Cette thèse s’inscrit dans une volonté d’adapter un procédé hydrothermal au traitement de la surface de fibres céramiques utilisées lors de la fabrication des composites à matrice céramique (CMCs). Le procédé conventionnel développé par la société Safran Ceramics se réalise en plusieurs étapes dont la principale consiste à dissoudre les phases oxydées de la surface des fibres Nicalon dans des bains d’acides. En conséquence, leurs propriétés chimiques de surface sont homogènes et un film de carbone microporeux est généré à la surface des fibres afin d’améliorer sa compatibilité chimique avec l’interphase de pyrocarbone qui y est déposée. Nous avons proposé de substituer ce procédé par un traitement par voie hydrothermale. En effet, l’eau possédant des propriétés physicochimiques ajustables en fonction des paramètres pression et température, il a été possible de modifier les propriétés de surface des fibres Nicalon d’une manière identique être productible au procédé conventionnel. L’efficacité et la compétitivité de ce traitement ont pu être démontrées par l’obtention de fibres avec des propriétés de surface optimales en une seule étape. Par la suite, l’étude du mécanisme réactionnel a révélé une attaque sélective des atomes de Si de la fibre selon des réactions d’hydrolyse. Puis, l’étude thermodynamique réalisée a mis en avant un régime à dominante cinétique. Finalement, les propriétés mécaniques des composites fabriqués à partir de tissus de fibres traités selon ce nouveau procédé ont été conformes aux objectifs. Ceci nous a donc permis de qualifier le traitement des fibres Nicalon par voie hydrothermale. / This thesis project was carried out in order to develop a hydrothermal processfor the surface treatment of ceramic fibres which are integrated into the fabrication of ceramicmatrix composites (CMCs). A conventional process was developed by Safran Ceramics tomodify the surface chemistry of the Nicalon fibres following 3 steps. The main step consistsin dissolving the oxidised phases at the fibre surface by the use of strong acids. As aconsequence, the chemical homogeneity of the surface is enhanced and a microporouscarbon film is generated helping its compatibilization with the pyrocarbon interphase that isdeposited in between the fibres and the matrix. It was suggested to substitute thisconventional process by a hydrothermal treatment. Indeed, as water displays tunablephysico-chemical properties regarding the temperature and pressure conditions, it waspossible to recover fibres demonstrating reproducible and similar characteristics. Theefficiency and competitivity of the hydrothermal treatment have been assessed throughoptimised surface properties obtained after one single step. Next, the mechanisminvestigation revealed a selective attack of the Si atoms contained in the fibre via hydrolysisreactions. Then, the thermodynamic study pointed out the fact that the process wasdominated by a kinetic regim. Finally, the mechanical caracterisation of the CMCs made ofhydrothermal treated fibres showed results which met all the requirements. These finalobservations allowed us to complete the qualification of the hydrothermal process to treat thesurface of Nicalon fibres.

O sucesso da conclusão de um poço por perfuração e o custo do projeto estão relacionados às propriedades dos fluidos de perfuração. O estudo experimental foi realizado a partir da determinação e análise das curvas de tensão de cisalhamento versus taxa de deformação de suspensões aquosas de bentonita e carboximetilcelulose com diferentes concentrações de NaCl. Investigou-se, inicialmente, o comportamento reológico de suspensões de carboximetilcelulose 0,5% (em massa) com concentrações de sal, NaCl de 0 a 4% (em massa), para temperaturas variando de 14 a 26ºC. Os resultados experimentais possibilitam a caracterização reológica destas soluções como fluidos pseudoplásticos e indicam que a adição de NaCl em soluções com CMC alteram significativamente o comportamento reológico desse tipo de solução. Numa segunda etapa, estudou-se o comportamento reológico de suspensões de bentonita e carboximetilcelulose em diferentes concentrações de sal, NaCl. Empregaram-se soluções contendo 4,8 % de bentonita, 0,5 % de carboximetilcelulose e concentrações de 0 a 4% de NaCl. Constata-se o comportamento tixotrópico destas suspensões e a forte dependência com a concentração de sal. O estudo foi complementado com uma análise comparativa dos resultados do comportamento reológico obtidos por reômetro de cilindros coaxiais modelo Brookfield e o viscosímetro FANN 35 A, usualmente empregado na análise de fluidos de perfuração. O equacionamento do escoamento do fluido nos aparelhos permitiu uma interpretação mais detalhada dos valores descritos na norma, obtendo-se uma equivalência dos valores medidos em campo com os obtidos no reômetro Brookfield apesar de as faixas de operação de taxas de deformação serem distintas. / The properties of drilling fluids have a very significant effect on the successful of a well completion and the project costs. The experimental study was conducted based on the determination and analysis of the curves of shear stress and shear rate of aqueous suspensions composed of bentonite and carboxymetil cellulose at different concentrations of NaCl. The rheological behaviour of carboxymetil cellulose suspensions 0.5% w/w at NaCl concentrations in the range of 0 to 4% w/w from 14 to 26°C was studied. The experimental results allow the rheological characterization of these solutions as pseudoplastic fluid. It was observed that the addition of NaCl to CMC solutions changes its rheological behaviour significantly. In addition, the rheological behaviour of 4,8% bentonite suspensions with 0,5% carboxymethyl cellulose at different concentrations of NaCl in the range of 0 to 4% was studied. The characterization of these solutions showed thixotropic behaviour and a strong dependence on the salt concentration. The study was complemented with a comparative analysis of the results obtained by using a coaxial cylinders rheometer model Brookfield and the FANN Model 35 A viscometer, usually employed in drilling fluids analysis. The analytical solutions allowed a more detailed interpretation of the values described in the standard resulting in an equivalence between the measured values obtained in the field and in the Brookfield rheometer despite the differents shear rate ranges.

The present study investigated Computer-Mediated Communication (CMC) as situated phenomenonin Massive Multiplayer Online (MMO) servers. The popular videogame of Minecraft was chosen as a testbed to examine CMC within its simulated environment. Previous research on videogames explored CMC without considering the role of the server. This research suggests that the onlineserver represents an integral part of the digital environment, in which communication is situated. Data were collected from four servers that shared the same game play mode. A total of 11,658 chatmessages were collected and analyzed with Basic Content Analysis based on word frequencies. Codes were developed and sorted into three predetermined categories: socioemotional positive, socioemotional negative and task area. Results showed that communication significantly differed between almost all servers. Furthermore, it also appeared that in three of the four servers, communication varied between the two weeks of recordings. Future research on CMC is encouraged to consider the role of the online servers. The social construct that may be represented by the MMO servers ought to be explored more thoroughly. / I föreliggande studie så undersöks datormedierad kommunikation (CMC) som fenomen baserat iMMO-servrar (Massive Multiplayer Online). Detta utförs genom det populära TV-spelet Minecraft. Tidigare forskning har fokuserat på CMC utan att överväga olika servrar som faktorer. Resultatet av föreliggande studie indikerar att online-servern väsentligen hör ihop med den digitala miljön, där den kontextuella kommunikationen sker. Datainsamling skedde från fyra servrar som har överensstämmande spellägen. Totalt 11 658 chatmeddelanden samlades in samt analyserades genom innehållsanalys vilket baserades på ordfrekvens. Koder utvecklades och sorterades i tre förutbestämda kategorier: socioemotionell positiv, socioemotionell negativ och ”task area”. Resultatet indikerar att kommunikationen skiljde sig signifikant mellan servrar. Dessutom såvarierade kommunikationen mellan de två veckorna av insamlade data på tre av fyra servrar. Framtida forskning rörande CMC bör vidare överväga serverns roll. Därutöver bör det sociala konstrukt som framkommit ur MMO-servrar vidare utforskas.

Social networking includes social networking sites (SNSs) as well as apps. The purpose of this thesis was to investigate the impact of social networking tech-nology on students.  The  research questions  focused  how university students experience  their  interaction  with  social  networking  regarding  advantages and disadvantages, and for what purposes they are using it personal, professional or study). A quantitative surveys study was used and data was collected through online questionnaires delivered via SNSs, e-mails and through delivery and col-lection  method. 122  valid  responses  were collected  and 17 invalid responses were discarded. The questionnaire framework was built by means of the con-cept of ease of use from Technology Acceptance Model (TAM) and the five values of Uses and Gratification Theory; “purposive value”, “self-discovery”, “maintaining interpersonal interconnectivity”, “social enhancement value” and “entertainment value”. The findings showed that 64% considered themselves to be positively influenced by SNSs and 27% to be neither positively or nega-tively influenced. Only 11 % considered that SNSs influenced them negatively. According to our findings, some of the most frequent advantages are keeping in touch with family and friends, cost and time efficient, easy to use and entertaining. And for the disadvantages, the responses were mostly time consuming, health  issues,  privacy  issues,  addiction  to  technology  and  cyber  bulling.  The majority of respondents reported using SNS firstly for personal use, secondly for study use and the professional use was the least selected. 88% of the respondents thought that it is easy to use SNSs. The purposive value of SNS use was to get information, the self-discovery value to learning about oneself and others, for the maintaining interpersonal connectivity, to stay in touch, and for the entertainment value, it was to pass time away when bored. The results indicated  that  the  social  enhancement  value  was  not  very  important  for  the  respondents.

This dissertation examines the “buffer effect,” an important but understudied feature of computer-mediated communication (CMC). Research on the buffer effect posits that CMC venues provide a buffering “screen” that users can literally and figuratively hide behind. The buffer can make people feel more comfortable during interactions, and is theorized to be especially relevant in contexts where self-presentation is threatened. This study employs transgressions as ideal sites for examining the buffer effect because of the high level of threatened self-presentation involved therein. The current project tests whether people perceive different levels of a buffer in different channels of communication, and how the buffer effect is related to other widely studied features of CMC, such as interactivity, synchronicity, and social presence. It also tests outcomes of the buffer effect for both senders and receivers of transgressive messages. Specifically, it posits that the buffer effect is beneficial to senders of transgressive messages, and is detrimental to receivers of those messages. Furthermore, in the context of transgressions, the amount of responsibility that a person takes for the transgression is a factor that influences how others perceive the situation. Therefore, the current study also considers receivers' perceptions of the level of responsibility the sender accepts, and specifically posits that senders' higher levels of responsibility are associated with positive outcomes for receivers. The dissertation is comprised of two studies. In Study One, participants responded to a survey to test their perceptions of the buffer effect and of other features of CMC in various channels. Participants also responded to a hypothetical situation to indicate how the buffer effect influences outcomes when sending a transgressive message. Study Two employed an experimental procedure to test how senders and receivers perceive the buffer effect in actual interactions, as well as how senders' acceptance of responsibility affects outcomes for receivers. Half of the participants were assigned the role of sender and were trained to provide a transgressive message to the receiver. Specifically, senders were trained to say that they had to leave the experiment early without completing the study, rendering the receiver ineligible for course credit. Both the channel (i.e., face-to-face, instant messaging, text messaging) and the senders' level of responsibility (i.e., low/high) were manipulated. Results suggested that the buffer effect manifests in different levels for various channels of communication, such that face-to-face environments provide the lowest buffer, followed by video chat, social networking sites, instant messaging, and email. Text messaging provides the highest buffer. The buffer effect is negatively related to other features of CMC (i.e., synchronicity, interactivity, and social presence) for low-buffer channels, and is either positively or not significantly related to these features in high-buffer channels. Results also suggest that the buffer effect is associated with benefits for senders in both hypothetical and actual interactions, but does not affect receivers' outcomes. Receivers' perceptions of the level of responsibility that senders accept affects receivers' outcomes, but only within environments with a low and moderate buffer. These results extend research on CMC and on transgressive communication. Results also offer practical implications for how people might elect to use channels and modify the content of their message when communicating a transgression to a friend.

This dissertation examines the “buffer effect,” an important but understudied feature of computer-mediated communication (CMC). Research on the buffer effect posits that CMC venues provide a buffering “screen” that users can literally and figuratively hide behind. The buffer can make people feel more comfortable during interactions, and is theorized to be especially relevant in contexts where self-presentation is threatened. This study employs transgressions as ideal sites for examining the buffer effect because of the high level of threatened self-presentation involved therein. The current project tests whether people perceive different levels of a buffer in different channels of communication, and how the buffer effect is related to other widely studied features of CMC, such as interactivity, synchronicity, and social presence. It also tests outcomes of the buffer effect for both senders and receivers of transgressive messages. Specifically, it posits that the buffer effect is beneficial to senders of transgressive messages, and is detrimental to receivers of those messages. Furthermore, in the context of transgressions, the amount of responsibility that a person takes for the transgression is a factor that influences how others perceive the situation. Therefore, the current study also considers receivers' perceptions of the level of responsibility the sender accepts, and specifically posits that senders' higher levels of responsibility are associated with positive outcomes for receivers. The dissertation is comprised of two studies. In Study One, participants responded to a survey to test their perceptions of the buffer effect and of other features of CMC in various channels. Participants also responded to a hypothetical situation to indicate how the buffer effect influences outcomes when sending a transgressive message. Study Two employed an experimental procedure to test how senders and receivers perceive the buffer effect in actual interactions, as well as how senders' acceptance of responsibility affects outcomes for receivers. Half of the participants were assigned the role of sender and were trained to provide a transgressive message to the receiver. Specifically, senders were trained to say that they had to leave the experiment early without completing the study, rendering the receiver ineligible for course credit. Both the channel (i.e., face-to-face, instant messaging, text messaging) and the senders' level of responsibility (i.e., low/high) were manipulated. Results suggested that the buffer effect manifests in different levels for various channels of communication, such that face-to-face environments provide the lowest buffer, followed by video chat, social networking sites, instant messaging, and email. Text messaging provides the highest buffer. The buffer effect is negatively related to other features of CMC (i.e., synchronicity, interactivity, and social presence) for low-buffer channels, and is either positively or not significantly related to these features in high-buffer channels. Results also suggest that the buffer effect is associated with benefits for senders in both hypothetical and actual interactions, but does not affect receivers' outcomes. Receivers' perceptions of the level of responsibility that senders accept affects receivers' outcomes, but only within environments with a low and moderate buffer. These results extend research on CMC and on transgressive communication. Results also offer practical implications for how people might elect to use channels and modify the content of their message when communicating a transgression to a friend.

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Abstract This study in second language acquisition (SLA) investigates the influence of self-portrayal of language learners in an interactive online L2 learning environment from a social-interactionist research perspective. This thesis has a mainly theoretical focus and will integrate concepts of online communication with SLA methodology. This work reviews some classical perspectives on chats and message boards as environment for online communication in chapter two and develops a list of features to classify them from a second language acquisition perspective. In order to assist the main argument of the thesis that an integrated view of learners within a learning context is necessary to fully use the advantages of an interactive online learning environment, the second language acquisition model of Marysia Johnson (2004) is discussed in chapter three. Using the premises of the model, which result from the application of Lev Vygotskys sociocultural theory and Mikhail Bakhtins dialogized heteroglossia, key features for the later data analysis are pointed out. Those are the dismissal of the separation of language competence and language performance, a view of language that exceeds mere morphosyntactical concerns and the overcoming of the mainstream mentalist SLA approach in favor of a socioculturally oriented dialogical language learning model. The approach of Bonny Norton (2000) to identity is used as an analytical framework to complete Johnsons model developing a methodology for chapter four. The data analysis in chapter five is used to prove the validity of the model in showing that the developed model is applicable for the analysis of an online context. After a description of the course environment and a preliminary analysis, an in depth qualitative approach is used to point out the links between sociocultural theory and identity theory. Afterwards, I will give a short summary of my most important results and finish my thesis with some suggestions for further research.

Organizational support for cooperative work has been shifted from using Face-to-Face (FTF) communication in collocated groups to using Communication-Mediated-Communication (CMC) in dispersed groups. This new and growing form of communication has stimulated scholars to study the differences of group performance between FTF and CMC. Task categorization has been the methodology chosen for several empirical research studies. These studies conclude that the effectiveness of a communication medium for a given task depends on the degree to which there is a fit between the richness of information that can be transmitted via a system’s technology and the information richness requirements of that task. However, there are numerous problems associated with using task categorization in such studies. One of these limitations is that categorization forces the researcher to enclose a task situation into a general predetermined category that may not describe the real nature of the activity. For instance, task categorization does not capture the dynamic interaction of groups performing tasks that involve variation. This thesis discusses the weakness and limitations of this approach and, using conclusions drawn from experimental results, propose the adoption of a more systematic approach based on the concept of Ashby’s law of requisite variety. Findings on the differences in performance of FTF groups versus CMC groups of 39 three-person groups of engineering undergraduate students revealed that the group performance was not affected by the communication medium but rather by variation in the task (low and high complexity).

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