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101.
Joaquim J. Moura Ramos 《Molecular physics》2013,111(5):644-660
This study of the thermal behaviour of two glass formers showed that rofecoxib has a good ability to vitrify while celecoxib displays a moderate glass forming ability. On the other hand, celecoxib forms an instable glass while rofecoxib displays moderate glass stability. The α-relaxation of the two amorphous drugs was studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The values of the dynamic fragility obtained by the two techniques are in good mutual agreement and suggest that both drugs are moderately fragile glass formers. These values are however considerably lower than those obtained by dielectric relaxation spectroscopy (DRS) and published in the literature. In the present work we will compare the values of the dynamic fragility obtained by TSDC and DRS for a set of ~30 glass-forming liquids, in order to evaluate their relative suitability for the determination of the m-index. The observed differences are discussed and interpreted. Finally, secondary mobility modes were detected by TSDC in both celecoxib and rofecoxib. The kinetic parameters are identical in both cases and similar to those found by DRS for the slow-b relaxation of celecoxib. These secondary relaxations, that are precursors of the main relaxation on its lower temperature side, are believed to be Johari-Goldstein relaxations. 相似文献
102.
Comparison of the 1H and 13 C NMR spectra of a series of substituted 5‐benzylidene‐N,N′‐dimethylbarbituric acids (1) revealed chemical‐shift variations of different centers that correlated with the theoretical electrophilicities or with the substituent electrophilic constant σω , in an example of the usefulness of these DFT‐based indices. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
103.
N.Tz. Dintcheva S. AlessiR. Arrigo G. PrzybytniakG. Spadaro 《Radiation Physics and Chemistry》2012,81(4):432-436
In this paper two systems, polyethylene (LDPE) and polyethylene/commercial organo-modified montmorillonite (LDPE/OMMT) nanocomposite, were subjected to e-beam irradiation at different doses and both the molecular modifications and mechanical properties have been investigated through solubility, FT-IR, calorimetric and tensile tests. Moreover, in some of the irradiated systems photo-oxidation aging was performed and its effects were studied. The results show an enhancement with irradiation of the positive effect of the nano-filler loading, related to the increase of the mechanical properties, due to the increase of the nano-filler polymer interaction.Nevertheless calorimetric and FT-IR data indicate that the well known reduction of LDPE/OMMT nanocomposite resistance to photo-oxidation ageing, with respect to LDPE, is amplified by ionizing radiation. 相似文献
104.
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106.
刘明 《数学的实践与认识》2014,(20)
综合评价指数是一种广义上的统计指数,在讨论了综合评价指数与一般统计指数不同的基础上,引述了综合评价指数一般编制步骤并详细分析研究了综合评价指数编制过程中的权重确定,提出了基于等权设计思想的加权修正综合评价指数编制方法,最后以甘肃省装备制造产业为例进行了展示. 相似文献
107.
李敏 《数学的实践与认识》2012,42(6):145-150
引进诱导有序加权平均算子,建立诱导有序加权平均组合预测模型,借助它对四川省普通高等学校招生人数进行预测.通过两个误差指标值的比较,说明这种方法的合理性,从而为教育部门制定相关的就业体制提供依据. 相似文献
108.
This study looked at establishing a correlation between the variable melt flow index (VMFI) values of molten polypropylene (PP) with different piston-load masses using a standard MFI analyser. The study was done using virgin PP and recycled PP obtained from recycling Pb-acid batteries. The study showed that the results would fit a suitable power function equation where the size of the exponent reflects the increase in flow characteristics of the polymer with increased piston-load mass. The established correlation was then compared to the average molecular weight distribution of virgin PP determined by gel permeation chromatography (GPC). Good agreement was obtained for the range of grades of virgin PP samples that correlated well with the Mark-Houwink power law where the inverse of the MFI (1/MFI) would be proportional to the average molecular weight to the power of 3.4 (Mw3.4). GPC analysis cannot be effectively used to study recycled PP, where a number of factors can influence the melt flow properties such as fillers, impurities and the presence of polyethylene in the polymer matrix. Instead, a comparative understanding of the flow behaviour of recycled PP to that of virgin PP was done by using the VMFI method to possibly show the dissimilar polymer melt flow behaviour of using virgin and recycled PP material in injection moulding of new battery cases and lids, or when attempting to seal the lid to the battery case during manufacturing. 相似文献
109.
表面活性剂的临界胶束浓度(CMC)是个非常重要的物质特性参数, CMC在研究表面活性剂的工业应用和生物利用方面发挥着关键作用. 本工作提出了一个新的拓扑指数—扩展距离矩阵, 建立了一个稳定的构效关系模型, 并对175种表面活性剂的临界胶束浓度进行了计算预测. 结果表明, 基于新的拓扑指数建立的构效关系模型计算临界胶束浓度能给出稳定可靠的预测结果, 其预测结果相关性系数R2(training set)=0.9295, 相对标准偏差ARD(training set)=8.20%, R2(testing set)=0.9257, ARD(testing set)=6.76%. 与文献中模型预测结果的对比表明, 本工作在稳定性和可靠性上均有显著改善. 相似文献
110.
《Particuology》2022
The coaxial mixers enhance the suspension of concentrated slurries in an agitated reactor. In this research work, the complex slurry suspension and dissemination behavior in a coaxial slurry mixing system (comprised of a close clearance anchor rotating with a low speed and an inner axial impeller rotating with a high speed) was analyzed employing ERT (electrical resistance tomography, a non-intrusive flow visualization technique), and computational fluid dynamics (CFD). The numerical models were validated by comparing the axial solid concentration profiles generated using the ERT data and the CFD simulation results. The influences of various important parameters such as the diameter of the inner axial impeller, the inner impeller type, and the inner impeller spacing on the hydrodynamic characteristics of the slurry suspensions in a coaxial mixing vessel were thoroughly analyzed. The radial and axial velocity profiles of solid particles were generated using the validated mathematical models. The assessment of energy loss due to the solid–solid collisions, the particle–fluid frictions, and the particle–vessel wall collisions was conducted. The evaluation of optimum inner impeller clearance and inner impeller diameter is essential to attain a high degree of solids suspension and dissemination in a coaxial slurry mixing system. 相似文献