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Cinefra, Maria. "Refined and advanced shell models for the analysis of advanced structures." Thesis, Paris 10, 2012. http://www.theses.fr/2012PA100051/document.
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La thèse est décomposée en trois parties. Dans la première partie, les modèles de la CUF sont présentés. La CUF permet d’obtenir, dans un formalisme générale, de nombreux modèles qui diffèrent 1) selon l’ordre d’expansion dans l'épaisseur choisie pour les variables primaires; 2) selon le type de modèle: modèles couche équivalente (ESL) ou couche discrète (LW); 3) selon le principe variationnel : “Principle of Virtual Displacements” (raffinée) ou “Reissner’s Mixed Variational Theorem” (avancée). Des géométries cylindrique et à double courbure sont traités. La deuxième partie de la thèse est consacrée à l'obtention des équations fondamentales en utilisant différentes méthodes: la méthode analytique de Navier et deux méthodes numériques approchées; la “Finite Element Method” (FEM) et la “Radial Basis Functions” (RBF). La méthode RBF est une méthode sans maillage “meshless” et peut être considérée comme une méthode alternative à la FEM. La FEM est la plus utilisée dans la littérature et le sujet principal de cette thèse.Dans la dernière partie, différents problèmes sont proposés. Navier est utilisé pour l’analyse thermomécanique de coques FGM, l’analyse de coques piézo-électrique et l’analyse dynamique de nanotubes de carbone. Un élément fini coque, présenté dans cette thèse, est utilisé pour l’analyse de coques composites et FGM. Les résultats obtenus démontrent la supériorité de cet élément par rapport aux éléments finis basés sur les théories classiques pour l’analyse des matériaux avancés. Enfin, la méthode RBF est utilisée pour l’analyse de coques composites, permettant d'illustrer l'avantage des méthodes sans maillageThe dissertation is organized in three main parts. In the first part, the shell models contained in the CUF are presented. The CUF permits to obtain, in a general and unified manner, several models that can differ by 1) the chosen order of expansion in the thickness direction, 2) the equivalent single layer or layer wise approach and 3) the variational statement used: “Principle of Virtual Displacements” (refined models) or “Reissner’s Mixed Variational Theorem” (advanced models). Both the cylindrical and the double-curvature geometries are considered. The second part is devoted to the derivation of the governing equations by means of different methods: an analytical method, that is the Navier method, and two approximated numerical methods, that are the Finite Element Method (FEM) and the Radial Basis Functions (RBF) method. The RBF method is based on a meshless approach and it can be considered a good alternative to the FEM. The finite element method is the most common method used in literature and it is the main topic of this thesis. In the last part, different problems are analyzed. The thermo-mechanical analysis of FGM shells, the electromechanical analysis of piezoelectric shells and the dynamic analysis of carbon nanotubes are performed by means of the Navier method. Then, the CUF shell finite element, presented in this thesis, is tested and used for the analysis of composite and FGM shells. The superiority of this element in respect to finite elements based on classical theories is shown. Finally, the RBF method is combined with the CUF for the analysis of composite and FGM shells in order to overcome the numerical problems relative to the mesh that usually affect the finite elements
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Peterson, Emily Cassidy. "Shear-induced microstructure in hollow fiber membrane dopes." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50245.
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Hollow fiber membranes offer the opportunity to dramatically reduce the energy required to perform gas separations in the chemical industry. The membranes are fabricated from highly non-Newtonian precursor materials, including concentrated polymer solutions that sometimes also contain dispersed particles. These materials are susceptible to shear-induced microstructural changes during processing, which can affect the characteristics of the resulting membrane. This thesis explores several shear-related effects using materials and flow conditions that are relevant for fiber spinning. The findings are discussed as they relate to membrane processing, and also from the standpoint of enhancing our fundamental understanding of the underlying phenomena.
First, the effect of shear on polymeric dope solutions was investigated. Shear-induced demixing—a phenomenon not previously studied in membrane materials—was found to occur in membrane dopes. Phase separation experiments also showed that shear-induced demixing promotes macrovoid formation. The demixing process was found to depend not only on the instantaneous shear conditions, but also on the shear history of the solution. This suggests that low-shear flow processes that occur in the upstream tubing and channels used for fiber spinning can affect macrovoid formation.
The effect of viscoelastic media on dispersed particles was also explored. Shear-small-angle light scattering results showed that particles suspended in membrane dope solutions formed aggregated, vorticity-oriented structures when shear rates in the shear-thinning regime of the polymer solution were applied. Shear rates well below the shear-thinning regime did not produce any structure. In fact, the application of a Newtonian shear rate to a sample already containing the vorticity structure caused the sample to return to isotropy. Measurements using a highly elastic, constant-viscosity Boger fluid showed that strong normal forces alone are not sufficient to form the vorticity structures, but that shear thinning is also required.
Lastly, a study was conducted examining cross-stream migration of particles dispersed in viscoelastic media. Fluids exhibiting varying degrees of shear thinning and normal forces were found to have different effects on the particle distribution along the shear gradient axis in Poiseuille flow. Shear thinning was found to promote migration toward the channel center, while normal stresses tended to cause migration toward the channel walls.
In addition to hollow fiber spinning, many other industrially relevant applications involve polymer solutions and suspensions of particles in viscoelastic media. Often, the properties and performance of the material depend strongly on the internal microstructure. The results from the research described in this thesis can be used to guide the design of materials and processing conditions, so that the desired microstructural characteristics can be achieved.
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Kuang, Jun Shang. "Punching shear failure of concrete slabs with compressive membrane action." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240241.
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Salim, Wijaya. "Punching shear failure in reinforced concrete slabs with membrane restraint." Thesis, University of Bristol, 2006. http://hdl.handle.net/1983/e2a8f32a-0fc2-40ee-8183-a9100122e429.
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Kovalsky, Peter Chemical Sciences & Engineering Faculty of Engineering UNSW. "Characterisation of fouling behaviour on membrane filtration of aggregated suspensions." Publisher:University of New South Wales. Chemical Sciences & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41531.
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It is widely accepted that flocculation improves filtration performance by increasing cake permeability. This principle is important in submerged membrane filtration for drinking water applications where the feed material can potentially contain fouling components which prohibit the extended operation of the filter. Less well understood is the impact of floc properties on the hydraulic properties of the fouling layer formed on the membrane or the impact of hydrodynamic conditions during treatment on the floc-fouling layer relationship. In order to advance knowledge of this area, a set of tools were developed to characterise the cake formed during constant pressure filtration in terms of the compressive yield stress and permeability as a function of solid volume fraction. Using an iterative procedure, the optimal parameters for these models are calculated as are pressure and solid fraction distribution profiles. Input parameters to the numerical analysis are flux and final cake height data obtained from batch filtration experiments which are driven to steady state. The calculated material properties are compared against piston and centrifuge data with good agreement. Application of the material properties to constant flux filtration involved development of a numerical model for simultaneous consolidation and cake formation. Flocculated yeast was used as the test system with the predicted transmembrane pressure rise as a function of time under constant flux conditions compared with experimental data. Good agreement is observed between model and experimental trends. The close correspondence between experimental and predicted results also suggests that it may be possible to predict trans-membrane pressure rise during constant flux filtration on the basis of material properties determined through simple constant pressure steady state experiments. A good account of the data was also achieved through extension of the general equation to include an empirical model for the consolidation time constant. These new tools were applied to characterise the cakes formed under well controlled shear conditions. To avoid complications with modeling the sheared filtration system, the filtration was performed below the critical shear rate for particle rejection. This was verified by in-situ particle counts and size measurement. The material properties were determined for flocculated yeast filtered in a coni-cylindrical Couette at several shear rates below the critical shear. Comparison of the compressive yield stress showed that cakes subjected to shear required less compressive stress to collapse. It is shown that the general equation for constant flux could be modified to encompass this effect through inclusion of an empirical shear parameter. The transmembrane pressure rise is able to be described well by this model. DEM particle simulation was performed to investigate the effect of floc size and structure on cake permeability. Flocs of known size and structure were placed in a virtual suspension and the process of consolidation simulated by application of a compressive force. The permeability of the cake was calculated by computational fluid dynamics at various stages of the consolidation showing that the larger compact floc showed the highest permeability despite the highly compact structures formed. Comparison of pore size distribution also confirmed that several larger pores remained after consolidation of the larger compact flocs. Further work needs to be undertaken to pin point the microstructural mechanism governing this behaviour and whether the presence of fluid passing through these pores under normal filtration flows affects the retention of permeability of cakes under compression. Furthermore, the shear environment required to minimise the detrimental effects caused by shear enhanced cake collapse and also to form flocs of compact structure and large size needs to investigated.
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Quaglino, Alessio [Verfasser], Max [Akademischer Betreuer] Wardetzky, and Gert [Akademischer Betreuer] Lube. "Membrane locking in discrete shell theories / Alessio Quaglino. Gutachter: Max Wardetzky ; Gert Lube. Betreuer: Max Wardetzky." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1042969213/34.
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Oh, Kyung Hee. "Effect of shear, elongation and phase separation in hollow fiber membrane spinning." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53992.
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The spinning process of hollow fiber membranes was investigated with regards to two fundamental phenomena: flow (shear and elongation) and phase separation. Quantitative analysis of phase separation kinetics of binary (polymer/solvent) and ternary (polymer/solvent/volatile co-solvent) polymer solution was carried out with a newly developed microfluidic device. The device enables visualization of in situ phase separation and structure formation in controlled vapor and liquid environments. Results from these studies indicated that there was a weak correlation between phase separation kinetics and macroscopic defect (macrovoid) formation. In addition, the effect of shear and elongation on membrane morphology was tested by performing fiber extrusion through microfluidic channels. It was found that the membrane morphology is dominated by different factors depending on the rate of deformation. At high shear rates typical of spinning processes, shear was found to induce macrovoid formation through normal stresses, while elongation suppressed macroscopic defect formation. Furthermore, draw resonance, one of the key instabilities that can occur during fiber spinning, was investigated. It was found that draw resonance occurs at aggressive elongation condition, and could be suppressed by enhanced phase separation kinetics. These results can be used as guidelines for predicting hollow fiber membrane spinnability.
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Fulton, Blair G. "Making membranes more efficient: mapping surface shear in a pilot-scale submerged hollow-fibre membrane cassette using electrochemical shear probes." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/9550.
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Optimization of gas sparging (ie. gas flow rate used for gas scouring) and module design has great potential to decrease fouling and improve energy efficiency in submerged membrane systems. Shear stress has been widely recognized as a controlling factor in the fouling of most types of membrane systems, but despite its relevance few researchers have attempted to quantify this variable in submerged hollow fiber systems, forcing membrane designers to infer processes at the membrane surface indirectly from flux and transmembrane pressure data. The present study utilized electrochemical probes to map the shear stresses on full-scale hollow fiber membrane modules in a pilot-scale air sparged submerged membrane system (GE-Zenon Zeeweed-500c). The effects of sparging rate, membrane module spacing, fiber tension, and sparging pattern were investigated, and all were determined to significantly affect shear stress profiles. The results of this study, presented largely as ‘shear maps’, provide insight into the roles of gas sparging and module configuration on shear stress profiles in submerged membrane systems.
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Zhang, Xiaoyan. "THE INFLUENCE OF MEMBRANE CHOLESTEROL-RELATED SHEAR STRESS MECHANOSENSITIVITY ON NEUTROPHIL FLOW BEHAVIOR." UKnowledge, 2012. http://uknowledge.uky.edu/cbme_etds/6.
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Hypercholesterolemia is a dominant risk factor for a variety of cardiovascular diseases and involves a chronic inflammatory component in which neutrophil activity plays a critical role. Recently, fluid shear stress mechanotransduction has been established as a control mechanism that regulates the activity of neutrophils by reducing the formation of pseudopods and the surface expression of CD18 integrins, thereby rendering these cells rounded, deformable, and non-adhesive. This is critical for maintaining a healthy circulation, because chronically activated neutrophils not only release excess cytotoxic and degradative agents but also exhibit a reduced efficiency to pass through the small vessels of the microcirculation leading to increased microvascular resistance. We hypothesized that aberrant neutrophil mechanosensitivity to fluid shear stress due to the altered blood environment (i.e., excess plasma cholesterol) is a contributing factor for elevated hemodynamic resistance in the microcirculation associated with hypercholesterolemia. For this purpose, the present work firstly showed that the sensitivity of neutrophils to fluid shear stress depends on the cholesterol-dependent fluidity of the cell membrane, and that, in the face of hypercholesterolemia, the neutrophil mechanosensitivity highly correlated with the plasma levels of free cholesterol. The second part of this project demonstrated that, when subjected to shear stress fields, leukocyte suspensions exhibited transient (within 10 min of flow onset) time-dependent reductions in their apparent viscosity. Moreover, shear-induced changes in viscosity of cell suspensions were influenced by disturbances of membrane cholesterol and fluidity in a fashion similar to that for shear-induced pseudopod retraction. Finally, the third part of this work provided evidence that neutrophils played a role in hypercholesterolemia-related impairment of flow recovery response to transient ischemia. In conclusion, results of the current work provided the first evidence that cholesterol is an important component of the neutrophil mechanotransducing capacity and impaired neutrophil shear mechanotransduction may disturb the blood flow rheology, leading to elevations in the apparent viscosity as well as in the resistance. This cholesterol-linked perturbation may be a contributing factor for the pathologic microcirculation associated with hypercholesterolemia.
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Albuquerque, Arthur Álax de Araújo. "Implementação de elementos finitos de barra e placa para a análise de esforços em tabuleiros de pontes por meio de superfícies de influência." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-28072014-093844/.
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Este trabalho consiste em analisar os esforços em tabuleiros de pontes por meio de superfícies de influência. Para isto, o método dos elementos finitos (MEF) é utilizado e os resultados são comparados com os das tabelas de Rüsch. Os elementos finitos de barra, representando longarinas e transversinas, e placa, as lajes do tabuleiro, são implementados no código SIPlacas. Estes elementos finitos são formulados pelas teorias de viga Timoshenko e placa Reissner-Mindlin, respectivamente. Estes apresentam problema de travamento de força cortante (Shear Locking), que é contornado por duas propostas: o artifício matemático da integração reduzida e elementos finitos com campo assumido de deformação de força cortante (CADFC). Verifica-se que os elementos com aproximações quadráticas para os deslocamentos e com CADFC são os que melhor se adequam à proposta de análise da presente pesquisa. Tais elementos apresentam convergência de resultados considerando estruturas com baixa discretização. Os resultados analisados foram o deslocamento, momento fletor e força cortante. Posteriormente realiza-se um estudo de caso de uma ponte em viga. O tabuleiro da ponte é calculado utilizando-se as tabelas de Rüsch e o código SIPlacas. O cálculo dos esforços pelo SIPlacas é realizado de três maneiras. Na primeira consideram-se os painéis de lajes do tabuleiro isolados; na segunda o tabuleiro está sobre apoios não deslocáveis; e na terceira, o tabuleiro apresenta-se com vigas acopladas. Foi concluído que a terceira configuração, cuja representação melhor se aproxima da estrutura real de análise, apresentou os menores esforços internos.This work aims at the analysis of bridge deck stresses through influence surfaces. The finite element method (FEM) is used and the results are compared with those of Rüsch\'s tables. The bar and plate finite elements represent stringers, cross beams and slabs bridge deck. These finite elements are implemented in the SIPlacas code and the theories of Timoshenko beam and Reissner-Mindlin plate are used to theirs formulation. The Shear Locking problem is solved by two proposals: reduced integration and definition of element with transversal shear strain assumed (TSSA). The elements with quadratic approximations for the displacements and TSSA are the best suited to the proposed analysis of this research. Such elements have convergence of results considering structures with low discretization. Displacement, bending moment and shear force were the results analyzed. Subsequently a case study on a beam bridge was carried out. The bridge deck is calculated using Rüsch\'s tables and SIPlacas code. The calculation of the internal forces by SIPlacas is performed in three ways. The first one considers the slabs isolated panels; the second, the slab deck is on a rigid support; and third, the slab deck is on deformable supports. It was concluded that the third configuration showed the lowest internal forces. This configuration is the optimum representation to the structure analysis.
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PETROVIC, Mario. "Wrinkle generation mechanism in flat and cylindrical membranes undergoing shear deformation." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199271.
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Ye, Dongying. "Shear stress and fouling control in hollow fiber membrane systems under different gas sparging conditions." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42951.
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The shear stress created by gas sparging has been widely recognized as a controlling factor in the fouling of submerged membrane systems. Effective gas sparging can significantly reduce the fouling and improve the membrane performance. Several factors, such as membrane module configuration, gas sparging tank configuration, gas sparging pattern and temperature, affect the hydrodynamic conditions around the membrane. Chan et al. (2011) reported that different types of shear profiles exist inside the submerged hollow fiber membrane module, and the different types of shear conditions have different effects on fouling control. In this thesis, the relationship between the shear stress generated by conventional sparging and a novel sparging approach on fouling control were studied. The results indicate that, to achieve the similar fouling control (fouling rate), only a quarter of energy (i.e air flow rate) input was required for the novel slug bubble sparger, compared to the conventional coarse bubble sparger.
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Öz, Pinar Verfasser], Fred [Akademischer Betreuer] Wolf, and Tobias [Akademischer Betreuer] [Moser. "Theoretical analysis of membrane properties underlying action potential phase-locking in noise-driven cells / Pinar Öz. Gutachter: Fred Wolf ; Tobias Moser. Betreuer: Fred Wolf." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2011. http://d-nb.info/1042305080/34.
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Francis, Patrick. "Modeling of controlled-shear affinity filtration using computational fluid dynamics and a novel zonal rate model for membrane chromatography." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39128.
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Controlled-shear affinity filtration (CSAF) is a novel integrated bioprocessing technology that positions a rotor directly above an affinity membrane chromatography column to permit protein capture and purification directly from cell culture. The rotor provides a tunable shear stress at the membrane surface that inhibits membrane fouling and cell cake formation allowing for a uniform filtrate flux that maximizes membrane column performance. However, the fundamental hydrodynamics and mass transfer kinetics within the CSAF device are poorly understood and, as a result, the industrial applicability of the technology is limited.
A computational fluid dynamic (CFD) model is developed that describes the rotor chamber hydrodynamics of the CSAF device. Once evaluated the model is used to show that a rotor of fixed angle does not provide uniform shear stress at the membrane surface. This results in the need to operate the system at unnecessarily high rotor speeds to reach a required shear stress threshold across the membrane surface, compromising the scale-up of the technology. The CFD model is then used to model design improvements that result in an in silico design of a preparative CSAF device capable of processing industrial feedstocks.
To describe mass transfer in stacked-membrane chromatography a novel zonal rate model (ZRM) is presented that improves on existing hold-up volume models. The ZRM radially partitions the membrane stack and external hold-up volumes to better capture non-uniform flow distribution effects. Global fitting of model parameters is first used under non-retention conditions to build and evaluate the appropriate form of the ZRM. Through its careful accounting of transport non-idealities within and external to the membrane stack, the ZRM is then shown to provide, under protein retention conditions, a useful framework for characterizing putative protein binding models, for predicting breakthrough curves and complex elution behavior, and for simulating and scaling separations using membrane chromatography.
By elucidating the intrinsic physical processes ongoing in CSAF the mathematical models presented in this thesis represent essential theoretical tools for the further development of the technology; a technology which has the potential to increase productivity and decrease costs in the downstream processing of biopharmaceuticals.
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Dunlap, Myles Derrick. "Experimental Measurement of the Utricle's Dynamic Response and the Mechanoelectrical Characterization of a Micron-Sized DIB." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/52862.
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Within the vestibular system are otolith organs, both the utricle and saccule. The primary function of these organs is to transduce linear head accelerations and static head tilts into afferent signals that are sent to the central nervous system for the utilization of image fixation, muscle posture control, and the coordination of musculoskeletal movement in dynamic body motion. The utricle of the red ear slider turtle was studied in this dissertation. The turtle's utricle is composed of several layers. The base layer contains a set of neural receptor cells, called hair cells, and supporting cells. The three layers above the base layer compose the utricle's otoconial membrane (OM) and are: 1.) a saccharide gelatinous layer, 2.) a column filament layer, and 3.) a calcite and aragonite otoconial crystal layer.
The primary goal of this research was to study the dynamic response of the turtle's OM to a variety of natural inertial stimuli in order to characterize its inherent mechanical properties of natural frequency ("n), damping ("), and shear modulus (G). The medial-lateral (ML) and anterior-posterior (AP) anatomical axes parameters were measured for the utricle. The ML axis median with 95% confidence intervals was found to be "n = 374 (353, 396) Hz, " = 0.50 (0.47, 0.53), and G = 9.42 (8.36, 10.49) Pa. The AP axis median with 95% confidence intervals was found to be "n = 409 (390, 430) Hz, " = 0.53 (0.48, 0.57), and G = 11.31 (10.21, 12.41). Nonlinearites were not found to occur in the OM for the tested inertial stimuli and no significant difference was found between the mechanical properties for the ML and AP axes.
Additionally, this research presents the initial steps to form a novel bio-inspired accelerometer based on the morphology of the utricle. The primary transducer element for this possible otolith organ inspired accelerometer design is a droplet interface bilayer (DIB). A DIB is a lipid bilayer that is formed when the interface of two aqueous droplets, that contain free-floating lipids, are joined. The aqueous droplets are suspended in a nonpolar environment (oil) and the oil/water interface forms a lipid monolayer. This research developed and used an experimental test setup to characterize the mechanoelectrical characteristics of a micron-sized DIB. This information, along with examples in the text, could be used to further design the aforementioned accelerometer.Ph. D.
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Syme, C. A. "Patch-clamp studies on endothelial cell and chromaffin cell K'+ channels : effects of shear stress, membrane stretch and fatty acids." Thesis, University of Strathclyde, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298575.
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Masciola, David A. "Effects of feed oil content, transmembrane pressure and membrane rotational speed on permeate water quality in high-shear rotary ultrafiltration." Morgantown, W. Va. : [West Virginia University Libraries], 1999. http://etd.wvu.edu/templates/showETD.cfm?recnum=465.
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Thesis (M.S.)--West Virginia University, 1999.Title from document title page. Document formatted into pages; contains x, 128 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 123-128).
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Akenhead, Michael L. "The Influence of Cholesterol-Related Membrane Fluidity on the Shear Stress Control of Neutrophil Adhesion and Its Implications in Hypercholesterolemia." UKnowledge, 2016. http://uknowledge.uky.edu/cbme_etds/41.
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Hypercholesterolemia is a significant risk factor in the development of cardiovascular disease and is associated with chronic leukocyte adhesion in the microvasculature. While the underlying mechanisms behind this have yet to be determined, it may be possible that hypercholesterolemia impairs the fluid shear stress (FSS) inactivation of neutrophils through the rigidifying effect of cholesterol on membrane fluidity. FSS restricts surface expression of CD18 integrins through cathepsin B (ctsB) proteolysis, which minimizes neutrophil adhesivity. If hypercholesterolemia blocks FSS mechanotransduction, then the inhibition of CD18 cleavage may link pathologic blood cholesterol elevations with dysregulated neutrophil adhesion. We hypothesized that elevated cholesterol contributes to dysregulated neutrophil adhesion by impairing ctsB FSS-induced CD18 cleavage through membrane fluidity changes.
In the first part of this study, we demonstrated that FSS-induced CD18 cleavage is a robust response of neutrophils and involves selective cleavage of macrophage 1-antigen (Mac1) through ctsB proteolysis. The second part of this study confirmed that ctsB regulates neutrophil adhesion through its proteolytic actions on Mac1, an important integrin involved in adhesion and chemotaxis. Specifically, ctsB accelerated neutrophil motility through an effect on Mac1 integrins during pseudopod retraction. Furthermore, by using a flow-based assay to quantify the mechanoregulation of neutrophil adhesivity, we demonstrated that FSS-induced ctsB release promoted neutrophil detachment from platelet-coated substrates and unstimulated endothelium. For the third part of this study, we linked cholesterol-related membrane fluidity changes with the ability of FSS to restrict neutrophil adhesion through Mac1. We also determined that pathologic cholesterol elevations associated with hypercholesterolemia could block FSS-induced Mac1 cleavage and were linked to disrupted tissue blood flow. This was accomplished using low-density lipoprotein receptor deficient (LDLR-/-) mice fed a high-fat diet.
Ultimately, the results provided in the present study confirmed that cholesterol-related changes in membrane fluidity blocked the ability of ctsB to regulate neutrophil adhesion through FSS-induced Mac1 cleavage. This implicates an impaired neutrophil FSS mechanotransduction response in the dysregulation of neutrophil adhesion associated with hypercholesterolemia. Since dysregulated adhesion may be one of the earliest upstream features of cardiovascular disease associated with hypercholesterolemia, the present study provides a foundation for identifying a new mechanobiological factor in the pathobiology of microcirculatory dysfunction.
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Alaei, Zohreh. "Molecular Dynamics Simulations of Axonal Membrane in Traumatic Brain Injury." Thesis, KTH, Skolan för teknik och hälsa (STH), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-211109.
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The following project presents in silico investigation of axonal damage in Diffuse Axonal Injury (DAI). When axons face a shear force, orientation of the lipids in the axonal membrane gets disrupted. Depending on the value of the force, a tensile strain causes the axons to get partially or fully deformed and in some cases a pore forms in the membrane. Using Molecular Dynamic (MD) simulation and a coarse grain model, a series of bilayers with various bilayer structure (single bilayer, parallel bilayer and cylindrical bilayer) and similar composition to biological axonal membrane were simulated. This was initially done to investigate the strain rate dependency of the bilayers, and their viscoelastic ability on returning to their original shape from their deformed forms. To achieve this, various deformation velocities were applied to the bilayers reaching 20% strain and relaxing the bilayer after. Additionally, the bilayers were deformed further until they reached a pore. It was found that the bilayers can almost recover from their deformed forms to their original length when they were deformed at 20% strain level. In conjunction, no correlation between the deformation velocity and lipid deformation was observed. Further, it was found that bilayers with different lipid percentage to axonal bilayer has different strain values for water penetration and for pore formation. The strain value for cylindrical bilayer was found very high compared to the strain values found in vitro. The strain for pore formation of parallel and single bilayer was found to be around 80% to 90% and for water penetration was found to be 70% for single bilayer and 50% for parallel bilayer. A slight difference in strain for pore formation between single and parallel bilayer was found which showed the bilayer structure can play a role in simulation results. The effect of the length in the simulations results was also observed where shorter bilayers showed lower strain for pore formation compared to longer bilayers.
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Lu, Ye. "Reconstruction, characterization, modeling and visualization of inherent and induced digital sand microstructures." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37176.
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Strain localization, the phenomenon of large shear deformation within thin zones of intensive shearing, commonly occurs both in-situ and in the laboratory tests on soils specimens. The intriguing mechanism of strain localization and how it will affect the general behavior of soil specimens have been investigated by many researchers. Some of the efforts have focused on finding the links between material properties (void space, fabric tensor) and mechanical behavior (stress, strain, volumetric strain). In the last ten years, several extensive studies have been conducted at Georgia Tech to investigate the mechanism of strain localization and link the microstructural properties with the engineering behavior of Ottawa sands. These studies have included 2-D and 3-D characterization of soil microstructures under either triaxial or biaxial shearing conditions. To extend and complement these previous studies, the current study focuses particularly on 3-D reconstruction, analysis and modeling of specimens of Ottawa sand subject to triaxial or biaxial loading. The 3-D microstructure of biaxial specimens was reconstructed using an optical microscopy based montage and serial sectioning technique. Based on the reconstructed 3-D digital volumes, a series of 2-D and 3-D characterizations and analyses, including local void ratio distributions, extent of shear bands, influence of soil fabrics and packing signature effects, were conducted. In addition to the image analysis based reconstruction and characterization, the 3-D discrete element method (DEM) code, PFC3D, was used to explore both biaxial and triaxial shear related soil behaviors at the global and particulate scale. Void ratio distributions, coordination numbers, particle rotations and displacements, contact normal distributions and normal contact forces as well as global stress and strain responses were investigated and analyzed to help understand the mechanism of strain localization. The microstructures of the numerical specimens were also characterized in the same way as the physical specimens and similar strain localization patterns were identified. Combined with the previous related studies, the current study provides new insights into the strain localization phenomenon of Ottawa sands subject to triaxial and biaxial loading. In addition, the reconstructed digital specimens were subject to a series of dissection studies which revealed exciting new insights into "microstructure signatures" which exist at both meso and micro scales within the real and simulated specimens.
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Abdul-Rahim, Haïfa. "Étude par anisotropie de fluorescence de la déformation de membranes cellulaires sous contrainte de cisaillement." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL141N.
Full textAbstract:
La déformabilité de la membrane cellulaire est un des facteurs régissant le rôle de la membrane dans le fonctionnement cellulaire. L’idée originale de ce travail est l'application de l'anisotropie de fluorescence à l'étude de la déformation de membranes soumises à une contrainte de cisaillement. Un appareillage permettant la mesure de l'anisotropie de fluorescence d'une suspension dans un viscosimètre de Couette a été réalisé. Il a été appliqué à l'étude de membranes isolées (ghosts d'érythrocytes) avec deux sondes fluorescentes le TMA-DPH et l'acide 6-(9-anthroyloxy) stéarique. Un modèle théorique a été développé permettant de simuler l'anisotropie de fluorescence en prenant en compte un modèle de déformation de la membrane sous la forme d'un ellipsoïde et un modèle de rotation moléculaire restreinte attachée à la structure lipidique. Le modèle permet de reproduire de façon satisfaisante les résultats expérimentaux, conduisant à la valeur de l'indice de déformation de la membrane et à son orientation par rapport à l'écoulement. Les valeurs de l'indice de déformation sont en accord avec celles d'études utilisant d'autres techniques. Cette étude fondamentale est complétée par une étude à fortes contraintes de cisaillement qui indique une résistance progressive de la membrane à la déformation. Par ailleurs, des essais positifs en utilisant une sonde plus spécifique du milieu lipidique permettent d'envisager une étude sur des cellules intactes. En conclusion, le phénomène observé est interprété et quantifié par des paramètres géométriques. La sensibilité et la maitrise de la mesure suggèrent d'étudier une corrélation avec des états pathologiques pour le développement d'éventuels tests cliniques
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Zhang, Wenxiang. "Optimization of protein concentration from alfalfa juice by high shear rate dynamic filtration." Thesis, Compiègne, 2016. http://www.theses.fr/2016COMP2281/document.
Full textAbstract:
Les protéines extraites des feuilles de luzerne sont une source importante de protéines. La filtration membranaire, technologie de séparation respectueuse de l’environnement avec une productivité élevée et de faible coût a été utilisée pour séparer et concentrer les protéines des feuilles de luzerne à partir de leur jus. Cependant le phénomène du colmatage de la membrane qui réduit sérieusement le flux et la séparation des protéines est un facteur limitant important dans l'application de la filtration membranaire. Pour améliorer la récupération des protéines et amenuiser le phénomène du colmatage, la filtration membranaire associée à fort cisaillement a été utilisée pour la filtration du jus de luzerne. Toujours dans l’objectif d'optimiser le processus de la filtration, "le mode de la filtration" et "les paramètres de fonctionnement" ont été étudiés pour réduire le colmatage de la membrane et améliorer le rendement de la filtration. Puis, l’effluent du jus de luzerne a été filtré par des membranes dans des conditions de fort cisaillement afin de recycler les protéines. En outre, le mécanisme du colmatage a été étudié et a permis d’évaluer les stratégies de contrôle du colmatage. L'optimisation du procédé membranaire, via l’étude du "mode de filtration" et des "paramètres de fonctionnement" a été conduit dans le but d’améliorer la séparation et la concentration des protéines et de réduire le colmatage. Trois types de « mode de filtration » ont été testés : la filtration frontale sur le module de la cellule amicon (DA), la filtration tangentielle dynamique sur le module à disque rotatif (CRDM) et la filtration frontale sur le module à disque rotatif (DRDM)). Les « paramètres de fonctionnement » qui ont été étudiés sont les suivants : le type de membranes (ultrafiltration (UF) et microfiltration (MF)), la vitesse de rotation, la température et la pression transmembranaire (TMP). Le comportement du débit (évolution du flux du perméat au cours de la filtration), les performances de la séparation (taux de clarification et de concentration), l’efficacité du nettoyage de la membrane (récupération de la perméabilité membranaire) et la productivité lors des tests de recyclage et de concentration ont été étudiés dans le but de définir des stratégies dans le contrôle du colmatage. Puis, l’effluent de luzerne a été filtré par UF afin de séparer et purifier les protéines. Le mécanisme du phénomène du colmatage des membranes lors de la filtration du jus de luzerne a été étudié. Le processus du colmatage de la membrane a montré une tendance d’un colmatage multi-site progressif. Le modèle du colmatage multisite progressif selon la loi de Darcy (SMDM) a été proposé afin de mieux décrire et comprendre le processus du colmatage. Les effets de la composition du fluide d’alimentation, du choix de la membrane et des conditions hydraulique ont joué un rôle important dans le processus progressif du colmatage. De plus, les coefficients de résistance et de compressibilité dans les différentes étapes et sites ont été calculés afin d’expliquer le processus complexe du colmatage et d’évaluer l'efficacité des stratégies du contrôle du colmatage. Une série d'essais avec de longues durées de filtration a été réalisée pour étudier le déclin du flux et le colmatage de la membrane à diverses étapes du processus. Ces résultats présentent une utilité pour améliorer la récupération des protéines et contrôler le colmatage dans le processus de la filtration membranaire à fort cisaillement du jus de luzerne. Ces résultats sont aussi utiles pour la conception et la mise en place des technologies membranaires dans les processus industrielsAlfalfa leaf proteins extracted from plants are an important protein source. As an environmentally friendly separation technology with high productivity and low cost, membrane filtration was used to separate and concentrate leaf protein from alfalfa juice. However membrane fouling seriously reduces flux and protein separation and is an important limitation in the application of membrane filtration. To improve protein recovery and fouling control, dynamic shear-enhanced membrane filtration with high shear rate on membrane surface and excellent anti-fouling capacity was used for alfalfa juice filtration in this work. In order to optimize filtration process, filtration mode and operation parameters were investigated to reduce membrane fouling and improve separation performance. Then, alfalfa wastewater was also treated by dynamic shear-enhanced membrane filtration to recycle proteins. Furthermore, the fouling mechanism was studied and served as a valuable evaluation for fouling strategies. In this study, process optimization including “Filtration mode” and “Operation parameters” was studied to improve protein recovery and fouling control. In “Filtration mode”, three types of filtration modules (dead end filtration using laboratory Amicon cell (DA), dynamic cross filtration using rotating disk module (CRDM) and dead end filtration using rotating disk module (DRDM)) were used to investigate the filtration performance. As for “Operation parameters”, the operation parameters including membranes (ultrafiltration (UF) and microfiltration (MF)), rotating speed, temperature and transmembrane pressure (TMP) were studied to optimize the filtration process. Flux behavior (permeate flux and flux decline), separation performance (clarification and concentration capacity), membrane cleaning efficiency (permeability recovery) and productivity in full recycling tests and concentration tests were utilized to evaluate the various operation strategies. In addition, alfalfa wastewater was treated by UF membrane, while waste proteins were recycled. Fouling mechanism for alfalfa juice filtration was investigated. The fouling process showed significantly stepwise multisite patterns. Based on Darcy’s law, the stepwise multisite Darcy’s law model (SMDM) was proposed to better describe and understand the fouling process. The effects of feed composition, membrane and hydraulic conditions played an important role in stepwise fouling process. Moreover, the resistance coefficient and compressibility for different steps and sites were calculated to explain the complex fouling process and estimate the efficiency of flux decline control strategies. Besides, a series of long tests were utilized to study flux decline and membrane fouling at various fouling step process. These results can be used to understand the protein recovery and fouling control during shear-enhanced membrane filtration process of alfalfa juice. They have important implications for process design of membrane technology in industrial scale
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Chen, Wei. "The force regulation on binding kinetics and conformations of integrin and selectins using a bio-membrane force probe." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33814.
Full textAbstract:
Cell adhesion plays an important role in inflammation and immunological responses. Adhesion molecules (e.g., selectins and integrins) are key modulators in mediating these cellular responses, such as leukocyte trafficking under shear stress. In this thesis, we use a bio-membrane force probe (BFP) to study force regulation on kinetics and conformations of selectin and LFA-1 integrin. A new BFP was built up, and a new assay, using thermal fluctuation of the BFP, was developed and used to monitoring selectins and their ligands association and dissociations. The new BFP was also used to investigate the force and force history dependence of selectin-ligand interactions. We found tri-phasic transition of force-dependent off-rates and force-history dependence of selectin/ligaind interactions. The BFP was also used to characterize force-dependent lifetimes of the LFA-1-ICAM-1 interaction. We found that LFA-1/ICAM-1 bonds behaved as catch bond and that LFA-1-ICAM-1's catch bonds were abolished blocking the downward movement of αA domain α7 helix. Finally, the BFP was applied to dynamically probe the global conformational changes of LFA-1 and to characterize force-regulated transitions among different conformational states on a living cell. We observed dynamic transitions of LFA-1 between extended and bent conformations on living cells. The observed average distance change of LFA-1's extensions was about 18nm, while that of the bending was only about 14nm. We also found that forces could facilitate extension but they slow down the bending of LFA-1. The observed transition time of extension was less than 0.1s, while that of contraction was longer than 0.2s. Our observations here are the first in-situ evidence to demonstrate how integrins dynamically transit different conformations and how force regulates these transitions.
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Galera, Laporta Letícia 1985. "Dynamical aspects of the regulation of bacterial proliferation." Doctoral thesis, Universitat Pompeu Fabra, 2019. http://hdl.handle.net/10803/666296.
Full textAbstract:
Bacterial proliferation has been studied for more than 100 years, but
our knowledge of the mechanisms that control its dynamical aspects
is still very limited. In this Thesis we have studied, at both singlecell
and population levels, different aspects of the main regulators
of bacterial proliferation, namely the cell cycle, biomass production
and membrane stability. Our goal has been to shed light on how perturbation
of these regulators affects their dynamical responses in a
variety of situations. Specifically, we show that the periodic doubling
of genes through the bacterial cell cycle partially entrains a genetic oscillator,
but that significant coupling only arises when the oscillator is
fed back to cell cycle. We have also studied perturbations in the ability
of cells to produce biomass, for instance through antibiotics that
affect ribosomal function. Our results suggest that survival in the
presence of these antibiotics is determined by the ability of the cells
to incorporate magnesium ions, which can be captured by membrane
potential changes. Finally, we show that interplay between different
bacterial species with diverse sensitivities to membrane-targeting antibiotics
can have an unexpected outcome in co-culture, which can be
explained in a simple manner by the sharing of the antibiotic between
the two species.La proliferació bacteriana ha estat estudiada durant més de 100 anys, però el nostre coneixement dels mecanismes que controlen els aspectes dinàmics d’aquesta encara són molt limitats. En aquesta Tesi hem estudiat, tant en cèl.lules individuals com a nivell poblacional, diferents aspectes dels principals reguladors de la proliferació cel.lular, concretament el cicle cel.lular, la producció de biomassa i la estabilitat de la membrana. El nostre objectiu ha estat ajudar a explicar com pertorbacions en aquests reguladors afecten la dinàmica de les seves respostes en una varietat de situacions. Específicament, mostrem que el doblament periòdic de gens a través del cicle cel.lular bacterià entrena parcialment un oscil.lador genètic, però aquest acoblament només és significatiu quan l’oscil.lador retorna la resposta al cicle cel.lular. Tamée hem estudiat pertorbacions en l’habilitat de les cèl.lules de produir biomassa, per exemple a través d’antibiòtics que afecten la funció ribosomal. Els nostres resultats suggereixen que la supervivència sota l’efecte d’aquests antibiòtics ve determinada per l’habilitat de les cèl.lules d’incorporar ions de magnesi, la qual pot ser capturada a través de canvis en el potencial de membrana. Finalment, mostrem que les interaccions entre diferents espècies bacterianes amb diverses sensitivitats a antibiòtics que afecten la membrana cel.lular poden donar lloc a resultats inesperats quan es troben en co-cultiu, els quals poden ser explicats de forma senzilla a partir del compartiment de l’antibiòtic entre les dues espècies.
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David, Carlos Rodrigo Pinheiro. "Simulação numérica de painéis de concreto armado submetidos ao corte puro." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/21421.
Full textAbstract:
A análise de painéis de concreto armado submetidos a corte puro é um tópico que tem recebido atenção de pesquisadores ao longo dos anos. Isto se deve, principalmente, à dificuldade encontrada na aplicação do carregamento e das condições de vinculação sobre a estrutura. Esta dificuldade é constatada tanto experimentalmente como na análise numérica. O objetivo deste trabalho é apresentar um modelo numérico para simular o comportamento de painéis de concreto simples e de concreto armado submetidos ao corte. Na análise computacional via Elementos Finitos, será utilizado um modelo de fissura incorporada que considera a contribuição da armadura no equilíbrio interno de forças do elemento. Estes modelos se baseiam no conceito de descontinuidades incorporadas dentro de elementos finitos padrão. O modelo incorporado implementado é uma continuação dos trabalhos desenvolvidos por d’Avila (2003) e Brisotto (2006), baseados no modelo de Dvorkin, Cuitiño e Gioia (1990). O modelo de transferência de tensão por aderência de Russo, Zingone e Romano (1990) foi usado por d’Avila para incluir a contribuição da armadura no equilíbrio interno de forças do elemento. Para representar as barras de aço da armadura, é utilizado o modelo incorporado desenvolvido por Elwi e Hrudey (1989) que permite a disposição arbitrária das barras no interior dos elementos de concreto. Os resultados dos ensaios numéricos de painéis de concreto armado submetidos ao corte puro com diferentes taxas de armadura são comparados com os resultados experimentais apresentados por Vecchio (1981). São incluídos dois diferentes modelos de efeito de pino (resistência ao corte das barras da armadura), analisando-se a influência dos mesmos no comportamento dos painéis ensaiados. O efeito do engrenamento dos agregados na fissura também foi estudado. Vários painéis com diferentes formas de ruptura experimental foram simulados, obtendo-se respostas muito boas para a maioria deles. Comparações da resposta tensão tangencial x distorção com e sem efeito de pino foram feitas, verificando-se a grande importância deste efeito na resposta global.The analysis of reinforced concrete panels submitted to in-plane shear has received the attention of researchers along the years. It is mainly due to the difficulty to simulate the application of the external loads and the structural boundary conditions. The purpose of this work is to present a numerical model to represent reinforced concrete panels submitted to inplane shear. In the computational analysis via Finite Elements, an embedded crack model that considers the inclusion of the reinforcement contribution in the internal force equilibrium of the element is presented. This type of model is based in discontinuities embedded into standard finite elements. The implemented formulation uses the model presented by Dvorkin, Cuitiño and Gioia (1990), which does not have the reinforcement contribution in the element internal equilibrium. The adherence stress transfer model of Russo, Zingone and Romano (1990) is used to include this reinforcement contribution. An embedded model was employed to represent the reinforcement bars, allowing that they can be placed in an independent position and shape in the FEM elements. The numerical results are compared with Vecchio’s work. Also are included two different dowel action models (transversal shear resistance of the bars) and is studied their influence in the panels’ behavior. Panels with different experimental rupture modes were simulated with good responses in the most cases. Comparisons of shear stress x shear strain curve with and without dowel action are performed, showing the importance of this effect on the global response.
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Nana, Wendpanga Serge Auguste. "Etudes expérimentales et numériques du comportement des dalles épaisses en béton armé sous chargement de cisaillement et interaction cisaillement/effet de membrane : Application aux bâtiments nucléaires." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI108/document.
Full textAbstract:
Cette contribution, en s’appuyant sur expérimentation et modélisation numérique vise à une meilleure compréhension du comportement des dalles en béton armé sous sollicitations de cisaillement. Une campagne expérimentale a été réalisée sur des dalles épaisses à pleine échelle de centrales nucléaires. Ces dalles sans armatures d’effort tranchant sont soumises à une sollicitation de cisaillement en chargement quasi-statique. Les essais sont réalisés en faisant varier différents paramètres qui peuvent influencer le comportement au cisaillement. Sont ainsi étudiés : résistance en compression du béton, épaisseur, taux d’armatures longitudinales et transversales, taille des granulats, longueur de la plaque de chargement. L’influence des efforts de membrane, de compression ou de traction, sur le comportement au cisaillement a également été analysée. Les résultats des essais sont ensuite comparés aux prédictions des codes de calcul. Ces résultats ont d’abord permis d’apporter une réponse aux divergences qui existent entre l’Eurocode 2 et l’Annexe Nationale Française quant à la prédiction du cisaillement. Ont également été évalués le niveau de précision donné par d’autres normes de dimensionnement au cisaillement: la norme américaine ACI 318-14, le code nucléaire AFCEN ETC-C 2010, le fib-Model Code 2010 et l’approche par la théorie de la fissure critique de cisaillement CSCT. Ensuite est évalué la possibilité d’analyses non-linéaire par élément finis (EF) pour reproduire le phénomène du cisaillement dans les dalles. Un modèle de béton élastoplastique avec endommagement est combiné à une analyse quasi-statique à schéma de résolution explicite. Des lois de comportement non linéaires appropriées du béton avec des comportements post-pic associés à un critère énergétique ont été considérées. La bonne concordance entre le modèle proposé et les résultats expérimentaux en termes de résistance au cisaillement et de modes de rupture permet de valider la modélisation proposée. Une étude paramétrique a été réalisée sur la base du modèle proposé avec les mêmes propriétés mécaniques de béton. Des lois simplifiées permettant d’estimer les capacités en cisaillement en fonction des différents paramètres étudiés sont finalement proposéesThis study, based on experiments and numerical modeling, aims at a better understanding of the shear behavior of reinforced concrete slabs. An experimental campaign was carried out on full-scale thick slabs typical of nuclear power plant slabs. These slabs without shear reinforcement are subjected to a quasi-static shear loading. The tests are carried out by varying different parameters that can influence the shear behavior: the concrete compressive strength, the slab depth, the bottom longitudinal and transverse reinforcement ratio, the concrete aggregate size, the loading plate length. The influence on shear behavior of compression or tension membrane forces has also been analyzed. The results of tests are then compared with the predictions of the calculation codes. These results first of all helped to answer the differences between the Eurocode 2 and the French National Annex concerning the prediction of the shear capacity of reinforced concrete slabs. The level of accuracy given by other shear dimensioning standards was also assessed: The American standard ACI 318-14, the AFCEN ETC-C 2010 code used for nuclear buildings, the fib-Model 2010 and the Critical Shear Crack Theory. Next, we evaluate the possibilities of a non-linear finite element analysis (EF) to reproduce the phenomenon of shear in slabs. An elastoplastic concrete model with damage was used and combined with a quasi-static analysis using an explicit resolution scheme. Appropriate nonlinear behavior laws of concrete with post-peak behaviors associated with an energy criterion were considered. The good agreement between the proposed model and the experimental results in terms of shear strength and failure modes allowed validating the proposed modeling. A parametric study was conducted based on the numerical proposed model with the same mechanical properties of concrete. Simplified laws allowing estimating the shear capacities according to the different parameters studied are proposed
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Braak, Etienne. "Aération pour le décolmatage dans les bioréacteurs à membranes immergées pour le traitement des eaux usées : impact sur le milieu biologique et la filtration." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/8859/1/braak.pdf.
Full textAbstract:
Cette étude présente les travaux réalisés pour comprendre l'effet de l'aération sur le milieu
biologique et sur la filtration dans les bioréacteurs à membranes immergées pour une gamme de paramètres opératoires proche de celles utilisées sur stations réelles. Notre démarche fait le lien entre paramètres opératoires (débit d'aération), hydrodynamique à l'échelle macroscopique (tailles et vitesses de bulles), hydrodynamique à l'échelle locale (contraintes de cisaillement) et propriétés du milieu biologique (taille de flocs et substances polymériques extracellulaires solubles). De moins bonnes performances de filtration à plus forte aération pourraient être expliquées par une plus grande déstructuration des boues sur le court terme. Par ailleurs tout effet d'évolution des boues sur le long terme en fonction des conditions d'aération a été écarté.
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Le, Thi Huyen Cham. "Robust variable kinematics plate finite elements for composite structures." Thesis, Paris 10, 2019. http://faraway.parisnanterre.fr/login?url=http://bdr.parisnanterre.fr/theses/intranet/2019/2019PA100053/2019PA100053.pdf.
Full textAbstract:
Le but de ce travail est de développer deux nouveaux éléments finis quadrilatéraux à quatre et à huit nœuds implantés dans le code commercial de calcul par Eléments Finis (EF) Abaqus pour plaques composites. Les modèles plaques à cinématique variable sont formulés dans le cadre de la formulation unifiée de Carrera (CUF), qui regroupent des descriptions de type: couche équivalente (ESL) et couches discrètes (LW), avec les variables définies par des polynômes jusqu’au 4ème ordre suivant épaisseur z. Les deux formulations variationnelles sont utilisées pour dériver les matrices des éléments finis: le Principe des Déplacements Virtuels (PVD) et le Théorème Variationnel Mixte de Reissner (RMVT). Grâce à la technique de condensation statique, une formulation hybride basée sur le RMVT est introduite. Afin d’éliminer la pathologie de verrouillage en cisaillement transverse, deux approximations compatibles pour le champ de déformations de cisaillement transverse indépendantes en z, notée QC4 et CL8, sont étendues aux éléments plaques à cinématique variable basés sur CUF. De plus, les QC4S et CL8S interpolations sont également introduites pour les contraintes de cisaillement transverse dans les éléments mixtes et les éléments hybrides. Les résultats numériques comparés à ceux disponibles dans la littérature montrent que les FE proposés sont efficaces pour modéliser des éléments finis robustesThe aim of this work is the development of two classes of new four-node and eightnode quadrilateral finite elements implemented into the commercial finite element (FE) code Abaqus for composite plates. Variable kinematics plate models are formulated in the framework of Carrera’s Unified Formulation (CUF), which encompasses Equivalent Single Layer (ESL) as well as Layer-Wise (LW) models, with the variables that are defined by polynomials up to 4th order along the thickness direction z. The two classes refer to two variational formulations that are employed to derive the finite elements matrices, namely the Principle of Virtual Displacement (PVD) and Reissner’s Mixed Variational Theorem (RMVT). Thanks to the static condensation technique, a Hybrid formulation based on the RMVT is derived. For the purpose of eliminating the shear locking pathology, two field compatible approximations for only the z−constant transverse shear strain terms, referred to as QC4 and CL8 interpolations, are extended to all variable kinematics CUF plate elements. Moreover, the QC4S and CL8S interpolations, are also introduced for the transverse shear stress field within RMVT-based and Hybrid mixed-based elements. Numerical results in comparison with those available in literature show that the proposed FEs are efficient for modeling a robust finite elements
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Callens, Natacha. "Développement, étude expérimentale et visualisation par holographie digitale de mini-séparateurs fluidiques (STEP-SPLITT) en vue de la séparation d'objets de taille micrométrique." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210976.
Full textAbstract:
Cette thèse expérimentale s’inscrit dans le domaine des sciences séparatives et se base sur la technique de SPLITT (SPLIT-flow Thin fractionation). Son objectif consiste en l’étude des mécanismes qui sont à l’origine de la séparation, en continu et sans membrane, d’objets de taille micrométrique dans des mini-séparateurs fluidiques (Step-SPLITT). Les expériences menées, en laboratoire et lors de vols paraboliques, ont révélé le couplage complexe comme l’influence des effets hydrodynamiques et du champ gravitationnel sur la migration transverse des espèces en écoulement. Des visualisations tridimensionnelles par holographie digitale ont corroboré nos résultats et dévoilé des comportements inattendus. Les capacités séparatives des Step-SPLITT ont rendu possible l’analyse et la séparation d’objets biologiques et biomimétiques. Enfin, cette étude complétée par une modélisation tridimensionnelle de l’écoulement nous a permis de mettre au point un nouveau prototype de séparateur.This experimental thesis belongs to the field of separative sciences and is based on the SPLITT technique (SPLIT-flow Thin fractionation). The objective is to study the mechanisms that are at the origin of continuous and membraneless separation of micron-size species in mini fluidic separators (Step-SPLITT). Experiments undertaken in laboratory and during parabolic flights revealed the complex coupling of the hydrodynamic effects and the gravitational field influencing the transverse migration of the flowing species. Three-dimensional visualizations performed by digital holography confirmed our results and disclosed unexpected behaviours. The separation capacities of Step-SPLITT made the analysis and the separation of biological and biomimetic species possible. In addition this study in conjunction with a three-dimensional flow modelling enabled us to develop a new prototype of separator.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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Čech, Tomáš. "Nové směry provádění hydroizolací dopravních podzemních staveb." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-392356.
Full textAbstract:
This diploma thesis focuses on the implementation of waterproofing of underground constructions using an LLDPE membrane hinged on anchors. In the future, this method will replace the commonly used waterproofing system in Scandinavia with extruded polyethylene foam. This method of tunnel construction and waterproofing is compared with the NRTM method, often used in Central Europe. The thesis describes the installation of a waterproofing system, especially materials, accessories, welding devices and auxiliary installation equipment. The main focus of the thesis is to verify the reliability of the individual types of welds and to assess the waterproofing system in terms of implementation and environmental demands.
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Quaglino, Alessio. "Membrane locking in discrete shell theories." Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F063-B.
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Öz, Pýnar. "Theoretical analysis of membrane properties underlying action potential phase-locking in noise-driven cells." Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-0006-B5D6-B.
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Menniti, Adrienne L. "The influence of shear on extracellular polymeric substance production in membrane bioreactors /." 2009. 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:3363034.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3714. Adviser: Eberhard Morgenroth. Includes bibliographical references (leaves 125-132) Available on microfilm from Pro Quest Information and Learning.
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Cao, Yingchen. "Examinations of the shear stress on MBR-membrane plates by a single bubble using CFD." Master's thesis, 2016. https://tuprints.ulb.tu-darmstadt.de/5273/1/Abschlussarbeit%20Cao%20Yingchen%20Final.pdf.
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Nowadays the use of membrane filtration process is rapidly increasing in industrial fields, especially in the field of water and wastewater treatment. Aeration is one of the most important processes in MBR systems. The cost of aeration is the main operating cost. It can provide the biomass with oxygen and prevent them from settling down. Besides, the shear stress created by the aeration process can scour the solid from the membrane surface to control the growth of cake layer and increase the filtration flux.
At the same time computational fluid dynamics (CFD) has become a leading modeling and analysis tool for fluid simulation because of its advances in computational performance. Recently more and more studies have used CFD techniques to investigate and model the fluid flow through a membrane module and to study the membrane performance.
The aim of this thesis is to investigate the shear stress on the membrane plate induced by a single bubble in the MBR system. A better understanding of the shear stress caused by aeration in MBR, which depend greatly on operating conditions and bubble size, can be achieved by using numerical simulation. This thesis focuses on the operation conditions, bubble sizes and the geometry of the membrane models etc. as well as their influence on shear stress.
The thesis firstly introduces the basics of membrane and CFD as well as the model theories. Then a model for simulation of the membrane systems is established and its independence on the mesh size and model geometry was tested. Experiments for validation are conducted. The results of this simulation and the results from the experiments and from literature are presented and compared. Finally in models with an appropriate geometry, an appropriate mesh size and most importantly reliable results, different simulations are carried out to simulate the bubble formation, to investigate the effect of different parameters on the bubble motion, to study what affects the shear stress and shear force, especially in the escape zone, where the bubble moves out of the gap between the submerged flat sheet membranes.
The novel of this study lies in the flexibility of membranes. The membrane in almost all CFD simulations for membrane in previous studies was set as rigid wall. In the last part of this thesis, the membrane was set to be flexible. A two-way system coupling was applied for the simulation of the membrane movement and the rise of the bubble.
At first the formation of bubbles was studied. The amount of gas injected into the water, the way it is injected (continued aeration and discontinued aeration), the inlet configurations and the inlet velocity of the gas determine the bubble shape and size. Then it was found out that the bubble size has a very powerful impact on the bubble motion and shear stress exerted by rising bubbles. An increase in bubble size leads to an increase in maximal shear stress, which also means an increase in cleaning effect on the membrane surface in the filtration. When the bubble size is larger than the gap width, this cleaning effect is no longer that much significant. As for the bubble rising velocity, it reaches its maximal value at a bubble diameter of 5 mm, above which, the wall effect of the membrane makes the bubble slow down. This effect was more significant for the bubbles, whose diameter is larger than the channel gap of membranes. For these bubbles a slug flow could be observed, and according to their spherical-cup shape, they belong to Taylor bubbles. To identify the most effective multi-phase flow pattern for fouling control, membrane module configurations with different gap width were evaluated with CFD. The shear stress was found out to be highest at the smallest gap distance. Considering the clogging problem for small membrane gaps, it is concluded that the rise of a 5 mm bubble between the membranes with a gap of 6 mm might be the optimal conditions for the aeration during the filtration process. The fluid velocity was also investigated in this study. The averaged shear stress shows a linear dependence on the fluid velocity and the bubble motion can increase the shear stress at low fluid velocity significantly. 2d simulation and 3d simulation were also compared in this study. The numerical results from 3d simulation were more reliable. At last a two-way system coupling simulation was performed to investigate the effect of membrane movement on the shear stress. It was found out that the maximal shear stress produced by membrane movement and bubble rising is more than ten times greater than that only induced by the rise of a single bubble.
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Tabouillot, Tristan Butler Peter J. "Shear stress elicits a transient domain-dependent alteration of the plasma membrane fluidity in endothelial cells." 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4086/index.html.
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Padmasiri, Sudini Indramali. "Effect of high shear on anaerobic digestion in an anaerobic membrane bioreactor (AnMBR) treating high strength wastewater /." 2007. 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:3301208.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1243. Adviser: Lutgarde Raskin. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.
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Alevriadou, Barbara Rita. "Effect of shear stress on surface membrane potassium ion permeability of calf pulmonary artery endothelial cells (Potassium ion)." Thesis, 1989. http://hdl.handle.net/1911/13339.
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This study aims to determine the effect of shear stress on membrane potassium (K$\sp+$) permeability in vascular endothelial cells. Cultured monolayers of calf pulmonary artery endothelial cells, preloaded with $\rm \sp{86}Rb\sp+$, were subjected to different levels of fluid shear stress in the range 1-10 dynes/cm$\sp2$, in a parallel-plate geometry flow chamber, and the radioactivity of the effluent was monitored with time. Increase in laminar shear stress, from 1 dyne/cm$\sp2$ to a higher level, resulted in a rapid transient increase in the rate constant for $\rm \sp{86}Rb\sp+$ release. The difference of efflux rate coefficients, between the peak and the baseline at 1 dyne/cm$\sp2$, varied with shear stress in a "dose-dependent" manner. Changes in K$\sp+$ permeability may occur via activation of shear-stress-activated K$\sp+$ channels, Ca$\sp{2+}$-activated K$\sp+$ channels, or both. The Ca$\sp{2+}$-activated K$\sp+$ channels were shown to respond to bradykinin stimulation under flow conditions. The significance of such flow studies is that they provide more knowledge about the flow-associated changes in ionic channels and intracellular second messengers in endothelial cells.
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Young, Edmond. "Accessible Microfluidic Devices for Studying Endothelial Cell Biology." Thesis, 2009. http://hdl.handle.net/1807/17850.
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Endothelial cells (ECs) form the inner lining of all blood vessels in the body, and coat the outer surfaces of heart valves. Because ECs are anchored to extracellular matrix proteins and are positioned between flowing blood and underlying interstitium, ECs are constantly exposed to hemodynamic shear, and act as a semi-permeable barrier to blood-borne factors. In vitro cell culture flow (ICF) systems have been employed as laboratory tools for testing endothelial properties such as adhesion strength, shear response, and permeability. Recently, advances in microscale technology have introduced microfluidic systems as alternatives to conventional ICF devices, with a multitude of practical advantages not available at the macroscale. However, acceptance of microfluidics as a viable platform has thus far been reserved because utility of microfluidics has yet to be fully demonstrated. For biologists to embrace microfluidics, engineers must validate microscale systems and prove their practicality as tools for cell biology. Microfluidic devices were designed, fabricated, and implemented to study properties of two EC types: aortic ECs and valve ECs. The objective was to streamline experimentation to reveal phenotypic traits of the two types and in the process demonstrate the usefulness of microfluidics. The first task was to develop a protocol to isolate pure populations of valve ECs because reported methods were inadequate. Dispase and collagenase in combination for leaflet digestion followed by clonal expansion of cell isolates was optimal for obtaining pure valve EC populations. Using a parallel microfluidic network, we discovered that valve ECs adhered strongly and spread well only on fibronectin and not on type I collagen. In contrast, aortic ECs adhered strongly on both proteins. Both aortic and valve ECs were then exposed to shear and analyzed for cell orientation. Morphological analyses showed aortic and valve ECs both aligned parallel to flow when sheared in a macroscale flow chamber, but aortic ECs aligned perpendicular to flow when sheared in a microchannel. Finally, a microfluidic membrane device was designed and characterized as a potential tool for measuring albumin permeability through sheared endothelial monolayers. Overall, these studies revealed novel EC characteristics and phenomena, and demonstrated accessibility of microfluidics for EC studies.