• 한국분말재료학회지
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• 제24권3호
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• pp.202-209
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• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

• 한국패류학회지
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• 제32권1호
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• pp.37-43
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• 2016

This study was carried out to determine the optimal water temperature for the embryonic development and laboratory culture of larvae of an intertidal mud snail, Nassarius festivus. The embryos and hatched veliger larvae of N. festivus were incubated at six different temperatures (5, 10, 15, 20, 25 and $30^{\circ}C$). Developmental time for each stage decreased as water temperature increased. The elapsed time to develop to the veliger larva at 15, 20, 25 and $30^{\circ}C$ was 559, 155, 131 and 103 hrs, respectively. At 5 and $10^{\circ}C$, embryo developed to veliger larvae but failed to hatch out of the egg capsule. In contrast, all embryos successfully hatched in the temperature range from 15 to $30^{\circ}C$. The biological minimum temperature during the embryonic development of N. festivus was estimated to be $9.5{\pm}0.4^{\circ}C$. The cumulative water temperatures for blastula, gastrula and veliger stages were calculated as $111{\pm}84$, $486{\pm}185$, $1,164{\pm}72^{\circ}C$, respectively. Temperature also affected the larval survival. Five days after hatching, more than 84% of larvae survived at all experimental temperatures. However, survival began to decrease after 6 days. It was 0% at $30^{\circ}C$. Survival of larvae incubated for 8 days was higher at 15 and $20^{\circ}C$ than other experimental temperatures. We therefore suggest that the optimal range of temperature for embryonic development and larval survival of N. festivus is $15-20^{\circ}C$.

• Asian-Australasian Journal of Animal Sciences
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• 제3권2호
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• pp.121-123
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• 1990

A CRD experiment with unequal numbers of hens were assigned at random to three treatment groups, 1) separation of chicks from hen at 21 days after hatching 2) separation of chicks from hen at 7 days and 3) hens were allowed to brood the chicks(no separation) up to 10 weeks of age, to determine the productive and reproductive performance of hens and their chicks. The mean cycle length (one hatch to another) was 72.8 days for the 7-day group as compared with 87.7 days and 83.4 days for the 21-day and the no separation groups, respectively (p<.0l). The broody period was 28.5 days for the 7-day group compared with 43.9 and 42.6 days for the 21 days and the no separation groups, respectively (p<.0l). The end of the broody period to the start of lay varied from 8.0 to 8.7 days. The number of eggs laid per clutch were 12.3 for the 21-day group, compared with 11.5 and 10.1 for the 7-day and no separation groups, respectively (p<.05). This is due to the longer (p<.05) clutch length of the 21-day group as compared with the 7-day and no separation groups, respectively. The chicks separated from the hens at 21 and 7 days were heavier (p<.01) than the chicks not separated from the hens. Mortalities were highest (p<.05) for chicks separated at 7 days as compared with chicks separated at 21 days and those not separated. We concluded that separating chicks at 7 days from the hen gave the shortest cycle length and broody period, separating the chicks at 21 days gave the longest clutch length and the maximum number of eggs, separating the chicks at 21 and 7 days resulted in heavier chicks and separating the chicks at 7 days resulted in the highest mortality.

• Asian-Australasian Journal of Animal Sciences
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• 제25권7호
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• pp.1009-1014
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• 2012

Environmental stress boosts the levels of stress hormones and accelerates energy expenditure which subsequently imbalance the body's homeostasis. L-ascorbic acid (L-AA) has been recognized to mitigate the negative impact of environmental stress on production performances in birds. The present investigation was carried out to elucidate the effect of different dietary levels of L-AA on production performance, egg quality traits and fertility in Japanese quail at low ambient temperature. Sixty matured females (15 wks) were equally divided into three groups (20/group) based on the different dietary levels of L-AA (0, 250 and 500 ppm) and coupled with an equal number of males (1:1) obtained from the same hatch. They were managed in uniform husbandry conditions without restriction of feed and water at 14 h photo-schedule. Except for feed efficiency, body weight change, feed consumption and hen-day egg production were recorded highest in 500 ppm L-AA supplemented groups. Among the all egg quality traits studied, only specific gravity, shell weight and thickness differed significantly (p<0.05) in the present study. Fertility was improved significantly ($p{\leq}0.01$) to a dose dependent manner of L-AA. The findings of the present study concluded that dietary L-AA can be a caring management practice at least in part to alleviate the adverse effect of cold induced stress on production performance in Japanese quail.

• Journal of Microbiology and Biotechnology
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• 제12권6호
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• pp.865-871
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• 2002

A bacterium having strong chitinolytic activity on $0.2\%$ colloidal chitin-containing agar medium was isolated from coastal soil in Korea. Based on the nucleotide sequence of conserved segment of a 165 rRNA gene, the bacterium was identified as Paenibacillus illinoisensis KJA-424. The population of P. illinoisensis KJA-424 and chitinase activity significantly increased for the first 2 days of incubation. On SDS-PACE analysis with $0.01\%$ glycol chitin, three protein bands (63, 54, and 38 kDa) with chitinolytic activity were detected tooted. The effect of P illinoisensis KJA-424 on the egg hatch of root-knot nematode (Meloidogyne incognita) was investigated. After 7 days of incubation with the chitinase-producing P. illinoisensis KJA-424, none of the eggs hatched, whereas a $39.8\%$ egg hatching rate was observed in the water control. Inverted and scanning electron microscopic observations demonstrated that P. illinoisensis KJA-424 deformed and destroyed the eggshell of M. incognita. In conclusion, chitinase-produced by p. illinoisensis KJA-424 caused the lysis of M. incognita eggshell and resulted in the inhibition of egg hatching in vitro.

• 한국응용과학기술학회지
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• 제19권1호
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• pp.25-32
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• 2002

Two PU flame-retardant coatings, 2,3-DBPO/N-l00 (DBPON) and 2,3-DBPO/IL (DBPOI), were prepared by curing 2,3-dibromo modified polyester (2,3-DBPO) with isocyanate curing agent Desmodur N-l00 (or Desmodur IL) at room temperature. The physical properties and flame-retardancy of the two coatings were tested and compared. As a result, the pot-life, yellowness index, lightness index difference, $60^{\circ}$ specular gloss, cross-hatch adhesion, viscosity, and accelerated weathering resistance of DBPON were better than those of DBPOI; the fineness of grind of the two coatings were the same; and the drying time, hardness, and abrasion resistance of DBPOI were better than those of DBPON. The flame retardancy of the flame-retardant coatings increased with the content of the flame retarding component, 2,3-dibromopropanoic acid (2,3-DBP); and the LOI values of the two coatings were in a range of $27{\sim}29%$ when the content of 2,3-DBP was 30wt%.

• 한국응용과학기술학회지
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• 제24권2호
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• pp.149-159
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• 2007

In order to prepare high-solid coatings, acrylic resins, HSCs [poly (EA/EMA/2-HEMA/CLA)] that contain 90% solid, were synthesized by copolymerization of ethyl acrylate (EA), ethyl methacrylate (EMA), 2-hydroxyethyl methacrylate (2-HEMA) and caprolactone acrylate (CLA). The high-solid coatings named as CHSCs (HSCs/HDI-trimer) were prepared by the curing reaction between the acrylic resins containing 90% solid contents and the isocyanates (HDI-trimer) curing agent room temperature. The curing behavior and various properties were examined on the film coated with the both high-solid coatings. The glass transition temperatures $(T_g)$ of CHSCs increased proportionally with increasing the predicted $T_g$ value by Fox equation, and had nothing to do with the solid contents. The prepared film showed good properties for $60^{\circ}$ specular gloss, impact resistance, cross-hatch adhesion and heat resistance, and bad properties for pencil hardness, drying time, and pot-life. Among the film properties, the heat resistance was very excellent and could be explained by the introduction of functional monomers of CLA.

• 한국수산과학회지
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• 제48권5호
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• pp.696-703
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• 2015

We investigated the characteristics of embryonic and abnormal organ development in haploid olive flounder, Paralichthys olivaceus, by comparing egg development and histological sections in haploid and diploid individuals. After the mid-blastula transition, abnormal development was observed in haploid fish, including delayed epiboly and malformation of the germ ring and embryonic body. In haploid flounder, Kupffer’s vesicles are irregularly shaped and of variable size compared to diploids. The embryonic body of haploids was shorter and broader than that of diploids and the tail length and size were variable. Most haploid embryos failed to hatch and the few larvae that did, did not survive for more than 6 h. The histological analysis of haploid larvae revealed deformed development in diverse organs, including the eye, otic vesicles, notochord, and neural tube. These results may be related to an abnormality in the axial system of haploid larvae. This study confirmed that the abnormalities of haploid olive flounder were similar to the reported characteristics of haploid syndrome. The abnormalities are caused by delayed epiboly and involution and deformity of Kupffer’s vesicle during egg development.

• 대한지리학회지
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• 제39권3호
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• pp.297-320
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• 2004

1904년 대한제국 정부에서 간행한 $\boxDr$경상남도가호안$\boxUl$은 총 31개군 가운데 11개군의 자료가 현전하는데, 이 자료는 당시 이 지방의 민가에 대한 상세한 정보를 담고 있다. 이 논문은 제1차자료인 가호안의 분석을 통하여 동ㆍ면ㆍ군별 가좌의 토지등급ㆍ가옥의 규모, 가좌와 가옥의 소유관계, 초ㆍ와가의 분포 등을 파악한 연구이다. 가호안의 분석결과 전체 가호의 약 20%는 사유지 또는 국공유지를 임대한 가좌에 지어졌다. 또한 가옥의 90%는 방 한칸 또는 두칸에 부엌이 딸린 집이었으므로 지역의 가옥규모는 2.75칸에 불과하였다. 다시 말하면 100년전 경상남도의 가옥규모는 조선시대의 이상 가옥형인 삼간초옥에도 못미쳤던 것이다. 이러한 열악한 주거조건 때문에 1인당 점유공간이 2-4평방미터에 불과하며 결과적으로 수용가능한 가족의 수도 4인 내외로 한정되었다.

• 한국어류학회지
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• 제24권2호
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• pp.101-109
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• 2012

중국으로부터 유입되어 일본의 이바라키현에서 정착한 큰납지리 Acheilognathus macropterus의 난발생과 자치어의 특성에 대해 관찰하였다. 담황색 수정란의 장타원형으로 난경은 장경이 2.68~2.86 mm (평균 $2.78{\pm}0.12mm$, n=40), 단경이 1.42~1.49mm(평균 $1.44{\pm}0.04mm$, n=40)였다. 암컷의 개체 당 채란된 알의 수는 124~180개 (평균 151개)였다. 수정란은 수온 $20{\pm}1.0^{\circ}C$에서 수정 후 78시간 만에 부화하였다. 부화 직후 자어의 크기는 3.8mm이고, 3일째부터는 S자 모양의 빠른 움직임을 보였다. 부화 후 25일 경에 소화기관이 완성되어 먹이를 먹기 시작하고 부출기에 이르렀다. 한국산 큰납지리와 외부형태나 미토콘드리아 cytochrome oxidase I (COI) 유전자의 차이는 크지 않았으나 수정란의 형태가 두 집단 간 뚜렷이 구별되어 분류학적인 논의가 필요하다.