丁二烯在乙酰基丙酮镍和一氯二烷基铝均相催化体系中的定向聚合

本工作研究了丁二烯在乙酰基丙酮镍-一氯二烷基铝体系中聚合的一般规律、聚合动力学及链转移过程。实验结果表明:聚合速率对单体浓度、主催化剂(镍络盐)浓度均呈一级关系,而对一氯二异丁基铝浓度呈二级关系,即 -(dM/dt)=k[M][NiA_2][Al(i-C_4H_9)_2Cl]~2对一氯二乙基铝浓度则呈1/2级关系,即 -(dM/dt)=k[M][NiA_2][Al(C_2H_5)_2Cl]~(1/2)对这二种体系反应级数的不同作了解释。 实验测得丁二烯在乙酰基丙酮镍-一氯二异丁基铝体系中聚合的总活化能为8.0±0.5千卡/克分子,而在一氯二乙基铝体系中为 8.9±0.5千卡/克分子。 研究了丁二烯在本体系中聚合时单体浓度、主助催化剂浓度、聚合转化率、溶剂以及某些添加剂等因素对聚合物分子量的影响。结果表明:聚合物的分子量随单体浓度的增大而增大;随镍组份浓度的增大而减小;当体系中水分含量很低时,一氯二乙基铝浓度的改变对聚合物分子量基本无影响;在5—60％转化率及0—35℃范围内聚合物分子量变化不明显;庚烷中所得聚合物的分子量比苯中所得者低;添加水、吡啶、三溴化铝、三乙基铝、甲基环己烷及蒽等都不能显著提高聚合物的分子量。 计算链转移常数,得到对含镍组份为 84,对单体为 1.9× 10~(-3),终止常数为 2.3×10~(-3)。因而得知本体系中主要的链转移过程是     

DYNAMIC RESPONSE AND STABILITY ANALYSIS OF AN AUTOMATIC BALL BALANCER FOR A FLEXIBLE ROTOR

Dynamic stability and time responses are studied for an automatic ball balancer of a rotor with a flexible shaft. The Stodola-Green rotor model, of which the shaft is flexible, is selected for analysis. This rotor model is able to include the influence of rigid-body rotations due to the shaft flexibility on dynamic responses. Applying Lagrange's equation to the rotor with the ball balancer, the non-linear equations of motion are derived. Based on the linearized equations, the stability of the ball balancer around the balanced equilibrium position is analyzed. On the other hand, the time responses computed from the non-linear equations are investigated. This study shows that the automatic ball balancer can achieve the balancing of a rotor with a flexible shaft if the system parameters of the balancer satisfy the stability conditions for the balanced equilibrium position.     

均匀恒磁场中载流导线的磁场计算问题

对于任意截面的载流导体在垂直均匀磁场中所生的影响问题研究得还不够,最近看到有关椭圆截面的导线表面上的磁场的文献。本文指出,如果导线的截面曲线是由保角变换得到的曲线坐标中的一个坐标等于常数表出,则此问题可以容易地解出,即导线内外的磁场可以求得。     

On an Anisotropic Equation with Critical Exponent and Non-Standard Growth Condition

Using variational methods, we prove the existence of a nontrivial weak solution for the problem
{-∑i=1^Nδxi（｜δxiu｜pi-2δxiu）=λα（x）｜u｜q（x）-2u＋｜u｜p＊-2u,in Ω,
u=0 inδΩ,
where Ω R^N（N≥3） is a bounded domain with smooth boundary δΩ,2≤pi〈N,i=1,N,q：Ω→（1,p＊）is a continuous function, p＊ =N/∑i=1^N 1/pi-1 is the critical exponent for this class of problem, and λ is a parameter.     

An efficient selectivity estimation method for spatial query optimization with topological relationships

Many commercial database systems maintain histograms to summarize the contents of relations and permit the efficient estimation of query result sizes and the access plan cost. In spatial database systems,most spatial query predicates are consisted of topological relationships between spatial objects,and it is very important to estimate the selectivity of those predicates for spatial query optimizer. In this paper, we propose a selectivity estimation scheme for spatial topological predicates based on the multidimensional histogram and the transformation scheme. Proposed scheme applies two-partition strategy on transformed object space to generate spatial histogram and estimates the selectivity of topological predicates based on the topological characteristics of the transformed space. Proposed scheme provides a way for estimating the selectivity without too much memory space usage and additional I/Os in most spatial query optimizers.     

Mult ifragment Emission by Nucleation-Evaporation Approach

Nuclear fragmentation events are Monte-Carlo simulated in the nucleation-evaporation picture, with charge and energy conservations. We investigate how the fragment energy spectrum, the charge distribution and the intermediate mass fragment (IMF) multiplicity depend upon the breakup density. The results are compared with some recent 4n experimental data.     

MIXED TRANSFORM FINITE ELEMENT METHOD FOR SOLVING THE NON-LINEAR EQUATION FOR FLOW IN VARIABLY SATURATED POROUS MEDIA

A new computational method is developed for numerical solution of the Richards equation for flow in variably saturated porous media. The new method, referred to as the mixed transform finite element method, employs the mixed formulation of the Richards equation but expressed in terms of a partitioned transform. An iterative finite element algorithm is derived using a Newton–Galerkin weak statement. Specific advantages of the new method are demonstrated with applications to a set of one— dimensional test problems. Comparisons with the modified Picard method show that the new method produces more robust solutions for a broad range of soil– moisture regimes, including flow in desiccated soils, in heterogeneous media and in layered soils with formation of perched water zones. In addition, the mixed transform finite element method is shown to converge faster than the modified Picard method in a number of cases and to accurately represent pressure head and moisture content profiles with very steep fronts. © 1997 by John Wiley & Sons, Ltd.     

A SPECTRAL METHOD FOR UNSTEADY FLOW AND HEAT TRANSFER PAST A SPHERICAL DROPLET: PRIMITIVE VARIABLE FORMULATION

Abstract

A spectral method is developed based on the primitive variables for the time-dependent solution of the flow and the temperature past a spherical droplet. Both Chebyshev and Legendre polynomials are used to expand the velocity, pressure, and temperature in the radial and angular directions, respectively. The fractional time-stepping method suggested by Orszag (Orszag et al., 1980) is used for solving the flow and the pressure fields. Euler backward differencing is used for the integration of the energy equation. The computed steady-state drag coefficients are compared to those found in the literature for Reynolds numbers in the range from 0.5 to 50 for both the continuous and the dispersed phase. The transient drag coefficients and Nusselt numbers are compared with our previous study using a stream function-vorticity formulation (Nguyen et al, 1993). The comparison indicates that the present model is capable of predicting the correct nature of the flow and heat transfer associated with a droplet.     

γMn基合金反铁磁畸变与高阻尼孪晶的形成

根据反铁磁序引起的点阵畸变与磁长程序参量之间的关系，计算了γMn-Cu合金顺磁→反铁磁转变引起的点阵畸变，并将计算值与实验数据进行了比较，通过γMn-Fe基合金高阻尼特性测定，验证了反铁磁序与孪晶高阻尼的关系在其他锰基合金中同样存在的推测，讨论了γMn基合金高阻尼行为的物理本质，结果表明，γMn-Cu和γMn-Fe合金顺磁→反铁磁转变引起的四方畸变均可触发微孪晶的形成，且在一定条件下可能诱发马氏体相变。     

Fe3+离子在钠-硼玻璃中的顺磁共振

研究了Fe³⁺离子在钠-硼玻璃中的顺磁共振。在表观g=4.27处,有一条尖锐的大致对称的共振线。实验结果表明Fe³⁺离子代替接触二个钠离子的[BO₄]四面体中的硼离子位置。