增敏剂改进超级微波消解-电感耦合等离子体质谱(ICP-MS)法测定食品中硒元素

合适比例增敏剂会对超级微波消解-电感耦合等离子体质谱法(ICP-MS)测定食品中硒元素含量具有一定的优化效果。本文采用超级微波消解仪对1.0 g食品样品进行全消解,采用碰撞池模式规避质谱干扰,内标校正非质谱干扰,选择甲醇、乙醇、乙酸、异丙醇、丙三醇作为增敏剂,并调整测试过程中的添加比例,用电感耦合等离子体质谱法测定。结果表明：2%异丙醇存在时硒元素各同位素响应值最高,其中78Se具有低至0.0003 mg·kg-1的方法检出限;用以上方法对食品标准物质（GSB-8、GSB-9、GSB-24、GSB-30）及实际样品进行分析,标准物质测定值均在其认定值及不确定度范围内,相对误差小于-5.4%;实际样品测定值的相对标准偏差（n=7,RSD）为0.3~1.7%,加标回收率为99.2~105%。本方法操作简便,精密度好,准确度高,可以作为各类食品样品中硒含量测试方法。     

超级微波消解-电感耦合等离子体发射光谱（ICP-OES）法测定土壤中18种元素

为提高土壤多元素同时检测的效率,采用超级微波消解-电感耦合等离子体发射光谱法测定土壤中钾、钠、钙、镁、铜、铁、锰、锌、磷、硫、硼、砷、镉、铬、铅、钴、镓、锂等18种元素含量。比较了超级微波消解、常规微波消解和电热板消解的处理效果,采用超级微波消解法对样品进行前处理,并优化了消解条件。在最优条件下,各元素的检出限在0.05~20 mg/kg,加标回收率在86.2%~107.5%,RSD在0.1%~3.0%,方法准确度及精密度可以满足多元素同时测定的需求,且该方法具有简单、快速、成本低、用酸量少、重现性好等特点。     

利用高吸水树脂优化3个中学化学实验*

尝试利用高吸水树脂对“酸碱中和反应、碳酸钠和碳酸氢钠分别与稀盐酸反应、探究分子运动现象”这3个实验进行创新改进,充分利用了高吸水树脂特殊的结构作用,使3个实验的现象更加显著。改进实验操作简便,高效简洁,值得推广到一线化学课堂的演示实验或学生分组实验。     

分子筛超强酸SO_4~(2-)/TiO_2/USY催化合成胡萝卜酸乙酯的研究

以USY分子筛为载体,采用共沉淀-浸渍法制备分子筛超强酸SO42-/Ti O2/USY,用其催化丙二酸、无水乙醇合成胡萝卜酸乙酯。考察了不同反应时间、带水剂种类、带水剂用量、醇酸比、催化剂用量、催化剂重复使用性等因素对反应酯化率的影响。结果表明:在丙二酸用量为0.1mol,醇酸摩尔比为3.1:1,催化剂用量为1.0g,反应时间为3h,带水剂环已烷用量为5m L时,酯化率达到92.13%,催化剂重复使用5次以后仍然有很高的活性。说明SO42-/Ti O2/USY对该反应具有很强且极稳定的催化活性。     

ЧАПЛЫГИН方程的代数结构

研究非完整系统Чаплыгин方程的代数结构．首先给出Чаплыгин方程的逆变代数形式，其次证明它具有相容代数结构并给出它具有Ｌｉｅ代数结构的条件，最后举例说明结果的应用     

A torus bifurcation theorem with symmetry

A general theory for the study of degenerate Hopf bifurcation in the presence of symmetry has been carried out only in situations where the normal form equations decouple into phase/amplitude equations. In this paper we prove a theorem showing that in general we expect such degeneracies to lead to secondary torus bifurcations. We then apply this theorem to the case of degenerate Hopf bifurcation with triangular (D₃) symmetry, proving that in codimension two there exist regions of parameter space where two branches of asymptotically stable 2-tori coexist but where no stable periodic solutions are present. Although this study does not lead to a theory for degenerate Hopf bifurcations in the presence of symmetry, it does present examples that would have to be accounted for by any such general theory.     

On the application of the Wiener–Hopf technique to problems in dynamic elasticity

Many problems in linear elastodynamics, or dynamic fracture mechanics, can be reduced to Wiener–Hopf functional equations defined in a strip in a complex transform plane. Apart from a few special cases, the inherent coupling between shear and compressional body motions gives rise to coupled systems of equations, and so the resulting Wiener–Hopf kernels are of matrix form. The key step in the solution of a Wiener–Hopf equation, which is to decompose the kernel into a product of two factors with particular analyticity properties, can be accomplished explicitly for scalar kernels. However, apart from special matrices which yield commutative factorizations, no procedure has yet been devised to factorize exactly general matrix kernels.

This paper shall demonstrate, by way of example, that the Wiener–Hopf approximant matrix (WHAM) procedure for obtaining approximate factors of matrix kernels (recently introduced by the author in [SIAM J. Appl. Math. 57 (2) (1997) 541]) is applicable to the class of matrix kernels found in elasticity, and in particular to problems in QNDE. First, as a motivating example, the kernel arising in the model of diffraction of skew incident elastic waves on a semi-infinite crack in an isotropic elastic space is studied. This was first examined in a seminal work by Achenbach and Gautesen [J. Acoust. Soc. Am. 61 (2) (1977) 413] and here three methods are offered for deriving distinct non-commutative factorizations of the kernel. Second, the WHAM method is employed to factorize the matrix kernel arising in the problem of radiation into an elastic half-space with mixed boundary conditions on its face. Third, brief mention is made of kernel factorization related to the problems of flexural wave diffraction by a crack in a thin (Mindlin) plate, and body wave scattering by an interfacial crack.     

平板网架结构分析的超级条元法

本文针对复杂杆系结构提出一种超级有限条的分析方法。这种方法基于半连续半离散思想将各杆件结点自由度归结为整体结构自由度；进一步又将整体自由度简化为少数结线自由度上机计算。这将为复杂结构体系开拓一条简便、实用的工程分析途径。     

平板网架结构分析的超级有限元法

本文给出一种二维矩形超级单元，用以分析平板网架结构，其做法是将大型平板网架结构离散成一系列矩形超级单元，考虑弯曲、剪切、挤压、拉压、翘曲等多种非经典变形效应，采用构件自由度向超级元自由度的转换把大型多构件问题的求解变为二维问题的求解，可大大减少未知量，又能保证精度，并可方便地与一般有限元软件连接。     

两系非线性悬挂车辆的运行稳定性与分叉

本文选取两系具有滞后非线性悬挂的车辆为目标，建立其数学模型和运动微分方程，用常微分方程稳定性理论对车辆蛇行运动进行理论分析，并应用分叉理论研究了整车在蛇行失稳后的动力学行为，得出蛇行运动的分叉解及稳定判据，得到防止车辆蛇行运动的充分条件，并研究了系统参数对临界速度的影响、分叉解振幅及稳定性的影响，为车辆设计和参数选取提供依据。