Voronoi-based Model Research Articles

Mechanical modeling of lung alveoli: From macroscopic behaviour to cell mechano-sensing at microscopic level

The mechanical signals sensed by the alveolar cells through the changes in the local matrix stiffness of the extracellular matrix (ECM) are determinant for regulating cellular functions. Therefore, the study of the mechanical response of lung tissue becomes a fundamental aspect in order to further understand the mechanosensing signals perceived by the cells in the alveoli. This study is focused on the development of a finite element (FE) model of a decellularized rat lung tissue strip, which reproduces accurately the mechanical behaviour observed in the experiments by means of a tensile test. For simulating the complex structure of the lung parenchyma, which consists of a heterogeneous and non-uniform network of thin-walled alveoli, a 3D model based on a Voronoi tessellation is developed. This Voronoi-based model is considered very suitable for recreating the geometry of cellular materials with randomly distributed polygons like in the lung tissue. The material model used in the mechanical simulations of the lung tissue was characterized experimentally by means of AFM tests in order to evaluate the lung tissue stiffness on the micro scale. Thus, in this study, the micro (AFM test) and the macro scale (tensile test) mechanical behaviour are linked through the mechanical simulation with the 3D FE model based on Voronoi tessellation. Finally, a micro-mechanical FE-based model is generated from the Voronoi diagram for studying the stiffness sensed by the alveolar cells in function of two independent factors: the stretch level of the lung tissue and the geometrical position of the cells on the extracellular matrix (ECM), distinguishing between pneumocyte type I and type II. We conclude that the position of the cells within the alveolus has a great influence on the local stiffness perceived by the cells. Alveolar cells located at the corners of the alveolus, mainly type II pneumocytes, perceive a much higher stiffness than those located in the flat areas of the alveoli, which correspond to type I pneumocytes. However, the high stiffness, due to the macroscopic lung tissue stretch, affects both cells in a very similar form, thus no significant differences between them have been observed.

Investigation of the filtration performance for fibrous media: Coupling of a semi-analytical model with CFD on Voronoi-based microstructure

3D micro-scale model of fibrous media with controllable structural parameters (such as fiber diameter, solid volume fraction and cell configuration) was constructed by using Voronoi algorithm in this study. Compared with the fibrous media model having layer-structured topology, the Voronoi-based model can well characterize the penetration behavior between fibers and layer connections. The gas–solid flow characteristics in fibrous media under different structural and operating parameters were examined numerically and semi-analytically. The results show that the pressure drop of fibrous media between numerical results and experimental values in literature is not always consistent. A new pressure drop correlation for fibrous media is proposed. Additionally, numerical results of the filtration efficiency show similar tendencies to the results that are calculated by the semi-analytical model. For submicron particles, the Stokes-Cunningham drag law combined with Saffman’s lift force and Brownian force can accurately predict the capture action dominated by the combination of diffusion and inertia. The deviation of filtration efficiencies between numerical results and theoretical predictions increases with increase of the Peclet number. For micron particles, the semi-analytical model-determined filtration efficiency is generally higher than numerical results which adopting the spherical drag law and considering the gravity effect. Moreover, a threshold value of the Stokes number that determines the deviation between numerical and semi-analytical approaches is presented. When the Stokes number is greater than the threshold, a relatively small deviation can be achieved. It is concluded that the new pressure drop correlation can provide guidance for macro-scale model to study the filtration performance. As well, the correlation calculating of filtration efficiency between numerical simulation and semi-analytical model is obtained by using the Peclet number and the Stokes number as criteria.

A framework for integrated terminal airspace design

ABSTRACTRoute planning and airspace sectorisation are two central tasks in air traffic management. Traditionally, the routing and sectorisation problems were considered separately, with aircraft trajectories serving as input to the sectorisation problem and, reciprocally, sectors being part of the input to the path finding algorithms.In this paper we propose a simultaneous design of routes and sectors for a transition airspace. We compare two approaches for this integrated design: one based on mixed integer programming, and one Voronoi-based model that separates potential “hotspots” of controller activity resulting from the terminal routes.We apply our two approaches to the design of Stockholm Terminal Maneuvering Area.

Two-Dimensional Voronoi-Based Model and Detection for Shingled Magnetic Recording

In this paper, we present a model of a shingled magnetic recording system, where Voronoi regions are used to model the grains of the magnetic medium. A probabilistic model is used to represent imperfections in the write process, i.e., the head failing to write some grains correctly. A two-dimensional model of the head response is used to calculate the signal read back by the head over any place on the medium, thereby including both intertrack and intersymbol interference effects in the model. We also present simulation results from tests of this model using a multitrack detector and an intertrack interference canceller and give performance results of the channel/detector combination for various track offsets.

Voronoi-based k-order neighbour relations for spatial analysis

Spatial neighbour relations are a very important concept in spatial information science. Neighbourhood information is indispensable for many operations in spatial information systems, and it is therefore significant to describe and acquire it in an efficient way. In this paper, the concept of k-order neighbours is developed and a Voronoi-based model is formed for this type of neighbours, resulting in the so-called Voronoi k-order neighbours. Several methods for the computation of k-order neighbours for various given conditions are developed. An application in contour analysis is illustrated, i.e. the generation of a contour tree.