Biomedical subjects

Gemunu H. Gunaratne

Publications and source records attributed to Gemunu H. Gunaratne.

4 recordsLinked to original sources

PubMed2000

A method to Fourier filter textured images.

An algorithm is introduced to extract an underlying image from a class of textures. It is assumed that the image is bandwidth limited and the noise is broad-band. The initial step of the algorithm extends the signal to a larger periodic image using "Distributed Approximating Functionals." The second step introduces a low-pass filter which allows the identification and elimination of the high-frequency components of the noise. The periodicity of the resulting image allows it to be Fourier filtered without aliasing. The feasibility of the algorithm is demonstrated on several noisy patterns generated in experiments and model systems. (c) 2000 American Institute of Physics.

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PubMed1999

Modal decomposition of hopping states in cellular flames.

We use Karhunen-Loeve (KL) decomposition of video images from an experiment to analyze a spatiotemporal dynamic state, unique to cellular flames, referred to as a "hopping state." Ordered states of cellular flames on a circular burner consist of one or two concentric rings of luminous cells. The hopping states correspond to the motions of individual cells in a ring sequentially executing abrupt changes in their angular position, while the other cells in the ring remain symmetric and at rest. KL decomposition separates the spatial and temporal characteristics of the hopping motion. The underlying symmetries of the experiment allow us to deduce a set of normal form equations that describe the formation of these states. We find that they result from secondary bifurcations connecting two primary branches of traveling waves. The solutions corresponding to hopping states exist as mixed-mode solutions away from the secondary bifurcations. (c) 1999 American Institute of Physics.

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PubMed1997

Cellular pattern formation in circular domains.

An analysis of stationary and nonstationary cellular patterns observed in premixed flames on a circular, porous plug burner is presented. A phenomenological model is introduced, that exhibits patterns similar to the experimental states. The primary modes of the model are combinations of Fourier-Bessel functions, whose radial parts have neighboring zeros. This observation explains several features of patterns, such as the existence of concentric rings of cells and the weak coupling between rings. Properties of rotating rings of cells, including the existence of modulated rotations and heteroclinic cycles can be deduced using mode coupling. For nonstationary patterns, the modal decomposition of experimental data can be carried out using the Karhunen-Loeve (KL) analysis. Experimental states are used to demonstrate the possibility of using KL analysis to differentiate between uniform and nonuniform rotations. The methodology can be extended to study more complicated nonstationary patterns. In particular, it is shown how the complexity of "hopping states" can be unraveled through the analysis. (c) 1997 American Institute of Physics.

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PubMed1993

Rhombic patterns: Broken hexagonal symmetry.

Landau-Ginzburg equations derived to conserve two-dimensional spatial symmetries lead to the prediction that rhombic arrays with characteristic angles slightly differ from 60 degrees should form in many systems. Beyond the bifurcation from the uniform state to patterns, rhombic patterns are linearly stable for a band of angles near the 60 degrees angle of regular hexagons. Experiments conducted on a reaction-diffusion system involving a chlorite-iodide-malonic acid reaction yield rhombic patterns in good accord with the theory.

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