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21.
A study was made of the effects of electron irradiation of poly-vinylidene fluoride, using the DSC, FTIR, and X-ray techniques, as well as determining the percent cross-linking. Changes in crystallinity and melting point of the sample as a function of dose were found, the latter due to competition between cross-linking and crystallinity. The cross-linking was observed to increase with radiation dose. Chemical changes observed include the formation of carbonyl groups and double bonding, associated with the loss of HF. 相似文献
22.
A simple and rapid flow-injection spectrophotometric method for the determination of iron(III) and total iron is proposed.
The method is based on the reaction between iron(III) and O-acetylsalicylhydroxamic acid (AcSHA) in a 2 % methanol solution resulting in an intense violet complex with strong absorption
at 475 nm. Optimum conditions for the determination of iron(III) and the interfering ions were tested. The relative standard
deviation for the determination of 5 μg L−1 iron(III) was 0.85 % (n = 10), and the limit of detection (blank signal plus three times the standard deviation of the blank) was 0.5 μg L−1, both based on the injection volumes of 20 μL. The method was successfully applied in the determination of iron(III) and
total iron in water and ore samples. The method was verified by analysing a certified reference material Zn/Al/Cu 43XZ3F and
also by the AAS method. 相似文献
23.
24.
Ahmet Bekir Adem C. Cevikel 《Communications in Nonlinear Science & Numerical Simulation》2009,14(5):1804-1809
In this work, we established the exact solutions for some nonlinear physical models. The tanh–coth method was used to construct solitary wave solutions of nonlinear evolution equations. The tanh–coth method presents a wider applicability for handling nonlinear wave equations. 相似文献
25.
Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size,which facilitates circumvention of a directional band gap.Experiments reveal that two distinct beams emerge at crystal output,in agreement with the numerical results obtained through the finite-element method.Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space.Split beams propagate in equal amplitude,whereas beam splitting is destructed for oblique incidence above a critical incidence angle. 相似文献
26.
27.
π–π and CH···N interactions are vital in biological systems. In this study, stacking and hydrogen-bonded interactions in pyrazine
and triazine dimers were investigated by density functional theory combined with symmetry-adapted perturbation theory (DFT-SAPT)
and counterpoise (CP)-corrected supermolecular MP2, SCS-MP2, B3LYP-D and CCSD(T) calculations. All interaction energies were
computed using the optimized structures at the CP-corrected SCS/aug-cc-pVDZ level, which gave 1–2 kJ/mol lower interaction
energies than the ones computed at the MP2 level. For both dimers, doubly hydrogen-bonded and cross-(displaced) stacked orientations
were found to be the lowest energy ones. The reference CCSD(T) calculations favored the former structure in both dimer systems,
whereas MP2 and SCS-MP2 located the latter as the lowest energy isomer. In particular, the former was found to be lower in
energy than the latter by 2.28 and 1.01 kJ/mol at the CCSD(T)/aug-cc-pVDZ level for pyrazine and triazine, respectively. B3LYP-D
produced interaction energies in agreement with the CCSD(T) at the equilibrium geometries, but it overestimates them at the
short range and underestimates at the long intermonomer separations. Furthermore, it tends to give smaller equilibrium distances
compared to the CCSD(T). DFT-SAPT method was in a good agreement with the reference CCSD(T) calculations. This suggests that
DFT-SAPT can be employed to compute the full potential energy surface of these dimers. Moreover, DFT-SAPT calculations showed
that the electrostatic and dispersion contributions are the most important energy components stabilizing these dimers. The
present study aims to show which theoretical method is the most promising one for the investigation of intermolecular interactions
dominated by π–π and CH···N. Therefore, the findings obtained in this study can be used to unravel the structures of nucleic
acid bases and other systems stabilized by π–π and CH···N interactions. 相似文献
28.
Li MR Adem U McMitchell SR Xu Z Thomas CI Warren JE Giap DV Niu H Wan X Palgrave RG Schiffmann F Cora F Slater B Burnett TL Cain MG Abakumov AM van Tendeloo G Thomas MF Rosseinsky MJ Claridge JB 《Journal of the American Chemical Society》2012,134(8):3737-3747
Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO(3) (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO(3) has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO(3). 相似文献
29.
Deprotonation of a cyclotriphosphazene with a tert-butylamino group in the side chain results in ring expansion to a very stable, planar cyclohexaphosphazene derivative that still contains eight P-Cl bonds suitable for forming macromolecular structures. 相似文献