scholarly journals Geometrical model of lobular structure and its importance for the liver perfusion analysis

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0260068
Author(s):  
Eduard Rohan ◽  
Jana Camprová Turjanicová ◽  
Václav Liška
Keyword(s):  
Liver Perfusion ◽  
Blood Perfusion ◽  
Regular Structure ◽  
Geometrical Model ◽  
Homogenization Method ◽  
Computationally Efficient ◽  
Periodic Cell ◽  
Liver Acinus ◽  
Physiological Processes ◽  
Mesoscopic Level

A convenient geometrical description of the microvascular network is necessary for computationally efficient mathematical modelling of liver perfusion, metabolic and other physiological processes. The tissue models currently used are based on the generally accepted schematic structure of the parenchyma at the lobular level, assuming its perfect regular structure and geometrical symmetries. Hepatic lobule, portal lobule, or liver acinus are considered usually as autonomous functional units on which particular physiological problems are studied. We propose a new periodic unit—the liver representative periodic cell (LRPC) and establish its geometrical parametrization. The LRPC is constituted by two portal lobulae, such that it contains the liver acinus as a substructure. As a remarkable advantage over the classical phenomenological modelling approaches, the LRPC enables for multiscale modelling based on the periodic homogenization method. Derived macroscopic equations involve so called effective medium parameters, such as the tissue permeability, which reflect the LRPC geometry. In this way, mutual influences between the macroscopic phenomena, such as inhomogeneous perfusion, and the local processes relevant to the lobular (mesoscopic) level are respected. The LRPC based model is intended for its use within a complete hierarchical model of the whole liver. Using the Double-permeability Darcy model obtained by the homogenization, we illustrate the usefulness of the LRPC based modelling to describe the blood perfusion in the parenchyma.

scholarly journals Escalas do tempo

2021 ◽  
pp. 306-317
Author(s):  
Eric Landowski
Keyword(s):  
Great Effort ◽  
Mesoscopic Scale ◽  
Macroscopic Scale ◽  
Essential Variable ◽  
Physiological Processes ◽  
Long Duration ◽  
Singular Event ◽  
History Of ◽  
Mesoscopic Level ◽  
Different Time Scales

Viral epidemics are processes in which temporality obviously constitutes an essential variable. But different time scales must be distinguished. To see the current pandemic as a singular event is but an illusion due to the “mesoscopic” timescale we are embracing. There is a microscopic scale — that of physiological processes —, a mesoscopic scale, which only allows to see the closest evidence, and a macroscopic scale, that of the ecological determinisms which explain the emergence of the disease in the history of the relationships between species. The article focuses on the mesoscopic level and highlights some semiotic specificities of today’s experience : a temporal suspension, the threat of pure, dramatic and final discontinuity, the behavior of a virus that appears to have “intentionality”, a strong intensity coupled with a long duration, a time of exception, drawn to a final end, and a victory which will only be achieved with great effort.

scholarly journals Dynamic markers based on blood perfusion fluctuations for selecting skin melanocytic lesions for biopsy

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Gemma Lancaster ◽  
Aneta Stefanovska ◽  
Margherita Pesce ◽  
Gian Marco Vezzoni ◽  
Barbara Loggini ◽  
...  
Keyword(s):  
Malignant Melanoma ◽  
Substantial Reduction ◽  
Blood Perfusion ◽  
Wide Frequency Range ◽  
Physiological Processes ◽  
Vascular Regulation ◽  
Blood Flow Dynamics ◽  
Invasive Method ◽  
Atypical Nevi

Abstract Skin malignant melanoma is a highly angiogenic cancer, necessitating early diagnosis for positive prognosis. The current diagnostic standard of biopsy and histological examination inevitably leads to many unnecessary invasive excisions. Here, we propose a non-invasive method of identification of melanoma based on blood flow dynamics. We consider a wide frequency range from 0.005–2 Hz associated with both local vascular regulation and effects of cardiac pulsation. Combining uniquely the power of oscillations associated with individual physiological processes we obtain a marker which distinguishes between melanoma and atypical nevi with sensitivity of 100% and specificity of 90.9%. The method reveals valuable functional information about the melanoma microenvironment. It also provides the means for simple, accurate, in vivo distinction between malignant melanoma and atypical nevi and may lead to a substantial reduction in the number of biopsies currently undertaken.

scholarly journals Model reduction in computational homogenization for transient heat conduction

2019 ◽  
Vol 65 (1) ◽  
pp. 249-266 ◽  
Author(s):  
A. Waseem ◽  
T. Heuzé ◽  
L. Stainier ◽  
M. G. D. Geers ◽  
V. G. Kouznetsova
Keyword(s):  
Heat Conduction ◽  
Steady State ◽  
Contrast Material ◽  
Transient Heat Conduction ◽  
Homogenization Method ◽  
Computational Homogenization ◽  
Computationally Efficient ◽  
Reduced Basis ◽  
Static Condensation ◽  
Separation Of Scales

Abstract This paper presents a computationally efficient homogenization method for transient heat conduction problems. The notion of relaxed separation of scales is introduced and the homogenization framework is derived. Under the assumptions of linearity and relaxed separation of scales, the microscopic solution is decomposed into a steady-state and a transient part. Static condensation is performed to obtain the global basis for the steady-state response and an eigenvalue problem is solved to obtain a global basis for the transient response. The macroscopic quantities are then extracted by averaging and expressed in terms of the coefficients of the reduced basis. Proof-of-principle simulations are conducted with materials exhibiting high contrast material properties. The proposed homogenization method is compared with the conventional steady-state homogenization and transient computational homogenization methods. Within its applicability limits, the proposed homogenization method is able to accurately capture the microscopic thermal inertial effects with significant computational efficiency.

scholarly journals Double poroelasticity derived from the microstructure

2021 ◽  
Author(s):  
Laura Miller ◽  
Raimondo Penta
Keyword(s):  
Global Scale ◽  
Homogenization Method ◽  
Local Scale ◽  
Scale Model ◽  
The Novel ◽  
Periodic Cell ◽  
The Matrix ◽  
Poroelastic Material ◽  
The Given

AbstractWe derive the balance equations for a double poroelastic material which comprises a matrix with embedded subphases. We assume that the distance between the subphases (the local scale) is much smaller than the size of the domain (the global scale). We assume that at the local scale both the matrix and subphases can be described by Biot’s anisotropic, heterogeneous, compressible poroelasticity (i.e. the porescale is already smoothed out). We then decompose the spatial variations by means of the two-scale homogenization method to upscale the interaction between the poroelastic phases at the local scale. This way, we derive the novel global scale model which is formally of poroelastic-type. The global scale coefficients account for the complexity of the given microstructure and heterogeneities. These effective poroelastic moduli are to be computed by solving appropriate differential periodic cell problems. The model coefficients possess properties that, once proved, allow us to determine that the model is both formally and substantially of poroelastic-type. The properties we prove are a) the existence of a tensor which plays the role of the classical Biot’s tensor of coefficients via a suitable analytical identity and b) the global scale scalar coefficient $$\bar{\mathcal {M}}$$ M ¯ is positive which then qualifies as the global Biot’s modulus for the double poroelastic material.

scholarly journals Semi-Analytical Method for Computing Effective Thermoelastic Properties in Fiber-Reinforced Composite Materials

2021 ◽  
Vol 11 (12) ◽  
pp. 5354
Author(s):  
Rodolfo Avellaneda ◽  
Suset Rodríguez-Alemán ◽  
José A. Otero
Keyword(s):  
Composite Materials ◽  
Cross Section ◽  
Analytical Method ◽  
Effective Properties ◽  
Fibrous Composite ◽  
Transversely Isotropic ◽  
Homogenization Method ◽  
Elliptical Cross ◽  
Periodic Cell ◽  
Effective Coefficients

Effective elastic and thermal properties for isotropic or transversely isotropic thermoelastic fibrous composite materials are obtained. Fibers are distributed with the same periodicity along the two perpendicular directions to the fiber orientation. The periodic cell of the composite has a square or hexagonal distribution. Perfect contact between the fiber and the matrix is presented. The effective properties are calculated using a semi-analytical method. The semi-analytical method consists of obtaining the differential equations that describe the local problems using the Asymptotic Homogenization Method. Then, these equations are solved using the Finite Element Method. Effective elastic coefficient (C¯), effective thermal expansion coefficient (α¯) and the effective thermal conductivity (κ¯) are obtained. The numerical results are compared with the semi-analytical solution and with results reported by other authors. Additionally, the effective properties for a fiber with an elliptical cross section are calculated. Distributions of the fiber’s cross section with different orientations are also studied. A MATLAB program for computing the effective coefficients is presented.

Two-Step Design of Multicontact-Aided Cellular Compliant Mechanisms for Stress Relief

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George A. Lesieutre
Keyword(s):  
Compliant Mechanisms ◽  
Effective Properties ◽  
Compliant Mechanism ◽  
Stress Relief ◽  
Homogenization Method ◽  
Computationally Efficient ◽  
Cellular Mechanisms ◽  
Linear Elastic ◽  
Step Procedure ◽  
Contact Mechanism

A methodology for topology optimization to the design of compliant cellular mechanisms with and without internal contact is presented. A two-step procedure is pursued. First, a baseline noncontact mechanism is developed and optimized via an inverse homogenization method using the “solid isotropic material with penalization” approach. This compliant mechanism is optimized to yield specified elasticity coefficients, with the capability to sustain large effective strains by minimizing local linear elastic strain. In the second step, a system of internal contacts is designed. The initial continuum model of a noncontact mechanism is converted into a frame model, and possible contact links are defined. A computationally efficient algorithm is employed to eliminate those mechanisms having overlapping contact links. The remaining nonoverlapping designs are exhaustively investigated for stress relief. A differential evolution optimizer is used to maximize the stress relief. The results generated for a range of specified elasticity coefficients include a honeycomb-like cell, an auxetic cell, and a diamond-shaped cell. These various cell topologies have different effective properties corresponding to different structural requirements. For each such topology, a contact mechanism is devised that demonstrates stress relief. In one such case, the contact mechanism increases the strain magnification ratio by about 30%.

Multi-scale failure analysis of plain-woven composites

2012 ◽  
Vol 47 (6) ◽  
pp. 379-388 ◽  
Author(s):  
Omar Bacarreza ◽  
MH Aliabadi ◽  
Alfonso Apicella
Keyword(s):  
Damage Mechanics ◽  
Effective Properties ◽  
Progressive Failure ◽  
Continuum Damage Mechanics ◽  
Internal Variable ◽  
Homogenization Method ◽  
Woven Composites ◽  
Computationally Efficient ◽  
Efficient Manner ◽  
Multi Scale

A numerical model capable of dealing with progressive degradation of plain woven composites in a computationally efficient manner is presented in this article. A semi-analytical homogenization method is used to derive effective properties of the composite from the material properties of the constituents. The progressive failure is described using nonlocal continuum damage mechanics where the driving internal variable for the damage is the nonlocal strain. The model was implemented into Abaqus/Explicit, where the failure of a longitudinal tension and an open hole tension specimens were simulated in a multi-scale manner and verified experimentally.

Analytical Modeling

2018 ◽  
pp. 137-186
Keyword(s):  
Elastic Properties ◽  
Natural Fibers ◽  
Computation Time ◽  
Failure Criteria ◽  
Geometrical Model ◽  
Homogenization Method ◽  
Shear Moduli ◽  
Young’S Moduli ◽  
The Matrix ◽  
Composite Stiffness

The large number of available natural fibers emphasizes the use of a reliable, non-costly and easy to use, predictive tool with short computation time. In order to predict the ultimate strengths and Young's moduli of green composites, an analytical model known as the three Stages Homogenization Model (3SHM) is used. The model relies on three main parts: a geometrical model, a homogenization method and a strength model. Moreover, the last two models consist of four main parts: a micro-mechanical modeling for elastic properties and ultimate strengths for unidirectional (UD) composites, a homogenization method at meso and macro levels to determine the composite stiffness and stress-strain fields throughout the composite, two 3D failure criteria for the matrix and unidirectional composites and a damaged stiffness model. This model enables the prediction of the ultimate strengths and the 3D elastic properties; Young's and Shear moduli, in addition to the in plane and out plane tensile and shear strengths.

scholarly journals Numerical study on the effects of blood perfusion and tumor metabolism on tumor temperature for targeted hyperthermia considering a realistic geometrical model of head layers using the finite element method

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Adeleh Kazemi Alamouti ◽  
Mohammad Reza Habibi ◽  
Mohammad Mazidi Sharfabadi ◽  
Hossein Akbari Lalimi
Keyword(s):  
Finite Element ◽  
Temperature Distribution ◽  
Numerical Study ◽  
Blood Perfusion ◽  
Human Head ◽  
Tumor Metabolism ◽  
Geometrical Model ◽  
Thermal Simulation ◽  
Perfusion Rate ◽  
Blood Perfusion Rate

AbstractThe main aim of the present work is to determine the temperature distribution in the normal and cancerous tissues to achieve the desired condition of hyperthermia. Hyperthermia can be defined as the mild elevation of the temperature to 40–46 °C, which induces the cancer cell death and enhances the effects of the radiotherapy and chemotherapy. In the present research, the realistic geometry of the human head layers and the tumor are modelled, geometrically, and then simulated similar to the real samples of MRI images with the size of 5990 mm3. The temperature distribution in the tumor and healthy tissues was obtained based on the solution of Penne’s bio-heat transfer equation utilizing the Finite Element scheme. Employing the accurate boundary conditions for the thermal simulation of the problem, two main layers of the human brain, namely, white matter (WM) and gray matter (GM), as well as the cerebrospinal fluid (CSF) and the skull, are considered in the thermal analysis. In order to examine the hyperthermia conditions, the effects of the different blood perfusion rates and tumor metabolism on the tumor temperature are analyzed. The results showed that by reducing the blood perfusion rate from 0.0016 to 0.0005(ml/(ml.s)), the temperature increased by nearly 0.2 ℃ at the center of the tumor implying that the variations of the blood perfusion rate in the tumor have not a significant influence on its temperature. Moreover, it was found that when the tumor metabolism increases five times (equal to 125 × 103 W/m3) than its normal value (equal to 25,000 W/m3), the temperature reaches to the range needed for ablation of the brain tumor (40–46 ℃). The results also indicated that the manipulation of the cancer tissues metabolic rate via thermal simulation could be efficiently employed to estimate the amount of heat needed for the thermal ablation of the tumor.

Localization of Adenosine Triphosphatase Activity in the Phleom of Nicotiana Tabacum

1972 ◽  
Vol 30 ◽  
pp. 230-231
Author(s):  
James Cronshaw ◽  
Jamison E. Gilder
Keyword(s):  
Plasma Membrane ◽  
Atpase Activity ◽  
Adenosine Triphosphatase ◽  
Higher Plants ◽  
High Surface ◽  
Root Tip ◽  
Animal Cells ◽  
Physiological Processes ◽  
Tip Cells ◽  
Atpase Localization

Adenosine triphosphatase (ATPase) activity has been shown to be associated with numerous physiological processes in both plants and animal cells. Biochemical studies have shown that in higher plants ATPase activity is high in cell wall preparations and is associated with the plasma membrane, nuclei, mitochondria, chloroplasts and lysosomes. However, there have been only a few ATPase localization studies of higher plants at the electron microscope level. Poux (1967) demonstrated ATPase activity associated with most cellular organelles in the protoderm cells of Cucumis roots. Hall (1971) has demonstrated ATPase activity in root tip cells of Zea mays. There was high surface activity largely associated with the plasma membrane and plasmodesmata. ATPase activity was also demonstrated in mitochondria, dictyosomes, endoplasmic reticulum and plastids.

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