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Time-dependent viscoelastic properties along rat small intestine

World Journal of Gastroenterology 2005年第32期11卷 4974-4978页

作者： James B Smith Jing-Bo Zhao Yan-Ling Dou Hans Gregersen Institute of Experimental Clinical Research Aarhus University Denmark Center of Excellence in Visceral Biomechanics and Pain Aalborg Hospital and Center of SMI Aalborg University Aalborg Denmark Department of Gastroenterology China-Japan Friendship Hospital Beijing 100029 China

AIM： To measure the time-dependent （viscoelastic） behavior in the change of the small intestinal opening angle and to test how well the behavior could be described by the Kelvin model for a standard linear solid. METHODS： Segments from the duodenum, jejunum, and ileum were harvested from 10 female Wistar rats and the luminal diameter, wall thickness, and opening angle over time （θ（t）） were measured from rings cut from these segments. RESULTS： Morphometric variations were found along the small intestine with an increase in luminal area and a decrease in wall thickness from the duodenum to the ileum. The opening angle obtained after 60 rain was highest in the duodenum （220.8±12.9°）and decreased along the length of the intestine to 143.9±8.9° in the jejunum and 151.4±9.4° in the ileum. The change of opening angle as a function of time, fitted well to the Kelvin model using the equation θ（t）/θo = [1-ηexp （-λt）] after the ring was cut. The computed creep rate λ. did not differ between the segments. Compared to constant calculated from pig aorta and coronary artery, it showed that α agreed well （within 5%）, η was three times larger than that for vascular tissue, and λ ranged ±40% from the value of the pig coronary artery and was a third of the value of pig aorta. CONCLUSION： The change of opening angle over time for all the small intestine segments fits well to the standard linear spring-dashpot model. This viscoelastic constant of the rat small intestine is fairly homogenous along its length. The data obtained from this study add to a base set of biomechanical data on the small intestine and provide a reference state for comparison to other tissues,diseased intestinal tissue or intestinal tissue exposed to drugs or chemicals.

关键词： Biomechanics standard linear solid Creep Opening angle

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Stable and Efficient Modeling of Anelastic Attenuation in Seismic Wave Propagation

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Communications in Computational Physics 2012年第6期12卷 193-225页

作者： N.Anders Petersson Bjorn Sjogreen Center for Applied Scientific Computing L-422Lawrence Livermore National LaboratoryP.O.Box 808LivermoreCA 94551USA

We develop a stable finite difference approximation of the three-dimensional viscoelastic wave *** material model is a super-imposition of N standard linear solid mechanisms,which commonly is used in seismology to model a material with constant quality factor *** proposed scheme discretizes the governing equations in second order displacement formulation using 3N memory variables,making it significantly more memory efficient than the commonly used first order velocitystress *** new scheme is a generalization of our energy conserving finite difference scheme for the elastic wave equation in second order formulation[SIAM ***.,45(2007),pp.1902–1936].Our main result is a proof that the proposed discretization is energy stable,even in the case of variable material *** proof relies on the summation-by-parts property of the *** newscheme is implemented with grid refinement with hanging nodes on the *** experiments verify the accuracy and stability of the new ***-analytical solutions for a half-space problem and the LOH.3 layer over half-space problem are used to demonstrate how the number of viscoelastic mechanisms and the grid resolution influence the *** find that three standard linear solid mechanisms usually are sufficient to make the modeling error smaller than the discretization error.

关键词： Viscoelastic standard linear solid finite difference summation by parts

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