A computational fluid dynamic study on the filtering mechanics in suspension feeding marine invertebrates

Les suspensivores ont la tâche importante de séparer les particules de l'eau. Bien qu'une grande gamme de morphologies existe pour les structures d'alimentation, elles sont pratiquement toutes constituées de rangées de cylindres qui interagissent avec leur environnement fluide. Le mécanisme de capture des particules utilisé dépend des contraintes morphologiques, des besoins énergétiques et des conditions d'écoulement. Comme nos objectifs étaient de comprendre ces relations, nous avons eu recours à des études de comparaison pour interpréter les tendances en nature et pour comprendre les conditions qui provoquent de nouveaux fonctionnements. Nous avons utilisé la dynamique des fluides numérique (computational fluid dynamics, CFD) pour créer des expériences contrôlées et pour simplifier les analyses. Notre première étude démontre que les coûts énergétiques associés au pompage dans les espaces petits sont élevés. De plus, le CFD suggère que les fentes branchiales des ptérobranches sont des structures rudimentaires, d'un ancêtre plus grande. Ce dernier point confirme l'hypothèse qu'un ver se nourrit par filtration tel que l'ancêtre des deuterostomes. Notre deuxième étude détermine la gamme du nombre de Reynolds number critique où la performance d'un filtre de balane change. Quand le Re est très bas, les différences morphologiques n'ont pas un grand effet sur le fonctionnement. Cependant, une pagaie devient une passoire lorsque le Re se trouve entre 1 et 3,5. Le CFD s’est dévoilé être un outil très utile qui a permis d’obtenir des détails sur les microfluides. Ces études montrent comment la morphologie et les dynamiques des fluides interagissent avec la mécanisme de capture ou de structures utilisées, ainsi que comment des petits changements de taille, de forme, ou de vitesse d'écoulement peuvent conduire à un nouveau fonctionnement.

Synthesis of polyelectrolyte brushes on silica-based substrates through surface-initiated polymerization : brush characterization and responsiveness to variation in pH and ionic strength

Les brosses de polyélectrolytes font l’objet d’une attention particulière pour de nombreuses applications car elles présentent la capacité de changer de conformation et, par conséquent, de propriétés de surface en réponse aux conditions environnementales appliquées. Le contrôle des principaux paramètres de ces brosses telles que l'épaisseur, la composition et l'architecture macromoléculaire, est essentiel pour obtenir des polymères greffés bien définis. Ceci est possible avec la Polymérisation Radicalaire par Transfert d’Atomes - Initiée à partir de la Surface (PRTA-IS), qui permet la synthèse de brosses polymériques de manière contrôlée à partir d’une couche d'amorceurs immobilisés de manière covalente sur une surface. Le premier exemple d’une synthèse directe de brosses de poly(acide acrylique) (PAA) par polymérisation radicalaire dans l’eau a été démontré. Par greffage d’un marqueur fluorescent aux brosses de PAA et via l’utilisation de la microscopie de fluorescence par réflexion totale interne, le dégreffage du PAA en temps réel a pu être investigué. Des conditions environnementales de pH ≥ 9,5 en présence de sel, se sont avérées critiques pour la stabilité de la liaison substrat-amorceur, conduisant au dégreffage du polymère. Afin de protéger de l’hydrolyse cette liaison substrat-amorceur sensible et prévenir le dégreffage non souhaité du polymère, un espaceur hydrophobique de polystyrène (PS) a été inséré entre l'amorceur et le bloc de PAA stimuli-répondant. Les brosses de PS-PAA obtenues étaient stables pour des conditions extrêmes de pH et de force ionique. La réponse de ces brosses de copolymère bloc a été étudiée in situ par ellipsométrie, et le changement réversible de conformation collapsée à étirée, induit par les variations de pH a été démontré. De plus, des différences de conformation provenant des interactions du bloc de PAA avec des ions métalliques de valence variable ont été obtenues. Le copolymère bloc étudié semble donc prometteur pour la conception de matériaux répondant rapidement a divers stimuli. Par la suite, il a été démontré qu’un acide phosphonique pouvait être employé en tant qu’ amorceur PRTA-IS comme alternative aux organosilanes. Cet amorceur phosphonate a été greffé pour la première fois avec succès sur des substrats de silice et une PRTA-IS en milieux aqueux a permis la synthèse de brosses de PAA et de poly(sulfopropyl méthacrylate). La résistance accrue à l’hydrolyse de la liaison Sisubstrat-O- Pamorceur a été confirmée pour une large gamme de pH 7,5 à 10,5 et a permis l’étude des propriétés de friction des brosses de PAA sous différentes conditions expérimentales par mesure de forces de surface. Malgré la stabilité des brosses de PAA à haute charge appliquée, les études des propriétés de friction ne révèlent pas de changement significatif du coefficient de friction en fonction du pH et de la force ionique.

Individual and Collective Responsiveness to Climate Change: A Response to Dwyer

Commentaire / Commentary

Metamorphism and Fluid Inclusion Studies of Charnockites and Associated Rocks from the Madurai Granulite Block , Southern India with Special Reference to Graphite Mineralization

The present research is aimed at studying the charnockites and associated rocks of the Madurai Granulite Block (MGB), especially in terms of their field settings, texture, mineralogy, and mineral chemistry analyzing their petrogenesis with the help of thermobarometrical studies and geochronological constraints. The mechanism of charnockitization by the influx of CO2 rich fluids and its relation to the graphite mineralization is actually a matter of discussion and study. The objectives of the present study are, to delineate petrological and structural relationship of charnockites and associated gneissic rocks, to study the field and petrogenetic aspects of graphite mineralization in the MGB, to establish and re-evaluate the P-T conditions of formation of the rocks with the aid of thermbarometric computations and to compare with the earlier studies, characterization of graphite with XRD, Raman spectroscopy and isotope studies together with a search in to its genesis and its relation to the high-grade metamorphism of the terrain, to evaluate the role of CO2 bearing fluids in the processes of charnockitization as well as in the genesis of graphite within the high-grade terrain and to delineate the metamorphic geochronology of selected rocks using ‘monazite dating’ technique with EPMA.

HUMAN PERICARDIAL FLUID AT MICROWAVE FREQUENCIES

This article reports a new method of analyzing pericardial fluid based on the measurement of the dielectric properties at microwave frequencies. The microwave measurements were performed by rectangular cavity perturbation method in the S-band of microwave frequency with the pericardial fluid from healthy persons as well as from patients suffering from pericardial effusion. It is observed that a remarkable change in the dielectric properties of patient samples with the normal healthy samples and these measurements were in good agreement with clinical analysis. This measurement technique and the method of extraction of pericardial fluid are simple. These results give light to an alternative in-vitro method of diagnosing onset pericardial effusion abnormalities using microwaves without surgical procedure.

Studies of stability of fluid flowa using variational methods

The study of stability problems is relevant to the study of structure of a physical system. It 1S particularly important when it is not possible to probe into its interior and obtain information on its structure by a direct method. The thesis states about stability theory that has become of dominant importance in the study of dynamical systems. and has many applications in basic fields like meteorology, oceanography, astrophysics and geophysics- to mention few of them. The definition of stability was found useful 1n many situations, but inadequate in many others so that a host of other important concepts have been introduced in past many years which are more or less related to the first definition and to the common sense meaning of stability. In recent years the theoretical developments in the studies of instabilities and turbulence have been as profound as the developments in experimental methods. The study here Points to a new direction for stability studies based on Lagrangian formulation instead of the Hamiltonian formulation used by other authors.

Fluid mechanics-non-linear waves studies on korteweg-de vries equations

In this thesis the author has presented qualitative studies of certain Kdv equations with variable coefficients. The well-known KdV equation is a model for waves propagating on the surface of shallow water of constant depth. This model is considered as fitting into waves reaching the shore. Renewed attempts have led to the derivation of KdV type equations in which the coefficients are not constants. Johnson's equation is one such equation. The researcher has used this model to study the interaction of waves. It has been found that three-wave interaction is possible, there is transfer of energy between the waves and the energy is not conserved during interaction.

Some conservation laws of fluid mechanics

This thesis contains a study of conservation laws of fluid mechanics. These conservation laws though classical, have been put to extensive studies in t:he past many decades

Model Order Reduction for Determining Bubble Parameters to Attain a Desired Fluid Surface Shape

In this paper, a new methodology for predicting fluid free surface shape using Model Order Reduction (MOR) is presented. Proper Orthogonal Decomposition combined with a linear interpolation procedure for its coefficient is applied to a problem involving bubble dynamics near to a free surface. A model is developed to accurately and efficiently capture the variation of the free surface shape with different bubble parameters. In addition, a systematic approach is developed within the MOR framework to find the best initial locations and pressures for a set of bubbles beneath the quiescent free surface such that the resultant free surface attained is close to a desired shape. Predictions of the free surface in two-dimensions and three-dimensions are presented.

Meaning of the λ parameter of skew–normal and log–skew normal distributions in fluid geochemistry

The literature related to skew–normal distributions has grown rapidly in recent years but at the moment few applications concern the description of natural phenomena with this type of probability models, as well as the interpretation of their parameters. The skew–normal distributions family represents an extension of the normal family to which a parameter (λ) has been added to regulate the skewness. The development of this theoretical field has followed the general tendency in Statistics towards more flexible methods to represent features of the data, as adequately as possible, and to reduce unrealistic assumptions as the normality that underlies most methods of univariate and multivariate analysis. In this paper an investigation on the shape of the frequency distribution of the logratio ln(Cl−/Na+) whose components are related to waters composition for 26 wells, has been performed. Samples have been collected around the active center of Vulcano island (Aeolian archipelago, southern Italy) from 1977 up to now at time intervals of about six months. Data of the logratio have been tentatively modeled by evaluating the performance of the skew–normal model for each well. Values of the λ parameter have been compared by considering temperature and spatial position of the sampling points. Preliminary results indicate that changes in λ values can be related to the nature of environmental processes affecting the data

Thermodynamics and log–contrast analysis in fluid geochemistry

There are two principal chemical concepts that are important for studying the natural environment. The first one is thermodynamics, which describes whether a system is at equilibrium or can spontaneously change by chemical reactions. The second main concept is how fast chemical reactions (kinetics or rate of chemical change) take place whenever they start. In this work we examine a natural system in which both thermodynamics and kinetic factors are important in determining the abundance of NH+4 , NO−2 and NO−3 in superficial waters. Samples were collected in the Arno Basin (Tuscany, Italy), a system in which natural and antrophic effects both contribute to highly modify the chemical composition of water. Thermodynamical modelling based on the reduction-oxidation reactions involving the passage NH+4 -> NO−2 -> NO−3 in equilibrium conditions has allowed to determine the Eh redox potential values able to characterise the state of each sample and, consequently, of the fluid environment from which it was drawn. Just as pH expresses the concentration of H+ in solution, redox potential is used to express the tendency of an environment to receive or supply electrons. In this context, oxic environments, as those of river systems, are said to have a high redox potential because O2 is available as an electron acceptor. Principles of thermodynamics and chemical kinetics allow to obtain a model that often does not completely describe the reality of natural systems. Chemical reactions may indeed fail to achieve equilibrium because the products escape from the site of the rection or because reactions involving the trasformation are very slow, so that non-equilibrium conditions exist for long periods. Moreover, reaction rates can be sensitive to poorly understood catalytic effects or to surface effects, while variables as concentration (a large number of chemical species can coexist and interact concurrently), temperature and pressure can have large gradients in natural systems. By taking into account this, data of 91 water samples have been modelled by using statistical methodologies for compositional data. The application of log–contrast analysis has allowed to obtain statistical parameters to be correlated with the calculated Eh values. In this way, natural conditions in which chemical equilibrium is hypothesised, as well as underlying fast reactions, are compared with those described by a stochastic approach

Short-term storage and mental speed account for the relationship between working memory and fluid intelligence. 'El almacenamiento a corto plazo y la velocidad mental dan cuenta de la relaci??n entre memoria de trabajo e inteligencia fluida'

Resumen tomado de la publicaci??n

Viscous Flow and Fluid Dynamics

Exam questions and solutions for a third year maths course. Diagrams for the questions are all together in the support.zip file, as .eps files