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Modeling curvature-resisting material surfaces using isogeometric analysis
Full text linkImproved understanding of solid surface energy and its role in the overall mechanical properties is of great interest due to the emerging manufacturing techniques of nanostructures, coatings, and synthetic/biological bilayer-polymer hybrids. Continuum numerical modeling of surface stresses efficiently incorporates a zero-thickness membrane bonded to a bulk, intrinsically accounting for surface tension and surface elasticity. Compressive surface stresses are not possible in a purely membrane formulation, ignoring the surface flexural resistance. The extension of material surfaces to account for flexural resistance, i.e., the Steigmann–Ogden model, requires spatial derivatives of second order, posing significant challenges to standard discretization techniques. Hence, the effect of surface curvature resistance on the overall mechanical behavior of complex geometries remains elusive. Here, we develop a three-dimensional computational formulation of curvature-dependent surface energetics at finite strains using surface-enriched isogeometric analysis. Coupled with a hyperelastic bulk, bending-resistance of material surfaces furnishes a new physical length scale, i.e., the elastobending length. We quantify the effect of elastobending deformations for several numerical examples involving soft materials with thin coatings and liquid-shell surfaces, capturing budding-like behavior observed at cell membranes. Our results demonstrate a stiffer overall mechanical behavior when material surfaces resist bending deformations and illustrate how curvature effects lead to complex budding deformations at non-zero initial curvature states. The proposed methodology provides a robust computational foundation to help improve our understanding and mechanical characterization of soft solids, nanostructures, and biological membranes at small scales.Civil, Architectural, and Environmental Engineerin
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Modeling surface tension in liquid membranes and soft materials using surface-enriched Convected Particle Domain Interpolation (CPDI)
Full text linkFrom the deformation of soft gels to the stability of lipid bilayers and emulsions, surface tension forces critically shape the mechanics of ultra‑soft solids and liquid membranes. However, conventional mesh-based methods often break down under large mesh distortions. The material point method (MPM) handles large strains effectively, yet most MPM formulations approximate surfaces implicitly -- typically using level-set methods -- which introduces auxiliary equations to solve. In this work, we present the first physically consistent, sharp-interface formulation of surface tension in MPM that represents surface geometry explicitly. We extend the Convected Particle Domain Interpolation (CPDI) framework of MPM to define 2D and 3D Convected Surface Domain Interpolation (CSDI) shape functions. These zero-thickness surface elements, attached to the boundary of CPDI material points, allow direct incorporation of surface tension into the variational formulation. We further introduce the membrane point method, which uses CSDI to simulate zero-thickness liquid membranes with surface-only momentum balance. We present an open-source explicit surface-enriched MPM implementation that verifies this approach for fluids and hyperelastic bulks. Through several numerical examples—including minimal surfaces, pendant droplet, and soft body contact with surface tension—we demonstrate the accuracy and robustness of our method under large deformations. These results establish our framework as a foundational tool for elastocapillary and membrane modeling in soft matter mechanics.Computational Science, Engineering, and Mathematic
Replication Data for: A subdivision-stabilized B-spline mixed material point method
No full textSupporting data and figures for this publication
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Histomechanical characterization and microstructure-based modeling of right ventricular myocardium
Full text linkRight ventricular histomechanics have been historically overlooked, thus limiting our ability to describe the mechanisms underlying severe pathological conditions of the right heart. In this dissertation we set out to investigate the histomechanics of the right ventricular myocardium both in health and disease (pulmonary arterial hypertension), using a large animal (ovine) model. To this end, we combine mechanical testing, histology analysis, magnetic resonance imaging and microstructure-based modeling. Our computational approach is threefold, involving established homogenized models, novel machine learning metamodels and the use of embedded, discrete fiber networks. First, we found that the right ventricular myocardium in health exhibits nonlinear, anisotropic mechanical response. The homogenized models successfully captured this behavior at the cost of considerable computational time, subsequently accelerated by the machine learning metamodels. Moreover, we found that pulmonary arterial hypertension induced extracellular collagen deposition, spatially-dependent wall thickening, and increased stiffness at the low strain regime. Our embedded fiber network approach was able to account for these remodeling effects. Finally, throughout this work we have been making our experimental data and computational implementations publicly available, establishing for the first time a complete pipeline for the characterization of the right ventricular myocardium.Engineering Mechanic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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Towards understanding tricuspid valve mechanics & function in health, disease, and repair
No full textThe tricuspid valve ensures unidirectional blood flow from the right atrium to the right ventricle of the heart. In roughly 1.6 million Americans this valve leaks to a clinically significant degree. In most patients, this leakage, or regurgitation, is thought to be a consequence of valve extrinsic factors such as right ventricular remodeling in response to pulmonary hypertension. Consequently, the valve itself has been considered "inert" and deemed "functional" and has historically been undertreated. However, recently more aggressive treatment strategies have been recommended as tricuspid regurgitation is now considered a "public health crisis". Unfortunately, the gold standard treatment, ring annuloplasty, yields sub-optimal patient outcomes with nearly a third of patients redeveloping regurgitation within a few years of surgery. Similarly, newer transcatheter techniques such as clip-based repair fail at a comparable rate to their surgical counterparts. We submit that these sub-optimal outcomes are, at least in part, due to an incomplete understanding of tricuspid valve mechanics. To overcome this knowledge gap, we use in vitro experiments to characterize tricuspid valve mechanics in health and disease (Tachycardia-induced Cardiomyopathy) using a large animal model. Additionally, we reverse-engineer a human tricuspid valve to computationally investigate valve function in health, in disease, and post-repair. In this dissertation, we first compare and contrast the morphology, mechanics, and microstructure of tricuspid valve leaflets in healthy sheep against those with functional tricuspid regurgitation. To this end, we found several differences in microstructure and mechanical behavior amongst the tricuspid leaflets. Furthermore, we also found that the anterior tricuspid valve grows and remodels in response to pathologic stimuli. Secondly, we develop and validate a "true" subject-specific finite element model of the human tricuspid valve. Moreover, we showcase the utility of this computer model through two virtual tricuspid valve repair procedures. Thirdly, we computationally investigate the impact of leaflet remodeling and ring annuloplasty on valve function in two distinct studies. In the first study, we find that leaflet thickening and stiffening do, in fact, contribute to tricuspid valve dysfunction. In the second study, we find that leaflet mechanics and valve function are sensitive to both annuloplasty ring shape and size. Finally, we develop a novel soft-tissue thickness measurement technique as well as an open-source augmented reality visualization framework that may improve the accuracy and interactivity, respectively, of future tricuspid valve models. Altogether, this dissertation significantly advances our current understanding of tricuspid valve mechanics and function in health, disease, and repair.Mechanical Engineerin
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Boundary viscoelasticity theory at finite deformations and computational implementation using isogeometric analysis
No full textUse of surface elasticity theory has experienced a prolific growth recently due to its utility in understanding the mechanics of nanomaterials and soft solids at small scales. Various extensions of surface elasticity theory have been proposed. The main objective of this contribution is to formulate a finite deformation theory for boundary viscoelasticity in principal stretches by accounting for strain-dependent boundary stresses. We present a model that utilizes a nonlinear evolution law and thus is not restricted to the states that are close to the thermodynamic equilibrium. Boundary contributions include both surface and curve effects wherein boundary elasticity as well as boundary tension are accounted for. The boundary constitutive models are formulated such that fluid-like and solid-like viscoelastic behavior of boundaries are considered. A geometrically exact computational framework using isogeometric analysis inherently suited to account for boundaries is developed. Equipped with the theoretical and computational framework, the influence of boundary viscoelasticity on the material response is illustrated. Non-equilibrium counterpart of surface tension is introduced and its effects are elucidated via examples. Through numerical examples, various applications of the bulk–boundary coupled formulation which require further investigation are highlighted
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