Steady and unsteady shear flows of a viscoplastic fluid in a cylindrical Couette cell

Abstract Yield stress fluid flows in Couette cells have been widely studied in the last decades for their intriguingly exhibiting phenomena. In this paper, we use a {PIV} technique to investigate the axisymmetric flow and rheological properties of a Carbopol gel in a relatively wide cylindrical Couette device. Carbopol gel is known to exhibit viscoplastic behavior and is often described using a Herschel–Bulkley law, which is characterized by a plastic yield stress τ y and a shear-dependent nonlinear viscosity. In some cases, the elasticity of the material has to be accounted for to understand the whole dynamics of the system, in particular for unsteady flows as observed in the present study. Two set of experiments are conducted here in order to highlight these different rheological behaviors and the resulting dynamics: (i) a steady shear configuration and (ii) an unsteady shear configuration, in which the angular velocity of the inner cylinder is either constant or time dependent ( sin profile), respectively. In the steady configuration, a simple optimization model, based on the Herschel–Bulkley law, is developed to extract the rheological parameters of the viscoplastic contribution of the gel from the steady velocity fields. Results are shown to be in good agreements with rheological parameters obtained from a standard rheometer. On the other hand, the elastic contribution of the material is highlighted in the unsteady shear configuration, for which a spatio-temporal transition between solid-elastic and fluid behaviors is observed. Different models are proposed to describe the dynamics of the unsteady flow. First, quasi-steady state models allow to predict both the fluid shear zone close to the inner cylinder and the elastic deformation of the material as long as their contributions can be decoupled in space and in time. For more complex dynamics, i.e. when the flow becomes strongly unsteady, an elasto-viscoplastic model is developed to describe the flow dynamics. It is shown to quantitatively reproduce the experimental measurements. Finally, an elastic wave model is derived to describe an elastic front propagating from the inner cylinder to the outer one, and observed at every half forcing period. The front velocity is thus shown to scale on the phase velocity of an elastic wave in a deformable solid

Photochemical enrichment of deuterium in Titan's atmosphere: new insights from Cassini-Huygens

Cassini-Huygens data are used to re-examine the potential sources of the D/H enhancement over solar, measured in methane, in Titan's atmosphere. Assuming that the system is closed with respect to carbon, the use of constraints from the Huygens probe for the determination of the current mass of atmospheric methane and the most up-to-date determination of D/H from Cassini/CIRS infrared spectra allow us to show that photochemical enrichment of deuterium is not sufficient to be the sole mechanism yielding the measured D/H value. A possible fractionation between CH3D and CH4 during the escape process may slightly enhance the deuterium enrichment, but is not sufficient to explain the observed D/H value over the range of escape values proposed in the literature. Hence, alternative mechanisms such as a primordial deuterium enrichment must be combined with the photochemical enrichment in Titan's atmosphere in order to explain its current D/H value.Comment: 4 pages, 3 figures, accepted in ApJ

Inégalité de patrimoine et progressivité de l'impôt

On se propose d'analyser l'impact de la progressivité de l'impôt sur le revenu et sur les successions sur l'inégalité de patrimoine. Un modèle prenant en compte les principaux motifs d'accumulation permet de reproduire les inégalités de revenu et de patrimoine observées en France. En passant à une proportionnalité de chaque type d'impôt, on révèle que la progressivité de l'impôt sur le revenu permet de réduire davantage l'inégalité de patrimoine. La progressivité de l'impôt sur le revenu réduit le risque de revenu. L'épargne de précaution des plus riches se réduit et l'inégalité de patrimoine diminue. En revanche, la progressivité de l'impôt sur les successions modifie peu le risque de revenu. En outre, la progressivité de l'impôt sur les successions s'avère inefficace pour réduire l'inégalité de revenu à la différence de la progressivité de l'impôt sur le revenu.inégalité de patrimoine ; progressivité de l'impôt ; revenu ; succession

A particle in a wave : a self-study of an evolving consciousness and its concomitant art production, in the context of twentieth century contemporary spirituality.

Thesis (M.A.)-University of Natal, Pietermaritzburg, 2000.In this dissertation the tracing of a personal shift in consciousness is evidenced in my art production and through self-interrogation. Investigations into feminist theology proved resonant with a personal apostasy and provided a base for a feminine identity and language. The schism perpetrated by this pivotal thesis in the revisioning of women, its subsequent antithesis, motivated a search for synthesis. A scientific enlightenment in the field of quantum physics promotes the notion of a unified consciousness. Psychology investigates the realities of mysticism and exposes commonalities within eastern and western religions revealing a thread of unified metaphysical thought. The twentieth century has witnessed a radical in the art expression of the spiritual, some coincident with the revival of an interest in oriental art, and some as a manifestation of zeitgeist or collective consciousness. This past century of rapid technological change, clearly has its attendant spiritual shifting patterns. The process of creativity in art-making has proved to be a conduit for an evolving consciousness

Enhancements of online Bayesian filtering algorithms for efficient monitoring and improved uncertainty quantification in complex nonlinear dynamical systems

Recent years have seen a concurrent development of new sensor technologies and high-fidelity modeling capabilities. At the junction of these two topics lies an interesting opportunity for real-time system monitoring and damage assessment of structures. During monitoring, measurements from a structure are used to learn the parameters and equations characterizing a physics-based model of the system; thus enabling damage identification. Since monitored quantities are physical, these methods offer precious insight into the damage state of the structure (localization, type of damage and its extent). Furthermore, one obtains a model of the structure in its current condition, an essential element in predicting the future behavior of the structure and enabling adequate decision-making procedures. This dissertation focuses more specifically on solving some of the challenges associated with the use of online Bayesian learning algorithms, also called sequential filtering algorithms, for damage detection and characterization in nonlinear structural systems. A major challenge regarding online Bayesian filtering algorithms lies in achieving good accuracy for large dimensional systems and complex nonlinear non-Gaussian systems, where non-Gaussianity can arise for instance in systems which are not globally identifiable. In the first part of this dissertation, we show that one can derive algorithmic enhancements of filtering techniques, mainly based on innovative ways to reduce the dimensionality of the problem at hand, and thus obtain a good trade-off between accuracy and computational complexity of the learning algorithms. For instance, for particle filtering techniques (sampling-based algorithms) subjected to the so-called curse of dimensionality, the concept of Rao-Blackwellisation can be used to greatly reduce the dimension of the sampling space. On the other hand, one can also build upon nonlinear Kalman filtering techniques, which are very computationally efficient, and expand their capabilities to non-Gaussian distributions. Another challenge associated with structural health monitoring is the amount of uncertainties and variabilities inherently present in the system, measurements and/or inputs. The second part of this dissertation aims at demonstrating that online Bayesian filtering algorithms are very well-suited for SHM applications due to their ability to accurately quantify and take into account these uncertainties in the learning process. First, these algorithms are well-suited to address ill-conditioned problems, where not all parameters can be learnt from the available noisy data, a problem which frequently arises when considering large dimensional nonlinear systems. Then, in the case of unknown stochastic inputs, a method is derived to take into account in this sequential filtering framework unmeasured stationary excitations whose spectral properties are known but uncertain

Interaction dust-plasma in Titan's ionosphere: feedbacks on the gas phase composition

Titan's organic aerosols are formed in the ionosphere, a layer ionized by solar VUV photons and energetic particles from the magnetosphere of Saturn, forming a natural N2-CH4-H2 plasma. Previous works showed some chemical evolution processes: VUV photons slightly alter the aerosols nitrile bands, hydrogen atoms tend to hydrogenate their surface and carbon-containing species participate to the growth of the aerosols. This work investigates the effect of the other plasma species, namely the N2-H2 derived ions, radicals and excited states. Industrial plasmas often use N2-H2 discharges to form ammonia-based fertilizers, for metal nitriding, and to erode organic surfaces. Consequently, these are likely to affect Titan's organic aerosols. We therefore developed the THETIS experiment to study the interactions between analogues of Titan's aerosols (tholins) and the erosive N2-H2 plasma species found in Titan's ionosphere. Following a first paper on the evolution of the solid phase by Scanning Electron Microscopy and IR transmission spectroscopy (Chatain et al., Icarus, 2020), this paper focuses on evolution of the gas phase composition, by neutral and ion mass spectrometry. Newly formed HCN, NH3-CN and C2N2 are extracted from the tholins as well as some other carbon-containing species and their derived ions. On the other hand, the production of ammonia strongly decreases, probably because the H, NH and N radicals are rather used for the production of HCN at the surface of tholins. Heterogeneous processes are suggested: chemical processes induced by radicals at the surface would modify and weaken the tholin structure, while ion sputtering would desorb small molecules and highly unsaturated ions. The effect of plasma erosion on aerosols in Titan's ionosphere could therefore lead to the formation of CN bonds in the aerosol structure and the production of HCN or R-CN species in the gas phase.Comment: This paper has been accepted in Icarus (February 2023). The current version in arXiv is the submitted versio

Anti-fracture efficacy of intravenous ibandronate: how to translate epidemiological studies into daily clinical practice

peer reviewedNumerous epidemiological approaches are used to demonstrate the efficacy of a new chemical entity. In postmenopausal osteoporosis, anti-fracture efficacy can be assessed through prospective, randomized controlled trials, meta-analyses or real-life setting studies. Intravenous ibandronate was recently marketed, with the aim of optimizing drug absorption and adherence to treatment. Furthermore, this new formulation avoids gastrointestinal side effects and constrains linked to the oral intake of the medication. Spinal anti-fracture efficacy of IV ibandronate derives from a non-inferiority bridging study, using surrogate endpoints, i.e., bone mineral density and biochemical markers of bone turnover, compared to the oral daily formulation, previously registered for the treatment of osteoporosis in Europe. Coherent results from two separate meta-analyses have suggested that the non-vertebral anti-fracture efficacy of IV ibandronate is similar to that observed with oral, daily and weekly bisphosphonates. Similarly, a recent real-life setting study, based on claims from an US database, suggests that hip fractures are reduced, with IV ibandronate, to the same extend as they are with oral bisphosphonates. Notwithstanding, those results should probably be confirmed in an European setting, before being extrapolated, in daily practice, to the Belgian population

DC/DC converters in normally-ON GaN HEMT technology for the design of RF Power Amplifiers in MMIC technology

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