[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

From the Publisher: 
The accessible presentation of this book gives both a general view of the entire computer vision enterprise and also offers sufficient detail to be able to build useful applications. Users learn techniques that have proven to be useful by first-hand experience and a wide range of mathematical methods. A CD-ROM with every copy of the text contains source code for programming practice, color images, and illustrative movies. Comprehensive and up-to-date, this book includes essential topics that either reflect practical significance or are of theoretical importance. Topics are discussed in substantial and increasing depth. Application surveys describe numerous important application areas such as image based rendering and digital libraries. Many important algorithms broken down and illustrated in pseudo code. Appropriate for use by engineers as a comprehensive reference to the computer vision enterprise.

Computer vision : a modern approach = 计算机视觉 : 一种现代的方法

A paradigm shift is taking place in medicine from using synthetic implants and tissue grafts to a tissue engineering approach that uses degradable porous material scaffolds integrated with biological cells or molecules to regenerate tissues. This new paradigm requires scaffolds that balance temporary mechanical function with mass transport to aid biological delivery and tissue regeneration. Little is known quantitatively about this balance as early scaffolds were not fabricated with precise porous architecture. Recent advances in both computational topology design (CTD) and solid free-form fabrication (SFF) have made it possible to create scaffolds with controlled architecture. This paper reviews the integration of CTD with SFF to build designer tissue-engineering scaffolds. It also details the mechanical properties and tissue regeneration achieved using designer scaffolds. Finally, future directions are suggested for using designer scaffolds with in vivo experimentation to optimize tissue-engineering treatments, and coupling designer scaffolds with cell printing to create designer material/biofactor hybrids.

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Porous scaffold design for tissue engineering

In this paper we develop a new constitutive law for the description of the (passive) mechanical response of arterial tissue. The artery is modeled as a thick-walled nonlinearly elastic circular cylindrical tube consisting of two layers corresponding to the media and adventitia (the solid mechanically relevant layers in healthy tissue). Each layer is treated as a fiber-reinforced material with the fibers corresponding to the collagenous component of the material and symmetrically disposed with respect to the cylinder axis. The resulting constitutive law is orthotropic in each layer. Fiber orientations obtained from a statistical analysis of histological sections from each arterial layer are used. A specific form of the law, which requires only three material parameters for each layer, is used to study the response of an artery under combined axial extension, inflation and torsion. The characteristic and very important residual stress in an artery in vitro is accounted for by assuming that the natural (unstressed and unstrained) configuration of the material corresponds to an open sector of a tube, which is then closed by an initial bending to form a load-free, but stressed, circular cylindrical configuration prior to application of the extension, inflation and torsion. The effect of residual stress on the stress distribution through the deformed arterial wall in the physiological state is examined. The model is fitted to available data on arteries and its predictions are assessed for the considered combined loadings. It is explained how the new model is designed to avoid certain mechanical, mathematical and computational deficiencies evident in currently available phenomenological models. A critical review of these models is provided by way of background to the development of the new model.

https://hal.archives-ouvertes.fr/hal-01297725/document

A new constitutive framework for arterial wall mechanics and a comparative study of material models

Constitutive relations are fundamental to the solution of problems in continuum mechanics, and are required in the study of, for example, mechanically dominated clinical interventions involving soft biological tissues. Structural continuum constitutive models of arterial layers integrate information about the tissue morphology and therefore allow investigation of the interrelation between structure and function in response to mechanical loading. Collagen fibres are key ingredients in the structure of arteries. In the media (the middle layer of the artery wall) they are arranged in two helically distributed families with a small pitch and very little dispersion in their orientation (i.e. they are aligned quite close to the circumferential direction). By contrast, in the adventitial and intimal layers, the orientation of the collagen fibres is dispersed, as shown by polarized light microscopy of stained arterial tissue. As a result, continuum models that do not account for the dispersion are not able to capture accurately the stress–strain response of these layers. The purpose of this paper, therefore, is to develop a structural continuum framework that is able to represent the dispersion of the collagen fibre orientation. This then allows the development of a new hyperelastic free-energy function that is particularly suited for representing the anisotropic elastic properties of adventitial and intimal layers of arterial walls, and is a generalization of the fibre-reinforced structural model introduced by Holzapfel & Gasser (Holzapfel & Gasser 2001 Comput. Meth. Appl. Mech. Eng. 190, 4379–4403) and Holzapfel et al. (Holzapfel et al. 2000 J. Elast. 61, 1–48). The model incorporates an additional scalar structure parameter that characterizes the dispersed collagen orientation. An efficient finite element implementation of the model is then presented and numerical examples show that the dispersion of the orientation of collagen fibres in the adventitia of human iliac arteries has a significant effect on their mechanical response.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2005.0073

Hyperelastic modelling of arterial layers with distributed collagen fibre orientations

The present contribution focuses on the application of the multiscale finite element method to the modeling of actin networks that are embedded in the cytosol. These cell components are of particular importance with regard to the cell response to external stimuli. The homogenization strategy chosen uses the Hill-Mandel macrohomogeneity condition for bridging 2 scales: the macroscopic scale that is related to the cell level and the microscopic scale related to the representative volume element. For the modeling of filaments, the Holzapfel-Ogden β-model is applied. It provides a relationship between the tensile force and the caused stretches, serves as the basis for the derivation of the stress and elasticity tensors, and enables a novel finite element implementation. The elements with the neo-Hookean constitutive law are applied for the simulation of the cytosol. The results presented corroborate the main advantage of the concept, namely, its flexibility with regard to the choice of the representative volume element as well as of macroscopic tests. The focus is particularly placed on the study of the filament orientation and of its influence on the effective behavior.

Multiscale FEM simulations of cross-linked actin network embedded in cytosol with the focus on the filament orientation.

Arterial dissections Caused by balloon angioplasty has been implicated as a contributing factor to both acute procedural complications and chronic restenosis of the treatment site However, no related biomechanical studies are known in the literature The mechanical properties of the arterial wall are controlled by the rubber-like protein elastin, fibrous protein collagen and smooth muscle cells In the media of elastic arteries these constituents are found in thin layers that are arranged in repeating lamellar units and favor dissection type of failure The presented approach models the dissection of the media by means of strong discontinuities and the application of the theory of cohesive zones Thereby, the dissection is regarded as a gradual process in which separation between incipient material surfaces is resisted by cohesive traction The applied numerical frame is based on the Partition of Unity Finite Element Method (PUFEM) and has been utilized for tetrahedral elements A tracking algorithm for 3D non-planar cracks captures the evolution of multiple non-interacting dissections The proposed concept is applied to investigate the dissection of the media due to balloon angioplasty, where the associated material parameters are determined from failure experiments on human tissue

Physical and numerical modeling of dissection propagation in arteries caused by balloon angioplasty

Wave propagation in partially saturated porous continua is an interesting subject in Civil Engineering, Petroleum Engineering, Bioengineering, Earthquake Engineering, and Geophysics, etc. For such problems, there exist different theories, e.g., an extension of Biot’s theory, the Theory of Porous Media and the Mixture theory. Based on the Mixture theory, a dynamic three–phase model for partially saturated poroelasticity is established as well as the corresponding governing equations in Laplace domain. This model is applied to a one dimensional column and the related analytical solution in Laplace domain is deduced.The three different compressional waves, the fast wave, the second, and the third slow waves are calculated and validated with the Biot–Gassmann prediction and Murphy’s experimental results. The time domain results are obtained with the convolution quadrature method. Within the limit of a saturation nearly to one the results are as well compared with the corresponding results of saturated poroelasticity. For the three-dimensional governing equations, the fundamental solutions are deduced following Hörmander’s method. The boundary integral equations are established based on the weighted residual method. After regularization, spatial discretization, and the time discretization with the convolution quadrature method the boundary element formulation in time domain for partial saturated media is obtained. The implementation is done with the help of the open source C++ BEM library HyENA. Finally, the code is validated with the analytical one-dimensional solutions of the column. Two half-space applications are as well presented.

Peng Li: Boundary Element Method for Wave Propagtion in Partially Saturated Poroelastic Continua

Supersaturation and Crystallization Behaviors of Rare-Earth Based Cuprate Superconducting Films Grown by Chemical Solution Deposition

To date no adequate diagnostic strategy exists for the assessment of plaque stability. Current approaches focus on identification of high-risk morphological features in cross-sectional images, such as thin caps and large lipid pools. Plaque stability, however, is a 3D mechanical problem, whose solution requires information on both the geometry and the mechanical properties of the involved tissue components. This preliminary in vitro study is aimed to create multicomponent morphological and material models of human diseased arteries from cadavers. Morphological models are based on highly resolved MR images. Material models are fitted to mechanical testing data of single tissue components. Subsequent finite element analysis allows computation of local stresses and strains, whereas consideration of fracture properties provides a basis for the plaque stability assessment. Results demonstrate the complex mechanical behavior of diseased arteries, suggesting that reliable plaque stability assessment requires a combination of appropriate MR protocols, segmentation algorithms and mechanical analysis.

Gerhard Holzapfel

Papers

Multiscale FEM simulations of cross-linked actin network embedded in cytosol with the focus on the filament orientation.

Physical and numerical modeling of dissection propagation in arteries caused by balloon angioplasty

Peng Li: Boundary Element Method for Wave Propagtion in Partially Saturated Poroelastic Continua

Supersaturation and Crystallization Behaviors of Rare-Earth Based Cuprate Superconducting Films Grown by Chemical Solution Deposition

Assessment of plaque stability by means of high-resolution MRI and finite element analyses of local stresses and strains