L'objectif de ce travail est d'étudier l'effet thermoélectrique à l'échelle nanométrique des nanostructures chauffées. Dans un premier temps, nous étudions les mécanismes d'autopropulsion thermo-électrophorétique de particules Janus chauffées par laser. Ce mécanisme d'autopropulsion est principalement induit par l'effet Seebeck ou l'effet thermoélectrique. Cet effet provient de la séparation des charges survenues lorsqu'un gradient de température est présent dans la solution d'électrolyte: Une forte absorption du laser par la partie métallisée de la particule génère un gradient de température qui en retour agit sur les espèces ioniques (positive et négative) et les conduits vers les zones chaudes ou les zones froides. Ce mouvement d'ions entraine la création d'un champ électrique dipolaire qui, à proximité de la particule, dépend fortement des propriétés de surface. Ce changement de comportement de ce champ électrique sur une surface isolant ou conductrice n'affecte pas la vitesse de la particule. Dans un second temps, nous étudions les effets d'interactions hydrodynamiques et de la condensation des contre-ions sur la thermophorèse des polymères d'ADN. Comme résultat principal, la mobilité thermophorétique montre, en fonction de la longueur de la chaîne, un comportement non-monotone et se compose de deux contributions induites par les forces conductrices dominantes que sont l'effet Seebeck et le gradient de permittivité. À la fin, nous comparons notre résultat théorique avec une récente expérience sur l'ADN / The aim of this work is to study the nanoscale Seebeck effect at hot nanostructures. At first, we study the thermo-electrophoresis self-propulsion mechanism for a heated metal capped Janus colloid. The self-propulsion mechanism is mainly induced by the electrolyte Seebeck effect or thermoelectric effect. This effect takes its origin from the separation of charges occurring while a temperature gradient is present in a electrolyte solution: A strong absorption of laser light by the metal side of the particle creates a temperature gradient which in turn acts on ion-species (positive and negative) and drives them to the hot or the cold region. This motion of ion results in a dipolar electric field which, close to the particle, depends strongly on the surface properties. The change of behavior of the electric field at the insulating or conducting surface does not affect the velocity of the particle. At second, we study the effect of hydrodynamic interactions and counterion condensation in thermophoresis for DNA polymer. As the main result, the thermophoretic mobility shows, in function of the chain length, a non-monotonuous behavior and consists of two contributions induced by the dominant driving forces which are the thermally induced permittivity-gradient and the electrolyte Seebeck effect. At the end, we compare our theoretical result with recent experiment on single-stranded DNA.

This dissertation presents and explores a technique to confine and manipulate single and multiple nano-objects in solution by exploiting the thermophoretic interactions with local temperature gradients. The method named thermophoretic trap uses an all-optically controlled heating via plasmonic absorption by a gold nano-structure designed for this purpose. The dissipation of absorbed laser light to thermal energy generates a localized temperature field. The spatial localization of the heat source thereby leads to strong temperature gradients that are used to drive a particle or molecule into a desired direction. The behavior of nano-objects confined by thermal inhomogeneities is explored experimentally as well as theoretically. The monograph treats three major experimental stages of development, which essentially differ in the way the heating laser beam is shaped and controlled. In a first generation, a static heating of an appropriate gold structure is used to induce a steady temperature profile that exhibits a local minimum in which particles can be confined. This simple realization illustrates the working principle best. In a second step, the static heating is replaced. A focused laser beam is used to heat a smaller spatial region. In order to confine a particle, the beam is steered in circles along a circular gold structure. The trapping dynamics are studied in detail and reveal similarities to the well-established Paul trap. The largest part of the thesis is dedicated to the third generation of the trap. While the hardware is identical to the second generation, using the real-time information on the position of the trapped object to heat only particular sites of the gold structure strongly increases the efficiency of the trap compared to the earlier versions. Beyond that, the optical feedback control allows for an active shaping of the effective virtual trapping potential by applying modified feedback rules, including e.g. a double-well or a box-like potential. This transforms the formerly pure trapping device to a versatile technique for micro and nano-fluidic manipulation. The physical and technical contributions to the limits of the method are explored. Finally, the feasibility of trapping single macro-molecules is demonstrated by the confinement of lambda-DNA for extended time periods over which the molecules center-of-mass motion as well as its conformational dynamics can be studied.

Amicoumacin A (Ami) halts bacterial growth by inhibiting the ribosome during translation. The Ami binding site locates in the vicinity of the E-site codon of mRNA. However, Ami does not clash with mRNA, rather stabilizes it, which is relatively unusual and implies a unique way of translation inhibition. In this work, we performed a kinetic and thermodynamic investigation of Ami influence on the main steps of polypeptide synthesis. We show that Ami reduces the rate of the functional canonical 70S initiation complex (IC) formation by 30-fold. Additionally, our results indicate that Ami promotes the formation of erroneous 30S ICs; however, IF3 prevents them from progressing towards translation initiation. During early elongation steps, Ami does not compromise EF-Tu-dependent A-site binding or peptide bond formation. On the other hand, Ami reduces the rate of peptidyl-tRNA movement from the A to the P site and significantly decreases the amount of the ribosomes capable of polypeptide synthesis. Our data indicate that Ami progressively decreases the activity of translating ribosomes that may appear to be the main inhibitory mechanism of Ami. Indeed, the use of EF-G mutants that confer resistance to Ami (G542V, G581A, or ins544V) leads to a complete restoration of the ribosome functionality. It is possible that the changes in translocation induced by EF-G mutants compensate for the activity loss caused by Ami. / Russian Foundation for Basic Research / Revisión por pares

This dissertation presents a detailed account of the study undertaken on the subject of fouling of Exhaust Gas Recirculator (EGR) coolers. The fouling process in EGR coolers is identified to be due to two primary reasons — deposition of fine soot particles and condensation of hydrocarbons known as dry soot and wet soot fouling, respectively. Several numerical simulations are performed to study the fouling process. Preliminary analysis of the particle forces for representative conditions reveal that drag, thermophoresis and Brownian forces are the significant transport mechanisms and among them, the deposition process is dominated by thermophoresis. Soot deposition in a representative turbulent plain channel shows a direct relationship of the amount of deposition with the near-wall temperature gradient. Subsequently, periodic and developing flow simulations are performed on a wavy channel geometry, a common EGR design for various Reynolds numbers and thermal boundary conditions. Constant heat flux boundary condition is used in the periodic fully-developed calculations, which assist in establishing various deposition trends. The wavy nature of the walls is noted to affect the fouling process, resulting in specific deposition patterns. For the lower Reynolds number flows, significantly higher deposition is observed due to the higher particle residence times. On the other hand, the developing flow calculations facilitate the use of wall temperature distributions that typically exist in EGR coolers. The linear dependence of the amount of deposition on the near-wall temperature gradient or in other words, the heat flux, is ascertained. It is also observed in all the calculations, that for the sub-micron soot particles considered, the deposition process is almost independent of the particle size. In addition, the nature of the flow and heat transfer characteristics and the transition to turbulence in a developing wavy channel are studied in considerable detail. Finally, a study on the condensation of heavy hydrocarbons is undertaken as a post-processing step, which facilitates the prediction of the spatial distribution and time-growth of the combined fouling layer. From the calculations, the maximum thickness of the dry soot layer is observed to be near the entrance, whereas for the wet soot layer, the peak is found to be towards the exit of the EGR cooler. Further, parametric studies are carried out to investigate the effect of various physical properties and inlet conditions on the process of fouling. / Master of Science

L’objectif principal de ce travail de recherche est d’améliorer les connaissances concernant l’influence de la morphologie de particules issues de combustion sur leur comportement thermophorétique. A cet effet, un dispositif tri-therme (3T) original permettant le dépôt par thermophorèse de ce type de particules a été développé. Cet instrument est composé de trois tubes concentriques, permettant la création d’un espace annulaire où un gaz chargé en particules est injecté. Le tube interne est refroidi et le tube externe est chauffé, créant ainsi un gradient de température dans l’espace annulaire. Les particules se déposent donc par effet thermophorétique sur la paroi froide du tube interne du dispositif. Ce dernier est basé sur la méthode dite de pénétration, où des mesures de concentrations à l’amont et à l’aval du dispositif permettent l’évaluation de l’efficacité de dépôt par effet thermophorétique. Un modèle du rendement de dépôt développé dans cette étude a permis par la suite de calculer le coefficient de diffusion thermophorétique Kth. Afin de valider la mise en œuvre de ce dispositif expérimental, nous avons évalué les coefficients Kth de billes de latex monodispersées et de deux types de brouillards d’huiles mono et polydispersés. Le bon accord trouvé entre ces valeurs du coefficient Kth et celles déterminées par le modèle de Beresnev et Chernyak ou par des études expérimentales antérieure, a permis la validation du dispositif 3T. Nous avons par la suite appliqué le dispositif avec des agrégats de suies de morphologie et de nature physico chimique variables. Les résultats obtenus mettent en évidence l’augmentation du coefficient de diffusion thermophorétique avec le nombre de particules primaires, et donc avec la taille de l’agrégat, confirmant ainsi les résultats obtenus par Mackowski et Brugière. Une confrontation entre les coefficients de diffusion thermophorétique Kth obtenus pour les différents types d’agrégats a été proposée. Cette confrontation a permis de dégager des tendances vis-à-vis de l’influence de la taille des particules primaires, de la dimension fractale Df et du ratio EC/TC sur le comportement thermophorétique des agrégats de suies / The main objective of this study is to improve the knowledge about the morphological influence of fractal aggregates on their thermophoretic behavior. For this purpose, an original tri thermal device aimed to capture this kind of particles by thermophoresis deposition was developed. This device is composed of three concentric tubes where particles flows through an annular space between the inner and outer tubes with imposed temperatures, the inner one is cooled and the outer is heated. Particles will deposit by thermophoresis on the cold wall of the inner tube. This device is based on the so called penetration method, where the deposition rate on a cold wall is obtained by particles concentrations measurements upstream and downstream of the test section. A deposition model developed in this study allowed us to determine the thermophoretic diffusion coefficient Kth. We validated the tri thermal device using monodispersed spherical latex particles and also mono and polydispersed spherical oil particles distributions. Indeed, a good agreement was found between our experimental determination of the thermophoretic diffusion coefficient and the theoretical values of Beresnev and Chernyak and also experimental results of the litterature. We finally conducted a study where we applied the device with soot aggregates that have variable morphology and physicochemical nature. This study confirmed the results presented by Mackowski and Brugière about the increase of the aggregates thermophoretic diffusion coefficients Kth with the primary particle number and therefore with the electrical mobility diameter. A confrontation between the coefficients Kth of the different types of aggregates allowed us to find an influence of the primary particles diameter, the fractal dimension Df and also the ratio EC/TC on the thermophoretic behavior of soot aggregates

Beetle-killed trees and woody residues degenerate and may lead to wildfires and uncontrolled CO2 emission. Woody biomass is known as a neutral CO2 solid fuel since it generates the same amount of CO2 that takes from atmosphere during its growing up. Cofiring woody biomass with coal in existing coal power plants is a reasonable solution to reduce the net amount of CO2 emission and decrease the risk of wildfires. However, there are some challenges ranging from providing and handling the woody biomass to the operation of cofiring woody biomass with coal. Co-milling of the fuels and ash deposition on the heat exchanger surfaces during cofiring are among the most critical challenges. A CFD model simulated the behavior of the pulverized particles and evaluate the impact of geometry and operational changes on mill performance. In addition, we measured the ash deposit rate derived from cofiring woody biomass with coal in a pilot combustor (1500 kW) and full-scale furnace. Moreover, we developed a model to predict ash deposit rate during combustion of coal and its blend with a variety of biomass. The post-processing analysis of CFD modelling of co-milling woody biomass with coal shows that the entrained large woody biomass particles exit the pulverizer along with the fine coal particles due to their lower density than that of coal particles. Some simple geometry and operational changes can optimize mill performance by reducing the number of large biomass particles in the product stream. Therefore, it makes the particle size distribution (PSD) of the product stream of co-milling more like that of coal. The collected data set of fly ash particles and ash deposit samples shows that the ash formation and deposit rates were not impacted significantly by cofiring woody biomass with coal. The concentration of alkali metals in the ash aerosol during cofiring was slightly higher than that of coal. Cofiring in pilot scale combustor made a tri-modal PSD of ash aerosol particles; however, the distribution was bimodal in the full-scale boiler. The ash deposit rates during cofiring in 1500 kW combustor were higher (30 to 70%) at locations closer to the burner at short operation times. Our developed model of ash deposit rate investigated two types of stickiness models of fly ash particles to the surface of heat exchanger: melt fraction stickiness model (MFSM) and kinetic energy stickiness model (KESM). The developed model suggested that the MFSM, which is based on the melt fraction of ash and our novel approach to condensation of alkali vapor species, was more accurate in predicting ash deposit rate of a variety of fuel combustion of a 100-kW combustor. The model calculated four mechanisms: inertial impaction, thermophoresis, condensation, and eddy impaction.

Dans le but de montrer l’influence de la morphologie fractale d’un agrégat sur son comportement thermophorétique, un nouveau dispositif expérimental a été développé ; le SpectroMètreThermophorétique Circulaire (SMTC). Cet instrument permet de mesurer la vitesse moyenne de thermophorèse des particules dans une zone de sélection comprise entre une plaque chaude et une plaque froide. Pour cela, nous avons développé une fonction de transfert spécifique au principe de l’instrument sur la base des travaux existant sur les analyseurs différentiels de mobilité électrique.Une qualification expérimentale du SMTC a été réalisée avec des billes de latex monodispersées de tailles comprises entre 64 nm et 500 nm. Le bon accord entre les vitesses de thermophorèse obtenues et la théorie de Beresnev et Chernyak (1995) nous a permis de valider le fonctionnement de l’instrument.Par la suite, nous avons comparé les vitesses de thermophorèse expérimentales obtenues avec le SpectroMètre Thermophorétique Circulaire pour des particules sphériques et des agrégats produits par un générateur d’aérosol à combustion. Contrairement aux résultats obtenus avec les billes de latex, nous observons une augmentation de la vitesse de thermophorèse des agrégats avec leur diamètre de mobilité électrique.Grâce à une étude morphologique des agrégats, nous avons remarqué que la vitesse de thermophorèse est dépendante du nombre de particules primaires de l’agrégat. Ces résultats expérimentaux confirment pour la première fois les données théoriques de Mackowski (2006)obtenues par des simulations Monte-Carlo. De plus, une comparaison avec les travaux de Messerer et al. (2003) montre que la vitesse de thermophorèse des agrégats semble indépendante de la taille des particules primaires. / In order to show the influence of the morphology of a fractal aggregate on its thermophoretic behavior, a new experimental device has been developed; the SpectroMètre ThermophorétiqueCirculaire (SMTC). This instrument is used to measure the mean thermophoretic velocity of particles selected between a hot plate and a cold plate thanks to a transfer function based on the geometry of the radial flow differential mobility analyser RF-DMA or SMEC (Spectromètre de Mobilité Electrique Circulaire). For the experimental validation, effective thermophoretic velocities of monodispersed spherical latex particles for diameters ranging from 64 nm to 500 nm and a temperature gradient equal to 50 750 K/m are measured and compared with theoretical values. The good agreement between the experimentals results and theoretical values of Beresnev and Chernyak (1995) helps us to validate the operation of the instrument.Then we compare experimental thermophoretic velocity obtained with the SMTC for spherical particles and aggregates produced by a combustion aerosol generator. Contrary to the results obtained with the PSL particles, we observe that the thermophoretic velocity of aggregates increases with the electrical mobility diameter. Thanks to a morphological study of the aggregates, we showed that the thermophoretic velocity depends on the number of primary particles of the aggregate. These experimental results confirm,for the first time, the theoretical data of Mackowski (2006) obtained by a Monte Carlo simulation. Moreover, a comparison with the experimental results of Messerer et al. (2003) shows that thethermophoretic velocity of aggregates seems independent of the primary particle size.

The development of a biologic protein involves different stages and becomes a highly complex process which can be costly and time consuming to scale up for industrial production. Therefore, optimization is a necessary part of the production process development to lower the production expenses.An on-going project is working on upscaling the production of a protein derived from mussel adhesive proteins (MAPs) which has great properties to be used as a pharmaceutical drug or in medical devices. The protein is expressed in a bacterial host cell and the necessary post translational modifications (PTMs) are done in-vitro using enzymes. The work presented in this report was done to optimize both the protein production in lab scale bioreactors and the enzymatic reaction using an immobilized prolyl-4-hydroxylase (P4H) which does a post translational modification on prolyl-residues. Additionally, an interaction study was conducted to better understand the hydroxylation using the prolyl-4-hydroxylase.For the bioreactor optimization four initial trials were performed testing different growth and induction temperatures and also comparing exponential to linear feeding. From these trials it appeared that having 30 ℃ growth overnight and induction at the same temperature in combination with an exponential feeding rate gave the best results. The modifications done by the prolyl-4-hydroxylase were analysed by LC-MS and suggest that longer incubation time and more immobilized protein gives more modifications in the tested ranges and the possibilities of reusing the immobilized proteins looks promising. No conclusive data was discovered for the optimal substrate concentration. The interaction study revealed the importance of reagents used for catalysis with the enzyme to be present for interaction to occur, however more work needs to be done to discover an accurate KD for the interaction.

No description available.

Membrane proteins play a key role in numerous physiological processes such as transport, energy transduction in respiratory and photosynthetic systems, and signal transduction, and are of great pharmaceutical interest, comprising more than 60% of known drug targets. However, crystallisation of membrane proteins, and G protein-coupled receptors (GPCRs) in particular, still relies heavily on the use of protein engineering strategies, which have been shown to hamper protein activity. Here, a range of biophysical methods were used to study the structure and function of two membrane proteins, a prokaryotic peptide transporter, PepT_So and a GPCR, neurotensin receptor 1 (NTS1), using different membrane reconstitution methods to study the proteins in a native-like environment. Firstly, using the pulsed electron paramagnetic resonance (EPR) method of double electron-electron resonance (DEER) the conformation of PepT_So reconstituted into lipid bilayers was assessed and compared to previous structural data obtained from crystallography and modelling. The influence of the membrane potential and the presence of substrate on the conformational heterogeneity of this proton-coupled transporter were investigated. Secondly, NTS1 purification was optimized for biophysical study. Cysteine mutants were created and a labelling protocol was developed and optimized for fluorophore and nitroxide labelling studies. NTS1 was then studied by continuous-wave EPR, to assess the influence of ligand on local protein dynamics, and to assess the structure of a receptor segment known as helix 8, that was proposed to be an α-helix, but was only observed to be helical in one of the NTS1 crystallographic studies. Ensemble and single-molecule Förster resonance energy transfer (FRET), and DEER were combined to study the dimerisation behaviour of NTS1, showing novel dynamics of the interfacial associations. Finally, the signalling mechanism of NTS1 was also investigated using microscale thermophoresis (MST) to assess the affinity of the receptor for G protein in vitro in the absence of ligand, or in the presence of agonist or antagonist. MST measurements were performed in detergent and in nanodiscs of different lipid compositions, to assess the influence of the lipid environment on receptor function. In summary, this thesis demonstrates the potential of biophysical techniques to study various aspects of membrane protein structure and function in native-like lipid systems, complementing e.g. structural data obtained from crystallographic studies with functional data for membrane proteins in more native environments, as well as shedding light on protein dynamics. The work presented here provides novel insights into PepTSo transport, and in particular into NTS1 structure, signalling, and oligomerisation, opening up several avenues for future research.