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Vieillissement thermique d’isolants en PVC et PELX de câbles électriques en environnement automobile / Thermal ageing of PVC and XLPE insulators used in automotive electric wiresSalivon, Tetiana 31 March 2017 (has links)
Dans l’industrie automobile, la tâche de dimensionnement des faisceauxélectriques consiste à définir au plus juste la section du conducteur métallique, ce qui augmente l’échauffement du câble par effet Joule. Or, les polymères sont les matériaux d’isolation les plus utilisés malgré leur grande sensibilité au vieillissement thermique. C’est pourquoi leur durabilité en environnement automobile doit être déterminée pour pouvoir ensuite être prise en compte lors du dimensionnement des faisceaux électriques. Dans ce but, nous avons analysé le vieillissement thermique de deux gaines d’isolation en PVC et PELX dans l’air aux températures des essais de qualification (typiquement entre 100°C et 200°C). Dans le cas du PVC, le principal mécanisme de vieillissement est la perte physique du plastifiant. La fragilisation du matériau intervient orsque la concentration de la phase de plastifiant non-dissoute, qui est ispersée sous forme de nodules dans la matrice PVC faiblement plastifiée, atteint une valeur critique de l’ordre de 0,2 mol.L-1. En revanche, dans le cas du PELX, l’oxydation conduit à la fragilisation du matériau au terme de la période d’induction, c’est-à-dire dès que la totalité des antioxydants a été consommée. Pour chaque gaine d’isolation, un modèle cinétique a été dérivé des mécanismes de vieillissement et un critère de fin de vie structural a été établi. Ce modèle donne accès au potentiel de vie restant et à la durée de vie des câbles électriques en conditions de service. / In the automotive industry, the issue of electrical harness dimensioning consists in an optimal definition of the cross-section of metallic conductors, which increases the wire heating due to Joule effect. However, polymers are the most used materials for insulation despite their high sensitivity to thermal ageing. That is the reason why their durability must be determined in automotive environment to be then taken into account during the dimensioning of electrical harness. For this purpose, we analyzed the thermal aging of two insulation sheaths made of PVC and XLPE in air at temperatures of qualification tests (typically between 100°C and 200°C). For PVC, the main ageing mechanism is the physical loss of plasticizer. The material embrittlement occurs when the concentration of the non-dissolved plasticizer phase, which is dispersed as nodules in the weakly plasticized PVC matrix, reaches a critical value of about 0,2 mol.L-1. In contrast, for XLPE, oxidation leads to material embrittlement at the end of the induction period, i.e. when the totality of antioxidants has been consumed. For each insulation sheath, a kinetic model was derived from the ageing mechanisms and a structural end-of-life criterion was established. This model gives access to the remaining life potential and lifetime of electrical cables in service conditions.
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Multivariate data analysis for embedded sensor networks within the perishable goods supply chainDoan, Xuan Tien January 2011 (has links)
This study was aimed at exploring data analysis techniques for generating accurate estimates of the loss in quality of fresh fruits, vegetables and cut flowers in chilled supply chains based on data from advanced sensors. It was motivated by the recent interest in the application of advanced sensors, by emerging concepts in quality controlled logistics, and by the desire to minimise quality losses during transport and storage of the produce. Cut roses were used in this work although the findings will also be applicable to other produce. The literature has reported that whilst temperature was considered to be the most critical post-harvest factor, others such as growing conditions could also be important in the senescence of cut roses. Kinetic modelling was the most commonly used modelling approach for shelf life predictions of foods and perishable produce, but not for estimating vase life (VL) of cut flowers, and so this was explored in this work along with multiple linear regression (MLR) and partial least squares (PLS). As the senescence of cut roses is not fully understood, kinetic modelling could not be implemented directly. Consequently, a novel technique, called Kinetic Linear System (KLS), was developed based on kinetic modelling principles. Simulation studies of shelf life predictions for tomatoes, mushrooms, seasoned soybean sprouts, cooked shrimps and other seafood products showed that the KLS models could effectively replace the kinetic ones. With respect to VL predictions KLS, PLS and MLR were investigated for data analysis from an in-house experiment with cut roses from Cookes Rose Farm (Jersey). The analysis concluded that when the initial and final VLs were available for model calibration, effective estimates of the post-harvest loss in VL of cut roses could be obtained using the post-harvest temperature. Otherwise, when the initial VLs were not available, such effective estimates could not be obtained. Moreover, pre-harvest conditions were shown to correlate with the VL loss but the correlation was too weak to produce or improve an effective estimate of the loss. The results showed that KLS performance was the best while PLS one could be acceptable; but MLR performance was not adequate. In another experiment, boxes of cut roses were transported from a Kenyan farm to a UK distribution centre. Using KLS and PLS techniques, the analysis showed that the growing temperature could be used to obtain effective estimates of the VLs at the farm, at the distribution centre and also the in-transit loss. Further, using post-harvest temperature would lead to a smaller error for the VL at the distribution centre and the VL loss. Nevertheless, the estimates of the VL loss may not be useful practically due to the excessive relative prediction error. Overall, although PLS had a slightly smaller prediction error, KLS worked effectively in many cases where PLS failed, it could handle constraints while PLS could not.In conclusion, KLS and PLS can be used to generate effective estimates of the post-harvest VL loss of cut roses based on post-harvest temperature stresses recorded by advanced sensors. However, the estimates may not be useful practically due to significant relative errors. Alternatively, pre-harvest temperature could be used although it may lead to slightly higher errors. Although PLS had slightly smaller errors KLS was more robust and flexible. Further work is recommended in the objective evaluations of product quality, alternative non-linear techniques and dynamic decision support system.
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Influence of Soot on the Transport Mechanisms inside the Filter Wall of SCR-Coated Diesel Particulate FiltersPurfürst, Marcus 27 April 2018 (has links)
The effect of soot on the catalytic properties of a diesel particulate filter coated with a catalyst for the selective catalytic reduction of NOx with ammonia (SDPF) was studied by means of model-gas experiments. After loading of the SDPF with model soot from 0 to 10 g l-1, the NH3 storage as well as the catalytic DeNOx behavior of the standard SCR reaction was investigated. The model soot present in the filter was shown to have an NH3 storage capacity. The soot deposit inside the SDPF filter wall lead to a decreased NO conversion in SCR experiments of up to 20 %. The NH3 breakthrough was found to be shifted towards earlier time-on-stream during NH3 adsorption on soot loaded SDPF samples. Both effects could be attributed to a diffusive mass transport limitation of the gas species through the soot to reach at the chemically active sites inside SDPF filter wall. The self-diffusion coefficient of NH3 probe molecules within a soot layer could be measured using Pulsed Field Gradient-NMR technique. The unit collector model is capable of describing the backpressure upon soot loading with a depth filtered (inside filter wall) soot amount of 1 g l-1 and 0.36 g l-1, respectively, for both SDPF types under investigation. Based on Scanning Electron Microscopy (SEM) investigation a 1-D microscopic soot filter wall-model was set up. The model implies soot as diffusion barrier for mass transport. It was calibrated based on experimental observations and allows to conclude on the distribution of the soot within the filter wall. Thus, a high soot-coverage of the porous filter wall close to the inlet channel, a slightly covered middle part and a soot free zone close to the outlet explains the observed reduction in NO conversion as well as the NH3 breakthrough at earlier time-on-stream during NH3 adsorption experiments for SDPF samples loaded with soot. A modelled homogeneous soot distribution (0.6 µm soot layer on top of washcoat) within the whole SDPF was shown to result in NO conversion drop up to 45 %.
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Kinetic Modelling Simulation and Optimal Operation of Trickle Bed Reactor for Hydrotreating of Crude Oil. Kinetic Parameters Estimation of Hydrotreating Reactions in Trickle Bed Reactor (TBR) via Pilot Plant Experiments; Optimal Design and Operation of an Industrial TBR with Heat Integration and Economic Evaluation.Jarullah, Aysar Talib January 2011 (has links)
Catalytic hydrotreating (HDT) is a mature process technology practiced in the
petroleum refining industries to treat oil fractions for the removal of impurities (such as
sulfur, nitrogen, metals, asphaltene). Hydrotreating of whole crude oil is a new
technology and is regarded as one of the more difficult tasks that have not been reported
widely in the literature. In order to obtain useful models for the HDT process that can
be confidently applied to reactor design, operation and control, the accurate estimation
of kinetic parameters of the relevant reaction scheme are required. This thesis aims to
develop a crude oil hydrotreating process (based on hydrotreating of whole crude oil
followed by distillation) with high efficiency, selectivity and minimum energy
consumption via pilot plant experiments, mathematical modelling and optimization.
To estimate the kinetic parameters and to validate the kinetic models under different
operating conditions, a set of experiments were carried out in a continuous flow
isothermal trickle bed reactor using crude oil as a feedstock and commercial cobaltmolybdenum
on alumina (Co-Mo/¿-Al2O3) as a catalyst. The reactor temperature was
varied from 335°C to 400°C, the hydrogen pressure from 4 to10 MPa and the liquid
hourly space velocity (LHSV) from 0.5 to 1.5 hr-1, keeping constant hydrogen to oil
ratio (H2/Oil) at 250 L/L. The main hydrotreating reactions were hydrodesulfurization
(HDS), hydrodenitrogenation (HDN), hydrodeasphaltenization (HDAs) and
hydrodemetallization (HDM) that includes hydrodevanadization (HDV) and
hydrodenickelation (HDNi).
An optimization technique is used to evaluate the best kinetic models of a trickle-bed
reactor (TBR) process utilized for HDS, HDAs, HDN, HDV and HDNi of crude oil
based on pilot plant experiments. The minimization of the sum of the squared errors
(SSE) between the experimental and estimated concentrations of sulfur (S), nitrogen
(N), asphaltene (Asph), vanadium (V) and nickel (Ni) compounds in the products, is
used as an objective function in the optimization problem using two approaches (linear
(LN) and non-linear (NLN) regression).
The growing demand for high-quality middle distillates is increasing worldwide
whereas the demand for low-value oil products, such as heavy oils and residues, is
decreasing. Thus, maximizing the production of more liquid distillates of very high
quality is of immediate interest to refiners. At the same time, environmental legislation
has led to more strict specifications of petroleum derivatives. Crude oil hydrotreatment
enhances the productivity of distillate fractions due to chemical reactions. The
hydrotreated crude oil was distilled into the following fractions (using distillation pilot
plant unit): light naphtha (L.N), heavy naphtha (H.N), heavy kerosene (H.K), light gas
oil (L.G.O) and reduced crude residue (R.C.R) in order to compare the yield of these
fractions produced by distillation after the HDT process with those produced by
conventional methods (i.e. HDT of each fraction separately after the distillation). The
yield of middle distillate showed greater yield compared to the middle distillate
produced by conventional methods in addition to improve the properties of R.C.R.
Kinetic models that enhance oil distillates productivity are also proposed based on the
experimental data obtained in a pilot plant at different operation conditions using the
discrete kinetic lumping approach. The kinetic models of crude oil hydrotreating are
assumed to include five lumps: gases (G), naphtha (N), heavy kerosene (H.K), light gas
oil (L.G.O) and reduced crude residue (R.C.R). For all experiments, the sum of the
squared errors (SSE) between the experimental product compositions and predicted
values of compositions is minimized using optimization technique.
The kinetic models developed are then used to describe and analyse the behaviour of an
industrial trickle bed reactor (TBR) used for crude oil hydrotreating with the optimal
quench system based on experiments in order to evaluate the viability of large-scale
processing of crude oil hydrotreating. The optimal distribution of the catalyst bed (in
terms of optimal reactor length to diameter) with the best quench position and quench
rate are investigated, based upon the total annual cost.
The energy consumption is very important for reducing environmental impact and
maximizing the profitability of operation. Since high temperatures are employed in
hydrotreating (HDT) processes, hot effluents can be used to heat other cold process
streams. It is noticed that the energy consumption and recovery issues may be ignored
for pilot plant experiments while these energies could not be ignored for large scale
operations. Here, the heat integration of the HDT process during hydrotreating of crude
oil in trickle bed reactor is addressed in order to recover most of the external energy.
Experimental information obtained from a pilot scale, kinetics and reactor modelling
tools, and commercial process data, are employed for the heat integration process
model. The optimization problem is formulated to optimize some of the design and
operating parameters of integrated process, and minimizing the overall annual cost is
used as an objective function.
The economic analysis of the continuous whole industrial refining process that involves
the developed hydrotreating (integrated hydrotreating process) unit with the other
complementary units (until the units that used to produce middle distillate fractions) is
also presented.
In all cases considered in this study, the gPROMS (general PROcess Modelling
System) package has been used for modelling, simulation and parameter estimation via
optimization process. / Tikrit University, Iraq
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Étude fonctionnelle du cotransporteur Na+/glucose (hSGLT1) : courant de fuite, vitesse de cotransport et modélisation cinétiqueLongpré, Jean-Philippe 05 1900 (has links)
Les résultats présentés dans cette thèse précisent certains aspects de la fonction du cotransporteur Na+/glucose (SGLT1), une protéine transmembranaire qui utilise le gradient électrochimique favorable des ions Na+ afin d’accumuler le glucose à l’intérieur des cellules épithéliales de l’intestin grêle et du rein.
Nous avons tout d’abord utilisé l’électrophysiologie à deux microélectrodes sur des ovocytes de xénope afin d’identifier les ions qui constituaient le courant de fuite de SGLT1, un courant mesuré en absence de glucose qui est découplé de la stoechiométrie stricte de 2 Na+/1 glucose caractérisant le cotransport. Nos résultats ont démontré que des cations comme le Li+, le K+ et le Cs+, qui n’interagissent que faiblement avec les sites de liaison de SGLT1 et ne permettent pas les conformations engendrées par la liaison du Na+, pouvaient néanmoins générer un courant de fuite d’amplitude comparable à celui mesuré en présence de Na+. Ceci suggère que le courant de fuite traverse SGLT1 en utilisant une voie de perméation différente de celle définie par les changements de conformation propres au cotransport Na+/glucose, possiblement similaire à celle empruntée par la perméabilité à l’eau passive. Dans un deuxième temps, nous avons cherché à estimer la vitesse des cycles de cotransport de SGLT1 à l’aide de la technique de la trappe ionique, selon laquelle le large bout d’une électrode sélective (~100 μm) est pressé contre la membrane plasmique d’un ovocyte et circonscrit ainsi un petit volume de solution extracellulaire que l’on nomme la trappe. Les variations de concentration ionique se produisant dans la trappe en conséquence de l’activité de SGLT1 nous ont permis de déduire que le cotransport Na+/glucose s’effectuait à un rythme d’environ 13 s-1 lorsque le potentiel membranaire était fixé à -155 mV. Suite à cela, nous nous sommes intéressés au développement d’un modèle cinétique de SGLT1. En se servant de l’algorithme du recuit simulé, nous avons construit un schéma cinétique à 7 états reproduisant de façon précise les courants du cotransporteur
en fonction du Na+ et du glucose extracellulaire. Notre modèle prédit qu’en présence d’une concentration saturante de glucose, la réorientation dans la membrane de SGLT1 suivant le relâchement intracellulaire de ses substrats est l’étape qui limite la vitesse de cotransport. / The results presented in this thesis clarify certain functional aspects of the Na+/glucose cotransporter (SGLT1), a membrane protein which uses the downhill electrochemical gradient of Na+ ions to drive the accumulation of glucose in epithelial cells of the small intestine and the kidney.
We first used two microelectrodes electrophysiology on Xenopus oocytes to indentify the ionic species mediating the leak current of SGLT1, a current measured in the absence of glucose that is uncoupled from the strict 2 Na+/1 glucose stoichiometry
characterising cotransport. Our results showed that cations such as Li+, K+ and Cs+, which interact weakly with SGLT1 binding sites and are unable to generate the conformational changes that are triggered by Na+ binding, were however able to generate leak currents similar in amplitude to the one measured in the presence of Na+. This suggests that the leak current permeating through SGLT1 does so using a pathway that differs from the conformational changes associated with Na+/glucose cotransport. Moreover, it was found that the cationic leak and the passive water permeability could share a common pathway. We then sought to estimate the turnover rate of SGLT1 using the ion-trap technique, where a large tip ion-selective electrode (~100 μm) is pushed against the oocyte plasma membrane, thus enclosing a small volume of extracellular solution referred to as the trap. The variations in ionic concentration occurring in the trap as a consequence of SGLT1 activity made it possible to assess that the turnover rate of Na+/glucose cotransport was 13 s-1 when the membrane potential was clamped to -155 mV. As a last project, we focused our interest on the development of a kinetic model for SGLT1. Taking advantage of the simulated annealing algorithm, we constructed a 7-state kinetic scheme whose predictions accurately reproduced the currents of the cotransporter as a function of extracellular Na+ and glucose. According to our model, the rate limiting step of cotransport under a saturating glucose concentration is the reorientation of the empty carrier that follows the intracellular
release of substrates.
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Modélisation des phénomènes de corrosion du Zircaloy-4 sous mélanges oxygène-azote à haute température / Modelling of Zircaloy-4 degradation in oxygen and nitrogen mixtures at high temperatureLasserre-Gagnaire, Marina 17 December 2013 (has links)
Les gaines de zircaloy-4, assurent la première barrière de confinement des combustibles des Réacteurs à Eau Pressurisée. Plusieurs situations accidentelles au cours desquelles les gaines de crayons combustibles sont exposées l’air à haute température ont été envisagées. L’azote généralement utilisé en tant que gaz inerte, joue un rôle primordial lorsqu’il est combiné à l’oxygène à haute température. Les courbes cinétiques obtenues par la technique de thermogravimétrie révèlent la présence de deux domaines cinétiques : le domaine pré-transitoire et le domaine post-transitoire. Durant le domaine post-transitoire, la vitesse de corrosion augmente. Les images obtenues en microscopie optique révèlent l’existence de régions corrodées caractérisées par une couche de zircone poreuse et par la présence de précipités de nitrure de zirconium (ZrN) à l’interface métal - oxyde. La corrosion des plaquettes de Zy4 à 850°C sous mélanges oxygène - azote a été étudiée durant le domaine post-transitoire. Trois réactions successives permettent d’expliquer la présence des différentes phases. Ainsi, la dégradation catastrophique du métal est due à la progression auto-catalysée par ZrN du front de croissance des zones attaquées.Les hypothèses de modélisation ont été validées durant le domaine post-transitoire. L’étape déterminante a été identifiée. La réaction d’interface externe du mécanisme d’oxydation des précipités de ZrN impose sa vitesse aux autres étapes du mécanisme de croissance des régions corrodées. Par analogie avec les modèles de germination - croissance utilisés dans le cadre de la transformation thermique des poudres, nous avons pu décrire l’évolution des zones attaquées. / Zircaloy-4 claddings provide the first containment of UO2 fuel in Pressurised Water Reactors. It has been demonstrated that the fuel assemblies cladding could be exposed to air at high temperature in several accidental situations. When mixed to oxygen at high temperature, the nitrogen, usually used as an inert gas, causes the accelerated corrosion of the cladding.The kinetic curves obtained by thermogravimetry reveal two stages: a pre-transition and a post-transition one. In the post-transition stage, the kinetic rate increases with time. Images obtained by optical microscopy of a sample in the post-transition stage reveal the presence of corroded zones characterized by a porous scale with zirconium nitride precipitates at metal - oxide interface. Corrosion of Zy4 plates at 850°C under mixed oxygen - nitrogen atmospheres has been studied during the post-transition stage. A sequence of three reactions is proposed to explain the mechanism of nitrogen-enhanced corrosion. The accelerating effect of nitrogen in the corrosion scale can therefore be described on the basis of an autocatalytic effect of the zirconium nitride precipitates. Then, it is demonstrated that the steady-state approximation as well as the existence of an elementary step controlling the growth process are valid during the post-transition stage. The rate-determining step is identified as the external interface reaction step of the oxidation of the zirconium nitride precipitates. Finally, a nucleation and growth model used for thermal reactions in powders is used to describe both the nucleation and the growth of the attacked regions.
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Modelling genetic regulatory networks: a new model for circadian rhythms in Drosophila and investigation of genetic noise in a viral infection processXie, Zhi January 2007 (has links)
In spite of remarkable progress in molecular biology, our understanding of the dynamics and functions of intra- and inter-cellular biological networks has been hampered by their complexity. Kinetics modelling, an important type of mathematical modelling, provides a rigorous and reliable way to reveal the complexity of biological networks. In this thesis, two genetic regulatory networks have been investigated via kinetic models.
In the first part of the study, a model is developed to represent the transcriptional regulatory network essential for the circadian rhythms in Drosophila. The model incorporates the transcriptional feedback loops revealed so far in the network of the circadian clock (PER/TIM and VRI/PDP1 loops). Conventional Hill functions are not used to describe the regulation of genes, instead the explicit reactions of binding and unbinding processes of transcription factors to promoters are modelled. The model is described by a set of ordinary differential equations and the parameters are estimated from the in vitro experimental data of the clocks components. The simulation results show that the model reproduces sustained circadian oscillations in mRNA and protein concentrations that are in agreement with experimental observations. It also simulates the entrainment by light-dark cycles, the disappearance of the rhythmicity in constant light and the shape of phase response curves resembling that of experimental results. The model is robust over a wide range of parameter variations. In addition, the simulated E-box mutation, perS and perL mutants are similar to that observed in the experiments. The deficiency between the simulated mRNA levels and experimental observations in per01, tim01 and clkJrk mutants suggests some differences in the model from reality. Finally, a possible function of VRI/PDP1 loops is proposed to increase the robustness of the clock.
In the second part of the study, the sources of intrinsic noise and the influence of extrinsic noise are investigated on an intracellular viral infection system. The contribution of the intrinsic noise from each reaction is measured by means of a special form of stochastic differential equation, the chemical Langevin equation. The intrinsic noise of the system is the linear sum of the noise in each of the reactions. The intrinsic noise arises mainly from the degradation of mRNA and the transcription processes. Then, the effects of extrinsic noise are studied by means of a general form of stochastic differential equation. It is found that the noise of the viral components grows logarithmically with increasing noise intensities. The system is most susceptible to noise in the virus assembly process. A high level of noise in this process can even inhibit the replication of the viruses.
In summary, the success of this thesis demonstrates the usefulness of models for interpreting experimental data, developing hypotheses, as well as for understanding the design principles of genetic regulatory networks.
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Valorización de efluentes de decapado ácido metálico. Recuperación de zincSamaniego Peña, Henar 25 September 2006 (has links)
Este trabajo ha estado dirigido al estudio de un proceso eficaz de separación que posibilite la recuperación de zinc de efluentes de decapado ácido de elevada toxicidad, así como su posterior concentración en una fase de características físico-químicas adecuadas para posibilitar su reciclado en baños electrolíticos. Para ello se propone la extracción líquido-líquido no dispersiva como tecnología limpia de elevada eficacia y con bajo requerimiento energético.Tras una exhaustiva revisión bibliográfica, se seleccionan el fosfato de tributilo y el agua de red como agentes extractante y reextractante respectivamente. A lo largo del trabajo y tras una etapa previa dirigida a la evaluación de la viabilidad técnica del proceso, se caracterizaron experimentalmente las reacciones responsables de las etapas de extracción y reextracción, así como la cinética del proceso de separación, para a continuación plantear el modelo matemático y determinar los parámetros característicos del sistema necesarios para el diseño y optimización del proceso de separación-concentración de zinc de efluentes de decapado ácido metálico. / The work was focused on the study of the recovery of zinc from spent pickling effluents, under conditions that permitted the recovery of electrolytic grade metal, thus, reducing the effluent toxicity and with valorisation, at the same time, of the component of higher added value. After a deep literature review, non dispersive solvent extraction using tributyl phosphate (TBP) and service water as extraction and back extraction agents, respectively, was selected as the best separatión alternative. The work started with the analysis of the process viability and included an experimental design of the equilibrium, and kinetics of the phenomena involved in the metal valorisation. The kinetic analysis of the membrane assisted process of zinc recovery from spent pickling effluents was carried out, obtaining the mathematical model and parameters needed for design and optimisation of the metal separation step in a valorisation process.
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Étude fonctionnelle du cotransporteur Na+/glucose (hSGLT1) : courant de fuite, vitesse de cotransport et modélisation cinétiqueLongpré, Jean-Philippe 05 1900 (has links)
Les résultats présentés dans cette thèse précisent certains aspects de la fonction du cotransporteur Na+/glucose (SGLT1), une protéine transmembranaire qui utilise le gradient électrochimique favorable des ions Na+ afin d’accumuler le glucose à l’intérieur des cellules épithéliales de l’intestin grêle et du rein.
Nous avons tout d’abord utilisé l’électrophysiologie à deux microélectrodes sur des ovocytes de xénope afin d’identifier les ions qui constituaient le courant de fuite de SGLT1, un courant mesuré en absence de glucose qui est découplé de la stoechiométrie stricte de 2 Na+/1 glucose caractérisant le cotransport. Nos résultats ont démontré que des cations comme le Li+, le K+ et le Cs+, qui n’interagissent que faiblement avec les sites de liaison de SGLT1 et ne permettent pas les conformations engendrées par la liaison du Na+, pouvaient néanmoins générer un courant de fuite d’amplitude comparable à celui mesuré en présence de Na+. Ceci suggère que le courant de fuite traverse SGLT1 en utilisant une voie de perméation différente de celle définie par les changements de conformation propres au cotransport Na+/glucose, possiblement similaire à celle empruntée par la perméabilité à l’eau passive. Dans un deuxième temps, nous avons cherché à estimer la vitesse des cycles de cotransport de SGLT1 à l’aide de la technique de la trappe ionique, selon laquelle le large bout d’une électrode sélective (~100 μm) est pressé contre la membrane plasmique d’un ovocyte et circonscrit ainsi un petit volume de solution extracellulaire que l’on nomme la trappe. Les variations de concentration ionique se produisant dans la trappe en conséquence de l’activité de SGLT1 nous ont permis de déduire que le cotransport Na+/glucose s’effectuait à un rythme d’environ 13 s-1 lorsque le potentiel membranaire était fixé à -155 mV. Suite à cela, nous nous sommes intéressés au développement d’un modèle cinétique de SGLT1. En se servant de l’algorithme du recuit simulé, nous avons construit un schéma cinétique à 7 états reproduisant de façon précise les courants du cotransporteur
en fonction du Na+ et du glucose extracellulaire. Notre modèle prédit qu’en présence d’une concentration saturante de glucose, la réorientation dans la membrane de SGLT1 suivant le relâchement intracellulaire de ses substrats est l’étape qui limite la vitesse de cotransport. / The results presented in this thesis clarify certain functional aspects of the Na+/glucose cotransporter (SGLT1), a membrane protein which uses the downhill electrochemical gradient of Na+ ions to drive the accumulation of glucose in epithelial cells of the small intestine and the kidney.
We first used two microelectrodes electrophysiology on Xenopus oocytes to indentify the ionic species mediating the leak current of SGLT1, a current measured in the absence of glucose that is uncoupled from the strict 2 Na+/1 glucose stoichiometry
characterising cotransport. Our results showed that cations such as Li+, K+ and Cs+, which interact weakly with SGLT1 binding sites and are unable to generate the conformational changes that are triggered by Na+ binding, were however able to generate leak currents similar in amplitude to the one measured in the presence of Na+. This suggests that the leak current permeating through SGLT1 does so using a pathway that differs from the conformational changes associated with Na+/glucose cotransport. Moreover, it was found that the cationic leak and the passive water permeability could share a common pathway. We then sought to estimate the turnover rate of SGLT1 using the ion-trap technique, where a large tip ion-selective electrode (~100 μm) is pushed against the oocyte plasma membrane, thus enclosing a small volume of extracellular solution referred to as the trap. The variations in ionic concentration occurring in the trap as a consequence of SGLT1 activity made it possible to assess that the turnover rate of Na+/glucose cotransport was 13 s-1 when the membrane potential was clamped to -155 mV. As a last project, we focused our interest on the development of a kinetic model for SGLT1. Taking advantage of the simulated annealing algorithm, we constructed a 7-state kinetic scheme whose predictions accurately reproduced the currents of the cotransporter as a function of extracellular Na+ and glucose. According to our model, the rate limiting step of cotransport under a saturating glucose concentration is the reorientation of the empty carrier that follows the intracellular
release of substrates.
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The effects of chemical and physical properties of chars derived from inertinite–rich, high ash coals on gasification reaction kinetics / Gregory Nworah OkoloOkolo, Gregori Nworah January 2010 (has links)
With the increasing global energy demand and the decreasing availability of good
quality coals, a better understanding of the important properties that control the
behaviour of low–grade coals and the subsequent chars in various utilisation
processes, becomes pertinent. An investigation was therefore undertaken, to study the
effects of chemical and physical properties imparted on chars during pyrolysis on the
subsequent gasification reaction kinetics of typical South African inertinite–rich, high
ash Highveld coals. An attempt was made at following these changes in the transition
from coals to chars by a detailed characterisation of both the parent coals and the
respective chars. These changes were determined using various conventional and
advanced techniques, which included among others, carbon crystallite analysis using
XRD and char carbon forms analysis using petrography.
Three of the four original coals were characterised as Bituminous Medium rank C
(coals B, C and C2), while coal D2 was found to be slightly lower in rank
(Bituminous Medium rank D). The coals were rich in inertinites (> 54 vol. %, mmb
with coal C2 having as high as 79 vol. %, mmb) and high in ash content (> 26.7 wt. %,
db) and cabominerite and minerite contents (26 – 39 vol. %, mmb). The inertinitevitrinite
ratios of the coals were found to range from 1.93 to 26.3.
Characterization results show that both volatile matter and inherent moisture content
decreased, while ash, fixed carbon and elemental carbon contents increased from
coals to chars, indicating that the pyrolysis process was efficient. Elemental hydrogen,
oxygen and nitrogen contents decreased, whereas total sulphur contents increased
from coals to chars. This reveals that the total sulphur contained in the char samples
was associated with the char carbon matrix and the minerals. Hydrogen–carbon and
oxygen–carbon ratios decreased considerably from coals to chars showing that the
chars are more aromatic and denser products than the original coals. Despite the fact
that mineral matter increased from coals to chars, the relative abundance of the
different mineral phases and ash components did not exhibit significant variation
amongst the samples. The alkali index was, however, found to vary considerably
among the subsequent chars. Petrographic analysis of the coals and char carbon forms
analysis of the chars reveal that total reactive components (TRC) decrease while the total inert components (TIC) increase from coals to chars. The 0% gain in TIC
observed in char C2 was attributed to its relatively high partially reacted maceral char
carbon forms content. Total maceral reflectance shifted to higher values in the chars
(4.43 – 5.28 Rsc%) relative to the coals (1.15 – 1.63 Rsc%) suggesting a higher
structural ordering in the chars. Carbon crystallite analyses revealed that the chars
were condensed (smaller in size) relative to the parent coals. Lattice parameters: interlayer
spacing, d002, increased, while the average crystallite height, Lc, crystallite
diameter, La, and number of aromatic layers per crystallite, Nave, decreased from coals
to chars. Carbon aromaticity generally increased whereas the fraction of amorphous
carbon and the degree of disorder index decreased from parent coals to the respective
chars. Both micropore surface area and microporosity were observed to increase while
the average micropore diameter decreased from coals to chars. This shows that blind
and closed micropores were “opened up” during the charring process.
Despite the original coal samples not showing much variation in their properties
(except for their maceral content), it was generally observed that the subsequent chars
exhibited substantial differences, both amongst themselves and from the parent coals.
The increasing orders of magnitude of micropore surface area, microporosity, fraction
of amorphous carbon and structural disorderliness were found to change in the
transition, a good indication that the chars’ properties varied from that of the
respective parent coals.
Isothermal CO2 gasification experiments were conducted on the chars in a Thermax
500 thermogravimetric analyser in the temperature range of 900 – 950 °C with varying
concentrations of CO2 (25 – 100 mol. %) in the CO2–N2 reaction gas mixture at
ambient pressure (0.875 bar in Potchefstroom). The effects of temperature and CO2
concentration were observed to be in conformity with established trends. The initial
reactivity of the chars was found to increase in the order: chars C2 < C < B < D2, with
char D2 reactivity greater than the reactivity of the other chars by a factor > 4.
Gasification reactivity results were correlated with properties of the parent coals and
chars. Except for the rank parameter (the vitrinite reflectance), no significant trend
was observed with any other coal petrographic property. Correlations with char
properties gave more significant and systematic trends. Major factors affecting the
gasification reactivity of the chars as it pertains to this investigation are: parent coal vitrinite reflectance, and: aromaticity, fraction of amorphous carbon, degree of
disorder and alkali indices, micropore surface area, microporosity and average
micropore diameter of the chars.
The random pore model (chemical reaction controlling) was found to adequately
describe the gasification reaction experimental data (both conversions and conversion
rates). The determined activation energy ranged from 163.3 kJ·mol–1 for char D2 to
235.7 kJ·mol–1 for char B; while the order of reaction with respect to CO2
concentration ranged between 0.52 to 0.67 for the four chars. The lower activation
energy of char D2 was possibly due to its lower rank, lower coal vitrinite reflectance
and higher alkali index. The estimated kinetic parameters of the chars in this study
correspond very well with published results in open literature. It was possible to
express the intrinsic reactivity, rs, of the chars (rate of carbon conversion per unit total
surface area) using kinetic results, in empirical Arrhenius forms. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2011.
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