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See detailMathematical modeling of biogeochemical processes associated to a coccolithophorid (Emiliania huxleyi) bloom - Study of the seasonal and long-term variability of biogeochemical properties in the Black Sea using a Data Interpolating Variational Analysis (DIVA)
Joassin, Pascal ULg

Doctoral thesis (2011)

A OD biogeochemical model has been developed to represent coccolithophorid physiological features concerned by carbon export (primary production, active DOC excretion, TEP formation, and calcification ... [more ▼]

A OD biogeochemical model has been developed to represent coccolithophorid physiological features concerned by carbon export (primary production, active DOC excretion, TEP formation, and calcification) and susceptible to be sensitive to varying pCO2. The model is initially calibrated and validated using a large set of biogeochemical data monitored during Emiliania huxleyi blooms induced in a mesocosm experiment, under present-day pCO2 conditions. Afterwards, impacts of varying pCO2 conditions on Emiliania huxleyi physiology are investigated using biogeochemical variables monitored in mesocosms under low and high pCO2 conditions. The methodology promotes a double approach: the recalibration model parameters’ that optimizes the representation of observations from low and high pCO2 treatments, and the utilization of a RM ANOVA procedure to indicate significant differences between biogeochemical variables monitored during blooms induced in low and high pCO2 treatments. Since the early 1970’s, the Black Sea ecosystem has suffered significant ecological alterations, essentially caused by anthropogenic impacts. Dam constructions on the Danube River in combination with heavy nutrients discharge via the riverine run-off lead to strong modifications of its physical and biogeochemical properties, with final consequences consisting in an enhancement of the typical anoxic state of the deep waters. The long-term evolution of key biogeochemical variables (oxygen, hydrogen sulfide, and chlorophyll) has been studied through the reconstruction of horizontal fields, using long time data series and the DIVA interpolating tool. In addition, the examination during the best sampled period (1986-1993) of these biogeochemical variables’ fields, completed with nitrates and phosphates fields, highlighted seasonal and horizontal variability within typical sections of their profiles. [less ▲]

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See detailMathematical modeling of bone regeneration during fracture healing
Geris, Liesbet ULg; Vander Sloten, Hans; Van Oosterwyck, Hans

in proceedings of the National Conference on Theoretical and Applied Mechanics (2009)

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See detailMathematical modeling of bone regeneration during fracture healing and implant osseointegration
Geris, Liesbet ULg

Doctoral thesis (2007)

Despite the extensive body of literature on bone regeneration, many questions remain on e.g. the regulatory mechanisms and potential treatment strategies of pathological regeneration cases. The hypothesis ... [more ▼]

Despite the extensive body of literature on bone regeneration, many questions remain on e.g. the regulatory mechanisms and potential treatment strategies of pathological regeneration cases. The hypothesis underlying this work states that mathematical models of bone regeneration can make a substantial contribution to this domain by proposing pathological regeneration mechanisms and designing therapies, which can subsequently be tested experimentally. In the first part of this work, existing mechanoregulatory and bioregulatory models of bone regeneration are implemented and applied to both implant osseointegration and fracture healing set-ups. A quantitative comparison with experimental results is performed. Thorough sensitivity analyses are carried out to assess the influence of various modelling aspects on the simulation outcome. Shortcomings of these models are identified and suggestions for improvements are made. In the second part of this work, a novel bioregulatory model of bone regeneration is developed in which several of the previously defined shortcomings are addressed. This model includes key aspects of the regeneration process such as intramembranous and endochondral ossification, angiogenesis and directed cell motion. The results obtained with this novel model are corroborated both qualitatively and quantitatively by comparison with experimental data for normal fracture healing. Cases of pathological fracture healing are simulated and experimentally testable therapeutic strategies are implemented. The last part of this work describes the establishment of a mathematical framework, based on the previously developed bioregulatory model, in which the regulatory influence of both biological and mechanical factors is combined. This is the first model of bone regeneration in which the coupling between mechanical loading and angiogenesis is made in an explicit and mechanistic manner. Several examples are given to illustrate the added value of this approach in simulating normal and pathological bone regeneration. In summary, this work demonstrates the potential of mathematical models in advancing the knowledge on bone regeneration and designing treatment strategies for pathological healing cases. [less ▲]

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See detailMathematical modeling of bone regeneration including the angiogenic process
Geris, Liesbet ULg; Vander Sloten, Jos; Van Oosterwyck, Hans

in Journal of Biomechanics (2006), 39(S1), 411-412

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See detailMathematical modeling of cell-cell and cell-matrix adhesion in tissue engineering using continuum models
Geris, Liesbet ULg; Gerisch, A.

in Geffen, A. (Ed.) Cellular and Biomolecular Mechanics and Mechanobiology (2011)

Key factors in the formation of cell aggregates in tissue engineering and other fields are the cell-cell and cell-matrix interactions. Other important factors are culture conditions such as nutrient and ... [more ▼]

Key factors in the formation of cell aggregates in tissue engineering and other fields are the cell-cell and cell-matrix interactions. Other important factors are culture conditions such as nutrient and oxygen supply and the characteristics of the environment (medium versus hydrogel). As mathematical models are increasingly used to investigate biological phenomena, it is important that processes such as cell adhesion are adequately described in the models. Recently a technique was developed to incorporate cell-cell and cell-matrix adhesion in continuum models through the use of non-local terms. In this study we apply this technique to model adhesion in a cell-in-gel culture set-up often found in tissue engineering applications. We briefly describe the biological issues underlying this study and the various modeling techniques used to capture adhesive behaviour. We furthermore elaborate on the numerical techniques that were developed in the course of this study. Finally, we consider a tissue engineering model that describes the spatiotemporal evolution of the concentration of cells, matrix, hydrogel, matrix degrading enzymes and oxygen/nutrients in a cell-in-gel culture system. Sensitivity analyses indicate a clear influence of the different adhesive processes on the final cell and collagen density and distribution, demonstrating the significance of cell adhesion in tissue engineering and the potential of the proposed mathematical technique. [less ▲]

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See detailMathematical modeling of fracture healing in mice: comparison between experimental data and numerical simulation results.
Geris, Liesbet ULg; Gerisch, Alf; Maes, Christa et al

in Medical & Biological Engineering & Computing (2006), 44(4), 280-9

The combined use of experimental and mathematical models can lead to a better understanding of fracture healing. In this study, a mathematical model, which was originally established by Bailon-Plaza and ... [more ▼]

The combined use of experimental and mathematical models can lead to a better understanding of fracture healing. In this study, a mathematical model, which was originally established by Bailon-Plaza and van der Meulen (J Theor Biol 212:191-209, 2001), was applied to an experimental model of a semi-stabilized murine tibial fracture. The mathematical model was implemented in a custom finite volumes code, specialized in dealing with the model's requirements of mass conservation and non-negativity of the variables. A qualitative agreement between the experimentally measured and numerically simulated evolution in the cartilage and bone content was observed. Additionally, an extensive parametric study was conducted to assess the influence of the model parameters on the simulation outcome. Finally, a case of pathological fracture healing and its treatment by administration of growth factors was modeled to demonstrate the potential therapeutic value of this mathematical model. [less ▲]

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See detailMathematical modeling of fracture healing: coupling between mechanics, angiogenesis and osteogenesis
Geris, Liesbet ULg; Vander Sloten, Jos; VanOosterwyck, Hans

in IFMBE Proceedings 22 (2008)

Both mechanical and biological factors play an important role in normal as well as impaired fracture healing. This study aims to provide a mathematical framework in which both regulatory mechanisms are ... [more ▼]

Both mechanical and biological factors play an important role in normal as well as impaired fracture healing. This study aims to provide a mathematical framework in which both regulatory mechanisms are included and angiogenesis is explicitly incorporated. To illustrate the added value of such a framework, a coupled mechanobioregulatory model was proposed. This model was based on a previously developed bioregulatory model [1], using a simple coupling between mechanics and biology whereby certain parameters of the bioregulatory model were made dependent on local mechanical stimuli. As a first example, in this study, the proliferation of osteoblasts and endothelial cells were made dependent on the local fluid flow [2]. Various loading situations, ranging from non-loading to overloading, were simulated. Simulations of adverse mechanical circumstances predicted the formation of avascular nonunions, a result that was corroborated by various experimental observations. This model allows testing various hypotheses concerning the nature of the mechanical stimulus influencing the healing process, as well as the most important cellular processes influenced by mechanical loading. It is one of the first models that provides an explicit coupling between mechanical and angiogenic factors. As both factors have been identified to play a key role in the occurrence of delayed and nonunions, the model allows to further explore their etiology and treatment. [less ▲]

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See detailMathematical modeling of HIV dynamics after antiretroviral therapy initiation: A clinical research study
Moog, Claude; Rivadeneira, Pablo; Stan, Guy-Bart et al

in AIDS Research and Human Retroviruses (2014), 30(9), 831-834

Immunological failure is identified from the estimation of certain parameters of a mathematical model of the HIV infection dynamics. This identification is supported by clinical research results from an ... [more ▼]

Immunological failure is identified from the estimation of certain parameters of a mathematical model of the HIV infection dynamics. This identification is supported by clinical research results from an original clinical trial. Standard clinical data were collected from infected patients starting Highly Active Anti-Retroviral Therapy (HAART), just after one month following therapy initiation and were used to carry out the model identification. The early diagnosis is shown to be consistent with the patients monitoring after six months. [less ▲]

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See detailMathematical Modeling of HIV Dynamics After Antiretroviral Therapy Initiation: A Review
Rivadeneira, Pablo; Moog, Claude; Stan, Guy-Bart et al

in BioResearch Open Acces (2014), 3(5), 233-241

This review shows the potential ground-breaking impact that mathematical tools may have in the analysis and the understanding of the HIV dynamics. In the first part, early diagnosis of immunological ... [more ▼]

This review shows the potential ground-breaking impact that mathematical tools may have in the analysis and the understanding of the HIV dynamics. In the first part, early diagnosis of immunological failure is inferred from the estimation of certain parameters of a mathematical model of the HIV infection dynamics. This method is supported by clinical research results from an original clinical trial: data just after 1 month following therapy initiation are used to carry out the model identification. The diagnosis is shown to be consistent with results from monitoring of the patients after 6 months. In the second part of this review, prospective research results are given for the design of individual anti-HIV treatments optimizing the recovery of the immune system and minimizing side effects. In this respect, two methods are discussed. The first one combines HIV population dynamics with pharmacokinetics and pharmacodynamics models to generate drug treatments using impulsive control systems. The second one is based on optimal control theory and uses a recently published differential equation to model the side effects produced by highly active antiretroviral therapy therapies. The main advantage of these revisited methods is that the drug treatment is computed directly in amounts of drugs, which is easier to interpret by physicians and patients. [less ▲]

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See detailMathematical Modeling of HIV Dynamics After Antiretroviral Therapy Initiation: A Review
Rivadeneira, Pablo; Moog, Claude; Stan, Guy-Bart et al

in BioResearch Open Acces (2014), 3(5), 233-241

This review shows the potential ground-breaking impact that mathematical tools may have in the analysis and the understanding of the HIV dynamics. In the first part, early diagnosis of immunological ... [more ▼]

This review shows the potential ground-breaking impact that mathematical tools may have in the analysis and the understanding of the HIV dynamics. In the first part, early diagnosis of immunological failure is inferred from the estimation of certain parameters of a mathematical model of the HIV infection dynamics. This method is supported by clinical research results from an original clinical trial: data just after 1 month following therapy initiation are used to carry out the model identification. The diagnosis is shown to be consistent with results from monitoring of the patients after 6 months. In the second part of this review, prospective research results are given for the design of individual anti-HIV treatments optimizing the recovery of the immune system and minimizing side effects. In this respect, two methods are discussed. The first one combines HIV population dynamics with pharmacokinetics and pharmacodynamics models to generate drug treatments using impulsive control systems. The second one is based on optimal control theory and uses a recently published differential equation to model the side effects produced by highly active antiretroviral therapy therapies. The main advantage of these revisited methods is that the drug treatment is computed directly in amounts of drugs, which is easier to interpret by physicians and patients. [less ▲]

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See detailMathematical modelization of reduced luminance coefficients for dry road surfaces
Debergh, Nathalie; Embrechts, Jean-Jacques ULg

in Lighting Research & Technology (2008), 40

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See detailMathematical modelling and design of an advanced once-through heat recovery steam generator
Dumont, Marie-Noëlle ULg; Heyen, Georges ULg

in Computer Aided Chemical Engineering (2003), 14

The once-through heat recovery steam generator design is ideally matched to very high temperature and pressure, well into the supercritical range. Moreover this type of previous termboilernext term is ... [more ▼]

The once-through heat recovery steam generator design is ideally matched to very high temperature and pressure, well into the supercritical range. Moreover this type of previous termboilernext term is structurally simpler than a conventional one, since no drum is required. A specific mathematical model has been developed. Thermodynamic model has been implemented to suit very high pressure (up to 240 bar), sub- and supercritical steam properties. We illustrate the model use with a 180 bar once-through previous termboilernext term (OTB). [less ▲]

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See detailMathematical modelling and design of an advanced once-through heat recovery steam generator
Dumont, Marie-Noëlle ULg; Heyen, Georges ULg

in Computers & Chemical Engineering (2004), 28(5), 651-660

The once-through heat recovery steam generator (HRSG) design is ideally matched to very high temperature and pressure, well into the supercritical range. Moreover this type of boiler is structurally ... [more ▼]

The once-through heat recovery steam generator (HRSG) design is ideally matched to very high temperature and pressure, well into the supercritical range. Moreover this type of boiler is structurally simpler than a conventional one, since no drum is required. In a conventional design, each tube plays a well-defined role: water preheating, vaporisation, superheating. Empirical equations are available to predict the average beat transfer coefficient for each region. For once-through applications, this is no more the case and mathematical models have to be adapted to account for the disappearance of the conventional economiser, boiler and superheater. General equations have to be used for each tube of the boiler, and the actual heat transfer condition in each tube has to be identified. The mathematical complexity as well as the number of equations is increased. A thermodynamic model has been selected and implemented to suit very high pressure (up to 240 bar), sub- and supercritical steam properties. Model use is illustrated by two case studies: a 180 bar once-through boiler (OTB) and a conventional boiler superheater and reheater. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailMathematical modelling and parameter identification methods in systems
Hann, C. E.; Chase, J. G.; Shaw, G. M. et al

in Proceedings of the 7th joint Australia-New Zealand Mathematics Convention (ANZMC2008) (2008)

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See detailMathematical modelling applied to caspase activation reveals a requirement for additional control
Eißing, T.; Conzelmann, H.; Gilles, E. D. et al

Poster (2004)

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See detailMathematical modelling of an advanced once-through sub- or supercritical heat recovery steam generator
Dumont, Marie-Noëlle ULg

Poster (2001, October)

The design and the follow-up of a once-through circulation boiler differs from the design and the follow-up of a conventional boiler. A specific thermodynamic model has to suit very high pressure, sub ... [more ▼]

The design and the follow-up of a once-through circulation boiler differs from the design and the follow-up of a conventional boiler. A specific thermodynamic model has to suit very high pressure, sub- and supercritical steam properties. Mathematical models have to be adapted to account for the disappearance of the conventional economiser, boiler and superheater. Empirical equations corresponding to each part of the traditional boiler are no more possible. In a once-through heat recovery boiler the location of the boiling point is no more fixed. General equations have to be used for each tube of the boiler. The mathematical complexity as well as the number of equations is increased. This paper presents one subcritical 180 bar once-through heat recovery boiler model. Comparison with usual boilers in terms of mathematical results are presented, including the description of a specific mathematical model, especially developed, using the Belsim-VALI software, to represent a once-through boiler. [less ▲]

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See detailMathematical modelling of atrophic non-union and its treatment
Geris, Liesbet ULg; Vander Sloten, Jos; VanOosterwyck, Hans

in Proceedings of the International symposium on Biomechanics and Biology of Bone Healing (2008)

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See detailA mathematical modelling of bloom of the coccolithophore Emiliania huxleyi in a mesocosm experiment
Joassin, Pascal ULg; Delille, Bruno ULg; Soetaert, K. et al

in Biogeosciences Discussions (2008), 5

A dynamic model has been developed to represent biogeochemical variables and processes observed during a bloom of Emiliania huxleyi coccolithophore. This bloom was induced in a mesocosm experiment during ... [more ▼]

A dynamic model has been developed to represent biogeochemical variables and processes observed during a bloom of Emiliania huxleyi coccolithophore. This bloom was induced in a mesocosm experiment during which the ecosystem development was followed over a period of 23-days through changes in various biogeochemical parameters such as inorganic nutrients (nitrate, ammonium and phosphate), total alkalinity (TA), dissolved inorganic carbon (DIC), partial pressure of CO[SUB]2[/SUB] (pCO[SUB]2[/SUB]), dissolved oxygen (O[SUB]2[/SUB]), photosynthetic pigments, particulate organic carbon (POC), dissolved organic carbon (DOC), Transparent Exopolymer Particles (TEP), primary production, and calcification. This dynamic model is based on unbalanced algal growth and balanced bacterial growth. In order to adequately reproduce the observations, the model includes an explicit description of phosphorus cycling, calcification, TEP production and an enhanced mortality due to viral lysis. The model represented carbon, nitrogen and phosphorus fluxes observed in the mesocosms. Modelled profiles of algal biomass and final concentrations of DIC and nutrients are in agreement with the experimental observations. [less ▲]

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See detailA mathematical modelling of bloom of the coccolithophore Emiliania huxleyi in a mesocosm experiment
Joassin, Pascal ULg; Delille, Bruno ULg; Soetaert, Karline et al

Poster (2008, July 23)

A dynamic model has been developed to represent biogeochemical variables and processes observed during a bloom of Emiliania huxleyi coccolithophore. This bloom was induced in a mesocosm experiment during ... [more ▼]

A dynamic model has been developed to represent biogeochemical variables and processes observed during a bloom of Emiliania huxleyi coccolithophore. This bloom was induced in a mesocosm experiment during which the ecosystem development was followed over a period of 23-days through changes in various biogeochemical parameters such as inorganic nutrients (nitrate, ammonium and phosphate), total alkalinity (TA), dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2), dissolved oxygen (O2), photosynthetic pigments, particulate organic carbon (POC), dissolved organic carbon (DOC), Transparent Exopolymer Particles (TEP), primary production, and calcification. This dynamic model is based on unbalanced algal growth and balanced bacterial growth. In order to adequately reproduce the observations, the model includes an explicit description of phosphorus cycling, calcification, TEP production and an enhanced mortality due to viral lysis. The model represented carbon, nitrogen and phosphorus fluxes observed in the mesocosms. Modelled profiles of algal biomass and final concentrations of DIC and nutrients are in agreement with the experimental observations. [less ▲]

Detailed reference viewed: 20 (2 ULg)