Experimental study on temperature stress calculation and temperature control optimization of concrete based on early age parameters

Temperature control curve is the key to achieving temperature control and crack prevention of high concrete dam during construction,and its rationality depends on the accurate measurement of temperature stress.With the simulation testing machine for the temperature stress,in the present study,we carried out the deformation process tests of concrete under three temperature curves：convex,straight and concave.Besides,we not only measured the early-age elastic modulus,creep parameters and stress process,but also proposed the preferred type.The results show that at early age,higher temperature always leads to greater elastic modulus and smaller creep.However,the traditional indoor experiments have underestimated the elastic modulus and creep development at early age,which makes the calculated value of temperature stress too small,thus increasing the cracking risk.In this study,the stress values of the three curves calculated based on the strain and early-age parameters are in good agreement with the temperature stress measured by the temperature stress testing machine,which verifies the method accuracy.When the temperature changes along the concave curve,the law of stress development is in consistent with that of strength.Under this condition,the stress fluctuation is small and the crack prevention safety of the concave type is higher,so the concave type is better.The test results provide a reliable basis and support for temperature control curve design and optimization of concrete dams.     

多视无人机影像环形拼接算法

由于多视无人机影像拼接时误差的传播和累计经常导致拼接图扭曲偏斜或者拼接的失败.针对这个问题提出了构建拼接环并以多级拼接作为辅助的拼接策略.首先将待拼接图像分为多组,每组中以环形方式进行拼接,然后利用SIFT进行匹配,RANSAC实现误匹配的去除,而后计算透视变换关系,最后通过平差方程将误差削弱.通过实拍无人机影像进行的拼接实验表明该方式可以有效减少累计误差的影响,提高拼接精度.该方法的提出可以作为影像拼接消除累计误差的有效方式之一.     

Influence of static pre-loading on the dynamic bending strength of concrete with particle element modeling

Experimental tests show that static pre-loading has a significant effect on the dynamic strength of concrete.Based on meso-scale particle element model,numerical simulations of dynamic bending tests with pre-loading are performed.Complete stress–strain relationships are then obtained.Significant increase in dynamic strength is found when the pre-loadings are imposed within the elastic limit of concrete.However,when the imposition of pre-loadings reaches the plastic or softening range,dynamic strengths may gradually decrease along with the increase in pre-loadings.The distribution of energy components and the failure modes are discussed to explain the mechanisms of the phenomena.     

本科生导师制激励问题研究

运用博弈论的分析方法解释本科生导师制在推行过程中遇到的激励问题。通过构建一个非对称信息的静态模型,发现导师指导学生的努力程度将取决于学校的惩罚力度、考核成本以及该制度给学校带来的收益,而学校对教师指导情况的考核概率则主要受到其制定的奖惩规则和教师科研水平的影响。     

冶炼不锈钢泡沫渣的实验研究

从理论上阐述冶炼不锈钢时熔渣的发泡机理。并根据上海三钢公司的情况，在2500Hz的中频感应炉上时熔渣进行发泡高度的实验，找出发泡性能较好的渣系，研究渣中各成分对发泡性能的影响。     

大型饼类锻件锻造工艺研究综述

综述了饼类锻件锻造工艺的发展。大型饼类锻件是重型装备的核心部件之一,需要在液压机上进行自由锻造,由于其高径比远远小于1,实际生产中,废品率高,生产难度大,最严重的便是层状裂纹问题。为了克服这一问题,人们对饼类锻件进行了解剖检验,提出了压窝成形法、锥形板镦粗法等各种锻造工艺。     

表面氧化层对TiMn1.25Cr0.25储氢合金活化性能的影响

通过TiMn1.25Cr0.25合金粉活化前在空气中暴露不同的时间,探讨了表面氧化层的形成对其活化性能的影响。活化测试结果表明：合金的活化难度随着合金在空气中暴露时间的延长而加大。俄歇电子能谱(AES)结果表明,在空气中暴露后的合金表面形成了一层大约6nm-10nm厚的表面氧化层,正是这层氧化层的形成加大了合金的活化难度。扫描电镜(SEM)结果表明合金的活化过程与合金的碎化有着密切的联系。     

激光快速成形Rene′88DT高温合金的时效强化研究

研究了时效时间对激光快速成形后时效硬化镍基高温合金Rene′88DT中沉淀相组织演化和力学性能的影响。发现随时效时间的增加，沉淀相y’略有长大，颗粒之间发生大颗粒吞噬小颗粒的粗化，时效40h后沉淀相颗粒粗化明显。对经不同时间时效后的激光快速成形Rene′88DT试样进行了硬度测试。结果显示，在时效时间为28h时，硬度有一峰值HRC49。在此基础上，采用1165℃，2h固溶、空冷＋760℃，28h时效的热处理工艺对激光快速成形标准拉伸棒样进行了热处理，拉伸结果显示成形件的抗拉强度较激光沉积态提高了400MPa，屈服强度接近同种材料的粉末锻造水平。     

Redundancy filtering and fusion verification for video copy detection

Multimedia Systems - Recently, the frame fusion based video copy detection scheme provides a possibility to detect copies in a continuous query video stream. However, its computational complexity...