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141.
Al2O3/TiB2/SiCw三元复合材料的力学性能及显微结构 总被引:3,自引:0,他引:3
以Al2O3为基体,SiC晶须和TiB2颗粒两种增韧剂,采用热压烧结工艺制备了Al2O3/TiB2/SiCw三元复合陶瓷材料。研究了热压工艺参数对材料致密度的影响和晶须含量对该复合材料的力学性能和显微结构的影响。结果表明;随晶须含量的增加,该复合材料的热压温度和保温时间需要相应的增加;晶须拔出、裂纹偏转和晶须的桥接为该复合材料的主要增韧机理;随晶须含量的增加,该材料的室温断裂韧性增加;该材料的断裂韧性随温度的升高而呈增大趋势,并且晶须含量越高,材料的高温断裂韧性增幅越大。 相似文献
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针对我国建设领域招投标活动实施过程中存在的突出问题进行了初步的分析 ,并提出了一些应对措施 相似文献
143.
AI Gurevich RS Esipov TA Kachalina AL Kaiushin MD Korosteleva 《Canadian Metallurgical Quarterly》1997,23(11):888-894
The addition of vertebral disc degeneration to the job-related disease register raises the question of vertebral disc degeneration patterns according to loading strain. The readings of the lumbar vertebra of construction workers and nurses were compared with those of a group without workload. In the groups examined, aged 35 to 50, monosegmental damage was found in only 17% of the patients with high workload, as opposed to 29% of those with no workload, mostly with monosegmental damage at level L5/S1. Damage to the upper segments of the lumbar spine with intact discs in between was found exclusively in patients with high workload. Multiple segment damage in the age range examined was found in subjects with activities that add to the load of the spinal column. The value of MRI in assessing and evaluating illness originating from the vertebral discs is currently being discussed. 相似文献
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企业信息化递进发展模型及其水平指数 总被引:2,自引:0,他引:2
对企业信息化的发展阶段进行划分 ,提出了企业信息化递进发展模式 建立了企业信息化水平指数及测算方法 ,给出了实际应用案例 相似文献
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We have made reasonably comprehensive measurements of action potential activity in the Aplysia californica abdominal ganglion to determine the amount of feedback the central nervous system (CNS) receives from a movement which it initiates. Voltage-sensitive dye measurements of action potential activity of cells in the ganglion were made during the gill-withdrawal reflex elicited by siphon stimulation. We compared recordings in two situations which differed dramatically in the amount the gill moved. In the control sea water, the gill withdrawal was normal; in low-Ca2+, high-Mg2+ sea water, the gill movement was blocked. Both the timing and the number of spikes of the individual neurons were similar in the two situations. Histograms of the summed spike activity versus time and histograms of the number of active neurons versus time in the two conditions were also similar. Finally, two numerical measures of trial-to-trial differences, a paired t-test and a measure we named fractional similarity, did not indicate larger differences between two trials in the different sea waters than two trials in the same sea water. Feedback from sensory neurons activated by the gill movement itself does not make a large contribution to the spike activity in the abdominal ganglion. Apparently the Aplysia CNS issues the command for the withdrawal and does not make adjustments for the magnitude of the actual withdrawal. It may not even receive the information necessary for such adjustments to be made. A second motivation for these experiments was to test whether removing the feedback might simplify the neuronal activity that occurs during the gill-withdrawal reflex. This did not occur. 相似文献