The creep properties of calcium silicate hydrates (C-S-H) are assessed by means of nanoindentation creep experiments on a wide range of substoichiometric cement pastes. We observe that, after a few ...seconds, the measured creep compliance of C-S-H is very well captured by a logarithmic time function. The rate of the logarithmic creep is found to scale in a unique manner with indentation modulus, indentation hardness, and packing density, independent of processing, mix proportions, indenter geometry and load history. The comparison with macroscopic creep experiments on concrete shows that minutes-long nanoindentations enable a quantitative assessment of the long-term creep properties of cementitious materials, orders of magnitude faster than macroscopic testing. Finally, we show that a strong analogy exists between this logarithmic creep behavior of C-S-H and that of soils, which suggests a granular origin of creep of geomaterials.
Outre les facteurs cliniques propres aux diagnostics de pathologies mentales en général et de schizophrénie en particulier, et outre les facteurs sociaux pouvant précipiter ou contextualiser le ...recours à la violence de ces malades, la question de la comorbidité paraît devoir être soulevée. En effet, les troubles de la personnalité, notamment antisociale, les addictions et le triple diagnostic soulèvent la pertinence de s’interroger sur l’existence de typologies de patients violents, tant pour comprendre, prévoir, mais aussi orienter la prise en charge.
In addition to the clinical factors of the diagnoses of mental pathology in general and schizophrenia in particular, and in addition to the social factors being able to precipitate or contextualise the recourse to the violence of these patients, the question of the comorbidity appears to have to be raised. Indeed, personality disorders, in particular antisocial personality disorder, substances abuse and the comorbidities raise the relevance to wonder about the existence of typologies of patients violent one, understand, envisage and also direct the assumption of responsibility.
Enhanced coal bed methane recovery (ECBM) consists in injecting carbon dioxide in coal bed methane reservoirs in order to facilitate the recovery of the methane. The injected carbon dioxide gets ...adsorbed at the surface of the coal pores, which causes the coal to swell. This swelling in confined conditions leads to a closure of the coal reservoir cleat system, which hinders further injection. In this work we provide a comprehensive framework to calculate the macroscopic strains induced by adsorption in a porous medium from the molecular level. Using a thermodynamic approach we extend the realm of poromechanics to surface energy and surface stress. We then focus on how the surface stress is modified by adsorption and on how to estimate adsorption behavior with molecular simulations. The developed framework is here applied to the specific case of the swelling of CO2-injected coal, although it is relevant to any problem in which adsorption in a porous medium causes strains.
The reservoir response of unmineable coal seams to primary and enhanced natural gas recovery is strongly affected by gas sorption and the swelling properties of the coal reservoir rock. In-depth ...understanding of the process of gas sorption/desorption in the coal matrix, induced deformation and measurement of relevant physical parameters are critical for predictive reservoir management. Models used in industry practice are based on swelling strains measured in “free” swelling coal or on empirical correlations between strain and adsorption, and predict permeability changes based on changes of porosity or stress calculated assuming an analogy with thermoelasticity. However, not only coal seams are subjected to in-situ stresses and geometrical boundary conditions but also sorption and strain are strongly coupled. Representative experiments and a truly coupled model for coal seams are needed in challenging applications. We present a set of triaxial testing measurements on 38mm diameter fractured sub-bituminous/bituminous coal cores exposed to CO2. Testing includes the measurement of fluid uptake, adsorption-induced strains and stresses, and the impact on simultaneously measured permeability. Noteworthy, we measured increases in effective stress of up to 29MPa when injecting CO2 at 5MPa and preventing the coal core to swell. The results are analyzed with a poromechanical model in which coal matrix microporosity and adsorption-induced phenomena are embedded into a fractured reservoir rock with transverse isotropic properties. The adsorptive–mechanical coupling in the coal matrix is integrated through an adsorption stress function and fractured coal permeability is estimated as a function of Terzaghi's effective stresses (parallel and perpendicular to the bedding plane). The experimental results and model predictions help identify the characteristic response of coal microporosity and cleat macroporosity on the poromechanical response of coal cores, and suggest that order of magnitude changes of reservoir permeability observed in the field are linked to sorption-induced change on Terzaghi's effective horizontal stress under laterally constrained displacement condition. Together, the modeling and experimental characterization offer unprecedented insights into the mechanics of coal.
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•Coal seams have a complex and scale-dependent poromechanical response.•Sorption in the coal matrix induces swelling strains or stresses.•We derive a double porosity poromechanical model for transverse isotropic reservoirs.•Novel CO2 sorption experiments document swelling strains/stresses and permeability.•Sorption-induced stresses are the main driver for changing core permeability.
Skins symptoms during COVID‐19 have been recently described but their relation to SARS‐CoV‐2 is unclear while results for real‐time reverse transcriptase polymerase chain reaction (rRT‐PCR) testing ...were variable. Recalcati et al. reported 14 cases of patients with skin symptoms consistent with previous described COVID‐19 lesions but all the patients were tested negative. They asked for a serology to validate the hypothesis that these lesions are related to COVID‐19.
La littérature scientifique internationale est riche pour appuyer l’idée que la pathologie mentale est un facteur de risque majeur de comportements agressifs ou violents. La schizophrénie serait une ...pathologie mentale surreprésentée dans les phénomènes de violence individuelle, sans qu’il soit pour autant précisé dans quelle mesure la maladie ou ses multiples dimensions cliniques sont causales ou corrélées. Des signes psychopathologiques particuliers semblent prépondérants dans le risque de violence, indépendamment de l’entité diagnostique, notamment au détour d’une phase active de la maladie, laissant entendre la nécessité de prendre en compte les formes cliniques du diagnostic. Les mécanismes et les thèmes délirants ainsi que les facteurs infracliniques sont également revus. Cependant, et afin de destigmatiser ces personnes soupçonnées ou suspectées pour leur seule maladie, la définition ou la redéfinition des différentes dimensions cliniques, souvent indépendantes des diagnostics, susceptibles de précipiter ou favoriser le recours à la violence ne paraît pas suffisante. Il paraît nécessaire de prendre en considération les facteurs sociaux ou contextuels qui favoriseraient le recours à la violence d’une personne présentant une pathologie mentale. Cette revue de la littérature propose donc d’examiner les facteurs cliniques, infracliniques (biologiques) et sociaux qui entrent en jeu dans la violence des personnes présentant une pathologie mentale telle que la schizophrénie.
An abundant international scientific literature is supporting the idea that mental illness is a major risk factor for aggressive and violent behaviours. In addition, schizophrenia is the mental illness, which is over-represented in aggressive and violent behaviours. However, it is not clear to understand the real place of schizophrenia. In particular, some psychopathological signs, seem dominating in the risk of violence, independently of the diagnostic of schizophrenia. in the same way, active phase of the disease, clinical forms, the delirious mechanisms,
threat and control-override symptoms, and several other clinical or subclinical factors could play a major role in the relation schizophrenia–violence. This review of the literature proposes to examine these factors to understand the real place of schizophrenia in aggressive and violent behaviours. Mental illness is currently designated as a risk factor of violent behaviours. In order to destigmatise people, just suspected because of the disease, the definition of various clinical dimensions, often independent of diagnoses, likely to precipitate or cause the recourse to violence, don’t appear sufficient. It appears necessary to take into account social or contextual factors, which would explain the recourse to the violence by people suffering of a mental illness. This review of the literature proposes to examine the sociodemographic and socioeconomic factors playing a role in the violence among people having a mental illness in general or a schizophrenia in particular.
Poromechanics of microporous media Brochard, L.; Vandamme, M.; Pellenq, R.J.-M.
Journal of the mechanics and physics of solids,
April 2012, 2012-04-00, 20120401, 2012-04, Volume:
60, Issue:
4
Journal Article
Peer reviewed
Open access
Microporous media, i.e., porous media made of pores with a nanometer size, are important for a variety of applications, for instance for sequestration of carbon dioxide in coal, or for storage of ...hydrogen in metal-organic frameworks. In a pore of nanometer size, fluid molecules are not in their bulk state anymore since they interact with the atoms of the solid: they are said to be in an adsorbed state. For such microporous media, conventional poromechanics breaks down.
In this work we derive poroelastic constitutive equations which are valid for a generic porous medium, i.e., even for a porous medium with pores of nanometer size. The complete determination of the poromechanical behavior of a microporous medium requires knowing how the amount of fluid adsorbed depends on both the fluid bulk pressure and the strain of the medium. The derived constitutive equations are validated with the help of molecular simulations on one-dimensional microporous media. Even when a microporous medium behaves linearly in the absence of any fluid (i.e., its bulk modulus does not depend on strain), we show that fluid adsorption can induce non-linear behavior (i.e., its drained bulk modulus can then depend significantly on strain). We also show that adsorption can lead to an apparent Biot coefficient of the microporous medium greater than unity or smaller than zero.
The poromechanical response of a microporous medium to adsorption significantly depends on the pore size distribution. Indeed, the commensurability (i.e., the ratio of the size of the pores to that of the fluid molecules) proves to play a major role. For a one-dimensional model of micropores with a variety of pore sizes, molecular simulations show that the amount of adsorbed fluid depends linearly on the strain of the medium. We derive linearized constitutive equations which are valid when such a linear dependence of the adsorbed amount of fluid on the strain is observed.
As an application, the case of methane and coal is considered. Molecular simulations of an adsorption of methane on a microporous realistic model for coal are performed with a flexible solid skeleton. The applicability of the set of linearized constitutive equations to this case is discussed and the results are shown to be consistent with swelling data measured during a classical adsorption experiment.
► We derive poromechanical equations that are valid even for microporous media. ► Adsorption and strain in microporous media can be coupled. ► Adsorption of fluid can induce non-linear behavior of the medium. ► The poromechanical response of a microporous medium to adsorption significantly depends on the pore size distribution. ► The derived equations are relevant for adsorption of methane in coal.
The recovery of natural gas from coal bed seams is usually accompanied by a significant increase of permeability induced by coal matrix shrinkage and stress relaxation upon gas desorption. This ...advantageous increase in permeability may be impaired sometimes by mechanical failure of the reservoir rock and ensuing production of coal fines. Near-wellbore stress concentration and reduction of lateral stresses are known to promote shear failure during depletion in oil and gas reservoir formations. Yet, conventional analyses have shown limited success in predicting coal failure, since other chemo-physical mechanisms may be responsible in enhancing the conditions towards mechanical failure in the coal bed reservoir rock. We show a set of triaxial experiments involving gas desorption from coal cores under zero-lateral strain condition (radial stress measured and controlled) and constant total vertical stress meant to simulate the stress path during production far from the wellbore. CO2 is used as surrogate fluid for CH4. The experimental data indicates that desorption can significantly help reduce lateral stress (and increasing deviatoric stress) until shear failure occurs. The results suggest that depletion-induced shear failure is much more likely to occur in coal seams than in conventional non-sorbing reservoir rocks. The adsorptive-mechanical coupling turns out to be a key phenomenon in the process. Numerical simulations at the representative elementary volume scale adopting a double-porosity poromechanical model support the experimental findings and permit calculating a critical gas pressure for shear failure to happen. This emergent phenomenon is comparable to the outcome of other situations such as mineral dissolution or thermal contraction, where shrinkage relaxes lateral stress and acts as an intensifying driver for promoting shear failure within the reservoir rock. Coupled numerical simulation is needed to include near-wellbore effects and validate our findings with actual field observations. A thorough understanding of the coupled response of coal seams is necessary to enhance reservoir management and mitigate the effects of coal failure on fines production.
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•We show experiments of gas desorption from coal cores under triaxial conditions.•Desorption experiments are performed with CO2 under zero-lateral strain condition.•Desorption significantly helps reduce lateral stress and increases deviatoric stress.•Coal seams are more prone to depletion-induced shear than conventional reservoirs.•A poromechanical model offers further insight and supports the experimental findings.
This paper presents a poromechanical model for drying of unsaturated porous media valid for a large range of relative humidity. Using the proper laws of thermodynamics, this model is derived and ...permits to account for different effects that contribute to the effective stress development: the average pore pressure effect, the energy of the interfaces effect, the surface adsorption effect and the Shuttleworth effect. The majority of the input parameters of this model are simply assessed by using two commonly known techniques for the characterization of pores structures applied on experimental desorption isotherms: the B.E.T theory (Brunauer et al., 1938) and the BJH technique (Barrett et al., 1951). Another input parameter (linked to the Shuttleworth effect) is fitted on experimental drying shrinkage strains. This model is tested and validated with experimental data for different porous materials - hardened ordinary cement paste, high- performance concrete and Vycor glass - found in the literature. The obtained results show a satisfactory evaluation of the drying shrinkage strains for all three tested materials, with the possibility of considering zero fitting parameter. Compared to other poromechanical models found in the literature such as the classical Biot-Bishop (Biot, 1941) model and the (Coussy et al., 2003) model, our model appears to be capable of displaying the transition at a certain relative humidity between the capillary pressure effects and the surface adsorption effect, which manifests itself by a plateau in the drying shrinkage strains curve at this value of relative humidity.
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