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21.
Gabriel N. Gatica Ernst P. Stephan 《Numerical Methods for Partial Differential Equations》2002,18(1):105-128
This article deals with an expanded mixed finite element formulation, based on the Hu‐Washizu principle, for a nonlinear incompressible material in the plane. We follow our related previous works and introduce both the stress and the strain tensors as further unknowns, which yields a two‐fold saddle point operator equation as the corresponding variational formulation. A slight generalization of the classical Babu?ka‐Brezzi's theory is applied to prove unique solvability of the continuous and discrete formulations, and to derive the corresponding a priori error analysis. An extension of the well‐known PEERS space is used to define an stable associated Galerkin scheme. Finally, we provide an a posteriori error analysis based on the classical Bank‐Weiser approach. © 2002 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 18: 105–128, 2002 相似文献
22.
Mixed and hybrid finite element methods for the resolution of a wide range of linear and nonlinear boundary value problems (linear elasticity, Stokes problem, Navier–Stokes equations, Boussinesq equations, etc.) have known a great development in the last few years. These methods allow simultaneous computation of the original variable and its gradient, both of them being equally accurate. Moreover, they have local conservation properties (conservation of the mass and the momentum) as in the finite volume methods.The purpose of this paper is to give a review on some mixed finite elements developed recently for the resolution of Stokes and Navier–Stokes equations, and the linear elasticity problem. Further developments for a quasi-Newtonian flow obeying the power law are presented. 相似文献
23.
Uptake of trace elements into fish otoliths is governed by several factors such as life histories and environment in addition to stock and species differences. In an attempt to elucidate the elemental signatures of rare earth elements (REEs) in otoliths, a solid phase extraction (SPE) protocol was used in combination with electrothermal vaporization (ETV) as a sample introduction procedure for the determinations by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). Effects of various parameters, such as carrier gas flow rate, atomization temperature and chemical modification, were examined for optimization of the conditions by ETV-ICP-MS. Atomization was achieved at 2800 °C. Lower temperatures (i.e. 2600 °C) resulted in severe memory problems due to incomplete atomization. Palladium was used as a chemical modifier. It was found that an increase in Pd concentration up to 0.5 μg in the injection volume (70 μl) led up to four-fold enhancement in the integrated signals. This phenomenon is attributed to the carrier effect of Pd rather than the stabilization since no significant losses were observed for high temperature drying around 700 °C even in the absence of Pd. Preconcentration was performed on-line at pH 5 by using a mini-column of Toyopearl AF-Chelate 650M chelating resin, which also eliminated the calcium matrix of otolith solutions. After preconcentration of 6.4 ml of solution, the concentrate was collected in 0.65 ml of 0.5% (v/v) HNO3 in autosampler cups, and then analyzed by ETV-ICP-MS. The method was validated with the analysis of a fish otolith certified reference material (CRM) of emperor snapper, and then applied to samples. Results obtained from otoliths of fish captured in the same habitat indicated that otolith rare earth element concentrations are more dependent on environmental conditions of the habitat than on species differences. 相似文献
24.
María G. Armentano Ricardo G. Durn 《Numerical Methods for Partial Differential Equations》2003,19(5):653-664
In this article we analyze the effect of mass‐lumping in the linear triangular finite element approximation of second‐order elliptic eigenvalue problems. We prove that the eigenvalue obtained by using mass‐lumping is always below the one obtained with exact integration. For singular eigenfunctions, as those arising in non convex polygons, we prove that the eigenvalue obtained with mass‐lumping is above the exact eigenvalue when the mesh size is small enough. So, we conclude that the use of mass‐lumping is convenient in the singular case. When the eigenfunction is smooth several numerical experiments suggest that the eigenvalue computed with mass‐lumping is below the exact one if the mesh is not too coarse. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 653–664, 2003 相似文献
25.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
26.
E.D. Aydin C.R.E. de Oliveira 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(3):247-260
In this paper, we solve the steady-state form of the Boltzmann transport equation in homogeneous and heterogeneous tissue-like media with a finite element-spherical harmonics (FE-PN) radiation transport method. We compare FE-transport and diffusion solutions in terms of the ratio of absorption to reduced scattering coefficient, (μa/μs′) and the anisotropy factor g. Two different scattering phase function formulas are employed to model anisotropic scattering in the slab media with high g-value. Influence of void-like heterogeneities, and of their boundaries with the surrounding medium on the transport of photons are also examined. 相似文献
27.
藻类植物中钙、镁、铁、锰、铜和锌含量分析 总被引:15,自引:2,他引:13
本文采用火焰原子吸收光谱法测定了七种藻类植物中钙 ,镁 ,铁 ,锰 ,铜 ,锌六种元素的含量。结果表明 ,藻类植物中含有较丰富的钙 ,镁 ,铁 ,锰 ,锌元素 ,其含量由大到小顺序为Ca >Mg >Fe >Zn >Mn >Cu ,尤以钙的含量最为丰富 ,铜含量较少。本实验结果为探讨藻类植物作为资源开发利用提供了有用数据。 相似文献
28.
Marcos Almeida Bezerra Sérgio Mitihiro do Nascimento Maêda Eliane Padua Oliveira Maria de Fátima Batista de Carvalho Ricardo Erthal Santelli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
In the present paper a procedure is proposed for the determination of traces of Cd, Co, Mn and Cr in petroleum industry produced water by inductively coupled plasma optical emission spectrometry. The procedure is based on cloud point extraction of these metals, as their dithizonate complexes, into the surfactant-rich phase of octylphenoxypolyethoxyethanol surfactant (Triton X-114). Extractions were carried out in solutions with salinities between 10‰ and 70‰. Since residual salinity in the surfactant-rich phase caused differences in its transport to the plasma, yttrium was used as an internal standard to correct for this effect. The simultaneous metal extraction procedure was optimized by response surface methodology using a Doehlert design and desirability function. Enhancement factors of 21, 21, 9 and 19, along with limits of quantification of 0.093, 0.20, 0.73 and 1.2 μg L− 1, and precision expressed as relative standard deviation (n = 8, 20.0 μg L− 1) of 5.8, 1.2, 1.7 and 5.7% were obtained for Cd, Co, Mn and Cr, respectively. The accuracy was evaluated by spike recovery tests on the high salinity water samples with salinity of 40 and 63‰. 相似文献
29.
A time-dependent model corresponding to an Oldroyd-B viscoelastic fluid is considered, the convective terms being disregarded.
Global existence in time is proved in Banach spaces provided the data are small enough, using the implicit function theorem
and a maximum regularity property for a three fields Stokes problem. A finite element discretization in space is then proposed.
Existence of the numerical solution is proved for small data, so as a priori error estimates, using again an implicit function
theorem.
Supported by the Swiss National Science Foundation. Fellowship PBEL2–114311. 相似文献
30.
数码相机原理与系统设计研究 总被引:7,自引:0,他引:7
介绍了数码相机的工作原理 ,分析了数码相机的系统结构 ,提出了设计数码相机的处理流程。典型的数码相机系统有镜头、闪光灯、光学取景器、LCD显示屏、图像数据存储扩展设备接口、图像数据传输接口、供电系统以及核心处理器等八个主要模块。数码相机的数据流向从图像传感器开始 ,止于图像数据的存储和传输。数据流的处理主要包括模数转换、光学黑电平钳位、针对镜头的边缘畸变的运算修正、坏像素处理、白平衡处理、伽马校正、色彩合成处理、边缘检测 (锐度检测 )和伪彩色检测 (伪彩色抑制 )、JPEG压缩和图像存储器等模块 相似文献