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991.
992.
采用成核 /晶化隔离法合成镁铁双羟基复合金属氧化物MgFe LDH ,考察了Mg∶Fe摩尔比对MgFe LDH晶形的影响 ,探讨了晶化温度及晶化时间对晶面生长选择性及晶粒尺寸的影响规律 .结果表明 ,随Mg∶Fe摩尔比增大 ,层板阳离子排列更为规整 .晶化温度对晶粒尺寸的影响显著大于晶化时间的影响 .晶化温度相同 ,随晶化时间延长 ,MgFe LDH的晶体结构趋于完整 ,晶粒尺寸变化不大 ;晶化时间相同 ,随晶化温度升高 ,晶体结构趋于完整 ,晶粒尺寸明显增大 .所得到的MgFe LDH沿a轴方向的晶粒尺寸对晶化温度变化的敏感程度远大于对晶化时间变化的敏感程度 ,但总是沿a轴方向的晶粒尺寸大于沿c轴方向的尺寸 ,即 [110 ]晶面的生长速率比[0 0 2 ]晶面的生长速率快 相似文献
993.
Our main theorem asserts that for all odd
and 0 < , there exists a small constant, , such that if a simply connected n-manifold, M, with vanishing second Betti number admits a metric of sectional curvature, , then the injectivity radius of M is greater than .
Submitted: June 1998, revised: December 1998, final version: June 1999. 相似文献
994.
Xuefei Zhong Rong Yi Alison E. Holliday David D. Y. Chen 《Rapid communications in mass spectrometry : RCM》2009,23(5):689-697
Three‐dimensional computer models of electrospray ionization sources were constructed in COMSOL Multiphysics? to solve the static electric fields using finite element methods. The magnitude of the electric field strength for onset of electrospray and optimum signal was calculated under various conditions. The modification of the electric field distribution in the ion source by an atmospheric pressure ion lens was also investigated by plotting the equipotential surfaces, electric field lines and trajectories of charged droplets. Both the calculated and the experimental results demonstrate that the changes in the ion signal detected by the mass spectrometer are attributable to the focusing effect of the ion lens when appropriate voltages are applied on the sprayer and ion lens. The optimum signal was found by setting the sprayer voltage from 3000 to 5000 V while scanning the ion lens voltage. The calculated strengths of the electric field at the sprayer tip for optimum signals are similar although the applied voltages at the sprayer and ion lens are significantly different. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
995.
996.
This paper considers the problems of determining center or focus and isochronous centers for the planar quasi-analytic systems.
Two recursive formulas to determine the focal values and period constants are given. The convergence of first integral near
the center is proved. Using the general results to quasi-quadratic systems, the problem of the isochronous center of the origin
is completely solved.
This research is partially supported by the National Natural Science Foundation of China (10671179 and 10771196) and the Natural
Science Foundation of Yunnan Province (2005A0092M) 相似文献
997.
998.
As part of a study of viscous and elastic behaviors, over a range of temperatures from below the glass transition up to the hot melt, we here report steady-shear viscosities at 0.007 to 13 s?1 and at 160 to 220 °C of polystyrene containing 0 to 60% by mass of 0.18-micron diameter titanium dioxide particles. The materials were shearthinning without a yield stress, with a constant activation energy at constant stress, but having a shear-dependent activation energy at constant shear rate — proportional to the volume fraction of the polymer matrix. Superposition of the flow curves at different temperatures for the unfilled and filled systems was possible. All the data were represented by one equation with four parameters: 1) a shear stress coefficient (units Pa · s2); 2) a characteristic stress level for non-Newtonian behavior, independent of temperature and composition; 3) an activation energy at constant stress; and 4) an Einstein coefficient (or intrinsic viscosity of the filler). Other equations also fitted the data, but the others diverged widely when extrapolated. 相似文献
999.
1000.