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2007a): A modified Trefftz method for two-dimensional Laplace equation considering the domain’s characteristic length
- CMES: Computer Modeling in Engineering & Sciences
"... Abstract: A newly modified Trefftz method is developed to solve the exterior and interior Dirichlet problems for two-dimensional Laplace equation, which takes the characteristic length of problem domain into account. After introducing a circular artificial boundary which is uniquely determined by th ..."
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Cited by 20 (9 self)
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Abstract: A newly modified Trefftz method is developed to solve the exterior and interior Dirichlet problems for two-dimensional Laplace equation, which takes the characteristic length of problem domain into account. After introducing a circular artificial boundary which is uniquely determined by the physical problem domain, we can derive a Dirichlet to Dirichlet mapping equa-tion, which is an exact boundary condition. By truncating the Fourier series expansion one can match the physical boundary condition as accu-rate as one desired. Then, we use the colloca-tion method and the Galerkin method to derive linear equations system to determine the Fourier coefficients. Here, the factor of characteristic length ensures that the modified Trefftz method is stable. We use a numerical example to ex-plore why the conventional Trefftz method is fail-ure and the modified one still survives. Numerical examples with smooth boundaries reveal that the present method can offer very accurate numeri-cal results with absolute errors about in the orders from 10−10 to 10−16. The new method is pow-erful even for problems with complex boundary shapes, with discontinuous boundary conditions or with corners on boundary.
Matching Structural Images of the Human Brain Using Statistical and Geometrical Image Features
, 1994
"... The efficacy of using intensity edges, curvature of iso-intensity contours, and tissue classified data for image matching are examined. The image matching problem is formulated in such a way that the different features are handled uniformly, allowing the same code to be used in each instance. The re ..."
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Cited by 20 (1 self)
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The efficacy of using intensity edges, curvature of iso-intensity contours, and tissue classified data for image matching are examined. The image matching problem is formulated in such a way that the different features are handled uniformly, allowing the same code to be used in each instance. The results using both simulated and real brain images indicate that each feature affected an improvement in the correspondence after matching with it. 1. INTRODUCTION Image registration has recently emerged as an important area of research in medical image processing. It facilitates the integration or fusion of images taken of the same subject but from different modalities. This in turn offers better diagnostic capability, improves surgical and therapy planning and evaluation, facilitates localization of function and the study of its cerebral organization, and enhances the information from modalities which when considered alone are difficult to interpret because of their inherently poor resolut...
A 2002 Determination of cellular strains by combined atomic force microscopy and finite element modeling Biophys
- J
"... ABSTRACT Many organs adapt to their mechanical environment as a result of physiological change or disease. Cells are both the detectors and effectors of this process. Though many studies have been performed in vitro to investigate the mechanisms of detection and adaptation to mechanical strains, the ..."
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Cited by 17 (2 self)
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ABSTRACT Many organs adapt to their mechanical environment as a result of physiological change or disease. Cells are both the detectors and effectors of this process. Though many studies have been performed in vitro to investigate the mechanisms of detection and adaptation to mechanical strains, the cellular strains remain unknown and results from different stimulation techniques cannot be compared. By combining experimental determination of cell profiles and elasticities by atomic force microscopy with finite element modeling and computational fluid dynamics, we report the cellular strain distributions exerted by common whole-cell straining techniques and from micromanipulation techniques, hence enabling their comparison. Using data from our own analyses and experiments performed by others, we examine the threshold of activation for different signal transduction processes and the strain components that they may detect. We show that modulating cell elasticity, by increasing the F-actin content of the cytoskeleton, or cellular Poisson ratio are good strategies to resist fluid shear or hydrostatic pressure. We report that stray fluid flow in some substrate-stretch systems elicits significant cellular strains. In conclusion, this technique shows promise in furthering our understanding of the interplay among mechanical forces, strain detection, gene expression, and cellular adaptation in physiology and disease.
Cenozoic deformation of the Tarim Plate and the implications for mountain building
- in the Tibetan Plateau and the Tian Shan. Tectonics
, 2002
"... complex foreland basin in the Cenozoic in association with mountain building in the Tibetan Plateau to the south and the Tian Shan orogen to the north. We reconstructed the Cenozoic deformation history of the Tarim basement by backstripping the sedimentary rocks. Two-dimensional and three-dimensiona ..."
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Cited by 16 (0 self)
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complex foreland basin in the Cenozoic in association with mountain building in the Tibetan Plateau to the south and the Tian Shan orogen to the north. We reconstructed the Cenozoic deformation history of the Tarim basement by backstripping the sedimentary rocks. Two-dimensional and three-dimensional finite element models are then used to simulate the flexural deformation of the Tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts. The results suggest that uplift of both the western Kunlun Shan and the Tian Shan orogens started during or before Oligocene. Since the Miocene, mountain building accelerated in the western Kunlun Shan but showed segmented development in the Tian Shan. The results also indicate reduced tectonic load along the Altyn Tagh fault since late Miocene, consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the Cenozoic evolution. INDEX TERMS: 8105 Tectonophysics: Continental margins and sedimentary basins; 8102 Tectonophysics: Continental contractional orogenic belts;
Dynamic analysis for planar multibody mechanical systems with lubricated joints. Multibody Syst
- Dyn
"... Abstract. The dynamic analysis of planar multibody systems with revolute clearance joints, includ-ing dry contact and lubrication effects is presented here. The clearances are always present in the kinematic joints. They are known to be the sources for impact forces, which ultimately result in wear ..."
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Cited by 15 (8 self)
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Abstract. The dynamic analysis of planar multibody systems with revolute clearance joints, includ-ing dry contact and lubrication effects is presented here. The clearances are always present in the kinematic joints. They are known to be the sources for impact forces, which ultimately result in wear and tear of the joints. A joint with clearance is included in the multibody system much like a revolute joint. If there is no lubricant in the joint, impacts occur in the system and the corresponding impulsive forces are transmitted throughout the multibody system. These impacts and the eventual continuous contact are described here by a force model that accounts for the geometric and material characteristics of the journal and bearing. In most of the machines and mechanisms, the joints are designed to operate with some lubricant fluid. The high pressures generated in the lubricant fluid act to keep the journal and the bearing surfaces apart. Moreover, the lubricant provides protection against wear and tear. The equations governing the dynamical behavior of the general mechanical systems incorporate the impact force due to the joint clearance without lubricant, as well as the hydro-dynamic forces owing to the lubrication effect. A continuous contact model provides the intra-joint impact forces. The friction effects due to the contact in the joints are also represented. In addition, a general methodology for modeling lubricated revolute joints in multibody mechanical systems is
Structured Extended Finite Element Methods for Solids Defined By Implicit Surfaces
, 2003
"... this paper we describe a methodology for constructing the #nite elements for structured meshes for objects described by implicit surfaces, both for the outside boundary and interior surfaces. For existing parts, a laser scan of body can be immediately translated into an implicit description of the e ..."
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Cited by 15 (1 self)
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this paper we describe a methodology for constructing the #nite elements for structured meshes for objects described by implicit surfaces, both for the outside boundary and interior surfaces. For existing parts, a laser scan of body can be immediately translated into an implicit description of the external boundaries. By means of holography and other methods, implicit function descriptions of any internal surfaces can also be obtained. They can then be translated to #nite element models as described here. For CAD models or solid models, the construction of an implicit surface model is also straightforward, for it is only necessary to extract a set of surface points from the geometric model. Thus, the paradigm described here should enable #nite element analyses of complex engineering problems with almost no human intervention. The concept of describing internal surfaces of a problem independent of a mesh by implicit functions originated in Sukumar et al. [10]. It has been used to model crack growth with level sets in two dimensions by Stolarska et al. [11], crack growth in three dimensions by Gravouil et al. [12]. The methodology has also been applied to solidi#cation, Chessa et al. [13] and #uid interfaces, Chessa et al. [14], and for particles in #uids by Wagner et al. [15]
Bayesian Approach to the Brain Image Matching Problem
, 1995
"... The application of image matching to the problem of localizing structural anatomy in images of the human brain forms the specific aim of our work. The interpretation of such images is a difficult task for human observers because of the many ways in which the identity of a given structure can be obsc ..."
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Cited by 14 (3 self)
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The application of image matching to the problem of localizing structural anatomy in images of the human brain forms the specific aim of our work. The interpretation of such images is a difficult task for human observers because of the many ways in which the identity of a given structure can be obscured. Our approach is based on the assumption that a common topology underlies the anatomy of normal individuals. To the degree that this assumption holds, the localization problem can be solved by determining the mapping from the anatomy of a given individual to some referential atlas of cerebral anatomy. Previous such approaches have in many cases relied on a physical interpretation of this mapping. In this paper, we examine a more general Bayesian formulation of the image matching problem and demonstrate the approach on two-dimensional magnetic resonance images.
Local Changes in Gravity Resulting From Deformation
, 1979
"... The horizontal and vertical components of gravity change when tectonic stresses deform the earth because mass is redistributed relative to the gravity meter. We analyze the change in gravity resulting from deformation in a homogeneous elastic half-space. We derive expressions in closed form which gi ..."
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Cited by 14 (1 self)
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The horizontal and vertical components of gravity change when tectonic stresses deform the earth because mass is redistributed relative to the gravity meter. We analyze the change in gravity resulting from deformation in a homogeneous elastic half-space. We derive expressions in closed form which give the change in horizontal and vertical components of gravity measured at the surface for any specified distribution of dislocations at depth. For example, the change in the vertical component of gravity observed by a gravity meter fixed in space above an infinitely long thrust fault is found to be proportional to the local change in height, whereas the change due to a spherically symmetric source of dilatation is zero. Analysis of the change in the horizontal component shows that error in measurements of uplift resulting from changes in level is negligible for these sources.
2004), A three-dimensional semianalytic viscoelastic model for time-dependent analyses of the earthquake cycle
- J. Geophys. Res
"... of the earthquake cycle ..."
Pressure Drop of Fully Developed, Laminar Flow in Rough Microtubes,”
- U. of Toronto, Canada,
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