• Journal of the korean academy of Pediatric Dentistry
• /
• v.28 no.1
• /
• pp.146-153
• /
• 2001

The difference of composition of composite resin may affect the mechanical properties of composite resin and the environment is important for the properties of materials. The composite resin restoration is always exposed to fluid in oral cavity and the composite resin matrix is able to absorb water, which is accompanied by some swelling of the composite The uptake of water by composites has been correlated with decreases in surface hardness and wear resistance. The purpose of this study was to investigate the effects of water storage in $37^{\circ}C$ distilled water after 7days, 30days, 60days, 120days on compressive strength and flexural strength of dental composite resin, Z-100(group 1) Spectrum(group 2), Clearfil AP-X(group 3), Pyramid(group 4), Heliomolar(group 5). The compressive and flexural strength were measured by instron machine. The following results were obtained: 1. There were significant reduction of compressive strength as water storage time increased, 7days, 30days, 60 days, 120days(p<0.05). 2. There were significant reduction of flexural strength as water storage time increased, 7days, 30days, 60days, 120days(p<0.05). 3. Group 1, 2, 3 -hybrid type showed higher compressive and flexural strength than group 5-microfine type which had lower filler contents.

• Journal of Life Science
• /
• v.30 no.6
• /
• pp.491-500
• /
• 2020

Lactic acid bacteria are widely known to prevent and treat intestinal health conditions, heart disease, depression, and obesity. In Korea, such bacteria are commonly consumed through various fermented foods, although most are isolated from kimchi, and research on the lactic acid bacteria in fermented seafood is insufficient. This study was therefore conducted to observe changes in bacterial flora according to the culture date of lactic acid bacteria in the fermentation of traditional Korean Gajami Sikhae produced in Pohang and to isolate the bacteria of probiotic value. The bacteria were periodically isolated and identified from date of preparation to 50 days after preparation to investigate which Lactobacillus are involved in Gajami Sikhae. As fermentation progressed, it was confirmed that Pediococcus sp. and Lactobacillus sp. participate predominantly in the early and later periods of fermentation, respectively. During the entire fermentation period, 170 isolates were screened, and the following five species were found to be involved: Pediococcus pentosaceus, Pediococcus inopinatus, Leuconostoc mesenteroides, Lactobacillus brevis, and Lactobacillus plantarum. Five strains of these species were selected through acid and bile tolerance tests, and their coaggregation, autoaggregation, hydrophobicity, antibacterial, and antioxidant activities were then evaluated. As a result, it is thought that L. brevis GS1022, which has excellent digestive fluid resistance, and P. inopinatus GS316, which has excellent cohesiveness, may be useful as probiotic strains.

• Journal of Yeungnam Medical Science
• /
• v.24 no.2
• /
• pp.344-350
• /
• 2007

Laryngo-tracheal perforation caused by the use of a stylet during tracheal intubation is a rare complication. We present a case of subcutaneous emphysema and connective tissue inflammation after tracheal intubation. The patient was a 41-year-old male undergoing general anesthesia for an appendectomy. The intubation was difficult during laryngoscopy (Cormack- Lehane Grade III). An assistant provided an endotracheal tube with a stylet inside while the laryngoscope was in place. During intubation, a short, dull sound was heard with a sudden loss of resistance after the distal tip of the endotracheal tube passed the rima glottis. A sonogram and computerized tomography revealed subcutaneous emphysema from the neck to the upper mediastinum and fluid collection between the trachea and the thyroid. This lesion appeared to have been caused by the protruded, loose stylet. Anesthesiologists should be aware of the damage a loose stylet protruding beyond the tip of the endotracheal tube can cause.

• Journal of Sensor Science and Technology
• /
• v.12 no.3
• /
• pp.103-111
• /
• 2003

A chromel-alumel thermoelectric flow sensor using $Si_3N_4/SiO_2/Si_3N_4$ thermal isolation membrane was fabricated. Temperature coefficient of resistance of thin film Pt-heater was about $0.00397/^{\circ}C$, and Seebeck coefficient of chromel-alumel thermocouple was about $36\;{\mu}V/K$. The sensor showed that thermoelectric voltage decreased as thermal conductivity of gas increased, and $N_2$-flow sensitivity increased as heater voltage increased or the distance between heater and thermocouple decreased. When heater voltage was about 2.5 V, $N_2$-flow sensitivity and thermal response time of the sensor were about $1.5\;mV/sccm^{1/2}$ and 0.18 sec., respectively. Linear range in flow sensitivity of the flow sensor was wider than that of Bi-Sb flow sensor.

• Journal of Life Science
• /
• v.25 no.3
• /
• pp.263-268
• /
• 2015

Coelomocytes are specialized cells that continually and nonspecifically scavenge fluid from the body cavity through endocytosis in Caenorhabditis elegans. Our previous study revealed that coelmocytes were specifically required for dietary-restriction-induced longevity in C. elegans. In the present study, we examined the effect of coelomocyte ablation on the response to environmental stressors and reproduction in C. elegans. Coelomocytes were ablated using diphtheria toxin specifically expressed in coelomocytes. After exposing worms to 20 J/cm²/min of ultraviolet irradiation in vivo, the survival of the worms was monitored daily. To examine their response to heat stress, their survival after 10 h of 35℃ heat shock was measured. Oxidative stress was induced using paraquat, and the susceptibility to oxidative stress was compared between wild-type control and coelomocyte-ablated worms. The total number of progeny produced was counted, and the time-course distribution of the progeny was determined. The worms with ablated coelomocytes showed reduced resistance to ultraviolet irradiation, but the ablation of coelomocytes had no effect on their response to heat or oxidative stress. The number of progeny produced during the gravid period was significantly decreased in the coelomocyte-ablated worms. These findings suggest that coelomocytes specifically modulate the response to ultraviolet irradiation and are required for normal reproduction in C. elegans. The findings could contribute to understanding of the mechanisms underlying dietary-restriction-induced longevity.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.21 no.5
• /
• pp.558-570
• /
• 2015

A study on the green ship design for Ultra Large Container Ship (ULCS, 18,000 TEU Class Container Ship) was performed based on the four step procedures of the initial design and hull form optimization to maximize economic and propulsive performance. The first, the design procedure for ULCS was surveyed with economic evaluation considering environmental rules and regulations. The second, the characteristics of single and twin skeg container ships were investigated in view of initial design and performances. The third, the hull form optimization for single and twin skeg ships with the same dimensions was conducted to improve the resistance and propulsive performances at design draught and speed by several variations and the results of the optimization were verified by numerical calculations of CFD and model test. The last, for the estimated operating profile of draught and speed, the hull forms of single and twin sked ships were optimized by CFD. From this study, the methodologies to optimize the hull form of ULCS were proposed with considerations during the green ship design and the improvement of the energy efficiency for the optimized hull forms was confirmed by the proposed formula of the total energy considering design conditions, operating profile and fuel oil consumption.

• Korean Chemical Engineering Research
• /
• v.54 no.2
• /
• pp.145-151
• /
• 2016

In response to the cavitation caused by the partial vacuum caused by the fluid flow, a paint was developed by dispersing the lamella-shaped glass-flake in resin for anti-cavitation. This composite paint was developed by using the inorganic filler (lamella shaped glass-flake) and the NBR (Acrylonitrile-butadiene rubber) which was modified epoxy resin. Especially, the glass-flake was a thin film with a thickness of about 100~200 nm and length of about $20{\sim}30{\mu}m$, the aspect ratio was about 200 to 300 times that of the plate-shaped. So the paint for anti-cavitation have shown excellent performance in corrosion resistance. The results of evaluating anti-cavitation performance was below, tensile strength $4.8{\sim}6N/mm^2$ or more, rupture elongation 30% or higher, abrasive speed $10mm^2/h$ or less. In particular, it showed more than twice the superior performance compared to existing advanced foreign products in anti-cavitation performance evaluation.

• Journal of the Microelectronics and Packaging Society
• /
• v.16 no.3
• /
• pp.39-43
• /
• 2009

In this paper, the flow characteristics of underfill material driven by capillary action between flip-chip and substrate were investigated. Also, the effects of viscosity level and dispensing point of underfill on flow characteristics were investigated. Flip chip package size was $5mm{\times}5mm{\times}0.65^tmm$, the diameter of solder bump was 100 ${\mu}m$, and the pitch was 150 ${\mu}m$. It was full grid area-array type with 1024 I/Os. The glass substrate was used and the gap between the chip and substrate was 50 ${\mu}m$. For the experimental study, three different underfills with different viscous properties($2000{\sim}3700$ cps), and two different types of dispensing methods(center dot and edge dot) were used. The flow characteristics and filling time of underfill were investigated by using CCD camera. The results show that the edge flow was faster than center flow due to the edge effect, which was caused by the resistance of solder bumps. In case of edge dot dispensing type, the filling time was faster due to the large edge effect, compared to center dot dispensing type. Also, it was found that the underfill flow was faster and the filling time decreased as the viscosity level of underfill was decreased.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.8
• /
• pp.8-14
• /
• 2019

Bird-strike is one of the most important design factors for safety in the aviation industry. Bird-strikes have been the cause of significant damage to aircraft and rotorcraft structures and the loss of life. This study used DYTRAN software to simulate the transient response of an Euler-Lagrangian composite helicopter blade that has been impacted by a bird. The Arbitrary Lagrangian Eulerian (ALE) method and a suitable equation of state were applied to model the bird. ALE was applied to the bird-strike analysis due to the large difference between the properties of the blade and bird. The debris of the bird was assumed to be a fluid and applied as Euler elements after the collision. Through the analysis of bird impacts, the leading-edge of the rotor blade (50.8 mm) was used to identify a positive margin of 1.18 based on the TSAI-FILL criteria. The results are assessed to be sufficiently reliable and may be evaluated to replace tests with various analysis conditions. The structural stability of the rotor blade could be assessed by applying various load conditions and different modeling methods in the future.

• Journal of the Society of Naval Architects of Korea
• /
• v.56 no.1
• /
• pp.34-46
• /
• 2019

This paper provides the numerical results for the self-propulsion performance in waves of a car ferry vessel with damage in one of its twin-screw propulsion systems without flooding the engine room. The numerical simulations were carried out according to the Safe Return to Port (SRtP) regulation made by the Lloyd's register, where the regulation requires that damaged passenger ships should have an ability to return to port with a speed of 6 knots in a Beaufort 8 sea condition. For the validation of the present numerical analysis study, the resistance performance and the self-propulsion performance of the car ferry in intact and damaged conditions in calm water were calculated, which showed a satisfactory agreement with the model test results of Korea Research Institute of Ship and Ocean engineering (KRISO). Finally, the numerical simulation of self-propulsion performance in waves of the damaged car ferry ship was carried out for a normal sea state and for a Beaufort 8 sea state, respectively. The estimated average Brake Horse Power (BHP) for keeping the damaged car ferry ship advancing at a speed of 6 knots in a Beaufort 8 sea state reached about 47% of BHP at MCR condition or about 56% of BHP at NCR condition of the engine determined at the design state. In conclusion, it can be noted that the engine power of the damaged car ferry ship in single propulsion condition is sufficient to satisfy the SRtP requirement.