Simulation and analysis of solute transport in 2D fracture/pipe networks: The SOLFRAC program

International audienceThe Time Domain Random Walk (TDRW) method has been recently developed by Delay and Bodin (2001) and Bodin et al. (2003c) for simulating solute transport in discrete fracture networks. It is assumed that the fracture network can reasonably be represented by a network of interconnected one-dimensional pipes (i.e. flow channels). Processes accounted for are: (1) advection and hydrodynamic dispersion in the channels, (2) matrix diffusion, (3) diffusion into stagnant zones within the fracture planes, (4) sorption reactions onto the fracture walls and in the matrix, (5) linear decay, and (6) mass sharing at fracture intersections. The TDRW method is handy and very efficient in terms of computation costs since it allows for the one-step calculation of the particle residence time in each bond of the network. This method has been programmed in C++, and efforts have been made to develop an efficient and user-friendly software, called SOLFRAC. This program is freely downloadable at the URL http://labo.univ-poitiers.fr/hydrasa/intranet/telechargement.htm. It calculates solute transport into 2D pipe networks, while considering different types of injections and different concepts of local dispersion within each flow channel. Post-simulation analyses are also available, such as the mean velocity or the macroscopic dispersion at the scale of the entire network. The program may be used to evaluate how a given transport mechanism influences the macroscopic transport behaviour of fracture networks. It may also be used, as is the case, e.g., with analytical solutions, to interpret laboratory or field tracer test experiments performed in single fractures

Differential expression of a BMP4 reporter allele in anterior fungiform versus posterior circumvallate taste buds of mice

<p>Abstract</p> <p>Background</p> <p>Bone Morphogenetic Protein 4 (BMP4) is a diffusible factor which regulates embryonic taste organ development. However, the role of BMP4 in taste buds of adult mice is unknown. We utilized transgenic mice with LacZ under the control of the BMP4 promoter to reveal the expression of BMP4 in the tongues of adult mice. Further we evaluate the pattern of BMP4 expression with that of markers of specific taste bud cell types and cell proliferation to define and compare the cell populations expressing BMP4 in anterior (fungiform papillae) and posterior (circumvallate papilla) tongue.</p> <p>Results</p> <p>BMP4 is expressed in adult fungiform and circumvallate papillae, i.e., lingual structures composed of non-taste epithelium and taste buds. Unexpectedly, we find both differences and similarities with respect to expression of BMP4-driven ß-galactosidase. In circumvallate papillae, many fusiform cells within taste buds are BMP4-ß-gal positive. Further, a low percentage of BMP4-expressing cells within circumvallate taste buds is immunopositive for markers of each of the three differentiated taste cell types (I, II and III). BMP4-positive intragemmal cells also expressed a putative marker of immature taste cells, Sox2, and consistent with this finding, intragemmal cells expressed BMP4-ß-gal within 24 hours after their final mitosis, as determined by BrdU birthdating. By contrast, in fungiform papillae, BMP4-ß-gal positive cells are never encountered within taste buds. However, in both circumvallate and fungiform papillae, BMP4-ß-gal expressing cells are located in the perigemmal region, comprising basal and edge epithelial cells adjacent to taste buds proper. This region houses the proliferative cell population that gives rise to adult taste cells. However, perigemmal BMP4-ß-gal cells appear mitotically silent in both fungiform and circumvallate taste papillae, as we do not find evidence of their active proliferation using cell cycle immunomarkers and BrdU birthdating.</p> <p>Conclusion</p> <p>Our data suggest that intragemmal BMP4-ß-gal cells in circumvallate papillae are immature taste cells which eventually differentiate into each of the 3 taste cell types, whereas perigemmal BMP4-ß-gal cells in both circumvallate and fungiform papillae may be slow cycling stem cells, or belong to the stem cell niche to regulate taste cell renewal from the proliferative cell population.</p

The Early Phases of Ankylosing Spondylitis: Emerging Insights From Clinical and Basic Science

In our paper, we discuss how the early phases of ankylosing spondylitis (AS) are linked to peri-firbocartilagenous osteitis in the sacroiliac joint and entheseal bone related anchoring sites. This skeletal proclivity is linked to an abnormal immunological response to skeletal biomechanical stress and associated microdamage. A key event in the early stages of AS appears to be the association with subclinical Crohn's-like colitis with this gut inflammation being pivotal to the osteitis reaction. Whether this osteitis is consequent to non-specific intestinal innate immune activation or adaptive immune responses against specific microbiotal or self-antigens is unknown. Recurrent iritis is an HLA-B27 associated feature that may predate AS and pursues a course independent of joint involvement, and points toward the pivotal role of organ specific immunology over generalized systemic immune responses in disease expression. Human genetics and animal model studies strongly incriminate the IL23/17 axis and TNF-α in disease pathogenesis. Preliminary work shows a strong convergence of innate immune cells including type 3 innate lymphoid-cells (ILC3) and γδ T-cells in skin, gut, entheseal, and eye inflammation. Despite the HLA-B27 association, the role of adaptive immunity, especially CD8+ T-cells mediated responses remains unproven and alternative theories have been proposed. The emerging non-dependence of axial inflammation on IL-23 but dependence on IL-17A is an unexpected new twist that awaits full explanation. In this mini-review, we discuss the key events in the early stages of human AS from clinical and basic science aspects, which could be crucial for attempted disease prevention studies in at risk subjects

Transport de solutés dans des réseaux de fractures discrets (nouvelle approche Lagrangienne dans le domaine des temps)

PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Time domain random walk method to simulate transport by advection-dispersion and matrix diffusion in fracture networks

International audienceA method is proposed to calculate in one step the residence time of a particle by advection-dispersion and matrix diffusion in a bond of a fracture network. The calculation is very rapid and avoids the discretization of Eulerian methods or the multiple leaps of classical Lagrangian approaches. The method is accurate in most flow conditions prevailing in fracture networks. Therefore, the method will be useful to evaluate the conditions in which the different transport mechanisms are of influence at the scale of the entire network

Simulation of solute transport in discrete fracture networks using the time domain random walk method

International audienceThe time domain random walk (TDRW) method has been developed for simulating solute transport in discrete fracture networks. The following transport processes have been considered: advective transport in fractures, hydrodynamic dispersion along the fracture axis, sorption reactions on the fracture walls and decay reactions. The TDRW method takes advantage of both random walk and particle-tracking methods. It allows for the one-step calculation of the particle residence time in each bond of the network while avoiding mass balance problems at fracture intersections with contrasted dispersion coefficients. The accuracy of the TDRW method has been addressed by means of synthetic test problems into single fractures and into a 2D discrete fracture network. In each case, simulated and theoretical results compare very well

Solute transport in a single fracture with negligible matrix permeability: 1. fundamental mechanisms

International audienceThis report describes the fracture-scale mechanisms acting on solute transport in fractured aquifers under natural-flow conditions. It focuses on low-permeability rocks where advection in the matrix is negligible compared with that in fractures. The relevant transport mechanisms detailed have been identified by experimental and theoretical studies over the past 30 years: advection and hydrodynamic dispersion, channeling effects, matrix diffusion, and sorption reactions. This review is intended to emphasize the fundamental concepts and to draw up a reader's guide through an extensive bibliography by linking key problems to key papers. These concepts might be integrated into transport models, but their influence at the large scale, however, remains an open question that is not dealt with in this review

Solute transport in a single fracture with negligible matrix permeability: 2. mathematical formalism

International audienceThis report provides an overview of the mathematical expressions for modeling fundamental solute transport mechanisms at the fracture scale. It focuses on low-permeability rocks where advection in the matrix is negligible as compared to that in fractures. The following processes are considered: (1) advective transport in fractures, (2) hydrodynamic dispersion along the fracture axis, (3) molecular diffusion from the fracture to the porous matrix, (4) sorption reactions on the fracture walls and within the matrix, and (5) decay reactions. The aim of this review is to gather in a single article the transport equations and their analytical solutions, using a homogeneous notation to facilitate comparison and exploitation

Intégration - inversion de données géologique et mesures hydrodynamiques in-situ pour le conditionnement d'un modèle 3D d'aquifère calcaire (site expérimental hydrogéologique (SEH) de Poitiers, France)

L'étude présentée synthétise en premier lieu les connaissances sur la géologie de l'aquifère investigué par le Site Expérimental Hydrogéologique de Poitiers et sur la structure de l'écoulement à partir de l'analyse lithostratigraphique des carottes et des données de diagraphies de puits. L'écoulement est conditionné par des structures karstiques et des fractures. Les niveaux karstiques sont contraints à l'intérieur de 3 niveaux géologiques subhorizontaux. L'interconnectivité entre ces niveaux semble être assurée par la fracturation subverticale. La caractérisation hydrodynamique des chemins d'écoulement préférentiel repose sur l'interprétation des essais par chocs hydrauliques. Un modèle a été développé, à partir de la prise en compte d'effets inertiels et d'une dimension d'écoulement non-entière. L'analyse de sensibilité montre que les deux paramètres "clé" du modèle sont la dimension d'écoulement et la conductivité hydraulique. L'interprétation des données du SEH montre une grande variabilité des valeurs de diffusivité des connexions hydrauliques. Les fortes valeurs de diffusivité permettent l'observation de réponses à grande distance du puits pompé. Les connaissances sur la géologie et la structure de l'écoulement ont été incorporées dans une modélisation du SEH basée sur une approche mixte DFN / milieu continu hétérogène. Les résultats permettent de reproduire de façon satisfaisante le comportement hydrodynamique particulier du SEH, en particulier la similitude spatiale et temporelle des courbes de rabattements.This work synthesizes knowledge about the aquifer investigated by the Hydrogeological Experimental Site of Poitiers. Flowpath structure has been identified from lithostratigraphic core analysis and borehole logging data. The flow is governed by karstic structures and fractures. Karstic levels are constrained within 3 sub-horizontal geological levels. The interconnectivity between these levels seems controlled by the sub-vertical fractures. The hydrodynamic characterization of flowpaths is based on the interpretation of slug test. A new model has been developed, which takes into account inertial effects and fractional flow dimension. Sensibility analysis shows that the two key parameters are the flow dimension and the hydraulic conductivity. The results show that diffusivity values of hydraulic connection vary over several orders of magnitude and allow hydraulic response at far observation wells. Knowledge about geology and flowpath structure is incorporated into a model of HES based on a composite approach DFN / heterogeneous continuous medium. Results allow to reproduce satisfactorily the unusual hydraulic behavior of HES, particularly the spatial and time similarity of drawdown curves.POITIERS-BU Sciences (861942102) / SudocSudocFranceF