• 소성∙가공
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• 제19권7호
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• pp.416-422
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• 2010

The $\{10\bar{1}2\}$ twinning characteristics, such as active twin variants, volume fraction of twins with strain, twin morphology, twin texture and angle relationship between twins, were dependent on the activation mode (i.e., tension parallel to the caxis or compression perpendicular to the c-axis). The selection criterion of active twin variants was governed by the Schmid law. This activation of selected twin variants depending on the activation mode consequently caused a totally different plastic deformation behavior in two activation modes. The differences in the deformation characteristics, such as flow stress and work hardening rate, between both activation modes were explained in relation with activation stresses for slips and twinning, relative activities of twinning and slips during plastic deformation, grain refining effect by twin boundaries (Hall-Petch effect), and twinning-induced change in activities of slips.

• 한국임상수의학회지
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• 제29권1호
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• pp.33-37
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• 2012

This study was performed to evaluate the rate of twin pregnancy and parturition in dairy cows. Calving records of Holstein dairy cows from 1998 to 2009 comprising Goyang and Paju cities herd with 20,990 calving events representing 820 twin births were used to evaluate twinning rate, calf sex ratio, periods of pregnancy and complication after parturition in single and twin births. Overall, the reported twinning rate was 3.9% in Holstein dairy cows. Rate of bicornual pregnancy (75%) was larger than that of unicornual pregnancy (25%) among cows having twin. Regardless of parity, the greatest twinning rate was observed in fall season from September to November. Calf sex ratios (male, M; female, F) were 48.0% FM, 28.9% MM, 21.5% FF and 0.9% mummifications for twin calves. Parturition type among cows having twins included normal (4.7%), premature (66.9%), delayed (9.2%), abortion (18.4%) and mummification (0.8%). The period of pregnancy in twin pregnancy (mean 272.6 days) was shorter than single pregnancy (mean 278.1 days). The retained placenta after parturition was over fourth times such as twin parturition (34.8%) higher than single parturition (8.5%) and the abomasal displacement was over two times such as twin parturition (10.2%) higher than single parturition (4.9%). The distribution of twin pregnancy with parities was high rate during the 2~3 parities. The prevalence of complication such as retained placenta and abomasal displacement with twin parturition revealed higher than single parturition.

• 대한금속재료학회지
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• 제48권4호
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• pp.305-314
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• 2010

The development of textures and microstructures during plastic deformation in a hot-extruded AZ 31 Mg alloy was investigated using a compression test with such parameters as deformation temperature, strain rate. It was observed from true stress-strain curves that twinning involves changes of the flow stresses. In the early stages of deformation at temperatures lower than $200^{\circ}C$, the occurrence of twins resulted in a decrease of the work-hardening rate, which increased drastically at a true strain of -0.05. The evolution of the deformation textures were assessed with the aid of EBSD analyses in terms of the competition between twinning and slip activity.

• 한국재료학회지
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• 제27권12호
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• pp.643-651
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• 2017

Four types of high Mn TWIP(Twinning Induced Plasticity) steels were fabricated by varying the Mn and Al content, and the tensile properties were measured at various strain rates and temperatures. An examination of the tensile properties at room temperature revealed an increase in strength with increasing strain rate because mobile dislocations interacted rapidly with the dislocations in localized regions, whereas elongation and the number of serrations decreased. The strength decreased with increasing temperature, whereas the elongation increased. A martensitic transformation occurred in the 18Mn, 22Mn and 18Mn1.6Al steels tested at $-196^{\circ}C$ due to a decrease in the stacking fault energies with decreasing temperature. An examination of the tensile properties at $-196^{\circ}C$ showed that the strength of the non-Al added high Mn TWIP steels was high, whereas the elongation was low because of the martensitic transformation and brittle fracture mode. Although a martensitic transformation did not occur in the 18Mn1.9Al steel, the strength increased with decreasing temperature because many twins formed in the early stages of the tensile test and interacted rapidly with the dislocations.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.114-117
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• 2007

In the present study, the effects of initial texture on the twinning formation of AZ31 Mg rolled sheet was investigated. Uniaxial compression tests were performed on samples cut along the normal direction and rolling direction of rolled AZ31 Mg alloy sheet at various temperatures (RT, 200, 250, 300, 350, $400^{\circ}C$) with the 0.01/s strain rate. Pole figure of rolling planes showed that basal planes of most gain were located parallel to the rolling direction. After compression test, microstructures and stress-strain curves results indicated that active deformation twining occurred only at the specimen cut along the rolling direction. The slip-twin transition with the increase of temperature was also investigated.

• 소성∙가공
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• 제16권6호
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• pp.467-472
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• 2007

In this study, the effects of initial texture on the twinning formation of AZ31 Mg rolled sheet was investigated. Uniaxial compression tests were carried out on samples cut along the normal direction(ND) and roiling direction(RD), respectively, of rolled AZ31 Mg alloy sheet at various temperatures (RT, 200, 250, 300, 350, $400^{\circ}C$) with the fixed strain rate($10^{-2}/s$). The results showed that deformation twining occurred actively only in the RD specimens, which promoted homogeneous deformation as compared to the ND specimens. The effect of temperature on the formation of deformation twins was also investigated, and the slip/twin transition temperature was found to be approximately $250^{\circ}C$.

• Asian-Australasian Journal of Animal Sciences
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• 제18권12호
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• pp.1735-1740
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• 2005

Forty-two single-bearing and 42 twin-bearing mature Angus${\times}$Hereford cows were allocated, seven per cell to 3 replications of 2 stocking rates (3.2 cows/ha; medium stocking rate [MSR], and 3.8 cows/ha; high stocking rate [HSR]) to graze summer-active and winter-active pastures from late pregnancy to the weaning of their calves. Cow liveweights and growth of calves were recorded as well as estimates of pasture quantity and forage intake. Pasture quantity did not differ in the paddocks grazed by single- and twin-bearing cows during pregnancy, nor effectively did forage intake. Subsequently, intake was higher during mid-lactation especially with twin-rearing cows (25% higher than single-rearing cows at the MSR; 9% at the HSR). However, quantity of pasture decreased for twin-rearing cows and was less than that available to single-rearing cows as lactation progressed. Liveweights of twinrearing cows decreased by 16% from late pregnancy to weaning at the MSR, and by 14% at the HSR, compared to decreases of 1% for single-rearing cows. Twin calves were lighter at birth, had slower growth rates, and were lighter at weaning than single calves. In spite of weaning smaller calves twinning increased the output (kg of calf weaned) per cow and per ha, and increased the efficiency (kg calf weaned per unit of forage eaten by the cow) over single calf production by 46% at the MSR and by 58% at the HSR. Twinning also increased the marginal returns from investment in high input pastures required by the enterprise.

• 대한수의사회지
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• 제39권11호
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• pp.1020-1028
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• 2003

We analyzed the records that distribution of the twinning rate, sex of calves and complications of other diseases with twin pregnancy from 10,012 dairy cows for 5-year period from 70 dairy farms in Paju and Goyang cities. Twining rate was increased for 5-

• Clinical and Experimental Pediatrics
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• 제48권7호
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• pp.685-690
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• 2005

Recently, twinning rate increases in Korea since the early 1990s by delayed marriage and prevailing of assisted reproductive technology. But twin and higher-order multiples are at increased risk for perinatal and neonatal mortality over 5 fold despite of dramatic improvement of perinatal and neonatal care. Because twins are born more prematurely and have lower birth weights than singleton. In addition, twins are at increased risk for cerebral palsy mainly in monochorionic twins due to co-twin fetal death, twin to twin transfusion and congenital anomaly. So, this article reviews the factors contributing to the mortality and morbidity of the twins and the efforts to decrease the neonatal mortality of twins.

• 한국수정란이식학회지
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• 제21권4호
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• pp.299-306
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• 2006

본 연구는 수정란이식의 현장 적용 측면을 중심으로, 한우 체외 수정란의 발생 단계, 일자 및 등급이 젖소 대리모에 이식 후 임신과 유산, 분만과 관련된 임신기간, 생시체중, 난산 및 쌍자율을 조사하였다. 또한 단자 및 쌍자 분만에 따른 임신기간, 생시체중, 성비 및 폐사율을 분석하였다. 발생 단계에 따른 임신율은 배반포 단계(64.4%), 유산율은 부화 배반포(HB) 단계(21.4%)가 유의하게 높았다(p<0.05). 발생 일령에 따른 임신율은 7일령 배가 49.0%로서 8일 및 9일령의 36.4 및 15.4%보다 유의하게 높았으나(p<0.05), 유산율은 0$\sim$10.7%로 비슷한 경향이었다. 등급에 따른 임신율은 41.4$\sim$42.5%, 유산율은 9.3$\sim$16.5%로서 차이가 없었다. 발생 단계에 따른 임신기간, 송아지의 체중 및 난산율은 비슷한 경향이었으나, 쌍자율은 HB 단계가 44%로서 배반포 단계의 15.8%보다 유의하게 높았다(p<0.05). 발생 일령에 따른 임신 기간, 난산율 및 쌍자율은 차이가 없었으나, 송아지의 체중은 9일령의 것이 평균 35.5 kg으로서 7일령 및 8일령의 평균 25.2 및 26.2kg보다 유의하게 무거웠다(p<0.05). 등급에 따른 임신 기간은 1등 및 2등급이 평균 278.5 및 276.1일로서 3등급의 평균 273.7일에 비하여 유의하게 길었으나(p<0.05), 체중, 난산율 및 쌍자율은 차이가 없었다. 분만한 송아지의 개체 수에 따른 임신기간은 단자가 평균 278.5일로서 쌍자의 평균 272.5일보다 유의하게 길었다(p<0.05). 생시 체중도 단자가 평균 29.6 kg으로서 쌍자의 평균 22.3kg에 비하여 유의하게 무거웠으나(p<0.05), 성비와 폐사율은 유사한 경향이었다.