by examining detail characteristics of roofing tiles which have been confusingly termed as yusawa, similar roofing tiles, or donghyeongwa, roofing tiles of the same shape. The significance of identifying dongbeomwas could be emphasized by various facts resulting from researches on dongbeomwas; the ways to identify them correctly, their time sequence and their excavated sites. In conclusion, dongbeomwas were identified out of many kinds of convex tiles. If they were excavated from the same site, they share some common features. The sites where they were dug out also tell what changes were made with passage of time and what relations they had with neighboring Anapji. Since roofing tile molds haven't been found yet, the only way to identify dongbeomwas is to examine details of roofing tiles. Dongbeomwas excavated in Wolseong moat help to discuss the time of each district of it. Meanwhile it should be noted that the term 'dongbeomwa' be used only after exact examining.