[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

In a typical diarthrodial joint, like the human knee joint, t he opposing bones are covered with a layer of dense connective tissue known as articular cartilage, which provides articulating surfaces. Articular cartilage has a composition and mechanical structure well-suited to the required functions: (i) to provide a compliant, low-friction surface between the relatively r igid bones in diarthrodial joints, (ii) to provide a long-wearing and resilient surface, and (iii) to distribu te the contact pressure to the underlying bone structure. To meet these demands, articular cartilage cont ains a fluid phase of H 2O and electrolytes (approximately 68% to 85%), and a solid phase composed of chondrocytes, type I and II collagen fibers, proteoglycans and other glycoproteins (cf. [1]). Within the cartilage, fibers of predominantly type II collag en exhibit a high level of structural organization and provide tensile reinforcement to the solid phase, a proteoglycan gel. The collagen fibers support only tension and accommodate essentially no resistance to compression. Within the cartilage, three basic zones of collagen fiber orientation exist. Start ing from the surface, the superficial tangent zone (comprising approximately 10-20% of the total thickness) has fibers which are tangential to the articular surface. Next, the middle zone (40-60%) has fibers which are isotropically distributed and oriented. Finally, near the transition to subchondral bone, th e deep zone (approximately 30%) has fibers which are oriented perpendicular to the aforementioned surface. Clearly some simplifying assumptions are required to facilitate computational modeling and numerical simulation. By considering only two main components; a fluid and a solid embedded with type II collagen fibers, articular cartilage may be considered a biphasic fiber reinforced material [1]. Additionally, due in part to the interaction of solid and fluid, articular ca rtilage exhibits a time-dependent stress-strain response.

A sample-specific computational model of articular cartilage based on mri, histology, computer vision and mechanical testing

Commentary: May the force(s) be with you: Loading conditions and the aorta.

Background: Thoracic endovascular repair (TEVAR) stiffens the elastomechanical properties of the aorta from the moment of deployment. Chronically, the stent-wall interaction can lead (cardio)-vascular ramifications that stem from stent-induced biomechanical events. The present experimental study aims to investigate the early biomechanical impact of TEVAR against the aortic wall. 

Early Aortic Stiffening after TEVAR: An In Vitro Mock Perfusion Study

Materially stable constitutive equations for arterial walls based on polyconvex energies

This research is based on experimental and numerical investigations of human lumbar spine. Human intervertebral discs usually exhibit highly anisotropic mechanical responses in a finite strain regime under physiological loading conditions. Human disc body units basically consist of a fluid filled cavity (nucleus pulposus) approximately at the disc center and surrounding tissue reinforced by collagen fibers (annulus fibrosus). For the latter component a newly developed constitutive model is applied which accounts for nonlinear anisotropic stress response. By assuming appropriate nonlinear material parameters, this material law ensures numerical accuracy in the finite strain regime. In general, however, it is very complicated to obtain nonlinear constitutive data, since this requires exceptional anatomical expertise. This presentation enlightens numerical aspects on specimens obtained from the annulus fibrosus. By means of finite element (FE) analyses, the requirement for a careful specimen preparation is outlined. It proves that the entire constitutive theory can be based on this new experimental procedure for the determination of local, nonlinear and anisotropic stress response in annulus tissue. A distinct feature of the present theory compared with previous publications is the determination of nonlinear material parameters for single annulus lamellae. Besides a physically unique determination of the constituents, this also allows to account for stiffness variability within annulus fibrosus in radial and hoop directions, respectively. Based on the new experimental results and on the constitutive model implemented in a multi-purpose FE code, enhanced large scale FE analyses of lumbar disc bodies are discussed. Since all constitutive parameters can be interpreted in an unique and physically consistent way, the FE analyses show excellent performance and accuracy within the physiological range of human lumbar motion segments. Hence, the current approach is very attractive for refined spinal implant design and optimization.

Gerhard Holzapfel

Papers

A sample-specific computational model of articular cartilage based on mri, histology, computer vision and mechanical testing

Commentary: May the force(s) be with you: Loading conditions and the aorta.

Early Aortic Stiffening after TEVAR: An In Vitro Mock Perfusion Study

Materially stable constitutive equations for arterial walls based on polyconvex energies

Accurate FE modeling of human annulus tissue for refined spinal implant design