Parallel simulation of spiral waves in reacting and diffusing media

The propagation of the spiral waves in excitable media is governed by the non-linear reaction-diffusion equations. In order to solve these equations in the three-dimensional space, two methods have been implemented and parallelized on both shared- and distributed-memory computers. These implicit methods linearize the equations in time, following alternate directions in the first case (ADI), and using the Crank-Nicolson discretization in the second case. A linear system of algebraic equations has been obtained and it has been solved using direct methods in the ADI technique, while in the second case has been used the conjugated gradient (CG) method. An optimized version of the CG algorithm is presented here, in which the largest efficiency has been obtained

The Evolution of Reaction-diffusion Controllers for Minimally Cognitive Agents

No description supplie

Role of acoustics in flame/vortex interactions

The role of acoustics in flame/vortex interactions is examined via asymptotic analysis and numerical simulation. The model consists of a one-step, irreversible Arrhenius reaction between initially unmixed species occupying adjacent half-planes which are allowed to mix and react by convection and diffusion in the presence of an acoustic field or a time-varying pressure field of small amplitude. The main emphasis is on the influence of the acoustics on the ignition time and flame structure as a function of vortex Reynolds number and initial temperature differences of the reactants

Interstellar Turbulence II: Implications and Effects

Interstellar turbulence has implications for the dispersal and mixing of the elements, cloud chemistry, cosmic ray scattering, and radio wave propagation through the ionized medium. This review discusses the observations and theory of these effects. Metallicity fluctuations are summarized, and the theory of turbulent transport of passive tracers is reviewed. Modeling methods, turbulent concentration of dust grains, and the turbulent washout of radial abundance gradients are discussed. Interstellar chemistry is affected by turbulent transport of various species between environments with different physical properties and by turbulent heating in shocks, vortical dissipation regions, and local regions of enhanced ambipolar diffusion. Cosmic rays are scattered and accelerated in turbulent magnetic waves and shocks, and they generate turbulence on the scale of their gyroradii. Radio wave scintillation is an important diagnostic for small scale turbulence in the ionized medium, giving information about the power spectrum and amplitude of fluctuations. The theory of diffraction and refraction is reviewed, as are the main observations and scintillation regions.Comment: 46 pages, 2 figures, submitted to Annual Reviews of Astronomy and Astrophysic

Modelling chemotactic motion of cells in biological tissue with applications to embryogenesis

Perhaps one of the most amazing events that occurs in nature, is in the emergence and growth of biological life. Emergence speaks of the well-coined phrase Primordial ooze from which the chemical building blocks of life first gave rise to the complicated molecular structure of Deoxyribonucleic acid (DNA), that has the mind boggling task of encoding every chemical and physical attribute and trait of the organism for which it is encoded. This incredible feat of nature is only equalled by the ability of single fertilized cell (zygote) to undergo a seemingly magical transformation through enlargement, growth and change to give rise to a fully formed animal (or plant). The study and body of knowledge of this latter process is called Developmental Biology, and it seeks to define and explain all of the intricate sub-stages and bio-chemical, molecular and physical processes along the time-line of this transformation, that is from fertilization to birth, hatching or germination and beyond. One might consider, and quite reasonably, that the variety of different processes leading to the development of a complete biological organism would be so vast as to render the problem untenable. Indeed the almost inconceivable amount of genetic information contained within the nucleus of the simplest of cells would seem to corroborate this assumption. However when one takes a more holistic view, we can see that the development of any complex biological organism can be reduced to a set of five distinct processes, all of which are orchestrated to define structures from a body of cells. Viewed in this light the generation of any complex multi-cellular organism, be it small or large, must involve: cell-division, differentiation, pattern formation, change in form and growth [1]. To mediate and orchestrate these different processes during the development of the embryo are a enumerable number of bio-chemicals that are produced within the cells that can diffuse into the surrounding environment, activating (and de-activating) inter/intra-cellular signalling pathways that trigger further productions and possibly one or more of the processes suggested above. One such case of this, and which is of particular interest in this thesis, is in the role of morphogens in the growth of vertebrate embryos, where it is known that interacting morphogen gradients can give rise to spatially stable concentrations [2] that are known to be involved in organ growth [3], primitive streak formation [4] and the extension and patterning of the primary body axis [5, 6, 7]. In this thesis we are considering one such problem involving these mechanisms/processes, during the primary body axis extension in the chick embryo. During this phase of development the early brain is beginning to form and the central nervous system (CNS) is beginning to extend unilaterally in a posterior direction defining the main anteroposterior (head to tail) body axis; in simple terms one may see this as the generation of the spinal cord and surrounding structures. Extension of this axis is known to be orchestrated by a small cellular structure located at the posterior-most tip of the extension, encompassing what is known as the primary organising centre in the chick embryo: Hensen’s node. This structure including the node is known to move independently/autonomously of the rest of the embryo and as it does so the cells in the region are growing and proliferating, and ultimately differentiating and leaving this region to literally fuel the axial extension. This broad description leads us to the heart of our thesis, and which will preoccupy the rest of this dissertation. We postulate that the motile behaviour of the group is as a result of biochemical gradients to which the group is attracted toward areas of highest concentration or towards areas of lowest concentration of some as yet unnamed morphogen. That is we assume that the group moves as a result of a chemotaxis. Furthermore, the growth and subsequent differentiation of cells exiting the group, contributing to the growth of the CNS, are also regulated by the same morphogen. Therefore we propose that a singular bio-chemical mechanism can account for the motile and growth behaviour observed during CNS extension

Synchronization of spatiotemporal patterns and modeling disease spreading using excitable media

Studies of the photosensitive Belousov-Zhabotinsky (BZ) reaction are reviewed and the essential features of excitable media are described. The synchronization of two distributed Belousov-Zhabotinsky systems is experimentally and theoretically investigated. Symmetric local coupling of the systems is made possible with the use of a video camera-projector scheme. The spatial disorder of the coupled systems, with random initial configurations of spirals, gradually decreases until a final state is attained, which corresponds to a synchronized state with a single spiral in each system. The experimental observations are compared with numerical simulations of two identical Oregonator models with symmetric local coupling, and a systematic study reveals generalized synchronization of spiral waves. Modeling studies on disease spreading have been reviewed. The excitable medium of the photosensitive BZ reaction is used to model disease spreading, with static networks, dynamic networks, and a domain model. The spatiotemporal dynamics of disease spreading in these complex networks with diffusive and non-diffusive connections is characterized. The experimental and numerical studies reveal that disease spreading in these model systems is highly dependent on the non-diffusive connections

Aeronautical enginnering: A cumulative index to a continuing bibliography (supplement 312)

This is a cumulative index to the abstracts contained in NASA SP-7037 (301) through NASA SP-7073 (311) of Aeronautical Engineering: A Continuing Bibliography. NASA SP-7037 and its supplements have been compiled by the Center for AeroSpace Information of the National Aeronautics and Space Administration (NASA). This cumulative index includes subject, personal author, corporate source, foreign technology, contract number, report number, and accession number indexes