交流磁场对Al-11.4%Cu合金液相线、固相线温度的影响

通过测试和分析Al-11.4%Cu合金在交流磁场中凝固的电阻,确定了合金液相线和固相线温度以及结晶区间.试验结果表明,在不同磁感应强度的交流磁场作用下,Al-11.4%Cu合金的液相线和固相线温度均有所提高,结晶温度间隔变小,磁场强度越大,这种变化的幅度越大.     

氢化燃烧合成法制备镁基储氢合金Mg2NiH4

采用自行设计制作的反应设备，研究了氢化燃烧合成法制备Mg2NiH4的工艺参数。主要探讨了合成反应动力学因素：压力、合成温度、氢化保温时间对产物纯度的影响。实验结果表明，在初始压力为1．5MPa下，合成条件分别为：合成温度808K，合成保温时间120min，氢化保温时间60min及合成温度850K，合成保温时间60min，氢化保温时间90min时均可制备出纯的Mg2NiH4。     

环型空间阵列扭矩传感测量系统研究

针对恶劣环境下机械转轴扭矩动态测量的难题,利用交流电磁感应原理,采用环型空间阵列和专用的磁电式检测器,构建一种新型的非接触式扭矩传感器.分析了传感器的测量原理,建立了动态扭矩测量的数学模型,设计相应的测量系统.利用ANSYS有限元分析软件对传感器进行了建模和磁力分析,并进行了初步的扭矩测量实验,结果表明:系统的可测量最小扭转角≤±0.01°,可满足极端环境下机械转轴扭矩的动态测量,并具有较高的精度.     

Cytosine-cytosine+ base pairing stabilizes DNA quadruplexes and cytosine methylation greatly enhances the effect

Previous spectroscopic studies demonstrated that the oligodeoxynucleotide d(CGC G3 GCG) undergoes a reversible cation-dependent transition between Watson-Crick (WC) hairpin and parallel-stranded "G-DNA" quadruplex structures [Hardin, C.C., Watson, T., Corregan, M., & Bailey, C. (1992) Biochemistry 31, 833-841]. The relative stabilities of the structures were assessed as a function of pH, and it was found that the quadruplex was substantially stabilized (delta Tm = +15 degrees C) when the pH was shifted from 7.5 to 6 (apparent pKa = 6.8). In the present study, the effects of different cations and pH on four specific sequence varients were determined to test the proposal that this stabilization is due to C.C+ base pair formation mediated by N3-protonation of cytosine. Characteristically large differences in stability were observed when structures formed by d(TAT G3 ATA) and d(TAT G4 ATA) were thermally dissociated at pH 7 in the presence of different cations, verifying that Gn tracts bordered by TAT- and -ATA sequences form quadruplex structures. Imino proton NMR results indicate that the d(m5C G m5C G3 G m5C G)4 and d(TAT G4 ATA)4 quadruplex structures are parallel-stranded. It was necessary to increase the K+ concentration from 40 mM to ca. 200 mM to stabilize d(TAT G3 ATA)4, while the d(TAT G4 ATA)4 complex was nearly as stable as the quadruplex formed by d(CGC G3 GCG) under the same conditions. The d(TAT G4 ATA)4 quadruplex was only slightly stabilized at pH 6 relative to pH 7.5 (delta Tm = +3 degrees C), confirming that the unique stabilization that occurs in the pH 6.8 range with [d(CGC Gn GCG)4.ionn] complexes is due to the C residues. The sequence d(m5C G m5C G3 G m5C G) was found to form a very stable quadruplex in K+ or Ca2+. As with the quadruplex formed by the unmethylated analog, the stability is greatly enhanced when the pH is decreased below about 7.2 (pKa,obs = 6.8). Dissociation kinetic constants and activation energies were determined for quadruplexes formed by d(CGC G3 GCG), d(m5C G m5C G3 G m5C G) and d(TAT G4 ATA). Quantitative comparisons showed that methylation produces a complex that is much more stable at pH 7 in 40 mM Na+ than either of the unmodified structures; the rate-limiting activation energy for dissociation of d(CGC G3 GCG)4 was 22 kcal mol-1 less than for the methylated analog.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fast direct position determination method based on the sharpening function genetic algorithm

The traditional DPD algorithm has a slowly-varying cost function near the peak, which makes it ineffective to get the optimization location result. To solve the problem, a fast direct position determination method based on the sharpening genetic algorithm is proposed in this paper. First, the algorithm constructs a sharpening function to sharpen the target function of DPD and enhances the algorithm selection ability. Then the algorithm combines with the initialization in the convergence process to increase the diversity of the population and preventes the algorithm into a local optimum. Finally, the algorithm realizes the fast estimation of the target's position. Simulation results show that the algorithm proposed can obtain a higher positioning accuracy than a fast DPD method based on the traditional genetic algorithm in the high SNR condition. Compared with ML-DPD, the computation can be reduced 3 orders of magnitude at 95％ probability and the computational efficiency is greatly improved.     

城镇污水处理厂项目环境影响评价重点的研究

城镇污水处理厂作为一项环境保护工程,在发挥环境效益的同时,运行过程中排放的尾水、产生的恶臭和污泥等污染物对环境将产生不利影响。在进行污水处理厂项目环境影响评价时,应识别评价重点,目的是使环境影响预测和评价具有针对性,以发挥更大的环境效益。根据污水处理厂的工程特性,结合江门市江海污水处理厂工程环境影响评价的实践经验,提出污水处理厂环境影响评价应重点关注厂址环境合理性分析、污水处理工艺比选、尾水排放对水环境影响、恶臭对大气环境影响、污泥处置对环境影响等问题。     

低频泥石流特征及其危险性的模糊综合评判

低频泥石流由于物源形成周期长,因而爆发的周期长,容易为人们所忽视。以国内较典型的低频泥石流信息为依据,结合四川康定县宋家沟低频泥石流实例,在相关规范的基础上加入模糊数学的方法,对宋家沟泥石流进行了危险性评价;对低频泥石流的发生特性进行了分析;并结合人的心理因素,给出了低频泥石流30 a的周期下限。可为泥石流灾害防治参考。     

农村信息化综合服务平台的设计与实现

农村信息化服务平台是基于农村信息管理的原始数据,利用Java软件开发技术、Sql Server数据库管理技术以及JDBC数据库连接技术,实现综合信息服务功能。主要实现了户籍管理、财务管理、资源管理、党建工作、土产品介绍、论坛管理以及农村基本信息公布等功能;完成了户籍、财务、资源等数据的动态管理。为农村信息管理打下良好的基础,全面推进农村信息化和城镇化建设的步伐。     

x-射线前散射图像物体真实灰度级的图像处理

为了准确提取物体的有效特征值,得到目标物体的真实灰度级,以前散射图像为例,建立了目标物体、背景物体及重叠区域灰度级之间的数学模型来描述物体间的重叠关系,把多个物体重叠问题简化为两个物体重叠问题.根据x-射线与物质相互作用关系、x-射线源类型、探测器通道数等对重叠关系模型进行转换、简化、推导,得到目标物体真实灰度级模型.将测得的80组灰度级代入目标物体真实灰度级模型中进行求解,结果表明,模型误差在10%以内,该模型算法有效可行.     

一种拉杆式波纹管的形变监测系统设计

针对常规波纹管形变量监测法精度低及依赖人工读数效率低等问题,设计了一种基于光纤光栅传感技术的波纹管形变在线监测系统,可以实时监测拉杆式波纹管运行状态,并将故障及告警信息通过IEC 61850上传至远端.给出了整体系统架构及总体设计方案,当波纹管在拉杆移动范围内发生形变时通过四个方向的光纤光栅位移传感器进行测量;当超过拉杆移动范围后,增加四个方向的光纤光栅应变传感器进行测量.实验结果表明,该拉杆式波纹管形变监测方法设计合理,传感器可以准确反映位移及应变等数据且可以进行远传,具有较强的工程应用价值.