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991.
992.
Maurizio Cossi Benedetta Mennucci Roberto Cammi 《Journal of computational chemistry》1996,17(1):57-73
We present analytical expressions for the first derivatives of area and other geometrical quantities of polygonal tesserae defined on molecular surfaces. This is a necessary step in the calculation of free energy derivatives with respect to nuclear coordinates for molecular solutes, in the framework of the polarizable continuum method. An application to solute-solvent dispersion energy derivatives is presented. © 1996 by John Wiley & Sons, Inc. 相似文献
993.
994.
Polymers containing substituted 2-phenyl-benzoxazole side-chain groups: Synthesis and phase behavior
Roberto Centore Barbara Panunzi Antonio Roviello Augusto Sirigu Paola Villano 《Journal of polymer science. Part A, Polymer chemistry》1996,34(15):3203-3211
The synthesis of substituted 2-phenyl-benzoxazoles has been accomplished by ring closure of Schiff bases. The compounds have been used as precursors of acrylic derivatives displaying LC properties: Four comb-like homopolymers have been obtained by radical catalysis from the acrylic monomers. The polymers have been characterized by 1H-NMR, DSC, x-ray diffraction, viscometry, and polarizing microscopy. Three of the polymers exhibit liquid crystalline properties of smectic type. © 1996 John Wiley & Sons, Inc. 相似文献
995.
Soxhlet (methanol) and SFE extraction with carbon dioxide in the presence of modifiers at different temperatures (100–200°C) for the extraction of atrazine and its main metabolites from a soil sample were compared. The most effective extraction conditions for both atrazine and its metabolites (i.e. deethylatrazine and deisopropylatrazine) were Co2 modified with 20% molar methanol-trifluoroacetic acid (MeOH-TFA) (TFA 0.65M in MeOH) at 100°C, leading to an extraction efficiency comparable with that of Soxhlet extraction with MeOH for atrazine and ca. 20% higher for its main metabolites. The relative standard deviation (RSD) of SFE was lower than that obtained by Soxhlet extraction, probably because of less interference in the cGC-NPD determination. All the other modifiers evaluated (acetone, triethylamine, and methanol) were less effective than MeOH-TFA for the extraction of atrazine and its metabolites from a soil sample, even at high molar concentrations (20%) and use of higher extraction temperatures (200°C). These results indicate the importance of matrix effects and the need of the selection of an appropriate modifier in order to obtain quantitative extractions by SFE. 相似文献
996.
A conformational analysis has been performed on the isolated chains of copolymers of tetrafluoroethylene with hexafluoropropene, chlorotrifluoroethylene or perfluoromethyl vinyl ether, in comparison with polytetrafluoroethylene. The lowest energy conformations in accordance with the chain repeating distance of polytetrafluoroethylene in the low temperature crystal phase have been used in packing energy calculations. The results of both conformational and packing energy calculations suggest that the Cl group is easily tolerated in the crystal phase. The —CF3 group could also be tolerated in the crystal phase but at the cost of conformational and crystal lattice deformations. On the contrary, it can be concluded that the —OCF3 group is excluded from the crystal phase because its presence should require high energy values and wide deformations in the unit cell parameters. 相似文献
997.
A conversion - temperature - transformation (CTT) diagram was used to analyze several non-isothermal processes of polymer network formation: a) range of heating rates where reliable kinetic information can be obtained; b) a novel process involving part of the cure in the glassy state; c) phase separation in rubber-modified epoxies cured in heated molds. 相似文献
998.
999.
Eberhard Borsig Agnesa Fiedlerov Karl G. Husler Goerg H. Michler Roberto Greco 《Macromolecular Symposia》1994,83(1):147-156
A series of samples of polystyrene (PS) –polyethylene (PE) interpenetrating polymer network (IPN)–like system was prepared by synthesis in situ. The measurement of uniaxial compression modulus of the IPN samples was used for the determination of mean molar mass of the polymer chain between two junction points of the polymer network – M̌C. The electron microscopic records gave an evidence about two phase structure of the IPN samples. Generally, the crystalline part of PE network in all IPN investigated samples is relatively low. The influence of the concentration of crosslinking agent on mechanical behaviour of the IPN samples was studied. 相似文献
1000.
Despite the existence of an extensive literature, no definitive conclusion seems to emerge on the extent to which minorities are guaranteed by democratic rules in political systems. This paper contributes to this debate by proposing a modified Heigselmann and Krauss two-dimensional model of preferences in order to capture the role of abstention on minority representativeness. Regardless of the typology of abstention, simulation results show that voter abstention always benefits minorities. 相似文献