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5th IASTED International conference on modelling, Simulation and Optimization

作者： Segarra, J Raventós, J Silva, JF Univ Alicante Dept Ecol E-03080 Alicante Spain Univ Los Andes ICAE Merida Venezuela

ISBN: (纸本)0889865248

Savannas are one of the most extensive biomes of the world and are subject to intense pressures due to large human populations using this ecosystem, even though it is characterized by low crop yields and poor nutritional quality of natural pastures. Conversion to agriculture and fragmentation of Neotropical savannas, and increasing population pressures are promoting the extent and use of anthropogenic fire. In this paper we develop a mathematical model to account for spatial dynamics of the savanna grass community. This model is based on a matrix model of growth of three dominant grasses of the Neotropical savanna (Elyonurus adustus, Leptocoryphium lanatum and Andropogon semiberbis). The model integrates plant architecture and competition to simulate the dynamics of this system. Our model focuses on fire as an essential event in the dynamics of the savanna community, especially frequency of occurrence. We study the current frequency of one fire a year and how changes in fire frequency tend to destabilize the system. The phenology of the species is a key point to understand the behaviour of these species on relation to fire. Late growth species (i.e. A. semiberbis) are more adapted to the current frequency than early ones, showing a higher competitive ability. Our results suggest that if there is a change of the actual fire frequency this system could undergo a decrease of phenological and plant form diversity.

关键词： savannas matrix model fire competition grasses Venezuela phenology

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A mechanical model for the opening of the human female urethra

A mechanical model for the opening of the human female ureth...

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3rd IASTED International conference on Medical engineering 2005

作者： Bush, M.B. Moron, C. Messner-Pellenc, L. Petros, P.E. Millard, R. School of Mechanical Engineering University of Western Australia 35 Stirling Highway Crawley WA 6009 Australia Prince of Wales Hospital Barker Street Randwick NSW 2031 Australia

ISBN: (纸本)0889864780

This paper describes improvements in a three-dimensional finite element model of the human female urethral tube. The preliminary model[1] took into account the composite structure of the tube, the internal fluid pressure, external constraints and external active opening forces. However, the representation of external boundary constraints and fluid-solid interaction was relative crude. An improved version of the model is presented in the current paper, in which boundary conditions are taken into account in a more realistic fashion. The predicted behaviour of the tube is compared with X-ray photographs of actual urethral tubes. It is shown that the model captures the key features of the opening process.

关键词： Biomedical engineering

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modelling and profiling household car ownership in the post-apartheid South Africa

Modelling and profiling household car ownership in the post-...

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24th Annual Southern African Transport conference, SATC 2005: Transport Challenges for 2010

作者： Mokonyama, M. Venter, C. City of Johannesburg Metropolitan Municipality PO Box 30733 Braamfontein 2017 Pretoria University Department of Civil and Biosystems Engineering Pretoria 0002

ISBN: (纸本)1920017127

Data representation and interpretation found in transportation planning literature tends to overlook the role of influences such as political systems and related history in travel behaviour. This could be as a result of the mature nature of the democracies of the countries from which transportation research is mostly published. The importance of localised research in social sciences such as transportation planning therefore cannot be overemphasised, especially in South Africa where the socio-economic landscape is ever-changing, inherently related to the recent democratisation of the country. In line with the ever-changing socio-economic landscape of South Africa, the paper investigates an alternative household car ownership modelling approach for use in strategic transportation modelling exercises, founded on the spatial attributes of a typical South African city. Furthermore, the model is applied to critically review some of the spatial variables mooted in literature to have influence on household car ownership. The City of Johannesburg is used as a case study within the context of South African development planning paradigm. The findings of the research can be used in trip generation sub-models using household car ownership as a variable, and also in spatial planning exercises aimed at managing travel demand in an urban area.

关键词： mathematical models

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A sensitivity analysis of the fed-batch animal-cell bioreactor with respect to some control parameters

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BIOTECHNOLOGY AND APPLIED BIOCHEMISTRY 2005年第1期41卷 29-35页

作者： Lavric, V Ofiteru, ID Woinaroschy, A Univ Politehn Bucuresti Dept Chem Engn RO-011061 Bucharest Romania Univ Stuttgart Inst Syst Theory Engn D-70550 Stuttgart Germany

Animal cell culture is widely used in the manufacture of valuable products, and this process is nowadays seeing a rapid expansion. The growth of animal cells is a complex process, because the cells are very sensitive to environmental changes (in, for example, nutrients, pH, temperature, oxygen and osmolarity) during this phase and to the toxic compounds produced by the cell itself. Ammonia and lactate are the two major waste materials of cell culture. They can have inhibitory effects on cell growth and product (monoclonal antibodies among others) formation. In order to model the behaviour of a fed-batch animal cell bioreactor producing monoclonal antibodies, it is necessary to use a complex kinetic model with optimal operating patterns ensuring high productivities. Good knowledge of such domains of operating parameters, together with the understanding of the response of this rather complex system to small modifications in the working conditions, are essential for on-line control to improve the quality of product and the yield of an animal cell culture. The present study focuses on the sensitivity analysis of a fed-batch animal cell bioreactor with respect to some candidate control parameters (substrate set-point concentrations, feeding time-step patterns and concentration of feeding solutions), emphasizing the influence of these on the overall performance of the system.

关键词： animal cell kinetics bioreactor mammalian cells mathematical modelling monoclonal antibodies sensitivity analysis

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Boundary conditions in human movement I: Constraining constraints

Boundary conditions in human movement I: Constraining constr...

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3rd IASTED International conference on Medical engineering 2005

作者： Harris, Christopher M. Harwood, Mark R. Centre for Theoretical and Computational Neuroscience University of Plymouth Plymouth Devon PL4 8AA United Kingdom Department of Biology City College of New York New York 10031 United States

ISBN: (纸本)0889864780

Optimal control models (distal models) play an important role in understanding the principles of human motor control and bio-inspired robotic applications. A major goal has been to identify the cost function (performance index) of the motor behaviour, which has led to such influential models as the 'minimum jerk', 'minimum torque', and 'minimum variance' hypotheses (inter alia). Less attention has been paid to the boundary conditions (BCs) needed to obtain theoretical optimal solutions. The choice of BCs strongly affects solutions, particularly when cost functions depend on high-order derivatives, as in human movement. To avoid the problem of arbitrary hypothetical constraints it is essential to justify BCs biologically. We examine analytically the effects of different BCs on minimum square derivative trajectories (minimum acceleration;minimum jerk) as simple tractable illustrations. We also examine the difference between physical and neuro-musculo-skeletal constraints, and conclude that it is not possible to justify kinematic models without appealing to non-kinematic BCs. Ultimately, BCs are an empirical issue that need to be measured independent of any theoretical model.

关键词： Biomechanics

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Qualitative frameworks for early stage process design

Qualitative frameworks for early stage process design

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05AIChE: 2005 AIChE Annual Meeting and Fall Showcase

作者： Sharratt, Paul N. Wall, Kevin School of Chemical Engineering and Analytical Science University of Manchester Sackville St. Manchester United Kingdom

This papers considers ways of enhancing the contribution of chemical engineers in the early stages of process development. The use of qualitative models has been established as a mechanism to deliver many of the useful conclusions of a mathematical modelling approach, but much earlier in design. A suite of models will be presented that cover the range of behaviours that are relevant to process outcome (reactions and transformations, phase behaviour and spatial distribution of conditions. This extends the range of capabilities of the tools into multiphase reactions and separations (coupled or uncoupled with reaction). These models have been widely applied by a group of companies in the pharmaceutical and specialty chemicals sectors through a collaborative organisation called BRITEST Limited. The application and benefits of the tools is illustrated with examples from the experience of the BRITEST partners in process development and design.

关键词： Process control

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Bone marrow oxygen transport model in sickle cell disease

Bone marrow oxygen transport model in sickle cell disease

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3rd IASTED International conference on Medical engineering 2005

作者： Kumar, R. Ngai, S. Bardsley, M. Panoskaltsis, N. Stepanek, F. Mantalaris, A. Department of Chemical Engineering Imperial College London SW7 2AZ United Kingdom Division of Investigative Science School of Medicine Imperial College London SW7 2AZ United Kingdom

ISBN: (纸本)0889864780

There has been a relative paucity in the understanding of the in vivo bone marrow (BM) pathophysiology under sickle cell disease (SCD);especially in the human BM. In this study, a model that accounts for oxygen transport for sickle cell red blood cells (RBC) within an idealized heterogeneous structure of the human BM has been developed. This has been achieved by combining the well developed mathematical model for haemoglobin solutions in large microcirculatory vessels with the transport and the haemoglobin polymerisation model developed by Makhijani et al., 1990, and the oxygen transport model for human BM by Kumar ***., 2004. The resulting set of equations allows us to simultaneously simulate the important processes of oxygen delivery with polymerisation and its effect on the various cellular distributions within the BM under SCD. The model is solved using the commercial CFD software CFX 4.4 (CFX-ANSYS®). The development of such physiologically relevant models will enable further understanding of the BM under normal and pathological conditions.

关键词： Bone

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Development of numerical methods and computer code for the mathematical modelling of work piece heat transfer during processing

Development of numerical methods and computer code for the m...

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9th International conference on Computer Aided Optimum Design in engineering, OPTI 2005

作者： Tudball, A. Brown, S.G.R. Engineering Doctorate Centre Wales School of Engineering University of Wales Swansea United Kingdom Materials Research Centre School of Engineering University of Wales Swansea United Kingdom

ISBN: (纸本)1845640160

A key quality requirement for the production of steel strip is temperature control. During hot rolling, various processes are carried out which improve surface and rolling characteristics but which increase heat extraction from the slab or bar. Moreover, different hot mill configurations at different sites will give rise to different overall thermal behaviour. Temperature control is required to enable the basic properties of the steel strip to be produced. Rather than concentrate on individual sections of the hot strip mill a custom-written thermal finite element model has been developed for Corus to simulate the evolving temperature field in the slab and subsequent thinner bar over the entire hot rolling process. Localised cooling effects caused by hydraulic descale sprays, roll coolant and contact conduction, and local atmospheric conditions have all been included. Heat generation due to adiabatic heating of deformed material and rolling friction has also been combined into the model. Efficient modelling of the temperature effects occurring throughout processing can be used in the optimisation of the process operations. This paper will describe both the practical approach and the numerical methods used to develop the model and examples of simulations of different hot mill configurations will be described. © 2005 WIT Press.

关键词： Hot rolling

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modelling of growth and accumulation of carotenoids in Haematococcus pluvialis as a function of irradiance and nutrients supply

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BIOCHEMICAL engineering JOURNAL 2005年第2-3期26卷 107-114页

作者： García-Malea, MC Brindley, C Del Río, E Acién, FG Fernández, JM Molina, E Univ Almeria Dept Chem Engn Almeria 4071 Spain Univ Sevilla Inst Bioquim Vegetal & Fotosintesis E-41092 Seville Spain CSIC E-41092 Seville Spain

This paper analyzes the feasibility of the autotrophic production of vegetative cells of Haematococcus pluvialis under conditions resembling outdoors. The experimental design simulates in laboratory with artificial light an outdoors circadian cycle similar to solar illumination. The influence of the irradiance and nutrient concentration on the growth rate and carotenoids accumulation in batch cultures is studied. The cultures were not photoinhibited even under the maximum irradiance-level tested (2500 mu E m(-2) s(-1)). Growth was kept nutrient-limited by using nutrients concentration below the standard inorganic medium (10 mM nitrate). When no nutrient-limitation occurs, the growth rate and biomass productivity measured 0.57 day(-1) and 0.28 g L-1 day(-1), respectively, were similar to the maximum values reported, regardless of the nutritional regime: autotrophic, mixotrophic or heterotrophic. On the other hand, carotenogenesis was only observed under nutrient-limiting conditions when the medium strength was reduced to 0.2- or 0.3-fold of the standard medium. On the other hand, carotenogenesis ceased under severe nutrient deprivation (i.e. nutrient strength of 0.1-fold of the standard medium). The growth rate and the carotenoids accumulation rate were demonstrated to be a function of the average irradiance inside the culture, and of the nutrient content of the medium. A mathematical model for the observed behaviour is proposed. This model was adequate to fit all the experimental data obtained. The values determined for the characteristics parameters are in agreement with those found by other authors. Therefore, the proposed model can be a useful tool for the design and management of Haematococcus cultures, and could allow improving the yield of this production process. (c) 2005 Elsevier B.V. All rights reserved.

关键词： Haematococcus growth rate irradiance nutrients carotenoids secondary metabolism

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Solidification and modeling of cast iron - A short history of the defining moments

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MATERIALS SCIENCE AND engineering A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 2005年 413卷 322-333页

作者： Stefaneseu, DM Ohio State Univ Columbus OH 43210 USA

human civilization has evolved from the Stone Age, through the Bronze Age to reach the Iron Age around 1500 B.C. There are many to contend that today we are living in the age of engineered materials, yet the importance of iron castings continues to support the thesis that we are still in the Iron Age. Cast iron, the first man-made composite, is at least 2500 years old. It remains the most important casting material, with over 70% of the total world tonnage. The main reasons for cast iron longevity are its wide range of mechanical and physical properties coupled with its competitive price. This paper is a review of the fundamentals of solidification of iron-base materials and of the mathematical models that describe them, starting with the seminal paper by Oldfield, the first to attempt modeling of microstructure evolution during solidification, to the prediction of mechanical properties. The latest analytical models for irregular eutectics such as cast iron as well as numerical models with microstructure output are discussed. However, since the space does not permit an extensive description of the multitude of models available today, the emphasis is on model performance rather than the mathematics of model formulation. Also, because of space constrains, white iron and defect occurrence will not be covered. (c) 2005 Elsevier B.V. All rights reserved.

关键词： cast iron microstructure mechanical properties solidification analytical and computational modelling of solidification

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