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21.
Shiro Matsuoka 《Journal of research of the National Institute of Standards and Technology》1997,102(2):213-228
The high frequency end of the relaxation spectrum for polymer molecules involves the rotation of the segmental bonds. This fast relaxation process, however, cannot take place easily in the condensed state crowded by the densely packed conformers, necessitating the slower cooperatively synchronous relaxation. As the temperature is lowered, the domain of cooperativity grows towards the infinite size at the Kauzmann zero entropy temperature, though actually the system deviates from the equilibrium as the glass transition intervenes typically at 50 K above that temperature. The excess enthalpy and entropy drop faster than predicted by the rotational isomeric states which would reach zero only at 0 K. The real ΔCP is greater than that of the RIS value. The actual volume in excess of the crystalline lattice volume, however, points towards zero at 0 K. Thus, a polymer with higher Tg typically exhibits a lower density and modulus in the glassy state. Since the configurational entropy associated with the free volume is proportional to the logarithm of the latter, the Kauzmann temperature can be scaled by ln M, where M is the algebraic average of the conformer molecular weight. The temperature dependence of the most dominant, i.e., the largest equilibrium domain size will result in the Adam-Gibbs and Vogel equations for the characteristic relaxation time. The cooperative domain distribution leads to the relaxation spectrum that follows a power law. The relationship between the characteristic relaxation time and the rate of physical aging is derived. 相似文献
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不同粒度松散煤体的氧扩散特性实验研究 总被引:1,自引:0,他引:1
以自行研制的煤对氧扩散特性测试装置为实验手段,在常温环境条件下测试了不同粒度松散煤体对氧的自由扩散特性.实验结果表明:煤样粒度的变化对取气腔氧浓度流出曲线的影响表现出2个极限值,煤样粒度在20~100目之间时,取气腔氧气浓度梯度随煤样粒度的增大而增大;当煤样粒度<20目或>100目时,煤样粒度的再变化对氧浓度流出曲线的影响则微乎其微;取气腔氧浓度曲线流形基本符合指数曲线的变化规律. 相似文献
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ABSTRACT: The absorbance of 2,2-diphenyl-1-picrylhydrazyl (DPPH) at 517 nm in methanol and acetone decreased by 20 and 35% for 120 min at 25 °C under light, respectively; in the dark it did not change significantly for 150 min. Decomposition of DPPH under 21% oxygen after 90 min under light was significantly higher than that under 1% oxygen. Absorbance of DPPH in pH 4 buffer solution in methanol, and in pH 10 buffer solution in acetone, decreased by 55 and 80%, respectively, under light for 120 min. The evaluation of antioxidant activity by the changes of DPPH absorbance should be carefully interpreted since the absorbance of DPPH at 517 nm is decreased by light, oxygen, pH, and type of solvent in addition to the antioxidant. 相似文献
26.
Pomes R.; Willson R.C.; McCammon J.A. 《Protein engineering, design & selection : PEDS》1995,8(7):663-675
Free energy simulations are reported for the N31L-D mutation,both in the HyHEL-10-HEL antibody-lysozyme complex and in theunliganded antibody, using the thermo-dynamic-cycle perturbationmethod. The present study suggests that the mutation would changethe free energy of binding of the complex by 5.6 kcal/mol(unrestrained free energy simulations), by 0.5 kcal/mol(free energy simulations with a restrained backbone) and by1.8 kcal/ mol (Poisson-Boltzmann calculations, which also usea restrained geometry model). A detailed structural analysishelps in estimating the contributions from various residuesand regions of the system. Enhanced recognition of HEL by themutant HyHEL-10 would arise from the combination of thermodynamicallymore favorable conformational changes of the CDR loops uponassociation and subsequent charge pairing with Lys96 in theantigen. 相似文献
27.
Standard Gibbs free energy of formation (ΔGf0), an important property needed in design calculations has been estimated using molar refraction, RM. The linear relationships derived between ΔGf0 and RM tested with the data on 8 series of hydrocarbons at 228 compounds yielded average deviations comparable to the methods cited in recent literature. The method can be used as an alternative to the existing ones, because of its simplicity combined with reasonable accuracy. 相似文献
28.
无间隙原子钢的微观结构特征和塑性应变比 总被引:1,自引:0,他引:1
采用X射线衍射的ODF和LP分析技术,SEM电子通道花样和蚀坑技术观测,研究了超深冲无间隙原子钢板的微观结构特征。结果表明:控制化学成分、保证基体纯净、优选工艺参数,促进强的γ-〈111〉∥N.D纤维织构的形成是获得优异成型性的关键。用CMTP方法,由ODF织构数据从理论计算了塑性应变比(r),表明rm值高达3.18。文中讨论了再结晶织构形成机制。 相似文献
29.
Daniel WinnMichael F. Doherty 《Chemical engineering science》2002,57(10):1805-1813
A method for predicting the shape of organic crystals grown from polar solvents is presented. The model is an improvement of the recent method developed by Winn and Doherty (A.I.Ch.E. Journal 44 (1998) 2501) for predicting the shape of organic crystals grown from solvents in which the energy of adhesion at the interfaces is dominated by dispersive forces (e.g., non-polar solvents). The principal characteristic of the new method is that it can account for the role of hydrogen donor and hydrogen acceptor atoms in forming strong bonds at the interface. This technique is a first step towards predicting the shapes of organic crystals grown from polar solvents, and has been applied successfully to predict the shape of adipic acid grown from water, and succinic acid grown from water and from propanol. 相似文献
30.