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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Sol-gel Resorcinarene Sorbent for Capillary Microextraction Coupled to Gas Chromatography

Alhendal, Abdullah Awadh 01 January 2011 (has links)
For the first time, octahydroxyl methylresorcinarene with four hexyl groups on the lower rim was utilized in the in-situ preparation of a silica-based sol-gel organic-inorganic hybrid coating for sample preconcentration by capillary microextraction (CME). Tetraethoxysilane (TEOS) was chosen as a sol gel precursor to create a cross-linked sol-gel network via acid-catalyzed hydrolytic polycondensation reactions. Sol-gel chemistry helped in the in situ preparation of resorcinarene-containing extraction phase in the form of a surface coating. It also provided an effective means to chemically bind the coating to the inner surface of fused silica capillary via condensation of the hydroxyl groups in the sol-gel network with the silanol groups on the fused silica capillary inner surface. These chemically bonded sol-gel coatings demonstrated excellent thermal stability (up to 350 oC). The sol-gel resorcinarene coatings successfully extracted traces of polycyclic aromatic hydrocarbons (PAHs), ketones, phenols, amines, and alcohols from aqueous samples providing parts per trillion level detection limits (0.828 - 46.01 ng/L) in GC using a Flame Ionization Detector (FID). CME was performed by passing the aqueous samples through the resorcinarene coated microextraction capillary (10 cm). The extracted analytes where then thermally desorbed into the GC column connected to the exit end of the sol-gel microextraction capillary via a press-fit quartz connector. Peak area relative standard deviation (RSD %), a measure of the extraction performance reproducibility for the coated capillary, was found in the range of (1.1 % - 8.3 %). The sol-gel resorcinarene sorbent was characterized by FTIR spectrum which indicated the presence of hydroxyl groups in the coating even after the sol-gel reactions were completed which explains the affinity of the resorcinarene sol-gel coating toward polar analytes. Scanning Electron Microscopy (SEM) images of the coating reveraled the porous morphology and thickness of 3.5 - 4.0 µm for the coating. The sol-gel resorcinarene coated capillary provided excellent extraction performance for wide range of analytes.
32

Conteúdo iônico em testemunho de firn/gelo do monte Johns Antártica Ocidental: 1882–2008 A.D.

Thoen, Isaías Ullmann January 2017 (has links)
Esta dissertação investiga o registro de conteúdo iônico do testemunho de gelo monte Johns (79°55'28"S; 94°23'18"O) obtido na Antártica Ocidental, contribuindo para o adensamento espacial de informações glacioquímicas empregadas em estudos paleoclimáticos. As concentrações de Na+ (16,6 ± 28,2 μg L-1), K+ (1,3 ± 3,7 μg L-1), Mg2+ (3,7 ± 3,7 μg L-1), Ca2+ (5,4 ± 3,4 μg L-1), Cl- (33,3 ± 43,7 μg L-1), SO42- (25,9 ± 17,7 μg L-1), NO3- (50,8 ± 18,5 μg L-1) e H3CSO3- (7,1 ± 5,4 μg L-1) foram determinadas por cromatografia iônica em 2.164 amostras para o período 1882–2008. A variabilidade sazonal de NO3- e, especialmente do nssSO42-, em antifase com Na+, possibilitou a datação pela contagem de ciclos anuais ao longo do período estudado. A identificação dos sinais vulcânicos do Krakatoa (1883), Agung (1963) e Pinatubo/Hudson (1991) foi usada para determinar horizontes de referência (datação absoluta). Eventos de aporte significativo de aerossóis foram identificados e agrupados considerando o conteúdo iônico, proveniência e estação do ano. A avaliação da proveniência dos íons e do balanço iônico mostra a origem da carga iônica: 36% é oriunda de aerossóis de sal marinho, 13% de poeira mineral, 17% de atividade biogênica marinha e 34% de produtos da reatividade química na atmosfera. É observada uma leve redução nas concentrações de Mg2+ (-0,04 μg L-1 ano-1) e K+ (-0,01 μg L-1 ano-1), e mais forte para NO3- (-0,17 μg L-1 ano-1), no período 1909–2008. A média anual da acumulação líquida de neve foi 0,21 ± 0,04 m eq. H2O no período 1882–2008 sem apresentar tendência significante. A acumulação mostra alta correspondência com dados anuais de reanálise climática, com coeficiente de correlação cruzada de +0,42 (α < 0,05) para o período 1979–2008. / This dissertation investigates the ionic content record of the mount Johns ice core (79°55'28"S; 94°23'18"W) recovered from the West Antarctica, contributing to the spatial densification of glaciochemical information used in paleoclimatic studies. The concentrations of Na+ (16.6 ± 28.2 μg L-1), K+ (1.3 ± 3.7 μg L-1), Mg2+ (3.7 ± 3.7 μg L-1), Ca2+ (5.4 ± 3.4 μg L-1), Cl- (33.3 ± 43.7 μg L-1), SO42- (25.9 ± 17.7 μg L-1), NO3- (50.8 ± 18.5 μg L-1) e H3CSO3- (7.1 ± 5.4 μg L-1) were determined by ion chromatography on 2,164 samples for the period 1882–2008. The NO3- seasonal variability and, especially, of the nssSO42- in antiphase with the Na+, allowed the counting of annual cycles over the studied period. The identification of Krakatau (1883), Agung (1963) and Pinatubo / Hudson (1991) volcanic signals was used to determine reference horizons (absolute dating). Significant aerosols events were identified and grouped considering the ionic content, provenance and season of the year. The evaluation of the ions provenance and of the ionic balance points to ionic content origin: 36% come from sea salt aerosols, 13% from mineral dust, 17% originate from marine biogenic activity and 34% are chemical reactivity products in the atmosphere. It is observed a slight reduction in the Mg2+ (-0.04 μg L-1 y-1) and K+ (-0.01 μg L-1 y-1) concentrations, and stronger in the NO3- (-0.17 μg L-1 y-1), during the 1909–2008 period. The annual mean net accumulation rate averaged 0.21 ± 0.04 m w.e. y-1 in the period 1882–2008 did not show any significant trend and shows high correspondence with climatic reanalysis data in years with data overlap, with a cross-correlation coefficient of +0.42 (α < 0.05) for the period 1979–2008.
33

Conteúdo iônico em testemunho de firn/gelo do monte Johns Antártica Ocidental: 1882–2008 A.D.

Thoen, Isaías Ullmann January 2017 (has links)
Esta dissertação investiga o registro de conteúdo iônico do testemunho de gelo monte Johns (79°55'28"S; 94°23'18"O) obtido na Antártica Ocidental, contribuindo para o adensamento espacial de informações glacioquímicas empregadas em estudos paleoclimáticos. As concentrações de Na+ (16,6 ± 28,2 μg L-1), K+ (1,3 ± 3,7 μg L-1), Mg2+ (3,7 ± 3,7 μg L-1), Ca2+ (5,4 ± 3,4 μg L-1), Cl- (33,3 ± 43,7 μg L-1), SO42- (25,9 ± 17,7 μg L-1), NO3- (50,8 ± 18,5 μg L-1) e H3CSO3- (7,1 ± 5,4 μg L-1) foram determinadas por cromatografia iônica em 2.164 amostras para o período 1882–2008. A variabilidade sazonal de NO3- e, especialmente do nssSO42-, em antifase com Na+, possibilitou a datação pela contagem de ciclos anuais ao longo do período estudado. A identificação dos sinais vulcânicos do Krakatoa (1883), Agung (1963) e Pinatubo/Hudson (1991) foi usada para determinar horizontes de referência (datação absoluta). Eventos de aporte significativo de aerossóis foram identificados e agrupados considerando o conteúdo iônico, proveniência e estação do ano. A avaliação da proveniência dos íons e do balanço iônico mostra a origem da carga iônica: 36% é oriunda de aerossóis de sal marinho, 13% de poeira mineral, 17% de atividade biogênica marinha e 34% de produtos da reatividade química na atmosfera. É observada uma leve redução nas concentrações de Mg2+ (-0,04 μg L-1 ano-1) e K+ (-0,01 μg L-1 ano-1), e mais forte para NO3- (-0,17 μg L-1 ano-1), no período 1909–2008. A média anual da acumulação líquida de neve foi 0,21 ± 0,04 m eq. H2O no período 1882–2008 sem apresentar tendência significante. A acumulação mostra alta correspondência com dados anuais de reanálise climática, com coeficiente de correlação cruzada de +0,42 (α < 0,05) para o período 1979–2008. / This dissertation investigates the ionic content record of the mount Johns ice core (79°55'28"S; 94°23'18"W) recovered from the West Antarctica, contributing to the spatial densification of glaciochemical information used in paleoclimatic studies. The concentrations of Na+ (16.6 ± 28.2 μg L-1), K+ (1.3 ± 3.7 μg L-1), Mg2+ (3.7 ± 3.7 μg L-1), Ca2+ (5.4 ± 3.4 μg L-1), Cl- (33.3 ± 43.7 μg L-1), SO42- (25.9 ± 17.7 μg L-1), NO3- (50.8 ± 18.5 μg L-1) e H3CSO3- (7.1 ± 5.4 μg L-1) were determined by ion chromatography on 2,164 samples for the period 1882–2008. The NO3- seasonal variability and, especially, of the nssSO42- in antiphase with the Na+, allowed the counting of annual cycles over the studied period. The identification of Krakatau (1883), Agung (1963) and Pinatubo / Hudson (1991) volcanic signals was used to determine reference horizons (absolute dating). Significant aerosols events were identified and grouped considering the ionic content, provenance and season of the year. The evaluation of the ions provenance and of the ionic balance points to ionic content origin: 36% come from sea salt aerosols, 13% from mineral dust, 17% originate from marine biogenic activity and 34% are chemical reactivity products in the atmosphere. It is observed a slight reduction in the Mg2+ (-0.04 μg L-1 y-1) and K+ (-0.01 μg L-1 y-1) concentrations, and stronger in the NO3- (-0.17 μg L-1 y-1), during the 1909–2008 period. The annual mean net accumulation rate averaged 0.21 ± 0.04 m w.e. y-1 in the period 1882–2008 did not show any significant trend and shows high correspondence with climatic reanalysis data in years with data overlap, with a cross-correlation coefficient of +0.42 (α < 0.05) for the period 1979–2008.
34

Applications of Nanomanipulation Coupled to Nanospray Mass Spectrometry in Trace Fiber Analysis and Cellular Lipid Analysis.

Ledbetter, Nicole 12 1900 (has links)
The novel instrumentation of nanomanipulation coupled to nanospray mass spectrometry and its applications are presented. The nanomanipulator has the resolution of 10nm step sizes allowing for specific fine movement used to probe and characterize objects of interest. Nanospray mass spectrometry only needs a minimum sample volume of 300nl and a minimum sample size of 300attograms to analyze an analyte making it the ideal instrument to couple to nanomanipulation. The nanomanipulator is mounted to an inverted microscope and consists of 4 nano-positioners; these nano-positioners hold end-effectors and other tools used for manipulation. This original coupling has been used to enhance the current abilities of cellular probing and trace fiber analysis. Experiments have been performed to demonstrate the functionality of this instrument and its capabilities. Histidine and caffeine have been sampled directly from single fibers and analyzed. Lipid bodies from cotton seeds have been sampled indirectly and analyzed. The few applications demonstrated are only the beginning of nanomanipulation coupled to nanospray mass spectrometry and the possible applications are numerous especially with the ability to design and fabricate new end-effectors with unique abilities. Future study will be done to further the applications in direct cellular probing including toxicology studies and organelle analysis of single cells. Further studies will be directed in forensic applications of this instrument including gunshot residue sampled from fibers.
35

A Rewriting-based, Parameterized Exploration Scheme for the Dynamic Analysis of Complex Software Systems

Frechina Navarro, Francisco 17 November 2014 (has links)
Los sistemas software actuales son artefactos complejos cuyo comportamiento es a menudo extremadamente difícil de entender. Este hecho ha llevado al desarrollo de metodologías formales muy sofisticadas para el análisis, comprensión y depuración de programas. El análisis de trazas de ejecución consiste en la búsqueda dinámica de contenidos específicos dentro de las trazas de ejecución de un cierto programa. La búsqueda puede llevarse a cabo hacia adelante o hacia atrás. Si bien el análisis hacia adelante se traduce en una forma de análisis de impacto que identifica el alcance y las posibles consecuencias de los cambios en la entrada del programa, el análisis hacia atrás permite llevar a cabo un rastreo de la procedencia; es decir, muestra como (partes de) la salida del programa depende de (partes de) su entrada y ayuda a estimar qué dato de la entrada es necesario modificar para llevar a cabo un cambio en el resultado. En esta tesis se investiga una serie de metodologías de análisis de trazas que son especialmente adecuadas para el análisis de trazas de ejecución largas y complejas en la lógica de reescritura, que es un marco lógico y semántico especialmente adecuado para la formalización de sistemas altamente concurrentes. La primera parte de la tesis se centra en desarrollar una técnica de análisis de trazas hacia atrás que alcanza enormes reducciones en el tamaño de la traza. Esta metodología se basa en la fragmentación incremental y favorece un mejor análisis y depuración ya que la mayoría de las inspecciones, tediosas e irrelevantes, que se realizan rutinariamente en el diagnostico y la localización de errores se pueden eliminar de forma automática. Esta técnica se ilustra por medio de varios ejemplos que ejecutamos mediante el sistema iJulienne, una herramienta interactiva de fragmentación que hemos desarrollado y que implementa la técnica de análisis de trazas hacia atrás. En la segunda parte de la tesis se formaliza un sistema paramétrico, flexible y dinámico, para la exploración de computaciones en la lógica de reescritura. El esquema implementa un algoritmo de animación gen érico que permite la ejecución indeterminista de una teoría de reescritura condicional dada y que puede ser objeto de seguimiento mediante el uso de diferentes modalidades, incluyendo una ejecución gradual paso a paso y una fragmentación automática hacia adelante y/o hacia atrás, lo que reduce drásticamente el tamaño y la complejidad de las trazas bajo inspección y permite a los usuarios evaluar de forma aislada los efectos de una declaración o instrucción dada, el seguimiento de los efectos del cambio de la entrada, y obtener información sobre el comportamiento del programa (o mala conducta del mismo). Por otra parte, la fragmentación de la traza de ejecución puede identificar nuevas oportunidades de optimización del programa. Con esta metodología, un analista puede navegar, fragmentar, filtrar o buscar en la traza durante la ejecución del programa. El marco de análisis de trazas gen érico se ha implementado en el sistema Anima y describimos una profunda evaluación experimental de este que demuestra la utilidad del enfoque propuesto. / Frechina Navarro, F. (2014). A Rewriting-based, Parameterized Exploration Scheme for the Dynamic Analysis of Complex Software Systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/44234 / TESIS
36

An Interactive Visualization Model for Analyzing Data Storage System Workloads

Pungdumri, Steven Charubhat 01 March 2012 (has links)
The performance of hard disks has become increasingly important as the volume of data storage increases. At the bottom level of large-scale storage networks is the hard disk. Despite the importance of hard drives in a storage network, it is often difficult to analyze the performance of hard disks due to the sheer size of the datasets seen by hard disks. Additionally, hard drive workloads can have several multi-dimensional characteristics, such as access time, queue depth and block-address space. The result is that hard drive workloads are extremely diverse and large, making extracting meaningful information from hard drive workloads very difficult. This is one reason why there are several inefficiencies in storage networks. In this paper, we develop a tool that assists in communicating valuable insights into these datasets, resulting in an approach that utilizes parallel coordinates to model data storage workloads captured with bus analyzers. Users are presented with an effective visualization of workload captures with this implementation, along with methods to interact with and manipulate the model in order to more clearly analyze the lowest level of their storage systems. Design decisions regarding the feature set of this tool are based on the analysis needs of domain experts and feedback from a conducted user study. Results from our user study evaluations demonstrate the efficacy of our tool to observe valuable insights, which can potentially assist in future storage system design and deployment decisions. Using this tool, domain experts were able to model storage system datasets with various features to manipulate the visualization to make observations and discoveries, such as detecting logical block address banding and observe various dataset trends which were not readily noticeable using conventional analysis methods.
37

Examining the Effect of Self-Regulated Learning on Cognitive Engagement in Mastery-Based Online Courses: A Learning Analytics Perspective

Chen, Sheng-Bo 10 September 2020 (has links)
No description available.
38

Trace Visualization of Distributed and Centralized Applications / Trace-visualisering av distribuerade och centraliserade applikationer

Zhang, Siwei January 2023 (has links)
The Radio Access Network (RAN) plays a vital role in enabling mobile network connectivity using radio waves. Gaining a comprehensive understanding of RAN applications is crucial, and trace analysis provides valuable insights into their operations. Modern RAN applications can be deployed on different platforms and this can lead to the generation of different trace formats, which complicates the analysis process. Trace analysis and visualization tools, such as Trace Compass, can be used to ease the process, but for each new trace format the user often needs to create new code and visualizations. This is needed also when different trace formats generated by the same application contain similar information. To overcome this limitation, this thesis introduces an innovative approach to generalize the interpretation of traces, enabling to reuse existing analysis and visualization independently of the trace format. Moreover, a Domain Specific Language (DSL) is introduced to simplify the trace analysis procedure. The proposed thesis contributes to a generic approach for analyzing different trace formats, thereby facilitating the analysis of RAN applications deployed across diverse platforms. / Radio Access Network (RAN) spelar en viktig roll när det gäller att möjliggöra anslutning till mobilnät med hjälp av radiovågor. Att få en omfattande förståelse för RAN-applikationer är avgörande, och trace-analys ger värdefulla insikter i deras verksamhet. Moderna RAN-applikationer kan driftsättas på olika plattformar, vilket kan leda till att olika trace-format genereras, vilket komplicerar analysprocessen. Verktyg för trace-analys och visualisering, som Trace Compass, kan användas för att underlätta processen, men för varje nytt trace-format måste användaren ofta skapa ny kod och nya visualiseringar. Detta behövs även när olika traceformat som genereras av samma applikation innehåller liknande information. För att övervinna denna begränsning introducerar denna avhandling en innovativ metod för att generalisera tolkningen av trace-data, vilket gör det möjligt att återanvända befintlig analys och visualisering oberoende av traceformatet. Dessutom introduceras ett domänspecifikt språk (DSL) för att förenkla trace-analysförfarandet. Den föreslagna avhandlingen bidrar till en generisk metod för analys av olika trace-format, vilket underlättar analysen av RANapplikationer somanvänds på olika plattformar.
39

Methoden der spurenanalytischen Bestimmung von Estrogenen im Abwasser

Zorn, Eva-Christina 28 August 2003 (has links)
Spurenanalytische Untersuchungen von Umweltproben erfolgen meist standardmäßig mittels Festphasenextraktion (SPE) und anschließender GC/MS. Das Ziel der vorliegenden Arbeit bestand darin, alternative Methoden für die spurenanalytische Bestimmung von Estrogenen aus Umweltproben aufzuzeigen. Als Analyte wurden die natürlichen Estrogene Estron (E1), Estradiol (E2) und Estriol (E3), sowie das synthetische Ethinylestradiol (EE2) ausgewählt. Da als Haupteintragspfad dieser Substanzen in die Umwelt die Kläranlagen anzunehmen sind, erfolgte die Methodenentwicklung ausgehend von gereinigtem Abwasser. Als Probenvorbereitungstechniken kamen neben der Festphasenextraktion (SPE), die klassische Flüssig-Flüssig-Extraktion (LLE), sowie die relativ neue Methode der Festphasenmikroextraktion (SPME) zum Einsatz. Die analytische Bestimmung der angereicherten Extrakte erfolgte mittels HPLC/UV und HPLC/ELCD bzw. mittels GC/FID und GC/MS. Zur Entwicklung einer Screening-Methode wurde die adsorptive Anreicherung der Estrogene an Kohlenstoffelektroden sowie das Cathodic Stripping von EE2 an Quecksilber erprobt. Die Verfahrensschritte wurden zunächst anhand dotierter Proben optimiert, und die Methoden dann anhand der erzielten Bestimmungsgrenze, Selektivität und Präzision verglichen. Die Eignung der Verfahren wurde abschließend durch die Messung realer Abwasserproben überprüft. / Trace analytical environmental investigations are usually done by solid phase extraction (SPE) and GC/MS. The aim of the present thesis was the development of alternative methods for the trace analysis of estrogens in the environment. Estrone (E1), Estradiol (E2) and Estriol (E3) as well as the synthetic estrogen Ethynylestradiol (EE2) were chosen for this investigation. These estrogens enter the environment mainly via sewage treatment plants. Therefore the method development was launched on purified waste water. Solid phase extraction (SPE), liquid liquid extraction (LLE) and the relatively new solid phase micro extraction (SPME) were used for sample preparation. The analytical determination of the extracted analytes was done by HPLC/UV and HPLC/ELCD or GC/FID and GC/MS. Adsorptive enrichment of estrogens on different carbon electrodes and cathodic stripping of EE2 on mercury were tested as possible screening methods. The established methods were optimized using spiked samples. After comparing their quantitation limits, selectivity and precision, they were applied to real sewage water samples for showing qualification.
40

A trust framework for multi-organization environments / Un système de confiance pour les environnements multi-organisationnels

Toumi, Khalifa 01 April 2014 (has links)
De nos jours, la propagation rapide des technologies de communication, de stockage de données et des web services encouragent les entreprises à collaborer entre elles formant ainsi un environnement multi-organisationnels. Ces entreprises participent à cet environnement afin de profiter des opportunités offertes tels que: (1) la possibilité d'utilisation des ressources et des services externes et professionnels (2) la réduction du temps de production et (3) les bénéfices résultant des effets de synergie. Toutefois, cette collaboration n'est pas parfaite. Des nombreux problèmes peuvent apparaître tels que l'utilisation malveillante des ressources, la divulgation des données ou des services inadéquats. Par conséquent, la sécurité est une préoccupation importante des participants. Les principaux défis de sécurité pour un participant sont la gestion de la confiance et le contrôle d'accès. Dans cette thèse, nous avons abordé en particulier ces deux domaines et nous proposons une nouvelle approche de gestion de la confiance pour les systèmes mutli-organisationnels. Notre approche est divisée en quatre parties. Tout d'abord, nous avons défini un modèle de confiance basé sur la notion des vecteurs. Ces derniers sont composés d'un ensemble de paramètres qui permettent de fournir un degré de confiance sous certaines conditions. Dans notre approche, nous envisageons deux types de vecteurs. D'une part, un vecteur lié à une relation entre un utilisateur et une organisation et d'autre part un vecteur qui relie deux organisations. De plus, nous avons montré comment évaluer et partager ces vecteurs entre les organisations, et comment utiliser les informations évaluées pour améliorer la sécurité. Concernant notre deuxième contribution, nous avons intégré ce nouveau modèle de confiance dans le modèle de contrôle d'accès OrBAC (Organization Based Access Control). Cette intégration a donné naissance à notre modèle TRUST-OrBAC. En outre, nous avons appliqué cette solution à un cas d'étude de collaboration entre des entreprises. Troisièmement, nous avons proposé une nouvelle ontologie de confiance basée sur des concepts de contrôle d'accès. Cette ontologie sera utilisée pour partager les degrés de confiance entre les participants et pour définir l'équivalence entre leurs objectifs. Ainsi, comment définir cette relation de confiance, comment comprendre l'objectif de la confiance d'un demandeur, et comment évaluer la valeur de la recommandation sont toutes des problématiques auxquelles nous avons essayé de répondre dans le cadre de ce travail. Quatrièmement, nous avons amélioré notre travail par la conception d'une approche de test passif afin d'évaluer le comportement d'un utilisateur. Cette contribution a été basée sur l'outil de test MMT (Montimage Monitoring Tool). Finalement, nous avons conçu une architecture sécurisée d'un système distribué en se basant sur nos contributions / The widespread of inexpensive communication technologies, distributed data storage and web services mechanisms currently urge the collaboration among organizations. Partners are participating in this environment motivated by several advantages such as: (1) the ability to use external and professional resources, services and knowledge, (2) the reduction of time-consuming requirements and (3) the benefaction of experts experience. However, this collaboration is not perfect since several problems can arise such as the misuse of resources, disclosure of data or inadequate services. Therefore, security is an important concern of the participants. In particular trust management and access control are one of the major security issues for an organization. This thesis addresses these two areas in particular. It proposes a novel and comprehensive trust framework for Multi-Organization Environments. Our approach is organized in four parts. First, we propose a vector based model approach for defining trust vectors. These vectors evaluate a set of requirements, under conditions, and provide a degree of confidence. In our approach, we consider two different types of vectors. On the one hand, a vector that links a user to an organization and, on the other hand, a vector that links two organizations. We also show how these vectors are evaluated and shared among the different organizations, and how we combine the provided trust information in order to enhance the security. Second, the TRUST-OrBAC model was designed to add the previous trust approach to the ORBAC model. Moreover, this solution was applied with a real collaboration network between companies. Third, we present a trust ontology methodology based on access control concepts. This ontology will be used to share the trust beliefs between participants and to make equivalence between their trust objectives. How to define this trust relationship, how to understand the trust objective of a requester, and how to evaluate the recommendation value is addressed in this thesis. Fourth, we improve our work by designing a passive testing approach in order to evaluate the behavior of a user. This contribution is based on the monitoring tool MMT. Finally the entire architecture of our system is proposed

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