三角形约束的平面二次曲线的NURBS表示

非均匀有理Ｂ样条（ＮＵＲＢＳ）是ＣＡＤ设计中广泛使用的技术。本基于平面几何知识给出了三角形约束的圆与椭圆曲线的ＮＵＲＢＳ表示,为工程设计中使用这类曲线提供了可计算性。     

Restrictions on negative energy density for the Dirac field in flat spacetime

This paper investigates the quantum Dirac field in n+1-dimensional flat spacetime and derives a lower bound in the form of quantum inequality on the energy density averaged against spacetime sampling functions. The state-independent quantum inequality derived in the present paper is similar to the temporal quantum energy inequality and it is stronger for massive field than for massless one. It also presents the concrete results of the quantum inequality in 2 and 4-dimensional spacetimes.     

用推广的等效两体方法求解类氦离子三体问题

介绍了求解三体问题的等效两体方法,将等效两体方法推广到原子系统,利用该方法求解类氦离子的基态,与一般的单参数变分法相比得到了与实验值符合得更好的结果,进而利用双参数变分法对所得结果进行了检验。 结果表明,等效两体方法同样适用于求解原子系统中的三体问题。 An extended equivalent two body method for three body systems is introduced in this article. The method is applied to an atomic three body system. Energies and wave functions of a helium like ion are calculated,which are consistent with the experimental data much better,in contrast to the results obtained by a one parameter calculus of variations approach. Then we use a two parameter calculus of variations approach to verify the precision of the ground state energy and wave function obtained by the extended equivalent two body method. These results indicated that the extended equivalent two body method is applicable to an atomic three body problem.     

An improved boundary element-free method （IBEFM） for two-dimensional potential problems

The interpolating moving least-squares (IMLS) method is discussed first in this paper. And the formulae of the IMLS method obtained by Lancaster are revised. Then on the basis of the boundary element-free method (BEFM), combining the boundary integral equation (BIE) method with the IMLS method, the improved boundary element-free method (IBEFM) for two-dimensional potential problems is presented, and the corresponding formulae of the IBEFM are obtained. In the BEFM, boundary conditions are applied directly, but the shape function in the MLS does not satisfy the property of the Kronecker δ function. This is a problem of the BEFM, and must be solved theoretically. In the IMLS method, when the shape function satisfies the property of the Kronecker δ function, then the boundary conditions, in the meshless method based on the IMLS method, can be applied directly. Then the IBEFM, based on the IMLS method, is a direct meshless boundary integral equation method in which the basic unknown quantity is the real solution of the nodal variables, and the boundary conditions can be applied directly and easily, thus it gives a greater computational precision. Some numerical examples are presented to demonstrate the method.     

矩阵Hadamard积和Fan积的特征值界的一些新估计式

本文研究了非奇异M-矩阵A与B的Fan积的最小特征值下界和非负矩阵A与B的Hadamard积 的谱半径上界的估计问题.利用Brauer定理,得到了一些只依赖于矩阵的元素且易于计算的新估计式,改进 了文献[4]现有的一些结果.     

双-锌卟啉对DABCO分子识别的立体构象及其热力学研究

合成了系列不同长度以柔性侧链相连的p/p型双-锌卟啉配合物,用¹H NMR和UV-Vis研究了不同温度下该系列配合物与刚性双齿配体DABCO(1,4-二氮杂双环)的轴向配位反应,考察了侧链长度对双-锌卟啉与配体的分子识别能力影响。结果表明,主体分子双-锌卟啉可以对客体分子BABCO进行分子识别,合适长度的柔韧烷氧链可以调节主体分子的构象,使DABCO嵌入双卟啉两个卟啉环间空位中,形成锌卟啉-DABCO-锌卟啉三元夹心式配合物构象。探讨了配位反应中立体构象的变化过程,并测定了热力学参数。     

一种确定加速车道长度的概率统计模型

加速车道有利于次要道路上的车流平顺地汇入高速公路的车流 ,加速车道长度的确定是加速车道设计的核心内容。本文针对加速车道车流的运行特性 ,从概率统计角度研究了加速车道上车辆汇入高速公路车流的概率 ,并在此基础上得到了一种用于确定加速车道长度的实用模型     

单力矩器大角速率动调陀螺仪力矩再平衡回路的分析与综合

针对仅有一个力矩器的大角速率动调陀螺仪,力矩器线圈必须通以与陀螺仪自转角速率同频率变化的交变电流的特点,分析了采用合成施矩方式的力矩再平衡回路的工作原理。根据系统要求,对放大校正环节进行了设计。通过系统仿真及实例,验证了仿真模型的可信性及设计的合理性。     

统计机器翻译中汉维短语对抽取的研究

双语短语对抽取是基于短语的统计机器翻译中短语翻译模型训练的关键步骤,但由于汉维平行语料库规模有限,数据稀疏问题严重.本文提出了一种改进的短语抽取算法,该算法首先考虑词对齐矩阵中一个汉语词对齐到多个维吾尔语词的情况(包括不连续),然后利用Och方法抽取短语对,最后考虑维吾尔语SOV语序结构特点,抽取双语短语.实验表明,该算法能够较准确地且尽可能多地抽取汉维短语对,从而提高翻译模型的质量.     

大学物理教学中需要做到十个“一定”

大学物理对于工科学生在学习知识、提高能力、培养素质等方面的重要功能已经在学界得到公认．笔者认为教师在教学过程中如果能做到十个“一定”,将有助于实现大学物理的这一功能．