In order to succeed, it is imperative that all e-commerce systems include an effective and reliable trust and reputation modeling system. This is particularly true of decentralized e-commerce systems in which autonomous software engage in commercial transactions. Many researchers have sought to overcome the complexities of modeling a subjective, human concept like trust, resulting in several trust and reputation models. While these models each present a unique offering and solution to the problem, several issues persist. Most of the models require direct experience in the e-commerce system in order to make effective trust decisions. This leaves new agents and agents who only casually use the e-commerce system vulnerable. Additionally, the reputation ratings of agents who are relatively new to the system are often indistinguishable from scores for poorly performing agents. Finally, more tactics to defend against agents who exploit the characteristics of the open, distributed system for their own malicious needs are required. To address these issues, a new metric is devised and presented: seniority. Based on agent age and activity level within the e-commerce system, seniority provides a means of judging the credibility of other agents with little or no prior experience in the system. As the results of experimental analysis reveals, employing a reputation model that uses seniority provides considerable value to agents who are new agents, casual buyer agents and all other purchasing agents in the e-commerce system. This new metric therefore offers a significant contribution toward the development of enhanced and new trust and reputation models for deployment in real-world distributed e-commerce environments.

This PhD Thesis involves the development of a new synthetic protocol for iron oxide silica composite nanoparticles useful in MRI and magnetic hyperthermia. Our approximation combines the sol-gel chemistry and supercritical fluids to obtain biocompatible, spherical composite particles, with narrow particle size distribution. The composite particles showed very high values of relaxivity. We have also studied the dependence of the specific absorption rate with iron concentration. This manuscript is organized into seven chapters. Chapter 1 provides a general introduction to magnetic nanoparticles, their properties, synthesis, stabilization and applications, with special interest in the biomedical field. The aim of the chapter is to place the reader in the scientific context of the thesis. Chapter 2 describes the synthesis of nanoparticles by thermal decomposition of an iron complex, Fe(CO)5, and their characterization in solid and colloidal dispersion. Silica coating is a convenient approach to stabilize nanoparticles in a biocompatible way. In this thesis we have developed a new synthetic protocol to coat iron oxide nanoparticles with silica that combines the sol-gel chemistry and supercritical fluids. To understand and control the details of this procedure, we first synthesized nano- and microparticles of silica. They are described in Chapter 3. Chapter 4 includes the synthesis of the composite γ-Fe2O3@SiO2 nanoparticles. The core is composed of clustered iron oxide nanoparticles (described in Chapter 2) surrounded by a silica shell. Chapter 4 also describes the material characterization, with special emphasis on the magnetic properties, which will be exploited in the biomedical applications. We also succeeded in synthesizing composite ε-Fe2O3@SiO2 nanospheres from the previous γ-Fe2O3@SiO2 particles. The evaluation of the materials described in Chapters 2 and 4 as contrast agents for magnetic resonance imaging and as mediators for magnetic hyperthermia is included in Chapter 5. Chapter 6 lists the main conclusions derived from the present thesis. Finally, Chapter 7 gathers the annexes. It includes four publications arising from the main subject of this thesis, as well as five other publications and a patent on projects that I worked during the time that has lasted my doctoral thesis. The annexes also include a brief description of the experimental techniques used and protocols for sample preparation.

S’han sintetitzat quatre alquil i aril (9 anthry1) carbinol (metil, fenil isopropil, terc-butil, i) que van revelar la rotació restringida al voltant de l'enllaç C9-C11. La seva energia lliure d'activació per a la rotació s'ha determinat, sent 11.0, 14.0, 21.7, i 9.8 kcal / mol, respectivament. Es descriuen l’aplicació mètodes de mesura del NOE i del temps de relaxació per a la determinació de l'energia d'activació per a la rotació de bons. El bon acord amb els valors obtinguts amb el mètode de la temperatura de coalescència confirma que l'enfocament basat NOE és una bona alternativa per a la determinació de les elevades barreres de rotació. Els càlculs de Mecànica Molecular (MM2) donen valors propers als experimentals. S’han preparat els carbamats homoquirals del 9-anthryl-terc-butylcarbinol i s’ha estudiat el seu equilibri conformacional. La configuració absoluta es va determinar mitjançant la comparació de les dades de RMN amb càlculs de MM. Els enantiòmers de l'alcohol es van obtenir després de la separació cromatogràfica dels derivats de carbamat i la seva hidròlisi. Els alcohols homoquirals van ser preparats per columna de cromatografia quiral directa. S’han detectat i o separat a temperatura ambient els confòrmers cisoid i transoid del 9,10 dipivaloylantracè i del 9,10-bis(1-imino-2,2-dimetilpropil)antracè. La transformació entre dues atropisómers va ser estudiada per RMN i modelat pels mètodes de MM. La difracció de raigs X es va realitzar per als derivats imino. El 9-antril-terc-butilcarbinol es va provar com a agent de solvatació quiral (CSA) en presència de formes racèmica de p-toluenesulfinate de mentil, 9-(1-amino-2,2- dimetilpropil)-9,19-dihydroantracè, àcid R-methoxyfenylacetic i 1-phenyl-1,2- ethanediol. Es formaren els complexes diastereòmers entre el reactiu quiral i cada enantiòmer d'aquests últims compostos. Un dels enantiòmers de 9-antril-tertbutylcarbinol va ser estudiat mitjançant NOE intermolecular i càlculs de dinàmica molecular. Es trobaren les principals diferencies termodinàmiques i estructurals. / Se han preparado Cuatro alquil- y aril- (9-antril)carbinols (metil, isopropil, tert-butil, y fenil) y mostraron la rotación restringida del enlace de C9-Cll. Su energía libre de activación para la rotación ha sido determinada, siendo 11.0, 14.0, 21.7, y 9.8 kcal/mol, respectivamente. Hemos determinado la energía de activación para la rotación de enlace C9-C11 por la aplicación de medidas de NOE y de tiempo de relajación. El buen acuerdo con los valores obtenidos con el método de temperatura coalescencia confirma que el método basado en el NOE es una buena alternativa para la determinación de barreras de rotatorión altas. La Mecánica Molecular (MM2) da valores cercanos a los experimentales. Se ha preparado el carbamato homochiral de 9-antril-tert-butilcarbinol y se ha estudiado su equilibrio conformacional. La configuración absoluta fue determinada por la comparación de los datos NMR con cálculos de MM. Los enantiomers del alcohol fueron obtenidos después de la separación cromatográfica de los carbamatos y tres su hidrólisis. Los mismos alcoholes se obtuvieron a través de una columna HPLC quiral Se han detectado o separado, a temperatura ambiente, los confórmeros cisoide y transoide del 9,10 dipivaloylantraceno y del 9,10-bis(1-imino-2,2- dimetilpropil)antraceno. La transformación entre los dos atropoisómeros se estudió por RMN i se modeló por métodes de MM. La difracción de rayos X se realitzó con los derivados imino. Se ha probado el 9-anthryl-tert-butylcarbinol como agente solvatación chiral (CSA) en presencia de las formas de racemicas de p-toluenesulfinato de mentilo, 9-(1-amino-2,2- dimetilpropil) - 9,19-dihydroanthracene, ácido de R-methoxyphenylacetic y 1-phenyl- 1,2-ethanediol. Se formaron los complejos diastereoisómericos el reactivo quiral y cada enantiomer de estos últimos compuestos. Uno de los enantiomers de 9-anthryltertbutylcarbinol fue estudiado por medio de NOE intermolecular y cálculos de dinámica moleculares. Las diferencias termodinámicas y estructurales principales fueron encontradas. / Four alkyl- and aryl-(9-anthry1)carbinols (methyl, isopropyl, tert-butyl, and phenyl) were synthesized and revealed restricted rotation about the C9-Cll bond. Their free energy of activation for rotation has been determined, being 11.0, 14.0, 21.7, and 9.8 kcal/mol, respectively. The application of NOE enhancement and relaxation time measurements for the determination of the activation energy for bond rotation is described. The good agreement with the values obtained with the coalescence temperature method bears out that the NOE based approach is a good alternative for the determination of high rotational barriers. Molecular Mechanics (MM2) calculations give values close to the experimental ones. The homochiral carbamates of 9-anthryl-tert-butylcarbinol were prepared and their conformational equilibrium was studied. The absolute configuration was determined by comparison of the NMR data with MM calculations. The enantiomers of the alcohol were obtained after chromatographic separation of carbamate derivatives and their hydrolysis. The same homochiral alcohols were prepared by direct chiral column chromatography Cisoid and transoid conformations of 9,10-dipivaloylanthracene and 9,10-bis(1-imino- 2,2-dimethylpropyl) anthracene were separated and detected for the former and isolated for the latter at room temperature. The transformation between two atropisomers was studied by NMR and modeled by MM methods. X-ray diffraction was performed for the imino derivatives. The 9-anthryl-tert-butylcarbinol was tested as a chiral solvating agent (CSA) in the presence of racemic forms of mentil-p-toluenesulfinate, 9-(1-amino-2,2- dimethylpropyl)-9,19-dihydroanthracene, R-methoxyphenylacetic acid and 1-phenyl- 1,2-ethanediol. Diastereomeric complexes were found to form between each enantiomer of these last two compounds. One of the enantiomers of 9-anthryltert-butylcarbinol was studied by means of intermolecular NOE and molecular dynamics calculations. Major thermodynamic and structural differences were found.

Magnetic resonance imaging (MRI) is the leading imaging technique for disease diagnostics. MRI contrast agents facilitate MRI technique to obtain tissue-specific image with improved sensitivity and signal-to-noise ratio. However, the applications of current MRI contrast agents are hampered by their uncontrolled blood circulation time, low relaxivity, and low specificity. To address such need, I have developed a series of analitical methods to determine and evaluate the strong metal binding affinity and metal selectivity of developed protein-based contrast agents (ProCAs). In addition, we have successed designed contrast agents ProCA3 series based on key determinats for metal binding sites and relaxivity. We have dementrated that one of the ProCA3 variants, ProCA32, has a high Gd3+ affinity less than 10-21 M and high metal selectivity with relxivity of more than 30 mM-1s-1 per Gd and 60 mM-1s-1 per particle. Moreover, we have demonstrated that ProCA3 variants have proper blood circulation time, high relaxivity, high metal selectivity and low toxicity, which facilitate MR imaging of multiple organs, such as liver, kidney, and blood vessels, as well as tumors. ProCA32 is also able to image liver metastases a tumor size less than 0.25 mm, which is more than fourty times more sensitive than that of clinical diagnostics of liver metastases using MRI and our developed methodology. We have further created ProCA3 variants with targeting peptide moieties such as ProCA3.bomb or ProCA3.affi to against cancer biomarkers such as GRPR and HER2 with capability to imaging tumor biomarker expressions in vivo at molecular level. We have shown that ProCA3 has an excellent safety profile and pharmacokinetics for MRI in animals. With our additional effect in protein expression, modification, and scale up production of these developed protein contrast agents, ProCA3 is expected to be a promising MRI contrast for the diagnostics for disease, such as metastatic tumor and blood vessel abnormalities, and tumor biomarkers.

This paper examines the possible contribution of evolutionary economics to macro-economic modelling of flood impacts to provide guidance for future economic risk modelling. Most macro-economic models start from a neoclassical economic perspective and focus on equilibrium outcomes, either in a static or dynamic way, and describe economic processes at a high level of aggregation. As a consequence, they typically fail to account for the complexity of social interactions and other behavioural responses of consumers and producers to disasters, which may affect the macroeconomic impacts of floods. Employing evolutionary principles and methods, such as agent-based modelling, may help to address some of the shortcomings of current macro-economic models. We explore and discuss the implications of applying consumer and producer heterogeneity, bounded rationality, network effects, social and technological learning, co-evolution and adaptive policy-making concepts into existing economic frameworks for the assessment of macro-economic impacts of floods. (authors' abstract)

There is an increasing interest for nanomaterials in biomedical applications and in this work, nanoparticles of gadolinium oxide (Gd2O3) have been investigated as a novel contrast agent for Magnetic Resonance Imaging (MRI). Relaxation properties have been studied in aqueous solutions as well as in cell culture medium and the nanoparticles have been explored as cell labeling agents. The fluorescent properties of the particles were used to visualize the internalization in cells and doped particles were also investigated as a multimodal agent that could work as a fluorescent marker for microscopy and as a contrast enhancer for MRI. Results show that in aqueous solutions, there is a twofold increase in relaxivity for Gd2O3 compared to commercial agent Gd-DTPA. In cell culture medium as well as in cells, there is a clear T1 effect and a distinct increase in signal intensity in T1-mapped images. Fluorescent studies show that the Gd2O3 nanoparticles doped with 5% terbium have interesting fluorescent properties and that these particles could work as a multimodal contrast agent. This study shows that Gd2O3 nanoparticles possess excellent relaxation properties that are retained in more biological environments. Gd2O3 particles are suitable as a T1 contrast agent, but seem also be adequate for T2 enhancement in for instance cell labeling experiments.

Rising oil prices have been a concern for both developed and developing countries, especially in more recent years as it tends to have a crippling effect on production and transportation. Many countries have moved towards the development of fossil fuel alternatives as a means of achieving energy independence and achieving environmental targets (for example the Kyoto Protocol). Developments in both these types of energy markets (fossil fuel and renewable fuels) may impact Canadian Prairie agriculture. Most of Canadian prairie crops are exported. The Canadian prairies are land locked to some extent. The closest ocean access to the eastern portion of the prairies is the port of Churchill, but is closed during the winter season. Crops are therefore transported west through the Rocky Mountains or east through the Great Lakes to get to a port. This requires hundreds of kilometres of truck and rail transportation, which is fuel dependent. To a lesser extent, at the micro-level farmers depend on fossil fuels to operate machinery to facilitate efficient crop production. If oil prices continue on an upward trajectory, will farmers cropping behaviour change? Furthermore, the development of the bioethanol industry on the Canadian prairies has given wheat farmers another crop option. As oil prices increase, the price of ethanol increases as well. Also, demand is bolstered by renewable fuel standards and government tax exemptions or subsidies. This study seeks to put forward the notion that as oil prices increase, crop production and transportation costs also increase thereby reducing farmers’ gross margins. Also, ceteris paribus, as oil prices increase there will be an increased demand for, and an increase in the price of biofuels thereby increasing the price of biofuel feedstock. Higher feedstock prices are expected to increase the gross margins of farmers. Therefore higher oil prices drive increased crop competition between traditional cropping (cropping for food exports) and energy cropping. This thesis seeks to ascertain at what level of oil prices would farmers, in general, be willing to switch from producing wheat for traditional (hard/food wheat) purposes to bioenergy (soft/ biofuel wheat) cropping alternatives. Also under varying scenarios of oil price growth and government support to the biofuel industry, this thesis seeks to ascertain the impact of biofuel industry expansion on grain elevator pricing behaviour and the structure of the elevator industry, assuming elevators spatially compete with each other for farmers’ crops. An agent based model (ABM) is employed for this study. The model is selected over other types as the researcher wants to capture the increased complexity stemming from the competition between crops that belong to at least one distribution chain. Agent based networks allow for emergent behaviour that is obtained from the spatial competition of elevators. Finally, the agent based model allows for spatial heterogeneity in location of farmers in terms of soil quality and their proximity to an elevator, which affects crop productivity and transportation costs, respectively. The ABM (also called the FARMCHAIN model) is comprised of over 35000 farmer agents, 176 elevator agents, 6 canola crushing plant agents, 5 ethanol plant agents and 1 biodiesel plant agent located on the 20 census agricultural regions (CARs) of Saskatchewan. Farmers allocate land based on their expected gross margins. Farmers produce and truck crops to the designated distribution chain. Crops move through the chain and at every stage the associated costs are computed and apportioned to the farmer. At the end of the period, gross margins are computed and these gross margins are used in computing the expected gross margins for the subsequent period. It is found that real annual crude prices would have to be greater than $133 before farmers begin to switch to producing biofuel wheat (soft wheat) from food wheat (hard wheat). This would have to be approximately 30% higher than that of 2008 in which crude prices were at record levels. Also, if biofuel support is declining then it would take a considerably higher price to entice farmers, in aggregate, to switch.

En els sistemes multiagent els models de confiança són una eina important perquè les interaccions entre agents siguin efectives. Ara bé, la confiança és una noció inherentment subjectiva, i per això els agents necessiten informació addicional per poder comunicar les avaluacions de confiança. Aquesta tesi doctoral se centra en dos mètodes per comunicar la confiança: l'alineament de la confiança i l'adaptació de la confiança. En el primer mètode, el problema de la comunicació de la confiança es modela com un problema d'alineament. Mostrem que les solucions actuals basades en ontologies comunes o en l'alineament d'ontologies generen problemes addicionals. Per això proposem com a alternativa alinear la confiança, basant-nos en les interaccions que dos agents comparteixen per tal d'aprendre un alineament. Fent servir el marc matemàtic de la teoria de canals formalitzem com les avaluacions subjectives de dos agents sobre la confiança es relacionen a través de les interaccions que fonamenten aquestes avaluacions. Com que els agents no poden accedir a les avaluacions de confiança dels altres, cal establir una comunicació. Especifiquem la rellevància i la consistència com a propietats necessàries per a aquesta comunicació. L'agent receptor de la confiança comunicada pot generalitzar els missatges fent servir la θ-subsumció, el que duu a un model predictiu que permet a un agent traduir futures comunicacions rebudes del mateix agent emissor. Mostrem aquest procés d'alineament a la pràctica fent servir TILDE, un algorisme de regressió de primer ordre, per tal d'aprendre un alineament. També il·lustrem la seva aplicació en un escenari d'exemple. De forma empírica demostrem: (1) que la dificultat d'aprendre un alineament depèn de la complexitat relativa dels diversos models de confiança; (2) que el nostre mètode millora altres mètodes existents d'alineament de la confiança; i (3) que el nostre mètode funciona bé sota condicions d'engany. El segon mètode per comunicar la confiança es basa en permetre que els agents raonin sobre llurs models de confiança i que personalitzin les comunicacions per adaptar-se millor a les necessitats d'un altre agent. Els mètodes actuals no permeten la suficient introspecció o adaptació del models de confiança. Per això presentem AdaptTrust, un mètode per incorporar un model computacional de confiança a l'arquitectura cognitiva d'un agent. En AdapTrust les creences i els objectius d'un agent influencien les prioritats entre aquells factors que són importants per a la computació de la confiança. Aquests al seu torn defineixen els valors dels paràmetres del model de confiança, i així l'agent pot dur a terme canvis en el seu model computacional de confiança a base de raonar sobre les seves creences i objectius. D'aquesta manera és capaç de modificar proactivament el seu model i produir avaluacions de confiança que millor s'adaptin a les seves necessitats actuals. Donem una formalització declarativa d'aquest sistema integrant-lo en una representació ⎯ fonamentada en un sistema multicontext ⎯ d'una arquitectura d'agent basada en creences, desitjos i intencions (BDI). També mostrem com amb el nostre marc es poden incorporar tres dels actuals models de confiança en el sistema de raonament d'un agent. Finalment fem servir AdapTrust en un marc d'argumentació que permet als agents construir una justificació per a llurs avaluacions de confiança. A través d'aquest marc els agents justifiquen les seves avaluacions segons unes prioritats entre factors, les quals al seu torn són justificades per les creences i objectius dels agents. Aquestes justificacions es poden comunicar a altres agents a través d'un diàleg formal. Així un agent, a base d'argumentar i raonar sobre les prioritats d'un altre agent, pot adaptar el seu model de confiança per oferir-li una recomanació de confiança personalitzada. Aquest sistema l'hem comprovat empíricament i hem vist que millora els actuals sistemes que permeten argumentar sobre avaluacions de confiança. / In open multi-agent systems, trust models are an important tool for agents to achieve effective interactions; however, trust is an inherently subjective concept, and thus for the agents to communicate about trust meaningfully, additional information is required. This thesis focuses on Trust Alignment and Trust Adaptation, two approaches for communicating about trust. The first approach is to model the problem of communicating trust as a problem of alignment. We show that currently proposed solutions, such as common ontologies or ontology alignment methods, lead to additional problems, and propose trust alignment as an alternative. We propose to use the interactions that two agents share as a basis for learning an alignment. We model this using the mathematical framework of Channel Theory, which allows us to formalise how two agents' subjective trust evaluations are related through the interactions that support them. Because the agents do not have access to each other's trust evaluations, they must communicate; we specify relevance and consistency, two necessary properties for this communication. The receiver of the communicated trust evaluations can generalise the messages using θ-subsumption, leading to a predictive model that allows an agent to translate future communications from the same sender. We demonstrate this alignment process in practice, using TILDE, a first-order regression algorithm, to learn an alignment and demonstrate its functioning in an example scenario. We find empirically that: (1) the difficulty of learning an alignment depends on the relative complexity of different trust models; (2) our method outperforms other methods for trust alignment; and (3) our alignment method deals well with deception. The second approach to communicating about trust is to allow agents to reason about their trust model and personalise communications to better suit the other agent's needs. Contemporary models do not allow for enough introspection into ⎯ or adaptation of ⎯ the trust model, so we present AdapTrust, a method for incorporating a computational trust model into the cognitive architecture of the agent. In AdapTrust, the agent's beliefs and goals influence the priorities between factors that are important to the trust calculation. These, in turn, define the values for parameters of the trust model, and the agent can effect changes in its computational trust model, by reasoning about its beliefs and goals. This way it can proactively change its model to produce trust evaluations that are better suited to its current needs. We give a declarative formalisation of this system by integrating it into a multi-context system representation of a beliefs-desires-intentions (BDI) agent architecture. We show that three contemporary trust models can be incorporated into an agent's reasoning system using our framework. Subsequently, we use AdapTrust in an argumentation framework that allows agents to create a justification for their trust evaluations. Agents justify their evaluations in terms of priorities between factors, which in turn are justified by their beliefs and goals. These justifications can be communicated to other agents in a formal dialogue, and by arguing and reasoning about other agents' priorities, goals and beliefs, the agent may adapt its trust model to provide a personalised trust recommendation for another agent. We test this system empirically and see that it performs better than the current state-of-the-art system for arguing about trust evaluations.

Les systèmes tuteurs intelligents sont considérés comme un remarquable concentré de technologies qui permettent un processus d'apprentissage. Ces systèmes sont capables de jouer le rôle d'assistants voire même de tuteur humain. Afin d'y arriver, ces systèmes ont besoin de maintenir et d'utiliser une représentation interne de l'environnement. Ainsi, ils peuvent tenir compte des évènements passés et présents ainsi que de certains aspects socioculturels. Parallèlement à l'évolution dynamique de l'environnement, un agent STI doit évoluer en modifiant ses structures et en ajoutant de nouveaux phénomènes. Cette importante capacité d'adaptation est observée dans le cas de tuteurs humains. Les humains sont capables de gérer toutes ces complexités à l'aide de l'attention et du mécanisme de conscience (Baars B. J., 1983, 1988), et (Sloman, A and Chrisley, R., 2003). Toutefois, reconstruire et implémenter des capacités humaines dans un agent artificiel est loin des possibilités actuelles de la connaissance de même que des machines les plus sophistiquées. Pour réaliser un comportement humanoïde dans une machine, ou simplement pour mieux comprendre l'adaptabilité et la souplesse humaine, nous avons à développer un mécanisme d'apprentissage proche de celui de l'homme. Ce présent travail décrit quelques concepts d'apprentissage fondamentaux implémentés dans un agent cognitif autonome, nommé CTS (Conscious Tutoring System) développé dans le GDAC (Dubois, D., 2007). Nous proposons un modèle qui étend un apprentissage conscient et inconscient afin d'accroître l'autonomie de l'agent dans un environnement changeant ainsi que d'améliorer sa finesse. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Apprentissage, Conscience, Agent cognitif, Codelet.

Cette étude cible les questions relatives aux systèmes aqueux de fines particules près ou sous le micron qui sont importantes et nombreuses en environnement avec les résidus anthropiques et en particulier avec les matériaux anthropogéniques des sédiments de rivières et des lacs. Le but principal visé était de démontrer l'importance d'utiliser un surfactant comme agent pour améliorer la séparation colloïdale en milieu aqueux. Dans cette technique les surfactants altèrent la charge de surface des particules qui vont dicter le comportement et la destination des phases respectives du système par les floculations ou suspensions. À cause de leur masse extrêmement petite, l'effet de gravité est atténué et joue un rôle plus voilé avec le temps. Pour des études de caractérisation de tels systèmes, en environnement, où les difficultés tiennent à la présence des fines sous microniques et aux mélanges polyphasés, ces systèmes répondent mal à l'application des méthodes conventionnelles habituellement utilisées de séparation comme la séparation magnétique en milieu sec ou humide, la séparation électroacoustique et la séparation par liqueurs denses. Les paramètres fondamentaux du potentiel zêta déterminent l'état et les conditions pour une suspension ou pour une floculation. La mobilité des particules solides peut être mesurée par une technique acoustique ESA qui permet de calculer les valeurs du potentiel zêta. Cette détermination implique l'intégration des mesures de la distribution granulométrique, du poids spécifique et les considérations des paramètres chimiques du système soit le pH, la température et la conductivité. Nos résultats indiquent, comme l'hypothèse originale le supposait, que les minéraux naturels ont la même polarité de surface et des intensités de charges comparables aux composés anthropiques pour une composition chimique et structure atomique similaire. Les résultats confirment également que pour un système polyphasé, le signe de polarité et l'intensité du zêta initial sont la résultante de la sommation des valeurs de zêta des phases constituantes. L'équation suivante se vérifie: ζ (zeta) mV pour la system = Σζа X Cа + ζb X Cb +....... Plusieurs systèmes artificiels ont été étudiés et les données initiales du système mesuré servent de guides pour trouver les conditions qui permettront d'induire la floculation et le fractionnement en systèmes moins polyphasés et plus simples facilitant ainsi une caractérisation. Les essais et la détermination des paramètres influençant la séparation colloïdale par un surfactant ont été mises au point initialement sur un sédiment de lac comprenant des particules de sulfures de 2 à 3 µm. La présence de grains de sulfures dans le sédiment original n'avait pas été détectée par diffraction de rayons X mais suite au fractionnement et a une concentration résultant plus élevée dans les couches fractionnées, des sulfures pouvaient être identifier. Cette technique a d'ailleurs été utilisée pour caractériser le fractionnement en couches dans lesquelles on retrouve une forte variation dans la concentration des phases constituantes incluant les sulfures. Le fractionnement résultant est de qualité suffisante pour que cette technique soit considérée dans une remédiation environnementale, en particulier pour les résidus miniers où le potentiel de d'acidité excède la capacité de neutralisation engendrant une problématique de drainage minier acide (DMA). Initialement le projet a étudié et caractérisé des mélanges simples de suspension de minéraux suivis d'un ajout progressif des phases du système. pour éventuellement simuler un système naturel contaminé. Une comparaison des similitudes et des différences des systèmes artificiels et naturels sert de base aux conclusions. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Potentiel zêta, Minéraux naturels, Surfactant, Sulfures, Décontamination, Double couche électrique, Séparation colloïdale.