• Transactions of Materials Processing
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• v.19 no.7
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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.

• Journal of Veterinary Clinics
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• v.29 no.1
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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.

• Korean Journal of Metals and Materials
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• v.48 no.4
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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.

• Korean Journal of Materials Research
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• v.27 no.12
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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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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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.

• Transactions of Materials Processing
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• v.16 no.6
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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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• v.18 no.12
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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.

• Journal of the korean veterinary medical association
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• v.39 no.11
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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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• v.48 no.7
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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.

• Journal of Embryo Transfer
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• v.21 no.4
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• pp.299-306
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• 2006

This study examined the effects of the in vitro produced (IVP) Hanwoo blastocyst stage (blastocyst, expanded blastocyst and hatched blastocyst), in vitro culture day (7, 8, and 9) and blastocyst grade (1, 2 and 3) on the pregnancy rate, gestation length, birth weight, the incidence of dystocia and twining rate after embryo transfer (ET). The pregnancy and abortion rates were significantly higher in the blastocyst (B) stage (64.4%) and in the hatched blastocyst (HB) stage (21.4%), respectively, than in those of the other developmental stages (p<0.05). The pregnancy rate of Day 7 embryos (49.0%) was significantly higher than those of Days 8 and 9 embryos (36.4 and 15.4%), but the abortion rates were similar (0 to 10.7%). There were no significant differences in the pregnancy (41.4 to 42.5%) and abortion (9.3 to 16.5%) rates among the three grades of embryos. There were no significant differences in gestation length, birth weight and the incidence of dystocia among the three development stages, but the twinning rate was significantly higher in the HB stage (p<0.05). The pregnancy rate, the incidence rate of dystocia and twinning rate were similar among the three different culture days, however birth weight was significantly heavier in calves from Day 9 embryos than in those from Days 7 and 8 embryos. The mean gestation length of grades 1 and 2 embryos (278.5 and 276.1 days) were significantly longer than that of grade 3 (p<0.05), but birth weight, the incidence of dystocia and twinning rate did not significantly differ. The mean gestation length in single calves was significantly longer than that in twin calves (278.5 vs. 272.5 days, p<0.05). In addition, the mean birth weight in single calves was significantly greater than that in twin calves (29.6 vs. 22.3 kg, p<0.05). Finally, the sex ratios and mean mortality rates between single and twin calves were similar.