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排序方式: 共有316条查询结果,搜索用时 15 毫秒
91.
Composites of mesoporous alumina and Fe- or Co-containing ferromagnetic nanoparticles have been prepared from appropriate
aqueous metal chloride solutions by a sol-gel process. The synthesis products were heat-treated at different temperatures
in air or vacuum and then characterized by a variety of techniques. The results indicate that the mesoporous structure of
the nanostructured composites has a large specific surface area, a narrow, unior bimodal pore size distribution, and high
thermal stability. The phase composition of the magnetic particles in the X-ray amorphous oxide matrix strongly depends on
the heat-treatment conditions. 相似文献
92.
93.
A. V. Golovanov G. A. Men'shikova S. D. Zinchenko S. V. Efimov E. S. Popov A. A. Bat'kov P. P. Stepanov Yu. V. Ryabov I. G. Rodionova O. N. Baklanova T. M. Efimova A. A. Bykov A. A. Sharapov L. A. Malyshkina A. V. Drandusov 《Metallurgist》2005,49(5-6):211-219
Results obtained from comprehensive corrosion tests have established that in addition to limiting the content of corrosion-active
nonmetallic inclusions in steel to make it resistant to corrosion, it is also desirable to restrict the steel's contents of
sulfur, manganese, and silicon. The new specifications for steels 20-KS (corrosion-resistant) and 20-KSKh (corrosion- and
cold-resistant) were therefore developed based on steel 20sp, which is distinguished by its relatively low contents of manganese
and silicon. These steels also have a limited sulfur content, and they are microalloyed with niobium or vanadium to obtain
a fine-grained structure. All the other indices of the steels meet the requirements of SNiP. Mastering the production of welded
tubes made of steel 20-KSKh is an important step toward the goal of improving the durability of oil-field tubing in Western
Siberia. Such tubes are the first type of tubular metal product that has been guaranteed to be clean with respect to corrosion-active
nonmetallic inclusions, and guarantees of this kind are a prerequisite to ensuring that pipelines have satisfactory corrosion
resistance and last for their normal service life.
__________
Translated from Metallurg, No. 6, 43–48, June, 2005. 相似文献
94.
This study compared the quality of anaesthesia and surgical access afforded by two techniques for the administration of anaesthesia during paediatric chair dental procedures. A total of 50 ASA 1 paediatric day case patients were randomly assigned to receive anaesthesia through either the traditional Goldman nasal mask or through a nasopharyngeal airway. Patients in the nasal mask group were judged to have significantly worse airway patency (p = 0.0001) and significantly more episodes of airway obstruction (14 vs. 4; p = 0.0032) than those in the nasopharyngeal airway group. Anaesthetic, surgical and oxygen saturation data did not differ significantly between the two groups. Operating conditions were universally graded as excellent in the nasopharyngeal airway group, while those in the nasal mask group were graded as excellent/good in only 79% of cases (p < 0.0001). These results suggest that better quality anaesthesia and operating conditions can be achieved by using a nasopharyngeal airway rather than the traditional nasal mask for the administration of anaesthesia to paediatric chair dental patients. 相似文献
95.
96.
GP Amarante-Mendes AJ McGahon WK Nishioka DE Afar ON Witte DR Green 《Canadian Metallurgical Quarterly》1998,16(11):1383-1390
Bcr - Abl is the molecule responsible for both the transformation phenotype and the resistance to chemotherapeutic drugs found in chronic myelogenous leukemia (CML) cells. Wild-type HL-60, a transformed pro-myelocytic cell line, is very susceptible to apoptosis-inducing agents. We show here that expression of Bcr - Abl in HL-60 cells rendered them extremely resistant to apoptosis induced by a wide variety of agents. The anti-apoptotic effect of Bcr - Abl was found to be independent of the phase of the cell cycle. Treatment with antisense oligonucleotides directed to bcr decreased the expression of the ectopic bcr - abl and restored susceptibility to apoptosis. Double mutations affecting the autophosphorylation site and the phosphotyrosine-binding motif (FLVRES) have been previously shown to impair the transforming activity of Bcr - Abl in fibroblasts and hematopoietic cells, however HL-60 cells expressing this double mutant molecule exhibited the same level of resistance to apoptosis as those expressing the wild-type Bcr - Abl. Interestingly, wild type and mutant Bcr - Abl induced in HL-60 cells a dramatic down regulation of Bcl-2 and increased the levels of Bcl-xL. The level of Bax did not change in response to the presence of Bcr - Abl. Antisense oligonucleotides targeted to bcl-x downregulated the expression of Bcl-x, and increased the susceptibility of HL-60. Bcr - Abl cells to staurosporine. Importantly, HL-60 cells overexpressing Bcl-xL showed higher expression of Bcl-xL but lower resistance to apoptosis when compared to HL-60. Bcr - Abl cells. The results described here show that Bcr - Abl is a powerful mammalian anti-apoptotic molecule and can act independently of Bcl-2. Bcl-xL, however, seems to participate in part in Bcr - Abl-mediated resistance to apoptosis in HL-60 cells. 相似文献
97.
98.
This paper examines the possibility of modifying the surface of carbon fibers with tantalum carbide via reactive chemical vapor deposition at temperatures from 800 to 1000°C. We have studied the surface morphology and topography of the coatings on carbon fibers and determined their phase composition by a variety of physicochemical characterization techniques, including X-ray diffraction, high-resolution scanning electron microscopy, and atomic force microscopy. The strength of the modified fibers has been measured at room temperature. The results demonstrate that the coatings are continuous and uniform in thick-ness along and across the monofilaments, with good surface adhesion. The microstructure and surface topography of the coatings depend on the deposition time and temperature. 相似文献
99.
Victor V. Lozanov Aleksei V. Utkin Tatyana A. Gavrilova Anatoly T. Titov Anatoly I. Beskrovny Gleb A. Letyagin Galina V. Romanenko Natalya I. Baklanova 《Journal of the American Ceramic Society》2022,105(3):2323-2333
A variety of the ternary Hf–Ir–B phases formed via the reaction between iridium and hafnium diboride at elevated temperatures was found. The data on the phase and elemental composition, as well as crystal structure, obtained by powder and single-crystal X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometer, and time-of-flight neutron diffraction analysis unambiguously confirm that HfIr3Bx solid solution, two known ternary borides (HfIr3B4, Hf2Ir5B2), as well as two novel ternary HfIr2.1B1.3 and HfIr5.7B2.7 phases, are formed at elevated temperatures. This result is fundamentally different from that previously obtained by us for the Hf–Ir–C system in which only one binary intermetallic compound, HfIr3, was produced. The measured Vickers microhardness for all the aforementioned ternary borides (13–19 GPa) allows us to consider them hard. The coefficients of thermal expansion of ternary borides were measured by in situ high-temperature X-ray analysis. 相似文献
100.
Effect of frozen storage on protein denaturation in bovine muscle 1. Myofibrillar ATPase activity and differential scanning calorimetric studies 总被引:2,自引:0,他引:2
The effect of frozen storage on myofibrillar ATPase activity and thermal transitions in bovine muscle was investigated. Myofibrillar ATPase activity and total enthalpy of denaturation (ΔH) decreased with time of storage. The rate of decrease was lower at −20°C than at −5°C or −10°C. Differences in behaviour during storage of muscle after fast or slow freezing could be attributed to differences in ice recrystallization. The observed decreases in area of the first peak seen in the thermograms and Ca2+ -myo-fibrillar ATPase activity show that the myosin head denaturated progressively during storage. The myosin tail also denaturated during storage but the thin filament remained unaltered. Kinetic analysis suggested that the denaturation of the myofibrillar proteins took place through two consecutive first order reactions; an initial rapid reaction followed by a slower one. 相似文献