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1
Pehlivan, Yamac. "Matrix Quantum Mechanics And Integrable Systems". Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605065/index.pdf.
Testo completoAbstract (sommario):
In this thesis we improve and extend an algebraic technique pioneered by M. Gaudin. The technique is based on an infinite dimensional Lie algebra and a related family of mutually commuting Hamiltonians. In order to find energy eigenvalues of such Hamiltonians one has to solve the equations of Bethe ansatz. However, in most cases analytical solutions are not available. In this study we examine a special case for which analytical solutions of Bethe ansatz equations are not needed. Instead, some special properties of these equations are utilized to evaluate the energy eigenvalues. We use this method to find exact expressions for the energy eigenvalues of a class of interacting boson models.
In addition to that, we also introduce a q-deformation of the algebra of Gaudin. This deformation leads us to another family of mutually commuting Hamiltonians which we diagonalize using algebraic Bethe ansatz technique. The motivation for this deformation comes from a relationship between Gaudin algebra and a spin extension of the integrable model of F. Calogero. Observing this relation, we then consider a well known periodic version of Calogero's model which is due to B. Sutherland. The search for a Gaudin-like algebraic structure which is in a similar relationship with the spin extension of Sutherland'
s model naturally leads to the above mentioned q-deformation of Gaudin algebra. The deformation parameter q and the periodicity d of the Sutherland model are related by the formula q=i{pi}/d.
2
Dibelka, Jessica Anne. "Mechanics of Hybrid Metal Matrix Composites". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/50579.
Testo completoAbstract (sommario):
The appeal of hybrid composites is the ability to create materials with properties which normally do not coexist such as high specific strength, stiffness, and toughness. One possible application for hybrid composites is as backplate materials in layered armor. Fiber reinforced composites have been used as backplate materials due to their potential to absorb more energy than monolithic materials at similar to lower weights through microfragmentation of the fiber, matrix, and fiber-matrix interface. Composite backplates are traditionally constructed from graphite or glass fiber reinforced epoxy composites. However, continuous alumina fiber-reinforced aluminum metal matrix composites (MMCs) have superior specific transverse and specific shear properties than epoxy composites. Unlike the epoxy composites, MMCs have the ability to absorb additional energy through plastic deformation of the metal matrix. Although, these enhanced properties may make continuous alumina reinforced MMCs advantageous for use as backplate materials, they still exhibit a low failure strain and therefore have low toughness. One possible solution to improve their energy absorption capabilities while maintaining the high specific stiffness and strength properties of continuous reinforced MMCs is through hybridization. To increase the strain to failure and energy absorption capability of a continuous alumina reinforced Nextel" MMC, it is laminated with a high failure strain Saffil® discontinuous alumina fiber layer. Uniaxial tensile testing of hybrid composites with varying Nextel" to Saffil® reinforcement ratios resulted in composites with non-catastrophic tensile failures and an increased strain to failure than the single reinforcement Nextel" MMC. The tensile behavior of six hybrid continuous and discontinuous alumina fiber reinforced MMCs are reported, as well as a description of the mechanics behind their unique behavior. Additionally, a study on the effects of fiber damage induced during processing is performed to obtain accurate as-processed fiber properties and improve single reinforced laminate strength predictions. A stochastic damage evolution model is used to predict failure of the continuous Nextel" fabric composite which is then applied to a finite element model to predict the progressive failure of two of the hybrid laminates.Ph. D.
3
Francis, William H. IV. "Mechanics of post-microbuckled compliant-matrix composites". Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453575.
Testo completo
4
Wilkinson, Angus J. "Micro-mechanics of continuous fibre metal matrix composites". Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393899.
Testo completo
5
Ahn, Byung Ki. "Interfacial Mechanics in Fiber-Reinforced Composites: Mechanics of Single and Multiple Cracks in CMCs". Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29791.
Testo completoAbstract (sommario):
Several critical issues in the mechanics of the interface between the fibers and matrix in ceramic matrix composites (CMCs) are studied. The first issue is the competition between crack deflection and penetration at the fiber/matrix interface. When a matrix crack, the first fracture mode in a CMC, reaches the interface, two different crack modes are possible; crack deflection along the interface and crack penetration into the fibers. A criterion based on strain energy release rates is developed to determine the crack propagation at the interface. The Axisymmetric Damage Model (ADM), a newly-developed numerical technique, is used to obtain the strain energy in the cracked composite. The results are compared with a commonly-used analytic solution provided by He and Hutchinson (HH), and also with experimental data on a limited basis.
The second issue is the stress distribution near the debond/sliding interface. If the interface is weak enough for the main matrix crack to deflect and form a debond/sliding zone, then the stress distribution around the sliding interface is of interest because it provides insight into further cracking modes, i.e. multiple matrix cracking or possibly fiber failure. The stress distributions are obtained by the ADM and compared to a simple shear-lag model in which a constant sliding resistance is assumed. The results show that the matrix axial stress, which is responsible for further matrix cracking, is accurately predicted by the shear-lag model.
Finally, the third issue is multiple matrix cracking. We present a theory to predict the stress/strain relations and unload/reload hysteresis behavior during the evolution of multiple matrix cracking. The random spacings between the matrix cracks as well as the crack interactions are taken into account in the model. The procedure to obtain the interfacial sliding resistance, thermal residual stress, and matrix flaw distribution from the experimental stress/strain data is discussed. The results are compared to a commonly-used approach in which uniform crack spacings are assumed.
Overall, we have considered various crack modes in the fiber-reinforced CMCs; from a single matrix crack to multiple matrix cracking, and have suggested models to predict the microscopic crack behavior and to evaluate the macroscopic stress/strain relations. The damage tolerance or toughening due to the inelastic strains caused by matrix cracking phenomenon is the key issue of this study, and the interfacial mechanics in conjunction with the crack behavior is the main issue discussed here. The models can be used to interpret experimental data such as micrographs of crack surface or extent of crack damage, and stress/strain curves, and in general the models can be used as guidelines to design tougher composites.Ph. D.
6
林長淨 e Cheung-ching Lam. "The U-matrix theory and its applications". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1986. http://hub.hku.hk/bib/B31230635.
Testo completo
7
Lam, Cheung-ching. "The U-matrix theory and its applications /". [Hong Kong : University of Hong Kong], 1986. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12323901.
Testo completo
8
Cui, Wenping. "Statistical Mechanics of Microbiomes:". Thesis, Boston College, 2021. http://hdl.handle.net/2345/bc-ir:109135.
Testo completoAbstract (sommario):
Thesis advisor: Pankaj MehtaThesis advisor: Ziqiang Wang
Nature has revealed an astounding degree of phylogenetic and physiological diversity in natural environments -- especially in the microbial world. Microbial communities are incredibly diverse, ranging from 500-1000 species in human guts to over 1000 species in marine ecosystems. Historically, theoretical ecologists have devoted considerable effort to analyzing ecosystems consisting of a few species. However, analytical approaches and theoretical insights derived from small ecosystems consisting of a few species may not scale up to diverse ecosystems. Understanding such large complex ecosystems poses fundamental challenges to current theories and analytical approaches for modeling and understanding the microbial world. One promising approach for tackling this challenge that I develop in my thesis is to adapt and expand ideas from statistical mechanics to theoretical ecology. Statistical mechanics has helped us to understand how collective behaviors emerge from the interaction of many individual components. In this thesis, I present a unified theoretical framework for understanding complex ecosystems based on statistical mechanics, random matrix theories, and convex optimization. My thesis work has three key aspects: modeling, simulations, and theories. Modeling: Classical ecological models often focus on predator-prey relationships. However, this is not the norm in the microbial world. Unlike most macroscopic organisms, microbes relie on consuming and producing small organic molecules for energy and reproduction. In this thesis, we develop a new Microbial Consumer Resource Model that takes into account these types of metabolic cross-feeding interactions. We demonstrate that this model can qualitatively reproduce and explain statistical patterns observed in large survey data, including Earth Microbiome Project and the Human Microbiome Project. Simulations: Computational simulations are essential in theoretical ecology. Complex ecological models often involve ordinary differential equations (ODE) containing hundreds to thousands of interacting variables. Typical ODE solvers are based on numerical integration methods, which are both time and resource intensive. To overcome this bottleneck, we derived a surprising duality between constrained convex optimization and generalized consumer-resource models describing ecological dynamics. This allows us to develop a fast algorithm to solve the steady-state of complex ecological models. This improves computational performance by between 2-3 orders of magnitude compared to direct numerical integration of the corresponding ODEs. Theories:Few theoretical approaches allow for the analytic study of communities containing a large number of species. Recently, there has been considerable interest in the idea that ecosystems can be thought of as a type of disordered systems. This mapping suggests that understanding community coexistence patterns is actually a problem in "spin-glass'' physics. This has motivated physicists to use insights from spin glass theory to uncover the universal features of complex ecosystems. In this thesis, I use and extend the cavity method, originally developed in spin glass theories, to answer fundamental ecological questions regarding the stability, diversity, and robustness of ecosystems. I use the cavity method to derive new species backing bounds and uncover novel phase transitions to typicality
Thesis (PhD) — Boston College, 2021
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
9
Chia, Julian Yan Hon. "A micromechanics-based continuum damage mechanics approach to the mechanical behaviour of brittle matrix composites". Thesis, University of Glasgow, 2002. http://theses.gla.ac.uk/2856/.
Testo completoAbstract (sommario):
The thesis describes the development of a new continuum damage mechanics (hereafter, CDM) model for the deformation and failure of brittle matrix composites reinforced with continuous fibres. The CDM model is valid over sizes scales large compared to the spacing of the fibres and the dimensions of the damage. The composite is allowed to sustain damage in the form of matrix micro-cracking, shear delamination, tensile delamination and fibre failure. The constitutive equations are developed by decomposing the composite compliance into terms attributable to the fibre and matrix, and modelling the competing failure modes by intersecting failure surfaces based on maximum stress theory. The fibres are treated as being weakly bonded to the matrix so that the fibres only transmit axial loads, and fail in tension. The matrix is modelled as isotropic linear elastic and is treated as transversely-isotropic after damage has initiated. The effect of multiple matrix cracking on the stiffness was determined from experimental data, while failure was modelled by a rapid decay in the load bearing capacity. Although the model is motivated largely to proportional loading, matrix unloading and damage closure has been modelled by damage elasticity. During compression, the matrix stiffness is identical to the undamaged state with the exception that the fibres are assumed not to transmit compressive loads. The model was implemented computationally through a FORTRAN subroutine interfaced with the ABAQUS/Standard finite element solver. The CDM model was validated by comparing experimental and computational results of test specimens with unidirectional and balanced 0°-90° woven fibres of a brittle matrix composite, fabricated from polyester fibres in a polyester matrix. This composite system exhibits low elastic mismatch between fibres and matrix, and has similar non-dimensionalised stress-strain response to a SiC/SiC composite proposed for the exhaust diffuser unit of the Rolls-Royce EJ200 aero-engine.
10
Wang, Aiguo. "Abrasive wear of metal matrix composites". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305516.
Testo completo
11
Lyons, Jed S. "Micromechanical studies of crack growth in ceramic matrix composite". Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/16086.
Testo completo
12
Forsythe, Kristine M. "Mechanical behavior of transversely-loaded titanium matrix composite at elevated temperatures". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17028.
Testo completo
13
Davies, C. M. A. "Failure mechanisms in glass-ceramic matrix composite laminates". Thesis, University of Bath, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387305.
Testo completo
14
Li, Shanhu. "Extended voronoi cell finite element model for damage in brittle matrix composites". The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1135317411.
Testo completo
15
Messick, Casey Owen. "Examining the Mechanics Responsible for Strain Delocalization in Metallic Glass Matrix Composites". BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7043.
Testo completoAbstract (sommario):
Metallic glass matrix composites (MGMCs) have been developed to improve upon the ductility of monolithic metallic glass. These composites utilize a secondary crystalline phase that is grown into an amorphous matrix as isolated dendritic trees. This work seeks to understand the mechanisms underlying strain delocalization in MGMCs in order to better direct efforts for continual progress in this class of material. A mesoscale modelling technique based on shear transformation zone (STZ) dynamics is used to do so. STZ dynamics is a coarse grained technique that can provide insight into the microscopic processes that control macroscopic behavior, but which can be difficult to resolve experimentally. A combined simulated-experimental approach to extract the individual material properties of the amorphous and crystalline phases is presented. Numerically, STZ dynamics is used to simulate nanoindentation of the crystalline and amorphous phases respectively. The indented phases are modelled as discs with varying thickness embedded in the other phase. Indentation depths are held constant. Experimentally, nanoindentation is carried out on DH2 and DH3 MGMC composites under varying loads at Stony Brook University (SBU). Specimens are cross-sectioned and using scanning electron microscopy, indentation sites are chosen so that the indenter targets individual phases. For both experimental and simulated nanoindentation, hardness and modulus values are calculated from the load-displacement data. The experimental and simulated values are normalized and compared. Good agreement between results suggests accurate characterization of the individual phases at low loads on both DH2 and DH3 composites. Length scales at which indentations begin sampling outside the intended phase are presented. Work is then presented on simulated uniaxial tensile loading of MGMCs. Dendritic microstructural sizes are varied and shear banding characteristics are measured. A competition of shear band nucleation and propagation rates that previously had only been seen in monolithic metallic glasses under certain loading conditions is found to exist in MGMCs as well. The stages of shear banding in MGMCs are presented and the influence of dendrites on shear band nucleation and propagation are discussed. It is proposed that the introduction of dendrites into the amorphous matrix work to inhibit shear band propagation and encourage shear band nucleation to delocalize strain in MGMCs. In particular, it was found that smaller dendrite sizes and spacings are better at doing so.
16
Liew, Andrew Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "A study of a rotor system with ball bearing induced non-linearities; and the development of transfer matrix techniques suitable for analysing such systems". Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2003. http://handle.unsw.edu.au/1959.4/19227.
Testo completoAbstract (sommario):
This thesis is concerned with enhancing analysis tools for evaluating the non-linear dynamics of rotor bearing systems and in particular those where non-linearity is likely to result in aperiodic or chaotic behaviour, such as rolling element bearing systems. The tool to be enhanced was the transfer matrix approach which has been extensively used in the past for analysing linear rotor bearing systems. However, its use for evaluating non-linear behaviour has been virtually non-existent. Hence, the major aim of the thesis is to extend transfer matrix capabilities to handle non-linear systems. To this end a harmonic balance transfer matrix technique capable of analysing non-linear systems with multiple pedestal supported bearings was first developed. However, this approach is restricted to periodic response. To enable the analysis of non-linear systems with non-periodic response and provide a stability check for the harmonic balance technique, a transient transfer matrix has also been developed. The softwares for both of these newly developed transfer matrix techniques have been successfully verified for various non-linear rotor bearing systems using an established system matrix based transient rotordynamics software as the yardstick. These developments have been published in refereed journals. To investigate systems with rolling element bearings, appropriate bearing modelling which incorporates angular contact and rolling element inertia needed to be developed and incorporated into transient analysis softwares. Theoretical results from this were compared to data obtained from an experimental test rig which was designed to represent the salient features of an F/A-18 aircraft mounted accessory drive. The rig allowed for variation of bearing preload, unbalance loading and bearing support stiffness and could be run up to 17,000rpm. Full details of the design and commissioning are presented. Results showed better agreement than linear analyses but significant differences were encountered. Errors were largely due to estimated bearing parameters, in particular bearing damping, which was found to be a sensitive variable, so that agreement between theory and experiment was mainly qualitative. Other sources of error were those associated with experimental measurement and limitations of the bearing modelling. Further improvement of the bearing model is needed if better quantitative agreement is to be obtained between the predictions and experiment.
17
Saewong, Pakamard. "Erosion of glass and glass-ceramic matrix composites". Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300838.
Testo completo
18
Lee, Shi-Wei. "Analysis of Composite Laminates with Matrix Cracks". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45539.
Testo completoAbstract (sommario):
Analysis of the effects of matrix cracking on composite laminates is a well-known problem which has attracted considerable attention for the past decade. An approximate analytical solution is introduced in this thesis to study this type of problem.
The subjects of primary concern are the degradation of effective laminate properties, such as axial stiffness, Poisson's ratio, shear modulus, and coefficient of thermal expansion, as a function of crack density and the axial stress redistribution due to the existence of matrix cracks. Both transverse cracks (2-D problem) and cross (transverse and longitudinal) cracks (3-D problem) are studied. Results for graphite/epoxy cross-ply laminates are presented and compared to those of other approaches. Some other materials, for instance, glass/epoxy, are also studied. The results and comparisons will appear where appropriate. In general, the agreement between the results of the present analysis and those of other approaches, in particular, the finite element method, is good for the lower crack density. The present study shows that Poisson's ratio may be a good indicator of the degree of damage for a cracked laminate.Master of Science
19
劉英傑 e Yingjie Liu. "Damage characterization of multi-directional laminates with matrix cracks and delamination". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31235104.
Testo completo
20
Liu, Ying-jie. "Damage characterization of multi-directional laminates with matrix cracks and delamination /". Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B16504434.
Testo completo
21
Magid, Richard Allem. "Hemodynamic environment regulates matrix metalloproteinase-9 expression in vascular endothelial cells". Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/18993.
Testo completo
22
Jiang, Jian. "Formability and fracture mechanisms of particle reinforced metal matrix composites". Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360111.
Testo completo
23
Bedouet, Sylvain. "Study of damage evolution in a titanium matrix composite under quasi-static and dynamic loading". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/18225.
Testo completo
24
DiFrancia, Célene. "The single fiber pull-out test : a study of fiber/matrix interactions /". This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07282008-134341/.
Testo completo
25
Brauer, Erik [Verfasser]. "BMP-modulated extracellular matrix mechanics in the early phase of fracture healing / Erik Brauer". Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1203625057/34.
Testo completo
26
Messenger, C. R. "Investigation of delamination and matrix cracking in quasi-isotropic GFRP laminates". Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/842699/.
Testo completoAbstract (sommario):
Intra-laminar and inter-laminar cracking in GFRP laminates has been studied. The epoxy matrix used gave a transparent composite and was compatible with polyurethane, enabling a modified system (containing 20% urethane) to be investigated in addition to the standard epoxy. Three stacking sequences of quasi-isotropic laminates, (+45/-45/0/90)s, (0/90/-45/+45)s and (+45/90/-45/0)s were tested. Data were obtained for the growth of damage and its effect on laminate stiffness under increasing quasi-static load and as a function of number of fatigue cycles at two different stress levels. Using the transparent systems enabled a more complete set of damage data to be obtained than by previous workers. The damage comprised 90-ply cracking followed by +45 and -45 cracking and then for (+45/-45/0/90)s [and to a limited extent in (+45/90/-45/0)s], delamination. The initiation and growth of damage was examined with regard to matrix type and stacking sequence. The onset of matrix cracking and delamination are both delayed in the urethane-containing laminates; fracture mechanics tests showed that the urethane system was significantly tourer. Moreover, at a given quasi-static stress or number of fatigue cycles the urethane-modified laminates retain a greater proportion of their initial modulus. The stacking sequence influences interlaminar stresses (thereby controlling delamination) and determines parameters such as ply thickness and neighbouring ply orientation which in turn influence intralaminar cracking. Fracture mechanics has been applied to model the initiation and growth of delamination under quasi-static and cyclic loading using a modified compliance technique. Shear-lag models have been used to determine the stiffness loss due to intralaminar cracking, enabling the stiffness reduction associated with delamination to be deduced empirically. This enables the energy release rates associated with delamination to be derived leading to more sensible results than those obtained using an unmodified technique.
27
Zong, Bernie Yaping. "Strength and fracture of a metal matrix composite at elevated temperature". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260733.
Testo completo
28
Helgesson, Fredrik. "Analysis of a flight mechanics simulator". Thesis, KTH, Flygdynamik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-265616.
Testo completoAbstract (sommario):
Aircraft design is an act of art requiring dedication and careful work to ensure good results. An essential tool in that work is a flight mechanics simulator. Such simulators are often built up of modules/models that are executed in a sequential order in each time iteration. This project aims to analyze potential improvements to the model execution order based on the dependency structure of one such simulator. The analysis method Design Structure Matrix (DSM), was used to define/map the dependencies and then Binary Linear Programming (BLP) was utilized to find five new potentially improved model orders to minimize the number of feedbacks from one iteration to the next one. Those five proposed execution orders were next compared and evaluated. The result is a model order that reduce the number of models receiving feedbacks from the previous iteration from 13 to 6, with insignificant changes in the precision of the simulator.Vid flygplanskonstruktion krävs hårt och noggrant arbete för att säkerställa gott resultat. Ett oumbärligt verktyg är då en flygmekanisk simulator. Den typen av simulatorer är ofta uppbyggda av moduler/modeller som exekveras i en bestämd sekventiellt ordning i varje tidsteg. Syftet med detta projekt är att undersöka möjliga förbättringar av exekverings ordningen av de olika modellerna i en existerande simulator, baserat på beroendestrukturen. Analysmetoden Design Structure Matrix (DSM) användes för att bestämma beroendestrukturen och sedan utnyttjades Binär Linjär Programmering (BLP) för att hitta fem förbättrade modellordningar med avseende på att minimera antalet modeller som erhåller indata från föregående tidsiteration. De fem förbättringsförslagen jämfördes och utvärderades. Resultatet är en modellordning som kan minska antalet återkopplande modeller från 13 till 6, med insignifikanta skillnader i precisionen av simulatorn.
29
Huang, Xinyu. "Mechanics and Durability of Fiber Reinforced Porous Ceramic Composites". Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/26063.
Testo completoAbstract (sommario):
Porous ceramics and porous ceramic composites are emerging functional materials
that have found numerous industrial applications, especially in energy conversion
processes. They are characterized by random microstructure and high porosity.
Examples are ceramic candle filters used in coal-fired power plants, gas-fired
infrared burners, anode and cathode materials of solid oxide fuel cells, etc.
In this research, both experimental and theoretical work have been conducted to
characterize and to model the mechanical behavior and durability of this novel
class of functional material. Extensive experiments were performed on a hot gas
candle filter material provided by the McDermott Technologies Inc (MTI). Models at
micro-/meso-/macro- geometric scales were established to model the porous ceramic
material and fiber reinforced porous ceramic material. The effective mechanical
properties are of great technical interest in many applications. Based on the
average field formalism, a computational micromechanics approach was developed to estimate
the effective elastic properties of a highly porous material with random microstructure.
A meso-level analytical model based on the energy principles was developed to estimate
the global elastic properties of the MTI filament-wound ceramic composite tube.
To deal with complex geometry, a finite element scheme was developed for
porous material with strong fiber reinforcements. Some of the model-predicted elastic
properties were compared with experimental values. The long-term performance of ceramic
composite hot gas candle filter materials was discussed. Built upon the stress analysis
models, a coupled damage mechanics and finite element approach was presented to assess
the durability and to predict the service life of the porous ceramic composite
candle filter material.Ph. D.
30
Yilmaz, Hamdi Sencer. "Characterization Of Silicon Carbide Particulate Reinforced Squeeze Cast Aluminum 7075 Matrix Composite". Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605261/index.pdf.
Testo completoAbstract (sommario):
The aim of this study is to investigate the mechanical behavior and its relation with processing and microstructure of the silicon carbide particulate (SiCp) reinforced aluminum matrix composite. Aluminum 7075 alloy is chosen as matrix alloy, in which zinc is the main alloying element. Four different additions of SiCp were used and the weight fractions were 10%, 15%, 20% and 30%. Composites were processed by with squeeze casting and the applied pressure during casting was 80 MPa. The mould is specially designed to produce both specimens ready for tensile and three point bending tests.
Both as-cast and heat treated aluminum composites were examined and T6 heat treatment was applied. Three point bending tests were performed to reveal the fracture strength of aluminum composites. 10wt% SiCp aluminum composites showed the maximum flexural strength in both as-cast and heat treated composites. The mechanical test results revealed that precipitated phases in heat treated composites, behaved like fine silicon carbide particulates and they acted as barriers to dislocation motion. Maximum flexural strength increased about 40 MPa (10%) in as-cast and 180 MPa (44%) in heat treated composites. Tensile testing was also conducted to verify the results of the three point bending tests.
Hardness tests were done to find the effect of silicon carbide addition and to find the peak hardness in heat treatment. For as-cast specimens hardness values increased from 133 to 188 Vickers hardness (10 kg.) with increase in SiCp content from 0 to 30wt% and for heat treatment specimens hardness values increased from 171 to 221 Vickers hardness (10 kg.). The peak hardness values were obtained at 24 hours precipitation heat treatment. SEM studies were carried out to examine the heat treated composites, to take SEM photographs and to obtain a general elemental analysis. Theoretical volume percentage addition of SiCp was checked with Clemex Image Analyzer program. Distribution of SiCp was determined by mettalographic examination. Second phases that were formed during heat treatment was searched by x-ray analysis.
31
Pryce, A. W. "Matrix cracking and stress/strain behaviour of continuous fibre ceramic composite laminates". Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/843150/.
Testo completoAbstract (sommario):
Matrix damage and its effects on mechanical properties have been examined for SiC (Nicalon1) fibre reinforced glass and glass ceramic matrix composites under quasi-static and fatigue loading conditions. Nicalon/Pyrex laminates of different lay-ups have been tested under quasi-static tension. The elastic moduli have been measured and matrix damage monitored as a function of applied strain. The mechanical properties are strongly influenced by the presence of crystalline regions in the matrix which promote microcracking. Laminated plate theory is used to provide bounds to the moduli of the laminates. For unidirectional and simple crossply Nicalon/CAS2 laminates the quasi-static stress/strain behaviour and associated matrix damage accumulation have been examined in detail. The damage development with applied stress was quantified by counts of crack density (in both longitudinal and transverse plies), stiffness loss and cumulative residual strain. The quasi static stress/strain behaviour during continuous tests (accumulating damage) and discontinuous tests (constant damage) have been modelled using a stress analysis based on Aveston, Cooper and Kelly (ACK) theory. The continuous stress/strain behaviour of (0/90) crossply laminates has been modelled using a shear-lag analysis developed previously to describe the transverse ply cracking behaviour of polymer matrix composites. The analysis is modified to account for longitudinal ply cracking. Matrix damage development in unidirectional and (0/90) crossply laminates under quasistatic cycling and high frequency fatigue loading have been studied. For unidirectional laminates stable stress/strain hysteresis loops were obtained during quasi-static cycling, corresponding to stable matrix damage states. These and similar loops obtained after high frequency fatigue are modelled using, the discontinuous stress/strain analysis. It is suggested that the effect of high frequency fatigue is to decrease the interfacial shear strength.
32
Goodwin, Katharine Elizabeth. "Elucidating the role of cell to extracellular matrix adhesion in regulating tissue mechanics during development". Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55441.
Testo completoAbstract (sommario):
Tissue morphogenesis requires force-generating mechanisms to drive the organization of cells into complex three-dimensional structures. Although such mechanisms have been characterized across the metazoan lineage, we know little about how force transmission across a tissue is regulated. Here, using Drosophila melanogaster as a model system, I provide evidence that integrin-mediated cell-ECM adhesion is required for the regulation and transmission of forces in tissues. Specifically I show that during Dorsal Closure (DC), an integrin-dependent morphogenetic process that occurs during Drosophila embryogenesis, failure to regulate the level of cell-ECM adhesion results in abnormal levels of tension in the amnioserosa (AS), an extra-embryonic epithelium that is essential for DC. Integrin-containing adhesive structures were identified on the basal surface of the AS that share many features with focal adhesions. Using mutations that either increase or decrease integrin-based Cell-ECM adhesion, I show that DC is defective in both cases, and that the level of adhesion is inversely correlated with the mobility of cells in the AS. Mathematical modeling, quantitative image analysis, and in vivo laser ablation experiments reveal a relationship between cell mobility and the magnitude, distribution and transmission of tension in the AS. Finally, I provide evidence that mechanical coupling exists between AS cells and their substrate, the underlying ECM and the yolk membrane. Overall, my data shows that integrins regulate the transmission of forces across the AS, and thereby control a critical component of DC. I propose that modulating Cell-ECM adhesion could provide control over force transmission within developing tissues to promote specific outcomes.Medicine, Faculty of
Graduate
33
Antoine, Elizabeth Elena. "Mechanics and transport characterization of bioengineered tissue microenvironment platforms". Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/56954.
Testo completoAbstract (sommario):
The tissue microenvironment is a complex living system containing heterogeneous mechanical and biophysical cues. Cellular components are surrounded by extracellular matrix and interstitial fluid, while transport of nutrients and biochemical factors is achieved via the vasculature. Each constituent of the tissue microenvironment can play a significant role in its ability to function normally. Many diseases including cancer have been linked with dysfunction in the tissue microenvironment; therefore an improved understanding of interaction between components of this complex system is needed.
In vitro platforms mimicking the tissue microenvironment appear to provide the most promising avenue for studies of cell-cell and cell-matrix interactions as well as elucidation of the mechanisms leading to disease phenomena such as tumor metastasis. However, successful recapitulation of all three primary components of the tissue microenvironment in three dimensions has remained challenging. In particular, matching mechanical cues and biochemical transport to in vivo conditions is difficult because of lack of quantitative characterization of the physical properties and parameters of such platforms.
In this work, extensive characterization of collagen I hydrogels, popular for use as extracellular matrix mimics, was performed in order to enable tuning to specific in vivo conditions. Additionally, perfusion of blood in a 3D tissue microenvironment platform fabricated using collagen hydrogels was characterized to enable future advances in in vitro modeling of the in vivo microenvironment. Finally, the tissue microenvironment platform is modified to enable biochemical gradients within the hydrogel and used to examine directed migration (chemotaxis) of human breast cancer cells in response to gradients in growth factor combined with varied stiffness and pore diameter of the extracellular matrix.Ph. D.
34
Antoine, Elizabeth E. "Mechanics and transport characterization of bioengineered tissue microenvironment platforms". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/56954.
Testo completoAbstract (sommario):
The tissue microenvironment is a complex living system containing heterogeneous mechanical and biophysical cues. Cellular components are surrounded by extracellular matrix and interstitial fluid, while transport of nutrients and biochemical factors is achieved via the vasculature. Each constituent of the tissue microenvironment can play a significant role in its ability to function normally. Many diseases including cancer have been linked with dysfunction in the tissue microenvironment; therefore an improved understanding of interaction between components of this complex system is needed.
In vitro platforms mimicking the tissue microenvironment appear to provide the most promising avenue for studies of cell-cell and cell-matrix interactions as well as elucidation of the mechanisms leading to disease phenomena such as tumor metastasis. However, successful recapitulation of all three primary components of the tissue microenvironment in three dimensions has remained challenging. In particular, matching mechanical cues and biochemical transport to in vivo conditions is difficult because of lack of quantitative characterization of the physical properties and parameters of such platforms.
In this work, extensive characterization of collagen I hydrogels, popular for use as extracellular matrix mimics, was performed in order to enable tuning to specific in vivo conditions. Additionally, perfusion of blood in a 3D tissue microenvironment platform fabricated using collagen hydrogels was characterized to enable future advances in in vitro modeling of the in vivo microenvironment. Finally, the tissue microenvironment platform is modified to enable biochemical gradients within the hydrogel and used to examine directed migration (chemotaxis) of human breast cancer cells in response to gradients in growth factor combined with varied stiffness and pore diameter of the extracellular matrix.Ph. D.
35
Moore, Robert Hunter. "Elastic and time dependent matrix cracking in cross-ply composite laminates". Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/63971.
Testo completoAbstract (sommario):
The effects of time and stress level were investigated in cross-ply laminates to gain more understanding on the damage events in composites.
Analytical predictions of the effect of stress level were performed for the case of linear elastic materials. The predictions were based on energy methods and linear elastic fracture mechanics. Damage was simulated with a Monte Carlo numerical scheme. The predicted results corresponded well with experimental data in the literature.
Experimental testing was performed on cross-ply laminates to gain a better understanding of the effect of time and rate on matrix cracking. The tests were performed on Kevlar/epoxy and graphite/epoxy [0/90₃]₈ laminates. The results indicate that the stress levels required for matrix cracking are a function of how fast the specimens were loaded. Also, significant time dependent damage was observed in cross-ply laminates which were subjected to sustained loads.Master of Science
36
From, Erik. "Influence of matrix and alloying on the high cycle fatigue properties of compacted graphite iron for cylinder heads". Thesis, KTH, Hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277782.
Testo completoAbstract (sommario):
Continued improvements in combustion processes, introduction of biofuels, decreasing fuel consumption and increasing specific power will inevitably lead to an increase of the combustion pressure, which can be accompanied with a temperature increase. This will increase the loading on many components and drives the development of materials more resistant to the harsh conditions close to the engine. The cylinder head is one of the components that will be affected by the increased loads. Therefore, thermomechancial loads (TMF) originating from the cyclic temperature variations from the heating up and cooling down cycles of the engine and the high cycle fatigue load (HCF) emanating from the repeated combustion pressure pulses may cause failure of the component. Today, most cylinder heads for heavy trucks are cast in either lamellar graphite iron (LGI) or compacted graphite iron (CGI). In both cases, the graphite particles are embedded in a pearlitic matrix. A possible improvement of the endurance life of the component is to add silicon to the composition. Silicon promotes the formation of ferrite and the hypotheis is that the more ductile ferritic matrix enclosing the graphite particles will improve the resistance to macro crack initiation and propagation and thus the life of the component. The purpose of this master thesis is to investigate the effect of a ferritic matrix as well as other added alloying elements such as molybdenum and nickel on the high cycle fatigue properties of CGI. The HCF properties of three ferritic alloys with different amounts of molybdenum and four pearlitic alloys with additions of molybden or nickel were compared at a fatigue life of 2 miljon cycles and a stress ratio of R=0.1. The results show that the silicon alloyed ferritic base material, without molybdenum, had a fatigue strength that on average was about 10 % higher than the corresponding pearlitic base alloy without alloying elements. Adding 0.25 wt % molybdenum improved the fatigue strength for both the pearlitic and the ferritic alloy with about 5-10 %. Further, for the pearlitic materials, molybdenum also improved the static mechanical properties while no such effect was seen for the alloys with a ferritic matrix. It was also found that nickel did not alter the HCF or the static properties significantly on the materials with pearlitic matrix.
37
DiFrancia, Célene. "The single fiber pull-out test: a study of fiber/matrix interactions". Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/38866.
Testo completo
38
Osborne, Deborah J. "Experimental and computational study of interphase properties and mechanics in titanium metal matrix composites at elevated temperatures /". View online ; access limited to URI, 2007. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3277003.
Testo completo
39
Degnan, Craig Cambell. "Processing and wear properties of a (W,Ti)C particulate reinforced ferrous-based metal matrix composite". Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285253.
Testo completo
40
Edginton, Ryan Stuart. "The multiscale biomechanics and mechanochemistry of the extracellular matrix protein fibres, collagen & elastin". Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34619.
Testo completoAbstract (sommario):
Collagen is the most abundant protein in the animal kingdom and, together with elastin, forms extensive fibrous networks that constitute the primary structure of the mammalian extracellular matrix, respectively endowing it with the tensile and elastic properties that fulfil its principal role as the passive framework of the body. The fibrous proteins are distinctly hierarchically organised from the molecular scale upwards; for example, the nanoscale tropocollagen monomer assembles in arrays that form the micrometer scale microfibrils and fibrils, and thence into collections of millimetre scale collagen fibres, that in-turn, constitute functional tissues such as skin, tendon and bone. Much is known about the structure at each of these individual scales – collagen being the most extensively researched – and the macromechanics of the fibres are well established. However, far less is known about the micromechanics of these proteins, in particular how the monomers influence the functional mechanics of the macroscopic fibres. In this thesis, I explore the multiscale mechanics of collagen and elastin fibres over a range of hydrations – with fibres in direct contact with aqueous solution, and progressively dehydrated in humidity-controlled environments. I use quasi-static tensile testing to probe the macroscopic mechanical response (Young’s modulus and stress relaxation) of the fibres, and employ Brillouin and Raman microscopy to assess the longitudinal modulus in the GHz range and corresponding molecular properties of the proteins. Brillouin microscopy is an emerging technique in the biomedical field. It enables the all-optical, contact-free and non-destructive testing of tissue micromechanics through detection of frequency shifted light scattered off thermally excited acoustic waves or “phonons” in the GHz range. As one of the first studies of Brillouin light scattering in these fibres, it sets the basis for further investigation of tissue biomechanics. In particular, I provide the full description of the protein fibre micromechanics by performing angular measurements using a so-called platelet-like configuration with sample mounted onto a reflective substrate at 45° angle to the excitation beam. I derive the high-frequency longitudinal modulus, and discuss the results in comparison to the Young’s modulus, in terms of the different frequency and spatial scale of the measurements. I obtained a full description of elasticity using Brillouin spectroscopy applied to dried fibres; however, obtaining the same description in hydrated fibres is a challenge, as the Brillouin spectrum is dominated by water. An assessment of the mechanical differences between type-I and type-II collagens is also given here. Water is known to be a primary determinant of tissue biomechanics, and I identified for the first time, the critical hydration ranges between 100 and 85% relative humidity (RH) for collagen, and around 85% RH for elastin, at which point each macroscopic fibre switched from viscoelastic to plastic-like behaviour. Dehydration below these critical points was shown to severely diminish collagen fibrillar sliding, and completely rob elastin of its ability to reversibly deform under strain. The Young’s modulus increased markedly below these hydrations, and I observed a parallel increase in the longitudinal modulus at high frequencies in each protein, indicating a concomitant increase in stiffness at the two scales. The major difference observed between the two fibrous proteins is that, in the case of elastin, I observe a two-fold increase in the longitudinal modulus as the hydration is decreased from 100 to 21% RH, whilst the Young’s modulus increases by two orders of magnitude. This discrepancy was not observed in collagen, which confirmed that the protein maintained its long-range order in the form of the triple helix at all hydrations employed in this work, whilst the elastin ultrastructure experiences a liquid-to-solid state change at a critical hydration. I demonstrate through the analysis of the low-wavenumber region (< 500 cm-1) of the Raman spectrum, that the increase in molecular stiffness of both proteins, is reflected in an increase in torsional rigidity of the peptide backbone upon dehydration. Moreover in collagen, I observe a reduction in the number of inter-protein water bridges, which I propose causes a collapse of the lateral spacing between monomers and an increase in direct backbone-backbone hydrogen bonding, that further stiffens the fibre. Small strain induced reorientations of the amide III and C–C stretching modes in dehydrated collagen fibres suggest that macroscopic stresses may be transferred to the triple helix, otherwise left unperturbed in the hydrated state. I postulate that this is a result of the degraded intra- and interfibrillar sliding mechanism below the critical hydration. Hence in its dehydrated state, the collagen whole-fibre mechanics are similar to those at the molecular scale. The role of proteoglycans and glycosaminoglycans and their potential connection to hydration, is also discussed. In agreement with previous work, I found no Raman spectral changes as a result of stretching hydrated elastin fibres, indicating that even large strains e.g. 80%, have no significant effect on the structural scale probed by Raman microscopy, nor in the air-dried state where the brittle fibres break at low strains. I suggest this may imply a limited sensitivity of Raman bands to these changes, possibly an indication of elastin’s dynamic ultrastructure, or that stress is dissipated at a higher level of the fibre structure. On the macroscopic scale, it is the poroelastic nature of elastin which controls the stress relaxation under strain, and the elastic recovery is mediated by an interplay of hydrophobic interactions and hydration forces.
41
Fiore, Vincent F. "INVESTIGATION OF MECHANOTRANSDUCTORY MECHANISMS IN THE PATHOGENESIS OF LUNG FIBROSIS". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53424.
Testo completoAbstract (sommario):
Fibrosis of vital organs remains one of the leading causes of death in the developed world, where it occurs predominantly in soft tissues (liver, lung, kidney, heart) through fibroblast proliferation and deposition of extracellular matrix (ECM). In the process of fibrosis, remodeling and deposition of ECM results in stiffening of cellular microenvironment; cells also respond to these changes in the stiffness through engagement of their cytoskeleton and signaling via cell-ECM contacts. Thus, understanding to what extent the stiffness of the cellular microenvironment changes as a consequence of fibrotic progression, and how cells respond to this change, is critical. In this thesis, we quantitatively measured stiffness of the lung parenchyma and its changes during fibrosis. We find that the average stiffness increases by approximately 10-fold. We then investigated how changes in ECM rigidity affect the cytoskeletal phenotype of lung fibroblasts. We find a complex relation between expression of the glycoprotein Thy-1 (CD90) and ECM rigidity-dependent cytoskeletal phenotype (i.e. “mechanotransduction”). Finally, we investigate a mechanism for the regulation of rigidity sensing by Thy-1 and its involvement in intracellular signaling through cell-ECM contacts. Taken together, this work helps define in vivo parameters critical to the fibrogenesis program and to define unique cellular phenotypes that may respond or contribute to mechanical homeostasis in fibrotic diseases.
42
Lundholm, Douglas. "Zero-energy states in supersymmetric matrix models". Doctoral thesis, KTH, Matematik (Avd.), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12846.
Testo completoAbstract (sommario):
The work of this Ph.D. thesis in mathematics concerns the problem of determining existence, uniqueness, and structure of zero-energy states in supersymmetric matrix models, which arise from a quantum mechanical description of the physics of relativistic membranes, reduced Yang-Mills gauge theory, and of nonperturbative features of string theory, respectively M-theory. Several new approaches to this problem are introduced and considered in the course of seven scientific papers, including: construction by recursive methods (Papers A and D), deformations and alternative models (Papers B and C), averaging with respect to symmetries (Paper E), and weighted supersymmetry and index theory (Papers F and G). The mathematical tools used and developed for these approaches include Clifford algebras and associated representation theory, structure of supersymmetric quantum mechanics, as well as spectral theory of (matrix-) Schrödinger operators.QC20100629
43
Hill, Katherine I. "DNAPL migration in single fractures : issues of scale, aperture variability and matrix diffusion". University of Western Australia. School of Environmental Systems Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0003.
Testo completoAbstract (sommario):
[Truncated abstract] To date, many subsurface contaminant modelling studies have focused on increasing model complexity and measurement requirements to improve model accuracy and widen model application. However, due to the highly complex and heterogeneous nature of flow in the subsurface, the greater benefit in model development may lie in decreasing complexity by identifying key processes and parameters, simplifying the relationships that exist between them, and incorporating these relationships into simple models that recognise or quantify the inherent complexity and uncertainty. To address this need, this study aims to identify and isolate the key processes and parameters that control dense nonaqueous phase liquid (DNAPL) and aqueous phase migration through single, onedimensional fractures. This is a theoretical representation which allows the study of processes through conceptual and mathematical models. Fracture systems typically consist of multiple two-dimensional fractures in a three-dimensional network; however, these systems are computationally and conceptually demanding to investigate and were outside of the scope of this study. This work initially focuses on DNAPL migration in single, one-dimensional fractures. The similitude techniques of dimensional and inspectional analysis are performed to simplify the system and to develop breakthrough time scale factors. This approach relies heavily on the limitations of the equation used for the analysis and on the difficulty in representing variable aperture scenarios. The complexity of the conceptual model is then increased by embedding the fracture in a two-dimensional, porous matrix. ... These tools can be readily applied by the field investigator or computer modeller to make order-of-magnitude estimates of breakthrough times, reduce or target measurement requirements, and lessen the need to employ numerical multiphase flow models. To determine the implications of the results found in the one-dimensional studies to applications at the field scale, the complexity of the conceptual model was increased to a single, two-dimensional, planar fracture embedded in a three-dimensional porous matrix. The focus of this study was not DNAPL breakthrough times but the relative importance and interaction of different mass transport processes and parameters on plume migration and evolution. Observations clearly show that estimates of the size, location and concentration of the plume is highly dependent on the geologic media, the temporal and spatial location and resolution of measurements, and on the history, mass and location of the DNAPL source. In addition, the processes controlling mass transport (especially matrix diffusion and back diffusion) act in combination at the field scale in ways not always expected from an analysis of processes acting individually at smaller spatial and temporal scales. Serious concerns over the application of the common '1% Rule of Thumb' to predict DNAPL presence and the use of remediation efforts that rely largely on natural attenuation are raised. These findings have major implications for the field worker and computer modeller, and any characterisation, monitoring or remediation program development needs to be sensitive to these findings.
44
Thompson, Ronald H. "Plane frame element addition to the MESS finite element program". Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/80052.
Testo completoAbstract (sommario):
A plane frame element based on linear, elastic theory is developed and implemented into the MESS finite element program. Post-processed results include nodal displacements, end reactions, maximum tensile and average shear stress, and a deformed geometry plot. The element is tested for accuracy relative to simple beam theory and by comparison with results generated using another finite element program. In both cases agreement to within 6 significant figures was achieved.
Because the intended use is educational, a survey of its benefit as a design aid in undergraduate instruction is included. These benefits are based on test cases from senior design class projects. Results generated using analysis techniques presently available are contrasted with those using the plane frame element. Students' work that was examined contained mistakes resulting from large amounts of hand calculations. Conversely, results generated using the finite element method proved to be easily obtained and to have a higher degree of accuracy. A recommendation for further improvements in program capability is provided at the end of the study.Master of Science
45
Ma, Xiaoyue. "FINITE ELEMENT MODELING OF COLLAGEN FIBERS IN THE MECHANICAL INTERACTION BETWEEN CELLS AND THE EXTRACELLULAR MATRIX". The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343415336.
Testo completo
46
Griggs, Lauren. "FIBRONECTIN MECHANICS AND SIGNALING IN TGF-β1-INDUCED EPITHELIAL TO MESENCHYMAL TRANSITION". VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5539.
Testo completoAbstract (sommario):
Epithelial to Mesenchymal Transition (EMT) is a dynamic process by which a distinct change in the phenotype and function of epithelial cells render them as mesenchymal cells. Characteristics of mesenchymal cells include the ability to invade, increased migratory kinetics and heightened resistance to apoptosis. Therefore, there is a strong need to fully understand the mechanism for the induction of EMT in pathological conditions such as carcinoma progression. Recent advances highlight two pivotal contributors, soluble growth factor (gf) signals, and mechanical signals, in the process. However, to date, no clear mechanism exists linking the two in epithelial transdifferentiation. Transforming Growth Factor-β1 (TGF-β1), a gf known to induce EMT in breast cancer formation, induces EMT on rigid surfaces and apoptosis on compliant surfaces. It is our belief that a combination of mechanical signals, gf signals, and the type of extracellular matrix (ECM) proteins assembled by cells together drive the process of EMT. Here we investigated the role of the ECM protein fibronectin (FN) in EMT. Upon assembly into elastic, insoluble fibrils through cell-generated forces which become larger on stiffer surfaces, FN is able to serve as a gf delivery system. We examined the following hypothesis: Increased tissue stiffness drives FN assembly, which exposes cryptic binding sites for various gfs, such as TGF-β1, and creates a high concentration of these gfs at the cell surface, which in turn drives EMT. In this project we investigated three aims: (1) evaluate the effect of inhibiting FN fibrillogenesis and gf localization on TGF-β1-induced EMT, (2) assess the effect of TGF-β1 concentration on spatial patterning of ECM dynamics, cell phenotype and adherens junctional force, and (3) probe the role of the FN matrix in TGF-β1-induced spatial patterning of EMT. Results showed that both inhibition of FN fibril assembly and blocking the gf binding site on fibrils significantly attenuated the downstream effects of EMT. In microcontact patterns of epithelial colonies, increasing gf concentration led to spatial patterning of FN fibrils, cell phenotype and cell-cell junctional force. Elimination of FN fibrils effectively attenuated TGF-β1-induced spatial patterning. The knowledge acquired through these studies serves as an addition to an increasingly important body of work aimed at elucidating how physical changes within the microenvironment regulate physiology and pathology. By establishing a novel mechanism by which gf signaling induces EMT through interaction with the extracellular matrix, this research serves to combat the development and initiation of pathological phenomena, such as metastasis.
47
Karakas, Mustafa Serdar. "Effect Of Aging On The Mechanical Properties Of Boron Carbide Particle Reinforced Aluminum Metal Matrix Composites". Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608944/index.pdf.
Testo completoAbstract (sommario):
Metal matrix composites (MMCs) of Al - 4 wt.% Cu reinforced with different volumetric fractions of B4C particles were produced by hot pressing. The effect of aging temperature on the age hardening response of the composites was studied and compared with the characteristics exhibited by the matrix alloy. Reinforcement addition was found to considerably affect the age hardening behavior. Detailed transmission electron microscopy and differential scanning calorimetry observations were made to understand the aging response of the composites. The low strain rate and high strain rate deformation behavior of the MMCs were determined utilizing low velocity transverse rupture tests and true armor-piercing steel projectiles, respectively. Increasing the volume fraction of B4C led to a decrease in flexural strength. The flexural strength vs. strain rate plots showed a slight increase in strength followed by a decrease for all samples. The mechanical performance of the composites and the unreinforced alloy were greatly improved by heat treatment. The MMCs were found to be inferior to monolithic ceramics when used as facing plates in armors.
48
Keles, Ozgur. "Production And Characterization Of Alumina Fiber Reinforced Squeeze Cast Aluminum Alloy Matrix Composites". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609726/index.pdf.
Testo completoAbstract (sommario):
The aim of the present study was to investigate the effects of different levels of Saffil alumina fiber addition, magnesium content in aluminum alloy matrix and casting temperature on the mechanical behavior, microstructure and physical properties of short fiber reinforced aluminum matrix composites. The main alloying element silicon was kept constant at 10 wt%. Magnesium contents were selected as 0.3 wt% and 1 wt%. Saffil alumina fiber preforms varied from 10 to 30 vol%. The casting temperatures were fixed at 750 °C and 800 °
C. Micro porosity was present at the fiber-fiber interactions. Closed porosity of the composites increased when fiber vol% increased, however, variation in casting temperature and magnesium content in matrix did not have influence on porosity. Hardness of the composites was enhanced with increasing fiber vol%, magnesium content in matrix and decreasing casting temperature. Alignment of fibers within the composite had an influence on hardness
when fibers were aligned perpendicular to the surface, composites exhibited higher hardness. The highest hardness values obtained from surfaces parallel and vertical to fiber orientation were 155.6 Brinell hardness and 180.2 Brinell hardness for AlSi10Mg1 matrix 30 vol% alumina fiber reinforced composite cast at 800 °
C and at 750 °
C, respectively. 30 vol% Saffil alumina fiber reinforced AlSi10Mg0.3 matrix composite cast at 750 °
C showed the highest flexural strength which is 548 MPa. Critical fiber content was found as 20 vol% for all composites.
49
Sundberg, Jenny. "Heat Transfer Correlations for Gas Turbine Cooling". Thesis, Linköping University, Department of Mechanical Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5446.
Testo completoAbstract (sommario):
A first part of a ”Heat Transfer Handbook” about correlations for internal cooling of gas turbine vanes and blades has been created. The work is based on the cooling of vanes and blades 1 and 2 on different Siemens Gas Turbines. The cooling methods increase the heat transfer in the cooling channels by increasing the heat transfer coefficient and/or increasing the heat transfer surface area. The penalty paid for the increased heat transfer is higher pressure losses.
Three cooling methods, called rib turbulated cooling, matrix cooling and impingement cooling were investigated. Rib turbulated cooling and impingement cooling are typically used in the leading edge or mid region of the airfoil and matrix cooling is mostly applied in the trailing edge region.
Literature studies for each cooling method, covering both open literature and internal reports, were carried out in order to find correlations developed from tests. The correlations were compared and analyzed with focus on suitability for use in turbine conditions. The analysis resulted in recommendations about what correlations to use for each cooling method.
For rib turbulated cooling in square or rectangular ducts, four correlations developed by Han and his co-workers [3.5], [3.8], [3.9] and [3.6] are recommended, each valid for different channel and rib geometries. For U-shaped channels, correlations of Nagoga [3.4] are recommended.
Matrix cooling is relatively unknown in west, but has been used for many years in the former Soviet Union. Therefore available information in open literature is limited. Only one source of correlations was found. The correlations were developed by Nagoga [4.2] and are valid for closed matrixes. Siemens Gas Turbines are cooled with open matrixes, why further work with developing correlations is needed.
For impingement cooling on a flat target plate, a correlation of Florschuetz et al. [5.7] is recommended for inline impingement arrays. For staggered arrays, both the correlations of Florschuetz et al. [5.7] and Höglund [5.8] are suitable. The correlations for impingement on curved target plate gave very different results. The correlation of Nagoga is recommended, but it is also advised to consult the other correlations when calculating heat transfer for a specific case.
Another part of the work has been to investigate the codes of two heat transfer programs named Q3D and Multipass, used in the Siemens offices in Finspång and Lincoln, respectively. Certain changes in the code are recommended.
50
Andre, Daniel Batista. "Weyl expansion for multicomponent wave equations". Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310887.
Testo completo