李白、崔颢《黄鹤楼》诗案考辨

分析了李白、崔颢《黄鹤楼》诗案本末,认为肯定诗案的观点缺乏有力的依据,质疑诗案的观点值得重视。提出否定诗案的5个视点及澄清诗案的4点意义。     

从原子结构探讨负价金

对于重金属相对论效应不可忽视。由于金的相对论效应显著大于其他元素,因此原子半径收缩大,惰性电子对效应也大,加之金特有的电子构型,使金具有独特的化学性质,即金不仅可氧化为正一价和正三价,还可以呈负一价。     

Thermal expansion anomaly and spontaneous magnetostriction of Gd2Fe17 compound

Materials with negative thermal expansion have many practical applications. However, these materials are known in only several oxide systems, and when the negative thermal expansion occurs, the contraction is usually small and limited to a narrow temperature range beyond room temperature. For obtaining a compound with negative thermal expansion in broad temperature range, the structural and magnetic properties of Gd2Fe17 compound were investigated by means of X-ray diffraction and magnetization measurements. The Gd2Fe17 compound annealed at 1050 oC had a Th2Zn17-type structure. There existed an anisotropic strong spontaneous magnetostriction and a negative thermal expansion in Gd2Fe17 compound. The average thermal expansion coefficients was =-7.40×10-6/K in the temperature range of 294-453 K and =-1.80×10-5/K in 453-534 K, respectively. The spontaneous magnetostrictive deformation ωS decreased from 4.34×10-3 to near zero with temperature increasing from 294 to 572 K. The spontaneous linear deformation λc was much larger than λa at the same temperature below about 500 K.     

Coping with indefinite and negative data in deductive databases: A survey

A problem with current database systems is the limitation placed on the type of data which may be represented and manipulated within such systems. In an attempt to broaden this to a wider class of data (i.e. rules as well as facts) and a more powerful set of manipulations, the concept of a deductive database was introduced. However, for the sake of efficiency the type of rule which is allowed in a deductive database is restricted in form. This paper surveys a number of attempts to move towards less restrictive forms of rules in deductive databases which allow indefinite and negative data to be handled.     

实值n维混沌映射否定选择算法

针对传统的基于二进制的混沌否定选择算法在检测器生成阶段对混沌映射产生的混沌序列离散化生成的候选检测器,不利于知识和数据的分析,也会造成检测器集生成速度慢及检测效率低等问题,提出了基于实值的混沌否定选择算法.引入混沌理论,采用混沌特性更好的自映射构造n维混沌映射生成候选检测器中心点,改进了传统的检测器生成机制,更适合处理高维空间问题;对原有的V-detector算法进行了优化,通过定向移动与计算几何中心相结合的思想确定检测半径.旨在满足预期覆盖率条件下尽量使半径取值最大化,扩大检测器集的覆盖范围,减少检测器数量.实验结果表明,该算法提高了检测器集的生成速度和检测效率.     

负电容压电阻尼振动系统控制器参数研究

实验中发现负电容电路参数对负电容压电阻尼振动系统的振动幅值的衰减影响很大,推导了负电容压电阻尼振动系统的振动幅值随负电容电路参数的变化关系,并进行了仿真和实验研究,理论仿真和实验结果表明:负电容值越接近于压电片的固有电容,压电阻尼控制系统的衰减性能越好,串联电阻越小,压电阻尼控制系统的衰减性能越好.     

种子检测器刺激-应答变异算法研究

为降低阴性选择算法(NSA)的时间复杂度,提出了一种应用种子个体连续位刺激变异的检测器生成策略:首先随机生成种子检测器集合,根据其与自体的亲和度选定变异个体和变异片段;其次在被选个体的特定基因片段发生刺激-应答变异(SRM),产生新的候选检测器个体;最后应用r位连续匹配准则筛选候选个体生成新的检测器.该策略的算法特点在于利用种子个体和自体集合的模式信息指导变异过程,降低候选检测器与自体的匹配成功率.实验表明,在保持高检测率的同时,种子检测器SRM算法比穷举算法、个体随机变异算法和检测器连续胞体超变异(CSH)算法的生成效率更高.     

大直径盾构负环管片拆除及隧道换装技术

通过对北京铁路地下直径线2标工程的研究,确定在刀盘改造期间进行负环管片拆除的一系列工作,重点如部分反力架的拆除方法、负环管片的详细拆除方法以及拆除反力架后临时支撑的架设方法,同时就泥水盾构隧道的换装技术进行了叙述,最终在7d之内成功拆除了7环负环管片,节约了工期,保证了后继施工的材料运输速度。     

带分布时滞分数阶微分方程非振动解的存在性北大核心CSCD

研究了一类中立型部分带有分布时滞且具有正负系数的分数阶微分方程,利用Banach压缩映像原理,通过克服算子构造和不等式放缩技巧,得到了方程有界的非振动解存在的充分条件,将其系数的适用范围拓展成不等于1和-1的实数,并通过算例验证了相关结果。     

X-ray Diffraction Study of MgB2 at Low Temperatures

We have performed powder X-ray diffraction of MgB₂ superconductor between 10 and 300 K. Temperature dependence of integrated intensities of both (002) and (110) X-ray reflections shows a peak at around T_C, superconducting transition temperature. The integrated intensity of the X-ray reflection is related to the phonon frequency through a Debye--Waller factor. Lattice parameters a and c show negative thermal expansions at low temperatures. The negative thermal expansion might be due to an electronic origin and not directly related to the superconducting transition.