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971.
High-temperature oxide scale growth at the ceramic-metal interface is a major contributor to the thermomechanical resistance
of thermal barrier coatings for hot stages of gas turbines. In order to better understand this phenomenon, microstructural
observations of the alumina scales formed at 1100 and 1200 °C under air, between low-pressure plasma-sprayed NiCrAlY and air
plasma-sprayed ZrO2-8.5 wt % Y2O3, have been performed by classical and analytical transmission electron microscopy on transverse thin foil specimens. The
evolution of the oxide grain morphology from the metal-oxide to the oxide-oxide interface suggests that the scale growth principally
takes place at the metal-oxide interface. Segregation of yttrium at oxide grain boundaries has been detected as well as significant
quantities of zirconium inside the alumina grains. The oxide growth seems to be dominated by a classical grain-boundary oxygen
diffusion mechanism. The presence of zirconium inside the alumina grains also suggests that Al2O3 partially forms by chemical reduction of ZrO2 by AI. The comparison between the microstructures observed and that of alumina scales grown under similar conditions on bare
MCrAlY alloys gives some insight into how the ceramic top-coat modifies NiCrAlY high-temperature oxidation mechanisms. 相似文献
972.
A procedure that facilitates at least-squares synthesis of periodic, discrete-time signals from Wigner quasi-distributions is proposed. The scheme is based on expanding the desired time sequence on a generally nonorthogonal, Gabor-type basis whose associated biorthogonal function presumably exists. The specific basis selection may crucially affect the efficiency and quality of the ensuing synthesis procedure. The cited basis type constitutes a considerable generalization over the standardly used orthogonal variety, thus creating previously unavailable degrees of freedom. Of primary significance is the acquired capability of generating time-frequency basis functions that are well localized. Localization is a highly desirable property that can advantageously serve in various applications. It is shown and numerically demonstrated that benefits of localization as well as the fact that achieving effective time-frequency basis localization renders a certain degree of oversampling unavoidable 相似文献
973.
This paper presents the results of laboratory measurements of relative permeability for two phase flow in partially saturated samples of unconsolidated sands. Relative permeabilities for tap water and air, de-aired water and nitrogen were measured using a steady—state technique. Three different sand samples (fine sand, heterogeneous sand and coarse sand) were tested. 相似文献
974.
975.
Eugene S. Ferguson 《Research in Engineering Design》1992,4(1):3-11
Engineering designers, who decide the physical shape and technical features of the built world, tend to forget that their predecessors have been making design decisions for hundreds of years. This paper gives several historical examples of design experience which can supply useful insights today, because the essential nature of engineering has not changed.Adapted from: Eugene S. Ferguson,Engineering and the Mind's Eye. Cambridge, Massachusetts: MIT Press, 1992 相似文献
976.
This paper develops and demonstrates by computer simulations new nonlinear system stochastic techniques to determine the amplitude-domain and frequency-domain properties of nonlinear systems as described in nonlinear differential equations of motion. From measurements of input excitation data and output response data, this new method, based upon multiple-input/single-output (MI/SO) linear analysis of reverse dynamic systems, allows for the efficient identification of different nonlinear systems. Nonlinear systems simulated here include Duffing, Van der Pol, Mathieu, and Dead-Band systems. Features of this new method are: (1) it can be implemented using established MI/SO linear procedures and computer programs; (2) it determines nonlinear system amplitude properties separate from nonlinear system frequency properties; (3) it quantifies relative contributions from different nonlinear terms by using appropriate coherence functions; (4) it gives results that are independent of the input or output probability distributions, spectral properties, and input excitation levels. 相似文献
977.
Kiang S.-Z. Baker R.L. Sullivan G.J. Chiu C.-Y. 《IEEE transactions on image processing》1992,1(2):162-169
A pruning algorithm of P.A. Chou et al. (1989) for designing optimal tree structures identifies only those codebooks which lie on the convex hull of the original codebook's operational distortion rate function. The authors introduce a modified version of the original algorithm, which identifies a large number of codebooks having minimum average distortion, under the constraint that, in each step, only modes having no descendents are removed from the tree. All codebooks generated by the original algorithm are also generated by this algorithm. The new algorithm generates a much larger number of codebooks in the middle- and low-rate regions. The additional codebooks permit operation near the codebook's operational distortion rate function without time sharing by choosing from the increased number of available bit rates. Despite the statistical mismatch which occurs when coding data outside the training sequence, these pruned codebooks retain their performance advantage over full search vector quantizers (VQs) for a large range of rates. 相似文献
978.
979.
980.
Migun N. P. Prokhorenko P. P. Chizh S. G. 《Russian Journal of Nondestructive Testing》2002,38(9):704-708
A new mechanism of aw development has been discovered and experimentally tested. The mechanism is based on the film ow of the penetrant inside the aw channel. 相似文献