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991.
992.
993.
Gabriel N. Gatica Ricardo Oyarzúa Francisco-Javier Sayas 《Computer Methods in Applied Mechanics and Engineering》2011,200(21-22):1877-1891
In this paper we develop an a posteriori error analysis of a new fully mixed finite element method for the coupling of fluid flow with porous media flow in 2D. Flows are governed by the Stokes and Darcy equations, respectively, and the corresponding transmission conditions are given by mass conservation, balance of normal forces, and the Beavers–Joseph–Saffman law. We consider dual-mixed formulations in both media, which yields the pseudostress and the velocity in the fluid, together with the velocity and the pressure in the porous medium, and the traces of the porous media pressure and the fluid velocity on the interface, as the resulting unknowns. The set of feasible finite element subspaces includes Raviart–Thomas elements of lowest order and piecewise constants for the velocities and pressures, respectively, in both domains, together with continuous piecewise linear elements for the traces. We derive a reliable and efficient residual-based a posteriori error estimator for the coupled problem. The proof of reliability makes use of the global inf–sup condition, Helmholtz decompositions in both media, and local approximation properties of the Clément interpolant and Raviart–Thomas operator. On the other hand, inverse inequalities, the localization technique based on element-bubble and edge-bubble functions, and known results from previous works, are the main tools for proving the efficiency of the estimator. Finally, some numerical results confirming the theoretical properties of this estimator, and illustrating the capability of the corresponding adaptive algorithm to localize the singularities of the solution, are reported. 相似文献
994.
A. Leite G. Costa W. Hajjaji M.J. Ribeiro M.P. Seabra J.A. Labrincha 《Dyes and Pigments》2009,81(3):211-217
The structural stability of the pigment was investigated using X-ray diffraction coupled with SEM and UV–vis–IR analysis, as a function of the relative Co content and calcination temperature. A standard formulation prepared from commercial reagents was also prepared and characterized for the sake of comparison. The pigment was added to a transparent glaze and to a porcelain stoneware body. Since the relative amount of cobalt was low and the sintering temperature of the pigment was not too high (1350–1400 °C), the new pigment system offers an interesting alternative to spinel, olivine and willemite commercial blue pigments. Moreover, the use of several wastes in the pigment formulation does not diminish its colouring performance. 相似文献
995.
996.
Abril Zoraida Graciano-Verdugo Herlinda Soto-Valdez Elizabeth Peralta Pavlov Cruz-Zárate Alma Rosa Islas-Rubio Saúl Sánchez-Valdes Armida Sánchez-Escalante Natalia González-Méndez Humberto González-Ríos 《Food research international (Ottawa, Ont.)》2010,43(4):1073-1078
The migration of α-tocopherol (α-T) from low density polyethylene (LDPE) films, added with 20 (film A) and 40 mg g?1 (film B) to corn oil for 12 weeks at 5, 20 and 30 °C was determined. A LDPE film added with no α-T was used as control (film C). Diffusion coefficient (D) values for the film A system were 1.4 × 10?11, 7.1 × 10?11 and 30.3 × 10?11 cm2 s?1 at 5, 20 and 30 °C, respectively. Meanwhile, D values for the film B system were 1.3 × 10?11, 9.6 × 10?11 and 51.1 × 10?11 cm2 s?1 at the same temperatures. The activation energy (Ea) for the diffusion of α-T was 126.5 (film A) and 105.9 kJ mol?1 (film B). The effect of the migration of α-T on the oxidative stability of corn oil was evaluated by monitoring hexanal content by solid phase micro-extraction (SPME) and gas chromatography. The hexanal content in the oil showed that both films added with α-T resulted suitable to maintain the oxidative stability of the oil for about 16 weeks at 30 °C, compared to 12 weeks for the oil in contact with the film C. 相似文献
997.
José M. Pardillo-Mayora Carlos A. Domínguez-Lira Rafael Jurado-Piña 《Accident; analysis and prevention》2010,42(6):2018-2023
Crash records and roadside data from Spanish two-lane rural roads were analyzed to study the effect of roadside configuration on safety. Four indicators were used to characterize the main roadside features that have an influence on the consequences of roadway departures: roadside slope, non-traversable obstacles distance from the roadway edge, safety barrier installation, and alignment. Based on the analysis of the effect of roadside configuration on the frequency and severity of run-off-road injury crashes, a categorical roadside hazardousness scale was defined. Cluster analysis was applied to group the combinations of the four indicators into categories with homogeneous effects on run-off-road injury crashes frequency and severity. As a result a 5-level Roadside Hazardousness Index (RHI) was defined. RHI can be used as reference to normalize the collection of roadside safety related information. The index can also be used as variable for inclusion of roadside condition information in multivariate crash prediction models. 相似文献
998.
Christiane Reis Fonseca José Luiz Paiva Eva Maria Rodriguez Fernando Juan Beltrán Antonio Carlos Silva Costa Teixeira 《臭氧:科学与工程》2017,39(4):255-263
The sugar industry is concerned with color formation due to the oxidation of phenolic compounds in the presence of carbohydrates. In this study, we investigated the ozonation of a mixture of five phenolic compounds in water and aqueous sucrose solution: p-coumaric (p-COU), caffeic (CAF), syringic (SYR), and chlorogenic (CHO) acids, as well as the flavonoid quercetin (QUE). The experiments were carried out in a 3-L glass reactor with magnetic stirring and a diffuser plate at the bottom to feed the ozone-oxygen gas mixture. Initial solution concentrations of 5 mg L?1 of each acid, 15 mg L?1 of quercetin, and 40 g L?1 of sucrose were used. The degradation of phenolic compounds followed apparent first-order kinetics, with rate constants and percent removals decreasing in the presence of sucrose. In water, average consumed ozone dosages of 10.4 and 18.7 mg L?1 were necessary for 50% and 90% removals, respectively, for CHO, CAF, and p-COU; for QUE they were slightly higher (13.9 and 20.5 mg L?1, respectively). At a consumed dosage of 20.8 mg O3 L?1, more than 99% removal was obtained for CHO, CAF, and p-COU, while 96.2% was achieved for SYR. In contrast, QUE revealed to be more recalcitrant during ozonation in the absence of sucrose, with only 70% removal at the highest consumed O3 dosage. The consumed ozone dosages for 50% and 90% removals were higher for CHO, CAF, and p-COU in aqueous sucrose solution, which may impact ozone consumption during real sugarcane juice treatment. Sucrose and t-butanol were the main influential parameters that significantly affected the total amount of phenolic compounds degraded. 相似文献
999.
Juan Carlos Escanciano David T. Jacho-Chávez 《Computational statistics & data analysis》2010,54(3):625-610
A numerical approximation of the critical values of Cramér-von Mises (CvM) tests is proposed for testing the correct specification of general conditional location parametric functionals. These specifications include conditional mean and quantile models. This method is based on estimation of the eigenelements of the covariance operator associated with the CvM test, and it has the advantage that it requires the practitioner to estimate the model only one time under the null hypothesis. A Monte Carlo experiment shows that the proposed approximation compares favorably with respect to the subsampling method in terms of size accuracy, power performance and computational time. 相似文献
1000.
Estíbaliz Sánchez-González Pedro Miranda Fernando Guiberteau Antonia Pajares 《Journal of the European Ceramic Society》2009,29(12):2635-2641
The elasto-plastic properties and contact damage evolution of a commercial polycrystalline silicon nitride are evaluated as a function of temperature up to 1000 °C, using a recently developed method combining Hertzian indentation and FEM simulation. The results of the study are compared to existing data for other ceramic materials such as alumina and zirconia. Silicon nitride is found to exhibit an excellent combination of elasto-plastic properties in the pre-creep temperature range and good contact damage resistance. These qualities make this material ideal for high temperature applications in general, and in particular to be used in spherical indenters for the evaluation of mechanical properties of other materials at elevated temperature using the procedure applied in this work. 相似文献