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911.
The catalytic activity for the gas phase combustion of ethylene of an IrO2 film, used as electrode in a solid electrolyte cell, can be increased by polarizing the metal–solid electrolyte interface. The catalytic activity remains higher even after current interruption. To explain the increase in the open circuit rate after polarization we speculate that the IrO2 catalyst is oxidized at the catalyst–solid electrolyte interface, forming IrO2+delta, which is transported by surface and/or bulk diffusion to the gas exposed catalyst, thus modifying its catalytic activity. 相似文献
912.
Robust observer-based OMF vibration control of flexible linkage mechanisms using piezoelectric films
Jyh-Horng Chou Ing-Rong Horng Wen-Hwei Liao 《International Journal of Mechanical Sciences》1998,40(8):65
Based on the state-space model of the flexible linkage mechanism equipped with piezoelectric films, a robust control methodology for actively suppressing the elastodynamic responses of the high-speed flexible linkage mechanism with linear structured time-varying parameter perturbations by employing an observer-based optimal model-following (OMF) controller is presented. The advantage of the proposed robust observer-based OMF control methodology is that it not only can avoid the problem of how to choose the appropriate weighting matrices in the quadratic cost function of the linear-quadratic/linear-quadratic-Gaussian (LQ/LQG) control method but also can make the controlled closed-loop system to have the specified system response characteristics. Besides, in order to guarantee that the designed observer-based OMF controller can make the controlled flexible linkage mechanism system to avoid the possibilities of both spillover-induced instability and time-varying-parameter-perturbation-induced instability, a robust stability criterion is also presented in this paper. The control method, presented in this paper, can not only make the controlled closed-loop system to have the specified system response characteristics, but also guarantee the controlled closed-loop system to have robust stability properties by using the proposed robust stability criterion; while those control methods reported recently do not have these above-mentioned merits. Finally, an active robust vibration control problem of a slider-crank mechanism is provided for illustrating the applicability of the proposed method. 相似文献
913.
Weighted universal image compression 总被引:1,自引:0,他引:1
We describe a general coding strategy leading to a family of universal image compression systems designed to give good performance in applications where the statistics of the source to be compressed are not available at design time or vary over time or space. The basic approach considered uses a two-stage structure in which the single source code of traditional image compression systems is replaced with a family of codes designed to cover a large class of possible sources. To illustrate this approach, we consider the optimal design and use of two-stage codes containing collections of vector quantizers (weighted universal vector quantization), bit allocations for JPEG-style coding (weighted universal bit allocation), and transform codes (weighted universal transform coding). Further, we demonstrate the benefits to be gained from the inclusion of perceptual distortion measures and optimal parsing. The strategy yields two-stage codes that significantly outperform their single-stage predecessors. On a sequence of medical images, weighted universal vector quantization outperforms entropy coded vector quantization by over 9 dB. On the same data sequence, weighted universal bit allocation outperforms a JPEG-style code by over 2.5 dB. On a collection of mixed test and image data, weighted universal transform coding outperforms a single, data-optimized transform code (which gives performance almost identical to that of JPEG) by over 6 dB. 相似文献
914.
LW Lee HC Peng WC Ko WC Hung CH Su CH Lin TF Huang MH Yen JR Sheu 《Canadian Metallurgical Quarterly》1999,364(2-3):239-246
In this study, specific platelet activating factor (PAF) receptor antagonist ginkgolide B (BN52021) was tested for its antiplatelet activity in zymosan activated polymorphonuclear neutrophil-induced platelet aggregation. Triflavin was also tested for its antiplatelet activity compared with PAF receptor antagonist. Triflavin, an Arg-Gly-Asp-containing disintegrin purified from venom peptide inhibited platelet aggregation by interfering with the interaction of fibrinogen with the glycoprotein IIb/IIIa complex. Furthermore, we also report an efficient high resolution method for quantitative analysis of PAF using high-performance capillary electrophoresis (HPCE). The supernatant of polymorphonuclear neutrophils after their activation by opsonized zymosan induces the aggregation of washed rabbit platelets. In rabbit platelets, BN52021 (100-1000 microM) only partially inhibited activated polymorphonuclear neutrophil-induced platelet aggregation, and its maximal inhibition was estimated to be about 79%. Triflavin also partially inhibited platelet aggregation about 82% induced by activated polymorphonuclear neutrophils. Furthermore, after treatment with a combination of triflavin (0.26 microM) with various concentrations of BN52021 (4-1000 microM), the inhibitory effect of platelet aggregation was almost completely. This inhibition was greater than that produced by the individual drugs alone. These results indicate that a combination of glycoprotein IIb/IIIa complex and PAF receptor antagonist could completely inhibit activated polymorphonuclear neutrophil-induced platelet aggregation. In addition, the amount of PAF released from zymosan (6 mg/ml)-activated polymorphonuclear neutrophils was accurately calculated about 11.8+/-1.5 ng/10(6) cells, and did not further increase even at a high concentration of zymosan (10 mg/ml). These results suggest that PAF play a major role in the interaction between platelets and polymorphonuclear neutrophils. This interaction may be important in the pathogenesis of thrombosis and inflammatory diseases. Our present findings support the hypothesis that combination therapy with glycoprotein IIb/IIIa complex antagonists and PAF receptor antagonists may represent a new approach to the treatment of ischemic disorders. 相似文献
915.
A multiple linear regression model was developed for the prediction of the 28-day compressive strength of Portland Pozzolan
Cement (PPC) containing Santorin Earth as an admixture. The independent variables of the model were: (1) the compressive strength
at the age of 2 days, (2) the compressive strength after autoclave hydrothermal treatment at 2.07 N/mm2 (300 psi) and 214°C for 3 h, (3) the C3S/C2S ratio of the clinker, (4) the insoluble residue of the cement, (5) the pozzolanic activity factor and (6) the C3A content of the clinker. The evaluation of the proposed model was performed by various statistical tests, all of which were
successful. These tests included: multiple correlation, test of the significance of coefficients (t-test), estimation of confidence
intervals for coefficients, test for outliers and unusual residuals, test for influential points, conditional sums of squares,
R-squared and analysis of variance. There was very good agreement between the strength predicted by the multiple regression
model and experimental results.
Résumé Un modèle de régression multiple linéaire a été developpé pour la prédiction de la résistance en compression du ciment pozzolanique Portland, contenant de la Terre de Santorin comme mélange. Les variables indépendantes du modèle étaient: (1) la résistance en compression pour l’age de 2 jours, (2) la résistance en compression après un traitement de 3 heures dans un autoclave à 2,07 N/mm2 (300 psi) et 214°C, (3) le rapport C2S/C2S du clinker, (4) la quantité d’insolubles du ciment, (5) le facteur d’activité pozzolanique et (6) la quantité de C3A du clinker. L’évaluation du modèle proposé à été effectuée par une série d’essais statistiques: une corrélation multiple, un essai de signification des coefficients (t-test), estimation des intervalles de confiance pour les coefficients, essai pour les substances étrangères et les résidus inhabituels, essai pour les points d’influence, somme des moindres carrés conditionnels, carré et une analyse de variance. Un très bon accord entre la résistance prévue par le modèle de régression et les résultats expérimentaux, a été constaté.相似文献
916.
OBJECTIVE: To identify the individual, dyad, and family variables that influence young women's perceptions of risk for sexually transmitted diseases (STDs), including human immunodeficiency virus (HIV). DESIGN: Cross-sectional telephone survey using forced-choice questioning. Data were analyzed using first-order correlations and logistic regression. SETTING: Participants were recruited from a mid-Atlantic study of young adults and from volunteers at a mid-Atlantic university and surrounding community. PARTICIPANTS: A convenience sample of 93 sexually active, unmarried, heterosexual women, ages 17-26 years. The majority of the study sample was white. MAIN OUTCOME MEASURE: Respondents were asked to estimate their own level of risk for STDs, including HIV, using the responses no, low, moderate, and high risk. Responses were later recoded into no risk versus some risk. RESULTS: Communication with parents about sexual risk decreased the odds that women would see themselves as being at no risk. Consistent condom use, relationship satisfaction, and perceiving the partner as no risk increased the odds that women would believe they were at no risk. CONCLUSIONS: Nurses can incorporate these and other study findings into the design of sexual risk reduction programs. Programs that enhance parent-teen communication about sexual risks and assist young women to examine their perceptions of their partners may be more effective than programs that provide information only. 相似文献
917.
918.
919.
S. Boralingiah C. K. Chua T. Ong S. M. Chou 《The International Journal of Advanced Manufacturing Technology》1999,15(2):119-126
This paper presents the technique used for converting a 3D ArtCAM™ relief file into the stereolithography (STL) format. This
3D file is obtained from a 2D picture using a 3D CNC engraving software called ArtCAM™.
The problem is to convert the 3D relief files into an STL format without compromising the accuracy and details of therelief.
This paper discusses the size of the files which have been converted, and steps taken to reduce the file size by reducing
the number of triangles or facets in the STL file. The discussion involves the verification of the converted model by comparing
it with the original relief. The problems associated with the reduction of triangles when the file has been converted to STL
format are also discussed. 相似文献
920.