A novel approach for modeling the non-Newtonian behavior of simple liquids: application to liquid water viscosity from low to high shear rates

The aim of this paper is to present a modeling for the rheological behavior of simple liquids as a function of the amplitude of the imposed shear stress or strain. The elastic mode theory (Ref. 6) is first generalized to take into account the fact that during a flow experiment, mechanical energy is injected in a system initially at thermodynamic equilibrium. This generalized theory can be seen as a particular aspect of the general problem of perturbation by the measurement, associated with that of the coupling between fluctuation and dissipation. This generalization leads to a "finitary" character of the model. It is then combined with the inertial mode theory (Ref. 7). The formalism thus obtained allows to model the rheological behavior of liquids over a wide range of velocity gradients, including the intermediate narrow range corresponding to the Newtonian regime. As experimental tests, viscosity measurements with two kinds of moving rotor rheometers were performed. Only data obtained with liquid water at room temperature are presented and quantitatively analyzed here. It is also shown that liquid n-octane exhibits the same qualitative behaviors as those of liquid water. In the appendices, connection of this theory with quantum mechanics and turbulence phenomena are discussed, and the notion of viscous mass is introduced.Comment: 42 pages, 22 figures, 8 tables, 3 appendice

Selection for Improved Growth and Wood Density in Lodgepole Pine: Effects on Radial Patterns of Wood Variation

Changes in growth and wood density traits were investigated across annual rings of 12-year-old trees from four selected subpopulations in lodgepole pine (Pinus contorta Dougl. Ex Loud var. latifolia Engelm) based on X-ray densitometry profile data. Four subpopulations were constructed based on height growth and wood density as follows: 1) fast growth and high wood density (FH); 2) slow growth and high density (SH); 3) fast growth and low density (FL); and 4) slow growth and low density (SL). Annual ring density was initially high, declined with age until age 10, and then plateaued. Significant differences among subpopulations were found for ring density, earlywood and latewood densities, ring width, earlywood width, latewood proportion, and earlywood width after age 6. Wood density decreased less from the pith to the bark in both overall and earlywood densities in the FH subpopulation, resulting in denser, more homogeneous wood than in other subpopulations. This suggests that it may be possible to increase wood density and homogeneity in juvenile wood of this species by selecting FH families. Overall ring density may be better improved by selecting for earlywood and latewood components separately. The earliest age of which families combining fast growth and high wood density can be accurately identified is about 7 years

OSL-thermochronometry of feldspar from the KTB borehole, Germany

The reconstruction of thermal histories of rocks (thermochronometry) is a fundamental tool both in Earth science and in geological exploration. However, few methods are currently capable of resolving the low-temperature thermal evolution of the upper ∼2 km of the Earth's crust. Here we introduce a new thermochronometer based on the infrared stimulated luminescence (IRSL) from feldspar, and validate the extrapolation of its response to artificial radiation and heat in the laboratory to natural environmental conditions. Specifically, we present a new detailed Na-feldspar IRSL thermochronology from a well-documented thermally-stable crustal environment at the German Continental Deep Drilling Program (KTB). There, the natural luminescence of Na-feldspar extracted from twelve borehole samples (0.1–2.3 km depth, corresponding to 10–70 °C) can be either (i) predicted within uncertainties from the current geothermal gradient, or (ii) inverted into a geothermal palaeogradient of 29±2 °C km−1, integrating natural thermal conditions over the last ∼65 ka. The demonstrated ability to invert a depth–luminescence dataset into a meaningful geothermal palaeogradient opens new venues for reconstructing recent ambient temperatures of the shallow crust (200 °C Ma−1 range). Although Na-feldspar IRSL is prone to field saturation in colder or slower environments, the method's primary relevance appears to be for borehole and tunnel studies, where it may offer remarkably recent (<0.3 Ma) information on the thermal structure and history of hydrothermal fields, nuclear waste repositories and hydrocarbon reservoirs

Production of Superoxide Anions by Keratinocytes Initiates P. acnes-Induced Inflammation of the Skin

Acne vulgaris is a chronic inflammatory disorder of the sebaceous follicles. Propionibacterium acnes (P. acnes), a gram-positive anareobic bacterium, plays a critical role in the development of these inflammatory lesions. This study aimed at determining whether reactive oxygen species (ROS) are produced by keratinocytes upon P. acnes infection, dissecting the mechanism of this production, and investigating how this phenomenon integrates in the general inflammatory response induced by P. acnes. In our hands, ROS, and especially superoxide anions (O2•−), were rapidly produced by keratinocytes upon stimulation by P. acnes surface proteins. In P. acnes-stimulated keratinocytes, O2•− was produced by NAD(P)H oxidase through activation of the scavenger receptor CD36. O2•− was dismuted by superoxide dismutase to form hydrogen peroxide which was further detoxified into water by the GSH/GPx system. In addition, P. acnes-induced O2•− abrogated P. acnes growth and was involved in keratinocyte lysis through the combination of O2•− with nitric oxide to form peroxynitrites. Finally, retinoic acid derivates, the most efficient anti-acneic drugs, prevent O2•− production, IL-8 release and keratinocyte apoptosis, suggesting the relevance of this pathway in humans

Nouveau modèle thermodynamique permettant de prédire la formation, la taille et la mobilité des bulles électroniques et des ions positifs dans toutes les phases de l'helium

Electrons and positive ions are microscopic probes frequently used to explore transport, diffusion and quantum prope rties of liquid helium. Electrons introduced into liquid helium localise and build large cavities with radii up to 20 Å (at 4.2 K and 1 bar), depending on the pressure. The formation of such voids results from the repulsive interaction between ground state helium atoms and electrons because of the Pauli principle and the very long range van der Waals-like attraction. Positive ions in liquid helium behave the opposite way. In this case, electrostrictive forces between the positive charge and the surrounding polarised helium atoms dominate and attract the helium atoms towards the positive centre. As a consequence a dense, solid-like shell of helium is built, which is why the term ’Atkins-snowball’ is often used. Information of the size that electrons and ions occupy in helium is difficult to obtain in a direct fashion. On the contrary, thanks to the charged nature of electrons and ions, the measurement of their mobility is relatively straightforward to measure using electric fields. The mobility is related to a hydrodynamic radius r via the well known Stokes law for spherical objects and the deduction of the radius requires no other knowledge than the viscosity, of the fluid. A number of restrictions nevertheless apply. In particular at low densities where Knudsen number are greater than one the more general Millikan-Cunningham equation must be used instead of Stokes law. Finding a coherent description of ion and electron mobility in different density regions, especially the crossover from gas kinetic to Stokes flow is a challenge. An implicit challenge is that ions and electrons in helium are expected to change their structure depending on the density. We develop thermostatic state equations for electrons and He ions in helium and employ the free volume model to derive the hydrodynamic radius. In general terms, the free volume model relates the size of foreign objects, i.e. solute molecules within a fluid to the size occupied by a free volume unit cell, (V-b)/N, using as the first approximation a simple power law between the two. The state equations of P, V and T include parameters which are calibrated using experimentally determined mobilities reported in the literature. The mobilities, are related to the size via the hydrodynamic radius, in the Stokes-Einstein equation and by introducing the Millikan-Cunningham factor specifically developed for electrons and ions in helium to account for a large density coverage of our thermodynamic approach, including the gas, supercritical, liquid and superfluid phases.Les électrons et les ions positifs sont des sondes microscopiques fréquemment utilisés pour explorer transports, de diffusion et quantique prope les parties prenantes de l'hélium liquide. Les électrons introduits dans l'hélium liquide et localize construire de grandes cavités avec des rayons allant jusqu'à 20 Å (4,2 K et à 1 bar), en fonction de la pression. La formation de ces vides résulte de l'interaction de répulsion entre les atomes d'hélium de l'état du sol et des électrons en raison du principe Pauli et de la très longue portée van der Waals attraction semblable. Les ions positifs dans l'hélium liquide se comportent de la manière opposée. Dans ce cas, les forces électrostrictifs entre la charge positive et les atomes d'hélium polarisés autour dominent et attirent les atomes d'hélium vers le centre positif. Par conséquent, une enveloppe dense, solide comme de l'hélium est construit, ce est pourquoi le terme «Atkins-boule de neige» est souvent utilisé. Information de la taille des électrons et des ions occupent dans l'hélium est difficile d'obtenir de manière directe. Au contraire, grâce à la nature chargée des électrons et des ions, la mesure de leur mobilité est relativement simple pour mesurer l'aide de champs électriques. La mobilité est lié à un rayon hydrodynamique r via la loi de Stokes bien connue pour objets sphériques et la déduction du rayon ne nécessite aucune connaissance autre que la viscosité, du liquide. Un certain nombre de restrictions se appliquent néanmoins. En particulier à de faibles densités où nombre de Knudsen sont plus d'un l'équation Millikan-Cunningham plus générale doit être utilisé à la place de la loi de Stokes. Trouver une description cohérente de l'ion et la mobilité des électrons dans les différentes régions de densité, notamment le croisement de cinétique de gaz à l'écoulement de Stokes est un défi. Un défi implicite est que les ions et les électrons dans l'hélium se attend à changer de structure en fonction de la densité. Nous développons des équations d'état thermostatiques pour les électrons et les ions dans l'hélium Il et employons le modèle de volume libre pour calculer le rayon hydrodynamique. D'une manière générale, le modèle de volume libre concerne la taille des corps étrangers, à savoir des molécules de soluté dans un fluide à la taille occupée par un volume cellulaire libre de l'unité, (Vb) / N, en utilisant en tant que première approximation une loi de puissance simple entre les deux . Les équations d'état de P, V et T comprennent des paramètres qui sont calibrés en utilisant expérimentalement mobilités déterminés rapportés dans la littérature. Les mobilités, sont liées à la taille via le rayon hydrodynamique, dans l'équation de Stokes-Einstein et en introduisant le facteur Millikan-Cunningham spécifiquement développé pour des électrons et des ions dans l'hélium à représenter une couverture de grande densité de notre approche thermodynamique, y compris le gaz , supercritique, phases liquide et superfluides

A thermodynamic model to predict the formation, sizes and mobilities of electron cavities and positively charged "snowballs" in all fluid phases of helium

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MODÉLISATION DES PHÉNOMÈNES INDUITSPAR UNE INJECTION FORTEMENT LOCALISÉED'ÉNERGIE DANS UN LIQUIDE

This work is a fheoretical study of certain predisruptive phenomena in liquids which lead to the formation of a gas bubble. The séries of events experimentally observed to occur when a dielectric liquid is stressed by enough electric field (some kV/cm) is as follows: an électron avalanche occurs in the liquid with the conséquent formation of a cold plasma. This plasma emits light. A shock wave is then seen to form and propagate outwards with a gaseous cavity growing in its wake. This bubble appears for ail values of the applied hydrostatic pressure P„, including those above the critical pressure.In the model developed hère the électron avalanche is replaced by the équivalent electrical energy injected into the System, Wj. Close examination of this non-equilibrium thermodynamic System has lead to the formulation of a new phase transition term separate from the usual latent heat of vaporisation. Assuming Gaussian distributions for both température and pressure within the plasma volume %, expressions are extracted for ail the characteristic parameters of the plasma, the shock wave and the bubble. The model only requires information on the nature of the liquid, the injected energy and the plasma volume.Comparison of the model results with observed values taken from both electrical prebreakdown and laser breakdown experiments shows good agreement. In particular. the dynamic régime of the bubble can be predicted, i.e. with or without rebounds.Ce travail présente une étude théorique des phénomènes prédisruptifs dans les liquides, menant à la formation d'une bulJe de gaz. En effet, lorsqu'un liquide diélectrique est soumis à un champ électrique suffisamment intense (quelques MV/cm), on observe expérimentalement les événements dans l'ordre chronologique suivant: déclenchement d'une avalanche électronique suivi de la formation d'un plasma froid avec émission de lumière, puis émission d'une onde de choc et enfin formation d'une cavité gazeuse; cette bulle est observée quelle que soit la pression hydrostatique P„=, appliquée sur le liquide, P„ étant inférieure ou supérieure à la pression critique.La modélisation que nous avons donc développée consiste à remplacer l'avalanche électronique par une énergie électrique injectée W,. Le bilan d'énergie effectué pour le plasma de volume %, qui est un système thermodynamique hors équilibre, a permis de mettre en évidence un nouveau terme de transition de phase, différent du terme de chaleur latente de vaporisation. En considérant ensuite une distribution gaussienne de pression et de température dans %, on en déduit l'expression de toutes les grandeurs caractéristiques du plasma, de l'onde de choc et de la bulle. Le modèle ainsi développé requiert seulement la connaissance des caractéristiques du liquide, de l'énergie injectée W; et du volume^La confrontation du modèle avec les grandeurs observables dans les expériences de préclaquage électrique et de claquage laser a montré un accord satisfaisant; notamment, on arrive à prévoir le régime dynamique de la bulle (avec ou sans rebonds)

On the basic mechanism of electrocoalescence

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