• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.737-742
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• 2015

Course correction munition are a weapson system for precision attacks and are assembled by applying a ballistic control system to existing projectiles. The roll control system is a subsystem of the ballistic control system and is placed between the guidance and control units inside of the projectile, which undergoes a 5000g lateral acceleration. Thus, it is very important to design the system to endure this load. Many developed countries evaluate the performance and safety of course correction munitions' parts using live-fire gun launch tests or a soft recovery system. However, these methods are expensive and slow. Thus, in this study, we develop impact analysis model of the roll control system using CAE. We apply the code to simulate impact phenomenon and use Johnson-Cook material model for modeling the high strain rate effect on the materials. We also design bearings in detail to analyze their behavior and verify the reliability of CAE model through gas-gun impact tests of the roll control system.

• Korean Journal of Food Science and Technology
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• v.35 no.6
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• pp.1135-1142
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• 2003

The purification and characteristics of the biosynthesis enzyme of vitamin C from microorganisms related with kimchi fermentation were investigated to define vitamin C biosynthetic pathways in yeast. A yeast strain (Pichia onychis 16-4) which synthesizes vitamin C with galacturonic acid as substrate at high rate was isolated from kimchi. The enzyme $L-galactono-{\gamma}-lactone$ oxidase isolated from the yeast was purified and characterized. The specific activity of the crude enzyme was 7.26 unit/mg protein, which increased to 4,698 unit/mg protein with a chromatography of Sephacryl S-200HR; indicating a 647.1-fold level of purification. The molecular weights of the dissociated enzymes were estimated to be 31,000, 39,000, and 50,000 KD. Among the substrates tested, $L-galactono-{\gamma}-lactone$ was the most effective. The enzyme showed optimum activity ah pH 7.8 and 35c. The purified enzyme uses $O_2$ as the electron acceptor for oxidation of $L-galactono-{\gamma}-lactone$.

• Korean Journal of Microbiology
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• v.44 no.3
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• pp.221-227
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• 2008

Bordetella pertussis is pathogenic bacteria causing pertussis, a infectious respiratory disease for the infants. The incidence rate of pertussis was significantly decreased after introduction of vaccine. However, increased pertussis cases are recently reported in several countries with high vaccine coverage. One of the inferred reasons is genotype or serotype variation between circulating strains and vaccine strains. Therefore, it is required to confirm the variation status of the isolates by genotype or serotype analysis and the possibility of pertussis outbreak in Korea should be estimated. For this, the serotype variations of the isolates from $1999\sim2006$ were investigated in agglutinogen and fimbriae. As the result, the most frequent serotype in the isolated strains was agglutinogen 1 and fimbriae 2 serotypes. Moreover, serotype transition from vaccine serotypes to non-vaccine serotypes was observed. Especially, the transition pattern of agglutinogen serotype was directed to increase a different type (agg 1) from the vaccine type (agg 1,2). However, in case of fimbriae, the same type (fim 2) with vaccine strain was increased. These results were also observed in other countries with increasing incidence of pertussis. For more predictable results to know increasing possibility of pertussis incidence in Korea, the studies on genetic variations of antigenic determinant genes and prevalence of antibody titer in normal population should be performed in the further.

• The Journal of the Korean Society for Microbiology
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• v.19 no.1
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• pp.11-24
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• 1984

Shigella remains to be an important enteric pathogen in this country for the present. Moreover, most of the isolates have become multiple resistant to various antibiotics which used to be drugs of choice for shigellosis. This study was made as an attempt to assess the present stage of antibiotic resistance and the incidence and transferability of R factors of Shigella. A total of one hundred and seventeen strains of Shigella isolated from patients in Seoul and provincial area between 1982 and 1983 were tested for their resistant to antimicrobial agents and transmission of R-plasmid. Antibiotic susceptibilities were determined by an agar dilution method. Muller hinton agar were used for the assay of drug resistance and tryptic soy broth were used for propagating medium for conjugation. Shigella isolated found to be one or more antibiotics were considered potential donor of R-plasmid. The following results were obtained. 1. Among 117 strains of Shigella isolated, 111 strains(94.9%) were found to be resistant to one or more drugs tested and 97.3% of these resistant strains were multiply resistant, indicating the multiply resistant strains were more than the single resistant strains. Only six strains were susceptible to all drugs tested. 2. Among 117 strains of Shigella isolated, 107 strains(91.5%) were resistant to Tetracyclin(Tc), 106 strains(90.6%) to Chloramphenicol(Cp) and Streptomycin(Sm), 97 strains(82.9%) to Ampicillin(Ap), 68 strains(58.1%) to Cephaloridine(Cr), 10 strains(8.5%) to Nalidixic acid(Na), 5 strains(4.3%) to Kanamycin(Km) and 2 strains(1.7%) to Rifampicin. No strain was resisfant to Amikacin(Ak) and Gentamicin(Gm). 3. All drug-resistant Shigella strains, except three, were multiply resistant to two or more drugs. Fifty eight strains were resistant to five drugs, followed by 26 strains resistant to dour drugs, 12 strains resistant to three drugs and 11 strains resistant to six drugs. 4. The 73% of multiply drug-resistant Shigella transferred their resistance to E. coli by conjugation and the resistance was considered to be mediated by R-plasmid. Resistance to Nalidixic acid and Rifampicin were not transferred by conjugation to recipient. As for the transferability of resistance to each seperate drug, Ap resistance was transferred with 73.2% frequence and Cm and Tc resistance were transferred with approximately 50-60% frequence whereas Sm and Cr resistance were transferred in 19.1-21.4% The other four drugs resistant failed to transfer their resistance to recipient. 5. As for the incidence and transferability of resistance to each seperate drug, the strains resistant to Tc and Cm were encountered most frequently with the rate of 91-92%, whereas transfer of Tc and Cm were low, 51-52%. The incidence of Sm resistance was very high(90.6%) but transferability of drugs resistance was much lower(25.4%). Though the incidence of Km reristance was much lower(4.3%) transferability of Km resistance was considerably higher(60%). 6. The greater the multiplicity of resistance, the greater was the likelihood that part of all of the resistance markers would be transferable.

• Food Science of Animal Resources
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• v.28 no.5
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• pp.587-595
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• 2008

In order to develop a new starter for fermented milk, 1037 bacterial strains were isolated from raw milk. The strain that showed excellent acid producing and angiotensin converting enzyme (ACE) inhibitory activity (88.6%) was selected and identified as a Lactobacillus zeae based on the result of API carbohydrate fermentation pattern and 16S rDNA sequence. Lactobacillus zeae RMK354 was investigated further to study its physiological characteristics. It showed strong ACE inhibitory activity compared with commercial LAB starters tested. The optimum growth temperature of L. zeae RMK354 was $40^{\circ}C$ and it took 10 hr to reach pH 4.3 under this condition. L. zeae RMK354 showed more sensitive to penicillin-G, bacitracin, novobiocin, in a comparison of 14 different antibiotics, and showed most resistance to polymyxin B and vancomycin. It showed higher esterase and leucine arylamidase activities compared with 16 other enzymes. It was comparatively tolerant to bile juice and able to survive at pH 2 for 3 hr. It showed inhibitory activity against Salmonella Typhimurium with the rate of 60%. Based on these and previous results, L. zeae RMK354 could be an excellent starter culture for fermented milk with high level of ACE inhibitory activity.

• Elastomers and Composites
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• v.43 no.2
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• pp.88-103
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• 2008

This study was purposed to investigate the effects of surfactants and fillers on physical properties of hydrophilic polyvinylsiloxane dental impression materials (PVS). Incorporation of surfactants enhanced the hydrophilicity of the PVS, however, it induced increased viscosity and permanent deformation ratio, delayed setting, and decreased tensile strength. At high concentrations of surfactant, the tensile strength was observed to decrease significantly due to the internal pore formation. Especially, the hydrophilicity of the PVS was significantly enhanced with the addition of Silwet L-77. However, the viscosity, strain in compression, pore formation, and setting time increased whereas the elastic recovery rate and strength remarkably decreased. The PVS dental materials containing Span 20 showed the lowest degree of viscosity increase, delayed setting, pore formation, and hydrophilicity. The delayed setting, pore formation, and strength decrease caused by the incorporation of surfactant were improved by substituting the crystalline quartz filler with diatomaceous earth while the contact angle of PVS dental materials increased.

• Food Science and Preservation
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• v.8 no.4
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• pp.356-361
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• 2001

This study was conducted to improve the storability of onion bulbs by assembly simple house storage and the reduce the rotteness caused by field open storage. Allium cepa cv. Changnyungdeago, late strain was used for the test at the storage condition of natural ventilation of levels 2, forced ventilation of levels 2, field open storage and 75mm, 100mm, and 125mm ventilating holes. Mean tamperature and relative humidity were not significantly different by ventilation conditions. Mean temperature was lower in forced ventilation than that of in natural ventilation and non-ventilation, and relative humidity was a little higher in ventilation treatment than those of the others. Weight loss of onion bulbs were 2.5%, 2.9%, 3%, 4.3% in field open storage, non ventilation, natural ventilation of levels 2 and forced ventilation of levels 2 respectively. Rotting rate in natural ventilation of levels 2 and farced ventilation of levels 2 were 27.7% and 25.4% respectively but 34.6% and 37.8% in non ventilation and field open storage. Therefore, the treatment of ventilation reduced the rotteness of storage onion bulbs. The smaller the size of a ventilating hole, the lower mean temperature was maintained. The relative humidity was some high in July, but didn’t showed significantly difference in August and September. With small size of a ventilating hole, the strong wind velocity was obtained, and wind velocity by position was weaker in the middle part than both ends. Rutting rates in 75㎜, 100㎜, and 125㎜ ventilating holes were 17.9%, 15.3% and 14.1% respectively.

• Restorative Dentistry and Endodontics
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• v.22 no.2
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• pp.505-518
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• 1997

The objective of this investigation was to compare the effects of water storage on the aspect of hardness and diametral tensile strengths of four hybrid glass ionomer cements(two compomers and two resin-reinforced glass ionomers) with a resin composite material. One composite resin(Degufill Ultra), two compomers(Dyract, Compoglass Cavifil), and two resin-reinforced glass ionomers(Fuji Duet, Vitremer) were used in this study. Cylindrical specimens were prepared and stored at $36{\pm}1^{\circ}C$ in distilled water for 10 minutes after set, and then tested on an Instron testing machine(No.4467) at 1.0 mm/min displacement rate. Vicker's hardness and diametral tensile strengths as time elapsed were measured after aging in water for 10 minutes, 1 hour, 3 hours, 1 day, 3 days, 5 days and 7 days at $36{\pm}1^{\circ}C$. During the test of diametral tensile strength, stress-strain curves were obtained, from which the compressive modulus were calculated and compared. The structure of four set glass ionomer cement mass was observed on SEM(Hitachi, S-2300) after being etched with 9.6% hydrofluoric acid for 1 minute. The results were as follows; 1. The hardness of the experimental group(compomer and the resin reinforced glass ionomer cement) did not exceed the value of control group(Degufill Ultra). 2. Vicker's hardness of the Fuji Duet tended to increase succeedingly, Dyract was decreased after 3 hours in water, and Vitremer was the lowest. 3. The control group(Degufill Ultra) presented progressively on increased diametral tensile strength with time, Fuji Duet were decreased after 3 days, Compoglass Cavifil and Vitremer were decreased after 5 days in water storage. 4. Compressive modulus of the control group(Degufill Ultra) and Dyract were increased sharply timely, Fuji Duet and Vitremer were increased smoothly by lapse of time in water. Fuji Duet were stronger than Vitremer. On the other hand, Vitremer exhibited the lowest toughness. 5. The microstructure of compomer was similar with that of the composite resin(Degufill Ultra), and the fillers in resin-reinforced glass ionomer cements were noticed. It can be concluded that mechanical properties of hybrid glass ionomer cements is weaker than composite resin, and that the compomers or the resin-reinforced glass ionomers can not substitute the composite resins. A plenty of considerations should be done on the application of them to the area under the loading and high wear has a little adverse effect on the mechanical properties on the water storage for 7 days. The further research should be needed to confirm the advantage of the compomer.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1115-1120
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• 1998

The sliding wear behavior of Ni-base hardfacing alloy, Deloro 50, was investigated at the contact stresses of 15ksi and 30ksi under the various wear environments. In air at room temperature, Deloro 50 showed lower wear resistance than Stellite 6 even at 15ksi due to the occurrence of severe adhesive wear. This seems to be caused by the lower hardness and work- hardening rate of Deloro 50 than those of Stellite 6. In water at room temperature, Deloro 50 showed as good wear resistance as Stellite 6 at 15ksi. It was considered to be due to that water could effectively prevent metal to metal contact through contacting asperities. However, Deloro 50 showed severe adhesive wear at 30ksi in water at room temperature. It seems to be that the water could not suppress adhesion wear at 30ksi. At $300^{\circ}C$ in air, Deloro 50 exhibited higher wear resistance than Stellite 6 even at 30ksi. It was considered that the oxide glaze layers formed on wear surface during sliding, effectively prevented direct metal-to-metal contacts.

• Microbiology and Biotechnology Letters
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• v.42 no.4
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• pp.347-353
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• 2014

${\beta}$-Glucosidase from Aspergillus usamii KCTC 6954 was used to convert ginsenoside Rb1 to compound K, which has a high bio-functional activity. The enzymatic activities during culturing for 15 days were determined using ${\rho}$-nitrophenyl-${\beta}$-glucopyranoside. The growth rate of the strain and the enzymatic activity were maximized after 6 days (IU; $175.93{\mu}M\;ml^{-1}\;min^{-1}$). The activities were maximized at $60^{\circ}C$ in pH 6.0. During culturing, Rb1 was converted to Rd after 9 d and then finally converted to compound K at 15 d. In the enzymatic reaction, Rb1 was converted to the ginsenoside Rd within 1 h of reaction time and compound K could be detected after 8 h. As a result, this study demonstrates that $Rb1{\rightarrow}Rd{\rightarrow}F2{\rightarrow}$compound K is the main metabolic pathway catalyzed by ${\beta}$-glucosidase and that ${\beta}$-glucosidase is a feasible option for the development of specific bioconversion processes to obtain minor ginsenosides such as Rd and compound K.