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Strengthening and toughening mechanisms in composite ceramics is complex. A change in a single parameter induces multiple property variations. The multiple changes in properties are often incompletely represented in theoretical models. This incompleteness in the parameter chosen fails to explain the mechanism of failure in composite ceramics. The exponential toughness function is used to represent the pull-out toughening mechanism, which dominates the crack growth resistance curve(R-curve). The strengthening-toughening model is established based on the Mori-Tanaka method(M-T method). The influence of inherent defects on toughness function and strength is analyzed by using this model. The theoretical result is compared with the experiment data. This model exactly reflects the change in strength. The theoretical result indicates that defects change the toughness function. Moreover, micro-cracks increase toughness size ac, and the strength of crack instable extensions acutely decreases as defect content increases. This presented model establishes the relationship among the important mechanical parameters of defect, strength, elastic modulus, and the R-curve.- 中国机械工程学报文章来源： 万方数据
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四维超声时空关联成像纳入常规胎儿心脏筛查的可行性
目的 探讨四维超声时空关联成像技术纳入常规胎儿心脏筛查的可行性.方法 应用STIC技术获取的数据库中随机选择30例心脏结构畸形和30例心脏结构正常的胎儿作为研究对象.60例胎儿心脏经产后随访或尸解有54例获得明确诊断结果.后由4组(A、B、C、D组)不同水平的医师在不知道诊断结果的情况下对先前存盘的心脏容积数据做快速离线分析.从事产科超声检查5年及以上者定为具有产前二维超声筛查经验的高水平医师,和5年以下者定为中低水平医师;应用STIC技术1年及以上即定为STIC技术应用经验丰富.A组具有中低水平的产前二维超声筛查经验无STIC技术应用经验,B组具有中低水平产前二维超声筛查经验但有STIC技术应用经验,C组具有高水平产前二维超声筛查经验而无STIC技术应用经验,D组既有高水平产前二维超声筛查经验又有丰富的STIC技术应用经验.结果 A、B、C、D4组正确诊断率分别为:75.00%、77.78%、84.26%、87.04%;A组与B组、C组与D组、A组与C组、B组与D组比较正确诊断率均无明显差别(x2值分别为0.23、0.34、2.85、3.19,P均>0.05);A组与D组比较有差别(x2 =5.09,P<0.05).总正确诊断率为81.02% (350/432).结论 STIC技术易于掌握且对医师的专业经验依赖性小,可以纳入常规胎儿先天性心脏病的筛查中.赵艳春,吕国荣,陈秋月,刘金蓉,候敏,凌乐文,陈晓康,李丽雅 - 中国超声医学杂志文章来源： 万方数据
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