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1
Jenkins, Richard J. "The mechanisms whereby the sodium, potassium-ATPhase undergoes adaptive changes in human lymphocytes in response to lithium." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236273.
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Schmidt, Stephanie Ann. "Mathematical models of ion transport through nafion membranes in modified electrodes and fuel cells without electroneutrality." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/734.
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Electrodes are modified with polymer films to grant novel permeability. Often, redox probes partition from solution into film and are electrolyzed at the electrode. This creates a flux of probe into the polymer film and a flux of electrolyzed probe out of the polymer film. Transport of the probe through the film is governed by diffusion and migration, mathematically described from the Nernst-Planck equation as J_{i}=-D_{i}((∂C_{i}(x,t))/(∂x))-((z_{i}F)/(RT))D_{i}C_{i}(x,t)((∂Φ(x,t))/(∂x)) where x is the distance from the electrode, t is time, C_{i}(x,t) is space and time dependant concentration of the probe i, z_{i} is the charge of the probe i, F is Faraday's constant, R is the gas constant, T is absolute temperature, J_{i} is the flux of the probe i, D_{i} is the diffusion constant of the probe i and Φ(x,t) is the space and time dependant potential.
In most natural systems, charge accumulation is not appreciably noticed, the system behaves in such a way that a charged ion is neutralized by a counterion. This is called electroneutrality and is mathematically represented by Laplace's condition on the potential, ((∂²Φ)/(∂x²))=0. In some systems, it is not clear if counterions are readily available to neutralize an ion. In such a system, there may not be electroneutrality, giving Poisson's equation to replace Laplace's condition as ((∂²Φ)/(∂x²))=-(F/ɛ)∑_{i}z_{i}C_{i}(x,t) where ɛ is the relative permittivity. The addition of Poisson's condition makes the system nonsolvable. In addition, the magnitude of F/ɛ creates difficulty simulating the system using standard techniques. The first system investigated determines the concentration and potential profiles over the polymer membrane of a fuel cell without electroneutrality.
In some systems, the probes can not easily diffuse around each other, certain polymer film environments prevent such a swap of location as diffusion is commonly thought to occur. A more generalized form of the Nernst-Planck equation describes spatially varying diffusion coefficient as J=-D(x,t)((∂C(x,t))/(∂x))-((zF)/(RT))D(x,t)C(x,t)((∂Φ(x,t))/(∂x)). D(x,t) is space and time dependent diffusion, usually thought of with a physical diffusion term and an ion hopping term. The second system this thesis investigates is a modified electrode system where electron hopping is responsible for a majority of the probe transport within the film.
Lastly, the beginnings of a method are presented to easily determine the physical diffusion rate of a probe within a modified electrode system based on known system parameters.
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Hsu, Viktoria R. T. "Ion transport through biological cell membranes : from electro-diffusion to Hodgkin-Huxley via a quasi steady-state approach /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/6755.
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García, Gamuz José Antonio. "Caracterización hidrodinámica y fenomenológica de membranas selectivas." Doctoral thesis, Universidad de Murcia, 2009. http://hdl.handle.net/10803/10842.
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El objetivo principal de este trabajo es desarrollar un modelo sencillo que permita la caracterización hidrodinámica de membranas selectivas integradas en sistemas bi-iónicos, mediante la determinación de coeficientes de difusión y de espesores de las capas límite alrededor de la membrana. A tal fin, se empleó una célula de difusión rotatoria (CDR), que permite el establecimiento de condiciones hidrodinámicas bien definidas para el sistema de membrana, dado que la variación de la frecuencia de giro del cilindro interior (ω), permite disminuir el espesor de la capa límite sobre la membrana, lo que favorece el intercambio iónico a su través. Se puede comprobar éste comportamiento, mediante consideraciones en torno al coeficiente de difusión de los cationes en el sistema de membrana y del cálculo del propio espesor de la capa límite. El mencionado coeficiente se obtendrá a partir del flujo iónico en la membrana, determinado a partir de medidas de pH, junto a medidas de conductividad, en la fase externa (receptora), a diferentes temperaturas y a distintas valores de ω.La medida de los flujos, una vez establecida su dependencia con ω, permite obtener los coeficientes de difusión catiónicos en el sistema de membrana, en función de la temperatura y de ω. Las medidas de la conductividad permiten testar el modelo propuesto, mediante su correlación con los valores de pH obtenidos, proporcionando información adicional acerca de los coeficientes de difusión de los cationes.From the experimental study of the ionic transport through selective membranes in biionic systems, a simple model which allows the characterising hydrodynamic of the membrane systems through the determination of diffusion coefficients and the thickness of the limit layer has been developed. With this purpose, a rotating diffusion cell that allows the setting of hydrodynamic conditions clearly for the membrane system has been used, studying the variation of the conductivity and the pH in the external phase (receiving) at different temperatures from 20ºC to 50ºC and at different rotating velocities ω. The measurement of the fluxes, once set its dependence with ω, allows obtained the diffusion coefficients cationics in the membrane system in accordance with the temperature and ω. The measurements of the conductivity allow the testing of this model, through its correlation with the values of the pH measured, obtaining additional data about the diffusion coefficient of the cations in the receiving phase.
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Touchard, Pascale. "Propriétés d'échange et de transport ioniques des parois végétales isolées de cals de lin." Rouen, 1988. http://www.theses.fr/1988ROUES017.
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Winschel, Christine A. "Accurate Methodology for Monitoring Biomembrane Events." VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/2860.
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Abstract ACCURATE METHODOLOGY FOR MONITORING BIOMEMBRANE EVENTS By Christine A. Winschel, Ph.D. A Dissertation submitted in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Chemistry at Virginia Commonwealth University. Virginia Commonwealth University, 2012 Major Director: Dr. Vladimir A. Sidorov ASSOCIATE PROFESSOR, DEPARTMENT OF CHEMISTRY This study describes the synthesis and characterization of a new receptor (cyclen 1) capable of strong selective binding of pyrene-based anionic dyes under near-physiological conditions. This receptor comprises four naphthylthiourea groups tethered to a cyclen core via an ester linkage. The most important finding was the ability of cyclen 1 to bind efficiently to a pH-sensitive pyranine dye, a dye that is commonly used in various biomembrane assays. The high affinity of cyclen 1 to pyranine, its impermeability to the lipid bilayer membrane, fast kinetics of binding, and ability to quench pyranine’s fluorescence were used as a basis for a new membrane leakage assay. This membrane leakage assay is fully compatible with the commonly applied pH-stat transport assay, and therefore it allows for differentiation of ion transport and nonselective leakage mechanisms within a single set of experiments. In the second part of this study a new methodology for the detection of lipid flip was developed. This methodology relies on the quenching of the fluorescence of a newly synthesized cascade-blue-labeled lipid through complex formation with cyclen 1. This receptor-dye complexation also has high affinity for binding at micromolar concentrations and can be reversed by either competitive displacement of the lipid probe or by enzymatic degradation of the receptor leading to the label release and fluorescence dequenching. This new methodology is suitable for the study of lipid flip in both model spherical bilayer membranes and in-vitro experiments, and is less invasive to the model and cell membranes than the commonly utilized 7-nitro-1,2,3-benzoxadiazol-4-yl (NBD)-dithionite methodology. Lastly, new pH-sensitive lipids were synthesized and utilized in the formulation of liposomes suitable for controlled drug release. These liposomes contain various amounts of internal NaCl and undergo internal acidification upon the exogenous addition of an HCl co-transporter in a physiologically relevant NaCl solution. Therefore, acidification ultimately leads to the hydrolysis of the pH-sensitive lipids and subsequent contents release. These liposomes were found to be insensitive to physiological concentrations of human serum albumin and to be non-toxic to cells at concentrations exceeding pharmacological relevance. These results render this new drug release model potentially suitable for in vivo applications.
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Agostinelli, Simone. "A compartmentalised microchip platform with charged hydrogel to study protein diffusion for Single Cell Analysis." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20333/.
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Within one tumor, cancer cells exist as different sub-populations due to the variations in expression of crucial bio-markers. The prevalence of even minor cell sub-populations can determine overall cancer progression and treatment response. Single-cell protein analysis is a way to identify these cell sub-populations; therefore we developed a microfluidic platform with ultrahigh-sensitivity for single-cell protein analysis. As the key step to develop such a platform, protein migration under the application of an electric field has to be understood. COMSOL multi-physics software is used as a tool to understand the protein migration in microfluidic channels, which contain ion-selective hydrogels as the separation matrix. The objective of this thesis work, is to minimize the protein losses to diffusion and to maximize the fluorescent signal in order to quantify the protein expression in single cells. The novelty of this work lies in the use of ion-selective hydrogels to eliminate the diffusional losses and separate the proteins based on their mass and charge. This thesis project has been performed thanks to an Erasmus fellowship at MCS Department of the University of Twente.
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Monedero, Alonso David. "Characterization of cationic conductances of human erythrocytes and their involvement in health and disease." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS554.
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La membrane des globules rouges est dotée de plusieurs canaux ioniques. Normalement silencieux, ils peuvent dissiper rapidement les gradients ioniques une fois activés. Lors de cette étude, l'utilisation du NS3623 à des concentrations supérieures à celles requises pour l'inhibition des voies de conductances anioniques montre que ce composé active les canaux cationiques non sélectifs permettant ainsi leur étude y compris en conditions hyperpolarisantes. Le suivi en temps réel du potentiel membranaire à l'aide de l'ionophore à protons CCCP permet d’observer directement l'activité des canaux ioniques lorsque leur ouverture modifie le potentiel membranaire. Cette méthode a été utilisée pour décrire l'homéostasie cationique dysfonctionnelle dans des cellules de patients affectés par différentes mutations sur les canaux Gárdos ou Piezo1. Elle pourrait constituer un outil de diagnostic alternatif. L'activité des canaux ioniques a été caractérisée tout au long de la période de stockage réglementaire des globules rouges stockés à 4 °C (42 jours), afin de mieux comprendre les lésions de stockage. Il a été démontré que l’activité du NSC augmentait avec le temps, devenant spectaculaire la dernière semaine de stockage. En conclusion, les canaux cationiques non sélectifs jouent un rôle dans l'homéostasie des globules rouges matures. Ils contribuent ou peuvent constituer l'origine de la fuite de cations. Ils sont à l'origine de maladies en cas de dysfonctionnement et la compréhension de leur fonctionnement dans ces conditions peut fournir des stratégies thérapeutiques. Enfin, ils sont impliqués dans les lésions de stockage compromettant par leur activité l'efficacité transfusionnelleRed cell membranes are endowed with several ion channels. Normally silent, they will rapidly dissipate ionic gradients once activated. I present a pharmacological means (NS3623) for the enhancement of NSC channels in hyperpolarizing conditions with concomitant chloride conductance inhibition in freshly drawn healthy mature RBCs. Membrane potential estimation aided by proton ionophore CCCP allows the recording of membrane potential changes in real time, enabling the observation of ion channel activity as their opening alters the membrane potential. This method was used to describe dysfunctional cation homeostasis in hereditary anemia using patient cells affected by different mutations on Gárdos or Piezo1 channels. The technique is fast, reliable and inexpensive providing an alternative diagnostic tool with the added advantage of producing ion channel activity information. Ion channel activity was characterized throughout 42-day storage period of RBCs stored at 4 C in CPD-SAGM according to French regulations to address the issue of storage lesions, which reduce transfusion efficacy. NSC activity was shown to increase over time during storage and dramatic ion channel activity was observed during the last week. Consequently, NSC activity may jeopardize cell volume and morphology upon reinfusion. In conclusion, Non-Selective Cation channels play an important role in mature RBCs. They contribute or may constitute the origin of cation leak. They cause disease when malfunctioning and insight into their operation in these conditions may supply with therapeutic strategies. They are involved in the storage lesion, and may account for RBCs demise once back in the circulation
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Schaumann-Gaudinet, Annick. "Perturbation par les ions lithium de caractéristiques ioniques des suspensions cellulaires d'Acer pseudoplatanus L." Rouen, 1988. http://www.theses.fr/1988ROUES018.
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Ermolayeva, Elena. "Plasma membrane ion transport in phytochrome signal transduction." Thesis, University of York, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319767.
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Calvert, Caroline M. "Ion transport at the vacuolar membrane of Candida albicans." Thesis, University of York, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317860.
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Lubelski, Ariel, and Joseph Klafter. "Lateral diffusion of proteins in cell membrane." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194600.
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We present a method describing the lateral movement of proteins in cell membranes as observed in FRAP experiments. We extend earlier results derived for normal diffusion [1] to account for the case of anomalous subdiffusion. Our analytic closed forms are compared to computer simulations of anomalous diffusion and both show excellent agreement. The approach sheds light on the behavior of proteins in such complex systems and provides a tool to analyze experimental results.
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Vatish, M. "Ion transport and its regulation in human placental membrane vesicles." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333245.
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Mancini, Nicholas D. (Nicholas David). "Systems-level design of ion transport membrane oxy-combustion power plants." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67797.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 187-192).
Oxy-fuel combustion, particularly using an integrated oxygen ion transport membrane (ITM), is a thermodynamically attractive concept that seeks to mitigate the penalties associated with CO 2 capture from power plants. Oxygen separation in an ITM system consists of many distinct physical processes, ranging from complex electrochemical and thermochemical reactions to conventional heat and mass transfer. The dependence of ITM performance on power cycle operating conditions and system integration schemes must be captured in order to conduct meaningful process flow and optimization analyses. An axially spatially-distributed, quasi two-dimensional ITM model is developed based on fundamental conservation equations, semi-empirical oxygen transport equations obtained from the literature, and simplified fuel oxidation kinetic mechanisms. Aspects of reactor engineering such as geometric structure, flow configuration and the relationship between oxygen transport, fuel conversion and pressure drop are explored. Emphasis is placed on model robustness, modularity, and low computational expense. The model seeks to bridge the gap between detailed CFD studies and overly-simplified black-box models and provides a tool for the analysis and design of ITM systems. The ITM model is used to explore the dependence of ITM performance on reactor geometric structure, flow configuration, operating conditions, membrane material properties, and uncertainty in key modeling assumptions. Many operational constraints are presented that are usually overlooked by black-box modeling strategies, and the implications of these constraints are explored. Further, a comparison is made between reactive and separation-only ITMs to assess the relative merits and disadvantages of each. The results show that although a reactive ITM significantly improves the partial pressure driving force, practical reactor engineering considerations indicate that this concept is not superior to counter-current separation-only ITMs, mainly due to stringent temperature limitations of the membrane material. A Second Law assessment of certain ITM configurations is performed to evaluate the potential of ITM technology to reduce the air separation penalty and to guide effective systems-level integration. Finally, simulations of various ITM-based zero-emissions power cycles using the intermediate fidelity ITM model are performed. The first objective is to analyze the prevalent ITM-based power cycle designs and develop novel design modifications. The second objective is to investigate the effect of reactive ITM improvement design strategies proposed herein, such as the multiple compartment reactive ITM (MCRI), the low activation energy (LAE) materials reactive ITM, and hybrid reactive and separation-only concepts. An assessment of the potential for these novel ITM designs to reduce both the penalty and size associated with ITM air separation technology is conducted. The power cycle simulation and analysis clearly demonstrates the various challenges associated with implementing reactive ITMs. The hybrid cycle displays the potential to reduce the size of the ITM compared to the best separation-only concept while maintaining a comparable First Law efficiency. Additionally, the MCRI simulation results indicate comparable ITM size and pressure drops to the best separation only-concepts, greatly improving the attractiveness of reactive ITMs. Overall, the work herein finally allows for detailed optimization analyses to determine the best possible ITM oxy-combustion power cycles.
by Nicholas D. Mancini.
S.M.
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MATSUNO, NOBUNAKA. "THEORETICAL AND EXPERIMENTAL STUDIES OF ION TRANSPORT THROUGH BIOLOGICAL MEMBRANE CHANNELS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1060886930.
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Nowak, Sarah Alice. "Membrane mechanics and non-equilibrium transport in cell biology." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1970611221&sid=7&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Yang, Ruidong. "Studies on Molecular and Ion Transport in Silicalite Membranes andApplications as Ion Separator for Redox Flow Battery." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406820402.
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Zhang, Hao. "Chemoelectromechanical Actuation in Conducting Polymer Hybrid with Bilayer Lipid Membrane." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3074.
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Biological and bio-inspired systems using ion transport across a membrane for energy conversion has inspired recent developments in smart materials. The active mechanism in bioderived materials is ion transport across an impermeable membrane that converts electrochemical gradients into electrical and mechanical work. In addition to bioderived materials, ion transport phenomenon in electroactive polymers such as ionomeric and conducting polymers produces electromechanical coupling in these materials. Inspired by the similarity in transduction mechanism, this thesis focuses on integrating the ion transport processes in a bioderived material and a conducting polymer for developing novel actuation systems. The integrated membrane has a bilayer lipid membrane (BLM) formed on a conducting polymer, and the proteins reconstituted in the BLM regulate ion transport into the conducting polymer. The properties of the polymer layer in the integrated device are regulated through a control signal applied to the bioderived layer and hence the hybrid membrane resembles an ionic transistor. Due to the bioderived nature of this device, it is referred to as a ‘bioderived ionic transistor’. The research carried out in this thesis will demonstrate the fabrication, characterization and design limitations for fabricating a chemoelectromechanical actuator using the BIT membrane. The BIT membrane has been fabricated using BLM (DPhPC) reconstituted with protein (alamethicin) to gate Na$^+$ transport into conducting polymer membrane (PPy(DBS)). In this membrane, the bioderived layer is fabricated with proteins by vesicle fusion method and conducting polymer is fabricated by electropolymerization. The bioderived layers, the conducting polymer layers and the hybrid membrane are characterized using electrochemical measurements such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The fabrication, characterization and design effort presented in this thesis focuses on the integration of ion transport through the bioderived membrane into volumetric expansion and bending actuation. The characterization efforts are supported by empirical and physics-based models to represent the input-output relationship for both PPy(DBS) actuator and bioderived membrane, and design rules for the proposed actuation platforms are specified. The electropolymerized PPy(DBS) actuator is anticipated to be used in a bicameral device with the chambers kept separated by the DPhPC-alamethicin bioderived membrane. The relationship between the gradient potential, ionic current through the gate, ion concentration, ion transport coefficient in the conducting polymer layer, and the induced tip displacement in the polymer has been concluded from experiments and fitted to the actuation system model. This thesis will also address future directions for this research and anticipated applications for this hybrid actuation concept, such as artificial muscle, drug delivery.
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Michos, Ioannis. "Studies on Ion Transport in Mesoporous and Microporous Inorganic Membranes as Ion Separators for Redox Flow Batteries." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin149155938977993.
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Lubelski, Ariel, and Joseph Klafter. "Lateral diffusion of proteins in cell membrane: the anomalous case." Diffusion fundamentals 3 (2005) 7, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14295.
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We present a method describing the lateral movement of proteins in cell membranes as observed in FRAP experiments. We extend earlier results derived for normal diffusion [1] to account for the case of anomalous subdiffusion. Our analytic closed forms are compared to computer simulations of anomalous diffusion and both show excellent agreement. The approach sheds light on the behavior of proteins in such complex systems and provides a tool to analyze experimental results.
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Apo, Daniel Jolomi. "Experimental characterization of an Ion Transport Membrane (ITM) reactor for methane oxyfuel combustion." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70432.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-156).
Ion Transport Membranes (ITM) which conduct both electrons and oxygen ions have been investigated experimentally for oxygen separation and fuel (mostly methane) conversion purposes over the last three decades. The fuel conversion investigations typically involve converting methane to syngas or higher hydrocarbons. Over the past decade, ITMs have received considerable interest in the industry for oxygen separation and production of syngas. There is also a possibility that the future of ITM industrial use lies with clean power generation as long as stable ITMs are developed which separate oxygen from air and enable reaction of methane to produce carbon dioxide, steam, and the heat which powers turbines. This would hopefully provide CO 2 capture compatibilities at a lower financial and energetic cost than 'conventional' methods. In this thesis, an analysis of reported experimental ITM reactors is presented, with a view to understanding the processes which govern the permeation of oxygen, conversion of methane and production of desired gas species. The analysis shows that temperature and mass flow influence the oxygen permeation within the reactor. Also, the influence of fuel/0 2 ratio on fuel conversion and CO selectivity is discussed. The design and operation of a novel ITM reactor for the experimental investigation of oxygen separation and oxyfuel combustion (a relatively new ITM concept) is presented. The ITM reactor was designed with the aim of providing insight into the use of ITMs for power generation. The reactor has provisions for optical and spatial analysis. The reactor was used to conduct experiments using a La0.9Ca0.1FeO3-[delta] (LCF) membrane. The results of experiments conducted are presented to show the effects of temperature, mass transfer, and fuel on oxygen permeation, fuel conversion and species selectivity. A comparison is made between the observed results and reported values in literature.
by Daniel Jolomi Apo.
S.M.
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Hong, Jongsup. "Numerical simulations of ion transport membrane oxy-fuel reactors for CO₂ capture applications." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81700.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 185-190).
Numerical simulations were performed to investigate the key features of oxygen permeation and hydrocarbon conversion in ion transport membrane (ITM) reactors. ITM reactors have been suggested as a novel technology to enable air separation and fuel conversion to take place simultaneously in a single unit. Possessing the mixed ionic and electronic conductivity, perovskite membranes or ion transport membranes permeate selectively oxygen ions from the air (feed) side to the sweep gas or reactive gas (permeate) side of the membrane, driven by the oxygen chemical potential gradient across the membrane at elevated temperature. When a fuel such as methane is introduced into the permeate side as a sweep gas, hydrocarbon oxidation reactions occur by reacting the fuel with the permeated oxygen. The fuel can be partially reformed, completely oxidized or converted to produce higher hydrocarbons. To utilize this technology more effectively, it is necessary to develop a better understanding of oxygen transport and hydrocarbon conversion in the immediate vicinity of the membrane or on its surface. In this thesis, a planar, finite-gap stagnation flow configuration was used to model and examine these processes. A spatially resolved physical model was formulated and used to parameterize an oxygen permeation flux expression in terms of the oxygen concentrations at the membrane surface given data on the bulk concentration. The parameterization of the permeation flux expression is necessary for cases when mass transfer limitations on the permeate side are important and for reactive flow modeling. At the conditions relevant for ITM reactor operation, the local thermodynamic state should be taken into account when the oxygen permeation rate is examined, which has been neglected. To elucidate this, the dependency of oxygen transport and fuel conversion on the geometry and flow parameters including the membrane temperature, air and sweep gas flow rates, oxygen concentration in the feed air and fuel concentration in the sweep gas was discussed. The reaction environment on the sweep side of an ITM was characterized. The spatially resolved physical model was used to predict homogeneous-phase fuel conversion processes and to capture the important features (e.g., the location, temperature, thickness and structure of a flame) of laminar oxy-fuel diffusion flames stabilized on the sweep side. The nature of oxygen permeation does not enable pre-mixing of fuel and oxidizer (i.e., sweep gas and permeated oxygen), establishing non-premixed flames. In oxy-fuel combustion applications, the sweep side is fuel-diluted with CO₂ or/and H₂O, and the entire unit is preheated to achieve a high oxygen permeation flux. This study focused on the flame structure under these conditions and specifically on the chemical effect of CO₂ dilution. The interactions between oxygen permeation and homogeneous-phase fuel oxidation reactions on the sweep side of an ITM were examined. Within ITM reactors, the oxidizer flow rate, i.e., the oxygen permeation flux, is not a pre-determined quantity, since it depends on the oxygen partial pressures on the air and sweep sides and the membrane temperature. Instead, it is influenced by the hydrocarbon oxidation reactions that are also dependent on the oxygen permeation rate, the initial conditions of the sweep gas, i.e., the fuel concentration, flow rate and temperature, and the diluent. A parametric study with respect to key operating conditions, which include the fuel concentration in the sweep gas, its flow rate and temperature and the geometry, was conducted to investigate their interactions. The catalytic kinetics of heterogeneous oxygen surface exchange and fuel oxidation for a perovskite membrane in terms of the thermodynamic state in the immediate vicinity of or on the membrane surface was investigated. Perovskite membranes have been shown to exhibit both oxygen perm-selectivity and catalytic activity for hydrocarbon conversion. However, a description of their catalytic surface reactions is still required. The kinetic parameters for heterogeneous oxygen surface exchange and catalytic fuel conversion reactions were inferred, based on permeation rate measurements and a spatially resolved physical model that incorporates detailed chemical kinetics and transport in the gas-phase. It is shown that the local thermodynamic state at the membrane surface should be accounted for when constructing and examining membrane permeation and heterogeneous chemistry. The significance of modeling both homogeneous and heterogeneous chemistry and their coupling when examining the results was discussed.
by Jongsup Hong.
Ph.D.
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Lomba, Rosana Fatima Teixeira. "Membrane behavior of shales and ionic solutions /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Chapman, Joanna Claire. "Potassium ion channels and disorders of glucose regulation." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322879.
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Pouraghajansarhamami, Fezzeh. "Understanding the Relationships between Ion Transport, Electrode Heterogeneity, and Li-Ion Cell Degradation Through Modeling and Experiment." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8449.
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Electrode microstructure directly affects ion and electron transport and, in turn, has a strong correlation to battery performance. Understanding the separate yet complementary effects of ionic and electronic transport in cell behavior is a challenge. This work provides through a combination of experiments and modeling a better understanding of the relationship between three aspects of the cell: ion transport within the electrode, electrode uniformity, and cell degradation. The first part of this work compares two experimental methods that determine ion transport in terms of tortuosity, a dimensionless geometric factor. The polarization-interrupt and blocking-electrolyte methods measure effective diffusivity and conductivity, respectively. The tortuosity of several commercial-quality electrodes was measured using both methods, producing reasonable agreement between the two methods in most cases. Next, the effect of cell cycling on ionic and electronic transport of electrodes was investigated. Using the blocking electrolyte method, the tortuosity of electrode films at varying extents of cycling was determined. Variations in electronic resistivity were quantified by micro-scale measurements using a previously developed micro-four-line probe. The changes in tortuosity and electronic resistivity were investigated for a graphite anode and several cathode chemistries including LiCoO2, LiNixCoyMnzO2, LiFePO4, and blends of transition metal oxides. Clear evidence of changes in tortuosity and electronic resistivity was observed during cell formation and cycling. The magnitude of the changes strongly depended on the chemistry of electrodes and cycling conditions. The results indicate that, under normal cycling conditions, electronic resistivity increases while tortuosity unexpectedly decreases. However, accelerated cycling conditions (i.e. elevated temperature) can lead to both electronic resistivity and tortuosity increase. Finally, the interplay of electrode tortuosity heterogeneity and Li-plating was investigated. The Li-plating reaction was incorporated into a Newman-type model and validated using the voltage profile and capacity-loss data from experiments. The simulation result shows that a heterogeneous anode can cause non-uniform Li plating while cathode heterogeneity did not have a significant effect. The Li-plating profile across the thickness of the anode with cell cycling showed that Li tends to plate at the high tortuosity region near the separator. Unexpectedly, Li plating tends to shift to the current collector side upon a sufficient increase in porosity close to the separator. Simulated capacity loss vs. cycling data indicates that there is a feedback mechanism with cycling: as cycling continues the rate of Li plating for the high-tortuosity region decreases at the separator side and the other two regions will eventually catch up in terms of plating.
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El-Azzami, Louei Abdel Raouf. "CO2-SELECTIVE MEMBRANE FOR FUEL CELL APPLICATIONS." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/306.
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We have developed CO2-selective membranes to purified hydrogen and nitrogenfor fuel cell processes. Hydrogen purification impacts other industries such as ammoniaproduction and flue gas purification at reduced costs.Dense chitosan membranes were used for the first time to separate CO2 from amixture of 10% CO2, 10% H2, and 80% N2 at temperatures of 20 – 150oC and feedpressures of 1.5 atm – 5 atm. At 1.5 atm and 20 – 150oC, dry chitosan membranesachieved CO2 permeabilities, CO2/N2 and CO2/H2 separation factors of 0.383 – 24.3barrers, 10.7 – 3.40, and 4.54 – 1.50, respectively. The dry chitosan acted as an ordinarysolution-diffusion membrane: permeability increased with temperature but selectivitydecreased. The CO2/H2 and CO2/N2 separation factors at all temperatures enhanced CO2removal, making this membrane a candidate for fuel cell processes. The dual modetransport model fitted the transport data well.To achieve higher CO2 transport properties, chitosan was swollen with water.Water mediated the reaction of chitosan's amino groups with CO2. Humidifing the feedand sweep gases increased the membrane's performance. At 1.5 atm and 20 – 110 –150oC, CO2 permeabilities, CO2/N2 and CO2/H2 separation factors were 213 – 483 – 399barrers, 69.4 – 250 – 194, and 18.9 – 43.4 – 29, respectively. The presence of free waterand bound water facilitated the transport of CO2. Increasing feed pressure removed themaxima in permeability and selectivities at 110oC, but led to reduced CO2 permeabilities,CO2/N2 separation factors, and CO2/H2 separation factors to 156 – 286 barrers, 44.2 –131, and 12.0 – 16.7, respectively.To acquire higher CO2 transport properties, arginine-sodium salts wereincorporated in chitosan membranes as additional sites for facilitated transport. The salt'spercolation threshold was 40 wt %. At 1.5 atm and 20 – 110 – 150oC, CO2 permeabilities,CO2/N2 and CO2/H2 separation factors were 403 – 1498 – 1284 barrers, 122 – 852 – 516,and 31.9 – 144 – 75.5, respectively. Increasing feed pressure to 5 atm resulted indeclining CO2 permeabilities, CO2/N2 and CO2/H2 separation factors to 118 – 1078barrers, 21.6 – 352, and 5.67 – 47.9, respectively.Chitosan was characterized in terms of morphology, solution properties, thermalproperties, crystallinity, and degree of deacetylation.
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Mustafa, Morad. "Ion Permeation through Membrane Channels: Molecular Dynamics Simulations Studies." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2477.pdf.
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Fervenza, Fernando Custodio. "Membrane transport abnormalities in patients with renal failure." Thesis, University of Oxford, 1990. http://ora.ox.ac.uk/objects/uuid:9c345fc7-7e25-4f47-b41d-feddb8bc5cb7.
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The possibility that changes in membrane transport systems may contribute to the pathophysiology of the uraeraic syndrome has not been extensively studied. This thesis presents a study of eight erythrocyte membrane transport systems, namely the Na/K pump, the amino acid systems y+, ASC, gly, L and T, the nucleoside and choline transporters. The results indicate that, compared to normal controls, K+ flux through the Na/K pump was reduced in chronic renal failure patients (CRF), on haemodialysis (HD), and on continuous ambulatory peritoneal dialysis (CAPD), but was normal in functional transplant (FT) patients' erythrocytes. The number of Na/K pumps per erythrocyte was decreased in CRF and CAPD but showed no differences between HD, FT and Normal controls. The mean turnover rate per pump site was reduced in patients on HD, whereas other groups were not significantly different from controls. Cross-incubation experiments suggest that the lowered pump flux seen in the HD group was due to plasma factors since reversibility of the defect was achieved when those cells were incubated in normal plasma. The defect was completely reversed with a successful transplant. Erythrocytes from haemodialysis patients exhibited an increased uptake of L-lysine through the y+ system. The uptake of L-serine was decreased and the affinity of the ASC system for L-serine was increased in these patients compared with controls. The glycine transporter showed a significant increase in affinity for glycine. The flux of L-leucine and L-tryptophan showed no differences from control cells. Erythrocyte membrane transport of uridine was similar in normal control cells and in those obtained from uraemic patients. Choline influx rates were significantly increased and affinity of the transporter for choline reduced in dialysis patients' erythrocytes. Renal transplant and CRF patients showed variable influx rates which gave a significant negative correlation with creatinine clearance. These results show that there are selective abnormalities in some membrane transport system of the erythrocyte in patients with renal failure. The mechanism and possible significance of these changes are discussed.
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Cowan, David Scott Cambrai. "Properties of the plasma membrane H'+-ATPase from the stele and cortex of Zea mays roots." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241607.
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Bergström, Johan. "Utveckling av en experimentell uppställning för studie av massöverföring genom membran." Thesis, KTH, Skolan för kemivetenskap (CHE), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170632.
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The primary goal of this project is to develop an experimental setup for testing membrane materials. The membranes tested are all porous, hydrophilic and non- selective. The secondary goal is that the module finds use as an educational tool for learning about diffusion on a university level. The final setup consisted of two modified 250 ml polyethylene bottles with a wide neck joined together with a flange pinning the test object in between. In the experiments one side is loaded with a sodium chloride solution, while the other is loaded with pure deionized water. The conductivity change is then monitored in the chamber loaded with deionized water using a conductivity probe. Two test subjects are tested, an alpha Cellulose filter and a polycarbonate membrane. The mass transfer coefficient are determined to be 8.99*10-6 ± 3.90*10-6 [cm/min] and 3.62*10-5 ± 1.49*10-6 [cm/min] respectively. The large inconsistencies in the alpha cellulose filters results in large standard deviations, whereas the polycarbonate is very consistent and therefore have very small error bars. Meaning that the largest error in this design originates from inconsistencies between samples of the test subject. The setup is suitable as an educational tool due to short run times of one hour, the generated data only requires simple linear regression to extract mass transfer coefficients from the slope. The experiment can be varied further by adjusting temperature and stirring.Det primära målet med det här projektet är att utveckla en experimentell uppställning för att testa membran. Alla testade membran är porösa, hydrofila och icke-selektiva. Det sekundära målet är att uppställningen kan användas som ett pedagogiskt verktyg för kurser i masstransport. Den slutliga uppställningen består av två modifierade 250 ml polyeten flaskor med vid hals, ihopsatta med en fläns som håller testobjektet på plats emellan flaskorna. I experimenten fylls en av kamrarna med saltlösning och den andra med avjoniserat vatten, konduktiviteten mäts i kammaren som laddas med avjoniserat vatten. Två objekt testades, ett alfacellulosa filter och ett polykarbonat membran. Massöverförings koefficienter bestämdes till 8.99*10-6 ± 3.90*10-6 [cm/min] för alfacellulosa filtret och 3.62*10-5 ± 1.49*10-6 [cm/min] för polykarbonat membranet. Det finns stora variationer i alfacellulosa materialet vilket leder till stora standardavvikelse i körningarna på alfacellulosa filtret, medan polykarbonat membranen var identiska och därmed har väldigt små felstaplar. Därmed kunde det fastslås att stora avvikelser nästan bara beror på variationer i testobjektet. Uppställningen lämpar sig för undervisning eftersom körningstiden är kort (1 timme) och massöverföringskoefficienten kan tas fram med linjär regression. Experimentet kan bland annat varieras genom att ändra temperatur och omrörning.
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Reancharoen, Tharnkamol. "Ion transporting activities of an epithelial cell line, HCA-7 colony 30." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338258.
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Bursell, James David Hingston. "Swelling-activated membrane transport systems in vertebrate and protozoan cells : a comparative study." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337564.
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Larsson, Caroline. "Critical aspects of Understanding of the Structure and Function of the Cell Membrane : Students' interpretation of visualizations of transport through the cell membrane." Thesis, Linköping University, Department of Behavioural Sciences and Learning, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11045.
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The aim for this research report is to categorize and describe students’ conceptions about the structure and function of the cell membrane from a phenomenographic and variation theory perspective. Students’ ability to understand different concepts depends on their ability to comprehend certain critical features of the content. The critical feature of understanding the structure of the cell membrane investigated here is the polar and non-polar properties of molecules. The critical feature of understanding the function of the cell membrane is transport through the cell membrane. Another aim is to investigate what animations, concerning cellular transport, can contribute to teaching and students understanding of the cell membrane. Furthermore, a subordinated aim is to distinguish whether there are any existing differences and similarities between South Africa and Sweden in consideration to students’ conceptions about the cell membrane.
Two different methods of data collection, questionnaires and semi-structured interviews, were used in this investigation. 80 students participated in the questionnaire and 5 students participated in the interviews.
Four categories of conceptions about the characteristics of polar and non-polar molecules have been identified. Furthermore, one of the most remarkable and notable findings discovered are that most teachers and students are not aware of the current scientific view on how water molecules are transported through the cell membrane. Knowledge about aquaporines, discovered by Agre in 1992, seems to be almost non-existing in science education in upper secondary school, in Sweden and South Africa as well. Furthermore, students experience animations to be complex and which in some cases seem to be regarded as messy representation. Simultaneously they strongly emphasise the need for animations to support learning and remembering. Animations can be seen as a source of variation in teaching. The conceptions described occurred both among the South African students as well among the Swedish students. Also similarities concerning students’ conceptions have been discerned between the two countries investigated. For example there could be that South African students possess a richer understanding for the concept of the cell membrane than the Swedish students, but find it more difficult to move between different contexts.
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Pollet, Benoît. "Transport-reactions dans les membranes echangeuses d'ions : extraction et transport facilites d'acides faibles, cas particulier de l'acide borique." Paris 6, 1987. http://www.theses.fr/1987PA066584.
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Le transport de substrat a travers une membrane echangeuse d'ions peut etre accelere lorsqu'un contre ion joue le role de transporteur. L'acide borique par reaction de neutralisation avec le contre ion hydroxyle et par reaction de condensation avec l'ion borate forme des complexes polyborates (tri-, tetra- et penta-borates) de stabilite moyenne
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Teh, Ooi-kock. "Characterisation of membrane trafficking mutants in Arabidopsis thaliana." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670105.
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Morrow, James. "INVESTIGATION OF THE MATERIAL PROPERTIES OF CERIUM OXIDE WITH DOPANTS FOR AN OXYGEN TRANSPORT MEMBRANE." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2250.
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AN ABSTRACT OF THE THESIS OF James Morrow, for the Master of Science degree in Mechanical Engineering, presented on November 3, 2017, at Southern Illinois University Carbondale. TITLE: INVESTIGATION OF THE MATERIAL PROPERTIES OF CERIUM OXIDE WITH DOPANTS FOR AN OXYGEN TRANSPORT MEMBRANE MAJOR PROFESSOR: Dr. Kanchan Mondal Many physical properties of cerium oxide both undoped and doped have been studied herein. These properties include electrical conductivity, hardness, sintered density, and microstructure. These will be used to help determine a cerium oxide compound to use as an oxygen transport membrane in a combustion system. These compounds have been readily studied beforehand with exception to compounds with multiple dopants. Along with single doped cerium oxide, dual doped was investigated as well. The samples to be tested were created using co-precipitation and the subsequent powders were sintered at 1500°C to generate solid pellets. Once the pellets were formed the physical properties were tested. It was found that hardness and sintered density had little to no effect on electrical conductivity and the microstructures of the samples were shown to be favorable. As far as single or dual dopants were concerned, it was found that by including a second dopant along with zirconium that the electrical conductivity was reduced. Except for in the case where iron was doped along with zirconium, where the conductivity was increased. It was suggested to use samarium as the second dopant along with zirconium for the membrane.
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Bos, Cindy Renee. "Characterization of membrane traffic from the cell surface to the Golgi complex." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059144443.
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Grant, Alastair C. G. "The effect of cell volume on mammary gland metabolism." Thesis, University of Glasgow, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368747.
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Matulef, Kimberly Irene. "Cysteine-scanning mutagenesis of the ligand-binding domain of cyclic nucleotide-gated channels /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/5032.
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Roghmans, Florian Georg Verfasser], Matthias [Akademischer Betreuer] [Wessling, and Rob G. H. [Akademischer Betreuer] Lammertink. "Ion transport through microgel-modified membrane surfaces / Florian Georg Roghmans ; Matthias Wessling, Rob G. H. Lammertink." Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/1228979782/34.
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Stange, Christoph. "Combining artificial Membrane Systems and Cell Biology Studies: New Insights on Membrane Coats and post-Golgi Carrier Formation." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-102218.
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In mammalian cells, homeostasis and fate during development relies on the proper transport of membrane-bound cargoes to their designated cellular locations. The hetero-tetrameric adaptor protein complexes (APs) are required for sorting and concentration of cargo at donor membranes, a crucial step during targeted transport. AP2, which functions at the plasma membrane during clathrin-mediated endocytosis, is well characterized. In contrast, AP1 a clathrin adaptor mediating the delivery of lysosomal hydrolases via mannose 6-phosphate receptors (MPRs) and AP3 an adaptor ensuring the proper targeting of lysosomal membrane protein are difficult to study by classic cell biology tools. To gain new insights on these APs, our lab has previously designed an in vitro system. Reconstituted liposomes were modified with small peptides mimicking the cytosolic domains of bona fide cargoes for AP1 and AP3 respectively and thereby enabling the selective recruitment of these APs and the identification of the interacting protein network.
In the study at hand we utilize above-described liposomes to generate supported lipid bilayers and Giant Unilamellar Vesicles (GUVs), large-scale membrane systems suited for analysis by fluorescence microscopy. By using cytosol containing fluorescently-tagged subunits, we visualized clathrin coats on artificial membranes under near physiological conditions for the first time. Moreover, we demonstrated clathrin-independent recruitment of AP3 coats on respective GUVs. Presence of active ARF1 was sufficient for the selective assembly of AP1-dependent clathrin coats and AP3 coats on GUVs. By using dye-conjugated ARF1, we show that ARF1 colocalized with AP3 coats on GUVs and that increased association of ARF1 with GUVs coincided with AP1-dependent clathrin coats.
Our previous study identified members of the septin family together with AP3 coats on liposomes. Here we show on GUVs, that active ARF1 stimulated the assembly of septin7 filaments, which may constrain the size and mobility of AP3 coats on the surface. Subsequent cell biology studies in HeLa cells linked septins to actin fibers on which they may control mobility of AP3-coated endosomes and thus their maturation. An actin nucleation complex, based on CYFIP1 was identified together with AP1 on liposomes before. Here we show on GUVs, that CYFIP1 is recruited on the surface surrounding clathrin coats. Upon supply of ATP, sustained actin polymerization generated a thick shell of actin on the GUV surface. The force generated by actin assembly lead to formation of long tubular protrusions, which projected from the GUV surface and were decorated with clathrin coats. Thereby the GUV model illustrated a possible mechanism for tubular carriers formation. The importance of CYFIP1-reliant actin polymerization for the generation of MPR-positive tubules at the trans-Golgi network (TGN) of HeLa cells was subsequently demonstrated in our lab.
The notion that tubulation of artificial membranes could be triggered by actin polymerization allowed us to perform a comparative mass spectrometry screen. By comparing the abundance of proteins on liposomes under conditions promoting or inhibiting actin polymerization, candidates possibly involved in stabilization, elongation or fission of membrane tubules could be identified.
Among the proteins enriched under conditions promoting tubulation, we identified type I phosphatidylinositol-4-phosphate 5-kinases. Their presence suggested an involvement of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in tubule formation. By cell biology studies in HeLa we show, that down regulation of these enzymes altered the dynamics of fluorescently-tagged MPRs, illustrating the importance of locally confined PI(4,5)P2 synthesis during formation of coated carriers at the TGN.
Bin–Amphiphysin–Rvs (BAR) domains are known to sense membrane curvature and induce membrane tubulation. Among various BAR domain proteins, Arfaptin2 was enriched under conditions allowing tubulation of liposomes. By microscopy studies on HeLa cells we show, that Arfaptin2 as well as its close paralog Arfaptin1 were present on AP1-coated MPR tubules emerging from the TGN. We further show, that tubule fission occurred at regions were Arfaptin1 is concentrated and that simultaneous down regulation of both Arfaptins lead to increased number and length of MPR tubules. Since fission of coated transport intermediates at the TGN is poorly understood, our findings contribute a valuable component towards a model describing the entire biogenesis of coated post-Golgi carriers. In conclusion, combining artificial membrane systems and cell biology studies allowed us to propose new models for formation as wall as for fission of AP1-coated transport intermediates at the TGN. Further we gained new insights on AP3 coats and the possible involvement of septin filaments in AP3-dependent endosomal maturation.
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Takei, Jiro. "Structural and functional studies of membrane peptides : Glycophorin A transmembrane domain and melittin analogues." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262734.
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Thomas, Emma J. "Production and characterisation of conditionally immortal cystic fibrosis cell lines." Thesis, University of Brighton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311434.
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Ouahid, Soumia. "Transport facilité du glucose à travers une membrane échangeuse d'anions avec l'ion borate comme transporteur." Rouen, 1994. http://www.theses.fr/1994ROUES029.
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Par couplage diffusion-réaction, le transport d'un substrat non ionique à travers une membrane échangeuse d'ions, peut être facilité en choisissant un contre-ion apte à réagir réversiblement avec le substrat. Dans ce travail, nous avons réalisé le transport facilité à travers une membrane échangeuse d'anions. L'ion borate était utilisé comme transporteur et sa teneur dans la membrane était fixée par l'activité de l'acide borique. Nous avons mené simultanément la modélisation et l'expérimentation du transport. Par des études d'équilibre et de conductivité, nous avons déterminé les paramètres physicochimiques, tels que le coefficient de stabilité du complexe glucose-borate et le coefficient de diffusion des différentes espèces présentes. Nous avons, de plus, mis en évidence en présence de glucose, deux aspects originaux: la variation de l'accessibilité des sites membranaires et la variation de leurs interactions avec certains contre-ions. Dans la majorité des cas, nous avons choisi une activité d'acide borique relativement faible afin que les polyborates soient minoritaires devant les autres contre-ions. Dans une première série de mesures, nous avons réalisé le transport facilité du glucose en fonction de son activité, en maintenant constante celle de l'acide borique. Dans une seconde série, le transport a été réalisé en fonction de l'activité du transporteur. A partir des paramètres préalablement déterminés, nous avons élaboré un modèle théorique qui permet de comparer les valeurs théoriques et expérimentales des flux du glucose. Nous parvenons à un bon accord lorsque le transport a été réalisé en imposant pour l'acide borique une activité pour laquelle les paramètres du modèle ont été caractérisés
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Singh, Himansha. "On the mechanisms of transport and energy coupling in ABC exporters." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/276108.
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The rapid emergence of multidrug resistant bacterial strains represents a major global healthcare issue. Amongst five known classes of membrane transporters, which play a huge role in multidrug efflux, primary-active ATP-binding cassette (ABC) transporters are ATP powered whilst secondary-active transporters utilize electrochemical ion gradients to drive substrate transport. Mechanistic insights into transport by these proteins can help with the design and development of novel therapeutic agents against multidrug resistance, and can increase our understanding of the physiological functions of these transporters. Although available crystal structures illustrate a common alternate access model for transport by ABC transporters, the mechanisms by which metabolic energy is coupled to the transport cycle is still elusive. This thesis presents a series of functional studies using whole cells as well as artificial phospholipid membranes to study the energetics of transport, and the influence of membrane phospholipids on substrate transport by the homodimeric Escherichia coli lipid A/multidrug ABC exporter MsbA. Current alternating access models for ABC exporters involve cycling between conformations with inward- and outward-facing substrate-binding sites in membrane domains (MDs) in response to engagement and hydrolysis of ATP at the nucleotide-binding domains (NBDs). Here we report that MsbA also utilizes another major energy currency in the cell by coupling substrate transport to a transmembrane electrochemical proton gradient. In this thesis, analogous substrate transport reactions are also studied for two other ABC exporters, the MsbA homologue LmrA and the human multidrug transporter ABCG2. The dependence of ATP-dependent transport on proton coupling, and the stimulation of MsbA-ATPase by the chemical proton gradient highlight the functional integration of both forms of metabolic energy. It also raises questions about the role of NBDs in the transport process. Comparisons of drug transport and resistance in cells expressing MsbA-MD (truncated MsbA lacking the NBD) and full length MsbA (MsbA-WT) demonstrate increased transport efficiency of MsbA-WT compared to MsbA-MD. In addition, growth studies using E. coli WD2 cells, which are conditionally defective in MsbA’s essential activity in lipid A transport, show that lipid A transport can be restored by the expression of MsbA-WT but not MsbA-MD or ATP-hydrolysis impaired Walker A mutant (MsbA- ΔK382). Lastly, we also present biochemical experiments with proteoliposomes with a defined phospholipid composition, which suggest that cardiolipin is essential for the transport activity of MsbA. These techniques open the way to further explore lipid-proteins interactions and examine the physiological role(s) of MsbA. In conclusion, this thesis produces new insights in the mechanisms of transport and energy coupling in ABC exporters.
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Hickner, Michael Anthony. "Transport and Structure in Fuel Cell Proton Exchange Membranes." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28895.
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Transport properties of novel sulfonated wholly aromatic copolymers and the state-of-the-art poly(perfluorosulfonic acid) copolymer membrane for fuel cells, Nafion, were compared. Species transport (protons, methanol, water) in hydrated membranes was found to correspond with the water-self diffusion coefficient as measured by pulsed field gradient nuclear magnetic resonance (PFG NMR), which was used as a measure of the state of absorbed water in the membrane. Generally, transport properties decreased in the order Nafion > sulfonated poly(arylene ether sulfone) > sulfonated poly(imide). The water diffusion coefficients as measured by PFG NMR decreased in a similar fashion indicating that more tightly bound water existed in the sulfonated poly(arylene ether sulfone) (BPSH) and sulfonated poly(imide) (sPI) copolymers than in Nafion.
Electro-osmotic drag coefficient (ED number of water molecules conducted through the membrane per proton) studies confirmed that the water in sulfonated wholly aromatic systems is more tightly bound within the copolymer morphology. Nafion, with a water uptake of 19 wt % (λ = 12, where λ = N H2O/SO3H) had an electro-osmotic drag coefficient of 3.6 at 60°C, while BPSH 35 had an electro-osmotic drag coefficient of 1.2 and a water uptake of 40 wt % (λ = 15) under the same conditions.
Addition of phosphotungstic acid decreased the total amount of water uptake in BPSH/inorganic composite membranes, but increased the fraction of loosely bound water. Zirconium hydrogen phosphate/BPSH hybrids also showed decreased bulk water uptake, but contrary to the results with phosphotungstic acid, the fraction of loosely bound water was decreased. This dissimilar behavior is attributed to the interaction of phosphotungstic acid with the sulfonic acid groups of the copolymer thereby creating loosely bound water. No such interaction exists in the zirconium hydrogen phosphate materials. The transport properties in these materials were found to correspond with the water-self diffusion coefficients.
Proton exchange membrane (PEM) transport properties were also found to be a function of the molecular weight of sulfonated poly(arylene thioether sulfone) (PATS). Low molecular weight (IV ~ 0.69) copolymers absorbed more water on the same ion exchange capacity basis than the high molecular weight copolymers (IV ~ 1.16). Surprisingly, protonic conductivity of the two series was similar. Moreover, the methanol permeability of the low molecular weight copolymers was increased, resulting in lower membrane selectivity and decreased mechanical properties.
The feasibility of converting the novel sulfonated wholly aromatic systems to membrane electrode assemblies (MEAs) for use in fuel cells was studied by comparing free-standing membrane properties to those of MEAs assembled with standard Nafion electrodes. Significantly higher interfacial resistance was measured for BPSH samples. Fluorine was introduced into the copolymer backbone by utilizing bisphenol-AF in the copolymer synthesis (6F copolymers). These 6F copolymers showed a markedly lower interfacial resistance with Nafion electrodes and correspondingly greater direct methanol fuel cell performance. It was proposed that the addition of the hexafluoro groups increased the compatibility of the PEM with the highly fluorinated Nafion electrode.Ph. D.
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Rodríguez, Lázaro Guillermo. "Red Blood Cell mechanics: from membrane elasticity to blood rheology." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/283973.
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The mechanics and elasticity of red blood cells (RBCs) determine the capability to deform of these cells when passing through the thinnest capillaries, where the delivery of oxygen takes place. The understanding of the elastic properties of RBCs is fundamental for improving our knowledge about microcirculation and it also has important biomedical applications, such as control of blood storage, or cell manipulation for pathology diagnosis. In this Thesis, we study the elasticity of RBCs under different conditions, understanding their mechanical response to different type of perturbations. In a first Part, we study the shape morphologies observed in the disco-echinocyte transition, when the cell is subjected to an imbalance in the membrane asymmetry, for instance after ATP depletion when lipids flip from the inner to the outer leaflet. Affected cells deform, adopting crenated morphologies known as echinocytes. We develop a theoretical study which allows us to identify and quantify the relevant aspects that trigger the shape transition. The lipid bilayer tries to expand its outer leaflet in order to accommodate the excess area, whereas the cytoskeleton opposes resistance to this type of deformations, preserving more compact shapes. The subtle interplay between both membrane structures determines the equilibrium morphology of the cell. The cytoskeleton is fundamental to ensure the stability of the healthy shape, the discocyte, against changes in the membrane composition. However, it is not severely stressed under weak deformations in which low curvatures are involved. Our results show that the energetic scale of these shape transitions is of hundreds of kbT, demonstrating the large stability of these shapes. Based on the knowledge gained from the theoretical study we also analyze a series of experiments in which echinocytes are mechanically perturbed by a AFM tip, inducing shape transitions towards the healthy discocyte in a controlled manner. In the second Part, we derive a phase-field method for membrane modeling. Phase-field methods have been extensively used for the study of interface phenomena, though with few applications to membranes. We present a new model which accounts for the membrane elasticity, and couples the membrane dynamics with an external fluid, whose hydrodynamics is dictated by the Navier-Stokes equation. We derive the expression of the stress tensor which allows us to recover the stress profile of the membrane. We also obtain the membrane equilibrium equations, proving that in the macroscopic limit our phase-field model recovers the correct expressions given by the elastic theory of membranes. In the third Part we make use of this phase-field model to study the behaviour of RBCs in flow in narrow channels, of width similar to that of the cell. We consider pressure-driven flows as they relevant for both in vivo and in vitro circulation. We carry out simulations by means of a lattice-Bolztmann method. Our study highlights the crucial role of the RBC shape, softness and deformability to explain its complex behaviour and rheological properties. RBCs flowing at low concentratrions, when they do not interact with other cells and the dynamics is governed by the interaction with the cell, are shown to migrate lateral towards the wall, avoiding the axial position. The RBC assumes an asymmetric shape and orients with the flow, reducing the viscosity of the fluid which presents a shear-thinning behaviour. The lateral position can be controlled by tuning the channel geometry and flow velocity, and it is also dependent on the shape of the cell, as sherical cells as shown to occupy and axial position. The control of these factors is important for the manipulation of different cell species, such as RBCs and leukocytes, in microfluidic devices.
Finally, we study the behaviour of RBC suspensions at intermediate concentrations, when hydrodynamic interactions between RBCs govern the dynamics. The focusing to lateral positions induced by the walls is inhibited and cells are shown to order along the channel section, occupying the core of the channel. RBCs adopt and horizontal inclination, forming a relatively ordered structure of parallel rows. The rheology of the suspension is also affected, as the interactions between cells attenuate the orientation with the flux and higher flow velocities are required to induce the shear-thinning decay of the viscosity. The results presented in this Thesis highlight the delicate dependence of the cell mechanics in the balance of the cell membrane composition and elastic properties. They also demonstrate that the elastic behaviour of the cell, determined by its membrane, is also crucial for the rheological behaviour of blood, and any process of membrane damage or stiffening can substantially alter the correct blood functioning.El estudio del comportamiento mecánico de los glóbulos rojos es fundamental para entender aspectos relevantes acerca de la elasticidad de membranas y reología de la sangre, incluyendo importantes aplicaciones biomédicas. En esta tesis se aborda la respuesta elástica de estas células bajo diferentes tipos de deformaciones morfológicas. Por un lado, se estudia el efecto de la microestructura de la membrana en las formas de equilibrio de los glóbulos, identificando la función del citoesqueleto celular cuando la asimetría en la bicapa lipídica es alterada (por ejemplo, reduciendo los niveles de ATP). Nuestros resultados muestran que la bicapa tiende a expandirse formando estructuras puntiagudas, mientras que el citoesqueleto se opone a estas deformaciones y mantiene formas más compactas cercanas al discocito. El citoesqueleto aparece como un elemento fundamental para estabilizar la célula en su conformación de equilibrio. En la segunda parte de la tesis, se deriva un modelo de interfase difusa para membranas. Para ello obtenemos el perfil de esfuerzos que muestra cómo el modelo captura correctamente las propiedades elásticas de las membranas. También se obtienen las ecuaciones macroscópicas que definen el comportamiento de equilibrio y dinámico del modelo, y que convergen correctamente a los resultados clásicos de la teoría general de membranas. Finalmente, en la tercera parte realizamos simulaciones haciendo uso de este modelo de interfase difusa para estudiar el comportamiento de glóbulos rojos fluyendo en canales confinados. El estudio refleja la compleja respuesta de las células, en las que la elasticidad y deformabilidad forman un papel clave. Los glóbulos a bajas concentraciones evitan la posición central del canal y se desplazan hacia un lateral, adquiriendo morfologías asimétricas y orientándose con el flujo. Esto permite que la viscosidad del fluído disminuya. En cambio, a mayores concentraciones, cuando varias células fluyen juntas, la interacciones hidrodinámicas inhiben este comportamiento, y las células fluyen alineadas con una orientación horizontal, organizadas en filas tanto en los laterales como en el centro del canal. La interacción y apantallamiento entre las células hace que el decaimiento en la viscosidad requiera de velocidades considerablemente mayores.
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Volhinava, Anastasiya. "Vliv hydroxykyselin na rychlost transdermální absorpce vybraných farmaceuticky aktivních ingrediencí." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2020. http://www.nusl.cz/ntk/nusl-414117.
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Diploma thesis deals with the experimental study of transdermal transport of individual hydroxyacids and their combination with water-soluble vitamins. During this work the literature review was prepared, which was focused on the use of hydroxyacids in the cosmetic and pharmaceutical industries. At the same time the current state of use of water-soluble vitamins for topical applications was studied. Series of experiments was performed using Franz diffusion cells to simulate transdermal transport in vitro across cutaneous, synthetic and artificial Strat M ® membranes. The methodology of sample preparation and analysis of their transport properties was invented and optimized. The optimized methodology was subsequently used in a series of diffusion experiments in which the penetrated amount of hydroxyacids was analyzed by ion chromatography. The concentration of water-soluble vitamins was determined by HPLC. All examined active substances demonstrate positive penetration properties. The best results were obtained with combination of glycolic acid with pyridoxine.
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Zhang, Yan. "Studies on the calcium-regulated bicarbonate ion permeability in the apical membrane of bovine corneal endothelium." [Bloomington, Ind.] : Indiana University, 2004. http://wwwlib.umi.com/dissertations/fullcit/3162273.
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Thesis (Ph.D.)--Indiana University, School of Optometry, 2004.Title from PDF t.p. (viewed Dec. 2, 2008). Source: Dissertation Abstracts International, Volume: 66-01, Section: B, page: 0050. Chair: Joseph A. Bonanno.
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Chen, Yuanxin. "POLYMER MEMBRANES FOR FLUE GAS CARBON CAPTURE AND FUEL CELL APPLICATION." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440069742.
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