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31.
采用大变形弹塑性有限元理论,用DYNA3D(研究版)有限元软件,对无缝钢管局部径向模具塑性成形过程中当凸模的凹槽尺寸与凸模的圆弧半径发生变化时进行了数值模拟研究,得出了对成形钢管表面质量控制具有重要参考价值的结论,解决了成形钢管表面的压痕问题。 相似文献
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H. Cuckle N. Wald J. D. Stevenson H. M. May M. A. Ferguson-Smith A. Milford Ward H. M. Barbour K. M. Laurence B. Norgaard-Pedersen 《黑龙江环境通报》1990,10(2):71-77
Data on maternal serum alpha-fetoprotein (AFP) levels at 13–24 weeks' gestation in 46 twin pregnancies with open neural tube defects (22 with anencephaly, 24 with open spina bifida) and 169 unaffected twins were used to estimate the detection and false-positive rates associated with different cut-off levels. Using the conventional cut-off level of 2·5 multiples of the median (MoM) for unaffected singleton pregnancies of the same gestation and laboratory, the detection rate in twins was 99 per cent for anencephaly and 89 per cent for open spina bifida, with a false-positive rate of 30 per cent. Using a 5·0 MoM cut-off level to maintain a similar false-positive rate to that found among singleton pregnancies at 16–18 weeks' gestation (about 3 per cent), the detection rate was 83 per cent for anencephaly and 39 per cent for open spina bifida. Estimates are provided of the odds of having an affected twin pregnancy given a positive AFP result as well as the odds for individual women with a raised AFP level. 相似文献
35.
Iniencephaly is an uncommon, but not rare, lesion involving a fusion between the posterior occipital bone and the cervical spine. Many cases are associated with other cranio-cervical abnormalities and anencephaly, and most are associated with other structural abnormalities. The prognosis is thought to be dismal. We describe a male infant, one of twins, who was diagnosed prenatally as having iniencephaly. The child was born without complication and has grown and thrived. This is the fourth patient with long-term survival with iniencephaly. We recommend that non-directive counselling be applied when presenting the findings of iniencephaly to parents. 相似文献
36.
The outcome of the pregnancy following (a) a mid-trimester termination of pregnancy (TOP) for fetal neural tube defect (NTD) (77 women=group 1); (b) mid-trimester TOP for fetal Down's syndrome (13 women=group 2); (c) delivery of a baby with NTD (119 women=group 3) was studied. The prenatal fetal loss was relatively high in all groups. In group 1 it was similar to that found in other studies after first trimester TOP, in group 2 it was associated with advanced maternal age and the unexpected finding in group 3 was not attributable to advanced maternal age. It is suggested that a previous NTD per se might increase the risk of fetal loss in the next pregnancy. A previous mid-trimester TOP for NTD was not associated with an increase in premature labour, small for dates babies or congenital abnormality in the next pregnancy, but there was a slight increase in the number of babies weighing less than 2500 g. 相似文献
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J. G. Hooker M. Lucas B. A. Richards I. M. Shirley B. D. Thompson R. H. T. Ward 《黑龙江环境通报》1984,4(1):29-33
Estimation of maternal serum alpha-fetoprotein (AFP) was used as a screening method for the detection of neural tube defects (NTDs) in 6344 women over three years. Of 88 (1.4 per cent) who had one or more serum AFP levels equal to, or greater than, 2.5 multiples of the median (MoM) for the relevant gestational age, 43 (0.68 per cent) underwent amniocentesis. There were eight NTDs. Four of these were screened by serum AFP, and all cases of spina bifida had serum AFP levels greater than 3.0 MoM, including one small open defect which was not seen on ultrasound. The other four cases of NTD, which were not screened, were identified by ultrasound. Of 64 singleton pregnancies 32 (50 per cent) had serum AFP levels between 2.5 and 3.0 MoM, and low birthweight (⪕2500 g) occurred in 29 per cent. Because of improvements in ultrasound techniques and the apparent falling incidence of NTD, the role of serum AFP as the primary screening procedure should be regularly reviewed. Effective screening is dependent on mothers booking early. 相似文献
38.
Howard S. Cuckle 《黑龙江环境通报》1983,3(4):287-289
Data from 280 sibships in three published series were used to see if the increased risk of neural tube defect (NTD) associated with having had a miscarriage in the immediately preceding pregnancy was also found in women with a previous affected pregnancy. A statistically significant relative risk of 4.0 (2-tail P=0.0111, Fisher exact test) was found among such women, and this could not be accounted for by the effect of parity or of a history of miscarriage in general. The finding may be useful when counselling patients. 相似文献
39.
一种预测左半部成形极限图的简单方法 总被引:1,自引:0,他引:1
板材成形性能的评价一般基于成形极限图(FLD)。然而,无论是经由理论计算还是实验方法来获得成形极限图依然很困难而且很耗时。提出了一种预测深拉延部分成形极限图的新方法。假设对所有钢板来说其成形极限图的形状几乎都是一样的,而深拉延变形区域内其失效厚度应变也几乎一样,据此可利用体积不变原理推导出主应变和次应变之间的关系。结果表明,根据此方法计算的左半侧(拉深应变区)成形极限图与实验获得的FLD基本一致。 相似文献
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