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Mathematical Modelling (mathematical + modelling)
Selected AbstractsMATHEMATICAL MODELLING OF THIN-LAYER DRYING OF KIWIFRUIT SLICESJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 2009M DOYMAZ ABSTRACT The effect of temperature on the drying kinetics of kiwifruit was investigated. The drying process was carried out at temperatures of 50, 55 and 60C, air velocity of 2.4 m/s and relative humidity between 10,25%. Drying time decreased considerably with increased air temperature. Drying process took place in the falling rate period. Twelve mathematical models available in the literature were fitted to the experimental data. The models were compared by four statistical parameters; i.e., determination of coefficient, mean relative percent error, reduced chi-square and root mean square error, and the best-fit model was selected. The modified Henderson and Pabis and Verma et al. models were given the best results in describing thin-layer drying of kiwifruits. The effective diffusivity of water during air-drying varied from 1.743 to 2.241 × 10,10 m2/s over the temperature range investigated, with activation energy equal to 22.48 kJ/mol. PRACTICAL APPLICATIONS Drying can be described as an industrial preservation method in which water content and activity of agricultural products are decreased by heated air to minimize biochemical, chemical and microbiological deterioration. Kiwifruit has a very short life because of softening and vitamin loss during cold storage. The use of drying prolongs the shelf-life of the kiwifruit, as the water content reduction slows down deterioration reactions. In this study, drying characteristics of kiwifruits were studied in a convectional hot-air dryer. The objectives of the present study were to determine experimentally the thin-layer drying characteristics and rehydration capacity of samples, and to fit the experimental data to 12 mathematical models available from the literature. [source] Mathematical Modelling and Simulation of Polymer Electrolyte Membrane Fuel Cells.FUEL CELLS, Issue 2 2002Part I: Model Structures, Solving an Isothermal One-Cell Model Abstract Amongst the various types of fuel cells, the polymer electrolyte membrane fuel cell (PEM-FC) can be used favourably in vehicles and for in house energy supply. The focus of the development of these cells is not only to provide cost-effective membranes and electrodes, but also to optimise the process engineering for single cells and to design multi-cell systems (cell stacks). This is a field in which we have successfully applied the methods of mathematical modelling and simulation. Initially, in this work, a partial model of a single membrane-electrode unit was developed in which the normal reaction technology fields (concentration, temperature, and flow-speed distributions) were calculated, but also the electrical potential and current density distribution in order to develop model structures for technically interesting PEM-FC. This allows the simulation of the effects that the geometric parameters (electrode and membrane data and the dimensions of the material feed and outlet channels) and the educt and coolant intake data have on the electrical and thermal output data of the cell. When complete, cell stacks consisting of a number of single cells, most of which have bipolar switching, are modelled the distribution of the gas flows over the single cells and the specific conditions of heat dissipation must also be taken into consideration. In addition to the distributions mentioned above, this simulation also produces characteristic current-voltage and power-voltage curves for each application that can be compared with the individual process variations and cell types, thus making it possible to evaluate them both technically and economically. The results of the simulation of characteristic process conditions of a PEM-FC operated on a semi-technical scale are presented, which have been determined by means of a three-dimensional model. The distributions of the electrical current density and all component voltage drops that are important for optimising the conditions of the process are determined and also the water concentration in the membrane as an important factor that influences the cell's momentary output and the PEM-FC's long-term stability. [source] Mathematical Modelling of Non-Isothermal Venturi ScrubbersTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2005Amir Rahimi Abstract A mathematical model consisting of differential equations for energy, momentum and material exchange is developed for a non-isothermal Venturi-type scrubber. By this model, the effects of heat and mass transfer on droplets concentration distribution and removal efficiency of particulate in a non-isothermal Venturi scrubber can be investigated. In order to approach a realistic model, the liquid film flow on the walls and droplet size distribution are considered. The model is validated by comparing the results of mathematical model by plant and experimental data reported in the literature. The Results section of this work reveals that the inlet humidity and temperature of the gas can affect the removal efficiency of the scrubber. On a mis au point un modèle d'équations différentielles pour l'échange d'énergie, de quantité de mouvement et de matière pour un épurateur venturi non isotherme. Grâce à ce modèle, on peut étudier les effets du transfert de chaleur et de matière sur la distribution de concentration des gouttelettes et l'efficacité de retrait des particules dans un épurateur venturi non isotherme. Pour s'approcher le plus possible d'un modèle réaliste, l'écoulement liquide sur les parois et la distribution de taille des gouttelettes sont considérés. Le modèle est validé en comparant les résultats du modèle mathématique à des données expérimentales parues dans la littérature scientifique et des données d'usine. Les résultats de ce travail révèlent que l'humidité et la température de gaz à l'entrée peuvent influer sur l'efficacité de retrait de l'épurateur. [source] Mathematical modelling elucidates sex disparities in human cardiac physiologyACTA PHYSIOLOGICA, Issue 4 2006Pasi Tavi No abstract is available for this article. [source] Age-related increase in haemoglobin A1c and fasting plasma glucose is accompanied by a decrease in , cell function without change in insulin sensitivity: evidence from a cross-sectional study of hospital personnelDIABETIC MEDICINE, Issue 3 2002A. P. Yates Abstract Aims To examine the influence of age on glucose homeostasis in a population of healthy, non-diabetic hospital personnel. Methods One hundred and twenty female and 71 male non-diabetic individuals (fasting plasma glucose < 7.0 mmol/l) were fasted overnight prior to blood sampling. Glycated haemoglobin (HbA1c), fasting plasma glucose (FPG) and fasting plasma insulin (FPI) were measured using a BioRad Diamat automated HPLC, a Hitachi 747 analyser and a sensitive in-house radioimmunoassay, respectively. Mathematical modelling of the fasting glucose and insulin pairs (homeostasis model assessment (HOMA)) generated indices of pancreatic , cell function, HOMA-B and tissue insulin sensitivity HOMA-S. Results Spearman rank correlation analysis showed that in the whole group there was a significant negative correlation between age and HOMA-B (rs= ,0.218, P = 0.0022) and a significant positive correlation between age and both HbA1c (rs= 0.307, P = 0.0001) and FPG (rs= 0.26, P = 0.0003). There was no correlation between age and either FPI (rs= ,0.08, P = 0.266) or HOMA-S (rs= 0.024, P = 0.75). Analysis by gender showed the above associations to be present in the females (rs= ,0.243, P = 0.0076; rs= 0.304, P = 0.0007; rs= 0.32, P = 0.0004 for age vs. HOMA-B, HbA1c, and FPG, respectively). Again there was no correlation of age with FPI or insulin sensitivity. In the males there was a significant correlation of HbA1c with age (rs= 0.35, P = 0.002), but no significant correlation of age with any of the other parameters. Conclusions Glycaemic control deteriorates with age in healthy, non-diabetic individuals. Age-related rises in FPG and haemoglobin A1c result from a small but steady decline in pancreatic , cell function. Diabet. Med. 19, 254,258 (2002) [source] Catabolite repression in Escherichia coli, a comparison of modelling approachesFEBS JOURNAL, Issue 2 2009Andreas Kremling The phosphotransferase system in Escherichia coli is a transport and sensory system and, in this function, is one of the key players of catabolite repression. Mathematical modelling of signal transduction and gene expression of the enzymes involved in the transport of carbohydrates is a promising approach in biotechnology, as it offers the possibility to achieve higher production rates of desired components. In this article, the relevance of methods and approaches concerning mathematical modelling in systems biology is discussed by assessing and comparing two comprehensive mathematical models that describe catabolite repression. The focus is thereby on modular modelling with the relevant input in the central modules, the impact of quantitative model validation, the identification of control structures and the comparison of model predictions with respect to the available experimental data. [source] Mathematical modelling of fire development in cable installationsFIRE AND MATERIALS, Issue 4 2001P. Van Hees In 1996 DG XII of the European Commission (Research and Development) approved a 3 year project on the fire performance of electrical cables. Within this FIPEC project, a major part of the work involved correlation and mathematical modelling of flame spread and heat release rate in cable installations. The FIPEC project has developed different levels of testing ranging from a small-scale, cone calorimeter test procedures developed for cables and materials, a full-scale-test procedure based on the IEC 60332-3, but utilizing HRR and SPR measurements, and a real scale test conducted on model cable installations. Links through statistical correlations and mathematical fire modelling between these levels were investigated and the findings are presented in this paper. These links could form the scientific foundations for standards upon which fire performance measurements can be based and for new fire engineering techniques within fire performance based codes. Between each testing level correlation, numerical and mathematical models were performed. All of the models were based on the cone calorimeter test method. The complexity of the models varied from correlation models to advanced physical pyrolysis models which can be used in CFD codes. The results will allow advanced prediction of cable fires in the future. Also a bench mark was established for the prediction of cable performance by means of data obtained from the constituent materials. Copyright © 2002 John Wiley & Sons, Ltd. [source] Mathematical modelling of hydrogen storage in a LaNi5 hydride bedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2003Yuksel Kaplan Abstract This paper presents a numerical investigation of hydrogen storage in a metal hydrid bed. For this purpose, a two-dimensional mathematical model which considers complex heat and mass transfer and fluid flow during the hydriding process is accomplished in this study. The coupled differential equations are solved with numerical method based on integrations of governing equation over finite control volumes. The driving force for fluid flow is considered to be pressure difference due to the temperature distribution in the system. It is found that fluid flow enhances the local hydriding rate in the system by driving the hot fluid to the colder regions. The numerical results were found to agree satisfactorily with the experimental data available in the literature. Copyright © 2003 John Wiley & Sons, Ltd. [source] Review article: Basic steps in adapting response surface methodology as mathematical modelling for bioprocess optimisation in the food systemsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2010Titus U. Nwabueze Summary Techniques involving choosing process combinations for optimisation without due consideration for relevant experimental designs is scientifically unreliable and irreproducible. Mathematical modelling, of which response surface methodology (RSM) is one, provides a precise map leading to successful optimisation. This paper identified key process variables, building the model and searching the solution through multivariate regression analysis, interpretation of resulting polynomial equations and response surface/contour plots as basic steps in adapting the central composite design to achieve process optimisation. It also gave information on appropriate RSM software packages and choice of order in RSM model and data economy in reducing the factorial experiments from large number parameter combinations to a far less number without losing any information including quadratic and interaction (if present) effects. It is expected that this paper will afford many food scientists and researchers the opportunity for adapting RSM as a mathematical model for achieving bioprocess optimisation in food systems. [source] Mathematical modelling of moisture sorption isotherms and determination of isosteric heat of blueberry variety O,NeilINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 10 2009Antonio Vega-Gálvez Summary The sorption isotherms of blueberry variety O'Neil were determined at 20, 40 and 60 °C, for a range of water activity of 0.10,0.95. The isotherms showed that the equilibrium moisture content increased when temperature decreased at constant water activity. The BET, GAB, Halsey, Henderson, Caurie, Smith, Oswin and Iglesias-Chirife equations were tested for modelling the sorption isotherms. The results showed that GAB, BET and Halsey models gave the best fit quality for the experimental desorption data, and BET, Oswin and Henderson for adsorption data as suggested by the statistical tests employed. The net sorption heat was calculated using the Clausius,Clapeyron equation giving 38.62 kJ mol,1 (desorption) and 30.88 kJ mol,1 (adsorption) at a moisture content of 0.01 g water (g d.m.,1). Tsami equation was applied to estimate the net isosteric heat of sorption as function of equilibrium moisture content with satisfactory results. [source] Mathematical modelling of the heat inactivation of trypsin inhibitors in soymilk at 121,154,°CJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2002Kin-Chor Kwok Abstract Response surface methodology (RSM) was used to investigate the effects of processing temperature and time on the inactivation of trypsin inhibitors (TI) in soymilk. The factorial experimental design consisted of four levels of temperature and six levels of time in a temperature range of 121,154,°C and a time interval of 10,90,s. A quadratic polynomial equation, relating log(% TI retained) as a function of heating time and temperature, was satisfactorily fitted to the experimental data by least squares regression with r2 (correlationcoefficient),=,0.959. Within the range of heating times investigated, TI in soymilk was satisfactorily destroyed to 10% retained at 143 and 154,°C with 62 and 29,s heating time respectively. © 2002 Society of Chemical Industry [source] The role of configuration and coupling in autoregulatory gene circuitsMOLECULAR MICROBIOLOGY, Issue 2 2010Kang Wu Summary Autoregulatory gene circuits can be physically encoded within the genome in a number of different configurations. By physical encoding, we mean the orientation and relative proximity of the genes within the circuit. In this work, we quantified the behaviour of an inducible, negatively autoregulated gene circuit arranged in different transcriptional configurations using the tetRA circuit from Tn10 as our basis. Mathematical modelling predicted that circuits arranged in configurations where the expression of the transcription factor is decoupled from its target genes afforded more flexibility relative to configurations where expression is coupled. We found that these decoupled configurations reduced the concentration of transcription factor needed to regulate inducible expression from the circuit. As lower concentrations of transcription factor were required, these decoupled configurations could also be activated at much lower concentrations of the inducer. We experimentally validated these predictions in Escherichia coli by comparing the response of synthetic circuits based on the tetRA circuit arranged in different configurations. Collectively, these results provide one example of how the arrangement of a gene circuit within the genome can affect its behaviour. [source] The Na+ transporter AtHKT1;1 controls retrieval of Na+ from the xylem in ArabidopsisPLANT CELL & ENVIRONMENT, Issue 4 2007ROMOLA JANE DAVENPORT ABSTRACT HKT-type transporters appear to play key roles in Na+ accumulation and salt sensitivity in plants. In Arabidopsis HKT1;1 has been proposed to influx Na+ into roots, recirculate Na+ in the phloem and control root : shoot allocation of Na+. We tested these hypotheses using 22Na+ flux measurements and ion accumulation assays in an hkt1;1 mutant and demonstrated that AtHKT1;1 contributes to the control of both root accumulation of Na+ and retrieval of Na+ from the xylem, but is not involved in root influx or recirculation in the phloem. Mathematical modelling indicated that the effects of the hkt1;1 mutation on root accumulation and xylem retrieval were independent. Although AtHKT1;1 has been implicated in regulation of K+ transport and the hkt1;1 mutant showed altered net K+ accumulation, 86Rb+ uptake was unaffected by the hkt1;1 mutation. The hkt1;1 mutation has been shown previously to rescue growth of the sos1 mutant on low K+; however, HKT1;1 knockout did not alter K+ or 86Rb+ accumulation in sos1. [source] Mathematical modelling of the impact of haematopoietic stem cell-delivered gene therapy for HIVTHE JOURNAL OF GENE MEDICINE, Issue 12 2009John M. Murray Abstract Background Gene therapy represents a new treatment paradigm for HIV that is potentially delivered by a safe, once-only therapeutic intervention. Methods Using mathematical modelling, we assessed the possible impact of autologous haematopoietic stem cell (HSC) delivered, anti-HIV gene therapy. The therapy comprises a ribozyme construct (OZ1) directed to a conserved region of HIV-1 delivered by transduced HSC (OZ1+HSC). OZ1+HSC contributes to the CD4+ T lymphocyte and monocyte/macrophage cell pools that preferentially expand under the selective pressure of HIV infection. The model was used to predict the efficacy of OZ1 in a highly active antiretroviral therapy (HAART) naïve individual and a HAART-experienced individual undergoing two structured treatment operations. In the standard scenario, OZ1+HSC was taken as 20% of total body HSC. Results For a HAART-naïve individual, modelling predicts a reduction of HIV RNA at 1 and 2 years post-OZ1 therapy of 0.5 log10 and 1 log10, respectively. Eight years after OZ1 therapy, the CD4+ T-lymphocyte count was 271 cells/mm3 compared to 96 cells/mm3 for an untreated individual. In a HAART-experienced individual HIV RNA was reduced by 0.34 log10 and 0.86 log10 at 1 and 2 years. The OZ1 effect was maximal when both CD4+ T lymphocytes and monocytes/macrophages were protected from successful, productive infection by OZ1. Conclusions The modelling indicates a single infusion of HSC cell-delivered gene therapy can impact on HIV viral load and CD4 T-lymphocyte count. Given that gene therapy avoids the complications associated with HAART, there is significant potential for this approach in the treatment of HIV. Copyright © 2009 John Wiley & Sons, Ltd. [source] Mathematics-aided quantitative analysis of diffusion characteristics of pHEMA sponge hydrogelsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007X. Lou Abstract This study reports the current progress in quantitative analysis of the release characteristics of pHEMA spongy hydrogels using prednisolone 21-hemisuccinate sodium salt as a model drug. Extraction of effective diffusion coefficients of the drug from various pHEMA matrices was made using a novel mathematical model that handles both boundary layer and initial burst effects. Drug loading level and entrapment efficiency were also determined. The computed diffusion coefficients and the drug loading capacity in relation to the device porous structure and drug concentration of the loading solution, as well as the size of device are discussed. Mathematical modelling proves to be a powerful tool not only for establishing and interpreting structure and performance relationships but also for handling experimental ambiguity. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Compartmental factors influencing tear film osmolarityACTA OPHTHALMOLOGICA, Issue 2008AJ BRON Purpose To illustrate how compartmental factors could influence the distribution of tear osmolarity at the ocular surface in normals and dry eye. Methods Mathematical modelling using parameters in the literature. Results Tear film hyperosmolarity is a final common pathway causing ocular surface damage in dry eye. Modelling predicts that tear osmolarity is higher in the tear film than the meniscus, which may influence the distribution of ocular surface damage and the initiation of symptoms caused by hyperosmolarity. Once tear film break up occurs within the blink interval it is likely that this differential is amplified locally. The model allows the effect of compartmental factors on tear osmolarity to be addressed, including: regional differences in air flow and surface temperature, variations in ambient temperature and humidity, imperfect tear mixing, differential corneal and conjunctival exposure and individual differences in reflex tear flow, evaporation rate and blink interval. We hypothesise that interactions between these factors determine the dry eye phenotype in an individual. Additional considerations suggest that events at the ocular surface differ in aqueous-deficient and evaporative dry eye. Conclusion Hyperosmolarity at the ocular surface is affected by multiple factors, each of which may make different contributions to distribution and severity of surface damage in a given individual. This may determine the phenotype, frequency and severity of dry eye in a population. [source] Heterogeneity Of The Properties Of INa in Epicardial And Endocardial Cells Of Rat VentricleCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 3 2002Bonny N Honen SUMMARY 1. Ventricular INa heterogeneity was investigated in adult rat hearts. Differences in transient outward potassium current (Ito) were used to confirm isolation of subepicardial and subendocardial cells. Mean peak Ito was 6.0 ± 0.7 and 1.6 ± 0.45 pA/pF in epicardial and endocardial cells, respectively (P < < 0.01). 2. Maximum sodium conductance was smaller in subendocardial cells compared with subepicardial cells (2.39 ± 0.11 vs 2.78 ± 0.12 nS/pF, respectively; n = 17 for both; 0.01 < P < 0.05) and 50% activation occurred at a slightly more negative potential (,47.6 ± 0.8 vs,44.9 ± 0.9 mV, respectively; n = 10 for both; 0.01 < P < 0.05). 3. The potential for 50% inactivation was not significantly different in subepicardial compared with subendocardial cells (72.2 ± 1.0 vs 72.8 ± 2.2 mV, respectively; n = 17 for both; NS). 4. Persistent sodium current density appeared smaller in subendocardial (n = 19) compared with subepicardial (n = 11) cells (at a test potential of ,25 mV current, density was 0.118 ± 0.041 vs 0.144 ± 0.085 pA/pF, respectively), although this was not statistically significant due to large variability between cells. 5. Mathematical modelling of the cardiac action potential indicated that the combined effects of differences in current density and voltage dependence of sodium currents are unlikely to contribute to ventricular action potential heterogeneity between epicardial and endocardial cells. [source] Pre- and post-test mathematical modelling of a plan-asymmetric reinforced concrete frame building,EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2006Peter Fajfar Abstract Pre- and post-test analyses of the structural response of a three-storey asymmetric reinforced concrete frame building were performed, aimed at supporting test preparation and performance as well as studying mathematical modelling. The building was designed for gravity loads only. Full-scale pseudo-dynamic tests were performed in the ELSA laboratory in Ispra. In the paper the results of initial parametric studies, of the blind pre-test predictions, and of the post-test analysis are summarized. In all studies a simple mathematical model, with one-component member models with concentrated plasticity was employed. The pre-test analyses were performed using the CANNY program. After the test results became available, the mathematical model was improved using an approach based on a displacement-controlled analysis. Basically, the same mathematical model was used as in pre-test analyses, except that the values of some of the parameters were changed. The OpenSees program was employed. Fair agreement between the test and numerical results was obtained. The results prove that relatively simple mathematical models are able to adequately simulate the detailed seismic response of reinforced concrete frame structures to a known ground motion, provided that the input parameters are properly determined. Copyright © 2006 John Wiley & Sons, Ltd. [source] An integrative approach to understanding microbial diversity: from intracellular mechanisms to community structureECOLOGY LETTERS, Issue 9 2010Ivana Gudelj Ecology Letters (2010) 13: 1073,1084 Abstract Trade-offs have been put forward as essential to the generation and maintenance of diversity. However, variation in trade-offs is often determined at the molecular level, outside the scope of conventional ecological inquiry. In this study, we propose that understanding the intracellular basis for trade-offs in microbial systems can aid in predicting and interpreting patterns of diversity. First, we show how laboratory experiments and mathematical models have unveiled the hidden intracellular mechanisms underlying trade-offs key to microbial diversity: (i) metabolic and regulatory trade-offs in bacteria and yeast; (ii) life-history trade-offs in bacterial viruses. Next, we examine recent studies of marine microbes that have taken steps toward reconciling the molecular and the ecological views of trade-offs, despite the challenges in doing so in natural settings. Finally, we suggest avenues for research where mathematical modelling, experiments and studies of natural microbial communities provide a unique opportunity to integrate studies of diversity across multiple scales. [source] Catabolite repression in Escherichia coli, a comparison of modelling approachesFEBS JOURNAL, Issue 2 2009Andreas Kremling The phosphotransferase system in Escherichia coli is a transport and sensory system and, in this function, is one of the key players of catabolite repression. Mathematical modelling of signal transduction and gene expression of the enzymes involved in the transport of carbohydrates is a promising approach in biotechnology, as it offers the possibility to achieve higher production rates of desired components. In this article, the relevance of methods and approaches concerning mathematical modelling in systems biology is discussed by assessing and comparing two comprehensive mathematical models that describe catabolite repression. The focus is thereby on modular modelling with the relevant input in the central modules, the impact of quantitative model validation, the identification of control structures and the comparison of model predictions with respect to the available experimental data. [source] Mathematical modelling of fire development in cable installationsFIRE AND MATERIALS, Issue 4 2001P. Van Hees In 1996 DG XII of the European Commission (Research and Development) approved a 3 year project on the fire performance of electrical cables. Within this FIPEC project, a major part of the work involved correlation and mathematical modelling of flame spread and heat release rate in cable installations. The FIPEC project has developed different levels of testing ranging from a small-scale, cone calorimeter test procedures developed for cables and materials, a full-scale-test procedure based on the IEC 60332-3, but utilizing HRR and SPR measurements, and a real scale test conducted on model cable installations. Links through statistical correlations and mathematical fire modelling between these levels were investigated and the findings are presented in this paper. These links could form the scientific foundations for standards upon which fire performance measurements can be based and for new fire engineering techniques within fire performance based codes. Between each testing level correlation, numerical and mathematical models were performed. All of the models were based on the cone calorimeter test method. The complexity of the models varied from correlation models to advanced physical pyrolysis models which can be used in CFD codes. The results will allow advanced prediction of cable fires in the future. Also a bench mark was established for the prediction of cable performance by means of data obtained from the constituent materials. Copyright © 2002 John Wiley & Sons, Ltd. [source] Mathematical Modelling and Simulation of Polymer Electrolyte Membrane Fuel Cells.FUEL CELLS, Issue 2 2002Part I: Model Structures, Solving an Isothermal One-Cell Model Abstract Amongst the various types of fuel cells, the polymer electrolyte membrane fuel cell (PEM-FC) can be used favourably in vehicles and for in house energy supply. The focus of the development of these cells is not only to provide cost-effective membranes and electrodes, but also to optimise the process engineering for single cells and to design multi-cell systems (cell stacks). This is a field in which we have successfully applied the methods of mathematical modelling and simulation. Initially, in this work, a partial model of a single membrane-electrode unit was developed in which the normal reaction technology fields (concentration, temperature, and flow-speed distributions) were calculated, but also the electrical potential and current density distribution in order to develop model structures for technically interesting PEM-FC. This allows the simulation of the effects that the geometric parameters (electrode and membrane data and the dimensions of the material feed and outlet channels) and the educt and coolant intake data have on the electrical and thermal output data of the cell. When complete, cell stacks consisting of a number of single cells, most of which have bipolar switching, are modelled the distribution of the gas flows over the single cells and the specific conditions of heat dissipation must also be taken into consideration. In addition to the distributions mentioned above, this simulation also produces characteristic current-voltage and power-voltage curves for each application that can be compared with the individual process variations and cell types, thus making it possible to evaluate them both technically and economically. The results of the simulation of characteristic process conditions of a PEM-FC operated on a semi-technical scale are presented, which have been determined by means of a three-dimensional model. The distributions of the electrical current density and all component voltage drops that are important for optimising the conditions of the process are determined and also the water concentration in the membrane as an important factor that influences the cell's momentary output and the PEM-FC's long-term stability. [source] The Hill equation: a review of its capabilities in pharmacological modellingFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 6 2008Sylvain Goutelle Abstract The Hill equation was first introduced by A.V. Hill to describe the equilibrium relationship between oxygen tension and the saturation of haemoglobin. In pharmacology, the Hill equation has been extensively used to analyse quantitative drug,receptor relationships. Many pharmacokinetic,pharmacodynamic models have used the Hill equation to describe nonlinear drug dose,response relationships. Although the Hill equation is widely used, its many properties are not all well known. This article aims at reviewing the various properties of the Hill equation. The descriptive aspects of the Hill equation, in particular mathematical and graphical properties, are examined, and related to Hill's original work. The mechanistic aspect of the Hill equation, involving a strong connection with the Guldberg and Waage law of mass action, is also described. Finally, a probabilistic view of the Hill equation is examined. Here, we provide some new calculation results, such as Fisher information and Shannon entropy, and we introduce multivariate probabilistic Hill equations. The main features and potential applications of this probabilistic approach are also discussed. Thus, within the same formalism, the Hill equation has many different properties which can be of great interest for those interested in mathematical modelling in pharmacology and biosciences. [source] Diagnosed and undiagnosed HIV-infected populations in EuropeHIV MEDICINE, Issue 2008FF Hamers This article aims to build a picture of HIV epidemiology in Europe by combining existing surveillance data to mathematical modelling to achieve observations closer to the dynamic reality of HIV infections across different parts of Europe. In the European Union (EU), where it is estimated that 30% of HIV-infected persons have not been diagnosed, the number of new HIV diagnoses has risen in recent years. However, trends must be interpreted with some caution around the differences and variations in surveillance systems and testing rates among affected populations and regions. By introducing mathematical models, we can build an overall picture from the pieces of information available. We present a mathematical model of the course of infection and the effect of ART which has been developed to fit as closely as possible to observed data from HIV cohorts. The preliminary estimates for the entire WHO European Region are that around 2.3 million people were living with HIV in Europe at the end of 2006, of whom around 50% have not been diagnosed. The model can also be used to assess the potential impact of earlier diagnoses. Observations show how a combination of surveillance data and modelling allows an estimation of the current state of the epidemic in Europe, though further developments in both areas are needed. [source] Experimental study and mathematical modelling of flashover on extra-high voltage insulators covered with iceHYDROLOGICAL PROCESSES, Issue 18 2004J. Farzaneh-Dehkordi Abstract Using a test method developed at the high-voltage laboratory of the NSERC/Hydro-Quebec/UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE), the relation between the minimum flashover voltage VMF and the insulator dry arcing distance for standard porcelain station post insulators, as typically used in Hydro-Quebec substations, was investigated under icing conditions. The experimental results show that, under wet-grown ice, known as the most dangerous type of ice for power transmission systems, the VMF increases nonlinearly with an increase in insulator length. Based on these results, an improved mathematical model for predicting the critical flashover voltage versus length of ice-covered insulators is presented. This model is helpful for understanding the flashover phenomenon on ice-covered insulators and presents a powerful tool for choosing the proper length of outdoor insulators in cold climate regions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Potential performance bottleneck in Linux TCPINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 11 2007Wenji Wu Abstract Transmission control protocol (TCP) is the most widely used transport protocol on the Internet today. Over the years, especially recently, due to requirements of high bandwidth transmission, various approaches have been proposed to improve TCP performance. The Linux 2.6 kernel is now preemptible. It can be interrupted mid-task, making the system more responsive and interactive. However, we have noticed that Linux kernel preemption can interact badly with the performance of the networking subsystem. In this paper, we investigate the performance bottleneck in Linux TCP. We systematically describe the trip of a TCP packet from its ingress into a Linux network end system to its final delivery to the application; we study the performance bottleneck in Linux TCP through mathematical modelling and practical experiments; finally, we propose and test one possible solution to resolve this performance bottleneck in Linux TCP. Copyright © 2007 John Wiley & Sons, Ltd. [source] Along-channel mathematical modelling for proton exchange membrane fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005Wenbo Huang Abstract Proper water and thermal management is essential for obtaining high performance of proton exchange membrane fuel cells (PEMFCs). A steady, two-dimensional water and thermal management model was developed, aiming at considering pressure effects (i.e. the effects of local pressure on the cell performance), pressure drop, open circuit voltage variation with stack temperature, water vapour effects on membrane conductivity, which made the model physically more reasonable and more suitable for various operating conditions. The model could predict the distributions of a series of important parameters along the flow channel, and thus the effects of various operating and design parameters on the fuel cell performance could be investigated easily by numerical trial-and-error method. The modelling results compared well with the available experimental results from the literatures. The results also showed that the humidification of both anode and cathode is crucial for the performance of PEMFCs. The model could be a very useful engineering tool for the optimization of PEMFCs. Copyright © 2005 John Wiley & Sons, Ltd. [source] Review article: Basic steps in adapting response surface methodology as mathematical modelling for bioprocess optimisation in the food systemsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2010Titus U. Nwabueze Summary Techniques involving choosing process combinations for optimisation without due consideration for relevant experimental designs is scientifically unreliable and irreproducible. Mathematical modelling, of which response surface methodology (RSM) is one, provides a precise map leading to successful optimisation. This paper identified key process variables, building the model and searching the solution through multivariate regression analysis, interpretation of resulting polynomial equations and response surface/contour plots as basic steps in adapting the central composite design to achieve process optimisation. It also gave information on appropriate RSM software packages and choice of order in RSM model and data economy in reducing the factorial experiments from large number parameter combinations to a far less number without losing any information including quadratic and interaction (if present) effects. It is expected that this paper will afford many food scientists and researchers the opportunity for adapting RSM as a mathematical model for achieving bioprocess optimisation in food systems. [source] Water management tasks in the summer polders of the Nemunas lowland,IRRIGATION AND DRAINAGE, Issue 2 2006Antanas Lukianas plaine d'inondation; polders d'été; gestion des eaux Abstract Surplus water during floods as well as the low level of the soil surface determine the complicated ecological, economic and demographic conditions in the Nemunas delta. Subsequently, it leads to different types and intensity of use of farmland as well as different methods of water regime regulation: summer or winter type polders. The building of 17 summer polders in the 32,500,ha floodplain area was a compromise, seeking to improve farming conditions and maintain the stability of the flood regime and ecology in the delta. Field measurements and mathematical modelling were carried out. As study results have shown, grass yield losses due to flooding depend on the distribution of water levels and flood duration in the summer polders. Relative damage to agriculture is insignificant and makes up only 10,15% of the total amount of flood damage in the Nemunas lowland. The field measurements and hydraulic and mathematical modelling of flow and sediment regime as well as study of flooding and changed farming conditions also show that it is possible to reduce the height of floods and economic and ecological damage. Rearrangement of the system of protective dikes, regulation of the main river canal and water/sedimentation regime with the help of pumping stations, decrease of pollutant migration into the Curonian Lagoon and Baltic Sea, and recreation of natural meadows are important in that case. Copyright © 2006 John Wiley & Sons, Ltd. Des eaux excédentaires en période de crues et un faible niveau du sol déterminent les conditions écologiques, économiques et démographiques complexes du delta du fleuve Nemunas. En particulier, des types et intensités différentes dans l'utilisation des terres arables, ainsi que des méthodes différentes de régulation du régime des eaux: polders d'été ou d'hiver. La construction de 17 polders d'été sur 32 500,ha de plaine d'inondation a été une solution de compromis pour améliorer l'agriculture et maintenir la stabilité du régime des crues et de l'écologie du delta. Des mesures de terrain et des modèles mathématique ont été réalisés. D'après les résultats des études, les pertes de récolte d'herbe dûes aux crues dépendent de la distribution des niveaux d'eau et de la durée de la crue dans les polders d'été. L'impact négatif sur l'agriculture est négligeable et ne représente que 10 à 15% des dommages totaux dus aux crues dans le delta du fleuve Nemunas. Les mesures de terrain et la modélisation hydraulique et mathématique de l'écoulement et de la sédimentation, ainsi que l'analyse des crues et des modifications de production agricole, prouvent également qu'il est possible de réduire la hauteur des crues et de diminuer ainsi les dommages économiques et écologiques. Dans ce cas, il convient de réorganiser le système des digues de protection, de réguler le chenal principal du fleuve et le régime de sédimentation des eaux à l'aide de stations de pompage, de réduire les déversements polluants dans la lagune Curonian et la mer Baltique, et de régénérer des pâturages naturels. Copyright © 2006 John Wiley & Sons, Ltd. [source] Some Problems and Possibilities in the Study of Dynamical Social ProcessesJOURNAL FOR THE THEORY OF SOCIAL BEHAVIOUR, Issue 1 2000John E. Puddifoot The recent challenge of Dynamical Systems Theory (also known as ComplexityTheory or Chaos Theory) to the social sciences, is based largely on the beliefthat processes in the social arena can be considered as analogous to those of the natural world, and that in consequence general theoretical advances in explaining the latter might with advantage be applied to the former. This paper aims to show that claims for Dynamical Systems Theory with respect to the understanding or measurement of social processes would be premature; the reasons for this lying not only in the unfamiliarity and operational difficulties of Dynamical Systems Theory in itself, but also in the problematic nature and history of our usage of the term ,social process'. Reviewing some examples of such usage from Sociology and Social Psychology, it is concluded that Dynamical Systems Theory might serve as a catalyst for a re-examination of existing orthodoxies and major concepts, but that progress would be retarded by the uncritical application of it's terminology, concepts, and techniques of mathematical modelling, without this prior and demanding first step. [source] | ||||||||||||||||||||||||||||||||||