Pore-Scale Simulation Of Experimentally Realizable, Oscillatory Flow In Porous Rock

We report new simulations of oscillating flow in porous rock. Our goal is to better understand the frequency dependence of pore-scale fluid motion, which should ultimately help us to interpret attenuation and electroseismic measurements. We use a lattice gas cellular automaton (Rothman and Zaleski, 1997) to perform the calculations in a pore space geometry measured from Fontainebleau sandstone by X-ray microtomography (Spanne et al., 1994; Auzerais et al., 1996). We chose this method because it is fast and efficient in the complex geometry of the porous rock. We show that the Biot critical frequency (Biot, 1956) is accessible to simulation, and we perform simulations at a range of frequencies around the critical frequency. In addition, we show that the dynamical properties of the lattice gas fluid can be mapped onto reasonable real fluids. As the frequency varies through the critical range, we observe qualitative and quantitative changes in the amplitude and phase of fluid velocity distributions. We also report preliminary calculations of the local viscous dissipation, which should provide a means to compare our simulations with existing theories of attenuation (e.g., Johnston et al., 1979; Dvorkin and Nur, 1993; Akbar et al., 1994).Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation ConsortiumSaudi Aramc

Toward The Simulation Of Attenuation: Oscillatory Flow In Porous Rock

Fluid flow in porous rock due to an oscillatory pressure gradient is simulated. We observe distributions of density and velocity in the rock which point to viscous dissipation. We will use this method to seek a deeper understanding of the physics of attenuation.Massachusetts Institute of Technology. Earth Resources Laboratory (Founding Members Fellowship

Gene Expression in Experimental Aortic Coarctation and Repair: Candidate Genes for Therapeutic Intervention?

Coarctation of the aorta (CoA) is a constriction of the proximal descending thoracic aorta and is one of the most common congenital cardiovascular defects. Treatments for CoA improve life expectancy, but morbidity persists, particularly due to the development of chronic hypertension (HTN). Identifying the mechanisms of morbidity is difficult in humans due to confounding variables such as age at repair, follow-up duration, coarctation severity and concurrent anomalies. We previously developed an experimental model that replicates aortic pathology in humans with CoA without these confounding variables, and mimics correction at various times using dissolvable suture. Here we present the most comprehensive description of differentially expressed genes (DEGs) to date from the pathology of CoA, which were obtained using this model. Aortic samples (n=4/group) from the ascending aorta that experiences elevated blood pressure (BP) from induction of CoA, and restoration of normal BP after its correction, were analyzed by gene expression microarray, and enriched genes were converted to human orthologues. 51 DEGs with \u3e6 fold-change (FC) were used to determine enriched Gene Ontology terms, altered pathways, and association with National Library of Medicine Medical Subject Headers (MeSH) IDs for HTN, cardiovascular disease (CVD) and CoA. The results generated 18 pathways, 4 of which (cell cycle, immune system, hemostasis and metabolism) were shared with MeSH ID’s for HTN and CVD, and individual genes were associated with the CoA MeSH ID. A thorough literature search further uncovered association with contractile, cytoskeletal and regulatory proteins related to excitation-contraction coupling and metabolism that may explain the structural and functional changes observed in our experimental model, and ultimately help to unravel the mechanisms responsible for persistent morbidity after treatment for CoA

The evidence for automated grading in diabetic retinopathy screening

Peer reviewedPostprin

Nonequilibrium Approach to Bloch-Peierls-Berry Dynamics

We examine the Bloch-Peierls-Berry dynamics under a classical nonequilibrium dynamical formulation. In this formulation all coordinates in phase space formed by the position and crystal momentum space are treated on equal footing. Explicitly demonstrations of the no (naive) Liouville theorem and of the validity of Darboux theorem are given. The explicit equilibrium distribution function is obtained. The similarities and differences to previous approaches are discussed. Our results confirm the richness of the Bloch-Peierls-Berry dynamics

The Effect Of Image Resolution On Fluid Flow Simulations In Porous Media

Realistic simulations of flow in porous media are dependent upon having a three-dimensional, high resolution image of pore structure which is difficult to obtain. So, we ask the question, "How fine a resolution is necessary to adequately model flow in porous media?" To find the answer, we take a 7.5 p,m resolution image and coarsen it to five different resolutions. Lattice gas simulations are performed on each image. From the simulation results, we observe changes in permeability and velocity fields as the resolution is altered. The results show permeability varies by a factor of 5 over the resolution range. Flow paths change as the resolution is changed. We also find that the image processing has a large impact on the outcome of the simulations.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

Fluid Flow In Porous Media: NMR Imaging And Numerical Simulation

We use nuclear magnetic resonance (NMR) imaging to obtain a three-dimensional image of the pore structure in a limestone core, 4.5 mm in diameter and 10 mm in length, with a resolution of 40 μm. This image is converted into boundary conditions for simulation of fluid flow through the rock using the lattice gas method. The computed permeability is several orders of magnitude lower than the laboratory measured permeability, most likely a result of the image resolution being too coarse to resolve the smaller pore throats, which are believed to be significant for flow in this sample.Saudi AramcoMassachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

Microfocal X-Ray Computed Tomography Post-Processing Operations for Optimizing Reconstruction Volumes of Stented Arteries During 3D Computational Fluid Dynamics Modeling

Restenosis caused by neointimal hyperplasia (NH) remains an important clinical problem after stent implantation. Restenosis varies with stent geometry, and idealized computational fluid dynamics (CFD) models have indicated that geometric properties of the implanted stent may differentially influence NH. However, 3D studies capturing the in vivo flow domain within stented vessels have not been conducted at a resolution sufficient to detect subtle alterations in vascular geometry caused by the stent and the subsequent temporal development of NH. We present the details and limitations of a series of post-processing operations used in conjunction with microfocal X-ray CT imaging and reconstruction to generate geometrically accurate flow domains within the localized region of a stent several weeks after implantation. Microfocal X-ray CT reconstruction volumes were subjected to an automated program to perform arterial thresholding, spatial orientation, and surface smoothing of stented and unstented rabbit iliac arteries several weeks after antegrade implantation. A transfer function was obtained for the current post-processing methodology containing reconstructed 16 mm stents implanted into rabbit iliac arteries for up to 21 days after implantation and resolved at circumferential and axial resolutions of 32 and 50 μm, respectively. The results indicate that the techniques presented are sufficient to resolve distributions of WSS with 80% accuracy in segments containing 16 surface perturbations over a 16 mm stented region. These methods will be used to test the hypothesis that reductions in normalized wall shear stress (WSS) and increases in the spatial disparity of WSS immediately after stent implantation may spatially correlate with the temporal development of NH within the stented region