Flow network controlled shape transformation of a thin membrane through differential fluid storage and surface expansion

The mechanical properties of a thin, planar material, perfused by an embedded flow network, can be changed locally and globally by the fluid transport and storage, resulting in small or large-scale deformation, such as out-of-plane buckling. Fluid absorption and storage eventually cause the material to locally swell. Different parts can hydrate and swell unevenly, prompting a differential expansion of the surface. In order to computationally study the hydraulically induced differential swelling and buckling of such a membrane, we develop a network model that describes both the membrane shape and fluid movement, coupling mechanics with hydrodynamics. We simulate the time-dependent fluid distribution in the flow network based on a spatially explicit resistor network model with local fluid-storage capacitance. The shape of the surface is modeled by a spring network produced by a tethered mesh discretization, in which local bond rest lengths are adjusted instantaneously according to associated local fluid content in the capacitors in a quasi-static way. We investigate the effects of various designs of the flow network, including overall hydraulic traits (resistance and capacitance) and hierarchical architecture (arrangement of major and minor veins), on the specific dynamics of membrane shape transformation. To quantify these effects, we explore the correlation between local Gaussian curvature and relative stored fluid content in each hierarchy by using linear regression, which reveals that stronger correlations could be induced by less densely connected major veins. This flow-controlled mechanism of shape transformation was inspired by the blooming of flowers through the unfolding of petals. It can potentially offer insights for other reversible motions observed in plants induced by differential turgor and water transport through the xylem vessels, as well as engineering applications

Exploring phenotypic plasticity leaf trait relationships in fungal-resistant grapevines using linear regression: Implications of the genotype environment interaction

Accurate and non-destructive models for predicting leaf area (LA) are essential for monitoring vineyard growth and developing automated algorithms. In this study, we developed and compared the performance of eight linear regression models for predicting LA in eleven fungal-resistant grapevine genotypes. We also explored the phenotypic plasticity of leaf traits and their relationship with LA using kernel density estimation analysis. We found that genotype played a major role in defining leaf shape, and genotype-environment interaction was observed. The best models for LA estimation were identified for each genotype, and a leaf deformation index was proposed. Our results provide accurate and robust models for estimating LA in fungal-resistant grapevine genotypes and demonstrate the relationship between leaf traits and the environment. Additionally, we present a method for defining leaf asymmetry. Overall, this study contributes to the development of non-destructive and automated techniques for monitoring vineyard growth

The role of elastic stresses on leaf venation morphogenesis

We explore the possible role of elastic mismatch between epidermis and mesophyll as a driving force for the development of leaf venation. The current prevalent 'canalization' hypothesis for the formation of veins claims that the transport of the hormone auxin out of the leaves triggers cell differentiation to form veins. Although there is evidence that auxin plays a fundamental role in vein formation, the simple canalization mechanism may not be enough to explain some features observed in the vascular system of leaves, in particular, the abundance of vein loops. We present a model based on the existence of mechanical instabilities that leads very naturally to hierarchical patterns with a large number of closed loops. When applied to the structure of high order veins, the numerical results show the same qualitative features as actual venation patterns and, furthermore, have the same statistical properties. We argue that the agreement between actual and simulated patterns provides strong evidence for the role of mechanical effects on venation development.Comment: 10 figures, published in PLoS Computational Biolog

Computer graphics simulation of natural mummification by desiccation

© 2020 The Authors. Computer Animation and Virtual Worlds published by John Wiley & Sons, Ltd. Organic bodies are subject to internal processes after death, causing significant structural, and optical changes. Mummification by desiccation leads to volume shrinkage, skin wrinkling, and discoloration. We propose a method to simulate the process of mummification by desiccation and its effects on the corpse's morphology and appearance. The mummifying body is represented by a layered model consisting of a tetrahedral mesh, representing the volume, plus a high resolution triangle surface mesh representing the skin. The finite element method is used to solve the moisture diffusion and the resulting volume deformations. Skin wrinkling is achieved using position based dynamics. In order to model a visually believable reproduction of the skin coloration changes due to mummification, a skin shading approach is used that considers moisture content, hemoglobin content, and oxygen saturation. The main focus of the work in this article is to recreate the appearance changes of mummification by desiccation, which, to the best of our knowledge, has not been attempted before in computer graphics to this level of realism. The suggested approach is able to model changes in the internal structure and the surface appearance of the body which resemble the postmortem processes of natural mummification by desiccation

X-ray microtomography provides new insights into vacuum impregnation of spinach leaves

Vacuum impregnation is used in the food industry to facilitate the impregnation of porous products with, e.g. firming, antioxidant, antimicrobial or cryoprotective agents. X-ray micro-tomography (CT) was used to study the process of vacuum impregnation in spinach leaves. Low (300 mbar absolute pressure) and mild vacuum (150 mbar absolute pressure) impregnation protocols were used to impregnate an isotonic solution of trehalose in the leaves and CT was used to make observations of the cross section of the impregnated samples and quantify their porosity. Results revealed that the free volume in the spongy mesophyll is easier to impregnate than the spaces around the palisade mesophyll. The low vacuum impregnation protocol provoked less impregnation close to the edge of the leaf than in its centre, probably accounting for an influence of the tissue structure on impregnation. The vacuum impregnation protocols tested in this investigation drastically decreased the proportion of large pores (>100 m) and increased the proportion of small pores (<50 m). The mild vacuum impregnation protocol, which was designed on the basis of measured apparent porosity, did not achieve full impregnation of the tissue.V. Panarese acknowledges the financial support from the Portuguese Foundation of Science (FCT). F. Gomez Galindo acknowledges the financial support from European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement no. 245280, also known under the acronym PRESERF. Financial support of FWO Vlaanderen (project G.0645.13), the Flemish government agency for Innovation by Science and Technology (project IWT SBO120033 TomFood) and the University of Leuven (project OT 12/055) is gratefully acknowledged. Dennis Cantre is an IRO scholar of KU Leuven. We also acknowledge the Hercules foundation for supporting the X-ray CT facility (AKUL001(HER/09/016))

Leaf Morphology, Taxonomy and Geometric Morphometrics: A Simplified Protocol for Beginners

Taxonomy relies greatly on morphology to discriminate groups. Computerized geometric morphometric methods for quantitative shape analysis measure, test and visualize differences in form in a highly effective, reproducible, accurate and statistically powerful way. Plant leaves are commonly used in taxonomic analyses and are particularly suitable to landmark based geometric morphometrics. However, botanists do not yet seem to have taken advantage of this set of methods in their studies as much as zoologists have done. Using free software and an example dataset from two geographical populations of sessile oak leaves, we describe in detailed but simple terms how to: a) compute size and shape variables using Procrustes methods; b) test measurement error and the main levels of variation (population and trees) using a hierachical design; c) estimate the accuracy of group discrimination; d) repeat this estimate after controlling for the effect of size differences on shape (i.e., allometry). Measurement error was completely negligible; individual variation in leaf morphology was large and differences between trees were generally bigger than within trees; differences between the two geographic populations were small in both size and shape; despite a weak allometric trend, controlling for the effect of size on shape slighly increased discrimination accuracy. Procrustes based methods for the analysis of landmarks were highly efficient in measuring the hierarchical structure of differences in leaves and in revealing very small-scale variation. In taxonomy and many other fields of botany and biology, the application of geometric morphometrics contributes to increase scientific rigour in the description of important aspects of the phenotypic dimension of biodiversity. Easy to follow but detailed step by step example studies can promote a more extensive use of these numerical methods, as they provide an introduction to the discipline which, for many biologists, is less intimidating than the often inaccessible specialistic literature

Procedural Modeling and Constrained Morphing of Leaves

Ph.DDOCTOR OF PHILOSOPH

Insects

In this thematic series, engineers and scientists come together to address two interesting interdisciplinary questions in functional morphology and biomechanics: How do the structure and material determine the function of insect body parts? How can insects inspire engineering innovations

Modelling and Simulation of Lily flowers using PDE Surfaces

This paper presents a partial differential equation (PDE)-based surface modelling and simulation framework for lily flowers. We use a PDE-based surface modelling technique to represent shape of a lily flower and PDE-based dynamic simulation to animate blossom and decay processes of lily flowers. To this aim, we first automatically construct the geometry of lily flowers from photos to obtain feature curves. Second, we apply a PDE-based surface modelling technique to generate sweeping surfaces to obtain geometric models of the flowers. Then, we use a physics-driven and data-based method and introduce the flower shapes at the initial and final positions into our proposed dynamic deformation model to generate a realistic deformation of flower blossom and decay. The results demonstrate that our proposed technique can create realistic flower models and their movements and shape changes against time efficiently with a small data size