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排序方式: 共有1943条查询结果,搜索用时 14 毫秒
91.
TK Lin CH Cheng SD Chen CW Liou CR Huang YC Chuang 《International journal of molecular sciences》2012,13(7):8722-8739
Parkinson's disease (PD) is a progressive neurological disorder marked by nigrostriatal dopaminergic degeneration. Evidence suggests that mitochondrial dysfunction may be linked to PD through a variety of different pathways, including free-radical generation and dysfunction of the mitochondrial Complex I activity. In Lewis rats, chronic systemic administration of a specific mitochondrial Complex I inhibitor, rotenone (3 mg/kg/day) produced parkinsonism-like symptoms. Increased oxidized proteins and peroxynitrite, and mitochondrial or cytosol translocation of Bim, Bax or cytochrome c in the striatum was observed after 2-4 weeks of rotenone infusion. After 28 days of systemic rotenone exposure, imunohistochemical staining for tyrosine hydroxylase indicated nigrostriatal dopaminergic neuronal cell degeneration. Characteristic histochemical (TUNEL or activated caspase-3 staining) or ultrastructural (electron microscopy) features of apoptotic cell death were present in the striatal neuronal cell after chronic rotenone intoxication. We conclude that chronic rotenone intoxication may enhance oxidative and nitrosative stress that induces mitochondrial dysfunction and ultrastructural damage, resulting in translocation of Bim and Bax from cytosol to mitochondria that contributes to apoptotic cell death in the striatum via cytochrome c/caspase-3 signaling cascade. 相似文献
92.
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94.
S.‐P. Rwei A.‐Y. Liu G.‐S. Liou K.‐C. Cheng W. Guo 《Polymer Engineering and Science》2004,44(2):376-387
This study investigates the curing kinetics, thermal properties and decomposition kinetics of cresol novolac epoxy (CNE) with two curing agents, 2‐(6‐oxido‐6H dibenz(c,e)(1,2) oxaphosphorin‐6‐yl)‐1,4‐benzenediol (ODOPN), and phenol novolac (PN). In comparison with the conventional PN system, introducing ODOPN, a phosphorus‐containing bulky pendant group, into CNE increases Tg by 33°C, char yield from 30% to 38%, and LOI from 22 to 31. The DSC curing study reveals that the Ea of the CNE/ODOPN epoxy can be obtained by Kissinger's method. The resulting Ea values indicate that the catalytic effect of EMI is insignificant on CNE/ODOPN but is marked on CNE/PN, whose Ea was reduced from 131.5 to 75.6 KJ/mole. This result may be caused by the fact that the symmetric diol attached to the 1 and 4 positions of the naphthalene ring in ODOPN sets up a steadily resonating structure and inhibits the catalytic action. Further investigating the conversion ratio with curing temperature yielded experimental data that agreed closely with Kaiser's model. The orders of the autocatalyzed reaction, m, and the crosslinking reaction, n, are close to 0.5 and 1.0, respectively, independently of the scan rate. Finally, the TGA decomposition study by Ozawa's method demonstrates that the mean Ea declines with the phosphorus content, because the easy decomposition of the phosphorus compound in the initiation stage facilitates the formation of an insulating layer. However, results in this study further reveal an increasing tendency for Ea with decomposition conversion for an ODOPN/PN mixture with the ODOPN content of over 50%, probably because of the retardation of gas diffusion by the insulating layer of phosphorus compound. 相似文献
95.
Polystyrene‐clay nanocomposite (PsCN) materials were synthesized and their properties of crystallinity, thermal behavior, and dielectric characteristics were investigated. A polymerizable cationic surfactant, [2‐(dimethylamino)ethyl]triphenylphonium bromide, was used for the intercalation of montmorillonite (MMT). The organophilic MMT was prepared by Na+‐exchanged MMT and ammonium cations of a cationic surfactant in an aqueous medium. Organophilic styrene monomers were intercalated into the interlayer regions of organophilic clay hosts followed by a free‐radical polymerization. Exfoliation to 2 wt % MMT in the polystyrene (PS) matrix was achieved as revealed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal properties by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were also studied. The dielectric properties of PsCNs in the form of film with clay loading from 1.0 to 5.0 wt % were measured under frequencies of 100 Hz–1 MHz at 25–70°C. A decreased dielectric constant and low dielectric loss were observed for PsCN materials. The dielectric response at low frequency that originated from dipole orientation was suppressed due to the intercalation of clay materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1368–1373, 2004 相似文献
96.
Fabrication of alumina-chromium carbide composites was investigated by PTFE-activated Cr2O3/Al/C combustion synthesis. PTFE was employed as not only a reaction promoter, but a carburizing agent. Three reaction systems were prepared with different contents of carbon for the synthesis of Cr23C6, Cr7C3, and Cr3C2. The amounts of PTFE were selected to ensure combustion synthesis in the SHS (self-propagating high-temperature synthesis) mode and to provide carbon in quantities of 15 and 25?mol% of the total carbon. Experimental results showed that the combustion wave velocity and temperature decreased with increasing carbon, but increased with PTFE. A correlation between combustion wave velocity and temperature contributed to determination of the activation energy Ea =?89.15?kJ/mol for the combustion reaction. The increase of PTFE also improved formation of chromium carbides. As a result, the Cr23C6– and Cr7C3–Al2O3 composites were produced with almost no impurities. Due to a loss of carbon in carbothermic reduction, the Cr3C2–Al2O3 composite was obtained with Cr7C3 as the secondary carbide. SEM micrographs and DES analyses indicated that spherical carbide grains with a size of 0.5–3.0 μm were synthesized. 相似文献
97.
A soluble polyimide prepared from 7,7′‐bis(4‐aminophenoxy)‐4,4,4′,4′‐tetramethyl‐2,2′‐spirobichroman and 4,4′‐hexafluoroisopropylidenediphthalic anhydride was mixed with organo‐modified montmorillonite or synthetic mica in N,N‐dimethylacetamide. The content of the clay minerals was 1, 2, and 4 wt %, respectively. Transparent, flexible, and tough films could be cast from the hybrid solutions. The hybrid films were characterized with wide‐angle X‐ray scattering (WAXS), transmission electron microscopy, thermomechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. The WAXS results revealed that the montmorillonite was dispersed more homogeneously than the synthetic mica in the polyimide matrix. In both polyimide/clay hybrids the addition of clay caused thermal expansion coefficients to decrease, and the thermal stability was slightly enhanced. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2067–2072, 2001 相似文献
98.
Shibo Li Liou Xiao Guiming Song Xiaomin Wu Wim G. Sloof Sybrand van der Zwaag 《Journal of the American Ceramic Society》2013,96(3):892-899
This work reports the oxidation and crack healing behavior of a fine‐grained (~2 μm) Cr2AlC MAX phase ceramic. The oxidation behavior was investigated in the temperature range 900°C–1200°C for times up to 100 h. The material showed a good oxidation resistance, owing to the formation of a dense and thin α‐Al2O3 layer. The microstructure, composition and thickness of the oxide scale were characterized. Its oxidative crack healing behavior as a function of temperature, healing time, and initial crack size was studied systematically. The material showed excellent healing behavior. The main crack healing mechanism is the filling of the crack by oxides well adhering to the crack faces. The crack geometry before and after healing was characterized by X‐ray tomography. Three‐point bend tests showed the dependence of strength recovery at 1100°C as a function of initial crack length and healing time. 相似文献
99.
Ce0.9Gd0.1O1.95 ceramics were prepared using a simple and effective process in this study. Without any prior calcination, the mixture of raw materials was pressed and sintered directly. The reaction of the raw materials occurred during the heating up period by passing the calcination stage in the conventional solid-state reaction method. More than 99.5% of theoretical density was obtained for Ce0.9Gd0.1O1.95 sintering at 1500–1600 °C. Fine grains (<1 μm) formed in pellets sintered at 1450 °C. The homogeneity of grains increased with the sintering temperature. The grains grew to >4.5 μm in pellets sintered at 1600 °C. The reactive-sintering process is proved to be a simple and effective method in preparing Ce0.9Gd0.1O1.95 ceramics for solid electrolyte application. 相似文献
100.
Low-temperature synthesis of BiNbO4 ceramics using reaction-sintering process was investigated. Orthorhombic BiNbO4 phase together with minor triclinic BiNbO4 phase were found in the pellets. The phase transition temperature in BiNbO4 with 0.5 wt% CuO addition was lowered from 960 °C via traditional route to 880 °C when the reaction-sintering process was used. After 920 °C sintering for 4 and 6 h, densities 6.8–6.85 g/cm3 (94% of the theoretical value) were obtained. The abnormal grain growth in BiNbO4 via traditional route was not observed in this study. 相似文献