微量Sr对Mg-0.2Zn-0.1Mn-xSr医用可降解镁合金显微组织、力学性能及腐蚀性能的影响

本文主要研究在Mg-0.2Zn-0.1Mn中添加微量的Sr后,Mg-0.2Zn-0.1Mn-xSr（x=0.1、0.2、0.3）合金显微组织、力学性能及耐腐蚀性能的变化。显微组织观察结果表明随着Sr含量增加,晶粒尺寸明显降低;Mg17Sr2相在镁基体中呈颗粒状均匀弥散分布,且Mg17Sr2相体积随着Sr含量增加而长大。室温拉伸试验结果表明微量的Sr能够提高镁合金的抗拉强度和屈服强度,但延伸率却表现出下降的趋势。通过Kokubo模拟体液中的浸泡实验了解镁合金的降解行为。失重实验测得Mg-0.2Zn-0.1Mn-xSr (x=0,0.1,0.2,0.3)腐蚀速率为：6.85、6.01、6.80和7.52mm/a。微量Sr的添加能够提高镁合金的耐腐蚀性能;但随着Sr含量增加,镁合金更容易产生点蚀和晶间腐蚀,反而使镁合金耐腐蚀性能出现降低。这是因为添加微量Sr后镁合金晶粒细化,细小而弥散分布的Mg17Sr2相有助于腐蚀产物膜沉积形成对基体的保护,使得镁合金更耐蚀。而过大的Mg17Sr2相会加剧局部的微电偶腐蚀,破坏腐蚀产物膜,降低镁合金的耐腐蚀性能。结果表明Mg-0.2Zn-0.1Mn-0.1Sr具有最佳的力学性能和耐腐蚀性能配比。     

HilAnchor: Location Privacy Protection in the Presence of Users’ Preferences

Location privacy receives considerable attentions in emerging location based services.Most current practices however either ignore users’ preferences or incompletely fulfill privacy preferences.In this paper,we propose a privacy protection solution to allow users’ preferences in the fundamental query of k nearest neighbors (kNN).Particularly,users are permitted to choose privacy preferences by specifying minimum inferred region.Via Hilbert curve based transformation,the additional workload from users’ preferences is alleviated.Furthermore,this transformation reduces time-expensive region queries in 2-D space to range the ones in 1-D space.Therefore,the time efficiency,as well as communication efficiency,is greatly improved due to clustering properties of Hilbert curve.Further,details of choosing anchor points are theoretically elaborated.The empirical studies demonstrate that our implementation delivers both flexibility for users’ preferences and scalability for time and communication costs.     

Cationic porphyrin–anthraquinone dyads: Modes of interaction with G-quadruplex DNA

The interaction of a parallel, guanine quadruplex DNA with four, cationic porphyrin–anthraquinone dyads which comprise bridging linkages of differing lengths, was investigated for the first time. Using a combination of absorption and fluorescence titration, surface-enhanced Raman spectroscopy and induced circular dichroism spectroscopy as well as Job plot, it was found that the porphyrin and anthraquinone moieties in the dyads equipped with long linkages are able to bis-intercalate with the G4 structure whereas dyads that contain short linkages were unable to undergo such interaction. In addition, cationic dyads that contain long linkages are able to stabilize the quadruplex structure to a greater extent than dyads with shorter linkages.     

甜菜抗丛根病生理基础的研究之七 甜菜抗(耐)丛根病性不同的品种绿原酸和阿魏酸研究

对甜菜抗 (耐 )丛根病性不同的 6个品种的绿原酸和阿魏酸含量进行了研究 ,结果表明 ,4次取样时期中 ,4、6片真叶时绿原酸和阿魏酸含量在抗、感病品种之间有稳定一致的差异表现 ,抗病品种含量对应高于感病品种 ,且均与抗病性呈正相关 ,无病地上无稳定一致的规律。在病地上这两个时期的绿原酸和阿魏酸含量可作为品种抗病性鉴定和抗病生理选育种的参考生理指标。     

溶胶-凝胶法制备SiC前驱体

为了尽量减少硫、氯等有害元素的含量,本文用不含有害元素的草酸和六次甲基四胺（HMTA）为催化剂,正硅酸乙酯（TEOS）为硅源,酚醛树脂为碳源,成功探索出了制备SiC前驱体的两步法溶胶-凝胶工艺．第一步TEOS在草酸的催化下预水解,第二步用HMTA加速凝胶．实验得出了草酸含量、预水解时间、预水解温度等因素对凝胶形成的影响规律,进而讨论了水解和缩合的机理．所得SiC前驱体为黄色透明的玻璃态,由纳米级的颗粒组成,结构均匀而精细．     

阻抗式含水率计三相漂流模型校正的实验研究

多相流理论中经常采用的有均流模型、分流模型及漂流模型.漂流模型考虑了相间的滑脱影响及管道截面中混合物浓度分布和速度分布的影响,在油水两相含水率校正中获得广泛应用.通过对两相漂流模型的改进,将其应用于油气水三相流时阻抗式含水率的含水率校正,并在模拟井上进行了动态实验验证.将改进的漂流模型应用于阻抗式含水率计的油气水三相流测量校正,并采用线性拟合的方法确定相分布系数和油气泡绝对浮升速度,实验结果表明可以取得较高的校正精度,但是该模型适用于低含水、高产气情况,对于高含水、低产气情况,阻抗式含水率计的测量结果在不经校正的条件下可以满足测量精度要求.