Дисертації з теми "Neurons Growth Computer simulation"
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1
Brightman, Frances A. "Computer simulation of a growth factor signal transduction pathway." Thesis, Oxford Brookes University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340868.
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2
Westwood, Chris. "Computer simulation of diffusional creep failure of engineering alloys." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/843127/.
Повний текст джерелаАнотація:
A simplified model with only 2 degrees of freedom is developed for cavity growth along a grain-boundary by surface and grain-boundary diffusion following a similar model for a row of grains used by Sun et al, (1996). A variational principle for the coupled diffusion problem is used to follow the cavity growth. The approximate solution can be reduced to the well-established equilibrium cavity growth model at the fast surface diffusion extreme. By comparing the 2 degree of freedom model with the full finite element solution by Pan et al, (1997), a 'Validity Map' is constructed in terms of the relative diffusivity and applied stress relative to the capillarity stress. It is found that the simplified model accurately describes the evolution process, in terms of overall cavity profile and propagation rate for engineering alloys subject to normal levels of applied stresses. The 2 degree of freedom model for a single cavity was then extended to allow the modelling of multiple cavities. These cavities can be either pre-existing or nucleated during the lifetime of the system. The relative rotation between the grains is also considered. The initial 2 degrees of freedom were increased to six, and a cavity element has been derived. The cavity elements are assembled together using the classical finite element approach. This allows the evolution of multiple cavities and their interactions to be modelled under different applied loads and material parameters. This simplified multiple cavity finite element model was compared with a model for cavity evolution based on a 'smeared-out' approach. It was shown that the 'smeared-out' model does not accurately predict the creep damage for realistic engineering materials and conditions and results in an under prediction of creep lifetime. Using the simplified finite element model the effect of surface diffusion on the evolution of the creep damage was investigated. The evolution of a large pre-existing 'crack-like' cavity was modelled and the effects of nucleation, surface diffusion and loading were also investigated. It was shown that in the majority of cases as the surface diffusion was increased the rupture time was also increased. The results from the large 'crack-like' cavity simulations showed that there was very little crack propagation through the material and the smaller cavities tended to grow independently of the large 'crack-like' cavity.
3
Green-Petersen, Minna. "Diffusion-Limited Aggregation: a Model for Computer Simulation of Fractal Growth." Thesis, KTH, Teoretisk fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146038.
Повний текст джерелаАнотація:
Diffusion-limited aggregation (DLA) is a model for computer simulation of particle aggregation. It is known to generate aggregates with a characteristic appearance with many branches spreading in all directions and a specic fractal dimension. The aggregates resemble many created by processes in nature such as crystallization, uid ow and growth of bacteria colonies. In this thesis the DLA model and a few variations of it are investigated to illuminate its exibility. The variations investigated are a noise-reduced model, introducing surface tension and increasing the ux of particles. The fractal dimension is calculated in each case and compared to the results of similar experiments, both simulated and real.
4
Li, Xuefei. "A computational study of bacterial growth in complex environments." HKBU Institutional Repository, 2012. https://repository.hkbu.edu.hk/etd_ra/1410.
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5
Preyer, Amanda Jervis. "Coupling and synchrony in neuronal networks electrophysiological experiments /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/24799.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.Committee Chair: Butera, Robert; Committee Member: Canavier, Carmen; Committee Member: DeWeerth, Stephen; Committee Member: Hasler, Paul; Committee Member: Lanterman, Aaron; Committee Member: Prinz, Astrid.
6
Leung, Suet-ying, and 梁雪瑩. "A study of step kinetics by kinetic Monte Carlo simulation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31226322.
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7
Browne, David John. "Modelling columnar and equiaxed growth." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:3d8ae26b-e0b4-4d54-801d-4951705d53aa.
Повний текст джерелаАнотація:
A novel computer model of the evolution of columnar and equiaxed microstructure during alloy solidification has been developed. A control volume finite difference model of conduction heat transfer is applied to a two-dimensional domain bounded by a relatively cold mould. The initial condition is that of superheated liquid, and nucleation occurs either at the mould wall, leading to columnar dendritic growth, or within the bulk liquid, leading to the growth of equiaxed dendrites. The columnar front or the equiaxed grain boundaries are represented by computationally sharp interfaces, which separate liquid from partially solid alloy. Interpolation between discrete computational markers is employed to describe these interfaces, and a front-tracking technique is used to predict the evolution of the grain structure, via movement of the markers, across the fixed grid. The front velocity is determined via considerations of the kinetics of dendrite growth. The heat equation is fully coupled to the front-tracking algorithm by means of source terms which represent the evolution of latent heat due to the dendritic growth (advancing tips and thickening mushy zone). The model, applied to binary Al-Cu alloys, is computationally efficient. It predicts the variation of the extent of liquid undercooling ahead of the growing columnar front, and new metrics have been established to determine the likelihood of the formation of an equiaxed zone here. The employment of these metrics to establish the influence of heat extraction rate and alloy composition agrees with reports from the literature. The model does not distinguish between individual grains of the columnar zone, but it is shown that this is not an important limitation for most metal casting applications. Direct simulation of the nucleation and growth of multiple equiaxed crystals has been carried out, in which the nucleation and growth of individual grams can be observed via animation, and the influence of melt superheat and heat extraction rate on equiaxed solidification has been determined.
8
Torabmostaedi, Hosein. "Computer simulation of processing controls on the formation and growth of nanoparticles in FSP." Thesis, Kingston University, 2014. http://eprints.kingston.ac.uk/28222/.
Повний текст джерелаАнотація:
In this study, the effect of nozzle geometries and processing controls during Flame Spray Pyrolysis (FSP) process were investigated theoretically on a pilot-scale reactor (production rates up to 5 kg h-1 zirconia) and lab scale reactor (production rates up to 74 g h-1 titania). The focus was on the controlled synthesis and continuous production of nanoparticles at high production rates as well as the study of particle formation and growth inside spray flames. The computational models developed in this study were validated by the measured data available from literature for particle dynamics in spray flames and used to process optimization and reactor design. Chapter one presents an overview of applications of nanoparticles and recent advances in synthesis of nanoparticles by Vapour-fed Flame Synthesis (VFS) and Flame Spray Pyrolysis (FSP). A general introduction on the formation and growth of nanoparticles in the gas-phase synthesis of nanoparticles is presented with emphasis on the mechanisms that control the particle morphology after the initial formation of the monomers. Finally, some existing models in the field are presented and compared. The mathematical models adopted in this study are fully described in chapter two. Several numerical models were developed to predict dynamic viscosity and surface tension of precursor solutions, the pumping pressure of precursor solution, the sauter mean diameter (SMD) of droplets during atomization and the particle growth inside the flame by coagulation and sintering. These models were coupled with the computational fluid dynamic (CFD) code to simulate FSP process. The models were validated by comparison with experimental data developed in this study and literatures. In chapter four, the effect of reactor geometries and processing parameters on the temperature and velocity profiles, droplet evaporation and particle growth were predicted using the validated computational models. The results show that the oxidant/dispersion gas gap size and the oxygen content of oxidant/dispersion gas have a big impact on the flame structure and ultimately the particle growth in the flame. In chapter five, investigation is performed to examine the effect of process parameters on the growth of zirconia particles at low, medium and high precursor concentrations. The results show that fine nanoparticles could be synthesized at low precursor concentration and medium production rates while further studies are needed at higher precursor concentrations and production rates. Therefore, in the sixth chapter, emphasis is placed on industrial production of nanoparticles at higher precursor concentrations. A process operation window for industrial-scale production of zirconia nanoparticles using medium and high precursor concentration was developed. The possible solutions to optimize pump performance and atomization quality at industrial scale production rates using high precursor concentration in FSP were investigated. The quantitative results given in this section can be used as a design guide for a prototype industrial FSP nanoparticle production line. Chapter seven extends the work above and investigates the possibility of quenching the FSP flames at industrial scale production rate by using different reactor configurations. The simulations show how choosing the right configuration and process parameters can affect the characteristics and collection of particles at above the burner. In chapter eight, the applicability of the developed approach for particle simulation of zirconia in the previous chapters is examined for flame spray synthesis of titania. In addition, a series of parametric studies was performed to assist better understanding and control over FSP synthesis of Ti02 nanoparticles. In the ninth chapter, a short summary is given along with recommendations for future investigations.
9
Ma, Yingxiao. "Experimental investigation and computer simulation of grain growth and microstructur evolution in 2D polycristals /." Dortmund : Wulff, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=017070274&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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10
Hawick, Kenneth Arthur. "Domain growth in alloys." Thesis, University of Edinburgh, 1991. http://hdl.handle.net/1842/10605.
Повний текст джерелаАнотація:
This thesis describes Monte-Carlo computer simulations of binary alloys, with comparisons between small angle neutron scattering (SANS) data, and numerically integrated solutions to the Cahn-Hilliard-Cook (CHC) equation. Elementary theories for droplet growth are also compared with computer simulated data. Monte-Carlo dynamical algorithms are investigated in detail, with special regard for universal dynamical times. The computer simulated systems are Fourier transformed to yield partial structure functions which are compared with SANS data for the binary Iron-Chromium system. A relation between real time and simulation time is found. Cluster statistics are measured in the simulated systems, and compared to droplet formation in the Copper-Cobalt system. Some scattering data for the complex steel PE16 is also discussed. The characterisation of domain size and its growth with time are investigated, and scaling laws fitted to real and simulated data. The simple scaling law of Lifshitz and Slyozov is found to be inadequate, and corrections such as those suggested by Huse, are necessary. Scaling behaviour is studied for the low-concentration nucleation regime and the high-concentration spinodal-decomposition regime. The need for multi-scaling is also considered. The effect of noise and fluctuations in the simulations is considered in the MonteCarlo model, a cellular-automaton (CA) model and in the Cahn-Billiard-Cook equation. The Cook noise term in the CHC equation is found to be important for correct growth scaling properties.
11
Boatin, William. "Characterization of neuron models." Thesis, Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-04182005-181732/.
Повний текст джерелаАнотація:
Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006.Dr. Robert H. Lee, Committee Member ; Dr. Kurt Wiesenfeld, Committee Member ; Dr Robert J. Butera, Committee Member.
12
Tartas, Jean. "Computer simulation study of domain growth in the two-dimensional ferromagnetic spin-flip Ising model." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64103.
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13
Uwaha, Makio, and Katsunobu Koyama. "Transition from nucleation to ripening in the classical nucleation model." Elsevier, 2010. http://hdl.handle.net/2237/13867.
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14
Hunter, Russell I. "Improving associative memory in a network of spiking neurons." Thesis, University of Stirling, 2011. http://hdl.handle.net/1893/6177.
Повний текст джерелаАнотація:
In this thesis we use computational neural network models to examine the dynamics and functionality of the CA3 region of the mammalian hippocampus. The emphasis of the project is to investigate how the dynamic control structures provided by inhibitory circuitry and cellular modification may effect the CA3 region during the recall of previously stored information. The CA3 region is commonly thought to work as a recurrent auto-associative neural network due to the neurophysiological characteristics found, such as, recurrent collaterals, strong and sparse synapses from external inputs and plasticity between coactive cells. Associative memory models have been developed using various configurations of mathematical artificial neural networks which were first developed over 40 years ago. Within these models we can store information via changes in the strength of connections between simplified model neurons (two-state). These memories can be recalled when a cue (noisy or partial) is instantiated upon the net. The type of information they can store is quite limited due to restrictions caused by the simplicity of the hard-limiting nodes which are commonly associated with a binary activation threshold. We build a much more biologically plausible model with complex spiking cell models and with realistic synaptic properties between cells. This model is based upon some of the many details we now know of the neuronal circuitry of the CA3 region. We implemented the model in computer software using Neuron and Matlab and tested it by running simulations of storage and recall in the network. By building this model we gain new insights into how different types of neurons, and the complex circuits they form, actually work. The mammalian brain consists of complex resistive-capacative electrical circuitry which is formed by the interconnection of large numbers of neurons. A principal cell type is the pyramidal cell within the cortex, which is the main information processor in our neural networks. Pyramidal cells are surrounded by diverse populations of interneurons which have proportionally smaller numbers compared to the pyramidal cells and these form connections with pyramidal cells and other inhibitory cells. By building detailed computational models of recurrent neural circuitry we explore how these microcircuits of interneurons control the flow of information through pyramidal cells and regulate the efficacy of the network. We also explore the effect of cellular modification due to neuronal activity and the effect of incorporating spatially dependent connectivity on the network during recall of previously stored information. In particular we implement a spiking neural network proposed by Sommer and Wennekers (2001). We consider methods for improving associative memory recall using methods inspired by the work by Graham and Willshaw (1995) where they apply mathematical transforms to an artificial neural network to improve the recall quality within the network. The networks tested contain either 100 or 1000 pyramidal cells with 10% connectivity applied and a partial cue instantiated, and with a global pseudo-inhibition.We investigate three methods. Firstly, applying localised disynaptic inhibition which will proportionalise the excitatory post synaptic potentials and provide a fast acting reversal potential which should help to reduce the variability in signal propagation between cells and provide further inhibition to help synchronise the network activity. Secondly, implementing a persistent sodium channel to the cell body which will act to non-linearise the activation threshold where after a given membrane potential the amplitude of the excitatory postsynaptic potential (EPSP) is boosted to push cells which receive slightly more excitation (most likely high units) over the firing threshold. Finally, implementing spatial characteristics of the dendritic tree will allow a greater probability of a modified synapse existing after 10% random connectivity has been applied throughout the network. We apply spatial characteristics by scaling the conductance weights of excitatory synapses which simulate the loss in potential in synapses found in the outer dendritic regions due to increased resistance. To further increase the biological plausibility of the network we remove the pseudo-inhibition and apply realistic basket cell models with differing configurations for a global inhibitory circuit. The networks are configured with; 1 single basket cell providing feedback inhibition, 10% basket cells providing feedback inhibition where 10 pyramidal cells connect to each basket cell and finally, 100% basket cells providing feedback inhibition. These networks are compared and contrasted for efficacy on recall quality and the effect on the network behaviour. We have found promising results from applying biologically plausible recall strategies and network configurations which suggests the role of inhibition and cellular dynamics are pivotal in learning and memory.
15
Zhang, Changjiang. "COMPUTER SIMULATION OF A HOLLOW-FIBER BIOREACTOR: HEPARAN REGULATED GROWTH FACTORS-RECEPTORS BINDING AND DISSOCIATION ANALYSIS." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/816.
Повний текст джерелаАнотація:
This thesis demonstrates the use of numerical simulation in predicting the behavior of proteins in a flow environment.
A novel convection-diffusion-reaction computational model is first introduced to simulate fibroblast growth factor (FGF-2) binding to its receptor (FGFR) on cell surfaces and regulated by heparan sulfate proteoglycan (HSPG) under flow in a bioreactor. The model includes three parts: (1) the flow of medium using incompressible Navier-Stokes equations; (2) the mass transport of FGF-2 using convection-diffusion equations; and (3) the cell surface binding using chemical kinetics. The model consists of a set of coupled nonlinear partial differential equations (PDEs) for flow and mass transport, and a set of coupled nonlinear ordinary differential equations (ODEs) for binding kinetics. To handle pulsatile flow, several assumptions are made including neglecting the entrance effects and an approximate analytical solution for axial velocity within the fibers is obtained. To solve the time-dependent mass transport PDEs, the second order implicit Euler method by finite volume discretization is used. The binding kinetics ODEs are stiff and solved by an ODE solver (CVODE) using Newton’s backward differencing formula. To obtain a reasonable accuracy of the biochemical reactions on cell surfaces, a uniform mesh is used. This basic model can be used to simulate any growth factor-receptor binding on cell surfaces on the wall of fibers in a bioreactor, simply by replacing binding kinetics ODEs.
Circulation is an important delivery method for natural and synthetic molecules, but microenvironment interactions, regulated by endothelial cells and critical to the molecule’s fate, are difficult to interpret using traditional approaches. Growth factor capture under flow is analyzed and predicted using computer modeling mentioned above and a three-dimensional experimental approach that includes pertinent circulation characteristics such as pulsatile flow, competing binding interactions, and limited bioavailability. An understanding of the controlling features of this process is desired. The experimental module consists of a bioreactor with synthetic endotheliallined hollow fibers under flow. The physical design of the system is incorporated into the model parameters. FGF-2 is used for both the experiments and simulations. The computational model is based on the flow and reactions within a single hollow fiber and is scaled linearly by the total number of fibers for comparison with experimental results. The model predicts, and experiments confirm, that removal of heparan sulfate (HS) from the system will result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin. The model further predicts a significant loss of bound protein at flow rates only slightly higher than average capillary flow rates, corroborated experimentally, suggesting that the probability of capture in a single pass at high flow rates is extremely low. Several other key parameters are investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture. The combined system offers opportunities to examine circulation capture in a straightforward quantitative manner that should prove advantageous for biological or drug delivery investigations.
For some complicated binding systems, where there are more growth factors or proteins with competing binding among them moving through hollow fibers of a bioreactor coupled with biochemical reactions on cell surfaces on the wall of fibers, a complex model is deduced from the basic model mentioned above. The fluid flow is also modeled by incompressible Navier-Stokes equations as mentioned in the basic model, the biochemical reactions in the fluid and on the cell surfaces are modeled by two distinctive sets of coupled nonlinear ordinary differential equations, and the mass transports of different growth factors or complexes are modeled separately by different sets of coupled nonlinear partial differential equations. To solve this computationally intensive system, parallel algorithms are devised, in which all the numerical computations are solved in parallel, including the discretization of mass transport equations and the linear system solver Stone’s Implicit Procedure (SIP). A parallel SIP solver is designed, in which pipeline technique is used for LU factorization and an overlapped Jacobi iteration technique is chosen for forward and backward substitutions. For solving binding equations ODEs in the fluid and on cell surfaces, a parallel scheme combined with a sequential CVODE solver is used. The simulation results are obtained to demonstrate the computational efficiency of the algorithms and further experiments need to be conducted to verify the predictions.
16
Sorensen, Michael Elliott. "Functional Consequences of Model Complexity in Hybrid Neural-Microelectronic Systems." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6908.
Повний текст джерелаАнотація:
Hybrid neural-microelectronic systems, systems composed of biological neural networks
and neuronal models, have great potential for the treatment of neural injury and
disease. The utility of such systems will be ultimately determined by the ability of the engineered
component to correctly replicate the function of biological neural networks. These
models can take the form of mechanistic models, which reproduce neural function by describing
the physiologic mechanisms that produce neural activity, and empirical models,
which reproduce neural function through more simplified mathematical expressions.
We present our research into the role of model complexity in creating robust and flexible
behaviors in hybrid systems. Beginning with a complex mechanistic model of a leech
heartbeat interneuron, we create a series of three systematically reduced models that incorporate
both mechanistic and empirical components. We then evaluate the robustness
of these models to parameter variation, and assess the flexibility of the models activities.
The modeling studies are validated by incorporating both mechanistic and semi-empirical
models in hybrid systems with a living leech heartbeat interneuron. Our results indicate
that model complexity serves to increase both the robustness of the system and the ability
of the system to produce flexible outputs.
17
Shen, Wensheng. "Computer Simulation and Modeling of Physical and Biological Processes using Partial Differential Equations." UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/501.
Повний текст джерелаАнотація:
Scientific research in areas of physics, chemistry, and biology traditionally depends purely on experimental and theoretical methods. Recently numerical simulation is emerging as the third way of science discovery beyond the experimental and theoretical approaches. This work describes some general procedures in numerical computation, and presents several applications of numerical modeling in bioheat transfer and biomechanics, jet diffusion flame, and bio-molecular interactions of proteins in blood circulation.
A three-dimensional (3D) multilayer model based on the skin physical structure is developed to investigate the transient thermal response of human skin subject to external heating. The temperature distribution of the skin is modeled by a bioheat transfer equation. Different from existing models, the current model includes water evaporation and diffusion, where the rate of water evaporation is determined based on the theory of laminar boundary layer. The time-dependent equation is discretized using the Crank-Nicolson scheme. The large sparse linear system resulted from discretizing the governing partial differential equation is solved by GMRES solver.
The jet diffusion flame is simulated by fluid flow and chemical reaction. The second-order backward Euler scheme is applied for the time dependent Navier-Stokes equation. Central difference is used for diffusion terms to achieve better accuracy, and a monotonicity-preserving upwind difference is used for convective ones. The coupled nonlinear system is solved via the damped Newton's method. The Newton Jacobian matrix is formed numerically, and resulting linear system is ill-conditioned and is solved by Bi-CGSTAB with the Gauss-Seidel preconditioner.
A novel convection-diffusion-reaction model is introduced to simulate fibroblast growth factor (FGF-2) binding to cell surface molecules of receptor and heparan sulfate proteoglycan and MAP kinase signaling under flow condition. The model includes three parts: the flow of media using compressible Navier-Stokes equation, the transport of FGF-2 using convection-diffusion transport equation, and the local binding and signaling by chemical kinetics. The whole model consists of a set of coupled nonlinear partial differential equations (PDEs) and a set of coupled nonlinear ordinary differential equations (ODEs). To solve the time-dependent PDE system we use second order implicit Euler method by finite volume discretization. The ODE system is stiff and is solved by an ODE solver VODE using backward differencing formulation (BDF). Findings from this study have implications with regard to regulation of heparin-binding growth factors in circulation.
18
Thomas, Lorraine (Lorraine Marie). "Estimating phytoplankton growth rates from compositional data." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43755.
Повний текст джерелаАнотація:
Thesis (S.M.)--Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2008."February 2008."
Includes bibliographical references (p. 133).
I build on the deterministic phytoplankton growth model of Sosik et al. by introducing process error, which simulates real variation in population growth and inaccuracies in the structure of the matrix model. Adding a stochastic component allows me to use maximum likelihood methods of parameter estimation. I lay out the method used to calculate parameter estimates, confidence intervals, and estimated population growth rates, then use a simplified three-stage model to test the efficacy of this method with simulated observations. I repeat similar tests with the full model based on Sosik et al., then test this model with a set of data from a laboratory culture whose population growth rate was independently determined. In general, the parameter estimates I obtain for simulated data are better the lower the levels of stochasticity. Despite large confidence intervals around some model parameter estimates, the estimated population growth rates have relatively small confidence intervals. The parameter estimates I obtained for the laboratory data fell in a region of the parameter space that in general contains parameter sets that are difficult to estimate, although the estimated population growth rate was close to the independently determined value.
by Lorraine Thomas.
S.M.
19
Akyildiz, Oncu. "Computer Simulation Of Grain Boundary Grooving By Anisotropic Surface Drift Diffusion Due To Capillary, Electromigration And Elastostatic Forces." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12612034/index.pdf.
Повний текст джерелаАнотація:
The aim of this study is to develop a theoretical basis and to perform computational experiments for understanding the grain boundary (GB) grooving in polycrystalline thin film metallic conductors (interconnects) by anisotropic surface diffusion due to capillary, electromigration and elastostatic forces.
To this end, irreversible thermo&ndashkinetics of surfaces and interfaces with triple junction singularities is elaborated, and the resulting well-posed moving boundary value problem is solved using the front&ndash
tracking method. To simulate the strain conditions of the interconnects during service, the problem is addressed within the framework of isotropic linear elasticity in two dimensions (plane strain condition). In the formulation of stress induced surface diffusion, not only the contribution due to elastic strain energy density (ESED) but also that of the elastic dipole tensor interactions (EDTI) between the stress field and the mobile atomic species (monovacancies) is considered. In computation of the elastostatic and electrostatic fields the indirect boundary element method (IBEM) with constant and straight boundary elements is utilized. The resulted non&ndash
linear partial differential equation is solved numerically by Euler&rsquo
s method of finite differences. The dynamic computer simulation experiments identify well known GB groove shapes and shed light on their growing kinetics. They also allow generating some scenarios under several conditions regarding to the applied force fields and/or physicochemical parameters. The destruction of groove symmetry, termination of the groove penetration with isotropic surface diffusivity, ridge/slit formations with anisotropic diffusivity and the role played by the wetting parameter are all identified for electromigration conditions. The kinetics of accelerated groove deepening with an applied tensile stress is examined in connection with GB cavity growth models in the literature and a diffusive micro-crack formation is reported at the groove tip for high stresses. On the other hand, the use of EDTI provided a means to dynamically simulate GB ridges under compressive stress fields with surface diffusion. An incubation time for hillock growth and a crossover depth over which GB migration becomes energetically favorable is defined and discussed in this context.
20
Oguz, Cihan. "Control-oriented modeling of discrete configuration molecular scale processes applications in polymer synthesis and thin film growth /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19867.
Повний текст джерелаАнотація:
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Gallivan, Martha A.; Committee Member: Hess, Dennis; Committee Member: Lee, Jay H.; Committee Member: Li, Mo; Committee Member: Ludovice, Pete.
21
Thirion, Bertrand. "Méthodes structurales et probabilistes pour l'analyse de groupe en neuroimagerie fonctionnelle." Habilitation à diriger des recherches, École normale supérieure de Cachan - ENS Cachan, 2009. http://tel.archives-ouvertes.fr/tel-00438202.
Повний текст джерелаАнотація:
La neuro-imagerie est actuellement la principale modalité non-invasive pour explorer la structure et le fonctionnement dur cerveau. Dans cette présentation, nous allons nous concentrer sur l'Imagerie par Résonance Magnétique (IRM) qui est la seule modalité à fournir une couverture de tout le volume cérébral à la résolution du millimètre. L'utilisation des données d'IRM pour mieux comprendre le fonctionnement normal du cerveau et pour diagnostiquer différentes maladies implique quelques problèmes fondamentaux: i) La capacité à utiliser des informations hétérogènes, telles que la segmentation des tissus observés en IRM anatomique, la caractérisation fonctionnelle de certaines régions cérébrales en IRM fonctionnelle et les mesures de connectivité obtenues en IRM de diffusion; ii) la capacité à opérer des comparaisons inter-individuelles pertinentes, en dépit de la variabilité impressionnante de la forme des cerveaux observée même dans des populations saines. Nous allons présenter différentes propositions pour construire des modèles moyens de l'organisation cérébrale tout en mettant en évidence la variabilité inter-individuelle avec différents outils de traitement statistique. Enfin nous allons évoquer les problèmes soulevés par la comparison des données d'IRM avec celles obtenues par génotypage complet des individus, qui fournissent les marqueurs fondamentaux de la variabilité inter-individuelle.
22
Uwaha, Makio. "Steady chirality conversion by grinding crystals : Supercritical and subcritical bifurcations." Elsevier, 2011. http://hdl.handle.net/2237/20566.
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23
Jaeger, Marc. "Representation et simulation de croissance des vegetaux." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13224.
Повний текст джерелаАнотація:
L'image de synthese se heurte a la representation des vegetaux, etres complexes, varies et evolutifs. Le modele developpe ici utilise une modelisation fine de l'architecture des vegetaux a partir de deux approches complemezntaires. La premiere, botanique, decrit les hierarchies et processus intervenant dans l'elaboration de l'architecture des vegetaux: la deuxieme, de nature mathematique, definit l'architecture d'une plante precise par des lois stochastiques de croissance, de viabilite et de ramification des bourgeons. La traduction informatique du modele aboutit a un generateur de vegetaux compose d'un moteur de croissance (qui determine l'evolution topologique de la plante) et de fonctions geometrique (qui definissent les directions de developpement et l'effet de la pesanteur)
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Vallaghé, Sylvain. "Modélisation du problème direct de la magnéto et électroencéphalographie : méthodes numériques et calibration." Phd thesis, Université de Nice Sophia-Antipolis, 2008. http://tel.archives-ouvertes.fr/tel-00460772.
Повний текст джерелаАнотація:
Le travail présenté dans cette thèse s'inscrit dans l'étape de modélisation du problème direct en électroencéphalographie (EEG) et magnétoencéphalographie (MEG). La première partie traite du calcul des solutions du problème direct, gouvernées par des équations aux dérivées partielles. Nous présentons tout d'abord une nouvelle méthode éléments finis (FEM) basée sur des maillages cubiques réguliers et une description implicite du domaine qui permet de résoudre à faible coût le problème direct pour des géométries réalistes. Nous associons à cette méthode des équations réciproques générales, obtenues par la méthode de l'adjoint, qui permettent de calculer efficacement les lead fields de tout type de capteur EEG ou MEG. La deuxième partie concerne le choix des conductivités électriques dans les modèles directs en EEG. Dans un premier temps, nous effectuons une analyse de sensibilité globale des topographies EEG aux conductivités pour des modèles de tête classiques à trois ou quatre couches. S'appuyant sur les résultats de cette analyse, nous proposons ensuite une méthode de calibration des conductivités basée sur l'utilisation de potentiels évoqués somesthésiques.
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Jenson, Sage. "Digital Morphologies: Environmentally-Influenced Generative Forms." Oberlin College Honors Theses / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1499763863308499.
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Qi, Rui. "Optimization and optimal control of plant growth : application of GreenLab model for decision aid in agriculture." Phd thesis, Châtenay-Malabry, Ecole centrale de Paris, 2010. http://tel.archives-ouvertes.fr/tel-00494918.
Повний текст джерелаАнотація:
The objective of the thesis is to improve plant yield through optimization and optimal control based on the GreenLab plant growth model. Therefore, the thesis proposed a methodology for investigation of plant yield improvement，whose characteristics are that (1) investigations are all based on the functional-structural plant growth model GreenLab and (2) heuristic optimization algorithm and optimal control techniques are applied to the plant growth model in order to improve plant yield. By applying optimization techniques on different species of plants (crops or trees) and for different kinds of optimization problems, common characteristics that a plant with high yield should possess were obtained. The optimal results in the thesis revealed the source-sink dynamics during the plant growth. The optimization results can be considered as references to guide breeding for ideotype and to improve cultivation modes. The optimization application of GreenLab could thus be possibly used to the agricultural decision support system.To achieve the aims of the thesis, the thesis investigated the effects of endogenous factors and exogenous environmental factors of plant growth on plant yield separately. First, given environmental conditions, the thesis investigated endogenous factors, and then the thesis did optimal control on exogenous environmental factors given plant genotype. Therefore, the problems investigated in the thesis consist of general optimization problems and optimal control problems.The main contributions of the thesis include following issues: According to the species of plants, single optimization problems, multi-objective optimization problems and optimization problems with constraints with respect to plant endogenous factors were formulated and investigated, in order to find the ideotype of plants with high plant yield. A population based algorithm is more suitable for the optimization problems in this thesis. Due to its better performance compared with other heuristic optimization algorithms, all optimization problems were solved by a population-based, heuristic optimization algorithm, namely Particle Swarm Optimization (PSO). Optimal control on the pruning strategy was formulated and investigated in the thesis. As GreenLab can be considered as discrete dynamic system and the objective function of the optimal control problem is analytical, the gradient based method, which is based on the variational approach and Lagrange theory, was used to solve the optimal control problem. Moreover, the optimal solutions were compared with the ones found by PSO, in order to validate the PSO method. The insect population dynamics was modeled mathematically, which was compatible with the plant model GreenLab in terms of spatial and temporal scales, to study the effect of biotic factors on plant growth. The interaction among plants, pests and auxiliaries was implemented, and the ecosystem model, which involves the three tri-trophic components, was thus developed in the thesis. The tri-trophic ecosystem model can simulate the insect population dynamics and the plant growth with consideration of the interaction of insects. Moreover, the tri-trophic ecosystem model considered the partition of individuals in the insect population among plant organs, which is not taken into account in the previous works. A global sensitivity analysis method Morris method was used to analyze the most important parameters and the least influential parameters to model outputs of interest. Through optimization on pest management techniques, the optimal strategies of the application of the pest management techniques were obtained. Estimation of GreenLab parameters with about 400 sets of observation data of 44 tomato genotypes was done in the thesis, by using a generalized non-linear least square algorithm. Taking the estimated parameter values as parameter space, the GreenLab model parameters were optimized, in order to maximize the fruit yield. Through the analysis of the correlation of estimated and optimal parameters with the fruit yield by statistical analysis methods, the most important parameters that result in the difference of fruit yield were found. According to the correlation and optimization results, the phenotypic differences among genotypes were explained from the physiological point of view.
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Rougier, Nicolas P. "Fondements biologiques pour le calcul distribué, numérique et adaptatif." Habilitation à diriger des recherches, Université Nancy II, 2011. http://tel.archives-ouvertes.fr/tel-00596740.
Повний текст джерелаАнотація:
Ce document tente de promouvoir, au travers de recherches passées et de propositions nouvelles, un cadre computationel pour l'étude de la cognition. En ce sens, la notion de calculs numériques distribués et adaptatifs est détaillée afin de mieux comprendre pourquoi nous pouvons prétendre à la légitimité dans les modèles numériques que nous concevons pour décrire la Biologie et le Vivant.
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Vignais, Nicolas. "Mise en oeuvre et évaluation d'une méthodologie fondée sur la réalité virtuelle pour l'analyse de la prise d'informations visuelles du gardien de but de handball." Phd thesis, Université Rennes 2, 2009. http://tel.archives-ouvertes.fr/tel-00439397.
Повний текст джерелаАнотація:
La perception visuelle est un élément déterminant pour interagir avec notre environnement. Lors des activités physiques et sportives, la prise d'informations visuelles permet notamment à un athlète d'extraire et de sélectionner les indices visuels nécessaires pour anticiper le mouvement adverse. L'analyse de cette prise d'informations visuelles a fait l'objet de nombreuses recherches dans le domaine sportif, cependant toutes les méthodes employées semblent limitées sur le plan fonctionnel ou matériel. Ce travail a pour objectif l'évaluation et la mise en oeuvre d'une nouvelle méthodologie d'analyse de la prise d'informations visuelles fondée sur l'utilisation des environnements virtuels. Cette méthodologie est appliquée à l'activité du gardien de but de handball en situation de duel. Dans un premier temps, nous comparons les performances des gardiens de but face à notre méthodologie avec ceux obtenus face à une séquence filmée afin de démontrer l'intérêt des environnements virtuels dans ce domaine. Puis, nous abordons la mise en place de notre méthodologie en nous focalisant sur l'influence du niveau de détail et de la représentation graphique de l'action de tir sur la performance du gardien de but de handball. Enfin, nous utilisons notre méthodologie pour étudier la prise d'informations visuelles du gardien de but de handball. Plus précisément, nous estimons l'importance relative des informations visuelles issues de la trajectoire du ballon et du mouvement de tir.
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MUKHERJI, ABHISHEK. "SNIF TOOL - Sniffing for Patterns in Continuous Streams." Digital WPI, 2008. https://digitalcommons.wpi.edu/etd-theses/161.
Повний текст джерелаАнотація:
Recent technological advances in sensor networks and mobile devices give rise to new challenges in processing of live streams. In particular, time-series sequence matching, namely, the similarity matching of live streams against a set of predefined pattern sequence queries, is an important technology for a broad range of domains that include monitoring the spread of hazardous waste and administering network traffic. In this thesis, I use the time critical application of monitoring of fire growth in an intelligent building as my motivating example. Various measures and algorithms have been established in the current literature for similarity of static time-series data. Matching continuous data poses the following new challenges: 1) fluctuations in stream characteristics, 2) real-time requirements of the application, 3) limited system resources, and, 4) noisy data. Thus the matching techniques proposed for static time-series are mostly not applicable for live stream matching. In this thesis, I propose a new generic framework, henceforth referred to as the n-Snippet Indices Framework (in short, SNIF), for discovering the similarity between a live stream and pattern sequences. The framework is composed of two key phases: (1.) Off-line preprocessing phase: where the pattern sequences are processed offline and stored into an approximate 2-level index structure; and (2.) On-line live stream matching phase: streaming time-series (or the live stream) is on-the-fly matched against the indexed pattern sequences. I introduce the concept of n-Snippets for numeric data as the unit for matching. The insight is to match small snippets of the live stream against prefixes of the patterns and maintain them in succession. Longer the pattern prefixes identified to be similar to the live stream, better the confirmation of the match. Thus, the live stream matching is performed in two levels of matching: bag matching for matching snippets and order checking for maintaining the lengths of the match. I propose four variations of matching algorithms that allow the user the capability to choose between the two conflicting characteristics of result accuracy versus response time. The effectiveness of SNIF to detect patterns has been thoroughly tested through extensive experimental evaluations using the continuous query engine CAPE as platform. The evaluations made use of real datasets from multiple domains, including fire monitoring, chlorine monitoring and sensor networks. Moreover, SNIF is demonstrated to be tolerant to noisy datasets.
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Rougier, Nicolas P. "Modèles de mémoires pour la navigation autonome." Phd thesis, Université Henri Poincaré - Nancy I, 2000. http://tel.archives-ouvertes.fr/tel-00602997.
Повний текст джерелаАнотація:
Nous proposons une approche du problème de la navigation d'un agent autonome fondée sur une architecture connexionniste inspirée de données biologiques concernant le cortex cérébral et l'hippocampe, une sous-structure corticale. Notre approche se fonde sur la distinction des mémoires, le cortex cérébral étant fortement impliqué dans la mémoire procédurale, permettant l'apprentissage de procédures, alors que l'hippocampe est impliqué dans la mémoire déclarative, permettant la mémorisation explicite de faits et d'événements. Notre travail concerne la modé- lisation de ces mémoires dans le contexte du comportement autonome. L'étude des dfférentes mémoires met en évidence l'importance de cette dichotomie procédurale/déclarative dans les tâches cognitives et l'étude de la navigation autonome met en exergue la notion de carte cognitive topologique ainsi que la nécessité de disposer de systèmes de mémoires adéquats. Notre travail de modélisation s'articule alors en deux temps. Les données concernant le cortex humain ont permis de modéliser une mémoire procédurale pour la construction des liens reliant les différents lieux d'un environnement simulé permettant une recherche guidée par le but ainsi que le ralliement à tout instant d'un lieu visité auparavant. Par ailleurs, les différentes données concernant la structure de l'hippocampe ont permis de proposer un modèle de mémoire de type déclaratif. L'architecture de ce modèle ainsi que les mécanismes originaux participant à son fonctionnement lui assurent une efficacité et une robustesse aussi bien sur des données simulées que sur des données réelles. Ce modèle permet alors de caractériser de façon adéquate les différents lieux d'un environnement donné.
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Koneru, Narendra. "Quantitative analysis of domain testing effectiveness." [Johnson City, Tenn. : East Tennessee State University], 2001. http://etd-submit.etsu.edu/etd/theses/available/etd-0404101-011933/unrestricted/koneru0427.pdf.
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Silva, Ariosto Siqueira. "Uma abordagem de metodos computacionais para simulação de processos biologicos : simulação tridimensional e metabolica do desenvolvimento tumoral." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/316889.
Повний текст джерелаАнотація:
Orientador: Jose Andres YunesTese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
Made available in DSpace on 2018-08-11T17:40:29Z (GMT). No. of bitstreams: 1 Silva_AriostoSiqueira_D.pdf: 3970975 bytes, checksum: 7d1f1e04224af1b835486da199d18d00 (MD5) Previous issue date: 2008
Resumo: Neste trabalho criou-se uma ferramenta de simulação e modelos computacionais para estudo da carcinogênese a fim de se responder a perguntas biológicas pertinentes ao tratamento desta doença. Os modelos computacionais se basearam no modelo teórico de Evolução Somática e Invasão Mediada por Acidez, proposto por Gatenby e Gillies, e foi implementado em uma ferramenta desenvolvida pelo autor deste trabalho no âmbito deste projeto, o Tissue Simulator (TSim, www.i-genics.com). O modelo teórico de invasão mediada por acidez propõe que células tumorais possuem maior resistência a acidez, assim como produzem quantidade de ácido lático, originado da glicólise anaeróbica, suficiente para acidificar o meio extracelular, causando assim morte do tecido saudável por apoptose induzida por acidez, e facilitando a invasão do tecido saudável pelo tumor. Estudos experimentais, na literatura, mostraram que a administração de bicarbonato de sódio na água em ratos portadores de tumores reduz o número de metástases, o que seria uma indicação de que a hipótese sobre a importância da acidez na invasividade tumoral é válida. Neste estudo, criou-se um primeiro modelo computacional para testar se o aumento da concentração de bicarbonato no sangue poderia influenciar no gradiente de acidez entre o tumor (micrometástases) e o tecido saudável, e também identificaram-se as características físico-químicas de um tampão ideal a ser usado com esse propósito. O modelo teórico de Evolução Somática, adotado neste projeto, propõe que para que um tumor epitelial se torne invasivo, é necessário que suas células adquiram três fenótipos: hiperplasia, hiperglicólise e resistência a acidez. O segundo modelo criado neste trabalho consistiu na identificação de quais seriam os valores mínimos de hiperglicólise e resistência à acidez para o aparecimento da característica de invasividade em um tumor em desenvolvimento dentro de um duto epitelial (DCIS). Uma vez identificados os fenótipos mínimos para a invasão tumoral de um DCIS, restaria saber quais as mutações em enzimas ou transportadores específicos dessa via metabólica para que o dito fenótipo seja atingido. A título de exemplo de um estudo para responder perguntas desse tipo, fez-se uma análise comparativa da robustez do fluxo glicolítico em duas células distintas: uma levedura (S. Cerevisiae) e uma célula humana especializada (célula beta pancreática), cujas enzimas principais são reguladas por estratégias distintas. Este estudo foi implementado em uma ferramenta computacional disponível na literatura (Jarnac e Matlab) e resultou na publicação de um artigo. No todo, os resultados desta tese mostram que, com o uso de ferramentas computacionais e dados quantitativos da literatura, é possível criar modelos teóricoquantitativos que podem ser usados para validar teorias sobre fenômenos biológicos assim como extrapolar novas hipóteses e testá-las, integrando-se assim a modelagem computacional no processo de pesquisa científica
Abstract: In this work, we created a piece of software and computer models for studying carcinogenesis, in order to answer biological questions related to the treatment of this disease. The computer models were inspired in the theory of Somatic Evolution and Acid Mediated Tumor Invasion, proposed by Gatenby and Gillies, and were implemented in a tool developed by the author under the scope of this thesis, Tissue Simulator (TSim, www.i-genics.com). The theory of Acid Mediated Tumor Invasion proposes that cancer cells are more resistant to toxicity of an acidic environment that they help create by producing excess of lactic acid through anaerobic glycolysis. Acidification of the extra-cellular environment causes death of healthy tissue through acid-induced apoptosis and ultimately facilitates tumor invasion. Experimental studies, from literature, showed that administration of sodium bicarbonate in water to mice bearing tumors reduced the number of metastases, thus supporting the importance of acidity in tumor invasion. In this study a computer model was built to test if an increase in concentration of bicarbonate in blood serum could alter the pH gradient between the tumor (micrometastases) and halthy tissue, as well as to identify the chemical properties of and ideal buffer with this purpose. The theory of Somatic Evolution, proposes that epithelial tumor cells are submitted to environmental barriers and are selected for three main phenotypes: hyperplasia, hyperglycolysis and acid resistance. A second computer model was created in order to identify the minimum values of these phenotypes that allowed a DCIS to change into an invasive tumor. Once the minimum phenotypic values identified, one can study how mutations on specific enzymes can alter the flux of a metabolic pathway, such as glycolysis, to produce the altered phenotype. As an example of this, we performed a comparative study of robustness of glycolytic flux in two different cells: yeast (S. cerevisiae) and pancreatic human beta-cell, whose enzymatic regulatory strategies differ. This computer model was implemented on Matlab and Jarnac. Overall, our results show that the use of computational tools and quantitative data may be used to create theoretical-quantitative models that help adressing theories about biological systems, as well as to extrapolate and tes new hypothesis, integrating the approach of computational modeling in the scientific research process
Doutorado
Genetica Animal e Evolução
Doutor em Genetica e Biologia Molecular
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Chevallier, Sylvain. "Implémentation d'un système préattentionnel avec des neurones impulsionnels." Phd thesis, Université Paris Sud - Paris XI, 2009. http://tel.archives-ouvertes.fr/tel-00472849.
Повний текст джерелаАнотація:
Les neurones impulsionnels prennent en compte une caractéristique fondamentale des neurones biologiques : la capacité d'encoder l'information sous forme d'événements discrets. Nous nous sommes intéressés à l'apport de ce type de modèles dans le cadre de la vision artificielle, dont les contraintes nous ont orienté vers le choix de modèles simples, adaptés à la rapidité de traitement requise. Nous décrivons une architecture de réseaux pour encoder et extraire des saillances utilisant la discrétisation induite par les neurones impulsionnels. La carte de saillances est obtenue à partir de la combinaison, spatiale et temporelle, de différentes cartes de modalités visuelles (contrastes, orientations et couleurs) à différentes échelles spatiales. Nous proposons une méthode de filtrage neuronal pour construire les cartes de modalité visuelle. Cette méthode réalise le filtrage de façon graduelle : plus le temps de traitement alloué à l'algorithme est important, plus le résultat est proche de celui obtenu avec un filtrage par convolution. L'architecture proposée donne en sortie les saillances triées temporellement dans l'ordre de leur importance. Nous avons placé en aval de cette architecture un autre réseau de neurones impulsionnels, s'inspirant des champs neuronaux, qui permet de sélectionner la zone la plus saillante et de maintenir une activité constante sur cette zone. Les résultats expérimentaux montrent que l'architecture proposée est capable d'extraire des saillances dans une séquence d'images, de sélectionner la saillance la plus importante et de maintenir la focalisation sur cette saillance, même dans un contexte bruité ou quand la saillance se déplace.
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Fansi, Joseph. "PREDICTION PAR ELEMENTS FINIS DE LA RUPTURE DES ACIERS DUAL_PHASE EN UTILISANT UN MODELE DE GURSON AVANCE." Phd thesis, Ecole nationale supérieure d'arts et métiers - ENSAM, 2013. http://tel.archives-ouvertes.fr/tel-00869032.
Повний текст джерелаАнотація:
L'actuelle investigation numérique du Gurson-Tvergaard-Needleman (GTN) modèle avancé est une extension du travail de Ben Bettaieb et al. (2011). Le modèle a été implémenté à l'aide d'une sous routine (VUMAT) contenu dans le code commerciale d'éléments finis Abaqus/explicit. Le modèle d'endommagement améliore l'original en intégrant les trois mécanismes d'endommagement, la nucléation, la croissance, et la coalescence des cavités. Le modèle d'endommagement intègre les lois de nucléation et de croissance basés sur les phénomènes purement physiques. Ces nouvelles contributions incluant l'influence de l'écrouissage cinématique, ont été validées par les résultats de mesures expérimentales de tomographie à rayon X à haute résolution. Aussi, l'implémentation numérique de l'écrouissage cinématique dans le modèle modifié a contraint de proposer et de réarranger la définition de la triaxialité que l'on trouve habituellement dans la littérature. A coté de cela, un second critère d'initiation à la rupture basé sur l'ultime distance inter-cavités a été inclue afin de localiser et de quantifier avec plus de précision la distribution des déformations peu avant que le matériau ne casse complètement. L'actuel modèle d'endommagement a été appliqué dans des conditions industrielles pour prédire l'évolution de l'endommagement, l'état de contraintes, et l'initiation à la rupture pour différentes géométries de tôles et sur des essais d'emboutissage de tôles minces.
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Monir, Md M. "A COMPUTATIONAL INVESTIGATION OF SECTORAL ZONING OF RARE EARTH ELEMENTS (REE) IN FLUORITE." Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1438881165.
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Jönsson, Ingela, and Mattias Nilsson. "Klassiska populationsmodeller kontra stokastiska : En simuleringsstudie ur matematiskt och datalogiskt perspektiv." Thesis, Växjö University, School of Mathematics and Systems Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-2262.
Повний текст джерелаАнотація:
I detta tvärvetenskapliga arbete studeras från den matematiska sidan tre klassiska populationsmodeller: Malthus tillväxtmodell, Verhulsts logistiska modell och Lotka-Volterras jägarebytesmodell. De klassiska modellerna jämförs med stokastiska. De stokastiska modeller som studeras är födelsedödsprocesser och deras diffusionsapproximation. Jämförelse görs med medelvärdesbildade simuleringar.
Det krävs många simuleringar för att kunna genomföra jämförelserna. Dessa simuleringar måste utföras i datormiljö och det är här den datalogiska aspekten av arbetet kommer in. Modellerna och deras resultathantering har implementerats i både MatLab och i C, för att kunna möjliggöra en undersökning om skillnaderna i tidsåtgången mellan de båda språken, under genomförandet av ovan nämnda jämförelser. Försök till tidsoptimering utförs och även användarvänligheten under implementeringen av de matematiska problemen i de båda språken behandlas.
Följande matematiska slutsatser har dragits, att de medelvärdesbildade lösningarna inte alltid sammanfaller med de klassiska modellerna när de simuleras på stora tidsintervall. I den logistiska modellen samt i Lotka-Volterras modell dör förr eller senare de stokastiska simuleringarna ut när tiden går mot oändligheten, medan deras deterministiska representation lever vidare. I den exponentiella modellen sammanfaller medelvärdet av de stokastiska simuleringarna med den deterministiska lösningen, dock blir spridningen stor för de stokastiska simuleringarna när de utförs på stora tidsintervall.
Datalogiska slutsatser som har dragits är att när det kommer till att implementera få modeller, samt resultatbearbetning av dessa, som ska användas upprepade gånger, är C det bäst lämpade språket då det visat sig vara betydligt snabbare under exekvering än vad MatLab är. Dock måste hänsyn tas till alla de svårigheter som implementeringen i C drar med sig. Dessa svårigheter kan till stor del undvikas om implementeringen istället sker i MatLab, då det därmed finns tillgång till en uppsjö av väl lämpade funktioner och färdiga matematiska lösningar.
In this interdisciplinary study, three classic population models will be studied from a mathematical view: Malthus’ growth, Verhulst’s logistic model and Lotka-Volterra’s model for hunter and prey. The classic models are being compared to the stochastic ones. The stochastic models studied are the birthdeath processes and their diffusion approximation. Comparisons are made by averaging simulations.
It requires numerous simulations to carry out the comparisons. The simulations must be carried out on a computer and this is where the computer science emerges to the project. The models, along with the handling of the results, have been implemented in both Mat- Lab and in C in order to allow a comparison between the two languages whilst executing the above mentioned study. Attempts to time optimization and an evaluation concerning the user-friendliness regarding the implementation of mathematical problems will be performed.
Mathematic conclusions, which have been drawn, are that the averaging solutions do not always coincide with the traditional models when they are being simulated over large time. In the logistic model and in Lotka-Volterra’s model the stochastic simulations will sooner or later die when the time is moving towards infinity, whilst their deterministic representation keeps on living. In the exponential model, the mean values of the stochastic simulations and of the deterministic solution coincide. There is, however, a large spread for the stochastic simulations when they are carried out over a large time.
Computer scientific conclusions drawn from the study includes that when it comes to implementing a few models, along with the handling of the results, to be used repeatedly, C is the most appropriate language as it proved to be significantly faster during execution. However, all of the difficulties during the implementation of mathematical problems in C must be kept in mind. These difficulties can be avoided if the implementation instead takes place in MatLab, where a numerous of mathematical functions and solutions will be available.
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Ambard, Maxime. "Influence de l'inhibition synaptique sur le codage de l'information par les cellules mitrales du bulbe olfactif." Phd thesis, Université Henri Poincaré - Nancy I, 2009. http://tel.archives-ouvertes.fr/tel-00401813.
Повний текст джерелаАнотація:
Cette thèse étudie l'encodage de l'information sensorielle par les cellules relais du bulbe olfactif avec une approche associant analyse de données expérimentales et modélisation informatique. Le bulbe olfactif est principalement constitué de neurones excitateurs, dits cellules mitrales, interconnectés via des inter-neurones inhibiteurs, dits cellules granulaires.Dans un premier temps, l'analyse de données expérimentales recueillies en condition in vitro dans des tranches de bulbe olfactif de rats révèle le caractère phasé des potentiels d'action des cellules mitrales relativement aux oscillations du potentiel de champ local. Ce phasage est largement atténué lorsque l'on bloque pharmacologiquement l'inhibition provenant des granules, mettant ainsi en évidence le rôle primordial de l'inhibition synaptique. Afin d'extraire le décours temporel de la conductance synaptique inhibitrice, nous proposons une nouvelle méthode basée sur l'ajustement d'un modèle de neurone associé à l'injection de bloqueurs synaptiques. Grâce à celle-ci, nous observons que les fluctuations de la conductance synaptique inhibitrice sont corrélées à celles mesurées sur le potentiel de champ local. Une relation entre l'inhibition reçue et la phase des potentiels d'action est également dévoilée. Un neurone aura plus de chance d'émettre en phase s'il reçoit un nombre important d'événements synaptiques inhibiteurs et si ces événements sont eux-même phasés.
Dans un deuxième temps, les résultats de cette analyse sont rassemblés au sein d'un modèle informatique de bulbe olfactif afin d'explorer les capacités de codage de l'interaction mitrale-granule. Après avoir montré que le transfert d'information des cellules mitrales semble plus résider dans leurs instants précis d'émission de potentiels d'action au cours des oscillations que dans leurs fréquences de décharges, nous étudions analytiquement l'influence du nombre d'événements synaptiques inhibiteurs reçus et de leur dispersion temporelle sur la précision de l'activité des cellules mitrales. Notre étude conclut que la robustesse du code produit par les cellules mitrales lors des oscillations du réseau est conditionnée par une forte interaction synaptique entre les cellules mitrales et les cellules granulaires. En dernier lieu, nous appliquons notre modèle de bulbe olfactif pour reconnaître des odeurs à l'aide d'une matrice de capteurs de gaz artificiels.
38
Cisternino, Marco. "A parallel second order Cartesian method for elliptic interface problems and its application to tumor growth model." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00690743.
Повний текст джерелаАнотація:
Cette thèse porte sur une méthode cartésienne parallèle pour résoudre des problèmes elliptiques avec interfaces complexes et sur son application aux problèmes elliptiques en domaine irrégulier dans le cadre d'un modèle de croissance tumorale. La méthode est basée sur un schéma aux différences fi nies et sa précision est d'ordre deux sur tout le domaine. L'originalité de la méthode consiste en l'utilisation d'inconnues additionnelles situées sur l'interface et qui permettent d'exprimer les conditions de transmission à l'interface. La méthode est décrite et les détails sur la parallélisation, réalisée avec la bibliothèque PETSc, sont donnés. La méthode est validée et les résultats sont comparés avec ceux d'autres méthodes du même type disponibles dans la littérature. Une étude numérique de la méthode parallélisée est fournie. La méthode est appliquée aux problèmes elliptiques dans un domaine irrégulier apparaissant dans un modèle continue et tridimensionnel de croissance tumorale, le modèle à deux espèces du type Darcy . L'approche utilisée dans cette application est basée sur la pénalisation des conditions de transmission a l'interface, afin de imposer des conditions de Neumann homogènes sur le bord d'un domaine irrégulier. Les simulations du modèle sont fournies et montrent la capacité de la méthode à imposer une bonne approximation de conditions au bord considérées.
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Messé, Arnaud. "Caractérisation de la relation structure-fonction dans le cerveau humain à partir de données d'IRM fonctionnelle et de diffusion : méthodes et applications cognitive et clinique." Phd thesis, Université de Nice Sophia-Antipolis, 2010. http://tel.archives-ouvertes.fr/tel-00845014.
Повний текст джерелаАнотація:
La compréhension des mécanismes cognitifs est un défi que les prouesses technologiques en imagerie par résonance magnétique fonctionnelle et de diffusion permettent de relever. Les réseaux neuronaux, ensembles de régions interconnectées anatomiquement et fonctionnellement, sont à l'ori- gine des processus cognitifs. Nous nous sommes intéressés à la relation entre la structure anatomique et la fonction de ces réseaux, au travers des deux principes fondamentaux du fonctionnement céré- bral que sont la ségrégation et l'intégration, ainsi que via la notion d'intégrité. En premier lieu, nous nous sommes penchés sur la ségrégation anatomique des noyaux gris centraux et son interprétation fonctionnelle. Puis, nous avons abordé le principe d'intégration, d'un point de vue descriptif par le biais de la théorie des graphes, puis explicatif par l'utilisation du modèle spatial autorégressif. Enfin, nous avons étudié l'intégrité structurelle du cerveau en présence de déficits neurocomportementaux suite à un traumatisme crânien léger. Nous avons ainsi mis en évidence l'existence d'un substrat ana- tomique sous-jacent aux réseaux fonctionnels. Nos résultats suggèrent que la structure anatomique des réseaux cérébraux est un substrat complexe optimisant les processus fonctionnels. De plus, une perte d'intégrité de ce substrat anatomique lors d'un traumatisme crânien léger se répercute sur le comportement et les performances cognitives. Ceci démontre que le fonctionnement cérébral, traduit par les réseaux neuronaux, est intimement lié à la structure anatomique de ces réseaux.
40
Desnain, Philippe. "Influence de la convection sur la taille de grains de solidification d'alliages industriels d'aluminium." Grenoble INPG, 1989. https://hal.archives-ouvertes.fr/tel-01338778.
Повний текст джерелаАнотація:
Etude de la formation de la structure de grains lors de la solidification d'alliages industriels d'aluminium. Enregistrement des courbes de refroidissement et examen des phenomenes de recalescence lors de la solidification dans une lingotiere rectangulaire verticale munie d'un brasseur electromangetiques a champ glissant. Caracterisation des lingots et mesures de la taille des grains equiaxes. Modelisation de la nucleation et de la croissance des cristaux equiaxes. Influence du brassage et de la composition. Prevision a partir du modele etabli de l'affinement des grains resultant du brassage
41
Silga, Matthias. "Elaboration de monocristaux de hgi::(2) alpha par la methode du flux force : application a la detection de rayonnements X gamma et alpha." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21009.
Повний текст джерелаАнотація:
Elaboration de monocristaux hg1::(2)-alpha en vue de leur utilisation comme detecteurs de rayonnements. La purification du materiau de base, le controle du transport de matiere, le controle de la sursaturation a l'interieur des ampoules de croissance, la monogermination et l'etude de la morphologie du cristal sont traites en relation avec les proprietes de detection. Une approche theorique par simulation monte-carlo de la reponse d'un detecteur hgi::(2) a ete faite
42
Platkiewicz, Jonathan. "Dynamique de l'excitabilité neuronale : approches théorique et numérique." Phd thesis, Université René Descartes - Paris V, 2010. http://tel.archives-ouvertes.fr/tel-00612602.
Повний текст джерелаАнотація:
Les neurones émettent des impulsions électriques suivant une loi dite ''tout-ou-rien'' : un potentiel d'action stéréotypé est généré et propagé pour des amplitudes suffisamment grandes du stimulus, autrement aucune décharge n'a lieu. L'amplitude minimale au-delà de laquelle une impulsion est générée est appelée seuil d'excitabilité. Des expériences in vivo récentes, dans lesquelles l'activité membranaire des neurones du système nerveux central a été enregistrée, ont mis en évidence une variabilité significative de ce seuil. De plus, il a été observé une adaptation du seuil à la dynamique de l'activité membranaire précédant l'initiation des impulsions. Ces observations nous ont intéressées car elles concernaient à la fois les hypothèses fondamentales de la biophysique de l'excitabilité et les conceptions classiques de l'intégration synaptique. Nous nous sommes alors demandé dans quelle mesure et comment les différents mécanismes biophysiques impliqués dans l'excitabilité contribuent à la variabilité du seuil. Nous nous sommes aussi demandé quelle est l'influence spécifique sur la dynamique du seuil d'un mécanisme classique de régulation de la décharge, l'inactivation du canal sodium. Nous avons abordé ces questions à partir d'analyses mathématiques et de simulations numériques de modèles d'excitabilité. Nous avons montré qu'il est possible d'obtenir un seuil variable dans le cadre des hypothèses classiques et de le prédire quantitativement à partir des variables biophysiques de l'excitabilité. Nous avons aussi confirmé que l'inactivation du canal sodium permet de rendre compte des différentes caractéristiques du seuil. Ainsi, notre travail confirme la pertinence des modèles à seuil pour décrire la dynamique de l'excitabilité neuronale.
43
Campos, Giovana de Almeida Coelho. "Análise da influência do sombreamento causado pelos edifícios na zona central de Curitiba." Universidade Tecnológica Federal do Paraná, 2014. http://repositorio.utfpr.edu.br/jspui/handle/1/1095.
Повний текст джерелаАнотація:
O crescimento urbano e o ritmo acelerado na concentração de pessoas nas cidades são inevitáveis. A verticalização das construções como solução para atender a necessidade da máxima ocupação do solo e para justificar a infraestrutura investida pelo poder público nas áreas centrais, causa consideráveis impactos no entorno em que estão inseridas. Contudo, a urbanização em si não é um problema, e sim a forma como as cidades estão sendo construídas e ocupadas. Diante disso, o trabalho apresenta como objetivo principal a verificação da influência do sombreamento gerado pelos edifícios altos dentro de um recorte definido na zona com maior capacidade de verticalização em Curitiba. Esta pesquisa foi desenvolvida em quatro etapas: a primeira, de fundamentação teórica com o estudo da literatura existente sobre o tema, a segunda para definição da região de estudo na cidade e os períodos a serem analisados, a terceira etapa para delimitação do recorte de estudo com análises de cada período e, a quarta com a elaboração das simulações computacionais nos softwares Auto CAD, Sketchup Pro, Excel e Ecotect para obtenção de resultados. Durante a evolução da pesquisa, verificou-se que, de fato, o nsombreamento causado pelos edifícios altos comprometem consideravelmente as construções vizinhas a eles e todo o seu entorno imediato. Além disso, foi concluído que Curitiba, uma cidade considerada fria, sofre nos períodos de inverno com o excessivo sombreamento nas áreas públicas entre quadras. Em contrapartida, as áreas abertas de lazer estão posicionadas adequadamente e não se prejudicam com a verticalização da Zona Central. De qualquer forma, a intenção de redução de impacto gerado por esses processos deve ser planejada em um contexto mais significativo. A elaboração de projetos deve ter como premissa a adequação ao clima e ao contexto local, da mesma forma que devem ser analisados os impactos ambientais dessas sobre as construções vizinhas e os espaços externos localizados em uma área de influência. A idéia de preservar o skyline já consolidado na cidade, evitando edifícios muito altos, pode ser uma alternativa para minimização dos impactos de sombreamento.Urban growth and the fast pace in the concentration of people in cities are inevitable. Building verticalization as a solution to attend the need of maximum land use and to justify the infrastructure invested by the government in central areas, cause considerable impacts on the environment which they are. However, urbanization is not a problem itself, but how cities are being built and occupied. Thus, the main goal of this work is to verify the shadow influence caused by tall buildings in a specific area inside of the zone with more capacity of verticalization in Curitiba. This research was developed in four steps: the first one was to study the existing literature about this topic, second to define study section in the city and periods to be analyzed, third step to delimit a zoom of study with analysis about all periods and, fourth with computer simulations on Auto CAD, Sketchup Pro, Excel and Ecotect softwares to obtain important results. During the evolution of this work, it was verified that the shading caused by tall buildings undertake considerably neighboring buildings and all surrounding area. Furthermore, it was concluded that Curitiba, a cold city, suffers in winter season due to excessive shading in public spaces between blocks. On the other hand, open spaces as squares are correctly positioned and do not harm with verticalization on the downtown zone. Anyway, the intention to reduce the impact caused by these processes must be planned in a more embracing context. Project elaboration must consider local climate and urban context, just as the environmental impacts of those on neighboring buildings and on open spaces. The idea of preserving skylines already consolidate, avoiding tall buildings, can be an alternative to minimize shading impacts.
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Kono, Frank Augusto Micheletto. "Um modelo de representação computacional baseado em conceitos de crescimento urbano associados a alvarás e primitivas em banco de dados espacial." Universidade Tecnológica Federal do Paraná, 2016. http://repositorio.utfpr.edu.br/jspui/handle/1/2035.
Повний текст джерелаАнотація:
A expansão urbana resultante do rápido progresso das cidades é um grande desafio para o desenvolvimento sustentável. Deste modo a concepção de modelos computacionais adequados que permitam a simulação, visualização espacializada e análise do processo de crescimento urbano é fundamental. Políticas de gestão de bairros e tipos de crescimento urbano são constituídos por equipamentos representados por diferentes tipos de alvarás ou concessões para abertura e funcionamento de negócios. Também por sistemas viários, sistemas de transporte, limites políticos e administrativos, zoneamento e arruamento. Estes mecanismos podem ser evidenciados em um banco de dados espacial por (a) dados abertos georreferenciados, um termo que caracteriza elementos humanos, informações demográficas, socioeconômicas, infraestrutura, condições ambientais e históricas, (b) diferentes geometrias (ponto, linha e polígono) e (c) utilização de funções espaciais para representar relações topológicas, direcionais ou métricas entre os equipamentos. Para construção e implementação do modelo proposto neste trabalho são utilizados os itens acima descritos (a, b, c) e um conjunto de perguntas elaboradas por especialistas na área de urbanismo, apontadas como conceitos primordiais à área de crescimento urbano. Em relação ao objetivo e a modelagem as mais relevantes contribuições encontram-se: (1) na representação por meio de um pequeno conjunto de primitivas em banco de dados com extensão espacial, (2) na elaboração de um vocabulário ou atribuição de uma semântica ao modelo, (3) na interação entre diferentes conceitos associados ao processo de crescimento urbano, (4) na possibilidade de ampliação e integração de outros domínios de dados georreferenciados e abertos e (5) no tempo de execução inferior a 10 segundos para 70% das consultas espaciais. As contribuições em relação ao experimento com os usuários, considerado a interface web desenvolvida neste trabalho, encontram-se: (1) no fato de que a ferramenta atende as necessidades no tocante a geração e visualização espacializada de dados para 4 de 5 usuários, (2) na interação com dados georreferenciados de alvarás de funcionamento, divisa de bairros e ruas e (3) na visualização dos dados do ponto de vista histórico e espacial.The resulting urban expansion from the rapid development of cities is a major challenge for sustainable development. Thus, the design of appropriate computational models that enable the simulation, spatialized visualization and analysis of the process of urban growth is critical. Neighborhood Management policies and types of urban growth are made up of equipment represented by different types of permits or concessions for opening and business operation. Also for road systems, transportation systems, political and administrative boundaries, zoning and street layout. It can be demonstrated in a spatial database by (a) georeferenced open data, a term that characterizes human elements, demographic, socio-economic, infrastructure, environmental and historical conditions, (b) different geometries (point, line and polygon) and (c) use of spatial functions for topological relations, directional or metrics between devices. Construction and implementation of the proposed model in this paper are used the above items (a, b, c) and a set of questions prepared by experts in the planning area, identified as primordial concepts to urban growth area. In relation to the goal and modeling the most relevant contributions are: (1) the representation by means of a small set of primitives in a database with spatial extension, (2) the development of a vocabulary or assigning a semantic the model, (3) the interaction between different concepts associated with the process of urban growth, (4) the possibility of expansion and integration of other areas of georeferenced data and open and (5) in the lower run time to 10 seconds to 70% spatial queries. Contributions in relation to the experiment with users, considered the web interface developed in this work: (1) on the fact that the tool covers the needs as regards the generation and spatialized visualization of data for 4 of 5 users, (2 ) interacting with georeferenced data of business licenses, neighborhoods and streets boundary and (3) in the data visualization from the historical and spatial point of view.
45
Allain, Laurent. "Etude des effets de la temperature sur la diffraction des rayons x par des composes semiconducteurs iii-v." Paris 6, 1988. http://www.theses.fr/1988PA066016.
Повний текст джерелаАнотація:
Determination par diffraction rx haute resolution des parametres cristallins de couches epitaxiques de gaalas ou gainas deposees sur les supports si, ge, ga, as, gap, inp et inas, en fonction de la temperature. Les coefficients de dilatation sont determines sur des materiaux relaxes et une extrapolation a d'autres systemes est possible. L'accord parametrique pour gaalas est realise a une temperature superieure a la temperature de depot et pour gainas, cet accord est realise a une temperature de depot dependant du taux de substitution ga/in
46
Meacci, Giovanni. "Physical Aspects of Min Oscillations in Escherichia Coli." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1169728830839-77682.
Повний текст джерелаАнотація:
The subject of this thesis is the generation of spatial temporal structures in living cells. Specifically, we studied the Min-system in the bacterium Escherichia coli. It consists of the MinC, the MinD, and the MinE proteins, which play an important role in the correct selection of the cell division site. The Min-proteins oscillate between the two cell poles and thereby prevent division at these locations. In this way, E. coli divides at the center, producing two daughter cells of equal size, providing them with the complete genetic patrimony. Our goal is to perform a quantitative study, both theoretical and experimental, in order to reveal the mechanism underlying the Min-oscillations. Experimentally, we characterize theMin-system, measuring the temporal period of the oscillations as a function of the cell length, the time-averaged protein distributions, and the in vivo Min-protein mobility by means of different fluorescence microscopy techniques. Theoretically, we discuss a deterministic description based on the exchange of Minproteins between the cytoplasm and the cytoplasmic membrane and on the aggregation current induced by the interaction between membrane-bound proteins. Oscillatory solutions appear via a dynamic instability of the homogenous protein distributions. Moreover, we perform stochastic simulations based on a microscopic description, whereby the probability for each event is calculated according to the corresponding probability in the master equation. Starting from this microscopic description, we derive Langevin equations for the fluctuating protein densities which correspond to the deterministic equations in the limit of vanishing noise. Stochastic simulations justify this deterministic model, showing that oscillations are resistant to the perturbations induced by the stochastic reactions and diffusion. Predictions and assumptions of our theoretical model are compatible with our experimental findings. Altogether, these results enable us to propose further experiments in order to quantitatively compare the different models proposed so far and to test our model with even higher precision. They also point to the necessity of performing such an analysis through single cell measurements.
47
Meacci, Giovanni. "Physical Aspects of Min Oscillations in Escherichia Coli." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A23940.
Повний текст джерелаАнотація:
The subject of this thesis is the generation of spatial temporal structures in living cells. Specifically, we studied the Min-system in the bacterium Escherichia coli. It consists of the MinC, the MinD, and the MinE proteins, which play an important role in the correct selection of the cell division site. The Min-proteins oscillate between the two cell poles and thereby prevent division at these locations. In this way, E. coli divides at the center, producing two daughter cells of equal size, providing them with the complete genetic patrimony. Our goal is to perform a quantitative study, both theoretical and experimental, in order to reveal the mechanism underlying the Min-oscillations. Experimentally, we characterize theMin-system, measuring the temporal period of the oscillations as a function of the cell length, the time-averaged protein distributions, and the in vivo Min-protein mobility by means of different fluorescence microscopy techniques. Theoretically, we discuss a deterministic description based on the exchange of Minproteins between the cytoplasm and the cytoplasmic membrane and on the aggregation current induced by the interaction between membrane-bound proteins. Oscillatory solutions appear via a dynamic instability of the homogenous protein distributions. Moreover, we perform stochastic simulations based on a microscopic description, whereby the probability for each event is calculated according to the corresponding probability in the master equation. Starting from this microscopic description, we derive Langevin equations for the fluctuating protein densities which correspond to the deterministic equations in the limit of vanishing noise. Stochastic simulations justify this deterministic model, showing that oscillations are resistant to the perturbations induced by the stochastic reactions and diffusion. Predictions and assumptions of our theoretical model are compatible with our experimental findings. Altogether, these results enable us to propose further experiments in order to quantitatively compare the different models proposed so far and to test our model with even higher precision. They also point to the necessity of performing such an analysis through single cell measurements.
48
Bahmer, Andreas. "Computer simulation of chopper neurons." Phd thesis, 2007. https://tuprints.ulb.tu-darmstadt.de/817/1/Promotion_bahmer.pdf.
Повний текст джерелаАнотація:
The aim of this work was to test a new model for oscillating neurons (chopper neurons) in the cochlear nucleus of the auditory system. In the beginning, it is shown that multiples of 0.4 ms are apparent in intrinsic oscillations in the auditory system and in pitch shift experiments. The existence of a time constant of 0.4 ms is explained by the assumption of a minimum chemical synaptic delay of this size between chopper neurons. The large dynamic range of periodicity coding, the small dynamic range of pure tone response, and the sharp frequency tuning of chopper neurons can be explained as a functional result of simultaneous projections from both the auditory nerve fibers and onset neurons to chopper neurons. As a consequence, the topology of the simulation of chopper neurons is as follows: To ensure the preference for multiples of 0.4 ms as observed in physiological and psychophysical experiments, chopper neurons are arranged in a circular network. The minimum number of two chopper neurons in this network results in a chopper period of 0.8 ms which corresponds to the proposed minimum refractory period of 0.8 ms. In the topology, chopper neurons receive input from both auditory nerve fibers and onset neurons. Simulations of the model show that in contrast to previous models, the present model can explain the preference for multiples of 0.4 ms. The model has also the advantage of explaining their large dynamic range of periodicity encoding of chopper neurons in spite of their narrow frequency tuning. Like the models investigated previously by other authors, the present model is able to simulate interspike intervals of spike trains of the chopper responses with high precision. Moreover, the simulation can explain essential properties of real chopper neurons by input from onset neurons. Simulations of the chopper neurons show that variation of the integration widths of onset neurons results in a corresponding variation of the spectral resolution of chopper neurons with smaller widths resulting in a higher resolution of frequency components. Variation of the integration widths of onset neurons also results in variation of the periodicity encoding of chopper neurons. Narrow integration widths lead to better periodicity encoding at low levels. At high levels broader integration widths lead to better periodicity encoding. Therefore it is a conflicting demand at high levels for to adapt the width of the integration to tuning or to encoding periodicity. The observed pitch dichotomy of individual preferences of human subjects for either periodicity pitch or the pitch of low spectral components of harmonic sounds (Schneider et al., 2005) can be explained by assuming adaptations of the width of the integration to either spectral or temporal coding. In contrast to physiological data, Hodgkin-Huxley(HH)-like models of single chopper neurons (e.g. from Rothman and Manis, 2003c) show a strong dependency of their interspike intervals when changing the input strength and do not show any preference for multiples of 0.4 ms. My simulations show that networks of HH-like chopper neurons with a synaptic delay of 0.4 ms do exhibit this preference and their chopper intervals are independent of changing the input strength. The HH-like model of chopper neurons by Rothman and Manis (2003c) does not account for short oscillating intervals of real chopper neurons. The model has been modified with genetic algorithms to generate oscillating intervals as short as 0.8 ms. This "fast Rothman chopper" has been successfully integrated in simulation topology. An enlarged network which is synchronized by a circuit of two "fast Rothman choppers" can account for a preference of ISIs for multiples of 0.4 ms as found in physiological data.
49
Yu-Qing, Huang, and 黃郁青. "Computer simulation of fatigue crack growth." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/96965593571277243920.
Повний текст джерелаАнотація:
碩士國立清華大學
動力機械工程學系
87
Fracture mechanics is the basic theorem , especially for the question of fatigue crack propagation .In fracture mechanics, Stress intensity factor is proof to be a good parameter which can be a good index for the stress and strain of the crack tip. Therefore , stress intensity factor is the basic fundamental for the research of fatigue crack propagation .In the same material,if two cracks have the same length ,they will have the same stress intensity factor. so the two crack will have the same stress in the tip and will have the same rate of fatigue crack growth. As mention above, there will be one relation between fatigue crack growth rate and stress intensity factor. In the early 1960s, Paris, et at. Demonstrated that fracture mechanics is a useful tool for characterizing crack growth by fatigue. Since that time, the application of fracture mechanics to fatigue problems have become almost routine. Because the relation between stress intensity factor ,K,and fatigue crack growth,da,is actually a distribution function which distribute in probable range. Dr.Chiang[2] use the method of statistic to calculate the relation between the expect value of K and da. From 1961 far as,the direction of fatigue crack tip propagation , for convenient , is solved by Mode I crack, but in actually, crack tip will propagation if different direction. The paper will actually describe the propagation of fatigue crack. Therefore, several discrete direction is supposed to describe such condition. Suppose the probability of crack propagation is in proportion to its axial stress. And the method of choose the direction is done by Monte-Carlo method . Once the direction is chosen,the next step is to calculate the propagation length in this direction. This paper use equation (3-7) in this paper to calculate this value.Therefore, we can describe the propagation process of fatigue crack from its initial step to final step from computer simulation.
50
WANG, MEN-CHIEH, and 王門傑. "Computer Simulation of Thermobiological Effects on Tumor Growth." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/23136966512242935891.
Повний текст джерелаАнотація:
碩士國立臺灣大學
醫學工程學研究所
90
Abstract A computer simulation program was written based on the tumor cell growth factors and the changes of the tumor growth due to a series of hyperthermia treatments. The tumor cell growth factors are related to the cell-cycle and the spatial location of the tumor cell, and the Gompertz function was used to fit the cell growth curve. In addition, some supplementary programs were written to simulate the cell death based on the relationship between the survival rate and the thermal dose for a series of hyperthermia treatments. The simulation results show that thermal dose with 10% cell survival rate can kill tumor cells completely after a series of 3 to 4 treatments with an interval of 24 to 48 hours. A higher thermal dose equivalent to 1% of cell survival requires only 2 to 3 treatment with an interval of 24 to 48 hours effectively kill the entire tumor cells. However, the treatments will not be effective when the interval is longer than 72 hours. This computer program can be used to simulate the tumor cell growth and killing for a given series of thermal treatments. The treatment arrangement of a specific tumor may be based on the simulation result of this program when the conditions of the tumor are given. While, further study is required to modify the program based on the experimental and clinical results.