• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.20 no.1
• /
• pp.49-59
• /
• 1984

Optimizing investigation of characteristics of underwater welding by a gravity type arc welding process was experimentally carried out by using six types of domestic coated welding electrodes for welding of domestic marine structural steel plates (KR Grade A-1, SWS41A, SWS41B,) in order to develop the underwater welding techniques in practical use. Main results obtained are summarized as follows: 1. The absorption speed of the coating of domestic coated lime titania type welding-electrode became constant at about 60 minutes in water and it was about 0.18%/min during initial 8 minutes of absorption time. 2. Thus, the immediate welding electrode could be used in underwater welding for such a short time in comparison with the joint strength of in-atmosphere-and on-water-welding by dry-, wet-or immediate-welding-electrode. 3. By bead appearance and X-ray inspection, ilmenite, limetitania and high titanium oxide types of electrodes were found better for underwater-welding of 10 mm KR Grade A-1 steel plates, while proper welding angle, current and electrode diameter were 6$0^{\circ}C$, above 160A and 4mm respectively under 28cm/min of welding speed. 4. The weld metal tensile strength or proof stress of underwater-welded-joints has a quadratic relationship with the heat input, and the optimal heat input zone is about 13 to 15KJ/cm for 10mm SWS41A steel plates, resulting from consideration upon both joint efficiency of above-100% and recovery of impact strength and strain. Meanwhile, the optimal heat input zone resulting from tension-tension fatigue limit above the base metal's of SWS41A plates is 16 to 19KJ/cm. Reliability of all the empirical equations reveals 95% confidence level. 6. The microstructure of the underwater welds of SES41A welded in such a zone has no weld defects such as hydrogen brittleness with supreme high hardness, since the HAZ-bond boundary area adjacent to both surface and base metal has only Hv400 max with the microstructure of fine martensite, bainite, pearlite and small amount of ferrite.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
• /
• v.29 no.1
• /
• pp.87-103
• /
• 1999

Purpose: This study was undertaken to quantitatively estimate the degree of the damage and recovery of the irradiated rat condylar cartilage using the Image Analyzer. Materials and Methods: Experimental animals were 16 male rats of the Sprague-Dawley strain at the age of 20 day irradiated with the dose of 10 Gy in their head and neck region. Four rats were sacrificed at the each of the following time intervals - 1, 4, 7 and 14 days, respectively. The same number of control group animals were sacrificed at the each age of 21. 24, 27 and 34 days, respectively. The specimens were stained with 0.5％ toluidine blue and examined with light microscope. The condylar cartilage was divided into 4 zones; fibrous zone, proliferating zone, upper hypertrophic zone, and lower hypertrophic zone. And then, the proliferating zone was subdivided into 2 layers - upper and lower layer, and upper and lower hypertrophic zone were subdivided into three layers, respectively - upper, middle and lower layer. With the aid of Image Analyzer, morphometric analysis was performed. The thickness, the numerical density of cells, the cell area density, the extracellular matrix area density, the mean area of single cell, the mean area of extracellular matrix per single cell were measured and analysed. Results: In the experimental group, the thickness of the fibrous zone was slightly increased and that of the proliferating zone and the upper and the lower hypertrophic zone was markedly decreased. With time, the thickness of the fibrous zone was gradually increased and that of the proliferating zone and the upper and the lower hypertrophic zone was steadily in the decreased state. The numerical density of cells of the proliferating zone was increased on post-irradiated 1 day, but decreased after post-irradiated 4 day, and that of the upper hypertrophic zone was decreased. The numerical density of cells of the lower hypertrophic zone was decreased in the early stage and then was decreased or not significantly different from that of the control group with time. In the experimental group, the cell area density of the fibrous zone and the proliferating zone was decreased in the early stage and then gradually increased or not significantly different from that of the control group with time. The cell area density of the upper and the lower hypertrophic zone was varied with time. The extracellular matrix area density value were totally opposite to the cell area density values: The mean area of single cell of the fibrous zone and the proliferating zone was .decreased on post-irradiated 1 day, and increased after post-irradiated 4 day. The mean area of single cell of the upper hypertrophic zone was varied with each layer and time. In the experimental group, the mean area of extracellular matrix per single cell of the fibrous zone was not significantly different with control group, and that of the proliferating zone was decreased on post-irradiated 1 day, and increased after post-irradiated 4 day. The mean area of extracellular matrix per single cell of the lower hypertrophic zone was increased in the early stage. and that of upper hypertrophic zone was varied with each layer and time. Conclusion: The condylar cartilages of rats were affected by irradiation, but the changes were vaned with each layer and time. By morphometric analysis. the changes of the cells of the condylar cartilage of irradiated rat could be calculated quantitatively.

• Korean Journal of Agricultural Science
• /
• v.13 no.1
• /
• pp.82-89
• /
• 1986

This experiment was carried out to determine the optimum freezing and thawing rates of the hamster embryos. The female hamsters were induced to superovulate by intraperitoneal injections of 30 i.u. PMSG and mated with males of the same strain of 4 days the PMSG injection. They were killed and embryos were flushed from the oviduct and uterine horn on 3 days after mating. Embryos were flushed with a modified Dulbecco's phosphate-buffered saline and equilibrated with 1.5 M-dimethylsulphoxide by a 3-step procedure. The freezing rates of the samples were $1^{\circ}C/min$ from room temperature to $-6^{\circ}C$ and the samples were seeded at $-6^{\circ}C$. After being held for 3 min at the seeding temperature, the rates were $0.3^{\circ}C/min$ from $-6^{\circ}C$ to $-35^{\circ}C$. From $-35^{\circ}C$ to $-70^{\circ}C$, the rates were divided into $0.1^{\circ}C/min$, $1^{\circ}C/min$ and $10^{\circ}C/min$, respectively. At $-70^{\circ}C$ the samples were plunged directly into liquid nitrogen. The samples were thawed at $4^{\circ}C/min$ and $12^{\circ}C/min$ from $-196^{\circ}C$ to $37^{\circ}C$, and for 2 min in $37^{\circ}C$ water bath, respectively. The average numbers of ovulation points and embryos recovered were 35.1 and 27.0 appearing 77.0% recovery rates. Eight cell embryos in the embryos recovered were 24.8. The survival rates of embryos according to the freezing rates were 55.5~67.7% at $0.1^{\circ}C/min$, 58.8~64.9% at $1^{\circ}C/min$ and 40.5~44.7% at $10^{\circ}C/min$, respectively. The survival rates at $10^{\circ}C/min$ were significantly low. The survival rates of embryos according to the thawing rates were 53.5% at $4^{\circ}C/min$, 53.7% at $12^{\circ}C/min$ and 59.1% in $37^{\circ}C$ water bath. The survival rates, in $37^{\circ}C$ water bath were slightly higher, but we did not find any differences among them. In conclusion, the best freezing rates of hamster embryos were $1^{\circ}C/min$ from the room temperature to $-6^{\circ}C/min$, $0.3^{\circ}C/min$ from $-6^{\circ}C/min$ to $-35^{\circ}C$ and $-0.1^{\circ}C/min$ or $1^{\circ}C/min$ from $-35^{\circ}C$ to $-70^{\circ}C$. The hamster embryos thawed for 2 min in $37^{\circ}C$ water bath showed the best survival rates.