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891.
Several oxide dispersion strengthened (ODS) alloys have been tested for cyclic, long-term, high gas-velocity resistance to oxidation at 1100°C and hot corrosion at 900°C. Both nominally Ni-16Cr-4Al and Fe-20Cr-4.5Al ODS alloys were subjected up to 2500 cycles, where each cycle consisted of 1 hr in a hot, Mach 0.3 combusted gas stream followed by a 3-min quench in an ambient temperature, Mach 0.3 air blast. For comparison to existing technology, a coated superalloy was simultaneously tested. The ODS iron alloy exhibited clearly superior behavior, surviving 3800 oxidation and 2300 hot corrosion cycles essentially unscathed. While the ODS nickel alloys exhibited adequate oxidation resistance, the long-term hot corrosion resistance could be marginal, since the best life for such alloys under these conditions was only 1100 cycles. However, the hot corrosion resistance of the ODS Ni-base alloys is excellent in comparison to that of traditional superalloys. 相似文献
892.
The aim of the present study was to enhance the dissolution rate of valdecoxib using its solid dispersions (SDs) with polyethylene glycol (PEG) 4000. The phase solubility behavior of valdecoxib in the presence of various concentrations of PEG 4000 in water was obtained at 37°C. The solubility of valdecoxib increased with increasing amount of PEG 4000 in water. Gibbs free energy (ΔG°tr) values were all negative, indicating the spontaneous nature of valdecoxib solubilization, and they decreased with increase in the PEG 4000 concentration, demonstrating that the reaction conditions became more favorable as the concentration of PEG 4000 increased. The SDs of valdecoxib with PEG 4000 were prepared at 1:1, 1:2, 1:5, and 1:10 (valdecoxib: PEG 4000) ratio by melting method. Evaluation of the properties of the SDs was performed by using dissolution, Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM) studies. The SDs of valdecoxib with PEG 4000 exhibited enhanced dissolution rate of valdecoxib, and the rate increased with increasing concentration of PEG 4000 in SDs. Mean dissolution time (MDT) of valdecoxib decreased significantly after preparation of SDs and physical mixture with PEG 4000. The FTIR spectroscopic studies showed the stability of valdecoxib and absence of well-defined valdecoxib-PEG 4000 interaction. The DSC and XRD studies indicated the amorphous state of valdecoxib in SDs of valdecoxib with PEG 4000. The SEM pictures showed the formation of effective SDs of valdecoxib with PEG 4000, since well-defined changes in the surface nature of valdecoxib, SDs, and physical mixture were observed. 相似文献
893.
Solid dispersions of Celecoxib were prepared with hydroxypropyl β cyclodextrin by various methods such as physical mixture, cogrinding, kneading, and coevaporation. The dispersions were characterized by differential scanning calorimetry (DSC), X-ray diffraction patterns, infrared spectroscopy, and nuclear magnetic resonance studies. The DSC thermograms of the dispersions indicated potential of heat-induced interaction between Celecoxib and cyclodextrin that could influence in vitro drug dissolution. The dispersions exhibited faster rates of dissolution compared to that of Celecoxib. The kneaded dispersion with the fastest in vitro dissolution rate when compressed into tablets showed a better release profile compared to the tablets of pure Celecoxib. In vivo studies revealed that the kneaded dispersion provided for quicker response and was more effective in inhibiting rat paw edema as compared to Celecoxib alone, thus confirming the advantage of improved pharmacological activity of Celecoxib when administered as a solid dispersion with cyclodextrin. 相似文献
894.
本文分析和计算了瞬态啁啾对色散支持传输(Dispersion-SupportedTransmission)系统的作用,结果表明,在高速调制下瞬态啁啾可能严重影响系统性能。最后对如何改善系统性能进行了讨论。 相似文献
895.
地下水溶质径向弥散问题的混合拉普拉斯变换有限单元解 总被引:5,自引:0,他引:5
任理 《水动力学研究与进展(A辑)》1994,9(1):37-43
本文采用混合拉普接斯变换有限单元法,求解地下水溶质径向弥散问题,通过与精确解析解、数值解及砂槽试验资料对比,表明该算法效率高、精度好、能有效地克服数值困难。 相似文献
896.
本文用微扰法近似求解了含增益色散效应的NLS方程,由此解讨论了光纤放大器的增益色散对孤子的幅值和形状的影响。 相似文献
897.
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900.