En mouillage partiel, l'arrière de gouttes glissant sur un plan incliné développe, au-delà d'une vitesse critique, une singularité en coin, arrondie à petite échelle. L'inclinaison ou la courbure de la ligne de contact retardent la transition de mouillage. À plus grande vitesse, un filet liquide dont la largeur croît avec la vitesse des gouttes, se développe et se rompt en déposant des gouttes satellites sur le substrat. Un modèle de lubrification permet de retrouver divers aspects de ces phénomènes : interface conique, retard au démouillage, largeur du ligament...<br /> Une augmentation du débit conduit à un écoulement en filet droit qui se déstabilise au-delà d'un débit seuil pour former des méandres stationnaires. L'équilibre entre inertie, tension de ligne et hystérésis de mouillage rend compte du rayon de courbure des virages, mais également du seuil de méandrage. Les méandres présentent une très forte hystérésis en débit provenant de l'accrochage sur le substrat. L'augmentation de la viscosité induit des changements de comportement : déclenchement non spontané des méandres et croissance de leur amplitude avec la distance à l'injection. Ces méandres avec hystérésis sont comparés à des méandres sans hystérésis, en mouillage total, confinés dans une cellule de Hele-Shaw. Privés d'accrochage sur le substrat, ces derniers sont alors mobiles. Nous avons étudié quelques effets de la physico-chimie sur ces méandres et montré que les surfactants ne sont pas nécessaires au méandrage. L'équilibre entre inertie et capillarité donne le seuil de ces méandres sans hystérésis.

This thesis consists of a summary of two papers dealing with questions related to Legendrian submanifolds of contact manifolds together with exact Lagrangian cobordisms between Legendrian submanifolds. The focus is on studying Legendrian submanifolds from the perspective of their handle decompositions. The techniques used are mainly from Symplectic Field Theory. In Paper I, a series of examples of Legendrian surfaces in standard contact 5-space are studied. For every g &gt; 0, we produce g+1 Legendrian surfaces of genus g, all with g+1 transverse Reeb chords, which lie in distinct Legendrian isotopy classes. For each g, exactly one of the constructed surfaces has a Legendrian contact homology algebra admitting an augmentation. Moreover, it is shown that the same surface is the only one admitting a generating family. Legendrian contact homology with Novikov coefficients is used to classify the different Legendrian surfaces. In particular, we study their augmentation varieties. In Paper II, the effect of a Legendrian ambient surgery on a Legendrian submanifold is studied. Given a Legendrian submanifold together which certain extra data, a Legendrian ambient surgery produces a Legendrian embedding of the manifold obtained by surgery on the original submanifold. The construction also provides an exact Lagrangian handle-attachment cobordism between the two submanifolds. The Legendrian contact homology of the submanifold produced by the Legendrian ambient surgery is then computed in terms of pseudo-holomorphic disks determined by data on the original submanifold. Also, the cobordism map induced by the exact Lagrangian handle attachment is computed. As a consequence, it is shown that a sub-critical standard Lagrangian handle attachment cobordism induces a one-to-one correspondence between the augmentations of the Legendrian contact homology algebras of its two ends.

Rolling contact fatigue is a damage process that may arise in mechanical applications with repeated rolling contacts. Some examples are: gears; cams; bearings; rail/wheel contacts. The resulting damage is often visible with the naked eye as millimeter sized surface craters. The surface craters are here denoted spalls and the gear contact served as a case study. The work focused on the asperity point load mechanism for initiation of spalls. It was found that the stresses at asperity level may be large enough to initiate surface cracking, especially if the complete stress cycle was accounted for. The gear contact is often treated as a cylindrical contact. The thesis contains experimental and numerical results connected to rolling contact fatigue of cylindrical contacts. At the outset a stationary cylindrical contact was studied experimentally. The stationary test procedure was used instead of a rolling contact. In this way the number of contact parameters was minimized. The cylindrical contact resulted in four different contact fatigue cracks. The two cracks that appeared first initiated below the contact. The other two cracks developed at the contact surface when the number of load cycles and the contact load increased. The influence of a surface irregularity (asperity) was studied numerically with the Finite Element Method (FEM). Firstly, the stationary contact was modelled and investigated numerically. At the cylindrical contact boundary a single axisymmetric was included. The partially loaded asperity introduced a tensile surface stress, which seen from the asperity centre was radially directed. Secondly, FE simulations were performed where a single axisymmetric asperity was over-rolled by a cylindrical contact. The simulations were performed for pure rolling and rolling with slip. For both situations, tensile forward directed stresses in front of the asperity were found. The presence of slip and a surface traction greatly increased the stresses in front of the asperity. Finally, when rolling started from rest with applied slip, the distance to steady-state rolling was determined for elastic similar cylindrical rollers. / QC 20100702

An increasing number of mainland Chinese tourists are coming to Taiwan and offer material benefits for many vendors on Taipei's night markets. Using in-depth interviews, this thesis examines the effect of mainland Chinese tourists on attitudes of the night market vendors at Ningxia Night Market in Taipei on China related topics. The difference in economic transactions with Chinese tourists offers a possibility to study the influence of the related rational incentives and contact on policy attitudes and opinions toward: Chinese tourists, cross-Strait economic integration and the alienation from the PRC. Taking into account the variables of business transactions and identity, the study analyzes 22 interviews of night market vendors and suggests that vendors with more business transactions with Chinese tourists tend to have more favorable views on two of the three investigated attitudes. Vendors with more benefits from the increase in tourists also show a considerable amount of pragmatism in their opinions, which leads the study to assume a strong positive influence of economic incentives when compared to another possible factor like contact. While negative effects can be caused by identity, contact and incentives, the positive influence in this framework seems to be mainly affected by the incentives.

No description available.

The contact angle defined by Young's equation depends on the ratio between solid and liquid surface energies. Young's contact angle is constant for a given system, and cannot explain the stability of fluid droplets in capillary tubes. Within this framework, large variations in contact angle and explained aassuming surface roughness, heterogeneity or contamination. This research explores the static and dynamic behavior of fluid droplets within capillary tubes and the variations in contact angle among interacting menisci. Various cases are considered including wetting and non-wetting gluids, droplets in inclined capillary tubes or subjected to a pressure difference, within one-dimensional and three-dimensional capillary systems, and under static or dynamic conditions (either harmonic fluid pressure or tube oscillation). The research approach is based on complementary analytical modeling (total energy formulation) and experimental techniques (microscopic observations). The evolution of meniscus curvatures and droplet displacements are studied in all cases. Analytical and experimental results show that droplets can be stable within capillary tubes even under the influence of an external force, the resulting contact angles are not constant, and bariations from Young's contact angle aare extensively justified as menisci interaction. Menisci introduce stiffness, therefore two immiscible Newtonian fluids behave as a Maxwellian fluid, and droplets can exhibit resonance or relaxation spectral features.

Thin films that are functionally gradient improve the mechanical properties of film-substrate layered materials. Mechanical properties of such materials are found by using indentation tests. In this study, finite element models are developed to simulate the indentation test. The models are based on an axisymmetric half space of a specimen subjected to spherical indentation. The film layer through the thickness is modeled to have either homogeneous material properties or nonhomogeneous material properties that vary linearly. Maximum indenter displacement, and maximum normal and shear stresses at the interface are compared between the homogeneous model and the nonhomogeneous model for pragmatic contact length to film thickness ratios of 0.2 to 0.4, and film to substrate moduli ratios of 1 to 200 to 1. Additionally, a coefficient is derived from regression of the stress data produced by these models and compared to that used to define the pressure field in the axisymmetric Hertzian contact model. The results of this study suggest that a displacement boundary condition to an indenter produces the same results as a pressure distribution boundary condition. The critical normal stresses that occur between modeling a film as a nonhomogeneous and as a homogeneous material vary from 19% for a modulus ratio of 2.5:1 to as high as 66% for a modulus ratio of 200:1 indicating that the modeling techniques produced very different maximum normal stresses. The difference in the maximum shear stress between the nonhomogeneous and the homogeneous models varied from 19% for a 2.5:1 modulus ratio to 57% for the 200:1 modulus ratio but reached values as low as 6% for the 50:1 modulus ratio. The maximum contact depth between the nonhomogeneous and the homogeneous models varied from 14% for the 2.5:1 case to as much as 75% in the 200:1 case. The results from the reapplication of the pressure field derived from the regression coefficients and the R2 values from these regression models indicate the correctness of the regression model used as well as its ability to replicate the normal stresses in the contact area and maximum indenter displacements in a FEA model for both the homogeneous and the nonhomogeneous models for modulus ratios ranging from 2.5:1 to 200:1. The agreement between the regression based coefficients and the force based coefficients suggests the validity for the use of the theoretical axisymmetric Hertzian contact model for defining the pressure field in the contact area and displacements for both the homogeneous case and the nonhomogeneous case for the considered film to substrate moduli ratios and contact length to film thickness ratios.

M. Tech. Pharmaceutical Sciences Tshwane University of Technology 2013. / Aims of the present study was to evaluate the inhibitory activities of essential oils against Fusarium isolates and their corresponding biofilms. In this study, the chemical compositions of the oils were established using gas chromatography with both mass spectrometric and flame ionization detection, for identification and quantification, respectively.

As silicon-based transistor technology continues to scale ever downward, anticipation of the fundamental limitations of ultimately-scaled devices has driven research into alternative device technologies as well as new materials for interconnects and packaging. Additionally, as power dissipation becomes an increasingly important challenge in highly miniaturized devices, both the implementation and verification of high mobility, high thermal conductivity materials, such as low dimensional carbon nanomaterials, and the experimental investigation of heat transfer in the nanoscale regime are requisite to continued progress. This work furthers the current understanding of structure-property relationships in low dimensional carbon nanomaterials, specifically carbon nanotubes (CNTs) and graphene, through use of combined thermal conductance and transmission electron microscopy (TEM) measurements on the same individual nanomaterials suspended between two micro-resistance thermometers. Through the development of a method to measure thermal contact resistance, the intrinsic thermal conductivity, [kappa], of multi-walled (MW) CNTs is found to correlate with TEM observed defect density, linking phonon-defect scattering to the low [kappa] in these chemical vapor deposition (CVD) synthesized nanomaterials. For single- (S) and double- (D) walled (W) CNTs, the [kappa] is found to be limited by thermal contact resistance for the as-grown samples but still four times higher than that for bulk Si. Additionally, through the use of a combined thermal transport-TEM study, the [kappa] of bi-layer graphene is correlated with both crystal structure and surface conditions. Theoretical modeling of the [kappa] temperature dependence allows for the determination that phonon scattering mechanisms in suspended bi-layer graphene with a thin polymeric coating are similar to those for the case of graphene supported on SiO₂. Furthermore, a method is developed to investigate heat transfer through a nanoscale point contact formed between a sharp silicon tip and a silicon substrate in an ultra high vacuum (UHV) atomic force microscope (AFM). A contact mechanics model of the interface, combined with a heat transport model considering solid-solid conduction and near-field thermal radiation leads to the conclusion that the thermal resistance of the nanoscale point contact is dominated by solid-solid conduction. / text

published_or_final_version / Medicine / Master / Doctor of Medicine