Antistaling properties of enzymes (xylanase, bacterial maltogenic and conventional a-amylases), CMC and vital wheat gluten on corn tortillas were evaluated during storage for up to 21 days. Effect of storage time (0-21 days) and temperature (-40, -20, 3, 10 and 21 oC) on tortilla staling was evaluated with or without additives. Addition of 275-1650 AU of ICS maltogenic amylase effectively reduced amylopectin retrogradation without reducing tortilla yields, but did not improve tortilla flexibility. The combination of 825 AU of ICS amylase (to interfere with intra-granular amylopectin re-crystallization) and 0.25% CMC (to create a more flexible inter-granular matrix than retrograded amylose) produced less stiff, equally flexible and less chewy tortillas than 0.5% CMC. Corn tortilla staling followed the basic laws that control aging in starch-based semi-crystalline systems such as starch gels, bread and other baked products. Amylopectin re-crystallization was the driving force behind the staling of corn tortillas. Increasing levels of re-crystallized amylopectin measured by DSC correlated significantly with increased tortilla stiffness and reduction in tortilla rollability, pliability and rupture distance during storage. Re-crystallization of amylopectin in fresh tortillas was not detected. It increased rapidly during the first 24 hr reaching a plateau after 7 days storage. The level of amylopectin re-crystallization on tortillas showed a bell-shaped trend along the evaluated storage temperature range with a maximum around 7 oC. However, a negative linear relationship of peak pasting viscosity with storage temperature of tortilla extracts without additives after 21 days suggests other compounds besides amylopectin affect tortilla staling. Thus, interfering with amylopectin re-crystallization is not the only way to retard staling. Further research is required to optimize the addition of maltogenic amylases in continuous processing lines that use fresh masa instead of nixtamalized corn flour, to determine how these amylases interfere with amylopectin re-crystallization and to elucidate if amylose retrogradation continues during storage and plays a role in tortilla staling.

The following research and subsequent study look at identity construction and intergroup differences during computer-mediated communication (CMC) across two platforms with varying degrees of anonymity: Twitter and Yik Yak. A review of research conducted mainly within the framework of the social identity model of deindividuation (SIDE) demonstrates that, counter to popular beliefs heralding the individual freedoms of anonymity, anonymous environments act to strengthen salient social identities and perpetuate group norms. In a medium with such variability and flexibility, drawing comparisons across platforms based solely on content can lead to error. In an attempt to circumvent this difficultly, a linguistics analysis of function words was conducted in each condition. Statistical tests point to changes in usage frequencies of i, impersonal pronouns, you, and they as distinctive between the individuating environment of Twitter and anonymous Yik Yak, while an almost identical underlying proportional framework seen in both platforms brings new context to understanding the role of societal norms in language construction.

In recent years there has been increasing interest in novel forms of surfactants. Of particular interest are gemini surfactants, which consist of two conventional surfactants joined by a spacer at the head groups, as they exhibit lower critical micelle concentrations than can be achieved by conventional surfactants. In this work, the self-assembly behaviour of several nonionic gemini surfactants with polyethylene oxide head groups (GemnEm, where n (= 20) is the number of carbons per tail and m (= 10, 15, 20 and 30) is the number of ethylene oxides per head group) were investigated. The Critical Micelle Concentrations (CMCs) were measured using a fluorescence probe technique. The CMCs are all ~2 x 10?7 M, with almost no variation with m. The CMCs are several orders of magnitude lower than conventional C12Em nonionic surfactants. The mixing behaviour of the gemini surfactants with conventional surfactants was also studied. They obeyed ideal mixing behaviour with both ionic and nonionic surfactants. Micelle morphologies were studied using Small Angle Neutron Scattering. The gemini surfactants with the larger head groups (i.e. Gem20E20 and Gem20E30) formed spherical micelles. Gem20E15 showed strong scattering at low Q, characteristic of elongated micelles. As the temperature was increased towards the cloud point, the scattering approached the Q-1 dependence predicted for infinite, straight rods. The existence of anisotropic micelles was supported by the viscosity of Gem20E15, which increases by several orders of magnitude on heating towards its cloud point. Phase behaviour was determined using Diffusive Interfacial Transport coupled to near-infrared spectroscopy. Much of the behaviour of these systems is similar to conventional nonionic surfactants. For example, Gem20E10 forms a dilute liquid isotropic phase (W) coexisting with a concentrated lamellar phase (La) at around room temperature and forms a sponge phase at higher temperatures. This is similar to the behaviour of C12E3 and C12E4. The other surfactants studied are all quite soluble in water and form liquid isotropic and hexagonal phases from room temperature. At higher concentrations Gem20E15 formed a cubic and then a lamellar phase while Gem20E20 formed a cubic phase and then an intermediate phase. This is also comparable to the phase behaviour of conventional nonionic surfactants except the intermediate phase, which is often only observed for surfactant systems with long alkyl tails.

No description available.

No description available.

No description available.

Ces travaux portent sur le développement d’un matériau virtuel pour la simulation et l’optimisation des matériaux à microstructure hétérogène, en particulier des composites à matrice céramique de nouvelle génération. Pour ce faire une modélisation du fil est mise en place, au travers d’une démarche intégrée qui prend en compte la complexité de la microstructure et de sa variabilité issues du procédé de fabrication. La démarche proposée repose sur deux étapes : i) la construction d’une morphologie synthétique du fil, basée sur l’étude de micrographies et ii) une méthode de simulation multiéchelle inspirée de la méthode des éléments finis généralisée. L’originalité de cette dernière provient de l’utilisation de motifs, sorte de situations physiques ou topologiques élémentaires, pour décrire à la fois la microstructure et la cinématique locale. La démarche est validée et appliquée à diverses sections de fil synthétiques 2D, pour lesquelles le choix des motifs est discuté. L’extension au traitement de tronçon 3D du fil, ainsi qu’à la simulation de la fissuration à l’aide d’une méthode discrète est discutée et des premiers éléments de réponse sont apportés. / The thesis work focus on the development of a virtual material for heterogeneous materials simulation and optimization, especially in the case of now generation of ceramic-matrix composites. To do that, a model at the scale of the yarn is built up, by using an integrated approach that account for the complexity of the microstructure and its variability arising from the manufacturing process. This approach is made of two steps: i) the construction of a synthetic yarn, using micrographics studies and ii) a multiscale approach based on the generalized finites elements method. The originality of that method come from the use of pattern, sort of typical physical or topological situation, that describe both the local structure and kinematic. The approach is validated and applied to various 2D cross-sections of synthetic yarns, for which the choice of patterns is discussed. Extension to 3D section of the yarn, together with the simulation of the fracture in a discrete manner, is discussed and first elements of answer are proposed.

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.

Le carbure de silicium (SiC), grâce à sa légèreté, son caractère réfractaire, sa tolérance à l’oxydation et sa faible absorption des neutrons, constitue un candidat intéressant pour des applications comme l’aéronautique, l’aérospatiale ou le nucléaire du futur. Cependant, son comportement fragile est un inconvénient majeur qu’il convient de dépasser pour ces applications. La réduction de la taille des grains à une échelle nanométrique pourrait contribuer à améliorer son comportement mécanique pour être utilisé sous forme monolithique, en tant que revêtement ou bien encore en tant que matrice dans un compositeCette thèse s’inscrit dans ce contexte, et s’intéresse à l’élaboration et à l’étude des propriétés thermomécaniques de composites à matrice SiC nanostructurée renforcée par des nanotubes de carbone. Dans un premier temps les travaux se sont portés sur l’élaboration et l’étude de l’effet de la nanostructuration de la matrice seule de SiC frittée sans ajout de frittage. Des échantillons nanostructurés (taille moyenne des grains de 100 nm) et denses à plus de 95,5% ont été obtenus grâce à la mise en place d’un procédé de dispersion efficace et à l’étude des effets des paramètres de frittage. Associés à ces hautes densités, de très bonnes duretés (jusqu’à 2200 Hv) et des ténacités convenables (3,0 MPa.m1/2) ont été atteintes. Ces travaux ont également montré l’importance primordiale de l’effet de polluants fréquemment rencontrés dans les poudres (oxygène et carbone) sur la microstructure et les propriétés mécaniques du SiC. Si l’oxygène, présent sous forme de silice ou d’oxycarbure de silicium semble favoriser les mécanismes de densification, un excès de carbone libre (3,5%m) provoque au contraire une diminution de la taille des grains et des densités. Les propriétés mécaniques (950 Hv et 2,4 MPa.m1/2) sont également sensiblement affectées. Une telle dégradation est expliquée par la localisation spécifique du carbone structuré entre les grains de SiC. La deuxième partie des travaux s’est concentrée sur l’ajout de Nanotubes de Carbone (NTC) dans la matrice SiC nanostructurée dans le but d’améliorer les propriétés mécaniques et de compenser la forte réduction de la conductivité thermique, détériorée par l’augmentation importante de la densité de joints de grains. Des crus chargés jusqu’à 5%m en NTC individualisés et répartis de façon homogène ont été réalisés. De manière similaire au carbone libre, la localisation spécifique des NTC cause une diminution de la taille des grains. L’établissement d’un réseau de percolation de NTC au-dessus de 1%m, associé à la méthode de frittage non conventionnel SPS, permet cependant d’améliorer les densités jusqu’à 97%. L’apport de NTC contribue également à l’obtention de dureté (jusqu’à 2550 Hv) et de ténacité (4,0 MPa.m1/2) plus élevées. Malgré les bonnes propriétés thermiques des NTC, l’augmentation de la densité des joints de grains amoindrit la conductivité thermique de nos composites. / Ceramic carbides materials such as SiC, due to their refractory nature and their low neutron absorption are believed to be promising candidates for high temperature nuclear or aerospace applications. However, SiC brittleness has limited its structural application. In this context this work examines in a first part the possibilities to perform dense nanostructured SiC matrix by SPS without the use of sintering additive. Indeed a reduction of grain size (below 100 nm) accompanied by a high final density seem to be the solutions to counteract the brittleness and thus to improve mechanical properties. Dense (95%) and nanostructured (grain size around 100 nm) SiC samples were obtained thanks to the realization of an effective dispersion technique and the study on the sintering parameters effect. High hardness (2200 Hv) and decent fracture toughness (3.0 MPa.m1/2) were achieved. This first work also showed the preponderant influence of recurrent pollutants (oxygen and carbon) found in SiC powders on the final microstructure and mechanical properties of sintered samples. The oxygen as silica or silicon oxycarbide seems to promote densification mechanisms while free carbon (3.5%wt) causes lower grain size and densification state. Mechanical properties with carbon are also negatively impacted (950 Hv and 2.4 MPa.m1/2). Such degradation is due by the specific localization of carbon structure between the grains. In return of the expected mechanical properties improvement by reducing the grain size, the thermal conductivity is drastically decrease of due to the phonon scattering at the grain boundaries. With the aim of reducing this effect, a second study was initiated by introducing multiwalled carbon nanotubes (MWCNTs) into the SiC matrix. The MWCNTs by exhibiting a high toughness could also help to enhance the mechanical properties. Green bodies with different amounts of well dispersed MWCNTs (0%wt to 5%wt) were realized. Like free carbon, MWCNTs are located between the grains and induce a reduction of grain size. However the appearance of CNTs percolation for an amount above 1%wt, with the SPS sintering technique, allows an improvement of densification up to 97%. Hardness (up to 2550 Hv) and fracture toughness (4.0 MPa.m1/2) are also achieved with the SiC/NTC composites. Despite the good thermal properties of MWCNTs, the increase of grain boundary decreases the thermal conductivity of these composites.

In third world countries like Pakistan, companies are growing their trading business with remarkable pace. Increase in business volume has raised the challenges to keep growth sustainable. Communication is one of the biggest challenges for most of small size trading and marketing companies in the region. Face-to-face communication is only type of communication available in companies for inter departmental and intra departmental communication. Although face-to-face is one of the best type of communication but it is not possible to have face-to-face communication all the time with all employees especially when volume of company is growing with remarkable pace. In result company faces challenges like information delay, information lost or communication handicap. These challenges affect efficiency and effectiveness of company. We performed qualitative survey with directors and employees of Abuzar Marketing and Trading Company to develop deep understanding with communication problem to eliminate it. Analyzing empirical data and literature, it is found that Computer Mediated Communication (CMC) provides synchronous and asynchronous types of communication, which could help the company to overcome communication challenges with several other potential benefits e.g. knowledge sharing, employees training, democracy in batter manners.  Since every company in region is facing similar problem, general recommendation and precautions are made to introduce computer mediated communication (CMC).