Investigations on composition and morphology of electrochemical conversion layer/titanium dioxide deposit on stainless steel

In this study, the formation and characterization of conversion coatings modified by a sol-gel TiO2 deposit were investigated as a way to develop a new photocatalyst for water and air depollution. The conversion coating, characterised by strong interfacial adhesion, high roughness and high surface area facilitates the sol-gel deposition of titania and enhances its adhesion to the substrate. The conversion treatment is carried out in an acid solution. Observation by Scanning Electron Microscopy (SEM) reveals a rough surface with pores and cavities. According to SIMS measurements, the thickness of the initial conversion layer is evaluated at about 1.5 μm. On this pre-functionalised support, the titanium dioxide was deposited by the sol-gel method. The roughness measurements coupled with SIMS analysis allowed a precise evaluation of the surface state of the final layers. The coating consists of two layers: a TiO2 outer layer and an inner layer containing iron chromium oxides. Characterization by X-ray diffraction (XRD) showed the existence of the TiO2 anatase structure as the main compound

An efficient protection of stainless steel against corrosion: Combination of a conversion layer and titanium dioxide deposit

In the present work, a novel process has been developed to improve the corrosion properties of ferritic stainless steels. Titanium oxide coatings have been deposited onto stainless steel by sol–gel process after a pre-functionalization of the substrate in a conversion bath. Gel titania was prepared by hydrolysis of a titanium butoxide through a sol–gel process. Duplex systems "conversion layer/uniform TiO2 coating" have been prepared on stainless steels using a dipping technique and thermal post-treatments at 450 °C. The preparation of sol–gel coatings with specific chemical functions offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The morphology and structure of the coatings were analysed using scanning electron microscopy with field effect gun (SEM-FEG), Mass spectroscopy of secondary ions (SIMS) and X-ray diffraction (XRD). The anticorrosion performances and the ageing effects of the coatings have been evaluated in neutral and aggressive media by using several normalized tests. The results show that the conversion layer was not sufficient to protect steel but sol–gel TiO2 coatings, anchored on the metal substrate via the conversion layer, show good adhesion with the substrate and act as a very efficient protective barrier against corrosion. So, duplex layers with TiO2 nanoparticle coatings on steels exhibit an excellent corrosion resistance due to a ceramic protective barrier on metal surface. Analysis of the data indicates that the films act as geometric blocking layers against exposure to the corrosive media and increase drastically the lifetime of the substrate

Multinational firms in (global) cities: mimicry, knowledge networks, and economic growth

This dissertation examines the dynamic interrelationship between MNEs and cities. First, it examines cities as MNEs’ foreign direct investment location choice and imitation processes within these FDI location choices. Imitation not only enhances the attractiveness of the city by contributing to the generation of agglomeration economies and by encouraging additional imitation, but it also contributes to the further development of the international connectivity of the city and the creation of global knowledge networks. Second, this dissertation introduces a new measure of international connectivity of cities in terms of collaboration on innovation. In addition, it elaborates on the interrelated roles of different types of international connectivity on city economic growth and the influence of this connectivity on the surrounding areas of the city. The dissertation has four contributing chapters, in addition to an introduction (Chapter 1) and general conclusion (Chapter 6). Chapter 2 examines the role of domestic cultural characteristics and investor heterogeneity in shaping imitation of foreign direct investment location choices by MNEs. While existing research has indicated that firms may imitate their peers in order to gain legitimacy among stakeholders, a national cultural dimension has rarely been included. The chapter argues that imitation processes depend on the presence of three cultural traits of home countries, i.e. collectivism, power distance and uncertainty avoidance, which can jointly act as domestic conformity forces strengthening the incentive to imitate. This influence is most salient in particular for firms that lack substantial domestic legitimacy and those that have limited multinational operations. The empirical findings, using a conditional logit model on a sample of 1050 greenfield manufacturing investments in the United States by 662 firms based in 35 different home countries, confirm that the tendency to engage in imitation is stronger for firms based in home countries characterized by greater collectivism and overall national conformity forces. Furthermore, the empirical findings conclude that less legitimate firms and firms with limited multinational operations are significantly responsive to two domestic cultural traits, i.e. collectivism and power distance. This may imply that targeted policies in attracting FDI from countries with such domestic conformity forces may prove to be more effective by follow up investments, yet it will attract in particular smaller and younger firms and firms with limited multinational operations. Chapter 3 puts forward a new measurement of international connectivity of global cities focusing on collaborations in innovation, by drawing on a novel and extensive database of geocoded patent inventor addresses. While existing research has mainly measured international connectivity by the worldwide office networks of advanced producer services firms (e.g. consulting, accounting and insurance firms) in cities, a more inclusive understanding of city connectivity remains absent. Hence, this chapter looks at international connectivity based on another central function of global cities, i.e. their role as prominent spaces for knowledge exchange and collaboration on innovation. The findings of this chapter, focusing on the 125 cities in 46 countries, confirm the role of global cities as prominent places for knowledge exchange and collaboration of innovation and the growing importance of international collaboration for innovation. Chapter 4 compares the new measure of connectivity based on innovation collaboration to the traditional indicator on advanced producer services for 129 cities in 76 countries. The findings suggest broadly similar trends, but also highlight some important differences suggesting specialization advantages of a strong position in one of the two networks. When analyzing the simultaneous and interrelated influences of the knowledge network and the advanced producer services network of cities on their economic growth using a fixed effects panel regression, the findings suggest that both aspects of cities’ international connectivity may allow their economies to grow, but that they reduce each other’s association with city economic growth. This suggest that specialization in one type of network and connectivity and building on existing strengths may be more beneficial. Chapter 5 analyses the influence of global city international connectivity on collaborative linkages of the city with the surrounding area of these global cities. It argues that the international connectivity may render global cities less likely to establish intensive local innovation linkages with surrounding areas, but that the nature of this relationship may depend on the characteristics of the global city and their surroundings. More specifically, we argue that global linkages are more detrimental to the establishment of local linkages if the global city is a technology leader, but less so if the surrounding area has a greater absorptive capacity and features a smaller travel distance to the global city. The findings, based on the collaborative linkages of 21 US global cities and 614 surrounding counties using a fixed effects Poisson regression model, provide clear indications of international connectedness being associated with local disconnectedness. However, it also suggests that the relationship between global city international connectivity and their local linkages depends on the characteristics of both the global city and their surrounding area. This illustrates that knowledge exchange does not always cause an equal spread of opportunities across geographies and calls for innovation policies focusing on improving the knowledge convergence between the surrounding areas and cities.

Bubble Formation in Yield Stress Fluids Using Flow-Focusing and T-Junction Devices

International audienceWe study the production of bubbles inside yield stress fluids (YSFs) in axisymmetric T-junction and flow-focusing devices. Taking advantage of yield stress over capillary stress, we exhibit a robust break-up mechanism reminiscent of the geometrical operating regime in 2D flow-focusing devices for Newtonian fluids. We report that when the gas is pressure driven, the dynamics is unsteady due to hydrodynamic feedback and YSF deposition on the walls of the channels. However, the present study also identifies pathways for potential steady-state production of bubbly YSFs at large scale

On the stability of the production of bubbles in yield-stress fluid using flow-focusing and T-junction devices

International audienceWe investigate experimentally the stability of bubble production in yield-stress fluids (YSF) and highly viscous silicone oil, using flow-focusing and T-junction devices. When the exit channel is initially pre-filled with the fluid and the gas is pressure-driven, the production is highly unstable, despite a regular frequency of bubble production in the junction. As observed for pressure-driven bubble trains in Newtonian fluids, we report that two mechanisms can explain these observations : (i) drastic reduction of the hydrodynamic pressure drop along the channel during the transient bubble production, which induces a rapid increase of the gas flow rate and (ii) thin film deposition resulting in a cascade of plug break-up and bubbles coalescence. While the drastic reduction of the pressure drop is inevitable in such two-phase flows, we show that modifying the surfaces of the channel can help stabilizing the system when the continuous phase is a YSF. To do so, we measure the thickness of the film deposited on the channel wall for rough and smooth channels. Our results are rationalized by introducing the inverse of the Bingham number Bi −1 comparing the viscous stress to the yield stress. For Bi −1 ≥ 1, a fast fluidization process associated to efficient deposition of YSF on the channel wall leads to a rapid destabilization of the bubble production. However, for Bi −1 < 1, the deposition driven by capillarity can be hindered by the wall-slip induced by the existence of the yield stress: the thickness of the deposited film is very thin and corresponds to the equivalent roughness of the channels. It is typically 40 µm thick for rough surfaces and below the limit of resolution of our setup for smooth surfaces. In this regime of Bi −1 and for smooth surfaces, the length of the plugs barely vanishes, thus the start-up flow is less prone to destabilization. These results therefore potentially open routes to steady production of aerated YSF on smooth channels in the regime of small Bi −1

How coatings with hydrophobic particles may change the drying of water droplets: incompressible surface versus porous media effects

International audienceThere is no clear statement on the role of particles in the drying of liquid marbles, which are liquid drops coated with hydrophobic solid particles. While some works report a similar drying time for liquid marbles and bare water drops others observe a faster evaporation of either liquid marbles or of bare water drops. To provide insight into the subject, we report water drying experiments in different configurations. We first focus on the drying of flat water surfaces coated with a single or several layers of hydrophobic micronic particles. Quite surprisingly, surfaces coated with a single layer of densely packed particles dry at the same speed as the bare surfaces. However, when coated with several layers of particles, the drying rate per unit surface area is significantly diminished. This effect is quantitatively explained by considering vapor diffusion through the porous media formed by the stacking of micronic particles above the interface. Then, we consider the drying of curved interfaces which are liquid marbles, i.e. drops coated with one monolayer of micronic particles. Those systematically dry faster than pure drops of the same initial volume. As the presence of a single layer of particles does not significantly affect the drying rate, this "speed-up" effect is attributed to the conservation of the surface area of the coated drop during the drying. Our quantitative experiments and understanding of the drying of liquid marbles therefore support the different results found in the literature: liquid marbles coated with one monolayer of fine solid particles do dry faster than water drops, while those coated with several layers - that may be formed by aggregates of nanoparticles - experience slower drying

Increased Levels of Circulating IL-16 and Apoptosis Markers Are Related to the Activity of Whipple's Disease

BACKGROUND: Whipple's disease (WD) is an infectious disease caused by Tropheryma whipplei, which replicates in macrophages and induces the release of interleukin (IL)-16, a substrate of caspase 3, and macrophage apoptosis. The disease is characterized by intestinal, cardiac or neurological manifestations; its diagnosis is based on invasive analysis requiring tissue biopsies or cerebrospinal fluid puncture. The disease progression is slow and often complicated by relapses despite empirical antibiotic treatment. METHODOLOGY/PRINCIPAL FINDINGS: We monitored circulating levels of IL-16 and nucleosomes in 36 French patients with WD; among them, some patients were enrolled in a longitudinal follow-up. As compared to control subjects, the circulating levels of both IL-16 and nucleosomes were increased in untreated patients with WD presenting as intestinal, cardiac or neurological manifestations. This finding was specific to WD since the circulating levels of IL-16 and nucleosomes were not increased in patients with unrelated inflammatory diseases such as inflammatory bowel disease or Q fever endocarditis. We also found that increased levels of IL-16 and nucleosomes were related to the activity of the disease. Indeed, successful antibiotic treatment decreased those levels down to those of control subjects. In contrast, patients who suffered from relapses exhibited circulating levels of IL-16 and nucleosomes as high as those of untreated patients. CONCLUSIONS/SIGNIFICANCE: Circulating levels of both IL-16 and nucleosomes were increased in WD. This finding provides simple and non-invasive tools for the diagnosis and the prognosis of WD