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1.
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 相似文献
2.
DYNAMIC RESPONSE AND STABILITY ANALYSIS OF AN AUTOMATIC BALL BALANCER FOR A FLEXIBLE ROTOR 总被引:3,自引:0,他引:3
J. CHUNG 《Journal of sound and vibration》2003,259(1):31-43
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. 相似文献
3.
We study birational geometry of the moduli space of stable sheaves on a quadric surface with Hilbert polynomial and . We describe a birational map between the moduli space and a projective bundle over a Grassmannian as a composition of smooth blow-ups/downs. 相似文献
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5.
We prove that the moduli spaces of rational curves of degree at most 3 in linear sections of the Grassmannian are all rational varieties. We also study their compactifications and birational geometry. 相似文献
6.
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. 相似文献
{-∑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. 相似文献
7.
K. C. CHUNG 《理论物理通讯》1996,26(1):65-70
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. 相似文献
8.
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. 相似文献
9.
The orientation of E7 liquid crystal (LC) confined within 200 nm diameter cylindrical cavities of Anodisc membranes was investigated by FTIR dichroism techniques. The cavity walls of the confining pores were chemically modified with different length aliphatic acids (CnH2n+1COOH, n=5, 6, 7, 9) at 2 and 4% concentrations. From the FTIR spectra of the aliphatic acid-treated alumina Anodsic membranes, we found salt formation between the -COOH group of the aliphatic acids and the Anodisc membranes. From the FTIR spectra of LC-filled Anodisc membranes, we found an abrupt alignment direction change, from parallel to perpendicular, of the LC molecules along the long axis of the cavities between n=6 and n=7 for the 2% concentration of aliphatic acid. However for the 4% concentration of aliphatic acid the parallel to perpendicular alignment direction of LC molecules changed between n=5 and n=6. The same trend was previously observed for 2H NMR measurements by other researchers. 相似文献
10.
S. PAIK H. D. NGUYEN J. N. CHUNG 《International Journal of Computational Fluid Dynamics》2013,27(3-4):171-192
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. 相似文献