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71.
Hui Sun Hui Na Han‐Fu Wang Wan‐Jin Zhang Zhong‐Wen Wu Ryutoku Yosomiya 《Polymer International》2000,49(11):1539-1542
The synthesis of novel poly(ether ether ketone ketone)s containing a lateral group via the random copolymerization of 4,4′‐biphenol, tert‐butylhydroquinone and 1,4‐bis(p‐fluorobenzoyl)benzene is described. The copolymers were characterized by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and polarized optical microscopy (POM) observation. The results showed that the thermotropic liquid‐crystalline properties were achieved in the copolymers containing 30 mol% and 50 mol% tert‐butylhydroquinone, which have relatively lower melting temperatures due to the copolymerization effect. Both the crystalline–liquid‐crystalline transition (Tm) and the liquid‐crystalline–isotropic phase transition (Ti) were observable in the DSC thermograms, while the biphenol‐based poly(aryl ether ketone) has only one melting transition. The hydroquinone‐based polymer was shown to be amorphous. Thermogravimetric analysis (TGA) results showed that these copolymers are all high‐temperature resistant with higher glass transition temperature between 147 and 149 °C, and higher decomposition temperature Td in the range 480–520 °C. © 2000 Society of Chemical Industry 相似文献
72.
Formation of intermolecular excimers in polyethersulfone (PES) dichloromethane solutions were observed at a PES concentration about 2.7 × 10?2 mol/l by the fluorescence analysis. External light energy irradiation enabled the formation of intramolecular excimers in the PES dichloromethane solution. These chains can gain an access to each other in parallel though the molecular chains are considerably rigid. The electron micrograph of the PES film, heat treated at 200°C for 72 hours, presented a diffraction micrograph, which suggests that the PES molecular aggregation is changed from a randomly coiled amorphous phase to an ordered one. 相似文献
73.
74.
BaZrSi3O9:Eu2+, Sm3+ (Em:525 nm) is prepared. The role played by the trivalent co-doping ion Sm3+ in the afterglow and the type of trap are clarified. BaZrSi3O9:Eu2+, Sm3+ is found to produce Sm2+ during the excitation by X-ray absorption near-edge structure (XANES), etc., and it is thus proved that Sm3+ exists as an electron trap in the afterglow process. In the field of persistent phosphors activated by Eu2+ and Re3+ such as Sm3+ or Dy3+ having been widely utilized as emergency guide lights, clock faces, etc. for > 25 years, for the first time it is successfully observed that after excitation Re2+ is formed, transferring its electron to 5d band of Eu2+, returning to Re3+ by itself, where the decrease in Sm2+ coincides with the increase in Sm3+, and the two decay time τ1 and τ2 of PL (5D0→7F0) of Sm2+ coincides with the two evolution time of PL (5d→4f) of Eu2+. The behavior of electron transfer from Sm2+ to Eu2+ as a key of afterglow is detected. The detailed afterglow mechanism is proposed by analysis of thermoluminescence and defect reaction, which is very important for the in-depth investigation of the long afterglow material and the further improvement of the mechanism. 相似文献
75.
Summary Reaction of silanol groups on the surface of glass fiber with diisocyanates were investigated. It was found that the effect of organometallic catalysts upon the reaction varied with their metal ions or their ester substituents. Then the addition reaction of isocyanate group on glass fiber surface, with amino acid was carried out successfully to prepare a glass fiber-amino acid adduct. 相似文献
76.
Ohkuri Takatoshi; Yamagishi Akihiko 《Protein engineering, design & selection : PEDS》2003,16(8):615-621
We have investigated factors affecting stability at the subunitsubunitinterface of the dimeric enzyme 3-isopropylmalate dehydrogenase(IPMDH) from Bacillus subtilis. Site-directed mutagenesis wasused to replace methionine 256, a key residue in the subunitinteraction, with other amino acids. Thermal stability againstirreversible inactivation of the mutated enzymes was examinedby analyzing the residual activity after heat treatment. Themutations M256V and M256A increased thermostability by 2.0 and6.0°C, respectively, whereas the mutations M256L and M256Ihad no effect. Thermostability of the M256F mutated enzyme was4.0°C lower than that of the wild-type enzyme. To our surprise,increasing the hydrophobicity of residue 256 within the hydrophobiccore of the enzyme resulted in a lower thermal stability. Themutated enzymes showed an inverse correlation between thermostabilityand the volume of the side chain at position 256. Based on theX-ray crystallographic structure of Escherichia coli IPMDH,the environment around M256 in the B.subtilis homolog is predictedto be sterically crowded. These results suggest that Met256prevents favorable packing. Introduction of a smaller aminoacid at position 256 improves the packing and stabilizes thedimeric structure of IPMDH. The van der Waals volume of theamino acid residue at the hydrophobic subunit interface is animportant factor for maintaining the stability of the subunitsubunitinterface and is not always optimized in the mesophilic IPMDHenzyme. Received September 3, 2002; revised June 13, 2003; accepted June 20, 2003. 相似文献
77.
Novel Synthesis of Silica-Coated Ferrite Nanoparticles Prepared Using Water-in-Oil Microemulsion 总被引:2,自引:0,他引:2
Teruoki Tago Takatoshi Hatsuta Kanta Miyajima Masahiro Kishida Shizuka Tashiro Katsuhiko Wakabayashi 《Journal of the American Ceramic Society》2002,85(9):2188-2194
Ferrite nanoparticles (magnetite (Fe3 O4 ) and cobalt-ferrite (Co x Fe3− x O4 )) coated with silica (SiO2 ) were prepared using water-in-oil microemulsion of a polyoxyethylen(15)cetylether/cyclohexene system. Observation via transmission electron microscopy revealed that the ferrite nanoparticles were located nearly at the center of spherical SiO2 particles. The sizes of Fe3 O4 and Co x Fe3− x O4 nanoparticles were in the range of 8–12 nm and 10–14 nm, respectively, and the thickness of the SiO2 layer was ∼14.0 nm. The solid solution of cobalt ions into Fe3 O4 to form Co x Fe3− x O4 nanoparticles led to an increase in the coercivity of the SiO2 -coated ferrite nanoparticles. The coercivity increased with increasing amounts of added cobalt, obtaining a maximum value of 780 Oe around a Co/Fe ratio of 0.3–0.4. 相似文献
78.
Magnetic properties of metal layer deposited by reduction of polymer containing metal ions were investigated. Varying the ratio of the cobalt ion to the nickel ion in the polymer, the coercivity, the maximum flux density and the remanent flux density of the deposited metal layer were changed from 100 to 600 Oe, from 1 000 to 12 600 G and from 500 to 7 600 G, respectively. The X-ray diffraction pattern of the metal layer with excellent magnetic properties gives distinct peaks corresponding to the (101) and (100) planes of the crystal of α-Co. This suggests that such a deposited metal layer has the structure of highly crystalline metal layer. 相似文献
79.
Nanako Kato Tomoaki Masuzawa Yuki Kudo Yuka Kuwajima Hisato Yamaguchi Ken Okano Takatoshi Yamada Ichitaro Saito Tim Butler Nalin L. Rupesinghe Gehan A.J. Amaratunga 《Diamond and Related Materials》2008,17(2):95-99
An imaging device that could detect weak light of approximately 0.001 lx with high SN ratio is capable of opening up the possibility of creating artificial visions as a substitute for a human eye. In terms of sensitivity and SN ratio, amorphous selenium (a-Se) is known to be one of the best candidates among other photoconductive target. Combined with a-Se, a diamond cold cathode would be one of the best options in order to steadily emit electrons under low vacuum. The a-Se film is modified with Arsenic (As) and Tellurium (Te) to prevent crystallization and narrow the optical gap for red light detection. An RGB filtered light from a halogen light source was illuminated onto this modified a-Se film and the photo-response was measured for each color. The device could detect extremely weak illumination of under 0.39 lx, which is approximately the darkness under moonlight. Results of the photo-response compared between films with and without Te clarified that Te dopants enhances red light detection significantly. The illuminated light was then pulsed at 10 mHz and the current to time stability was observed. It showed clear correspondence between the intensity of the luminance and current, which the Te modified samples showed good response to other colored light as well. 相似文献
80.
Yahong Xie Shu Yin Takatoshi Hashimoto Yuichi Tokano Atsushi Sasaki Tsugio Sato 《Journal of the European Ceramic Society》2010,30(3):699-704
High purity tetragonal BaTiO3 powders were synthesized by a composite-hydroxide-mediated approach at low temperature using a novel hydrothermal reaction apparatus with a rolling system. The optimum synthesis conditions were explored, and the obtained samples were characterized by their XRD, TEM, TG-DTA and SEM. The powders with an average size of 150 nm in diameter were sintered to almost full theoretical density (ca. 99%) at 1200 °C for 5 h and the obtained ceramics presented a high dielectric constant (9500 at the Curie temperature). 相似文献