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1.
R Jover J Llach JM Bordas A Mas JM Salmerón S Navarro J Terés 《Canadian Metallurgical Quarterly》1997,20(7):344-346
There are evidence indicating that endoscopic retrograde cholangiopancreatography with sphincterotomy (ERCP+S) reduces the rate of complications in patients with severe acute biliary pancreatitis (ABP). The aim of this study was to analyze our experience in the treatment of severe ABP with ERCP+S and compare the evolution of the patients treated early (3 days or less following admission) with those treated late (after the 3rd day). A retrospective review of the clinical histories of the 16 patients with severe ABP treated with ERCP+S over the last two years is presented, analyzing their clinical features on admission and evolution. Biliary stones or biliary sludge was observed in 11 cases (69%). Nine patients had undergone early, and 7 late, ERCP+S. The patients of the latter group presented a greater number of complications during evolution than the former group (43% vs 0%; p = 0.025). The mortality of the patients of the late ERCP+S was also greater although without statistical significance (28.6% vs 0%; p = 0.15). No complication secondary to ERCP+S was detected. These findings confirm the fact that ERCP+S performed early in severe ABP significantly reduces the number of complications and is associated with a lower mortality. 相似文献
2.
Konstantinos Agathos Eleni Chatzi Stéphane P. A. Bordas Demosthenes Talaslidis 《International journal for numerical methods in engineering》2016,105(9):643-677
A variation of the extended finite element method for three‐dimensional fracture mechanics is proposed. It utilizes a novel form of enrichment and point‐wise and integral matching of displacements of the standard and enriched elements in order to achieve higher accuracy, optimal convergence rates, and improved conditioning for two‐dimensional and three‐dimensional crack problems. A bespoke benchmark problem is introduced to determine the method's accuracy in the general three‐dimensional case where it is demonstrated that the proposed approach improves the accuracy and reduces the number of iterations required for the iterative solution of the resulting system of equations by 40% for moderately refined meshes and topological enrichment. Moreover, when a fixed enrichment volume is used, the number of iterations required grows at a rate which is reduced by a factor of 2 compared with standard extended finite element method, diminishing the number of iterations by almost one order of magnitude. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Weakening the tight coupling between geometry and simulation in isogeometric analysis: From sub‐ and super‐geometric analysis to Geometry‐Independent Field approximaTion (GIFT)
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Elena Atroshchenko Satyendra Tomar Gang Xu Stéphane P.A. Bordas 《International journal for numerical methods in engineering》2018,114(10):1131-1159
This paper presents an approach to generalize the concept of isogeometric analysis by allowing different spaces for the parameterization of the computational domain and for the approximation of the solution field. The method inherits the main advantage of isogeometric analysis, ie, preserves the original exact computer‐aided design geometry (for example, given by nonuniform rational B‐splines), but allows pairing it with an approximation space, which is more suitable/flexible for analysis, for example, T‐splines, LR‐splines, (truncated) hierarchical B‐splines, and PHT‐splines. This generalization offers the advantage of adaptive local refinement without the need to reparameterize the domain, and therefore without weakening the link with the computer‐aided design model. We demonstrate the use of the method with different choices of geometry and field spaces and show that, despite the failure of the standard patch test, the optimum convergence rate is achieved for nonnested spaces. 相似文献
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Stéphane P. A. Bordas Sundararajan Natarajan 《International journal for numerical methods in engineering》2010,81(5):660-670
This letter aims at resolving the issues raised in the recent short communication (Int. J. Numer. Meth. Engng 2008; 76 (8):1285–1295. DOI: 10.1002/nme.2460 ) and answered by (Int. J. Numer. Meth. Engng 2009; DOI: 10.1002/nme.2587 ) by proposing a systematic approximation scheme based on non‐mapped shape functions, which both allows to fully exploit the unique advantages of the smoothed finite element method (SFEM) (Comput. Mech. 2007; 39 (6):859–877. DOI: 10.1007/s00466‐006‐0075‐4 ; Commun. Numer. Meth. Engng 2009; 25 (1):19–34. DOI: 10.1002/cnm.1098 ; Int. J. Numer. Meth. Engng 2007; 71 (8):902–930; Comput. Meth. Appl. Mech. Engng 2008; 198 (2):165–177. DOI: 10.1016/j.cma.2008.05.029 ; Comput. Meth. Appl. Mech. Engng 2007; submitted; Int. J. Numer. Meth. Engng 2008; 74 (2):175–208. DOI: 10.1002/nme.2146 ; Comput. Meth. Appl. Mech. Engng 2008; 197 (13–16):1184–1203. DOI: 10.1016/j.cma.2007.10.008 ) and resolve the existence, linearity and positivity deficiencies pointed out in (Int. J. Numer. Meth. Engng 2008; 76 (8):1285–1295). We show that Wachspress interpolants (A Rational Basis for Function Approximation. Academic Press, Inc.: New York, 1975) computed in the physical coordinate system are very well suited to the SFEM, especially when elements are heavily distorted (obtuse interior angles). The proposed approximation leads to results that are almost identical to those of the SFEM initially proposed in (Comput. Mech. 2007; 39 (6):859–877. DOI: 10.1007/s00466‐006‐0075‐4 ). These results suggest that the proposed approximation scheme forms a strong and rigorous basis for the construction of SFEMs. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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I Cirera J Panés JM Bordas J Llach J Bosch JM Piqué J Terés J Rodés 《Canadian Metallurgical Quarterly》1995,42(5):403-407
BACKGROUND: Previous studies in rats have demonstrated that anemia induces a significant increment in gastric mucosal blood flow. In the present study, we investigated whether chronic anemia induces similar changes in gastric blood perfusion in humans, and if this effect is also present in cirrhotic patients in whom gastric blood flow is usually increased in basal conditions. METHODS: Gastric mucosal blood perfusion was assessed by means of laser-Doppler flowmetry and reflectance spectrophotometry applied through the endoscope. RESULTS: Anemia significantly increases laser-Doppler signal in cirrhotic (2.3 +/- 0.11 vs 2.9 +/- 0.22 volts, p < 0.05) and noncirrhotic patients (1.71 +/- 0.15 vs 2.24 +/- 0.17, p < 0.05). In anemic patients the index of hemoglobin concentration of the gastric mucosa, assessed by reflectance spectrophotometry, was significantly decreased in cirrhotic patients (107.6 +/- 4.7 vs 95.5 +/- 3.3, p < 0.05) and noncirrhotic patients (93.9 +/- 4.1 vs 76.1 +/- 4.2, p < 0.01), whereas the index of oxygen saturation was increased (36.7 +/- 0.7 vs 40.4 +/- 1.4, p = 0.05; and 36.4 +/- 1.1 vs 43.2 +/- 1.9, p < 0.01, respectively). CONCLUSIONS: In conclusion, chronic anemia is associated with an enhanced gastric blood perfusion reflected by an increased laser-doppler signal and gastric mucosal oxygen index despite a decrease in gastric hemoglobin concentration. In cirrhotic patients, anemia promotes a further increment in its basal gastric hyperemia. 相似文献
9.
Mohammed Moumnassi Salim Belouettar Éric Béchet Stéphane P.A. Bordas Didier Quoirin Michel Potier-Ferry 《Computer Methods in Applied Mechanics and Engineering》2011,200(5-8):774-796
In this paper, we present some novel results and ideas for robust and accurate implicit representation of geometric surfaces in finite element analysis. The novel contributions of this paper are threefold: (1) describe and validate a method to represent arbitrary parametric surfaces implicitly; (2) represent arbitrary solids implicitly, including sharp features using level sets and boolean operations; (3) impose arbitrary Dirichlet and Neumann boundary conditions on the resulting implicitly defined boundaries. The methods proposed do not require local refinement of the finite element mesh in regions of high curvature, ensure the independence of the domain’s volume on the mesh, do not rely on boundary regularization, and are well suited to methods based on fixed grids such as the extended finite element method (XFEM). Numerical examples are presented to demonstrate the robustness and effectiveness of the proposed approach and show that it is possible to achieve optimal convergence rates using a fully implicit representation of object boundaries. This approach is one step in the desired direction of tying numerical simulations to computer aided design (CAD), similarly to the isogeometric analysis paradigm. 相似文献
10.
Alexander Menk Stéphane P. A. Bordas 《International journal for numerical methods in engineering》2011,85(13):1609-1632
The extended finite element method enhances the approximation properties of the finite element space by using additional enrichment functions. But the resulting stiffness matrices can become ill‐conditioned. In that case iterative solvers need a large number of iterations to obtain an acceptable solution. In this paper a procedure is described to obtain stiffness matrices whose condition number is close to the one of the finite element matrices without any enrichments. A domain decomposition is employed and the algorithm is very well suited for parallel computations. The method was tested in numerical experiments to show its effectiveness. The experiments have been conducted for structures containing cracks and material interfaces. We show that the corresponding enrichments can result in arbitrarily ill‐conditioned matrices. The method proposed here, however, provides well‐conditioned matrices and can be applied to any sort of enrichment. The complexity of this approach and its relation to the domain decomposition is discussed. Computation times have been measured for a structure containing multiple cracks. For this structure the computation times could be decreased by a factor of 2. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献