Analytical and numerical stability analysis of Soret-driven convection in a horizontal porous layer: the effect of conducting bounding plates

The aim of this study was to investigate the effect of conducting boundaries on the onset of convection in a binary fluid-saturated porous layer. The isotropic saturated porous layer is bounded by two impermeable but thermally conducting plates, subjected to a constant heat flux. These plates have identical conductivity. Moreover, the conductivity of the plates is generally different from the porous layer conductivity. The overall layer is of large extent in both horizontal directions. The problem is governed by seven dimensionless parameters, namely the normalized porosity of the medium ε, the ratio of plates over the porous layer thickness δ and their relative thermal conductivities ratio d, the separation ratio δ, the Lewis number Le and thermal Rayleigh number Ra. In this work, an analytical and numerical stability analysis is performed. The equilibrium solution is found to lose its stability via a stationary bifurcation or a Hopf bifurcation depending on the values of the dimensionless parameters. For the long-wavelength mode, the critical Rayleigh number is obtained as Racs=12(1+2dδ )/[1+ψ (2dδLe+Le+1)] and kcs=0 for ψ> ψ uni> 0. This work extends an earlier paper by Mojtabi and Rees (2011 Int. J. Heat Mass Transfer 54 293-301) who considered a configuration where the porous layer is saturated by a pure fluid

Tracking non-stationary dynamical system phase using multi-map and temporal self-organizing architecture

International audienceThis paper presents a multi-map recurrent neural architecture, exhibiting self-organization to deal with the partial observations of the phase of some dynamical system. The architecture captures the dynamics of the system by building up a representation of its phases, coping with ambiguity when distinct phases provide identical observations. The architecture updates the resulted representation to adapt to changes in its dynamics due to self-organization property. Experiments illustrate the dynamics of the architecture when fulfilling this goal

Discovering the phase of a dynamical system from a stream of partial observations with a multi-map self-organizing architecture

International audienceThis paper presents a self-organizing architecture made of several maps, implementing a recurrent neural network to cope with partial observations of the phase of some dynamical system. The purpose of self-organization is to set up a distributed representation of the actual phase, although the observations received from the system are ambiguous (i.e. the same observation may correspond to distinct phases). The setting up of such a representation is illustrated by experiments, and then the paper concludes on extensions toward adaptive state representations for partially observable Markovian decision processes

Vnode: Low-overhead Transparent Tracing of Node.js-based Microservice Architectures

Tracing serves as a key method for evaluating the performance of microservices-based architectures, which are renowned for their scalability, resource efficiency, and high availability. Despite their advantages, these architectures often pose unique debugging challenges that necessitate trade-offs, including the burden of instrumentation overhead. With Node.js emerging as a leading development environment, recognized for its rapidly growing ecosystem, there is a pressing need for innovative approaches that reduce the telemetry data collection efforts, and the overhead incurred by the environment instrumentation. In response, we introduce a new approach designed for transparent tracing and seamless deployment of microservices in cloud settings. This approach is centered around our newly developed Internal Transparent Tracing and Context Reconstruction (ITTCR) algorithm. ITTCR is adept at correlating internal metrics from various distributed trace files, to reconstruct the intricate execution contexts of microservices operating in a Node.js environment. Our method achieves transparency by directly instrumenting the Node.js virtual machine, enabling the collection and analysis of trace events in a transparent manner. This process facilitates the creation of visualization tools, enhancing the understanding and analysis of microservice performance in cloud environments

Advanced Strategies for Precise and Transparent Debugging of Performance Issues in In-Memory Data Store-Based Microservices

The rise of microservice architectures has revolutionized application design, fostering adaptability and resilience. These architectures facilitate scaling and encourage collaborative efforts among specialized teams, streamlining deployment and maintenance. Critical to this ecosystem is the demand for low latency, prompting the adoption of cloud-based structures and in-memory data storage. This shift optimizes data access times, supplanting direct disk access and driving the adoption of non-relational databases. Despite their benefits, microservice architectures present challenges in system performance and debugging, particularly as complexity grows. Performance issues can readily cascade through components, jeopardizing user satisfaction and service quality. Existing monitoring approaches often require code instrumentation, demanding extensive developer involvement. Recent strategies like proxies and service meshes aim to enhance tracing transparency, but introduce added configuration complexities. Our innovative solution introduces a new framework that transparently integrates heterogeneous microservices, enabling the creation of tailored tools for fine-grained performance debugging, especially for in-memory data store-based microservices. This approach leverages transparent user-level tracing, employing a two-level abstraction analysis model to pinpoint key performance influencers. It harnesses system tracing and advanced analysis to provide visualization tools for identifying intricate performance issues. In a performance-centric landscape, this approach offers a promising solution to ensure peak efficiency and reliability for in-memory data store-based cloud applications

Séparation des constituants d'un fluide binaire remplissant une cavité horizontale soumise à des flux croisés de chaleur

On étudie numériquement et analytiquement l'influence de l'effet Soret sur la séparation des espèces d'un mélange binaire confiné dans une enceinte parallélépipédique horizontale soumise à des flux de chaleur uniformes et croisés. L'écoulement unicellulaire induit par le flux de chaleur latéral peut conduire à une importante séparation des espèces. L'hypothèse d'écoulement parallèle est utilisée pour déterminer la solution analytique associée à l'écoulement de double diffusion unicellulaire. Le problème étudié en plus de l'allongement, dépend de cinq nombres adimensionnels qui sont les nombres de Rayleigh, de Prandtl,le facteur de séparation, le nombre de Lewis et le rapport des densités horizontale et verticale de flux. Les applications numériques choisies correspondent au mélange binaire d'eau (60%) et d'éthanol (40%). Les résultats analytiques sont corroborés par ceux obtenus par des simulations numériques directes

Etude analytique et numérique de la thermodiffusion en fluide binaire en présence de convection mixte

Lorsqu'on soumet une solution initialement homogène, constituée d'au moins deux espèces chimiques, à un gradient thermique, celui-ci engendre un transfert de matière au sein du mélange. Il en résulte la formation d'un gradient de concentration : ce phénomène est appelé thermodiffusion ou effet Soret. La thermodiffusion pure conduit à une très faible séparation des espèces. Le couplage de la thermodiffusion et de la convection naturelle appelée diffusion thermogravitationnelle peut conduire à une séparation des constituants du mélange beaucoup plus importante que celle induite par la thermodiffusion seule. Dans ce mémoire, nous proposons un nouveau dispositif de cellule thermogravitationnelle avec cavité rectangulaire horizontale, de grand rapport d'aspect, remplie d'un fluide binaire. Cette thématique qui consiste à mettre en mouvement, avec une vitesse uniforme la paroi supérieure (ou les parois supérieure et inférieure) de la cavité, permet de disposer de deux paramètres de contrôle que l'on peut faire varier indépendamment l'un de l'autre contrairement à ce qui est fait habituellement dans les colonnes de diffusion thermogravitationnelle où c'est le seul gradient thermique imposé qui induit l'importance de la thermodiffusion et celle du mouvement convectif. Nous avons étudié le problème en considérant deux types de conditions aux limites au niveau des parois horizontales : Températures constante et flux de chaleur constant et uniforme. Le problème considéré dépend de six paramètres adimensionnels, le rapport d'aspect A, le nombre de Lewis Le, le nombre de Prandtl Pr, le facteur de séparation ?, et les deux paramètres de contrôle, à savoir le nombre de Rayleigh thermique et le nombre de Péclet. Nous avons déterminé analytiquement la séparation (la différence des fractions massiques entre les deux extrémités de la cellule) en fonction du nombre de Péclet et du nombre de Rayleigh. Des simulations numériques directes, 2D et 3D, ont montré un très bon accord entre les résultats numériques et analytiques. Nous avons également étudié la stabilité linéaire de l'écoulement monocellulaire permettant d'assurer la séparation des espèces entre les deux extrémités de la cellule. Nous avons montré que le nombre de Rayleigh conduisant à la séparation optimale reste inférieur au nombre du Rayleigh critique conduisant à la perte de stabilité de cette écoulement monocellulaire. L'écoulement monocellulaire perd sa stabilité via une bifurcation de Hopf et donne lieu à un écoulement multicellulaire instationnaire.In the present work, an analytical and numerical study to determine the species separation process in a binary fluid mixture by decoupling the thermal gradient from the convective velocity was performed. The configuration considered is a horizontal rectangular cavity of large aspect ratio, filled with a binary fluid. A constant tangential velocity is applied to the upper horizontal wall only, or to the upper and bottom wall. Species separation is governed by two control parameters, the temperature difference and the velocity of the upper plate. The intensity of the thermodiffusion is controlled by the temperature gradient, while the velocity controls the convective flow. Two types of horizontal wall boundary conditions were investigated: a constant temperature and constant wall heat flux. The governing parameters of the problem are the aspect ratio, A, the Lewis number, Le, the Prandtl number, Pr, the separation ratio, ?, and the tow control parameters: the thermal Rayleigh number, Ra and the Péclet number Pe. The separation (mass fraction difference between the two ends of the cell) is obtained analytically as a function of Péclet number and Rayleigh number. The numerical results, obtained using the full governing equations, are in good agreement with the analytical results based on a parallel flow approximation. linear stability analysis of the unicellular flow is also performed. We have shown that the Rayleigh number leading to optimal separation remains below the critical Rayleigh number leading to the loss of stability of the unicellular flow. The unicellular flow loses its stability via a Hopf bifurcation and gives rise to a multicellular unsteady flow

Primary osteoblast-like cells from patients with end-stage kidney disease reflect gene expression, proliferation, and mineralization characteristics ex vivo.

Osteocytes regulate bone turnover and mineralization in chronic kidney disease. As osteocytes are derived from osteoblasts, alterations in osteoblast function may regulate osteoblast maturation, osteocytic transition, bone turnover, and skeletal mineralization. Thus, primary osteoblast-like cells were cultured from bone chips obtained from 24 pediatric ESKD patients. RNA expression in cultured cells was compared with RNA expression in cells from healthy individuals, to RNA expression in the bone core itself, and to parameters of bone histomorphometry. Proliferation and mineralization rates of patient cells were compared with rates in healthy control cells. Associations were observed between bone osteoid accumulation, as assessed by bone histomorphometry, and bone core RNA expression of osterix, matrix gla protein, parathyroid hormone receptor 1, and RANKL. Gene expression of osteoblast markers was increased in cells from ESKD patients and signaling genes including Cyp24A1, Cyp27B1, VDR, and NHERF1 correlated between cells and bone cores. Cells from patients with high turnover renal osteodystrophy proliferated more rapidly and mineralized more slowly than did cells from healthy controls. Thus, primary osteoblasts obtained from patients with ESKD retain changes in gene expression ex vivo that are also observed in bone core specimens. Evaluation of these cells in vitro may provide further insights into the abnormal bone biology that persists, despite current therapies, in patients with ESKD