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J. A. Sekhar

Publications and source records attributed to J. A. Sekhar.

2 recordsLinked to original sources

A Pathway Selection Process for Dynamically Self-Organizing Systems

Self-organization creates new order and shifts sub-boundaries while reorganizing energy and entropy within a control volume. This article examines pathway selection and tests whether maximizing the entropy generation rate can forecast process pathways. All entropy-generating processes distribute internal energy through temperature changes or structural responses, thereby creating new patterns or causing volume changes. Rapid self-organization, such as a supercooled liquid metal transforming into a solid, is a quasi-adiabatic process that tends to approach equilibrium or a steady state with respect to parameters like temperature. This is one of the main examples studied. Entropy generation is linked to internal energy redistribution, either as work performed (called stored work) or as thermal energy stored within a system. A system's resilience during and after self-organization is reflected in the emergence of measurable engineering properties. In the examples studied, the entropy generation rate is maximized throughout the process, regardless of the work needed to create new boundaries. Self-organization is a dissipative process, linked to pattern formation. The article discusses various patterns and shapes in physical systems, including grain size and morphology during thermo-mechanical deformation of crystalline solids, solid-liquid transformations, atmospheric effects, fluid-flow eddies, and patterned flight in birds that conserve energy within the framework of entropy-rate maximization. Morphological boundary limits are examined in terms of the ratio of the energy dissipation rate to the entropy generation rate for several examples. Processes can continue beyond an identifiable self-organizing phase, albeit with different time constants, thereby maintaining continuity and connectivity by maximizing the entropy-generation rate.

cond-mat.mtrl-sci↗

Interfacial instability of a planar interface and diffuseness at the solid-liquid interface for pure and binary materials

Topographical and diffuse interface reconfigurations occur with a change in the solidification rate. In this article we pursue the hypothesis that the interface configuration during solidification is determined by the rate of entropy production in the region between a rigorous solid and rigorous liquid phase. We posit that when an interface begins to migrate, there are several stable configurations that are possible. These include atomistically-planar, diffuse-planar, facet non-planar and cellular non-planar. The configuration and topographical condition that affords the maximum entropy production rate (MEPR) yields the most stable interface configuration. The principle of MEPR is applied to (1) describe atomistically smooth and diffuse interfaces, (2) provide quantitative results for the diffuse interface thickness and the number of pseudo-atomic layers in the interface region, and (3) predict the transition from planar to a non-planar facet or non-facet cellular morphology as a function of solidification velocity or temperature gradient. Numerous experimental investigations spanning over sixty years have failed to comprehensively validate any of the existing solid-liquid interface (SLI) growth instability models. With the MEPR model, for the first time, breakdown conditions are predicted with a fair degree of accuracy for a number of binary alloys where no previous theoretical model had predictability. The model considers steady state solidification at close-to and far-from equilibrium conditions.

cond-mat.mtrl-sci↗