812 research outputs found
Investigation of Gravity‐Driven Infiltration Instabilities in Smooth and Rough Fractures Using a Pairwise‐Force Smoothed Particle Hydrodynamics Model
No full textThis work investigates small-scale infiltration dynamics in smooth and rough single fractures using a three-dimensional multiphase pairwise-force smoothed particle hydrodynamics (PF-SPH) model. Gravity-driven infiltration instabilities in fractures under unsaturated conditions can significantly influence the arrival time of tracers or contaminants, and the rapid and localized recharge dynamics in fractured–porous aquifer systems. Here, we study the influence of roughness and injection rate on fluid flow modes and flow velocity. Three types of fractures are considered with different degrees of roughness, including a smooth fracture. Both the rough and smooth fractures exhibit flow instabilities, fingering, and intermittent flow regimes for low infiltration rates. In agreement with theoretical predictions, a flat fluid front is achieved when the flux q supplied to a fracture is larger than the gravitationally driven saturated flux [q > kρg/μcos(φ), where k is the intrinsic permeability of the fracture, ρ is a density, μ is the viscosity, and φ is the fracture inclination angle measured from the vertical direction]. To characterize the flow instability, we calculate standard deviations of velocity along the fracture width. For the considered infiltration rates, we find that an increase in roughness decreases the flow velocity and increases the standard deviation of velocity. This is caused by a higher likelihood of flow discontinuities in the form of fingering and/or snapping rivulets. To validate our unsaturated flow simulations in fractures, we estimate the scaling of specific discharge with normalized finger velocity, compute the relationship between fingertip length and scaled finger velocity, and find good agreement with experimental results
Smoothed particle hydrodynamics study of the roughness effect on contact angle and droplet flow
No full textNumerical and Analytical Modeling of Flow Partitioning in Partially Saturated Fracture Networks
No full textInfiltration processes in fractured-porous media remain a crucial, yet not very well understood component of recharge and vulnerability assessment. Under partially saturated condition flows in fractures, percolating fracture networks and fault zones contribute to the fastest spectrum of infiltration velocities via preferential pathways. Specifically, the partitioning dynamics at fracture intersections determine the magnitude of flow fragmentation into vertical and horizontal components, hence the bulk flow velocity and dispersion of fracture networks. Here we derive an approximate analytical solution for the partitioning process and validate it using smoothed particle hydrodynamics simulations. The transfer function is conceptually based on simulation results and laboratory experiments carried out in previous works. It allows efficient flow simulation through fracture networks with simple cubic structures and an arbitrary number of fractures and aperture sizes via linear response theory and convolution of a given input signal. We derive a nondimensional bulk flow velocity (urn:x-wiley:00431397:media:wrcr25145:wrcr25145-math-0001) and dispersion coefficient (urn:x-wiley:00431397:media:wrcr25145:wrcr25145-math-0002) to characterize fracture networks in terms of dimensionless horizontal and vertical time scales τm and τ0. The dispersion coefficient strongly depends on the horizontal time scale and converges toward a constant value of 0.08 within reasonable fluid and geometrical parameter ranges, while the nondimensional velocity exhibits a characteristic urn:x-wiley:00431397:media:wrcr25145:wrcr25145-math-0003 scaling. Given that hydraulic information is often only available at limited places within (fractured-porous) aquifer systems (boreholes or springs), our study intends to provide an analytical concept to potentially reconstruct internal fracture network geometries from external boundary information, such as the dispersive properties of discharge (groundwater level fluctuations).Peer reviewe
Effect of Unsaturated Flow Modes on Partitioning Dynamics of Gravity-Driven Flow at a Simple Fracture Intersection: Laboratory Study and Three-Dimensional Smoothed Particle Hydrodynamics Simulations
No full textMPINN-DataAssi-transport
No full textCode and data accompanying the following manuscript: QiZhi He, David Barajas-Solano, Guzel Tartakovsky, Alexandre M. Tartakovsky, Physics-Informed Neural Networks for Multiphysics Data Assimilation with Application to Subsurface Transport, Advances in Water Resources(2020), doi: https://doi.org/10.1016/j.advwatres.2020.10361
Emprisonnement, déchéance et abandon : Fort-de-France vue par Alfred Alexandre = Imprisonment, Degradation and Abandoning : Fort-de-France Seen by Alfred Alexandre
No full textThis article analyses Alfred Alexandre’s novel Bord de Canal (2004), in which the capital of Martinique turnes into a setting for human decay. The description of squalid environments,
populated by human debris, shows the lack of interest by the administration in taking responsibility for the lot of the most deprived inhabitants. They end up confined to working-class areas in inhuman living conditions. Through an analysis of places symbolising this degraded and degrading urban environment, which is transformed into a place of social exclusion and persecution, the study shows the renewal of the literary treatment of the city by Alexandre, an author of the post-creolité.Cet article propose une analyse du roman d’Alfred Alexandre
Bord de Canal (2004) où la capitale de la Martinique se révèle
un théâtre de déchéance humaine : l’évocation de milieux sor-
dides habités par des loques humaines montre le manque d’in-
térêt de la part de l’administration pour s’assumer le sort des
habitants les plus démunis qui se trouvent finalement confi-
nés dans les quartiers populaires dans des conditions de vie
inhumaines. À travers l’analyse de lieux symboles de ce cadre
urbain dégradé et dégradant, qui se transforme en lieu d’ex-
clusion et de persécution sociales, l’étude montre le renouveau
du traitement littéraire de la ville chez Alexandre, auteur de la
post-créolité
Smoothed dissipative particle dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations
No full textThermal fluctuations cause perturbations of fluid-fluid interfaces and highly nonlinear hydrodynamics in multiphase flows. In this work, we develop a multiphase smoothed dissipative particle dynamics (SDPD) model. This model accounts for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface tension is modeled by imposing a pairwise force between SDPD particles. We show that the relationship between the model parameters and surface tension, previously derived under the assumption of zero thermal fluctuation, is accurate for fluid systems at low temperature but overestimates the surface tension for intermediate and large thermal fluctuations. To analyze the effect of thermal fluctuations on surface tension, we construct a coarse-grained Euler lattice model based on the mean field theory and derive a semianalytical formula to directly relate the surface tension to model parameters for a wide range of temperatures and model resolutions. We demonstrate that the present method correctly models dynamic processes, such as bubble coalescence and capillary spectra across the interface.U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Collaboratory on Mathematics for Mesoscopic Modeling of Materials (CM4); New Dimension Reduction Methods and Scalable Algorithms for Nonlinear Phenomena project; DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences; DOE [DE-AC05-76RL01830]SCI(E)[email protected]
Gamma band plasticity in sensory cortex is a signature of the strongest memory rather than memory of the training stimulus
No full textGamma oscillations (∼30-120Hz) are considered to be a reflection of coordinated neuronal activity, linked to processes underlying synaptic integration and plasticity. Increases in gamma power within the cerebral cortex have been found during many cognitive processes such as attention, learning, memory and problem solving in both humans and animals. However, the specificity of gamma to the detailed contents of memory remains largely unknown. We investigated the relationship between learning-induced increased gamma power in the primary auditory cortex (A1) and the strength of memory for acoustic frequency. Adult male rats (n=16) received three days (200 trials each) of pairing a tone (3.66 kHz) with stimulation of the nucleus basalis, which implanted a memory for acoustic frequency as assessed by associatively-induced disruption of ongoing behavior, viz., respiration. Post-training frequency generalization gradients (FGGs) revealed peaks at non-CS frequencies in 11/16 cases, likely reflecting normal variation in pre-training acoustic experiences. A stronger relationship was found between increased gamma power and the frequency with the strongest memory (peak of the difference between individual post- and pre-training FGGs) vs. behavioral responses to the CS training frequency. No such relationship was found for the theta/alpha band (4-15 Hz). These findings indicate that the strength of specific increased neuronal synchronization within primary sensory cortical fields can determine the specific contents of memory.Peer reviewedAuthor's Manuscript is available open access in PubMed Central: http://www.ncbi.nlm.nih.gov/pubmed/23669065
Remodeling sensory cortical maps implants specific behavioral memory
No full textNeural mechanisms underlying the capacity of memory to be rich in sensory detail are largely unknown. A candidate mechanism is learning-induced plasticity that remodels the adult sensory cortex. Here, expansion in the primary auditory cortical (A1) tonotopic map of rats was induced by pairing a 3.66-kHz tone with activation of the nucleus basalis, mimicking the effects of natural associative learning. Remodeling of A1 produced de novo specific behavioral memory, but neither memory nor plasticity was consistently at the frequency of the paired tone, which typically decreased in A1 representation. Rather, there was a specific match between individual subjects' area of expansion and the tone that was strongest in each animal's memory, as determined by post-training frequency generalization gradients. These findings provide the first demonstration of a match between the artificial induction of specific neural representational plasticity and artificial induction of behavioral memory. As such, together with prior and present findings for detection, correlation and mimicry of plasticity with the acquisition of memory, they satisfy a key criterion for neural substrates of memory. This demonstrates that directly remodeling sensory cortical maps is sufficient for the specificity of memory formation.Peer reviewedAuthor's Manuscript is also available open access in PubMed Central: http://www.ncbi.nlm.nih.gov/pubmed/23639876
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