Biomedical subjects

P Meakin

Publications and source records attributed to P Meakin.

At least 19 recordsLinked to original sources

PubMed2006

Fracture patterns generated by diffusion controlled volume changing reactions.

A simple two-dimensional model was developed for the growth of fractures in a chemically decomposing solid. Simulations were carried out under rapid chemical decomposition conditions for which the kinetics of fracture growth is controlled by diffusion of the volatile reaction product or the kinetics of evaporation. The growth of the fracture pattern is self-sustaining due to the volume reduction associated with the decomposition process. Consistent with the theoretical analysis of Yakobson [Phys. Rev. Lett. 67, 1590 (1991)10.1103/PhysRevLett.67.1590], the fracture front propagates with a constant velocity v approximately=k2/3(Dl0)1/3 under evaporation controlled conditions and v approximately=D/l0 under diffusion controlled conditions, where k is the evaporation rate constant, D is the diffusion constant for the volatile reaction product in the solid, and l0 is the critical stable crack length. Under diffusion controlled conditions, the front width w scales as w approximately=(kl0/)D.

Journal Article↗

PubMed2005

Energy dissipation measures in three-dimensional disordered porous media.

The onset of nonlinear flow was analyzed in three-dimensional random, porous granular systems with 60% porosity using a lattice-Boltzmann model. Quantitative analysis was based on participation numbers built on local kinetic energies and energy dissipation rates computed via nonequilibrium kinetic (viscous stress) tensors. In contrast to the kinetic energy participation number, which characterizes the onset of nonlinearity in terms of a transition from a locally concentrated to a dispersed distribution of kinetic energy densities, the nonequilibrium kinetic tensor participation number characterizes the onset of nonlinearity in terms of a transition from a dispersed to a locally concentrated distribution of energy dissipation densities as the flow rate increases. The transition characterized by the nonequilibrium kinetic tensor participation number occurred over a nearly equal or a narrower range of Reynolds numbers when compared to the transition characterized by the kinetic energy participation number.

Journal Article↗

PubMed2005

Application of stereolithographic custom models for studying the impact of biofilms and mineral precipitation on fluid flow.

Here we introduce the use of transparent experimental models fabricated by stereolithography for studying the impacts of biomass accumulation, minerals precipitation, and physical configuration of flow paths on liquid flow in fracture apertures. The internal configuration of the models ranged in complexity from simple geometric shapes to those that incorporate replicated surfaces of natural fractures and computationally derived fracture surfaces. High-resolution digital time-lapse imaging was employed to qualitatively observe the migration of colloidal and soluble dyes through the flow models. In this study, a Sphingomonas sp. and Sporosarcina (Bacillus) pasteurii influenced the fluid dynamics by physically altering flow paths. Microbial colonization and calcite deposition enhanced the stagnant regions adjacent to solid boundaries. Microbial growth and calcite precipitation occurred to a greater extent in areas behind the fabricated obstacles and less in high-velocity orifices.

Bacteriological Techniques↗

PubMed2002

Ultrapermeable, reverse-selective nanocomposite membranes.

Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing.

Journal Article↗

PubMed1999

Dynamics of water coning.

Water beneath a layer of oil in a producing reservoir may rise and form a bell-shaped cone in the vicinity of the well. We discuss how the dynamics of cone formation in two dimensions depends on the gravitational contrast, the interfacial tension, and the flow rate of oil. For a constant flow rate below a critical rate Q(c), stable cones are formed. At rates above Q(c), two dynamical regimes are expected. These are slow initial formation and fast breakthrough to the well. Quasi-two-dimensional transparent porous models were used to perform cone formation experiments. Effective acceleration due to gravity was systematically varied. The experiments were simulated using a stochastic model based on invasion percolation in which capillary forces were explicitly taken into account. We find agreement between experiments and simulations, and consistency with the theoretical predictions.

Journal Article↗

PubMed1999

Extended Eden model reproduces growth of an acellular slime mold.

A stochastic growth model was used to simulate the growth of the acellular slime mold Physarum polycephalum on substrates where the nutrients were confined in separate drops. Growth of Physarum on such substrates was previously studied experimentally and found to produce a range of different growth patterns [Phys. Rev. E 57, 941 (1998)]. The model represented the aging of cluster sites and differed from the original Eden model in that the occupation probability of perimeter sites depended on the time of occupation of adjacent cluster sites. This feature led to a bias in the selection of growth directions. A moderate degree of persistence was found to be crucial to reproduce the biological growth patterns under various conditions. Persistence in growth combined quick propagation in heterogeneous environments with a high probability of locating sources of nutrients.

Algorithms↗

PubMed1996