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Finite growth models

Tejas S Khire, Barrett J Nehilla, Jirachai Getpreecharsawas, Maria E Gracheva, Richard E Waugh, James L McGrath
Silicon nanomembranes are ultrathin, highly permeable, optically transparent and biocompatible substrates for the construction of barrier tissue models. Trans-epithelial/endothelial electrical resistance (TEER) is often used as a non-invasive, sensitive and quantitative technique to assess barrier function. The current study characterizes the electrical behavior of devices featuring silicon nanomembranes to facilitate their application in TEER studies. In conventional practice with commercial systems, raw resistance values are multiplied by the area of the membrane supporting cell growth to normalize TEER measurements...
January 5, 2018: Biomedical Microdevices
Despoina C Petsepe, Stavros K Kourkoulis, Stavroula A Papadodima, Dimitrios P Sokolis
The ureters are retroperitoneal structures controlling urine transport from the kidneys to the bladder. Because of the relative scarcity of data on the biomechanical properties of human ureter and the established importance of knowing these properties for understanding its physiology, we initiated biomechanical studies in cadaveric tissue. Herein, we report definite zero-stress/no-load geometrical characterization at 15 regions along the ureter of human cadavers aged 23-82 years, estimating the opening angle, circumferential residual strains, axial curvature, and dimensional parameters...
December 1, 2017: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
A Abbas Nejad, Z Talebi, D Cheraghali, A Shahbani-Zahiri, M Norouzi
BACKGROUND AND OBJECTIVE: In this study, the interaction of pulsatile blood flow with the viscoelastic walls of the axisymmetric artery is numerically investigated for different severities of stenosis. The geometry of artery is modeled by an axisymmetric cylindrical tube with a symmetric stenosis in a two-dimensional case. The effects of stenosis severity on the axial velocity profile, pressure distribution, streamlines, wall shear stress, and wall radial displacement for the viscoelastic artery are also compared to the elastics artery...
February 2018: Computer Methods and Programs in Biomedicine
Tohnyui Ndinyanka Fabrice, Hannes Vogler, Christian Draeger, Gautam Munglani, Shibu Gupta, Aline Galatea Herger, J Paul Knox, Ueli Grossniklaus, Christoph Ringli
Leucine-rich repeat extensins (LRXs) are chimeric proteins containing an N-terminal leucine-rich repeat (LRR) and a C-terminal extensin domain. LRXs are involved in cell wall formation in vegetative tissues and required for plant growth. However, the nature of their role in these cellular processes remains to be elucidated. Here, we used a combination of molecular techniques, light microscopy, and transmission electron microscopy to characterize mutants of pollen-expressed LRXs in Arabidopsis thaliana. Mutations in multiple pollen-expressed lrx genes causes severe defects in pollen germination and pollen tube (PT) growth, resulting in a reduced seed set...
December 15, 2017: Plant Physiology
Arsalan Marghoub, Joseph Libby, Christian Babbs, Erwin Pauws, Michael J Fagan, Mehran Moazen
During postnatal calvarial growth the brain grows gradually and the overlying bones and sutures accommodate that growth until the later juvenile stages. The whole process is coordinated through a complex series of biological, chemical and perhaps mechanical signals between various elements of the craniofacial system. The aim of this study was to investigate to what extent a computational model can accurately predict the calvarial growth in wild-type (WT) and mutant type (MT) Fgfr2C342Y/+ mice displaying bicoronal suture fusion...
December 15, 2017: Journal of Anatomy
Sabin Lessard, Cíntia Dalila Soares
In this paper we consider class-structured populations in discrete time in the limit of weak selection and with the inverse of the intensity of selection as unit of time. The aim is to establish a continuous model that approximates the discrete model. More precisely, we study frequency-dependent growth in an infinite haploid population structured into a finite number of classes such that individuals in each class contribute to a given subset of classes from one time step to the next. These contributions take the form of generalized fecundity parameters with perturbations of order 1 / N that depends on the class frequencies of each type and the type frequencies...
December 13, 2017: Journal of Mathematical Biology
Chanyoung Lee, Joan T Richtsmeier, Reuben H Kraft
Bones of the murine cranial vault are formed by differentiation of mesenchymal cells into osteoblasts, a process that is primarily understood to be controlled by a cascade of reactions between extracellular molecules and cells. We assume that the process can be modeled using Turing's reaction-diffusion equations, a mathematical model describing the pattern formation controlled by two interacting molecules (activator and inhibitor). In addition to the processes modeled by reaction-diffusion equations, we hypothesize that mechanical stimuli of the cells due to growth of the underlying brain contribute significantly to the process of cell differentiation in cranial vault development...
June 2017: Journal of Mechanics in Medicine and Biology
S J Mousavi, S Farzaneh, S Avril
Dissections of ascending thoracic aortic aneurysms (ATAA) cause significant morbidity and mortality worldwide. They occur when a tear in the intima-media of the aorta permits the penetration of the blood and the subsequent delamination and separation of the wall in two layers, forming a false channel. In order to predict computationally the risk of tear formation, stress analyses should be performed layer-specifically and they should consider internal or residual stresses which exist in the tissue. In the present paper, we propose a novel layer-specific damage model based on the constrained mixture theory (CMT) which intrinsically takes into account these internal stresses and which can predict appropriately the tear formation...
November 23, 2017: International Journal for Numerical Methods in Biomedical Engineering
Nikita Cobetto, Stefan Parent, Carl-Eric Aubin
BACKGROUND: Anterior vertebral body growth modulation is a fusionless instrumentation to correct scoliosis using growth modulation. The objective was to biomechanically assess effects of cable tensioning, screw positioning and post-operative position on tridimensional correction. METHODS: The design of experiments included two variables: cable tensioning (150/200N) and screw positioning (lateral/anterior/triangulated), computationally tested on 10 scoliotic cases using a personalized finite element model to simulate spinal instrumentation, and 2years growth modulation with the device...
November 16, 2017: Clinical Biomechanics
Florian Joly, Gilles Soulez, Damien Garcia, Simon Lessard, Claude Kauffmann
Abdominal aortic aneurysms (AAA) are localized, commonly-occurring dilations of the aorta. When equilibrium between blood pressure (loading) and wall mechanical resistance is lost, rupture ensues, and patient death follows, if not treated immediately. Experimental and numerical analyses of flow patterns in arteries show direct correlations between wall shear stress and wall mechano-adaptation with the development of zones prone to thrombus formation. For further insights into AAA flow topology/growth interaction, a workout of patient-specific computational flow dynamics (CFD) is proposed to compute finite-time Lyapunov exponents and extract Lagrangian-coherent structures (LCS)...
November 6, 2017: Computers in Biology and Medicine
Lala I P Ray, B C Mal, S Moulick
Semi-intensive Indian Major Carp (IMC) culture was practised in polythene lined dugout ponds at the Aquacultural Farm of Indian Institute of Technology, Kharagpur, West Bengal for 3 consecutive years at three different stocking densities (S.D), viz., 20,000, 35,000 and 50,000 numbers of fingerlings per hectare of water spread area. Fingerlings of Catla, Rohu and Mrigal were raised at a stocking ratio of 4:3:3. Total ammonia nitrogen (TAN) value along with other fishpond water quality parameters was monitored at 1 day intervals to ensure a good water ecosystem for a better fish growth...
November 2017: Water Science and Technology: a Journal of the International Association on Water Pollution Research
Zhidong Wang, Kuizu Su, Tong Shu, Weihong Wang
It is widely known that the accumulation of solid matter forming a cake layer on the membrane surface is one of the major limitations of the filtration performance in submerged membrane bioreactors (SMBR). This study is focused on the influence of the cake porosity of different particle microscopic packed structures on the filtration performance of hollow fiber systems. An integrated model based on the finite element method to simulate numerically the flow in an SMBR is presented. The model coupled the Navier-Stokes and Darcy Brinkman equations to simulate a complete filtration run...
November 2017: Water Science and Technology: a Journal of the International Association on Water Pollution Research
F Hosseini, N Naghavi
BACKGROUND: Angiogenesis initiated by cancerous cells is the process by which new blood vessels are formed to enhance oxygenation and growth of tumor. OBJECTIVE: In this paper, we present a new multiscale mathematical model for the formation of a vascular network in tumor angiogenesis process. METHODS: Our model couples an improved sprout spacing model as a stochastic mathematical model of sprouting along an existing parent blood vessel, with a mathematical model of sprout progression in the extracellular matrix (ECM) in response to some tumor angiogenic factors (TAFs)...
September 2017: Journal of Biomedical Physics & Engineering
Hang Zhang, Qingyan Xu
Grain selection is an important process in single crystal turbine blades manufacturing. Selector structure is a control factor of grain selection, as well as directional solidification (DS). In this study, the grain selection and structure design of the spiral selector were investigated through experimentation and simulation. A heat transfer model and a 3D microstructure growth model were established based on the Cellular automaton-Finite difference (CA-FD) method for the grain selector. Consequently, the temperature field, the microstructure and the grain orientation distribution were simulated and further verified...
October 27, 2017: Materials
V P Weinberger, C Quiñinao, P A Marquet
Biodiversity is sustained by and is essential to the services that ecosystems provide. Different species would use these services in different ways, or adaptive strategies, which are sustained in time by continuous innovations. Using this framework, we postulate a model for a biological species (Homo sapiens) in a finite world where innovations, aimed at increasing the flux of ecosystem services (a measure of habitat quality), increase with population size, and have positive effects on the generation of new innovations (positive feedback) as well as costs in terms of negatively affecting the provision of ecosystem services...
December 5, 2017: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
T Bastogne, J-L Marchand, S Pinel, P Vallois
This paper deals with the dynamic modeling and simulation of cell damage heterogeneity and associated mutant cell phenotypes in the therapeutic responses of cancer cell populations submitted to a radiotherapy session during in vitro assays. Each cell is described by a finite number of phenotypic states with possible transitions between them. The population dynamics is then given by an age-dependent multi-type branching process. From this representation, we obtain formulas for the average size of the global survival population as well as the one of subpopulations associated with 10 mutation phenotypes...
October 18, 2017: Mathematical Biosciences
J M Duley, A C Fowler, I R Moyles, S B G O'Brien
We study the model of Keller & Rubinow (Keller & Rubinow 1981 J. Chem. Phys74, 5000-5007. (doi:10.1063/1.441752)) describing the formation of Liesegang rings due to Ostwald's supersaturation mechanism. Keller and Rubinow provided an approximate solution both for the growth and equilibration of the first band, and also for the formation of secondary bands, based on a presumed asymptotic limit. However, they did not provide a parametric basis for the assumptions in their solution, nor did they provide any numerical corroboration, particularly of the secondary band formation...
September 2017: Proceedings. Mathematical, Physical, and Engineering Sciences
Manuel Schneider, Jan Buschbaum, Alexander Joeris, Oliver Röhrle, Jonathan Dwyer, James B Hunter, Richard A K Reynolds, Theodor F Slongo, Boyko Gueorguiev, Peter Varga
Implants used to correct pathological varus-valgus deformities (VVD) and leg length discrepancies (LLD) may not be optimized for the specific treatment, as suggested by their off-label use. Detailed analysis of this issue has been limited by the poorly understood mechanical behavior of the growing physis and ignorance of the loads acting on the implants. The aim of this study was to predict and compare the loading conditions of a growth modulation implant in VVD and LLD treatments. Idealized finite element (FE) models of the juvenile distal femur treated with the eight-Plate implant were developed for VVD and LLD...
October 4, 2017: Journal of Orthopaedic Research: Official Publication of the Orthopaedic Research Society
Fangfei Ge, Xiao Li, Mir Jalil Razavi, Hanbo Chen, Tuo Zhang, Shu Zhang, Lei Guo, Xiaoping Hu, Xianqiao Wang, Tianming Liu
Recent studies have shown that quantitative description of gyral shape patterns offers a novel window to examine the relationship between brain structure and function. Along this research line, this paper examines a unique and interesting type of cortical gyral region where 3 different gyral crests meet, termed 3-hinge gyral region. We extracted 3-hinge gyral regions in macaque/chimpanzee/human brains, quantified and compared the relevant DTI-derived fiber densities in 3-hinge and 2-hinge gyral regions. Our observations consistently showed that DTI-derived fiber densities in 3-hinge regions are much higher than those in 2-hinge regions...
August 30, 2017: Cerebral Cortex
Alejandro Garzón, Roman O Grigoriev
The mechanisms underlying cardiac fibrillation have been investigated for over a century, but we are still finding surprising results that change our view of this phenomenon. The present study focuses on the transition from normal rhythm to spiral wave chaos associated with a gradual increase in the pacing rate. While some of our findings are consistent with existing experimental, numerical, and theoretical studies of this problem, one result appears to contradict the accepted picture. Specifically we show that, in a two-dimensional model of paced homogeneous atrial tissue, transition from discordant alternans to conduction block, wave breakup, reentry, and spiral wave chaos is associated with the transient growth of finite amplitude disturbances rather than a conventional instability...
September 2017: Chaos
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