Dissertations / Theses on the topic 'Conductive Elements'
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1
Gilvary, B. "Element by Element methods for heat conduction problems." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378333.
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Lediaev, Laura Marie. "Finite element modeling of piezoelectric bimorphs with conductive polymer electrodes." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/lediaev/LediaevL0510.pdf.
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The purpose of my research has been to find a good way to solve for the mechanical and electrical behavior of piezoelectric polymer bimorphs which are electroded with a low to medium conductivity material. Traditionally, metal with very high conductivity has been used as the electrode material. Any applied voltage to an electrode will be distributed nearly instantaneously and uniformly throughout the electrode. Because of this quality, the voltage was assumed to be known and uniform for any applied voltage signal, including high frequency signals. The disadvantage of metal is that it is stiffer than polymers, and thus impedes the bending of the bimorph to a greater extent than for comparable polymer electrodes. With the modern invention of conductive polymers with acceptably high conductivities, it is now possible to manufacture piezoelectric devices with finite conductivity electrodes. For all but the very lowest frequencies of applied voltage signals, the voltage distribution cannot be assumed to be uniform throughout the electrode, nor can it be assumed to be exactly in phase. With finite conductivity electrodes there will be a loss in voltage amplitude due to resistivity, and there will also be a phase lag. The piezoelectric problem involves solving a coupled set of differential equations which involve mechanical displacement and electric potential. The electrical behavior of the electrodes is also included in the formulation, so that the voltage distribution in the electrodes is solved for simultaneously with the mechanical displacement and electric potential in the piezoelectric sheets. In this dissertation the coupled set of differential equations was solved using the Finite Element Method with quadratic Lagrange finite elements. The piezoelectric polymer which was modeled was polyvinylidene fluoride (PVDF). The conductive polymer of interest was PEDOT-PSS, although the model is valid for any type of isotropic finite conductivity material. The results of the work show that for moderate conductivity, the mechanical response of the bimorph is very good. There will not be a large phase lag within the first frequency mode. The bimorph resonates at low frequencies, and so any large effect from finite conductivity would only occur at higher modes.
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Yin, John Zhihao. "Finite element model of cardiac electrical conduction." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/26859.
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Hamina, M. (Martti). "Some boundary element methods for heat conduction problems." Doctoral thesis, University of Oulu, 2000. http://urn.fi/urn:isbn:951425614X.
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Abstract
This thesis summarizes certain boundary element methods
applied to some initial and boundary value problems.
Our model problem is the two-dimensional homogeneous heat conduction
problem with vanishing initial data. We use the heat potential
representation of the solution. The given boundary conditions,
as well as the choice of the representation formula,
yield various boundary integral equations. For the sake of simplicity,
we use the direct boundary integral approach, where
the unknown boundary density appearing in the boundary integral
equation is a quantity of physical meaning.
We consider two different sets of boundary conditions, the Dirichlet problem,
where the boundary temperature is given and the Neumann problem,
where the heat flux across the boundary is given.
Even a nonlinear Neumann condition satisfying certain monotonicity
and growth conditions is possible. The approach yields
a nonlinear boundary integral equation of the second kind.
In the stationary case, the model problem reduces to a potential
problem with a nonlinear Neumann condition. We use the spaces of smoothest
splines as trial functions. The nonlinearity is approximated by using the
L2-orthogonal projection. The resulting collocation scheme retains
the optimal L2-convergence. Numerical experiments are in
agreement with this result.
This approach generalizes to the time dependent case.
The trial functions are tensor products of piecewise linear
and piecewise constant splines. The proposed projection method
uses interpolation with respect to the space variable and the orthogonal
projection with respect to the time variable. Compared to the
Galerkin method, this approach simplifies the realization of the
discrete matrix equations.
In addition, the rate of the convergence is of optimal order.
On the other hand,
the Dirichlet problem, where the boundary temperature is given,
leads to a single layer heat operator equation of the first kind.
In the first approach, we use tensor products of piecewise linear splines
as trial functions with collocation at the nodal points.
Stability and suboptimal L2-convergence of the method were proved in the
case of a circular domain. Numerical experiments indicate the
expected quadratic L2-convergence.
Later, a Petrov-Galerkin approach was proposed, where the trial functions were
tensor products of piecewise linear and piecewise constant splines.
The resulting approximative scheme is stable and
convergent. The analysis has been carried out in the cases of
the single layer heat operator and the hypersingular heat operator.
The rate of the convergence with respect to the L2-norm
is also here of suboptimal order.
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Baranowski, Robert Paul. "Numerical modelling of current transfer in nonlinear anisotropic conductive media." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/104785.
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Current transfer behaviour in anisotropic superconducting bodies is the central topic of this thesis and focuses on the effect that the nonlinearity of the electric field dependence upon the local current density value and anisotropy have on the nature of current transport. The main motivation for this work was the desire for a better understanding of the conceptually difficult behaviour of current transport in superconducting bodies and examines current transfer quantitatively for a number of important problems on the macroscopic and microscopic scale. This behaviour is examined both experimentally and using computer models. The successful development of a powerful, robust and adaptable numerical model for analysing the complex current transfer behaviour has been the primary aim of this work. The range of parameters appropriate to macroscopic models of the Bi-2212 CRT system has been experimentally examined using a specifically constructed apparatus for the measurement of current transport characteristics. A study of the self-field properties of the Bi-2212 CRT material using a new experimental technique and mathematical analysis is presented and has allowed the importance of the self-field effect in the numerical model to be assessed. An essential requirement for the practical application of high current superconducting devices is the development of low resistance current contacts. The research presented examines this macroscopic current transfer problem and aims to explain experimentally observed current transfer characteristics at high applied currents. Existing models cannot explain these characteristics. Current transfer on the microscopic scale is also examined. Models of current transfer have been developed from descriptions of specific microstructures that are thought to characterise the microstructure of Bi-2223 and Bi-2212 silver-sheathed tapes. This thesis specifically presents modelling of current transfer between c-axis, low-angle c-axis and edge-on c-axis tilt oriented grain interfaces; the principal current transfer paths between individual current elements of the microstructural models of current flow in polycrystalline HTSs.
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Fischer, Kristin Mckeon. "Creation and Characterization of Several Polymer/Conductive Element Composite Scaffolds for Skeletal Muscle Tissue Engineering." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/77305.
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After skeletal muscle damage, satellite cells move towards the injured area to assist in regeneration. However, these cells are rare as their numbers depend on the age and composition of the injured muscle. This regeneration method often results in scar tissue formation along with loss of function. Although several treatment methods have been investigated, no muscle replacement treatment currently exists. Tissue engineering attempts to create, repair, and/or replace damaged tissue by combining cells, biomaterials, and tissue-inducing substances such as growth factors. Electrospinning produces a non-woven scaffold out of biomaterials with fiber diameters ranging from nanometers to microns to create an extracellular-like matrix on which cells attach and proliferate. Our focus is on synthetic polymers, specifically poly(D,L-lactide) (PDLA), poly(L-lactide) (PLLA), and poly(ε-caprolactone) (PCL). Skeletal muscle cells grown on electrospun scaffolds tend to elongate and fuse together thus, mimicking natural tissue. Electrical stimulation has been shown to increase the number of cells fused in culture and decreased the time needed in culture for cells to contract. Therefore, a conductive element was added to each scaffold, specifically polyaniline (PANi), gold nanoparticles (Au Nps), and multi-walled carbon nanotubes (MWCNT). Our project goal is to create a polymeric, conductive, and biocompatible scaffold for skeletal muscle regeneration.
PANi and PDLA were mixed to form the following solutions 24% (83% PDLA/17% PANi), 24% (80% PDLA/20% PANi), 22% (75%PDLA/25% PANi), 29% (83% PDLA/17% PANi), and 29% (80% PDLA/20% PANi). Only the 75/25 electrospun scaffold was conductive and had a calculated conductivity of 0.0437 S/cm. Scaffolds with larger amounts of PANi were unable to be electrospun. PDLA/PANi scaffolds were biocompatible as primary rat skeletal muscle cells cultured in vitro did attach. However, the scaffolds shrunk, degraded easily, and became brittle. Although PDLA/PANi scaffolds were easily manufactured, our results indicate that this polymer mixture is not appropriate for skeletal muscle scaffolds.
PLLA and Au Nps were electrospun together to form three composite scaffolds: 7% Au-PLLA, 13% Au-PLLA, and 21% Au-PLLA. These were compared to PLLA electrospun scaffolds. Measured scaffold conductivities were 0.008 ± 0.015 S/cm for PLLA, 0.053 ± 0.015 S/cm for 7% Au-PLLA, 0.076 ± 0.004 S/cm for 13% Au-PLLA, and 0.094 ± 0.037 S/cm for 21% Au-PLLA. It was determined via SEM with a Bruker energy dispersive x-ray spectrometer (EDS) that the Au Nps were not evenly distributed within the scaffolds as they had agglomerated. Rat primary muscle cells cultured on the three Au-PLLA scaffolds displayed low cellular activity. A second cell study was conducted to determine Au NPs toxicity. The results show that the Au Nps were not toxic to the cells and the low cellular activity may be a marker for myotube fusion. Elastic modulus and yield stress values for the three Au-PLLA scaffolds measured on days 0, 7, 14, 21, and 28 were much larger than skeletal muscle tissue. Due to the larger mechanical properties and Au Nps agglomeration, a third polymer and conductive element scaffold was investigated.
PCL was chosen as the new synthetic polymer as it had a lower elastic modulus and high elongation. MWCNT were chosen as the conductive element as they disperse well within PCL when acid functionalized. A third component was added to the scaffold to help it move similar to skeletal muscle. Ionic polymer gels (IPG) are hydrogels that respond to an external stimulus such as temperature, pH, light, and electric field. A poly(acrylic acid)/poly(vinyl alcohol) (PAA/PVA) mixture is one type of IGP that responds to an electric field. The scaffolds were coaxially electrospun so that each fiber had a PCL-MWCNT interior with a PAA/PVA sheath. These scaffolds were compared to electrospun PCL and PCL-MWCNT ones. The addition of MWCNT to the PCL did increase scaffold conductivity. Actuation of the PCL-MWCNT-PAA/PVA scaffold occurred when 15V and 20V were applied. All three scaffolds had rat primary skeletal muscle cells attached but, more multinucleated cells with actin interaction were seen on PCL-MWCNT-PAA/PVA scaffolds. Once again the mechanical properties were greater than muscle, but because of its ability to actuate we believe the PCL-MWCNT-PAA/PVA scaffold has potential as a bioartificial muscle.
Further characterization of the PCL-MWCNT-PAA/PVA included varying the ratios of PAA/PVA, smaller crosslinking times, and lower amounts of MWCNT. Four ratios, 83/17, 60/40, 50/50, and 40/60, were successfully coaxially electrospun with PCL and MWCNT. Overall, very few differences were seen between the four ratios in conductivity, cellular biocompatibility, actuation angular speed, and mechanical properties. The 83/17 and 40/60 ratios were chosen for additional investigation into mechanical properties and actuation. As the mechanical properties of the two types of scaffolds did not change significantly through degradation, lower PVA crosslinking times were tested. No significant effects were found and it was hypothesized that the evaporation of the solution played a role in the crosslinking process. The smaller MWCNT amount scaffolds also did not significantly affect the mechanical properties or the actuation angular speeds. More work into lowering the scaffold mechanical properties while increasing the actuation angular speed is necessary.
Though the mechanical properties for the 83/17 and 40/60 scaffolds remained high compared to skeletal muscle, we also looked for differences in in vivo biocompatibility. Both scaffolds were implanted into the right vastus lateralis muscle of Sprague-Dawley rats. The left vastus lateralis muscle served as either the PBS injected sham surgery or an unoperated control. Biocompatibility was evaluated using enzymes, creatine kinase (CK) and lactate dehydrogenase (LDH), levels, fibrosis formation, inflammation, scaffold cellular infiltration, and neovascularization on days 7, 14, 21, and 28 post-implantation. Fibrotic tissue formation, inflammation, and elevated CK and LDH levels were observed initially but responses decreased during the four week study. Cells infiltrated the scaffolds and histological staining showed more fibroblasts than myogenic cells initially but over time, the fibroblasts decreased and myogenic cells increased. Neovascularization of both scaffolds was also recorded. PCL-MWCNT-PAA/PVA scaffolds were determined to be biocompatible, but some differences between the two types were noted. The 83/17 scaffolds caused less of a response from the body compared to the 40/60 scaffolds and had more myogenic cells attached. However, the 40/60 scaffolds had a larger number of blood vessels running through the scaffold. In conclusion, we have successfully fabricated a polymeric, conductive, and biocompatible scaffold that can actuate for skeletal muscle tissue engineering. Although our results are promising, more work is necessary to continue developing and refining the scaffold.Ph. D.
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Gaugele, Timo [Verfasser]. "Application of the Discrete Element Method to Model Ductile, Heat Conductive Materials / Timo Gaugele." Aachen : Shaker, 2011. http://d-nb.info/1075437350/34.
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Zhang, Lei Ph D. Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science. "A boundary element method with surface conductive absorbers for 3-D analysis of nanophotonics." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62462.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 127-132).
Fast surface integral equation (SIE) solvers seem to be ideal approaches for simulating 3-D nanophotonic devices, as these devices generate fields both in an interior channel and in the infinite exterior domain. However, many devices of interest, such as optical couplers, have channels that cannot be terminated without generating reflections. Generating absorbers for these channels is a new problem for SIE methods, as the methods were initially developed for problems with finite surfaces. In this thesis, we show that the obvious approach for eliminating reflections, making the channel mildly conductive outside the domain of interest, is inaccurate. We propose a new method in which the absorber has gradually increasing surface conductivity; such an absorber can be easily incorporated in fast integral equation solvers. We present two types of PMCHW-based formulations to incorporate the surface conductivity into the SIE method. The accuracy of the two-type formulations are examined and discussed using an example of the scattering of a Mie sphere with surface conductivities. Moreover, we implement two different FFT-accelerated algorithms for the periodic non-absorbing region and the non-periodic absorbing region. In addition, we use perturbation theory and Poynting's theorem, respectively, to calculate the field decay rate due to the surface conductivity. We show a saturation phenomenon when the electrical surface conductivity is large. However, we show that the saturation is not a problem for the surface absorber since the absorber typically operates in a small surface conductivity regime. We demonstrate the effectiveness of the surface conductive absorber by truncating a rectangular waveguide channel. Numerical results show that this new method is orders of magnitude more effective than a volume absorber. We also show that the transition reflection decreases in a power law with increasing the absorber length. We further apply the surface conductive absorber to terminate a waveguide with period-a sinusoidally corrugated sidewalls. We show that a surface absorber that can perform well when the periodic waveguide system is excited with a large group-velocity mode may fail when excited with a smaller group-velocity mode, and give an asymptotic relation between the surface absorber length, transition reflections and group velocity. Numerical results are given to validate the asymptotic prediction.
by Lei Zhang.
Ph.D.
9
Guven, Ibrahim. "A coupled finite element-boundary element method for two dimensional transient heat conduction and thermoelastic analyses." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/289183.
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A new algorithm for coupling boundary and finite element methods is developed for transient two dimensional heat conduction and thermoelastic analyses of regions with dissimilar materials and geometric discontinuities. Such regions are susceptible to failure initiation in electronic devices. As the component size decreases while enhancing performance, the accurate prediction of thermal and thermoelastic response of such devices is critical for achieving acceptable design. This study concerns both the conduction heat transfer and thermoelasticity. Solution to transient heat conduction equation provides the non-uniform thermal field for the thermoelastic analysis. Although the finite element method (FEM) is highly efficient and commonly used, its application with conventional elements to complex layered structures with length parameters varying in order of magnitudes leads to inaccurate and mesh dependent results. The accuracy of the results from the boundary element method (BEM) formulation, which requires computationally intensive integration schemes, is much higher than that of the FEM. This new algorithm combines the advantages of both methods while not requiring the commonly accepted iterations along the interfaces between BEM and FEM domains. The BEM part of the solution, acting as a global element, captures the singular nature of the solution variables arising from geometrical and material discontinuities and, eliminates the mesh dependency.
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Barnes, Johanna S. "Teachers' continuation of action research elements after conducting studies during a Master's program." Thesis, University of South Dakota, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3589862.
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Teachers are critical to student learning in the classroom, and just like students, teachers perform better when they are able to make choices based on what is relevant to them. Action research is a way for teachers to systematically inquire and reflect to make necessary improvements in practice for student learning. This study involved teachers who had conducted action research as a component of their Master's in Curriculum and Instruction program at one Midwest college. It examined teachers' perceived lasting benefits of conducting action research, the elements they continue to implement, and the supports of and limitations to continuation of the practice.
As part of a mixed-method study, a researcher-developed survey was first used. Seventy-seven teachers provided responses to the online survey. Fifteen survey participants volunteered to offer narrative elaboration of their responses in a follow-up telephone interview.
The compiled data included totals and percentages from the survey and themes and quotations from the teachers' narrative responses. Together, the findings revealed that 98% of the teachers felt they benefited from conducting action research. They perceived the greatest professional benefits of conducting action research to be thinking more reflectively, positively impacting student learning, and inquiring more about their practice.
Teachers were continuing to conduct action research based on the impact they perceived the practice had on their students' success in the classroom. The elements they continued most often were identifying a focus, collecting and analyzing data, and reflecting on the process. This practice allowed them to learn from evaluating the effectiveness of their implementations and realize there was rigor and relevance to what they were doing.
With 92% of participants desiring to continue action research, two major factors were given as greatest support for continuation. Teachers desired a combination of collaboration with peers on issues that mattered to them and time in the school day to collaborate and conduct action research.
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Samonds, M. T. "Finite element simulation of solidification in sand mould and gravity die castings." Thesis, Swansea University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384446.
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Wassef, Karim N. "Nonlinear transient finite element analysis of conductive and ferromagnetic regions using a surface admittance boundary condition." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/13318.
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Ayasoufi, Anahita. "Numerical Simulation of Heat Conduction with Melting and/or Freezing by Space-Time Conservation Element and Solution Element Method." See Full Text at OhioLINK ETD Center (Requires Adobe Acrobat Reader for viewing), 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1103147485.
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Dissertation (Ph.D.)--University of Toledo, 2004.Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Engineering." Bibliography: leaves 194-211.
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Kell, James. "Melt pool and microstructure manipulation using diffractive holographic elements in high power conduction laser welding." Thesis, Loughborough University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479315.
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Erhart, Kevin. "EFFICIENT LARGE SCALE TRANSIENT HEAT CONDUCTION ANALYSIS USING A PARALLELIZED BOUNDARY ELEMENT METHOD." Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2973.
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A parallel domain decomposition Laplace transform Boundary Element Method, BEM, algorithm for the solution of large-scale transient heat conduction problems will be developed. This is accomplished by building on previous work by the author and including several new additions (most note-worthy is the extension to 3-D) aimed at extending the scope and improving the efficiency of this technique for large-scale problems. A Laplace transform method is utilized to avoid time marching and a Proper Orthogonal Decomposition, POD, interpolation scheme is used to improve the efficiency of the numerical Laplace inversion process. A detailed analysis of the Stehfest Transform (numerical Laplace inversion) is performed to help optimize the procedure for heat transfer problems. A domain decomposition process is described in detail and is used to significantly reduce the size of any single problem for the BEM, which greatly reduces the storage and computational burden of the BEM. The procedure is readily implemented in parallel and renders the BEM applicable to large-scale transient conduction problems on even modest computational platforms. A major benefit of the Laplace space approach described herein, is that it readily allows adaptation and integration of traditional BEM codes, as the resulting governing equations are time independent. This work includes the adaptation of two such traditional BEM codes for steady-state heat conduction, in both two and three dimensions. Verification and validation example problems are presented which show the accuracy and efficiency of the techniques. Additionally, comparisons to commercial Finite Volume Method results are shown to further prove the effectiveness.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Rickelt, Stefan [Verfasser]. "Discrete Element Simulation and Experimental Validation of Conductive and Convective Heat Transfer in Moving Granular Material / Stefan Rickelt." Aachen : Shaker, 2011. http://d-nb.info/1071528858/34.
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Soto, Nathan Daniel. "Characterizing Nerve Fiber Activation By Varying Fiber Diameter And Depth Within a Conductive Medium: A Finite Element Approach." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/608.
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In some instances neuropathies can be diagnosed through a conduction velocity test. However, not all neuropathies can be classified using this method. Gaining an understanding of how the stimulus level varies for different fiber sizes at different fiber depths within a conductive medium will provide useful information for simulation studies.
Following a two-step approach using COMSOL and MATLAB, a simulation was implemented to investigate the stimulus necessary to activate different sized fibers at different depths. In this two-step approach, COMSOL was used to describe the voltage profile that would be present within a conductive medium after a stimulus was applied. This voltage profile could then be analyzed using a program written in MATLAB to determine if the applied stimulus was sufficient to activate a given fiber. The analysis was performed using a stimulus method using a constant DC source. Two finite element models were also used, one using a homogeneous medium and the other inhomogeneous.
A three dimensional plot was created to describe the effect of both the depth and diameter of a fiber on the required stimulus for fiber activation. From this plot, an equation was fit to the data to represent the activation function of a nerve fiber at various diameters and depths.
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Rosenband, Linda Maj. "The study of aberrant conduction in myocardial tissue using a finite-element computer simulation." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/72312.
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Figueiredo, Patric. "Iterative method for solving inverse heat conduction problems." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14400.
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Safi, Iyad. "A study of reactive magnetron sputtering of alloy transparent conducting oxides from elemental targets." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/14118.
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Methods of reactive magnetron sputtering using the sequential oxidisation of a sputtered metal film from two magnetron sources, in a rotating substrate system, have been developed. A rotation rate of around one revolution per second enhanced atomic level mixing of the film constituents on the substrate. Depending on the materials involved, two very fast feedback methods were employed to automatically control the admission rate of oxygen into the sputtering system. These methods were plasma emission monitoring (PEM), which was used to control the reactive sputter-deposition of In, Zn, W, V, Mo and Ti oxide, and voltage control, which was used to control the reactive sputter-deposition of Zn, Cu, Pb and Al oxide. The stoichiometry of the film was controlled by PEM or voltage control on one magnetron, and dopants were added by sputtering from the other magnetron. In other words, the former magnetron served two purposes; the first was to sputter metal and oxidise it, and the second purpose was to oxidise the metal sputtered from the other magnetron.
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Erhart, Kevin. "A Laplace Transform Boundary Element Method Approach to the Solution of Large-Scale Transient Heat Conduction Problems." Honors in the Major Thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/705.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering and Computer Science
Mechanical Engineering
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Lesnic, Daniel. "Boundary element methods for solving steady potential flow problems and direct and inverse unsteady heat conduction problems." Thesis, University of Leeds, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404773.
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Dang, Kai. "Modèles de conduction électrique pour la stimulation de l'implant cochléaire." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4043/document.
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De nombreux modèles numériques ont été proposés pour mieux comprendre comment le courant électrique est répartit lors d’une stimulation électrique par implant cochléaire. Ceci permet à terme d’optimiser la géométrie des électrodes et les stratégies de stimulation. Les modèles précédemment proposés modélisent les modèles d'interface électrochimique de façon très basique, et ne prennent généralement compte que de l'intensité du courant sur les électrodes. Par conséquent, il leur est difficile de simuler la dynamique temporelle de la stimulation ou de modéliser la répartition du courant en fonction de différents modes de stimulation contrôlés en tension, tels que le mode de de retour commun (Common Ground), ou de retour multiple (Multi-Mode Grounding). Dans cette thèse, nous avons développé un nouveau modèle surfacique de la cochlée. Le modèle géométrique dépend d'un ensemble de paramètres permettant d'ajuster la forme de la cochlée, en utilisant par exemple des données histologiques, des scans CT, ou encore des maillages de surface. Un modèle paramétrique nous a permis de comparer les courants générés par les modèles d'électrodes actuellement disponibles et par un nouveau type d'électrode - faisceau transmodiolaire. Le modèle peut prendre en compte des courants ou des tensions en entrée à chaque électrode, ce qui permet de simuler le mode de retour commun ou multiple. Afin de valider les résultats de simulation et calibrer les paramètres du modèle, nous avons créé un système permettant d'acquérir des mesures in-situ et in-vitro. Les données enregistrées ont permis de valider le modèle combinant le modèle d'interface électrochimique et le modèle tridimensionnel de cochléeComputational models have been widely used to improve the knowledge of the current distribution behavior in cochlear implant stimulations, optimizing electrode designs and stimulation strategies. The existing models employed no or simple electrochemical interface models and took current intensity on the electrodes as input. Therefore they have difficulties in making time domain simulations and simulating the stimulation modes that have voltage constraints, such as the Common Ground and the Multi-Mode Grounding modes. In this PhD work, a new parametric surface mesh model of the cochlea has been developed. The shape of the model is controlled by a set of input parameters which can be tuned to fit the cochlear shape acquired from histological images, CT scans or existing cochlear mesh models. The symmetric boundary element method, which was implemented in OpenMEEG, has been applied on the model to simulate the current distribution of the cochlear implant stimulation. Using the parametric model, comparisons on the current field has been made between the existing electrode layouts and a new transmodiolar electrodes. The new model can take either current or voltage as input for each electrode to simulate the common ground and multi-mode grounding modes. By coupling the surface model with lumped capacitor and constant phase element models, time domain simulation of the stimulation waveform has also been achieved. To validate the simulation results and calibrate the parameters of the model, in-situ and in-vitro measurements have been carried out with self-made devices. The recorded data proved the effectiveness of combining lumped components with the surface model
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Maréchal, Yves. "Modélisation des phénomènes magnétostatiques avec terme de transport : application aux ralentisseurs électromagnétiques." Grenoble INPG, 1991. http://www.theses.fr/1991INPG0021.
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La méthode des éléments finis nodaux est employée pour résoudre les phénomènes électromagnétiques avec terme de transport et alimentation continue en deux et trois dimensions. Toi discrimination spatiale de type "Petrov-Galerkine" rend la solution numérique inconditionnellement stable. Une technique générale de raccordement de maillages est développée pour traiter l'interface entre les régions en mouvement et les régions fixes. Une nouvelle formulation tridimensionnelle permet d'établir un couplage efficace entre régions à forte perméabilité et l'air. La modélisation des ralentisseurs électromagnétiques sert de support de validation
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Wood, Sandra Jean. "Determination of effective thermal conductivity of media surrounding underground transmission cables." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17390.
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Ghattassi, Mohamed. "Modélisation, observation et commande d’une classe d’équations aux dérivées partielles : application aux matériaux semi-transparents." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0123/document.
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Le travail présenté dans ce mémoire nous a permis d’étudier d’un point de vue théorique et numérique le transfert de chaleur couplé par rayonnement et conduction à travers un milieu semi-transparent, gris et non diffusant dans une géométrie multidimensionnelle 2D. Ces deux modes de transfert de chaleur sont décrits par un couplage non linéaire de l’équation de la chaleur non linéaire (CT) et de l’équation du transfert radiatif (ETR). Nous avons présenté des résultats d’existence, d’unicité locale de la solution pour le système couplé avec des conditions aux limites de type Dirichlet homogènes en utilisant le théorème du point fixe de Banach. Par ailleurs, les travaux réalisés nous ont permis de mettre au point un code de calcul qui permet de simuler la température. Nous avons utilisé la quadrature S_N pour la discrétisation angulaire de l’ETR. La discrétisationde l'ETR dans la variable spatiale est effectuée par la méthode de Galerkin discontinue (DG) et en éléments finis pour l'équation de la chaleur non linéaire. Nous avons démontré la convergence du schémanumérique couplé en utilisant la méthode du point fixe discret. Le modèle discret, sous la forme d’équations différentielles ordinairesnon linéaires obtenu après une approximation nous a permis de fairel’analyse et la synthèse d’estimateurs d’état et de lois de commandepour la stabilisation. Grâce à la structure particulière du modèle età l’aide du DMVT. Nous avons proposé un observateur d’ordre réduit.D’autre part nous avons réussi à construire une matrice de gain quiassure la stabilité de l’observateur proposé. Une extension au filtrage $\mathcal{H}_{\infty}$ est également proposée. Une nouvelleinégalité matricielle (LMI) est donnée dans le cas d’une commandebasée observateur. Nous avons étendu à l’approche d’ordre réduit dans le cas de la commande basée observateur et nous avons montré la stabilité sous l’action de la rétroaction. De même une extension au filtrage $\mathcal{H}_{\infty}$ est également proposée. Tous les résultats sont validés par des simulations numériquesThis thesis investigates the theoretical and numerical analysis of coupled radiative conductive heat transfer in a semi-transparent, gray and non-scattering 2D medium. This two heat transfer modes are described by the radiative transfer equation (RTE) and the nonlinear heat equation (NHE). We proved the existence and uniqueness of the solution of coupled systems with homogeneous Dirichlet boundary conditions using the fixed-point theorem. Moreover, we developed a useful algorithm to simulate the temperature in the medium. We used the quadrature $S_{N}$ for the angular discretization of the RTE. The spatial discretization of RTE was made by the discontinuous Galerkin method (DG) and the finite element method for the non-linear heat equation. We have shown the convergence and the stability of the coupled numerical scheme using the discrete fixed point. The discrète model obtained after an approximation allowed us to do the analysis and synthesis of state estimators and feedback control design for stabilization of the system. Thanks to the special structure of the model and using the Differential Mean Value Theorem (DMVT), we proposed a reduced order observer and we construct a gain matrix, which ensures the exponential stability of the proposed observer and guarantees the boundedness of the estimate vector. An extension to $\mathcal{H}_{\infty}$ filtering is also provided. We have extended the reduced order approach in the case of the observer-based controller and we proved the exponential stability under the control feedback law. Similarly, an extension to $\mathcal{H}_{\infty}$ filtering is also provided. The obtained results were validated through several numerical simulations
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Liang, Yan. "Integrated Frequency-Selective Conduction Transmission-Line EMI Filter." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26360.
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The multi-conductor lossy transmission-line model and finite element simulation tool are used to analyze the high-frequency attenuator and the DM transmission-line EMI filter. The insertion gain, transfer gain, current distribution, and input impedance of the filter under a nominal design are discussed. In order to apply the transmission-line EMI filter to power electronics systems, the performance of the filter under different dimensions, material properties, and source and load impedances must be known. The influences of twelve parameters of the DM transmission-line EMI filter on the cut-off frequency, the roll-off slope, and other characteristics of the insertion gain and transfer gain curves are investigated. The most influential parameters are identified. The current sharing between the copper and nickel conductors under different parameters are investigated. The performance of the transmission-line EMI filter under different source and load impedances is also explored.
The measurement setups of the DM transmission-line EMI filter using a network analyzer have been discussed. The network analyzer has a common-ground problem that influences the measured results of the high-frequency attenuator. However, the common-ground problem has a negligible influence on the measured results of the DM transmission-line EMI filter. The connectors and copper strips between the connectors and the filter introduce parasitic inductance to the measurement setup. Both simulated and measured results show that transfer gain curve is very sensitive to the parasitic inductance. However, the insertion gain curve is not sensitive to the parasitic inductance. There are two major methods to reduce the parasitic inductance of the measurement setup: using small connectors and applying a four-terminal measurement setup. The transfer gain curves of three measurement setups are compared: the two-terminal measurement setup with BNC connectors, the two-terminal measurement setup with Sub Miniature version B (SMB) connectors, and the four-terminal measurement setup with SMB connectors. The four-terminal measurement setup with SMB connectors is the most accurate one and is applied for all the transfer gain measurements in this dissertation.
This dissertation also focuses on exploring ways to improve the performance of the DM transmission-line EMI filter. Several improved structures of the DM transmission-line EMI filter are investigated. The filter structure without insulation layer can greatly reduce the thickness of the filter without changing its performance. The meander structure can increase the total length of the filter without taking up too much space and results in the cut-off frequency being shifted lower and achieving more attenuation. A prototype of the two-dielectric-layer filter structure is built and measured. The measurement result confirms that a multi-dielectric-layer structure is an effective way to achieve a lower cut-off frequency and more attenuation.
This dissertation proposes a broadband DM EMI filter combining the advantages of the discrete reflective LC EMI filter and the transmission-line EMI filter. Two DM absorptive transmission-line EMI filters take the place of the two DM capacitors in the discrete reflective LC EMI filter. The measured insertion gain of the prototype has a large roll-off slope at low frequencies and large attenuation at high frequencies. The dependence of the broadband DM EMI filter on source and load impedances is also investigated. Larger load (source) impedance gives more attenuation no matter it is resistive, inductive or capacitive. The broadband DM EMI filter always has more high-frequency attenuation than the discrete reflective LC EMI filter under different load (source) impedances.Ph. D.
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Ramos, Gustavo Roberto. "Método multiescala para modelagem da condução de calor transiente com geração de calor : teoria e aplicação." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/133134.
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O presente trabalho trata da modelagem da condução de calor transiente com geração de calor em meios heterogêneos, e tem o objetivo de desenvolver um modelo multiescala adequado a esse fenômeno. Já existem modelos multiescala na literatura relacionados ao problema proposto, e que são válidos para os seguintes casos: (a) o elemento de volume representativo tem tamanho desprezível quando comparado ao comprimento característico macroscópico (e como consequência, a microescala tem inércia térmica desprezível); ou (b) a geração de calor é homogênea na microescala. Por outro lado, o modelo proposto nesta tese, o qual é desenvolvido utilizando uma descrição variacional do problema, pode ser aplicado a elementos de volume representativos finitos e em condições em que a geração de calor é heterogênea na microescala. A discretização temporal (diferenças finitas) e as discretizações espaciais na microescala e na macroescala (método dos elementos finitos) são apresentadas em detalhes, juntamente com os algoritmos necessários para implementar a solução do problema. Nesta tese são apresentados casos numéricos simples, procurando verificar não só o modelo teórico multiescala desenvolvido, mas também a implementação feita. Para tanto, são analisados, por exemplo, (a) casos em que considera-se a microescala um material homogêneo, tornando possível a comparação da solução multiescala com a solução convencional (uma única escala) pelo método dos elementos finitos, e (b) um caso em um material heterogêneo para o qual a solução completa, isto é, modelando diretamente os constituintes no corpo macroscópico, é obtida, tornando possível a comparação com a solução multiescala. A solução na microescala para vários casos analisados nesta tese sofre grande influência da inércia térmica da microescala. Para demonstrar o potencial de aplicação do modelo multiescala, simula-se a cura de um elastômero carregado com negro de fumo. Embora a simulação demonstre que a inércia térmica não precise ser considerada para esse caso em particular, a aplicação da presente metodologia torna possível modelar a cura do elastômero diretamente sobre a microescala, uma abordagem até então não utilizada no contexto de métodos multiescala. Essa metodologia abre a possibilidade para futuros aperfeiçoamentos da modelagem do estado de cura.This work deals with the modeling of transient heat conduction with heat generation in heterogeneous media, and its objective is to develop a proper multiscale model for this phenomenon. There already exist multiscale models in the literature related to this proposed problem, and which are valid for the following cases: (a) the representative volume element has a negligible size when compared to the characteristic macroscopic size (and, as a consequence, the microscale has a negligible thermal inertia); or (b) the heat generation is homogeneous at the microscale. On the other hand, the model proposed in this thesis, which is developed using a variational description of the problem, can be applied to finite representative volume elements and in conditions in which the heat generation is heterogeneous at the microscale. The time discretization (finite difference) and the space discretizations at both the microscale and the macroscale (finite element method) are presented in details, together with the algorithms needed for implementing the solution of the problem. In this thesis, simple numerical cases are presented, aiming to verify not only the theoretical multiscale model developed, but also its implementation. For this, it is analyzed, for instance, (a) cases in which the microscale is taken as a homogeneous material, making it possible the comparison of the multiscale solution with the conventional solution (one single scale) by the finite element method, and (b) a case in a heterogeneous material for which the full solution, that is, modeling all constituents directly on the macroscale, is obtained, making it possible the comparison with the multiscale solution. The solution at the microscale for several cases analyzed in this thesis suffers a large influence of the microscale thermal inertia. To demonstrate the application potential of the multiscale model, the cure of a carbon black loaded elastomer is simulated. Although the simulation shows that the thermal inertia does not have to be considered for this case in particular, the application of the present methodology makes it possible to model the cure of the elastomer directly at the microscale, an approach not used in multiscale methods context until now. This methodology opens the possibility for future improvements of the state of cure modeling.
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Al-Jawary, Majeed Ahmed Weli. "The radial integration boundary integral and integro-differential equation methods for numerical solution of problems with variable coefficients." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/6449.
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The boundary element method (BEM) has become a powerful method for the numerical solution of boundary-value problems (BVPs), due to its ability (at least for problems with constant coefficients) of reducing a BVP for a linear partial differential equation (PDE) defined in a domain to an integral equation defined on the boundary, leading to a simplified discretisation process with boundary elements only. On the other hand, the coefficients in the mathematical model of a physical problem typically correspond to the material parameters of the problem. In many physical problems, the governing equation is likely to involve variable coefficients. The application of the BEM to these equations is hampered by the difficulty of finding a fundamental solution. The first part of this thesis will focus on the derivation of the boundary integral equation (BIE) for the Laplace equation, and numerical results are presented for some examples using constant elements. Then, the formulations of the boundary-domain integral or integro-differential equation (BDIE or BDIDE) for heat conduction problems with variable coefficients are presented using a parametrix (Levi function), which is usually available. The second part of this thesis deals with the extension of the BDIE and BDIDE formulations to the treatment of the two-dimensional Helmholtz equation with variable coefficients. Four possible cases are investigated, first of all when both material parameters and wave number are constant, in which case the zero-order Bessel function of the second kind is used as fundamental solution. Moreover, when the material parameters are variable (with constant or variable wave number), a parametrix is adopted to reduce the Helmholtz equation to a BDIE or a BDIDE. Finally, when material parameters are constant (with variable wave number), the standard fundamental solution for the Laplace equation is used in the formulation. In the third part, the radial integration method (RIM) is introduced and discussed in detail. Modifications are introduced to the RIM, particularly the fact that the radial integral is calculated by using a pure boundary-only integral which relaxes the “star-shaped” requirement of the RIM. Then, the RIM is used to convert the domain integrals appearing in both BDIE and BDIDE for heat conduction and Helmholtz equations to equivalent boundary integrals. For domain integrals consisting of known functions the transformation is straightforward, while for domain integrals that include unknown variables the transformation is accomplished with the use of augmented radial basis functions (RBFs). The most attractive feature of the method is that the transformations are very simple and have similar forms for both 2D and 3D problems. Finally, the application of the RIM is discussed for the diffusion equation, in which the parabolic PDE is initially reformulated as a BDIE or a BDIDE and the RIM is used to convert the resulting domain integrals to equivalent boundary integrals. Three cases have been investigated, for homogenous, non-homogeneous and variable coefficient diffusion problems.
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片峯, 英次, Eiji Katamine, 秀幸 畔上, Hideyuki Azegami, 雅美 小嶋, and Masami Kojima. "定常熱伝導場における境界形状決定." 日本機械学会, 1999. http://hdl.handle.net/2237/7265.
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Vieira, Alan Lima [UNESP]. "Aperfeiçoamento e avaliação de um novo sistema de digestão assistida por aquecimento condutivo em frasco fechado para preparar amostras de carne “in natura” para análise elementar." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/136387.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Estabelecer procedimentos simples, rápidos, eficientes e com preparo de amostras de baixo custo para determinar elementos em amostras de carne é um aspecto relevante para fins nutricionais e de saúde. Por esta razão, um sistema de digestão com aquecimento condutivo em frasco fechado (CHDS), foi avaliado recentemente para a decomposição de amostras “in natura” de músculo, fígado e rim (bovino, suíno e frango) visando a determinação de macronutrientes (Ca, Mg, Na, K, S e P), micronutrientes (Cu, Fe, Mn, Mo, Se e Zn) e contaminantes inorgânicos (As, Cd, Cr e Pb) por espectrometria de emissão óptica com plasma acoplado indutivamente (ICP OES) e espectrometria de massas com plasma acoplado indutivamente (ICP-MS). O aperfeiçoamento feito no CHDS foi planejado para melhorar a segurança, a praticidade e a robustez do sistema. Entre elas destaca-se a adaptação de um pistão a gás na tampa do gabinete de digestão; isolamento dos frascos no interior do gabinete de digestão; tampa de Teflon com sistema simples de alívio de pressão ao fim da decomposição sem manuseio do frasco. A precisão foi avaliada analisando três materiais de referência certificados digeridos pelo CHDS. As recuperações para Ca, Cu, Fe, Mg, Mn, Na, K, S, P e Zn determinados por ICP OES, variaram entre 85 a 106%. Para As, Cd, Cr, Mo, Pb e Se determinados por ICP-MS, foram obtidas recuperações entre 92 a 110%. A eficiência da digestão também foi avaliada pela determinação do teor de carbono residual, que variou de 10 a 12% m m-1. Quando as amostras de carne foram digeridas usando o CHDS, os resultados para Ca, Cu, Fe, Mg, Mn, Na, K, S, P e Zn determinados por ICP OES e para As, Cd, Cr, Mo, Pb e Se determinados por ICP-MS foram concordantes com aqueles obtidos após digestão ácida assistida por radiação micro-ondas em frasco fechado (MW-AD). Ao utilizar o CHDS, os limites de quantificação foram similares aos obtidos com a MW-AD para todos os analitos. O CHDS é capaz de digerir 800 mg de amostra de carne “in natura” utilizando 2 mL de HNO3 e 1 mL H2O2. O procedimento proposto foi capaz de atender a Instrução Normativa da Secretária de Defesa Agropecuária (SDA) nº 13 que trata do monitoramento de resíduos e contaminantes em carnes para As, Cd e Pb. Os resultados obtidos neste estudo estendem as aplicações do CHDS para amostras com maior teor de gordura, tais como músculo, fígado e rim. Este sistema de digestão simples e de baixo custo pode ser utilizado para preparar amostras para determinação subsequente de um grande número de elementos por espectrometria de ICP, incluindo espécies voláteis, tais como, As, Cd e Se.
Establishing simple, fast, efficient and low-cost sample preparation procedures to determine elements in meat samples is a relevant aspect for nutritional and health purposes. For this reason, the recently proposed closed-vessel conductivelyheated digestion system (CHDS) was evaluated for the decomposition of muscle, liver and kidney (cattle, pigs and chickens) samples fresh aiming for the determination of macronutrients (Ca, Mg, Na, K, S and P), micronutrients (Cu, Fe, Mn, Mo, Se and Zn) and inorganic contaminants (As, Cd, Cr and Pb) by inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS). The optimization of the CHDS was planned to improve safety, practicality and robustness such as adaptation of a gas piston in the digestion cabinet cover, isolation of vessels inside the digestion cabinet and a Teflon cap with a simple pressure relief system in the end of the decomposition without handling the vessel. The accuracy was evaluated by analyzing three certified reference materials digested by the CHDS. Recoveries for Ca, Cu, Fe, Mg, Mn, Na, K, S, P and Zn determinations by ICP OES varied from 85 to 106%. For As, Cd, Cr, Mo, Pb and Se determinations by ICP-MS, recoveries within the 92-110% were obtained. The digestion efficiency was also evaluated by determining the residual carbon content, which varied from 10 to 12% m m-1. When fresh meat samples were digested using the CHDS, results for Ca, Cu, Fe, Mg, Mn, Na, K, S, P and Zn determinations by ICP OES and for As, Cd, Cr, Mo, Pb and Se determinations by ICP-MS were in agreement with those obtained after closed-vessel microwave-acid digestion (MW-AD). When using the CHDS, limits of quantification were similar to those obtained with the MW-AD for all analytes. The CHDS enabled the digestion of 800 mg of fresh meat with 2 mL of HNO3 and 1 ml of H2O2. The proposed procedure was able to attend the normative instruction of agricultural defense secretary SDA N°. 13 for As, Cd and Pb. The results obtained in this study extend the applications of the CHDS to samples with higher contents of fat such as muscle, liver and kidney. This simple and low-cost digestion system can be used to prepare samples for subsequent determination of a large number of elements by ICP spectrometry, including volatile species such as As, Cd and Se.
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片峯, 英次, Eiji Katamine, 秀幸 畔上, Hideyuki Azegami, 易広 松浦, and Yasuhiro Matsuura. "非定常熱伝導場における形状同定問題の解法." 日本機械学会, 2000. http://hdl.handle.net/2237/7266.
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Padilla, Scott T. "Novel Transducer Calibration and Simulation Verification of Polydimethylsiloxane (PDMS) Channels on Acoustic Microfluidic Devices." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6922.
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The work and results presented in this dissertation concern two complimentary studies that are rooted in surface acoustic waves and transducer study.
Surface acoustic wave devices are utilized in a variety of fields that span biomedical applications to radio wave transmitters and receivers. Of interest in this dissertation is the study of surface acoustic wave interaction with polydimethylsiloxane. This material, commonly known as PDMS, is widely used in the microfluidic field applications in order to create channels for fluid flow on the surface of a piezoelectric substrate. The size, and type of PDMS that is created and ultimately etched on the surface of the substrate, plays a significant role in its operation, chiefly in the insertion loss levels experienced. Here, through finite element analysis, via ANSYS® 15 Finite Element Modeling software, the insertion loss levels of varying PDMS sidewall channel dimensions, from two to eight millimeters is investigated. The simulation is modeled after previously published experimental data, and the results demonstrate a clear increase in insertion loss levels with an increase in channel sidewall dimensions. Analysis of the results further show that due to the viscoelastic nature of PDMS, there is a non -linear increase of insertion loss as the sidewall dimensions thicken. There is a calculated variation of 8.31 decibels between the insertion loss created in a microfluidic device with a PDMS channel sidewall thickness of eight millimeters verse a thickness of two millimeters. Finally, examination of the results show that insertion loss levels in a device are optimized when the PDMS sidewall channels are between two and four millimeters.
The second portion of this dissertation concerns the calibration of an ultrasonic transducer. This work is inspired by the need to properly quantify the signal generated by an ultrasonic transducer, placed under a static loading condition, that will be used in measuring ultrasonic bone conducted frequency perception of human subjects. Ultrasonic perception, classified as perception beyond the typical hearing limit of approximately 20 kHz, is a subject of great interest in audiology. Among other reasons, ultrasonic signal perception in humans is of interest because the mechanism by which either the brain or the ear interprets these signals is not entirely understood. Previous studies have utilized ultrasonic transducers in order to study this ultrasonic perception; however, the calibration methods taken, were either incomplete or did not properly account for the operation conditions of the transducers. A novel transducer calibration method is detailed in this dissertation that resolves this issue and provides a reliable means by which the signal that is being created can be compared to the perception of human subjects.
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AZEGAMI, Hideyuki, Yutaro IWATA, Eiji KATAMINE, 秀幸 畔上, 侑太朗 岩田, and 英次 片峯. "放熱量最大化を目的とした非定常熱伝導場の形状最適化." 一般社団法人日本機械学会, 2008. http://hdl.handle.net/2237/21114.
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Chaouch, Mounir. "Effet de l'intensité du traitement sur la composition élémentaire et la durabilité du bois traité thermiquement : développement d'un marqueur de prédiction de la résistance aux champignons basidiomycètes." Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10027/document.
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Le traitement thermique est une méthode appropriée pour la valorisation d'essences européennes peu durables. Les modifications chimiques en résultant confèrent au bois une meilleure stabilité dimensionnelle et durabilité aux attaques fongiques, alors que les propriétés mécaniques diminuent plus ou moins. Le verrou actuel de ce procédé reste la grande difficulté à produire à l'échelle industrielle un produit de qualité constante (durabilité, stabilité dimensionnelle, couleur). Ces difficultés sont dues à l'hétérogénéité du matériau et des conditions de traitement réalisé généralement par convexion. La mise au point d'un pilote de traitement thermique par conduction permettant une mesure en dynamique de la perte de masse a été réalisée pour optimiser la conduite du traitement, mieux comprendre les réactions de thermodégradation et développer un outil de contrôle de la qualité du bois traité. Les résultats obtenus, réalisés dans des conditions de traitement proches des conditions industrielles, indiquent un effet important de l'essence de bois traitée sur les cinétiques de perte de masse observées, les feuillus étant généralement plus sensibles à la thermodégradation que les résineux. Il a ensuite été établi une forte corrélation entre le niveau de thermodégradation du bois estimé à partir de sa perte de masse et l'augmentation de sa durabilité aux champignons basidiomycètes. L'analyse fine et la compréhension des mécanismes réactionnels intervenant durant le traitement ont permis de mettre en évidence un lien direct entre la composition élémentaire du bois et la perte de masse due aux réactions de thermodégradation, permettant également de prédire la durabilité aux attaques fongiques. Le taux de carbone, d'oxygène ou encore le rapport O/C peuvent de ce fait être considérés comme des marqueurs pertinents permettant de contrôler la qualité du bois traité thermiquementThermal treatment has been used to improve properties of non durable European species. Chemical modification of some of the wood components provides improved dimensional stability and biological performance against decay fungi while mechanical properties such as modulus of rupture are reduced. Quality control of commercially made thermally treated wood is one of the major road blocks of its industrial development. The variability inherent within a wood species and between wood species, density and chemical compositions variation combined with the heat treatment parameters such as temperature duration and levels contribute to the production of heterogeneous heat treated wood. The development of a heat treatment process by conduction which monitors the weight changes during the process will facilitate and help in controlling, in understanding and predicting the properties of heat treated wood. Data collected from a pilot study of heat treated wood using conditions similar to commercial process show that hardwood species were more susceptible to thermal degradation as compared to softwood. It was also established that wood chemical composition is directly connected to the percent of weight loss due to thermodegradation, allowing the use of chemical composition to predict fungi durability. Carbon and oxygen contents and/or oxygen to carbon ratio of heat treated wood can be therefore used as valuable markers to develop quality control assessment of heat treated wood
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Pietromonaco, Joseph Allen. "A Heat Transfer Model for Industrial Food Processes." Youngstown State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1312936641.
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Husain, Muhammad Dawood. "Development of temperature sensing fabric." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/development-of-temperature-sensing-fabric(0e5e8367-c3b2-4cff-bcc9-f32fac97b50f).html.
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Human body temperature is an important indicator of physical performance and condition in terms of comfort, heat or cold stress. The aim of this research was to develop Temperature Sensing Fabric (TSF) for continuous temperature measurement in healthcare applications. The study covers the development and manufacture of TSF by embedding fine metallic wire into the structure of textile material using a commercial computerised knitting machine. The operational principle of TSF is based on the inherent propensity of a metal wire to respond to changes in temperature with variation in its electrical resistance. Over 60 TSF samples were developed with combinations of different sensing elements, two inlay densities and highly textured polyester yarn as the base material. TSF samples were created using either bare or insulated wires with a range of diameters from 50 to 150 μm and metal wires of nickel, copper, tungsten, and nickel coated copper. In order to investigate the Temperature-Resistance (T-R) relationship of TSF samples for calibration purposes, a customised test rig was developed and monitoring software was created in the LabVIEW environment, to record the temperature and resistance signals simultaneously. TSF samples were tested in various thermal environments, under laboratory conditions and in practical wear trials, to analyse the relationship between the temperature and resistance of the sensing fabric and to develop base line specifications such as sensitivity, resistance ratio, precision, nominal resistance, and response time; the influence of external parameters such as humidity and strain were also monitored. The regression uncertainty was found to be less than in ±0.1°C; the repeatability uncertainty was found to be less than ±0.5°C; the manufacturing uncertainty in terms of nominal resistance was found to be ± 2% from its mean. The experimental T-R relationship of TSF was validated by modelling in the thermo-electrical domain in both steady and transient states. A maximum error of 0.2°C was found between the experimental and modelled T-R relationships. TSF samples made with bare wire sensing elements showed slight variations in their resistance during strain tests, however, samples made with insulated sensing elements did not demonstrate any detectable strain-dependent-resistance error. The overall thermal response of TSF was found to be affected by basal fabric thickness and mass; the effect of RH was not found to be significant. TSF samples with higher-resistance sensing elements performed better than lower-resistance types. Furthermore, TSF samples made using insulated wire were more straightforward to manufacture because of their increased tensile strength and exhibited better sensing performance than samples made with bare wire. In all the human body wear trials, under steady-state and dynamic conditions both sensors followed the same trends and exhibited similar movement artifacts. When layers of clothing were worn over the sensors, the difference between the response of the TSF and a high-precision reference temperature were reduced by the improved isothermal conditions near the measurement site.
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Haňka, Jiří. "Měření a modelování skutečných impedančních výsledků v závislosti na poloze snímacích elektrod." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221079.
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ABSTRAKT Obsah této práce je směřován na řešení problematiky měření impedančních charakteristik dielektrických materiálů, zejména keramik, za pomocí simulace připojení elektrod na mě- řený vzorek. V práci je popsáno měření impedancí se zaměřením na metodu impedanční spektroskopie. Cílem práce je seznámení s problematikou měření komplexní impedance a popsání parazitních jevů, vyskytujících se v materiálu. Dále jsou v práci popisovány současné možnosti simulací a simulačních softwarů jako je zejména ANSYS Maxwell. S využitím simulací tohoto softwaru jsou v práci řešeny impedanční charakteristiky vodivé keramiky a jejich závislost na poloze napájecích elektrod. KLÍČOVÁ SLOVA Dielektrické materiály, elektrická polarizace, impedanční spektroskopie, komplexní impe- dance, vodivé keramiky, ANSYS, metoda konečných prvků. ABSTRACT Content of this thesis is aimed to solutions of issues, created due measurement impe- dance characteristics of dielectric materials, mainly ceramics, using simulation electrode position by specific software. In thesis is described impedance measurement with focusing to impedance spectroscopy. Goal of this thesis is to get acquainted with issues of mea- surement complex impedance and explain parasitics effects in ceramics material. Further goals of thesis are described current possibilities of simulation software ANSYS Ma- xwell. Using this simulation software was solved impedance characteristics of conductive ceramics and their dependence of electrodes position.
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Domeij, Bäckryd Rebecka. "Simulation of Heat Transfer on a Gas Sensor Component." Thesis, Linköping University, Department of Mathematics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-131.
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Gas sensors are today used in many different application areas, and one growing future market is battery operated sensors. As many gas sensor components are heated, one major limit of the operation time is caused by the power dissipated as heat. AppliedSensor is a company that develops and produces gas sensor components, modules and solutions, among which battery operated gas sensors are one targeted market.
The aim of the diploma work has been to simulate the heat transfer on a hydrogen gas sensor component and its closest surroundings consisting of a carrier mounted on a printed circuit board. The component is heated in order to improve the performance of the gas sensing element.
Power dissipation occurs by all three modes of heat transfer; conduction from the component through bond wires and carrier to the printed circuit board as well as convection and radiation from all the surfaces. It is of interest to AppliedSensor to understand which factors influence the heat transfer. This knowledge will be used to improve different aspects of the gas sensor, such as the power consumption.
Modeling and simulation have been performed in FEMLAB, a tool for solving partial differential equations by the finite element method. The sensor system has been defined by the geometry and the material properties of the objects. The system of partial differential equations, consisting of the heat equation describing conduction and boundary conditions specifying convection and radiation, was solved and the solution was validated against experimental data.
The convection increases with the increase of hydrogen concentration. A great effort was made to finding a model for the convection. Two different approaches were taken, the first based on known theory from the area and the second on experimental data. When the first method was compared to experiments, it turned out that the theory was insufficient to describe this small system involving hydrogen, which was an unexpected but interesting result. The second method matched the experiments well. For the continuation of the project at the company, a better model of the convection would be a great improvement.
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Fritsch, Julia. "Synthese und Charakterisierung molekularer Vorläuferverbindungen für den Einsatz in weichen lithographischen Verfahren sowie katalytisch aktiver elementorganischer Gerüstverbindungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-96328.
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In der vorliegenden Arbeit werden zwei Materialklassen behandelt. Im Hauptteil soll die Synthese und Charakterisierung von molekularen Organo-Silber-Komplexen und deren Einsatz als Tintenmaterial in weichen lithographischen Verfahren beschrieben werden. Dadurch sollen strukturierte Schichten des Komplexes zugänglich sein, welche durch entsprechende Nachbehandlung in elementares Silber umgewandelt werden können, wodurch man schließlich strukturierte Silberelektroden erhält. Der Einsatz solcher strukturierter Elektroden ist für die Weiterentwicklung transparenter elektrisch leitender Schichten, welche man im heutigen Alltag in nahezu jedem elektro-optischen Bauteil findet, essentiell. Bisher beruhen transparente Elektroden vorwiegend auf Zinn dotiertem Indiumoxid (ITO), welches zu den transparent leitfähigen Oxiden (TCOs) gehört und sehr gute elektrische Eigenschaften aufweist. TCOs sind transparente Oxide, welche ihre Leitfähigkeit durch den Einbau von Dotierstoffen und eine damit einhergehende Erzeugung von Störstellen im Kristallgitter erhalten. Aufgrund der anhaltenden Indiumverknappung wird allerdings zunehmend nach Alternativen zu ITO gesucht. Neben weiteren transparent leitfähigen Oxiden wie z.B. Antimon oder Fluor dotiertem Zinnoxid besteht die Möglichkeit, auf leitfähige Polymere, Kohlenstoffmaterialien oder Metalle zurückzugreifen. Diese drei Klassen haben den Vorteil des Einsatzes in flexiblen Bauteilen, welcher bei Verwendung der TCOs aufgrund ihrer Brüchigkeit nur begrenzt möglich ist. Metalle weisen dabei die geringsten elektrischen Widerstände auf und sind daher besonders interessant. Die Herausforderung bei der Verwendung von Metallen liegt allerdings im Erreichen der Transparenz. Durch die Strukturierung der Dünnfilme unterhalb des Wellenlängenbereiches des sichtbaren Lichts kann diese gewährleistet werden. Eine Strukturierung kann zum einen durch z.B. chemische oder physikalische Abscheideprozesse und zum anderen durch die bereits angesprochenen weichen lithographischen Verfahren realisiert werden. Die Entwicklung sogenannter Tinten für solche Druckverfahren auf Basis molekularer Organo-Silber-Komplexe stellt daher ein interessantes Forschungsgebiet dar.
In einem zweiten, kleineren Teil dieser Arbeit soll die Synthese neuartiger poröser elementorganischer Gerüstverbindungen (EOFs) auf Basis von Phosphor, Antimon und Bismut und deren katalytische Aktivität vorgestellt werden. Die EOFs wurden erstmals 2008 veröffentlicht und zeichnen sich im Gegensatz zu den ebenfalls bekannten metallorganischen Gerüstverbindungen durch kovalente Element-Kohlenstoff-Bindungen aus. Die Materialien, welche meist auf der Basis von Silanen aufgebaut sind, zeichnen sich durch ihre hohe Stabilität gegenüber Luftsauerstoff und Feuchtigkeit aus und zeigen interessante Eigenschaften in der Wasserdampfphysisorption. Die Adsorption von Wasserdampf findet erst in einem hohen Relativdruckbereich statt, was die stark unpolare Oberfläche der EOFs aufzeigt. Durch diese Eigenschaft weisen die Materialien ein großes Potential für die adsorptive Abtrennung von unpolaren Stoffen aus Wasser oder Luft auf. Durch die Substitution des Siliziums durch Zinn konnte gezeigt werden, dass mit geeigneten Metallpräkursoren ebenfalls EOF-Materialien hergestellt werden können, welche neben den bereits genannten Eigenschaften auch Potential für katalytische Anwendungen zeigen. Dieser Weg sollte in der vorliegenden Arbeit aufgegriffen werden. Durch die Integration der Elemente Phosphor, Antimon und Bismut sollten weitere EOF-Materialien synthetisiert und hinsichtlich ihrer katalytischen Eigenschaften untersucht werden. Ein phosphorhaltiges EOF ist vor allem interessant für postsynthetische Infiltration von Übergangsmetallen. Dadurch können essentielle heterogene Katalysatoren zugänglich sein, welche eine große Bedeutung für die Organokatalyse haben, bei denen bisher vorwiegend die homogenen Analoga verwendet werden. Der Ersatz durch heterogene Katalysatoren würde einen wesentlichen synthetischen Fortschritt mit sich bringen, da diese nach der Reaktion einfach abgetrennt werden können und keine aufwendige Aufarbeitung erforderlich ist.
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Argento, Claudio. "Modélisation du comportement thermique et mécanique des poudres métalliques : application à la compaction isostatique à chaud." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10084.
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Le but initial de cette these est de produire, a partir d'un code de calcul par elements finis existant, un outil fiable et souple pour la simulation du processus de compaction isostatique a chaud de poudres metalliques. Pour cela nous avons developpe un modele thermomecanique complet decrivant le comportement de la poudre pendant la compaction. Dans un premier temps, nous proposons une nouvelle loi constitutive elasto-viscoplastique avec ecrouissage en densite. Cette loi possede un parametre supplementaire qui permet de controler explicitement le couplage entre les parties isotrope et deviatoire des contraintes et des deformations. La deuxieme partie de ce travail est consacree au developpement d'un modele permettant de decrire la conductivite thermique des poudres metalliques tout au long de la densification. Nous proposons deux modeles: un modele utilisant la methode des elements discrets pour decrire la conduction a travers la phase solide et une methode de monte carlo associee a un programme de suivi de rayons pour decrire le rayonnement dans les pores. Nous montrons que ce dernier etait negligeable dans le cas des poudres metalliques. Dans la troisieme partie, nous decrivons le code de calcul par elements finis lagamine de l'universite de liege et la facon dont les lois constitutives mecaniques et thermiques presentees y sont integrees de facon objective. Finalement, dans la derniere partie de cette these, nous presentons une comparaison des reponses prevues par les differentes lois constitutives pour des pieces relativement simples en deux et trois dimensions. Nous mettons en evidence en particulier l'influence de la loi de comportement sur la prevision de la forme finale de la piece
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Vaverka, Jiří. "Výpočtové modelování srdeční kontrakce." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241725.
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This thesis aims to determine the impact of slowed myocardial conduction velocity and depressed myocyte contractility on the duration of isovolumic contraction time (ICT) of the left ventricle by carrying out simulations using finite element method. A 3D finite element model enabling to simulate both physiological and pathological states of myocardium was created. The model is based on simplified ellipsoidal geometry and accounts for anisotropic behavior of myocardium, its asynchronous contraction and variations in the arrangement of muscle fibers. Slowing of conduction velocity to a half of its physiological value resulted in prolongation of ICT by 27 %; slowing of shortening velocity of myocytes by the same percentage prolonged ICT by 73 %. It is therefore concluded that ICT can be much more prolonged due to depressed contractility than due to conduction slowing. The presented results give an idea of the extent to which ICT can be prolonged due to depressed contractility and conduction slowing and therefore can be useful in identifying the causes of decreased myocardial performance in heart disease.
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Rahmanian, Ima. "Thermal and mechanical properties of gypsum boards and their influences on fire resistance of gypsum board based systems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/thermal-and-mechanical-properties-of-gypsum-boards-and-their-influences-on-fire-resistance-of-gypsum-board-based-systems(d8eb4bf5-706a-4264-911f-9584ebfbbc83).html.
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Gypsum board assemblies are now widely used in buildings, as fire resistant walls or ceilings, to provide passive fire protection. The fire resistance of such systems is fundamentally due to the desirable thermal properties of gypsum. Yet there is wide variability in reported values of thermal properties of gypsum at high temperatures and a lack of understanding of its integrity in fire. To evaluate the fire protection performance of gypsum board assemblies, it is essential to quantify its thermal properties and obtain information on its mechanical properties at high temperatures. Gypsum boards shrink and crack at high temperatures, and this leads to collapse of parts of the gypsum boards in fire. Fall-off of gypsum in fire affects the fire resistance of the assembly considerably, and cannot be overlooked when evaluating the fire resistance of gypsum board assemblies. The current research proposes a model to define the temperature-dependent thermal properties of gypsum boards at high temperatures. Thermal conductivity of gypsum is considered as the most influential parameter in conduction of heat through gypsum, and a hybrid numerical-experimental method is presented for extracting thermal conductivity of various gypsum board products at elevated temperatures. This method incorporates a validated one-dimensional Finite Difference heat conduction program and high temperature test results on small samples of gypsum boards. Moreover, high temperature mechanical tests have been performed on different gypsum board products; thermal shrinkage, strength and stress-strain relationships of gypsum products at elevated temperatures are extracted for use in numerical mechanical analysis. To simulate the structural performance of gypsum boards in fire, a two-dimensional Finite Element model has been developed in ABAQUS. This model successfully predicts the complete opening of a through-thickness crack in gypsum, and is validated against medium-scale fire tests designed and conducted as part of this research. Gypsum fall-off in fire is a complex phenomenon; however, it is believed that delaying the formation of through-thickness cracking will delay falling off of gypsum in fire, and hence improve the fire resistance of gypsum board assemblies. Finally, a study has been performed on the effects of various detailing parameters in gypsum board wall assemblies, and recommendations are offered for improving the fire resistance of such systems.
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Jaiswal, Vinay Kumar. "Finite element modeling of electric field distributions around a resistive glazed post station insulator covered with ice = Modélisation par éléments finis de la distribution du champ électrique autour d'un isolateur de poste avec une couche semi-conductrice recouvert de glace /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2005. http://theses.uqac.ca.
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Lindqvist, Petter. "Validering av solida temperaturer i FDS genom jämförelse mot FE-beräkningar." Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79973.
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FDS (Fire Dynamics Simulator) använder en version av Navier-Stokes ekvationerna för att göra noggranna beräkningar av värme- och gastransport genom brandbelastade utrymmen. Utvecklarna av programmet arbetar kontinuerligt med att validera det allteftersom nya funktioner tillförs för att öka noggrannheten och bredda tillämpningsområdena. Väldigt lite av detta arbete fokuserar dock på FDS:s konduktionsmodell, den endimensionella Crank-Nicolson metoden. Det här examensarbetet ämnar därför undersöka noggrannheten i FDS:s konduktionsmodell genom jämförelse mot beräkningar med FEM (Finita elementmetoden). En FDS-modell skapades för att tillåta undersökning av en vägg och dess randvillkor med så liten påverkan från andra faktorer som möjligt. Detta för att skapa en kontrollerad omgivning som enkelt kunde replikeras i efterföljande FE-beräkningar av det konduktiva värmeflödet genom den solida obstruktionen. Tre väggar (10 cm betong, 20 cm betong och 1 mm stål) vardera med tre randvillkor (Exposed, Void och Insulated) utsattes för tre temperaturer (100 °C, 500 °C och 1000 °C) vilket ger 27 FDS simuleringar. Den adiabatiska yttemperaturen mättes i varje simulering och användes som indata till motsvarande FE-beräkningar. Resultatet påvisade inga signifikanta motsägelser vad gäller randvillkoren, med tillräcklig tid för termisk penetrering påverkade de den resulterande temperaturen som väntat. Undantaget var en mindre avvikelse i stålväggarna som utsattes för 100 °C och 500 °C med randvillkoren Exposed och Void där FDS aningen underskattade temperaturen relativt FE-beräkningarna. Gastemperaturerna i gridcellerna närmast väggen visade sig vara opålitliga. De tenderade att genomgå substantiella fluktuationer, troligen som ett resultat av hur FDS hanterar diskretiseringen av icke-solida volymer för Navier-Stokes beräkningarna. Dessa fluktuationer påverkade dock inte de resulterande solida temperaturerna eftersom medelgastemperaturen var korrekt. FDS påvisades även ha en tendens att aningen överskatta yttemperaturen under de första minuterna av simuleringarna relativt FE-beräkningarna. Temperaturerna från de två beräkningsmetoderna konvergerade dock efter några få minuter i samtliga tester. Dessa avvikelser ansågs ha för liten påverkan på de solida temperaturerna för att påvisa onoggrannhet i FDS. Därmed drogs slutsatsen att FDS:s beräkningar av temperaturer i solida material är tillräckligt noggranna inom dessa avgränsningar.FDS (Fire Dynamics Simulator) uses a version of the Navier-Stokes equations to make accurate calculations of heat and gas flow through enclosures exposed to fire. The developers of FDS have, and continue to, validate it as new features get added in an attempt to increase its accuracy and broaden its potential applications. However, little of this effort is focused on FDS’ conductive heat transfer model, based on the one-dimensional Crank-Nicolson method. Thus, this study aims to test the accuracy of FDS’ conduction model by comparing it to calculations using FEM (Finite Element Method). FDS simulations were created so as to facilitate the study of a wall and its boundary conditions with as little interference from other factors as possible. This to create a controlled environment which easily could be replicated in the subsequent FE-calculations of the conductive heat flow through the solid obstructions. Three different walls (10 cm concrete, 20 cm concrete and 1 mm steel), each with the three different boundary conditions for the rear surface (Exposed, Void and Insulated), were exposed to three different temperatures (100 °C, 500 °C and 1000 °C) for a total of 27 FDS simulations. The adiabatic surface temperature was measured in each simulation in FDS and used as input for the corresponding FE-calculations. The results showed no clear inconsistencies in the boundary conditions, given enough time for thermal penetration they affected the resulting temperatures as expected. Save a slight deviation in the steel walls exposed to 100 °C and 500 °C with boundary conditions Exposed and Void where FDS slightly underestimated the temperature relative to the FE-calculations. The gas temperatures in the grid cells closest to the wall were found to be unreliable as they tended to undergo substantial fluctuations, likely as a result of how FDS handles the discretization of non-solid space for the Navier-Stokes calculations. These fluctuations were however not found to affect the solid temperatures as the mean gas temperature was accurate. FDS was also found to have a tendency to slightly overestimate the surface temperature in the first few minutes of the simulations relative to the FE-calculations. Though the resulting temperatures from the two methods converged after a few minutes at most in all tests. These deviations were considered to have too minor an impact on the solid temperature to justify claims of inaccuracy in FDS. Thus, the general conclusion of this study is that FDS’ predictions of solid phase temperatures are sufficiently accurate within these delimitations.
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Dohnalík, Petr. "Návrh optimálních parametrů vícevrstvého keramického ochranného povlaku pro vysokoteplotní aplikace." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318659.
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The main objective of this work was to design a suitable composition of a protective coatings, made of several different layers of specific materials - with respect to residual stress, induced due to a mismatch in thermal expansion coefficients of each layer. Protective coating in this work means both the thermal and the environmental barrier. These coatings protect components against high temperatures and harsh environment. In this work, necessary theoretical background in the field of the thermal and environmental barrier coatings is introduced. There are mentioned some basic design approaches, commonly used materials and processing methods for the coating structure. The literature review gives an overview of modeling of such coated structures, in particular it is devoted to the thermal barrier coatings deposited by air plasma spray process. The next chapter closely describes classical laminate theory used for calculation of residual stresses in the coating. One of the assumptions of this theory is homogenous temperature field through the coating’s thickness. However, in this work was revealed a way to extend the classical lamination theory of such cases, in which the temperatures vary along the thickness of the coating. In the practical part, the analytical model was used for designing suitable properties of some coatings, which were consists of two, three and four layers. The calculations were performed both for constant temperature and for the temperature gradient. All results obtained from analytical approach were verified by numerical calculations.
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Goy, Laurent. "Mesure et modélisation des températures dans les massifs rocheux : application au projet de tunnel profond Maurienne-Ambin." Phd thesis, Université Joseph Fourier (Grenoble), 1996. http://tel.archives-ouvertes.fr/tel-00642650.
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Pour les projets de tunnels profonds; la prévision des températures naturelles au rocher est essentielle pour le choix des méthodes de perforation, de ventilation et de refroidissement. Une méthode numérique de prévision des températures a été développée à cet effet, à partir d'un logiciel 2D d'éléments finis. Les températures sont calculées dans un plan vertical du massif, à partir de l'équation fondamentale de la chaleur en conduction pure. La modélisation nécessite la connaissance de cinq paramètres de base que sont: le profil topographique, les températures de surface, la structure géologique, la conductivité anisotrope des roches et le flux géothermique profond. Une méthode de correction du profil topographique permet de prendre en compte la troisième dimension. Différents tests sont effectués sur un profil de montagne idéalisé, pour évaluer le poids des différents paramètres dans la modélisation. Le modèle est appliqué ensuite au massif comprenant le tunnel Maurienne-Ambin, dans le cadre du projet de ligne à grande vitesse entre Lyon et Turin. Une sonde de mesure des températures a été mise au point et utilisée dans les sondages de reconnaissance pour ce projet de tunnel profond (55km sous un recouvrement maximal de 2500m). Les forages nous permettent de déterminer la structure géologique, les valeurs de conductivité des roches et le flux géothermique de la région en appliquant la "méthode des intervalles". La température maximale calculée le long du tunnel est de 48,5°C. La confrontation entre les mesures de température dans les forages et la modélisation permet de valider les résultats, sauf dans les premières centaines de mètres du massif, où les circulations d'eau, qui ne sont pas prises en compte par notre modèle, modifient la distribution des températures.
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Ben, Moussa Rim. "Contribution to thermal radiation to dust flame propagation : application to aluminium dust explosions." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2401/document.
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Ces travaux de thèse sont consacrés à l’examen du rôle du rayonnement thermique dans le processus de propagation des flammes issues de la combustion des particules d’aluminium dans l’air. Le sujet étant complexe et d’un intérêt industriel, il nécessite de prendre en compte le couplage de nombreux phénomènes physico-chimiques afin de prédire finement les conséquences des explosions de poussières. Une analyse bibliographique approfondie est proposée, concernant les mécanismes d’inflammation et de combustion des particules d’aluminium et aussi concernant les connaissances relatives à la propagation des flammes de poussières. La question spécifique de la nature des échanges thermiques et de l’influence du rayonnement thermique est étudiée. La revue bibliographique souligne les approximations et les hypothèses simplificatrices utilisées dans la littérature permettant donc de définir les pistes d’améliorations. Compte tenu des limitations importantes concernant la physique de ces flammes, un outil de simulation de physique numérique nommé « RADIAN », proche de la simulation numérique directe, a été développé proposant un couplage fin entre les différents modes d’échanges thermiques et la combustion pour modéliser la propagation de la flamme dans un nuage de poussières. La méthode des éléments discrets (MED) est utilisée pour modéliser numériquement les échanges radiatifs entre les particules et les échanges conductifs entre gaz et particules. La méthode des différences finies est utilisée pour modéliser numériquement la conduction thermique dans la phase gazeuse et la combustion. Un modèle radiatif est proposé se basant sur la théorie de Mie sur les interactions rayonnement-particules. Les résultats des simulations sont comparés avec des solutions analytiques et des données expérimentales de la littérature. Mais en plus, une étude expérimentale est aussi conduite afin de mesurer la distribution du flux radiatif devant la flamme et la vitesse de combustion laminaire pour des flammes Méthane-Sic, Méthane-Alumine et Al-air. Un bon accord entre les simulations et les expériences est démontré. La loi de Beer-Lambert relative au transfert radiatif devant le front de flamme s’avère inapplicable et une nouvelle solution analytique est proposée. La présence de particules absorbantes du rayonnement promeut la propagation de la flamme. En particulier, il a été montré expérimentalement et confirmé numériquement que les mélanges riches d’AL-air sont susceptibles d’accélérer rapidementIn this thesis, the role of thermal radiation in aluminum-air flames propagation is studied. The subject being complex and of industrial interest, it requires the coupling of many physiochemical phenomena to accurately predict the consequences of dust explosions. A thorough literature review is proposed about the ignition and the combustion of aluminum particles and about the available theoretical models of dust flames propagation. The specific question of the nature of thermal exchanges and the influence of thermal radiation is studied. The bibliographic review underlines the simplifying assumptions and hypotheses used in the literature making possible the definition of improvement areas. Because of the limited amount of knowledge available to address these questions, a numerical tool “RADIAN” is developed enabling an accurate coupling between the different modes of heat exchange and combustion. The Discrete Element Method (DEM) is used to numerically model the radiative exchanges between particles and the gas-particle thermal conduction. The Finite Difference method is used to numerically model the thermal conduction through the gas phase and combustion. A radiative model based on Mie theory for radiation-particles interactions is incorporated. The results of the simulations are compared with available analytical solutions and experimental data. An original experimental study is also conducted to measure the distribution of irradiance ahead of the flame front and the laminar burning velocity for methane-air-Sic, methane-air-alumina and Al-air flames. A good agreement between numerical simulations and experiments is demonstrated. The Beer-Lambert’s law for radiative transfer in front of the flame front is found to be inapplicable and a new analytical solution is proposed. The presence of absorbing particles may promote the flame propagation. In particular, it is shown experimentally and confirmed theoretically/numerically that Al-air rich mixtures are likely to rapidly accelerate
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Ramahaleo, Tiana. "Conductances ioniques, élasticité et perméabilité osmotique de cellules racinaires de colza (brassica napus)." Rouen, 1996. http://www.theses.fr/1996ROUES012.
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La racine est un organe essentiel pour l'absorption des ions et de l'eau chez les plantes supérieures. Dans le but de comprendre les processus impliqués dans le transport des ions au niveau de cet organe, des protoplastes et des vacuoles de cellules racinaires de colza ont été étudiés par la technique du patch clamp. Les courants macroscopiques majeurs détectés sur ces matériels sont des courants qui quittent le cytoplasme. Les courants vacuolaires observes présentent les caractéristiques des courants SV (Slow Vacuolar channels). Aussi bien sur les fragments de membrane du plasmalemme que sur le tonoplaste, des courants activés par la variation de la tension mécanique membranaire ont été mis en évidence. Nous avons également caractérisé les propriétés mécaniques des membranes qui contrôlent l'activation des canaux mécanosensibles sur les protoplastes et les vacuoles par l'élastimètre de Mitchison et Swann. Les valeurs du module d'élasticité K obtenues sur les protoplastes et les vacuoles sont semblables (88 et 50 milli-newton par mètre respectivement). Si le gadolinium, un inhibiteur des canaux mécanosensibles ne semble pas affecter l'élasticité du protoplaste, il paraît en revanche augmenter la rigidité du tonoplaste (96 milli-newton par mètre). Enfin, nous avons mis au point une technique simple de transfert d'un protoplaste isolé d'un milieu isotonique vers un milieu hypertonique (gradient osmotique : 0. 2 osmol). Elle permet de mesurer la vitesse initiale de plasmolyse des protoplastes et d'en déduire la valeur du coefficient de perméabilité osmotique, Pf(14 - 40 x 10#-3 centimètre par seconde). Des valeurs de Pf semblables ont été obtenues lors de transfert de vacuoles de betterave rouge (Pf = 7 - 25 x 10#-3 centimètre par seconde). Ces fortes valeurs de Pf pourraient signifier la présence d'aquaporines dans nos membranes.
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Puech, Laurence. "Critères microstructuraux pour l'identification des causes abiotiques des dépérissements du sapin (Abies alba (Mill. )) et de l'épicéa (Picea abies (L. ) Karst. ) dans les Vosges et dans les Alpes dauphinoises externes." Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10175.
Full textAbstract:
Les deperissements forestiers observes depuis les annees 1970 chez les coniferes europeens resultent de l'action conjuguee de differents facteurs biotiques et abiotiques dont l'importance relative varie en fonction des sites. La presente etude vise a l'identification de stress abiotiques a partir de l'anatomie d'aiguilles de sujets atteints. Une comparaison de differents sites forestiers des vosges et des alpes dauphinoises externes avec des experimentations en conditions controlees a ete realisee. En conditions controlees, une augmentation de l'apport d'ammonium aggrave les effets de carences en magnesium sur de jeunes epiceas. Une augmentation de l'apport total d'azote provoque une stimulation de la xylogenese par le cambium secondaire, une diminution de l'accumulation d'amidon et une alteration des chloroplastes. L'exposition a des doses d'ozone augmentees provoque l'apparition de necroses dans le mesophylle et de cristaux intracellulaires d'oxalate de calcium chez de jeunes epiceas. Dans les aiguilles de l'annee de jeunes sapins, on observe une reduction de l'accumulation d'amidon alors que, dans les aiguilles de l'annee precedente, on observe de nombreuses necroses dans le parenchyme palissadique, une alteration des chloroplastes et une proliferation de cellules du parenchyme lacuneux. Sur le site des vosges, on retrouve l'effet des facteurs abiotiques etudies: un collapse du phloeme chez sapins et epiceas ainsi qu'une accumulation d'amidon chez l'epicea indiquent des carences en magnesium. Chez le sapin, la presence d'anomalies de croissance dans le cylindre central et dans le parenchyme lacuneux suggerent respectivement l'effet d'une augmentation de la nutrition azotee et de concentrations elevees l'ozone. Dans les sites des alpes dauphinoises externes, aucun signe de carences minerales n'est observable alors que des anomalies de croissance du mesophylle laissent suspecter une influence de l'ozone. Une lignification precoce a ete observee sur deux arbres de ces sites a l'aide de la met