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排序方式: 共有884条查询结果,搜索用时 15 毫秒
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Effect of grain boundary phase on the thermal conductivity of aluminium nitride ceramics 总被引:2,自引:0,他引:2
Ching -Fong Chen M. E. Perisse A. F. Ramirez N. P. Padture H. M. Chan 《Journal of Materials Science》1994,29(6):1595-1600
AIN with high thermal conductivity was fabricated by pressureless sintering with Y2O3 as the sintering aid. The thermal conductivity was observed to increase with sintering time (up to 8 h) at 1810 °C. The distribution of the sintering aid was identified as one of the major factors influencing the thermal conductivity in AIN. Non-uniform distribution of the grain boundary phase was found to be associated with a significant amount of porosity, resulting in the enhancement of phonon scattering and thereby lowering the thermal conductivity. 相似文献
4.
N. B. Kavukcuoglu E. Arteaga-Solis S. Lee-Arteaga F. Ramirez A. B. Mann 《Journal of Materials Science》2007,42(21):8788-8794
Absence of fibrillin 2 (Fbn2), a non-collagenous bone protein, causes a connective tissue disorder called congenital contractural arachnodactyly (CCA)
and has been associated with decreased bone mineral density. Nanoindentation and Raman microspectroscopy have been used to
compare the mechanical and chemical properties of cortical bone from femora of Fbn2−/− deficient mice and their wild-type controls (Fbn2+/+). It was found that Fbn2−/− bones have significantly lower hardness and elastic modulus compared to Fbn2+/+ bones, especially in the mid-cortical section. The Raman analysis showed little difference with genotype except for a decrease
in type-B carbonate substitution in the endosteal region of Fbn2−/− bones. The results indicate that Fbn2 plays a direct role in determining the mechanical properties of bone. 相似文献
5.
The recovery of copper from chalcopyrite by leaching is complex not only due to the slow dissolution kinetics of this mineral
in most aqueous media but also due to the production of solutions that are heavily contaminated with iron. On the contrary,
the leaching of sulfidized chalcopyrite is very attractive because of a faster and more selective dissolution of copper compared
to the leaching of the untreated chalcopyrite. In this work, the results of leaching in H2SO4-NaCl-O2 solutions of sulfidized chalcopyrite concentrate are discussed. Experiments were carried out with chalcopyrite concentrates
previously reacted with elemental sulfur at 375 °C for 60 minutes. The results showed that the concentration of chloride ions
below 0.5 M, temperature, and leaching time are important variables for the extraction of Cu. On the other hand, Fe extraction
was little affected by the same variables, remaining below 6 pct for all the experimental conditions tested. Microscopic observations
of the leached particles showed that the elemental sulfur produced by the reaction does not form a coherent layer surrounding
the particle, but rather concentrates in certain locations as large clusters. The leaching kinetics can be accurately described
by a nonreactive core-shrinking rim topochemical expression for spherical particles 1 − (1 − 0.45X)1/3=kt. The activation energy found was 76 kJ/mol for the range 85 °C to 100 °C. 相似文献
6.
I Ramirez 《Canadian Metallurgical Quarterly》1994,56(3):549-554
Previous studies suggest that rats might be able to discriminate between sucrose and fructose, but no previous study has examined this possibility in much detail. Rats were conditioned to avoid either sucrose or fructose by injecting them with lithium chloride when they drank these substances. Control rats were given the same injections but were not exposed to either sugar during training. After training, the rats were given a choice of fructose vs. sucrose. Data from control rats provided information about the relative taste intensity of the sugars. If the sugars possess only a single gustatory quality, control rats should prefer the sweeter sugar; under this assumption, sucrose appears to be two-four times sweeter than fructose. The two sugars share a common taste because rats trained to avoid sucrose avoided fructose when the fructose concentration was much greater than the sucrose concentration. Nevertheless, the two sugars are discriminable because, when the apparent sweetness of the sugars was matched, rats showed a greater aversion to the sugar they were trained to avoid. Aversions to sucrose and fructose also generalized to maltodextrins, but sucrose may have a somewhat greater maltodextrin flavor than does fructose. It is proposed that the biological function of maltodextrin taste is to allow animals to sense the ratio of glucose to fructose in foods. 相似文献
7.
We have applied near-edge X-ray absorption fine structure (NEXAFS) to characterize the surface and bulk properties of LixNi1–xO catalysts. In our experimental set-up, NEXAFS spectra of powder materials could be obtained by measuring the intensity of either electron-yield or fluorescence-yield. While the electron-yield method is sensitive only to the top few atomic layers, the fluorescence-yield method can detect species up to a few thousands angstroms deep into the bulk structure. The ability to distinguish surface and bulk compositions is demonstrated in studies of a number of Li0.5Ni0.5O samples, of which the surface compositions vary as a function of preparation procedures. In addition, NEXAFS investigations following the reaction of LixNi1–xO with CH4 have also been carried out and the results indicate that the initial surface reaction intermediates are Li2CO3. 相似文献
8.
F.J. Medellín‐Rodríguez J.M. Mata‐Padilla B.S. Hsiao M.A. Waldo‐Mendoza E. Ramírez‐Vargas S. Sánchez‐Valdes 《Polymer Engineering and Science》2007,47(11):1889-1897
The influence of organomodified nanoclay (montmorillonite) on the crystallization and melting mechanisms of isotactic polypropylene (iPP) was studied. Films of both neat polymer and clay nanocomposites were prepared after molecular weight optimization through melt extrusion. Products exhibited the tactoidlike morphology since no compatibilizers were used. The effect of introduction of nanoclay within the polymer was studied through isothermal crystallization and linear heating. The results indicated that low nanoclay concentrations induce the formation of the β‐crystalline structure, its formation being inhibited with high nanoclay contents. Dynamic nonisothermal bulk crystallization experiments indicated that nanoclays act as nucleating agents of iPP. Isothermal, bulk crystallization studies indicated that the crystallization process (induction time and crystallization kinetics) is proportionally accelerated by the nanoclay presence. There was also an accelerated formation of secondary crystallization when nanoclays were present in high concentrations. POLYM. ENG. SCI., 47:1889–1897, 2007. © 2007 Society of Plastics Engineers 相似文献
9.
Different thermal behavior of neonatal hepatic and cerebral 3-hydroxy-3-methylglutaryl-CoA reductase
The Arrhenius plots of hepatic and cerebral 3-hydroxy-3-methylglutaryl-CoA reductase activity were studied in neonatal chicks
fed with a standard diet. Supplementation of the diet with 2% cholesterol from hatching has no effect on the thermal characteristics
of the brain enzyme. The Arrhenius plot of brain reductase was practically similar to that found in control chicks. However,
hepatic reductase was inhibited by cholesterol feeding. Dietary cholesterol increased the cholesterol/lipidic phosphorus molar
ratio in liver microsomes, whereas no significant differences were observed in brain microsomes. These results are in agreement
with the hypothesis that activity of hepatic reductase is regulated by the fluidity of microsomal membrane and show that cholesterol
feeding does not alter the fluidity of microsomal membranes in neonatal chick brain having, thus, no effect on the thermal
behavior of cerebral reductase. 相似文献
10.
The concept of volume averaging is used to theoretically study the mechanisms of mass dispersion, adsorption, and dead-space volume. These mechanisms are important to the understanding of miscible surfactant flooding. After simpiffication based on order-of-magnitude scaling, a linear core model is solved using state variable finite-difference techniques. Mass dispersion and adsorption are shown to be important model parameters while dead-space volume is a rather insensitive model parameter. 相似文献