[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.

/pdf/porous-scaffold-design-for-tissue-engineering-2a1maztjuj.pdf

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

Biomechanics of Mitral Valve Leaflets: Second Harmonic Generation Microscopy, Biaxial Mechanical Tests and Tissue Modeling.

Failure analysis of arteries by means of discontinuous FE Modeling

Introduction A large number of contact algorithms have been developed for standard engineering problems. Thereby, the contact surfaces are described directly by the facets of the finite elements, yielding a C continuous contact surface. If the surface to be discretized is not flat, then the assumptions of smoothness, which are essential for the proofs of uniqueness and convexity of contact problems, are violated [3]. Therefore, if these algorithms are applied to biomechanical problems in which the surfaces are arbitrarily curved, several problems may occur: (i) in order to obtain convergence, an exceedingly fine mesh is required at the vicinity of the contact region, (ii) the error of the solution is beyond an acceptable limit, (iii) the time steps of the nonlinear solver have to be extremely small or (iv) no convergence of the solution can be obtained at all. For example, in [2] it was shown, that an error of 311% in the solution for the contact pressure is obtained for a facet-based contact simulation of an interference fit of two rings. An illustrative example of slow convergence is given in [10], where the numerical simulation of a stenting process is presented. This simulation took three weeks due to the small time steps required. One way to avoid these problems is to overlay a smooth contact surface on the finite element mesh. Various smoothing techniques have been explored by several authors. They all have in common a continuity of C for flexible surfaces. Higher levels of continuity have only been applied to rigid surfaces, because the applied smoothing techniques do not possess the property of local support. Hence, oscillations of the surface may occur and a large system of equations has to be solved when the smooth surface is fitted to the finite element mesh. However, the smooth surface concept of NURBS [8] provides local support. That means that only a few mesh points at the vicinity of the current finite element are involved in the fitting process which determine the shape of their associated smooth surface. This property holds for an arbitrary level of continuity. Although in many applications of contact simulation, C continuity seems to be sufficient, there are cases for which C continuity is an advantage: one example is the metastable process of expanding a stent via a pressurized balloon inside an artery (see [10]). Since the applied load is deformation dependent, it is influenced by the surface curvature, which can not be controlled sufficiently by C surfaces. The use of C surfaces has shown a significant improvement of convergence in this case (see [9]).

http://ninsight.at/v2/wp-content/uploads/2013/08/NURBSContactWroclaw.pdf

A novel approach for smooth contact surfaces using NURBS: application to the FE simulation of stenting

Cerebral aneurysms are thought to be present in 2–5% of the general population. Most aneurysms remain asymptomatic and of those that are detected, the risk of rupture is relatively low, i.e. 0.1–1% per year. However, very high morbidity and mortality rates are associated with an aneurysm that does rupture (30–50%). Consequently, elective repair of an aneurysm at high risk of rupture may be deemed appropriate. Unfortunately, interventional procedures are themselves not without risk and have morbidity rates of up to 6%. Moreover, it is difficult to quantify the risk of rupture on a patient specific basis: more sophisticated diagnostic criteria are required. Computational models of aneurysm evolution aim to improve the understanding of the aetiology of the disease. The ultimate aim is to predict future evolution and rupture.

Coupling the Haemodynamic Environment to the Evolution of Cerebral Aneurysms

Atrioventricular heart valves (AHVs) regulate the unidirectional flow of blood through the heart by opening and closing of the leaflets, which are supported in their functions by the chordae tendineae (CT) The leaflets and CT are primarily composed of collagen fibers that act as the load-bearing component of the tissue microstructures At the CT-leaflet insertion, the collagen fiber architecture is complex, and has been of increasing focus in the previous literature However, these previous studies have not been able to quantify the load-dependent changes in the tissue's collagen fiber orientations and alignments In the present study, we address this gap in knowledge by quantifying the changes in the collagen fiber architecture of the mitral and tricuspid valve's strut CT-leaflet insertions in response to the applied loads by using a unique approach, which combines polarized spatial frequency domain imaging with uniaxial mechanical testing Additionally, we characterized these microstructural changes across the same specimen without the need for tissue fixatives We observed increases in the collagen fiber alignments in the CT-leaflet insertion with increased loading, as described through the degree of optical anisotropy Furthermore, we used a leaflet-CT-papillary muscle entity method during uniaxial testing to quantify the chordae tendineae mechanics, including the derivation of the Ogden-type constitutive modeling parameters The results from this study provide a valuable insight into the load-dependent behaviors of the strut CT-leaflet insertion, offering a research avenue to better understand the relationship between tissue mechanics and the microstructure, which will contribute to a deeper understanding of AHV biomechanics

Quantification of load-dependent changes in the collagen fiber architecture for the strut chordae tendineae-leaflet insertion of porcine atrioventricular heart valves

Gerhard Holzapfel

Papers

Biomechanics of Mitral Valve Leaflets: Second Harmonic Generation Microscopy, Biaxial Mechanical Tests and Tissue Modeling.

Failure analysis of arteries by means of discontinuous FE Modeling

A novel approach for smooth contact surfaces using NURBS: application to the FE simulation of stenting

Coupling the Haemodynamic Environment to the Evolution of Cerebral Aneurysms

Quantification of load-dependent changes in the collagen fiber architecture for the strut chordae tendineae-leaflet insertion of porcine atrioventricular heart valves