Cassiano Oliveira - Academia.edu (original) (raw)

Papers by Cassiano Oliveira

Nuclear Science and Engineering, 2009

Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, beca... more Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and subcritical states are driven by the fuel material expansion or contraction. The material expansion or contraction is

Nuclear Technology, 2003

A genetic algorithm (GA)-based optimizer (GAOPT) has been developed for in-core fuel management o... more A genetic algorithm (GA)-based optimizer (GAOPT) has been developed for in-core fuel management of advanced gas-cooled reactors (AGRs) at HINKLEY B and HARTLEPOOL, which employ on-load and off-load refueling, respectively. The optimizer has been linked to the reactor analysis code PANTHER for the automated evaluation of loading patterns in a two-dimensional geometry, which is collapsed from the three-dimensional reactor model.

International Journal of Multiphase Flow, 2001

This paper reports ®nite element numerical simulations of gas±solid¯uidised beds using the two-¯u... more This paper reports ®nite element numerical simulations of gas±solid¯uidised beds using the two-¯uid granular temperature model. The aim of the study has been to investigate the various phenomena that have been observed in¯uidised beds but have not been subject to numerical investigation. Two¯uidised beds, operating in the slugging and bubbling regimes, were modelled, and the formation, elongation, coalescence and eruption of bubbles described. The eect of an obstruction on the¯uidisation eciency in a¯uidised bed was investigated. Granular temperature distribution inside the¯uidised bed provided an indication of the regions on the obstruction, which could be susceptible to erosion by particle impact. 7 (C.C. Pain). computers, numerical methods and solution techniques are now beginning to provide the tools necessary to model the dynamics of these complex systems.

FLUBER (Fluidized Bed Thermal Fission Nuclear Reactor) is a conceptual design of a modular reacto... more FLUBER (Fluidized Bed Thermal Fission Nuclear Reactor) is a conceptual design of a modular reactor utilizing the concept of fuel pellet suspension. It consists of TRISO coated fuel particles contained in a graphite-walled cylinder. Helium is used as a coolant and as fluidizing medium.

Progress in Nuclear Energy, 2001

A deterministic model for calculating the time dependent fission yield from solutions has been de... more A deterministic model for calculating the time dependent fission yield from solutions has been developed. The model is based on transient finite element methods and couples radiation transport modelling with computational fluid dynamics. Non-linear space dependent kinetic equations are derived, in which the non-linearities arise due to radiolytic gas generation, geometical changes in the liquid, the temperature dependent densities, cross sections and thermally/gas induced fluid motion. The latter advects the delayed neutron precursor concentrations together with the energy fields. Applications focus on the role of radiolytic gas evolution and buoyancy induced fluid motion on the criticality of fissile liquids with delayed and prompt supercritical step reactivity insertions. The analysis is performed with uranyl nitrate solutions.

Progress in Nuclear Energy, 2003

A theoretical model describing the coupling of neutronics, thermohydraulics and fluidization in a... more A theoretical model describing the coupling of neutronics, thermohydraulics and fluidization in a fluidized bed nuclear reactor is presented. The stability of the system is investigated by linearizing and perturbing the system around its equilibrium points and identifying the root loci of the system. It is found that within the operational range, the eigenvalues are located in the negative part of the phase plane, implying linear stability. Simulations of transient conditions are performed, viz. a hypothetical startup transient and a quasistatic transient related to noise resulting from stochastic movements of the fuel particles. These simulations show that although the total power of the reactor may reach high values, the fuel temperature is well below safety limits at all times.

Industrial Crops and Products, 2016

Carbohydrate Polymers, 2016

This study aimed to evaluate the effect of partial replacement of cashew gum by inulin used as wa... more This study aimed to evaluate the effect of partial replacement of cashew gum by inulin used as wall materials, on the characteristics of ginger essential oil microencapsulated by spray drying with ultrasound assisted emulsions. The characterization of particles was evaluated as encapsulation efficiency and particle size. In addition, the properties of the microcapsules were studied through FTIR analysis, adsorption isotherms, thermal gravimetric analysis, X-ray and scanning electron microscopy. It was found that the solubility of the treatments was affected by the composition of the wall material and reached higher values (89.80%) when higher inulin concentrations were applied. The encapsulation efficiency (15.8%) was lower at the highest inulin concentration. The particles presented amorphous characteristics and treatment with cashew gum as encapsulant exhibited the highest water absorption at high water activity. The cashew gum and inulin matrix (3:1(w/w) ratio) showed the best characteristics regarding the encapsulation efficiency and morphology, showing no cracks in the structure.

ACKNOWLEDGMENTS A great deal of gratitude is extended,to Professor Farzad Rahnema,for his instruc... more ACKNOWLEDGMENTS A great deal of gratitude is extended,to Professor Farzad Rahnema,for his instruction and guidance, and for his friendship throughout my many years at Georgia Tech. Meetings and discussions with Dr. Rahnema,have always been something,to look forward to and never failed to leave me,excited about,the ideas that were waiting to be explored. I am,deeply indebted to his kindness, his confidence

Water Science & Technology, 2007

In the pulp and paper industry, the water use minimization is a constant target. One way to reduc... more In the pulp and paper industry, the water use minimization is a constant target. One way to reduce water use is to recycle the effluent in a closed-cycle concept. In paper mills, the main source of liquid effluent is the so-called whitewater, which is the excess water, originated from pulp stock dewatering and other fiber contaminated water. This research studied the reuse of paper mill whitewater after membrane ultrafiltration (UF) in the paper machine and in the pulp bleach plant of an integrated mill. Contaminant removal and flux behavior of the UF system were evaluated. The treatment by ultrafiltration was technically feasible and the treated whitewater had good potential to be reused in some processes in the paper machine. The reuse of ultrafiltered whitewater in the bleaching plant was not recommended because of the high level of soluble calcium present in this stream. Therefore, a combined treatment of the whitewater using the principle of precipitation and ultrafiltration was proposed showing good results and enabling the use of the treated whitewater in the bleach plant.

Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, beca... more Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors heavily depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and sub-critical states are driven by the fuel material expansion or contraction. The material expansion or contraction is due to temperature gradient which results from fission power. In this paper, we introduce a numerical model for coupling of neutron diffusion and thermomechanics in fast burst reactors. We also provide some analysis of the coupled system. We studied material behaviors corresponding to different levels of power pulses.

International Journal of Food Science & Technology, 2013

The objective of this study was to evaluate the influence of whey protein isolate (WPI) and inuli... more The objective of this study was to evaluate the influence of whey protein isolate (WPI) and inulin blends on the properties of rosemary essential oil microencapsulated by spray drying. The following ratios (w/w) of WPI to inulin were evaluated: 1:1, 1:3 and 3:1. Increasing the WPI concentration increased the particle instantanisation times and decreased the moisture content. The samples did not differ significantly (P > 0.05) in hygroscopicity and porosity. The microcapsules produced at higher inulin concentration showed the highest bulk density and tapped density and were significantly different from other treatments. WPI/inulin blends of 1:1 and 3:1 proved to be effective carriers to entrap rosemary essential oil. The encapsulated oil composition in particles proved to be quite similar to pure oil, and no interaction between wall matrix and encapsulated oil was demonstrated. The analysis of particle size distribution revealed that the particle size varied from 11.5 to 11.9 lm and that all samples had an amorphous structure.

We develop a numerical model for coupling of neutron diffusion adn termomechanics in order to sti... more We develop a numerical model for coupling of neutron diffusion adn termomechanics in order to stimulate transient behavior of a fast burst reactor. The problem involves solving a set of non-linear different equations which approximate neutron diffusion, temperature change, and material behavior. With this equation set we will model the transition from a supercritical to subcritical state and possible mechanical vibration.

Progress in Nuclear Energy, 2004

Nuclear Science and Engineering, 2009

ABSTRACT Coupling neutronics to thermomechanics is important for the analysis of fast burst react... more ABSTRACT Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and subcritical states are driven by the fuel material expansion or contraction. The material expansion or contraction is due to the temperature gradient which results from fission power. In this paper, we introduce a numerical model for coupling of neutron diffusion and thermomechanics in fast burst reactors. The goal is to have a better understanding of the relation between the reactivity insertion and the thermomechanical response of fuel materials. We perform a non-dimensional analysis of the coupled system which provides insight into the behavior of the transient. We also provide a semianalytical solution model to the coupled system for partial verification of our numerical solutions. We studied material behavior corresponding to different levels of reactivity insertion.

Progress in Nuclear Energy, 2001

... CASSIANO RE DE OLIVEIRA, MATTHEW D. EATON, ADRIAN P. UMPLEBY and CHRISTOPHER C. PAIN ... 2 (s... more ... CASSIANO RE DE OLIVEIRA, MATTHEW D. EATON, ADRIAN P. UMPLEBY and CHRISTOPHER C. PAIN ... 2 (shield with a void duct) Figure 3: Kobayashi problem 3 (shield with a ... scattering and timedependence and has been incorporated into the EVENT code (de Oliveira, 1986 ...

International Journal of Numerical Methods for Heat and Fluid Flow, 2005

Purpose -To present dynamical analysis of axisymmetric and three-dimensional (3D) simulations of ... more Purpose -To present dynamical analysis of axisymmetric and three-dimensional (3D) simulations of a nuclear fluidized bed reactor. Also to determine the root cause of reactor power fluctuations. Design/methodology/approach -We have used a coupled neutron radiation (in full phase space) and high resolution multiphase gas-solid Eulerian-Eulerian model. Findings -The reactor can take over 5 min after start up to establish a quasi-steady-state and the mechanism for the long term oscillations of power have been established as a heat loss/generation mechanism. There is a clear need to parameterize the temperature of the reactor and, therefore, its power output for a given fissile mass or reactivity. The fission-power fluctuates by an order of magnitude with a frequency of 0.5-2 Hz. However, the thermal power output from gases is fairly steady.

Two stochastic optimization algorithms conceptually similar to Simulated Annealing are presented ... more Two stochastic optimization algorithms conceptually similar to Simulated Annealing are presented and applied to a core design optimization problem previously solved with Genetic Algorithms. The two algorithms are the novel Particle Collision Algorithm (PCA), which is introduced in detail, and Dueck's Great Deluge Algorithm (GDA). The optimization problem consists in adjusting several reactor cell parameters, such as dimensions, enrichment and materials, in order to minimize the average peak factor in a three-enrichment-zone reactor, considering restrictions on the average thermal flux, criticality and sub-moderation. Results show that the PCA and the GDA perform very well compared to the canonical Genetic Algorithm and its variants, and also to Simulated Annealing, hence demonstrating their potential for other optimization applications.

Nuclear Engineering and Design, 2003

In this paper we present numerical simulations of a conceptual helium-cooled fluidized bed therma... more In this paper we present numerical simulations of a conceptual helium-cooled fluidized bed thermal nuclear reactor. The simulations are performed using the coupled neutronics/multi-phase computational fluid dynamics code finite element transient criticality which is capable of modelling all the relevant non-linear feedback mechanisms. The conceptual reactor consists of an axi-symmetric bed surrounded by graphite moderator inside which 0.1 cm diameter TRISO-coated nuclear fuel particles are fluidized. Detailed spatial/temporal neutron flux and temperature profiles have been obtained providing valuable insight into the power distribution and fluid dynamics of this complex system. The numerical simulations show that the unique mixing ability of the fluidized bed gives rise, as expected, to uniform temperature and particle distribution. This uniformity enhances the heat transfer and therefore the power produced by the reactor. # Oliveira).

Medical Physics, 2002

Most researchers choose the diffusion approximation to the transport equation as the model to des... more Most researchers choose the diffusion approximation to the transport equation as the model to describe photon migration in biological tissues. However, the applicability of this approximation is limited and, in certain cases, invalid. In this paper we introduce a two-dimensional, finite element-spherical harmonics (FE-P(N)) radiation transport method for the simulation of light propagation in tissue. The propagation of light is investigated first in a layered cylinder, which can be seen as a very simplistic approximation of a human head. Effects of the anisotropy factor g on the photon migration is then examined in homogeneous and heterogeneous media for different values of g and mu(s). The influence of void-like heterogeneities and channels in which absorption and scattering are very small compared with the surrounding medium on the transport of photons is also investigated. Significant differences between transport and diffusion calculations are shown to occur in all cases.

Nuclear Science and Engineering, 2009

Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, beca... more Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and subcritical states are driven by the fuel material expansion or contraction. The material expansion or contraction is

Nuclear Technology, 2003

A genetic algorithm (GA)-based optimizer (GAOPT) has been developed for in-core fuel management o... more A genetic algorithm (GA)-based optimizer (GAOPT) has been developed for in-core fuel management of advanced gas-cooled reactors (AGRs) at HINKLEY B and HARTLEPOOL, which employ on-load and off-load refueling, respectively. The optimizer has been linked to the reactor analysis code PANTHER for the automated evaluation of loading patterns in a two-dimensional geometry, which is collapsed from the three-dimensional reactor model.

International Journal of Multiphase Flow, 2001

This paper reports ®nite element numerical simulations of gas±solid¯uidised beds using the two-¯u... more This paper reports ®nite element numerical simulations of gas±solid¯uidised beds using the two-¯uid granular temperature model. The aim of the study has been to investigate the various phenomena that have been observed in¯uidised beds but have not been subject to numerical investigation. Two¯uidised beds, operating in the slugging and bubbling regimes, were modelled, and the formation, elongation, coalescence and eruption of bubbles described. The eect of an obstruction on the¯uidisation eciency in a¯uidised bed was investigated. Granular temperature distribution inside the¯uidised bed provided an indication of the regions on the obstruction, which could be susceptible to erosion by particle impact. 7 (C.C. Pain). computers, numerical methods and solution techniques are now beginning to provide the tools necessary to model the dynamics of these complex systems.

FLUBER (Fluidized Bed Thermal Fission Nuclear Reactor) is a conceptual design of a modular reacto... more FLUBER (Fluidized Bed Thermal Fission Nuclear Reactor) is a conceptual design of a modular reactor utilizing the concept of fuel pellet suspension. It consists of TRISO coated fuel particles contained in a graphite-walled cylinder. Helium is used as a coolant and as fluidizing medium.

Progress in Nuclear Energy, 2001

A deterministic model for calculating the time dependent fission yield from solutions has been de... more A deterministic model for calculating the time dependent fission yield from solutions has been developed. The model is based on transient finite element methods and couples radiation transport modelling with computational fluid dynamics. Non-linear space dependent kinetic equations are derived, in which the non-linearities arise due to radiolytic gas generation, geometical changes in the liquid, the temperature dependent densities, cross sections and thermally/gas induced fluid motion. The latter advects the delayed neutron precursor concentrations together with the energy fields. Applications focus on the role of radiolytic gas evolution and buoyancy induced fluid motion on the criticality of fissile liquids with delayed and prompt supercritical step reactivity insertions. The analysis is performed with uranyl nitrate solutions.

Progress in Nuclear Energy, 2003

A theoretical model describing the coupling of neutronics, thermohydraulics and fluidization in a... more A theoretical model describing the coupling of neutronics, thermohydraulics and fluidization in a fluidized bed nuclear reactor is presented. The stability of the system is investigated by linearizing and perturbing the system around its equilibrium points and identifying the root loci of the system. It is found that within the operational range, the eigenvalues are located in the negative part of the phase plane, implying linear stability. Simulations of transient conditions are performed, viz. a hypothetical startup transient and a quasistatic transient related to noise resulting from stochastic movements of the fuel particles. These simulations show that although the total power of the reactor may reach high values, the fuel temperature is well below safety limits at all times.

Industrial Crops and Products, 2016

Carbohydrate Polymers, 2016

This study aimed to evaluate the effect of partial replacement of cashew gum by inulin used as wa... more This study aimed to evaluate the effect of partial replacement of cashew gum by inulin used as wall materials, on the characteristics of ginger essential oil microencapsulated by spray drying with ultrasound assisted emulsions. The characterization of particles was evaluated as encapsulation efficiency and particle size. In addition, the properties of the microcapsules were studied through FTIR analysis, adsorption isotherms, thermal gravimetric analysis, X-ray and scanning electron microscopy. It was found that the solubility of the treatments was affected by the composition of the wall material and reached higher values (89.80%) when higher inulin concentrations were applied. The encapsulation efficiency (15.8%) was lower at the highest inulin concentration. The particles presented amorphous characteristics and treatment with cashew gum as encapsulant exhibited the highest water absorption at high water activity. The cashew gum and inulin matrix (3:1(w/w) ratio) showed the best characteristics regarding the encapsulation efficiency and morphology, showing no cracks in the structure.

ACKNOWLEDGMENTS A great deal of gratitude is extended,to Professor Farzad Rahnema,for his instruc... more ACKNOWLEDGMENTS A great deal of gratitude is extended,to Professor Farzad Rahnema,for his instruction and guidance, and for his friendship throughout my many years at Georgia Tech. Meetings and discussions with Dr. Rahnema,have always been something,to look forward to and never failed to leave me,excited about,the ideas that were waiting to be explored. I am,deeply indebted to his kindness, his confidence

Water Science & Technology, 2007

In the pulp and paper industry, the water use minimization is a constant target. One way to reduc... more In the pulp and paper industry, the water use minimization is a constant target. One way to reduce water use is to recycle the effluent in a closed-cycle concept. In paper mills, the main source of liquid effluent is the so-called whitewater, which is the excess water, originated from pulp stock dewatering and other fiber contaminated water. This research studied the reuse of paper mill whitewater after membrane ultrafiltration (UF) in the paper machine and in the pulp bleach plant of an integrated mill. Contaminant removal and flux behavior of the UF system were evaluated. The treatment by ultrafiltration was technically feasible and the treated whitewater had good potential to be reused in some processes in the paper machine. The reuse of ultrafiltered whitewater in the bleaching plant was not recommended because of the high level of soluble calcium present in this stream. Therefore, a combined treatment of the whitewater using the principle of precipitation and ultrafiltration was proposed showing good results and enabling the use of the treated whitewater in the bleach plant.

Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, beca... more Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors heavily depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and sub-critical states are driven by the fuel material expansion or contraction. The material expansion or contraction is due to temperature gradient which results from fission power. In this paper, we introduce a numerical model for coupling of neutron diffusion and thermomechanics in fast burst reactors. We also provide some analysis of the coupled system. We studied material behaviors corresponding to different levels of power pulses.

International Journal of Food Science & Technology, 2013

The objective of this study was to evaluate the influence of whey protein isolate (WPI) and inuli... more The objective of this study was to evaluate the influence of whey protein isolate (WPI) and inulin blends on the properties of rosemary essential oil microencapsulated by spray drying. The following ratios (w/w) of WPI to inulin were evaluated: 1:1, 1:3 and 3:1. Increasing the WPI concentration increased the particle instantanisation times and decreased the moisture content. The samples did not differ significantly (P > 0.05) in hygroscopicity and porosity. The microcapsules produced at higher inulin concentration showed the highest bulk density and tapped density and were significantly different from other treatments. WPI/inulin blends of 1:1 and 3:1 proved to be effective carriers to entrap rosemary essential oil. The encapsulated oil composition in particles proved to be quite similar to pure oil, and no interaction between wall matrix and encapsulated oil was demonstrated. The analysis of particle size distribution revealed that the particle size varied from 11.5 to 11.9 lm and that all samples had an amorphous structure.

We develop a numerical model for coupling of neutron diffusion adn termomechanics in order to sti... more We develop a numerical model for coupling of neutron diffusion adn termomechanics in order to stimulate transient behavior of a fast burst reactor. The problem involves solving a set of non-linear different equations which approximate neutron diffusion, temperature change, and material behavior. With this equation set we will model the transition from a supercritical to subcritical state and possible mechanical vibration.

Progress in Nuclear Energy, 2004

Nuclear Science and Engineering, 2009

ABSTRACT Coupling neutronics to thermomechanics is important for the analysis of fast burst react... more ABSTRACT Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and subcritical states are driven by the fuel material expansion or contraction. The material expansion or contraction is due to the temperature gradient which results from fission power. In this paper, we introduce a numerical model for coupling of neutron diffusion and thermomechanics in fast burst reactors. The goal is to have a better understanding of the relation between the reactivity insertion and the thermomechanical response of fuel materials. We perform a non-dimensional analysis of the coupled system which provides insight into the behavior of the transient. We also provide a semianalytical solution model to the coupled system for partial verification of our numerical solutions. We studied material behavior corresponding to different levels of reactivity insertion.

Progress in Nuclear Energy, 2001

... CASSIANO RE DE OLIVEIRA, MATTHEW D. EATON, ADRIAN P. UMPLEBY and CHRISTOPHER C. PAIN ... 2 (s... more ... CASSIANO RE DE OLIVEIRA, MATTHEW D. EATON, ADRIAN P. UMPLEBY and CHRISTOPHER C. PAIN ... 2 (shield with a void duct) Figure 3: Kobayashi problem 3 (shield with a ... scattering and timedependence and has been incorporated into the EVENT code (de Oliveira, 1986 ...

International Journal of Numerical Methods for Heat and Fluid Flow, 2005

Purpose -To present dynamical analysis of axisymmetric and three-dimensional (3D) simulations of ... more Purpose -To present dynamical analysis of axisymmetric and three-dimensional (3D) simulations of a nuclear fluidized bed reactor. Also to determine the root cause of reactor power fluctuations. Design/methodology/approach -We have used a coupled neutron radiation (in full phase space) and high resolution multiphase gas-solid Eulerian-Eulerian model. Findings -The reactor can take over 5 min after start up to establish a quasi-steady-state and the mechanism for the long term oscillations of power have been established as a heat loss/generation mechanism. There is a clear need to parameterize the temperature of the reactor and, therefore, its power output for a given fissile mass or reactivity. The fission-power fluctuates by an order of magnitude with a frequency of 0.5-2 Hz. However, the thermal power output from gases is fairly steady.

Two stochastic optimization algorithms conceptually similar to Simulated Annealing are presented ... more Two stochastic optimization algorithms conceptually similar to Simulated Annealing are presented and applied to a core design optimization problem previously solved with Genetic Algorithms. The two algorithms are the novel Particle Collision Algorithm (PCA), which is introduced in detail, and Dueck's Great Deluge Algorithm (GDA). The optimization problem consists in adjusting several reactor cell parameters, such as dimensions, enrichment and materials, in order to minimize the average peak factor in a three-enrichment-zone reactor, considering restrictions on the average thermal flux, criticality and sub-moderation. Results show that the PCA and the GDA perform very well compared to the canonical Genetic Algorithm and its variants, and also to Simulated Annealing, hence demonstrating their potential for other optimization applications.

Nuclear Engineering and Design, 2003

In this paper we present numerical simulations of a conceptual helium-cooled fluidized bed therma... more In this paper we present numerical simulations of a conceptual helium-cooled fluidized bed thermal nuclear reactor. The simulations are performed using the coupled neutronics/multi-phase computational fluid dynamics code finite element transient criticality which is capable of modelling all the relevant non-linear feedback mechanisms. The conceptual reactor consists of an axi-symmetric bed surrounded by graphite moderator inside which 0.1 cm diameter TRISO-coated nuclear fuel particles are fluidized. Detailed spatial/temporal neutron flux and temperature profiles have been obtained providing valuable insight into the power distribution and fluid dynamics of this complex system. The numerical simulations show that the unique mixing ability of the fluidized bed gives rise, as expected, to uniform temperature and particle distribution. This uniformity enhances the heat transfer and therefore the power produced by the reactor. # Oliveira).

Medical Physics, 2002

Most researchers choose the diffusion approximation to the transport equation as the model to des... more Most researchers choose the diffusion approximation to the transport equation as the model to describe photon migration in biological tissues. However, the applicability of this approximation is limited and, in certain cases, invalid. In this paper we introduce a two-dimensional, finite element-spherical harmonics (FE-P(N)) radiation transport method for the simulation of light propagation in tissue. The propagation of light is investigated first in a layered cylinder, which can be seen as a very simplistic approximation of a human head. Effects of the anisotropy factor g on the photon migration is then examined in homogeneous and heterogeneous media for different values of g and mu(s). The influence of void-like heterogeneities and channels in which absorption and scattering are very small compared with the surrounding medium on the transport of photons is also investigated. Significant differences between transport and diffusion calculations are shown to occur in all cases.