Finite-Element Analysis of Temperature Increase in Vascularized Biological Tissues Exposed to RF Sources

A new model of numerical dosimetry is proposed for RF exposure. First, the specific absorption rate (SAR) is computed. Then, the heat transfer governed by the bio-heat equation with convection term is numerically solved by a finite-element method (FEM) procedure considering the discrete vascular model of the perfused tissue. By some manipulations of the FEM equations and by generating an adequate FEM mesh, it is possible to solve the thermal convection in the blood vessels considering a one-dimensional domain embedded in the fully three-dimensional domain where only the thermal diffusion is analyzed

Old-growth forests in the Pollino National Park (southern Italy): current status and future perspectives

Old-growth forests have a primary environmental and ecological value, as they closely recall primeval forests and the natural forest landscape that was spread throughout Italy and Europe before man intervention heavily altered the functioning of most natural ecosystems. These ecosystems are more and more recognized as keystones of environmental policies (i.e., the EU Biodiversity Strategy 2030) aimed to preserve biodiversity and mitigate the impacts of climate change. A recent report highlights that Europe’s old-growth forests account for only 3 percent of the overall forest surface. The majority of italian old-growth forests are located along the Apennines, especially in the Pollino, Sila and Aspromonte National Parks, in remote montane areas characterized by irregular topographical conditions (i.e., high slopes and/or shallow soils) which hamper the access and exploitation of these less productive stands, thus allowing the survival of old-growth forests for many centuries. The ongoing climate change is a significant challenge to the conservation of old-growth forests, particularly in areas such as the Mediterranean basin, where an intensification of extreme climate events is expected. Heat waves can exacerbate drought’s negative impacts on tree growth and survival, leading to reduced woody carbon stocks and biodiversity in old-growth forests. To date, there is poor understanding of such highly valuable and extremely fragile natural ecosystems in Italy. Insights are available based on data gathered as part of two research programs, funded by the Italian Ministry of the Environment and Land and Sea Protection, with the purpose of creating a Network of Old Growth Forests in Italy’s National Parks. In this study, we aimed to highlight the role and importance of old-growth forests, focusing on those located within the Pollino National Park. A comprehensive overview of the key strengths and weaknesses, that mark these peculiar forest ecosystems, was followed by a discussion of the future outlook, grounded on strategies that will ensure not only the protection and conservation of these ecosystems, but also their development and promotion

Autothermal reforming of palm empty fruit bunch bio-oil: thermodynamic modelling

This work focuses on thermodynamic analysis of the autothermal reforming of palm empty fruit bunch (PEFB) bio-oil for the production of hydrogen and syngas. PEFB bio-oil composition was simulated using bio-oil surrogates generated from a mixture of acetic acid, phenol, levoglucosan, palmitic acid and furfural. A sensitivity analysis revealed that the hydrogen and syngas yields were not sensitive to actual bio-oil composition, but were determined by a good match of molar elemental composition between real bio-oil and surrogate mixture. The maximum hydrogen yield obtained under constant reaction enthalpy and pressure was about 12 wt% at S/C = 1 and increased to about 18 wt% at S/C = 4; both yields occurring at equivalence ratio Φ of 0.31. The possibility of generating syngas with varying H2 and CO content using autothermal reforming was analysed and application of this process to fuel cells and Fischer-Tropsch synthesis is discussed. Using a novel simple modelling methodology, reaction mechanisms were proposed which were able to account for equilibrium product distribution. It was evident that different combinations of reactions could be used to obtain the same equilibrium product concentrations. One proposed reaction mechanism, referred to as the ‘partial oxidation based mechanism’ involved the partial oxidation reaction of the bio-oil to produce hydrogen, with the extent of steam reforming and water gas shift reactions varying depending on the amount of oxygen used. Another proposed mechanism, referred to as the ‘complete oxidation based mechanism’ was represented by thermal decomposition of about 30% of bio-oil and hydrogen production obtained by decomposition, steam reforming, water gas shift and carbon gasification reactions. The importance of these mechanisms in assisting in the eventual choice of catalyst to be used in a real ATR of PEFB bio-oil process was discussed

Safety Assessment of UWB Radio Systems for Body Area Network by the FD2TD Method

The paper deals with the numerical prediction of the specific absorption (SA) of ultra wideband (UWB) radio systems for wireless body area network (BAN). The electro-magnetic analysis is performed by a frequency-dependent finite difference time domain (FD2TD) method here proposed with a new formulation based on a total current density approach. A first order Debye approximation is used to model the frequency-dependent properties of the human body in the frequency range of the UWB signals. The proposed method permits to assess the specific absorption and power loss in the human body exposed to an UWB pulsed source. Different numerical models of the human bodies are finally considered in order to investigate safety aspects

Hybrid finite element/finite difference (FE/FD) model to analyze thermal transients in biological vascularized tissues

Purpose – The aim of the paper is to apply a numerical dosimetry procedure to a biological tissue with an embedded discrete vascularisation in order to evaluate the temperature increase produced by radio-frequency (RF) exposure. Design/methodology/approach – The blood temperature inside thin vessels is analysed by a 1D finite difference procedure to solve the convection-dominated heat problem. The tissue temperature inside the remaining 3D domain governed by the heat diffusion equation is calculated by the finite element method. Then, the two separate numerical methods are coupled by an iterative time domain procedure. Findings – The main advantage of the proposed hybrid method is found to be the considerable reduction of the number of unknowns respect to other traditional numerical techniques. Research limitations/implications – In this paper, only the numerical model of the new hybrid procedure has been proposed. In future work realistic biological regions will be examined and the proposed model will be improved by considering the artery/vein coupled structure. Originality/value – The originality of the proposed method regards the solution of the bio-heat equation by means of a new hybrid finite element/finite difference procedure. This procedure is applied inside a vascularized region considering a discrete blood vessel structure

Fd2td analysis of electromagnetic field propagation in multipole debye media with and without convolution

This paper deals with the time-domain numerical calculation of electromagnetic (EM) fields in linearly dispersive media described by multipole Debye model. The frequency-dependent finite-difference time-domain (FD2- TD) method is applied to solve Debye equations using convolution integrals or by direct integration. Original formulations of FD2-TD methods are proposed using different approaches. In the first approach based on the solution of convolution equations, the exponential analytical behavior of the convolution integrand permits an efficient recursive FD2-TD solution. In the second approach, derived by circuit theory, the transient equations are directly solved in time domain by the FD2-TD method. A comparative analysis of several FD2-TD methods in terms of stability, dispersion, computational time and memory is carried out

Circuit-Oriented Solution of Drude Dispersion Relations by the FD2TD Method

This paper deals with the time-domain numerical calculation of electromagnetic (EM) fields in media described by linear Drude dispersive models. The frequency-dependent finite-difference time-domain (FD2TD) method is applied to solve multipole Drude equations using equivalent circuit models. Two new different circuit methods, named as CIRC and PCRC, are proposed. The dispersion analysis and the stability conditions are carried out for these methods. Finally, illustrative examples are provided

Cole-Cole vs Debye models for the assessment of electromagnetic fields inside biological tissues produced by wideband EMF sources

The Cole-Cole model is considered the most reliable fitting tool to describe tissue dielectric properties, but it is not adequate for efficient numerical computation of electromagnetic fields (EMF). On the contrary the Debye model permits very fast computation, but it is not adequate to describe the tissue dispersion in the whole frequency spectrum. In this work we demonstrate that for a large class of actual wideband sources, the Debye model is accurate enough by retaining fast and efficient EMF calculations. © 2012 IEEE